The World War II era was an interesting time to be an aircraft engineer. Piston-engine technology was reaching a pinnacle of power and complexity, huge design and production demands were incoming from the war effort, and the advent of jet power had just emerged. It was a time to push up sleeves, sharpen pencils, and push boundaries.

This was certainly the case at Douglas Aircraft Co. When approached by the military to develop a small bomber that prioritized speed, Douglas responded with the XB-42, nicknamed “Mixmaster”—a decidedly unconventional, piston-powered design that it promised would achieve nearly 500 mph. When the military gave the go-ahead to build and fly two prototypes, it was up to the engineers to deliver the extreme performance.

To accomplish this, they focused on eliminating as much extraneous drag from the wing and airframe as possible. Rather than installing the two 1,800 hp Allison V-1710s (as used in the Bell P-39 Airacobra, Lockheed P-38 Lightning, Curtiss P-40 Warhawk, and others) in individual, wing-mounted nacelles, both engines were entirely housed within the aft fuselage. This kept the wing completely clean, without any of the parasite or interference drag inherent in the traditional nacelle configuration.

The engineers then developed a system of six individual drive shafts to link the engines to an aft gearbox, which drove a pair of three-bladed pusher propellers. The propellers were electrically controlled and able to feather, and the aft propeller was capable of adjusting its pitch even farther, providing reverse thrust. The feathering capability would be used later in the test program when one of the two engines would fail in flight.

The configuration didn’t deliver quite as much speed as Douglas had hoped. At 23,440 feet, the XB-42 could only achieve a maximum speed of 410 mph, and its cruise speed settled at 312 mph. Admirable numbers for a piston-powered bomber, but still well short of the company’s targets.

As other aircraft designers would also learn, pusher propellers located at the extreme aft end of the airframe create new and unique problems. Rotating too sharply during takeoff and flaring hard during landing, for example, would result in prop strikes. Douglas solved this by adding a ventral vertical stabilizer with an integrated shock absorber to isolate the airframe from the blows of tail strikes.

Another concern was the well-being of the flight crew in the event it became necessary to bail out of the aircraft. To prevent it from the grisly fate of entering two counter-rotating prop arcs after jumping, Douglas made it possible for the crew to first jettison the propellers and aft gearbox with an explosive charge. Instantly dumping more than 1,000 pounds from the extreme aft end of the airframe would wreak havoc on the center of gravity and produce a violent, nose-down pitching tendency.

One crew would experience this firsthand when it was forced to bail out during a test flight in December 1944. This crash would result in the loss of one of the two XB-42s. The remaining example would go on to fly in its original form and was later modified with two underwing turbojet engines, becoming the XB-42A.

Ultimately, the design would shed its propellers entirely and evolve into a pure jet when the static test airframe was developed into the jet-powered XB-43 Jetmaster. The sole surviving XB-42 awaits restoration at the National Museum of the U.S. Air Force in Dayton, Ohio.

The post The Douglas XB-42 ‘Mixmaster’ Flew Almost as Fast as It Looked appeared first on FLYING Magazine.

Generally, the more unique and unconventional an aircraft’s design, the more extreme its strengths and weaknesses become. A canard configuration, a wing optimized for high lift, and an amphibious airframe each provide specialized capability, and each also introduces a corresponding penalty with regard to other factors. This give and take in aircraft design and engineering applies to all aircraft, from the largest transports to the smallest homebuilts. 

Among the most interesting case studies are those that start with a common mission and reimagine the ordinary, eschewing the tried and true in favor of exploring new concepts. The Anderson Greenwood AG-14 is one such example. Aiming to gain a foothold in the personal aircraft market during the postwar years, it incorporated a decidedly unconventional layout that featured a single pusher engine and a twin-boom tail.

The fundamentals of the aircraft were common to existing types, however. Like many Cessna 140s, Luscombes, and Ercoupes, the AG-14 was equipped with a run-of-the-mill Continental C90 engine and a fixed-pitch propeller and weighed less than 1,000 pounds (empty) with a two-person capacity. This commonality of these foundational elements effectively isolated the pros and cons of the unique airframe layout, enabling an interesting side-by-side comparison with conventional types.

The most significant benefit of the unorthodox design was the completely unrestricted visibility from the cockpit. With no wing creating a blind spot either upward or downward, no engine cowling limiting forward visibility, and no propeller arc through which to look, the occupants’ field of vision is not unlike that of some helicopters. Indeed, had the design been given the opportunity to evolve, some panel reconfiguration could have enabled the introduction of a fully glazed forward cockpit like the Partenavia Observer. Such a modification might have appealed to the market as a low-cost helicopter alternative for duties such as pipeline inspection, law enforcement, and aerial survey missions.

A secondary benefit to the design is the configuration of the propeller and tail. Completely nested within the tail booms, the pusher propeller is shielded from wayward pedestrians who might carelessly wander around the airplane. Although the pilot cannot visually confirm the prop is indeed clear before engine start, the safety benefit of its position within the tail booms is legitimate.

Chief among the disadvantages of the AG-14’s layout is weight and balance. When it comes to aircraft design, it’s preferable to position the location with variable weight (such as fuel tanks and the passenger cabin) as close to the center of gravity (CG) as possible. This minimizes the effect varying weights will have on the CG, simplifying the concern of staying within that envelope. 

By positioning the passenger cabin well forward of the wing (and CG), the AG-14’s design introduces some unique characteristics. With little effort, one person can lift the nose wheel up and tip the airplane back onto its tail. Pilots report that the nose wheel can be held off the ground indefinitely while taxiing, even at low speeds. While Anderson Greenwood sufficiently addressed any issues related to this aft CG to achieve type certification, it was undoubtedly a major concern during the design and certification phase. It’s possible the decision to limit pitch authority and make the airplane stall and spin resistant was a decision driven by the negative effects of a particularly aft CG in stalls and spins.

The additional structure and complexity of the twin-boom tail inevitably add additional weight compared to conventional tails. This naturally limits useful load, adds drag, and makes inspections and maintenance more complex. Nevertheless, Anderson Greenwood managed to achieve performance comparable to the Cessna 150, with a cruise speed of 110 mph and a climb rate of 630 feet per minute. One minor downside with which the Cessna doesn’t contend is related to the pusher configuration—positioned directly behind the nose wheel, the propeller is susceptible to damage and wear from foreign object debris.

The AG-14’s design was intriguing enough to inspire a derivation in the form of the Cessna XMC research aircraft. First flown in 1971, Cessna studied the nearly identical side and configuration in pursuit of noise reduction and improved visibility for personal flying and training purposes. Ultimately, only one example was built, and Cessna did not pursue the concept any further.

After being introduced in 1950, only five AG-14s were produced. Today, four remain on the U.S. registry, and at least one or two are maintained in flying condition. Occasionally, one of the owners attends fly-ins like EAA AirVenture in Oshkosh, Wisconsin, where one can see and admire the unique little airplane in person. While it is unlikely the design will reemerge in the form of a modernized version, advanced materials such as carbon fiber could enable further evolution of the concept.

The post Anderson Greenwood AG-14 a Rare Breed, Indeed appeared first on FLYING Magazine.

In 1980, a small team of engineers from Lockheed explored a bizarre concept, the likes of which had never been studied before.

The group recognized that the transport aircraft category traditionally comprised three separate subcategories—passenger, cargo, and outsized cargo. It then created a concept that would combine all three. Aptly called the “Flatbed,” the concept aircraft would utilize an open platform and various modules to carry a wide variety of loads ranging from military equipment to passengers.

• READ MORE: The Unconventional, Bizarre Bell Airacuda

The most unconventional aspect of the Flatbed was the proposal that large pieces of military equipment be carried out in the open, completely unsheltered from the wind and elements. The team selected two sample military vehicles for the initial study, an XM-1 tank and an M60 bridge launcher, weighing 115,000 and 120,000 pounds, respectively. The big question was could this sort of outsized cargo effectively be carried out in the open at hundreds of miles per hour?

The group got to work on the drawing board and in the wind tunnel to answer that and explore how the Flatbed might serve as a multifunctional, “do-it-all” transport solution. The baseline Flatbed aircraft was a low-wing, turbofan-powered aircraft approximately the same size and weight as an Airbus A300. It utilized four CFM-56 engines, as found on the Airbus A320, Boeing 737, and Boeing KC-135R Stratotanker, and was optimized for a 2,600 nm range.

• READ MORE: That Time Cessna Made a Helicopter

Recognizing that carrying outsize cargo such as tanks out in the open would present serious drag and fuel-burn penalties, the team did not hedge its bets on this configuration alone. Instead, it designed the Flatbed to accept a variety of pressurized and unpressurized containers as well as a passenger module. The entire nose section of the aircraft was hinged, capable of being swung to the side to enable modules and vehicles to be quickly and easily loaded and unloaded using a variety of ramps, rollers, and latches. Raised engine pylons extending above the wing rather than below enabled shorter landing gear and a low, 7-foot cargo bed height.

With the cargo and passenger modules, the Flatbed was shown to be “generally fuel efficient in comparison with reference airplanes,” burning approximately 11 percent more fuel than a conventional design and targeting a 0.82 Mach cruise speed in these configurations. The primary benefit was presented as efficiency with regard to loading and unloading, particularly in the passenger configuration. In this role, the team proposed an entire restructuring of point-to-point travel.

• READ MORE: The Close Call of the Northrop YA-9A Prototype

By utilizing a large number of removable 180-seat modules, the passengers could board their module in a city center some distance away from their departure airport. Like multimodal containers, the module could be loaded onto a short-distance commuter train for transport to the airport, where it would be expeditiously loaded onto the waiting aircraft. The team proposed that this speedy loading and unloading of passengers would enable quick turns and high aircraft utilization. Similarly, it touted the ability of multimodal containers and even train cars to be quickly rolled onto and off the Flatbed.

But from the perspective of aircraft design in general and aerodynamics in particular, the most intriguing aspect of the Flatbed concept was the carrying of outsize cargo out in the open. Using scale models of both the Flatbed and tank and bridge launcher, aerodynamicists studied drag figures and later translated the data into speed and fuel-burn figures. The resulting performance numbers indicated the concept was surprisingly plausible.

Naturally, carrying external cargo was found to drastically increase drag compared to carrying the aerodynamically slick cargo and passenger modules. At higher altitudes, carrying the tank or bridge launcher would result in a 20 percent increase in fuel burn. At a lower 18,000 feet cruising altitude, this increased to approximately 55 percent. The external cargo also lowered the cruise speed to 0.5-0.6 Mach.

The team proposed multiple solutions to address the increased fuel burn. At the time of the study, engine manufacturers were looking at unducted “propfan” engines to improve fuel efficiency, and the team suggested exploring these new engines for the Flatbed. It also explored the possibility of “vortex control,” a system that introduced suction at the forward end of the cargo bed to smooth the air flowing around the back of the cockpit section, thus reducing drag. 

Ice accumulation on external cargo was identified as one potential challenge worthy of additional study. Engineers did observe that in-flight icing “does not appear to present a major problem,” however, as ice formation occurs only on the front part of the aircraft components. By tucking in the external cargo behind the cockpit section, it appeared to be sufficiently shielded from ice. 

While the Flatbed concept would never materialize beyond static and wind-tunnel models, the team partnered with NASA to publish a detailed initial study that evaluated the feasibility of the unconventional concept. The study ultimately concluded that the concept was both technically and economically feasible. They reasoned that the smaller size and increased versatility of such an aircraft would make it inherently more efficient to operate compared to existing military cargo aircraft.

Despite the overall finding that the Flatbed concept was worthy of additional examination, however, no such study ever occurred. The Lockheed Flatbed concept fizzled out after the publication of the NASA report.

The post The Fizzled-Out Promise of the Lockheed ‘Flatbed’ appeared first on FLYING Magazine.

Larry Bell, founder of the Bell Aircraft Corp., now known as Bell Helicopter, entered the aircraft manufacturing industry with a unique bang. After dropping out of high school in 1912, Bell worked for various aircraft companies, including Martin and Consolidated, before starting his own company in 1935. Rather than beginning with a conservative, basic aircraft type, he opted to respond to a military contract by proposing one that was so unconventional it bordered on bizarre.

That aircraft was the Bell YFM-1 Airacuda, a long-range and heavily armed escort fighter designed as an interceptor and bomber escort. It was part of a newly emerging category of aircraft containing models described by FLYING in 1941 as “virtually impregnable fortresses of themselves, yet maintaining considerable maneuverability and striking prowess which the big bombers lack.”

The design and configuration of the Airacuda was like nothing the industry had ever seen. The twin pusher engines were housed in glazed nacelles, each of which contained a crewmember, for a total of five. And while most of the 15 examples built were taildraggers, three incorporated tricycle gear—a cutting-edge aircraft development at the time.

In the fuselage, the pilot was accompanied by two other crewmembers. Seated in close proximity was an individual who handled three duties—copilot, navigator, and fire control officer. This multitasking expert was provided with a stowable control column and pedals to help fly the aircraft and was typically the one in charge of aiming and firing the various gyro-stabilized cannons and machine guns bristling from the airplane. In the back, a third crewmember handled radio communications and manned .50-caliber machine guns mounted in side pods to protect the aircraft from aggressors approaching from the rear.

Out in the engine nacelles, the remaining two crewmembers had somewhat simpler tasks. While they had the ability to aim and fire the .30-caliber machine guns in their respective nacelles, their usual duty was simply to reload them. Of somewhat more significant concern was what they would do in the event they had to bail out and fall through the path of the propellers churning the air immediately behind. While various sources refer to explosive bolts intended to jettison the propeller blades prior to bailout, the flight manual only refers to an emergency feathering procedure in which the electric props would feather and stop in six to eight potentially very long seconds.

Almost immediately upon making its first flight in September 1939, it became clear the Airacuda engineers had perhaps bitten off a bit more than they—and the flight crews—could chew. With 1,150 hp Allison V-1710 V-12 engines, the 21,625-pound aircraft could achieve 268 mph in high-speed cruise and reach a service ceiling of 29,900 feet. However, the flight control characteristics and single-engine handling were atrocious and would now be considered far too dangerous to approve for production.

The flight manual made no attempt to hide the unforgiving handling characteristics from pilots, warning that “due to close proximity of propeller to tall surfaces, a sudden reduction of power of one engine either through an engine failure or excessive movement of one throttle will result in a much more violent and immediate control reaction than on multiengine, tractor-type airplanes. Failure of one engine may result in a spin unless the other engine is retarded or trim tab control adjusted immediately.”

It went on to include some concerning limitations: “In case of failure of one engine the other engine should be retarded immediately and the throttle of [the] good engine advanced gradually as trim tab control is adjusted to counteract turning moment. With proper adjustment of [the] trim tab, airplanes can be safely flown on one engine. Single-engine practice flights will not be engaged in below [10,000] feet. This airplane should be flown only by experienced multiengine pilots.”

To provide sufficient electrical power for the various power-hungry systems, such as the targeting gyros, Bell designed the airplane around a 13.5 hp, 2-cylinder, four-cycle piston auxiliary power unit (APU) mounted in its forward belly. It ran at a constant speed of 4,000 rpm and powered the majority of systems, including the aforementioned propellers. Contrary to many reports, the APU was, in fact, not the sole source of electrical power—the right side engine was fitted with a backup generator to provide emergency electrical power to the aircraft in the event the APU failed.

Compounding the challenges of the Airacuda’s unconventional design was insufficient engine cooling. When idling on the ground for extended periods, the aircraft required special fan units with custom ducts that fed into the wing leading-edge intakes to prevent the engines from overheating. This also led to some operational difficulties in flight. 

Ultimately, no further examples of the Airacuda would be manufactured, as the combination of long-range bombers, such as the B-17, and traditional fighter escorts, such as the P-51, proved effective in the war. Two Airacudas were lost in accidents, and unfortunately, all remaining examples were scrapped by 1942.

While the small fleet never directly contributed to the war effort, Bell learned valuable lessons from its design, testing, and production. To keep the engines positioned forward, for example, and thus maintaining a proper center of gravity, each Airacuda engine incorporated a 64-inch driveshaft extension. The vibration and harmonics involved in such an extension are not trivial, and this experience likely helped refine similar extensions utilized in the later P-39 Airacobra and P-63 Kingcobra, both of which were manufactured in the thousands.

The post The Unconventional, Bizarre Bell Airacuda appeared first on FLYING Magazine.

If you’d like to stump everyone at aviation trivia, simply ask them to name the Cessna with the shortest takeoff-and-landing distances. More than likely, guesses would include the O-1 Birddog and possibly the 180 and 182. However, digging into the dustier corners of Cessna’s history reveals the true winner—its one and only helicopter the company ever produced, the CH-1 Skyhook.

The idea of introducing a helicopter to the Cessna product line began to gain traction in the early 1950s. This was a time when the company’s fixed-wing offerings were relatively modest but were on the brink of massive expansion. The lineup in the early part of the decade consisted of the 120/140, 170, 180, 190/195, O-1, and the 310/320 twins but by the following decade would more than double in size and encompass entirely new categories. A helicopter, Cessna thought, would be one more way to gain market share.

Rather than designing a helicopter from the ground up, Cessna went shopping for existing options. Its search eventually took it to the Seibel Helicopter Co., conveniently located on the other side of Wichita, Kansas. In 1952, Cessna acquired Seibel and its S-4B helicopter design, and founder Charles Seibel was retained to lead the engineering team.

The S-4B, while functional, utilized an entirely utilitarian design devoid of any niceties, such as an enclosed fuselage, soundproofing, or a finished interior. Cessna wasted no time replacing the skeletal design with an aluminum monocoque fuselage and cabin that utilized many of the same design principles as its fixed-wing aircraft. Before long, the first CH-1 emerged from the factory and made its first flight in July 1953.

Equipped with its new fuselage that later expanded to incorporate four seats, the CH-1 was sleeker and more modern looking than existing designs, and it was updated beneath the skin, as well. The Siebel’s original 125 hp piston engine was gone and in its place was a far more powerful alternative, ultimately a supercharged 6-cylinder Continental that produced 270 hp. This provided outstanding high-altitude performance, and the CH-1 went on to set several records. In addition to becoming the first helicopter to land on 14,000-foot Pikes Peak in Colorado, it set multiple altitude records by climbing to nearly 30,000 feet.

Cessna’s marketing team pursued both the civilian and military markets, securing a U.S. Army contract for 10 examples that would become known as the YH-41 Seneca. The Army was ultimately unimpressed with the helicopter’s performance, and Cessna bought back six, modifying some systems and converting them to civilian models. 

The company had better luck with the civil model, pursuing the short-range executive market as well as the utility helicopter market. In many respects, the CH-1 was impressive. The cabin was massive, enabling passengers to easily move from one seat to another in flight. At 64 inches wide, it was within 2 inches of a Citation Excel business jet and incorporated 360-degree panoramic visibility.

Unfortunately, the CH-1 was hobbled by several issues that ultimately proved insurmountable. Engine and transmission reliability reportedly was well below par for the market, reflected by the woefully short engine TBO of only 600 hours. This was a fraction of comparable helicopter engines and would have increased hourly operating costs noticeably.

Additionally, the CH-1 was quite expensive to purchase. In 1960, the CH-1C was offered for $79,960. The 1965 pricing for the Bell 47J and Brantley 305 was $67,000 and $54,000, respectively. While Cessna could justify a higher price for the nicer cabin and better high-altitude performance, it perhaps realized it would struggle to make a case against small turbine helicopters that would soon enter the market. Indeed, Hughes priced the 500 at $95,000 nine years later. 

Faced with reliability concerns and diminishing marketability, Cessna ended the CH-1 program and bought back nearly every example for scrapping, presumably to eliminate any product liability concerns. Today, of the 50 examples built, only one survives—a lone YH-41A Seneca in storage and awaiting restoration at the United States Army Aviation Museum at Fort Rucker, Alabama.

The post That Time Cessna Made a Helicopter appeared first on FLYING Magazine.

Historically, some of the most compelling aircraft prototypes have served as launching pads for new and emerging technologies. From clean-sheet engine designs to new aerodynamic concepts to unusual airframe layouts, X-planes from all eras were smorgasbords of cutting-edge engineering. And in the early 1940s, McDonnell combined a multitude of new ideas into its XP-67 in the hopes its performance would eclipse existing interceptors.

A safe, conservative method of introducing a new aircraft design might be to incorporate only a few completely new and unproven concepts at a time. This philosophy enables engineers to isolate the concepts and evaluate them for more widespread use. But in the case of the unique McDonnell XP-67, nicknamed the “Moonbat,” it seems airframe and powerplant engineers alike were given carte blanche to reimagine every component and integrate all the resulting ideas into a single aircraft.

At first glance, the XP-67 has the appearance of an aerodynamic study. With a semi-blended-wing body, a laminar-flow airfoil, and rounded, filleted junctions where different surfaces met, the airframe took on a one-piece, organic appearance. The effort spent on sculpting the airframe in such a manner was motivated by a blistering top speed target of 472 mph—a number McDonnell promised to the military in an effort to win a lucrative production contract.

However unconventional the aerodynamic aspects of the airframe may have been, additional complexities lurked beneath the skin. These came in the form of new and unproven Continental XL-1430 inverted V-12 engines. Liquid-cooled and rated at 1,350 hp each, these engines held much promise when they were developed in the 1930s.

They delivered roughly 1 hp per cubic inch of displacement, making them both smaller and more powerful than the Rolls-Royce Merlins of the same era. Unfortunately, this came at the cost of an inferior power-to-weight ratio. Together with various airframe modifications, the engines contributed to a massive increase in the XP-67’s weight as the development of the aircraft progressed—from an initial target weight of 18,600 pounds to an ultimate weight of more than 25,000.

While weight climbed, aerodynamic challenges emerged. The uniquely sculpted airframe, optimized for efficiency at high speeds, presented severe downsides in other aspects. Despite creative leading-edge intakes to feed cooling air to the radiators, the engines overheated and even caught fire during initial taxi tests and ground run-ups. This was likely attributable to the extremely tight cowlings and ductwork that favored low drag above all else as opposed to fundamental issues with the engines themselves. But it was nevertheless a problem, and when the first flight took place in January 1944, it had to be cut short after several minutes due to overheating in flight.

Engineers quickly revised the engine cooling to address these issues. Less easily solvable, however, were the aerodynamic and handling problems pilots discovered on subsequent test flights. The XP-67 exhibited concerning instability, leading to doubts it would be able to recover from a spin. Additionally, the climb performance fell short of expectations, the approach speed increased from 76 to 93 mph, and the aircraft only ever reached a maximum speed of 405 mph—67 mph lower than the target.

To solve some of these issues, the design team explored alternative engine and propeller options. While the unproven Continental had shown promise and was competitive in the preceding decade, newer developments of the Rolls-Royce Merlin had surpassed its specifications, and jet engines were beginning to emerge as the way forward. The XP-67 and its multitude of concerns appeared to be on borrowed time.

In September 1944, time ran out. During a test flight over St. Louis, an engine caught fire in flight. Although the pilot made a successful emergency landing at Lambert Field (KSTL), the flames spread to the rest of the airframe before emergency equipment could extinguish them, and the aircraft was destroyed. Faced with mounting challenges and a second prototype that was far from completion, the program was canceled and both examples were discarded.

The post McDonnell’s ‘Moonbat’ Definitely Stood Out in the Early 1940s appeared first on FLYING Magazine.

In the mid-1960s, the U.S. Air Force presented aircraft manufacturers with an interesting challenge—design a clean-sheet close air support (CAS) aircraft to replace the aging Douglas A-1 Skyraider. Accustomed to developing sleek fighters and bombers that ventured into supersonic speeds, this new request challenged them to instead prioritize cost, survivability, and low-speed maneuverability. It was a new set of requirements that required new thinking.

Just as the design requirements were unconventional for the time, so too was the appearance of each proposed contender. A total of six manufacturers submitted a wide variety of proposals, ranging from multiengine jets to a single-engine V-tail pusher turboprop. In each case, the manufacturers prioritized function over form, with most concepts utilizing straight wings, bulbous canopies, and a multitude of external hard points on their wings.

The Air Force selected two designs to progress to the final stage, in which the finalists would build flying prototypes. The unconventional-looking Fairchild-Republic A-10 Thunderbolt II, better known as the “Warthog” would ultimately win the contract for this role. But its competitor, the Northrop YA-9A, provided some intriguing design features despite losing the contract.

At a glance, some similarities between the two finalists are evident. Both sport the aforementioned straight wings with many hardpoints, and the external dimensions are nearly identical. Both also utilize twin turbofan engines. But a handful of key differences stand out.

Chief among them, the YA-9A was designed with a high wing, as opposed to the low wing on the A-10. While the specific reasoning for this is unclear, the high wing enables the use of shorter, lighter landing gear. Additionally, a side profile diagram depicts workers standing alongside the aircraft, eye level with the engine, suggesting Northrop touted the design as providing mechanics with easy engine access during maintenance.

The YA-9 also uses a conventional cruciform tail—significantly different from the A-10’s low tail with twin vertical stabilizers. While this design was less complex and presumably lighter than that of the A-10, it provided less redundancy. In practice, A-10s have successfully demonstrated their ability to fly with a single vertical stabilizer.

Like the A-10, the YA-9A utilized turbofan engines, but the engine similarities stopped there. Rather than using a common, simple design like the A-10, the YA-9A was fitted with a less common and more complex geared turbofan called the Lycoming ALF 502. These would ultimately prove less reliable than similar engines, and NASA later salvaged and used them for their QSRA experimental short takeoff and landing jet.

While both contenders employed large Gatling-style rotary cannons buried in their noses, these also differed. While the YA-9A used a six-barrel, 20mm M61 Vulcan, the A-10 used a larger seven-barrel, 30mm General Electric GAU-8/A Avenger. As the latter uses heavier ammunition and the Air Force claimed it has superior ballistics, it would help make the A-10 the more effective combat aircraft.

A deeper dive into the YA-9A’s flight manual reveals additional insight into the overall design. It states that Northrop engineered the aircraft with two primary goals in mind—to provide an extremely stable platform for on-target accuracy during weapons delivery and to provide a high degree of survivability for both aircraft and pilot. The latter was achieved in a similar manner to the A-10, with strategically-located armor.

The on-target accuracy during weapons delivery, however, was achieved through the use of some flight control trickery. Northrop engineers wanted to enable quick steering corrections during weapons targeting, and they wanted to do so without creating any bank or sideslip. Their solution was called SFC, or side force control.

SFC blended the control inputs of the rudder with that of the speed brakes, which, like the A-10, were provided in the form of split ailerons. As the pilot introduces rudder input, simultaneous asymmetric speed brake deployment negates the rudder’s yawing moment. This control and coordination occurred automatically when in SFC mode simply through rudder inputs by the pilot. 

Asked whether such a system would benefit the A-10, an A-10 pilot replied, “I mean…the rudders work just fine.” This underscores the philosophy of simplicity behind the A-10 and suggests complex systems like SFC might have hindered the YA-9A more than they helped.

In terms of flying performance, the YA-9A seemed quite competitive. Takeoff distance at a 2,300-feet pressure altitude (the elevation of Edwards Air Force Base) ranged from 3,800 feet at the maximum takeoff weight of 42,000 pounds down to only 640 feet at 23,000 pounds with full flaps. 

In the air, the YA-9A’s maximum speed was approximately 450 knots. Perhaps more impressive was its ability to maintain single-engine directional control down to only 75 knots. The control effectiveness necessary for this was likely a byproduct of the engineers’ emphasis on low-speed maneuverability in the intended CAS role.

Published landing distances were similarly impressive, with ground rolls ranging from 875 to 1,100 feet. This was helped in part by the massive ground spoilers that deployed to 60 degrees when the system sensed weight on wheels. Among the various performance objectives, this is one in which the YA-9A likely outscored the A-10 during the evaluation.

Ultimately, the A-10 would go on to win the competition, and Fairchild-Republic would go on to manufacture a total of 716 examples between 1972 and 1984. The Air Force mothballed the two YA-9As after the evaluation period but fortunately spared them from the fate of the scrapper. Today, both can be found at museums— one in storage at Edwards Air Force Base awaiting restoration and the other on display at the March Field Air Museum in California.

The post The Close Call of the Northrop YA-9A Prototype appeared first on FLYING Magazine.

Once upon a time, GA aircraft manufacturers pursued market niches with the ferocity of wild dingos. When marketing teams identified a potentially underserved customer segment, they wasted no time introducing minor variations to existing models to accommodate it. Compared to today’s offerings, the resulting variety of aircraft was spectacularly broad and varied.

When Cessna determined some customers would be willing to pay a bit more for a slightly more powerful 172, for example, the company introduced the 175 Skylark. This was little more than a 172 with a different engine, but the company was in pursuit of new market segments and opted to advertise it as an entirely different model.

Similarly, Beechcraft identified markets for both full-sized and smaller light twins in the forms of the Baron and Travel Air. With four seats instead of five or six, thriftier 4-cylinder engines, and significantly lighter weight, the Travel Air was presented as a simpler, more compact solution that emphasized economy rather than outright performance.

Fresh off the successful launch of the unique, twin-boom Skymaster, Cessna began exploring the same opportunity in 1965. Recognizing the market might have room for a smaller, lighter version of the Skymaster, it built a single prototype of the Cessna 327. While it was never given an official name, various sources use the nicknames “Baby Skymaster” and “Mini Skymaster.”

The rationale behind this model was likely rooted in findings shared by other manufacturers—that many owners and operators of twin-engine aircraft travel alone or with only one passenger most of the time. For these customers, it made little sense to haul around excess seats and cabin space while burning additional fuel and paying more to maintain larger, 6-cylinder engines. The diminutive Wing Derringer was an extreme example of minimalist light twins. 

The 327 was Cessna’s solution to this downsizing opportunity. Essentially a 172-sized Skymaster, it was both smaller and lighter than the larger centerline twin. Equipped with two 4-cylinder, 160 hp IO-320 engines, it utilized Cessna’s strutless, cantilever wing, and raked windscreen, similar in design to the 177 Cardinal series. 

The smaller size and sleek lines gave the 327 a sporty look compared with the more utilitarian Skymaster. But like the Skymaster, the front seats were positioned well ahead of the wing’s leading edge. Combined with the lack of wing struts, this would have provided outstanding outward visibility and positioned the 327 to be a favorite for aerial photography.

Cessna never published any dimensions or performance specifications for the 327. Using comparable light twins with the same engines as a reference, we can predict the 327 likely would have had a maximum takeoff weight of 3,500-4,000 pounds, with a maximum cruise speed of 150-175 mph. Fuel burn would also have been correspondingly lower, roughly on par with a Piper Twin Comanche with similar engines.  

First flight took place in December 1967, and Cessna flew the 327 until the following year, logging just less than 40 hours of test flights. At that time, the airplane was presumably placed into storage, and the registration—N3769C—was canceled in February 1972. But unlike many other prototypes, the 327 would serve one last purpose before vanishing forever.

The airplane’s final role would be filled at NASA’s Langley Research Center. There, it was used in the full-scale wind tunnel, or FST, for noise-reduction studies. This research was conducted by Cessna, NASA, and Hamilton Standard in 1975 to evaluate various propeller and propeller shroud designs.

The NASA team removed the front propeller and fitted the 327 with an assortment of three-blade and five-blade options housed within a custom-built shroud. Perhaps surprisingly, the shroud was found to actually increase propeller noise slightly as opposed to reducing it as expected. The airplane was later fitted with Hamilton Standard’s experimental “Q-Fan,” a ducted fan design that was touted to transition from full forward thrust to full reverse thrust in less than one second. 

No official record exists outlining the 327’s ultimate fate. The apparent lack of any information beyond the 1975 wind tunnel testing suggests the airplane was scrapped after that. This was perhaps part of a contractual agreement with Cessna, as the company was known to have discarded other prototypes during that era.

We’re left with a smattering of photos and a few piles of technical reports. Coincidentally, with the introduction of electric vertical takeoff and landing vehicles and a renewed interest in noise-reduction technologies in the GA sector, the studies might prove valuable even today. And for that matter, a compact, efficient piston twin with the safety of centerline thrust might as well.

The post Smaller, Lighter Cessna 327 ‘Mini Skymaster’ appeared first on FLYING Magazine.

For as long as homebuilt aircraft have existed, enthusiasts have enjoyed a wide selection of small, single-seat types from which to choose. From speedy, stub-winged racers like the Cassutt to the Monerai P powered sailplane that weighs less than 300 pounds, variety abounds even among these tiny machines. But in the early 1970s, one exceedingly creative specimen emerged that blended a multiengine configuration with an empty weight of only 440 pounds.

The Aerosport Rail is a tiny, multiengine aircraft and a rather interesting contradiction. On one hand, its designers whittled away at it until every last extraneous element of the aircraft, including a windscreen and enclosed fuselage, was omitted. On the other hand, they introduced complexity and parallel systems by integrating a second engine. 

Browsing through their circa-1970 marketing material, a backstory adds some context. Formed by a magazine editor and aeronautical engineer, the company prioritized safety, ease of assembly, low cost, and fun flying characteristics. And despite the outwardly primitive appearance, the unconventional design lends itself to these qualities.

The T-tail, for example, was chosen to place it out of the prop wash and eliminate buffet, which may have been a concern with a minimalist empennage that was perhaps more likely to bend and flex than other designs. The pusher engine configuration was selected to reduce noise and buffeting around the pilot, and having two engines offered a level of redundancy that made an engine failure a nuisance rather than a catastrophe. And the 2-cylinder, two-stroke, reengineered snowmobile engines were placed close together to minimize any asymmetric thrust resulting from an engine failure.

The designers apparently succeeded in all respects—and in the last one in particular. During initial testing, a pilot reportedly performed a takeoff with the left engine shut down and its propeller windmilling. Additionally, rudder effectiveness was reportedly maintained during single-engine flight all the way down to the 45 mph stall speed.

With both engines operating, performance was spritely. Marketing material promised a takeoff run of 230 feet, with the ability to clear a 50-foot obstacle in 1,230 feet. Cruise speed at 85 percent power and 2,000 feet was said to be 66 mph while burning just under seven gallons per hour total. Top speed was listed as 90 mph, the modest speed number reflecting the substantial parasite drag inherent in the entirely open design. Indeed, at lower speeds such as climbout, the Rail returned decent performance, with the 900 fpm climb rate easily exceeding that of, for example, a Cessna 150.

Considering the 440-pound Rail’s 100-mile range, 220-pound full-fuel payload, and complete lack of any design features related to comfort or ergonomics, this was clearly an airplane optimized for local flights. But for warm summer evenings bimbling around down low over hayfields and picturesque lakes, the peace of mind provided by the unique twin-engine configuration and completely unobstructed visibility would have made for a uniquely enjoyable experience. 

Unfortunately, the Rail was not a commercial success. In addition to the company prototype shown here, FAA records indicate a Rail registered as N44HW was completed in 1976. An article in Sport Aviation mentions it had accumulated more than 14 hours by June of that year, but it was deregistered only four years later. Another Rail, registered as a “Rail II” and wearing the registration N27T, was completed in 1975, but it’s unclear whether it was ever flown.

Whether the lack of success was the result of a technical obstacle not mentioned in Aerosport’s marketing material or whether the Rail simply succumbed to the business challenges that have claimed so many other designs over the years is unclear. Whatever the reason, the aircraft depicted in every photo of the type seems to have disappeared entirely, and its registration was canceled in 1976, six years after its first flight. 

Ultimately, it’s a sad and all-too-common end to an interesting chapter of aircraft design. A floatplane version was in the works, and had that come to fruition, the resulting machine would have amounted to a mini-AirCam, offering similar levels of fun and redundancy at a far lower price. Even comparing landplanes, the Rail, at $2,495 for the complete kit including engines, cost only 20 percent of a new Cessna 150. 

Though the Rail was unconventional to the point of bordering on crazy, and though it was, like many other private aircraft designs, a commercial failure, it looked to offer more fun per dollar than most other types of the era. Perhaps one day it will be resurrected. At the very least, it could enable aspiring professional pilots to build their multiengine time more affordably than ever.

The post The Unconventional, 440-Pound Aerosport Rail appeared first on FLYING Magazine.

In the years following World War II, the economy was booming, Americans were beginning to travel, and aircraft manufacturers were brimming with experienced teams of engineers. With the demand for military aircraft subsiding, virtually all of these companies began exploring new avenues for product development and innovation. It didn’t take Beechcraft long to identify civil aviation as a burgeoning opportunity.

Fresh off the success of the V-tail Bonanza and the larger, 8-to-10 passenger Model 18, Beechcraft management explored the market and noticed a gap in the industry’s product offerings. Prior to the war, types such as the Ford Trimotor, Boeing 247, and Curtiss taildraggers served as the era’s smaller “regional airliners,” but the war effort paused any further development of that segment. Referring to it as a “Feederliner,” Beechcraft reasoned that a small, modernized civil airliner was just what the industry needed.

Dedicating significant engineering and marketing resources to the project, the team got to work. It aimed to position the aircraft as a solution for passenger as well as cargo transport. It opted for a high-wing configuration, an easily convertible cabin layout, and a cargo door in the forward left fuselage, naming the final product the “Twin Quad.”

With a wingspan of 70 feet, a length of 51 feet, and a height of 19 feet, 4 inches, the Beechcraft 34 Twin Quad was a sizable machine. Ironically, each dimension is nearly identical—within 1 to 4 feet—to the Cessna SkyCourier, the latest offering from Beechcraft’s successor. Even the maximum takeoff weight of 19,500 pounds is within 500 pounds of the modern twin turboprop.

The team decided to incorporate a V-tail into the design, first installing it on an existing AT-10 Wichita twin for testing purposes. This enabled them to evaluate the tail’s effectiveness at providing directional control on a multi-engine aircraft of similar size and weight to the Twin Quad before finalizing and freezing the design.

It’s possible the V-tail was pursued primarily because of the technical advantages it was thought to provide. It’s also possible it offered more value to the marketing department as an instantly identifiable branding feature that visually differentiated it from the competition. Whatever the driving reason, Beechcraft ultimately incorporated the V-tail into the final design.

Though the V-tail was the most notable design feature of the aircraft from a visual standpoint, it paled in comparison to the originality and uniqueness of the engine layout. 

In an effort to harness the maximum power in the smallest, most aerodynamic packaging possible, the team opted to utilize four 375 hp Lycoming GSO-580 flat-8 piston engines and buried them entirely within the wing. The engines were configured in pairs, with each coupled together and driving a single propeller via clutches and a gearbox. The clutches were designed so that engine torque compressed and engaged the clutch discs. 

In the event of an engine failure, the failed engine would automatically disengage from the gearbox, and the remaining engine would continue to drive the propeller. This feature was presented as a safety improvement—although the loss of one engine would result in a power reduction, it would present no corresponding asymmetric control issues.  

The Twin Quad used two massive full-feathering, two-blade propellers for propulsion, and naturally, they were driven through reduction gearing. At 11 feet long, if the engines were to turn them directly at a normal cruise rpm, the propeller tip speeds would have exceeded Mach 1.5. The reduction gearing provided a ratio of 40:21, or roughly 2:1, bringing the propeller rpm range down to a quiet and comfortable 1,500 rpm in cruise flight.

During engine shutdown, the engine clutches would disengage entirely. A note in the operating manual advises that if high-velocity wind rotates the propellers after shutdown, the clutches may be reengaged to lock them into position. Presumably, standard operations would call for the clutches to be engaged regardless, as the sight of rotating propellers on a vacant, parked aircraft would naturally create concern for any observers on the ramp.

Because the Twin Quad was designed for airline operations, it was equipped with full anti-icing capability. Two combustion heaters—one for the wing, and one for the tail—provided heat for the leading edges that was distributed along the insides of the leading-edge skins. The propellers were electrically deiced, and the cabin heater ducted hot air into the space between the two panes of glass that made up each cockpit windscreen.

The Twin Quad made its first flight in autumn 1947. Shortly thereafter, the marketing team stopped using the term “Feederliner” to describe the aircraft, instead switching to “Beechcraft Transport.” This indicated a change in marketing strategy to emphasize non-airline operations, which likely included executive transport. 

Detailed cruise performance wasn’t provided in the preliminary flight manual, but VNE is listed as 270 mph and VNO as 220 mph. Minimum takeoff climb speed is listed as 96 mph, and the bottom of the white arc is 75 mph. 

Given the total horsepower available, the Twin Quad’s engine-out takeoff performance seems fairly decent. In the event of an engine failure after V1 at the maximum weight of 19,500 pounds, the charts indicate it will clear a 50-foot obstacle in just below 3,500 feet at sea level. By comparison, the modern Cessna SkyCourier requires 2,740 feet at roughly the same weight with both engines operating and twice as much power available. Landing distance over a 50-foot obstacle is listed as 2,000 feet at sea level and maximum weight.

The charts optimistically include separate listings showing performance with 40-mph headwinds. It is unclear whether this is a function of an overly optimistic marketing team or simply reflected the reality of everyday weather conditions in Wichita, Kansas. 

Range figures aren’t provided, but endurance can be calculated with the available data. Given the Twin Quad’s total fuel capacity of 536 gallons and the fuel consumption figures of 130 total gallons per hour at maximum continuous power and 80 total gallons per hour at 75 percent power, the resulting endurance would have been 4.1 to 6.7 hours.

Tragedy struck during a certification test flight in Wichita on January 7, 1949. Just after liftoff, an electrical fire occurred. While attempting to extinguish it, a crew member reportedly turned off an “emergency master switch” that resulted in both engines shutting down. The aircraft then stalled and went down, killing one of the pilots.

Following the incident, Beechcraft terminated the program entirely. No specific reason was provided, but it’s possible the decision was driven in part because of a lukewarm response from the market. Ultimately and unfortunately, what remained of the Twin Quad was scrapped.

Today, all that remains is a small handful of photos and scraps of documentation. And while the large Bristol Brabazon airliner flew with a nearly identical engine/propeller arrangement later that year, it would ultimately succumb to the same fate—canceled, scrapped, and relegated to the dusty shelves of aviation history.

The post Beechcraft Twin Quad: A ‘Feederliner’ That Almost Was appeared first on FLYING Magazine.

If an aerospace engineer was given their choice of time periods in which to work, it’s likely the 1960s would be a top pick. With swept-wing jets like the Boeing 707 and Douglas DC-8 having made their first flights just a few years prior, the decade ahead would see the introduction of such groundbreaking aircraft as Concorde, the Boeing 747, and the XB-70 Valkyrie. Research and development budgets were robust, competition was fierce, and a young engineer looking for employment must have felt like the proverbial kid in a candy store. 

While the majority of action in the U.S. centered around the production of civil airliners, military jets, and the space race, there were some less flashy but thoroughly intriguing programs taking place in some of the industry’s quieter, less-traveled corridors. One of which was a research program led by Northrop, the U.S. Air Force, and the U.S. Army. The objective? Explore how a wing’s lift could be artificially boosted to reduce drag and increase performance, particularly in large, long-range aircraft designs—some of which would be supersonic.

Drag reduction efforts were nothing new in those days. From simple efforts like flush riveting to more complex concepts like area ruling, massive progress was made in a relatively short amount of time. In the 1950s, boundary layer control (BLC) was integrated into a number of aircraft designs, a system in which compressed air was directed over sections of the wing and control surfaces to delay the separation of air over the airfoil’s surface, thus artificially increasing lift at lower airspeeds.

The team at Northrop opted to study and test something called laminar flow control, or LFC. The basic premise behind LFC is that a large number of tiny slots would be drilled into the upper surface of a wing, and a vacuum system would draw air inward through them. This would cause the thin film of air clinging to the surface of the airfoil to cling more effectively, thus reducing friction drag attributed to air turbulence over the wings by as much as 80 percent.

Because the program would be aimed at the development of civil airliners, the team chose an aircraft that would best replicate the category—the Douglas B-66 Destroyer. Specifically, it was the WB-66 weather reconnaissance version, of which 36 were built in the late 1950s. Using two examples as testbeds, the team modified them with all the necessary systems to test the LFC system.

The team began by cutting a vast series of ultra-thin slots in the upper surface of a newly-designed wing that was larger and less swept than the B-66’s original wing. These slots varied in thickness from approximately 50 percent to 200 percent of the width of the cutting edge of a razor blade. Perhaps drawing inspiration from the Bede XBD-2 that flew just a few years prior,  they utilized computers to drill an intricate pattern of 800,000 pin-sized holes beneath the slots and installed hundreds of small plastic ducts inside of the wing, each one carefully tuned to a specific length to ensure proper distribution of vacuum pressure across the entirety of the wing’s upper surface.

The X-21’s GE J79 non-afterburning turbojet engines—relocated to the lower aft section of the fuselage—provided bleed air to power special compressor pumps housed in a pair of sleek nacelles mounted beneath the wing. These pumps would draw air through the slots in the wing and through the ducting to activate the LFC system. Rather than simply ejecting this compressed air overboard, it was ignited and discharged through thrust-augmenting exhaust nozzles at the aft end of each nacelle.

By the time the X-21 was completed in 1963, only the landing gear and tail surfaces remained the same as the WB-66 once was. Even the engine intakes were altered, incorporating “egg-shaped forms” within each intake that could be moved forward and aft to alter the incoming airflow. This was in anticipation of developing movable inlet cones for supersonic flight—as would be utilized on the SR-71 the following year.

The X-21 proved docile to fly, and the LFC system worked as designed. Despite having no flaps, the modified aircraft demonstrated a ground roll of 2,600 feet—significantly shorter than the required takeoff distance of the standard B-66. But while a second X-21 was built, and both contributed valuable data to the program, the team discovered a number of concerns that would preclude the adaptation of LFC into operational aircraft fleets.

As detailed in an October 1964 NASA report, the LFC system could not be relied upon during flight in clouds, haze, and high humidity. Because the tiny holes in the upper surface of the airfoils had to be kept perfectly clean and free of contamination, issues such as icing, moisture, and even insect buildup were anticipated, all of which would result in erratic performance of the LFC system. Additionally, such factors could create a dangerous asymmetric lift condition that would lead to controllability issues.

When the test program was completed, both X-21s were placed into storage at Edwards Air Force Base. Later, as their condition deteriorated, they were unceremoniously parked out in the desert, in the Edwards Photo Impact Range. There, they continue to be used to test cameras, mapping systems, and remote sensors.

This is typically where the story of such unique aircraft ends. More often than not, the scrapper is the ultimate destination, and any physical examples of the aircraft are permanently erased from history. But in the case of the X-21s, there is hope. That hope comes in the form of the Air Force Flight Test Museum, also located at Edwards Air Force Base.

There, director George Welsh is keenly aware of the X-21s and their historical value. He has already begun laying the groundwork to one day recover both examples and eventually utilize parts from both to create one representative example for display in the museum. His team has even identified a number of missing parts and has proactively scavenged them from an unrelated donor B-66, to make the future restoration process go more smoothly.

As is typically the case with even the world’s most renowned museums, funding is the primary obstacle. Having begun construction of new museum facilities, the Flight Test Museum still has to raise millions of dollars to complete that project before embarking upon the transport, storage, and restoration of the X-21s. But the museum leadership has done its duty to ensure they will be spared from the scrapper.

For now, both X-21s remain out in the desert. With any luck, the museum will soon secure enough funding to complete the new facilities so the unique jets can be restored and put on display for future generations to appreciate.

The post The High Speed, Low Drag Northrop X-21 appeared first on FLYING Magazine.

It would surely require a unique set of circumstances to convert a utilitarian twin-turboprop cargo airplane into a swept-wing four-engine jet. It would be especially peculiar if these modifications resulted in a maximum cruise speed of only 160 knots and a maximum range of only 256 miles. But in the late 1970s, this is precisely what occurred when NASA designed and built the Quiet Short-Haul Research Aircraft, or QSRA.

The genesis for this unique aircraft occurred when researchers around the world were investigating the concept of inner-city airports. These airports, sometimes called STOLports, were envisioned to become the next evolution of air transport. Proponents claimed that by building smaller airports in urban centers, population centers could be more easily and quickly connected with the larger air travel network.

Because such airports would be limited in footprint, they would utilize shorter runways. And because the population surrounding these airports would be so dense, any aircraft utilizing them would have to be significantly quieter than existing types. These design constraints were among the key areas of study in the QSRA program, and NASA’s job was to explore how such aircraft might be designed and certified.

NASA was constrained by a tight budget, so when it discovered that it could acquire a deHavilland Canada C-8A Buffalo at no cost from the National Center for Atmospheric Research, they seized the opportunity. Their tactical frugality continued with the discovery of six used AVCO-Lycoming YF-102 turbofan engines left over from the Northrop A-9A prototype ground attack jet. As the A-9A had lost the military contract for which it was competing to the A-10, the engines were available and were provided to the QSRA team at no cost.

Now in possession of an airframe and engines, all that was left to do was design a wing and assemble the aircraft so testing could commence. NASA contracted Boeing to design and fabricate the wing. Rather than utilize a traditional straight wing as was originally fitted to the Buffalo, the QSRA was fitted with a swept wing that incorporated a complex system of flaps and Boundary Layer Control, or BLC.

The BLC system would divert bleed air from the engines to small nozzles positioned on top of the wing ahead of the flaps and ailerons. This bleed air would help to keep the boundary layer attached, delaying the onset of a stall, increasing control surface effectiveness, and enabling flight at slower airspeeds. In addition, the engines would be placed on top of the wing to utilize the Coanda effect, an aerodynamic effect deflecting thrust downward and increasing lift.

NASA recognized high-speed cruise efficiency would provide little value to the program. They also anticipated the steep approaches and high rates of descent necessary for their testing could easily result in significantly greater impacts upon touchdown. Accordingly, they modified the landing gear to be non-retractable and strengthened it to withstand firm landings that would routinely exceed 700 feet per minute.

The first flight of the QSRA took place on July 6, 1978, at Boeing Field in Seattle. A wide variety of testing followed shortly thereafter to fulfill data gathering for a number of projects. These projects ranged from the compilation of data to help regulatory agencies establish certification criteria for future STOL airliners to measuring the effects of steep approaches and departures on noise footprints.

The performance of the QSRA was impressive—65-knot approach speeds were standard, and low-speed flight was demonstrated down to only 50 knots. This is particularly notable as the aircraft’s maximum takeoff weight was 60,000 pounds—a full 7,000 pounds heavier than a fully-loaded, 50-passenger CRJ200 regional airliner.

Maximum-performance takeoffs resulted in ground rolls of 664 feet, and STOL landings produced ground rolls of only 550 feet. But the ability to utilize shorter runways wasn’t the only goal. In order to reduce the noise footprint during approaches and departures to and from urban airports in densely-populated cities, the team wanted to evaluate the feasibility of utilizing a steep, 7.5 degree approach path as opposed to the standard 3 degree glideslope.

As these tests were conducted, the team discovered that such approaches could reduce the aircraft’s noise footprint by 80 to 90 percent. This steep glideslope, they noted, would place the aircraft more than twice as high as a conventional passenger jet at any point along the approach. NASA even suggested touching down at the runway midpoint or performing spiraling descents directly above the airport to confine the noise footprint to that of the airport itself and thus not affect adjacent communities. It is unclear whether the team considered the effect such approaches might have on the passengers aboard.

The QSRA would go on to conduct a wide variety of testing. In addition to studying controllability and noise footprints, it was even utilized for a joint NASA/U.S. Navy test program in which it flew onto and off of the USS Kitty Hawk aircraft carrier. This particular testing evaluated the use of advanced propulsive-lift technology, and the QSRA successfully completed a series of unarrested landings and unassisted takeoffs from the carrier deck.

When the last test programs were completed, the QSRA was retired and put out to pasture. Today, visible on Google Maps, it resides on a quiet ramp at the NASA Ames facilities at Moffett Field in Mountain View, California, weathered from the elements but otherwise intact. With any luck, it will one day be fully restored and put on display indoors where future generations can fully appreciate the work it and its teams conducted.

The post The Quiet Little Life of NASA’s QSRA appeared first on FLYING Magazine.

In the film Back to the Future II, the antagonist Biff Tannen steals a sports almanac containing scores from every major sporting event over a 50-year time span and delivers it to his younger self via a time machine. Armed with this knowledge from the future, his younger self then utilizes the almanac to gamble, amassing a fortune estimated by fan websites to exceed $3.1 billion and forever altering the trajectory of that timeline. 

While there’s no concrete evidence a similar chain of events occurred in the world of aeronautical engineering, the concepts utilized by the Dayton Wright RB-1 certainly suggest at least one time machine was involved in its development.

When the RB-1 was constructed in 1920, the vast majority of aircraft were still rickety-looking contraptions. Most were biplanes utilizing fabric covering, external wire bracing, and spindly-looking fixed landing gear. World War I-era rotary radial engines were still commonplace, their crankcase and cylinders spinning in their entirety as though the engine manufacturers were sponsored by gyroscopic precession itself. 

At the time, developments like a variable-camber wing and retractable landing gear must have resembled science fiction to most, but not to the people at Dayton-Wright in Ohio. There, a small team of engineers was tasked with creating an aircraft specifically to compete in the Gordon Bennett trophy race in France. This prestigious race consisted of three laps of a 300 km (186 mile) course, and a victory would bestow enviable bragging rights to the aircraft manufacturer.

Favorites for the 1920 race included aircraft built by Neuport, Spad, and Verville-Packard. All were among the fastest aircraft in the world at that time. But all were also open-cockpit biplanes, seemingly designed and built with little regard for parasite drag. 

Dayton-Wright identified this as an opportunity. In a flight regime where any horsepower gains are quickly overshadowed by exponentially-increasing drag, they designed and utilized features unheard of in that era. Features that in the following decades would become commonplace on virtually all aircraft built for speed.

Prioritizing drag reduction from the beginning, they designed a fully-enclosed cockpit and opted for a single wing instead of a biplane configuration. They utilized a cantilever wing, avoiding extraneous wing struts or bracing cables that would slow the airplane down. They understood that a smaller wing would be more efficient at higher speeds, but they also understood that additional lift would be necessary for takeoff and landing. 

To balance these opposing demands, they introduced what is thought to be the first wing with adjustable camber via leading-edge and trailing-edge devices. Like a modern wing with slats and flaps, the RB-1’s wing could be configured in flight by the pilot. For takeoff and landing, camber would be increased and slower airspeeds would be possible, but for high-speed cruise, the wing could be flattened and streamlined to reduce drag.

The engineers didn’t stop there. Recognizing that landing gear is a massive source of drag at higher speeds, they developed (and patented) a novel retractable landing gear design. By turning a hand-operated crank linked to chains and gears, the pilot could raise the gear in approximately ten seconds and lower it in approximately six.

The engineers also linked the landing gear to the variable-camber wing. Retracting the gear also retracted the leading and trailing edges of the wing. When it was time to land, everything extended at once, in unison.

The entire front section of the airplane was dedicated to the engine’s massive radiator, which completely enveloped the crankshaft. No forward windscreen was provided to the pilot; like the Spirit of St. Louis, they would have to make do with the side windows and utilize their peripheral vision for takeoff and landing.

Having sculpted the monocoque fuselage and wing to their liking, Dayton-Wright turned to the powerplant. They chose a water-cooled inline six manufactured by Hall Scott and producing 250 horsepower. At the RB-1’s maximum takeoff weight of 1,850 pounds, this gave it a better horsepower-to-weight ratio than a similarly-loaded Republic P-47 Thunderbolt. 

The RB-1 first flew in 1920, not long before the trophy race. Test pilots conducted a short series of test flights at the company’s facilities near Dayton, Ohio, and estimated the airplane’s top speed would approach 200 mph. Afterward, the airplane was disassembled, packed into a crate, and shipped off to France.

When the big day came, the RB-1 took off from Ville Sauvage near Étampes in the company of the other competitors, only to have to abandon the race and return to the airport after only 15 minutes. Sources vary with regard to the reasoning. Most claim the pilot was unable to retract the gear and flaps, but Flight magazine reported that he experienced “difficulty with his steering.” 

Given the complexity of the wing, it’s possible only one wing had experienced mechanical issues, thus introducing asymmetry and affecting the control and steering. In any case, the RB-1 returned safely. It was shipped back to the U.S., and it never flew again. It remains unclear why no further flying attempts were made.

Today, the RB-1 is on display at the Henry Ford Museum near Detroit, Michigan. It has been properly restored and hangs with its gear and flaps retracted. An elevated walkway provides visitors with a view of the unique flap mechanism on top of the wing.

Although unsuccessful in its intended mission, the RB-1 brought a blend of remarkably futuristic technologies to light in an era of relatively primitive aircraft and permanently altered the trajectory of aircraft design. To date, no evidence of time travel has been discovered in the development of this groundbreaking aircraft.

The post Dayton Wright’s Race To Build a Time Machine appeared first on FLYING Magazine.

Mention the term “X-plane,” and most envision shadowy experimental military aircraft with mind-numbing performance. From the X-1, which was the first to break the sound barrier, to the X-15, which could cross the Karman line and enter space, X-planes have historically been defined by immense power, blinding speed, and sleek lines reminiscent of fictional spaceships.

Conversely, when discussing X-planes, most tend not to envision design features like an open cockpit, fixed landing gear, and a maximum speed only four knots faster than the cruise speed of a Cessna 182. Most also would not expect this category of aircraft to utilize second-hand Beechcraft parts. But these characteristics define the bizarre Bell X-14, an experimental vertical takeoff and landing (VTOL) jet with a somewhat agricultural aesthetic. Further differentiating it from other X-planes was a second life as a trainer for NASA astronauts to refine their moon-landing skills and a dramatic last-minute rescue from a scrapyard. 

Conceived by Bell Aircraft as part of a U.S. Air Force order to explore and develop VTOL technologies, the X-14 first achieved vertical flight in February 1957. It was among several of the first jet VTOL aircraft to take flight in the mid to late 1950s, a small group that included the Ryan X-13 and the British Short SC.1. The following year, the X-14 successfully transitioned from vertical to forward flight and began comprehensive flight testing at Bell’s facility in upstate New York.

Originally utilizing two nose-mounted Armstrong Siddeley Viper turbojet engines, the X-14 was later upgraded to General Electric J85 turbojet engines—as used in the Cessna A-37 Dragonfly—that produced a total of 6,000 pounds of thrust. This thrust was controlled by a series of vanes within the belly to maneuver the 4,269-pound aircraft. Rather than employ separate engines for forward thrust, the system could direct the thrust downward for takeoff and landing or rearward for conventional flight.

Accurate pitch, yaw, and roll control has historically been a challenge for jet-powered VTOL aircraft. To achieve this, the X-14 utilized a system of bleed air and mechanical spool valves at the tail and at each wingtip. With careful application of the stick and rudder pedals, the pilot could command short blasts of bleed air to nudge the aircraft into the desired attitude during flight.

Bell and the U.S. Air Force tested and evaluated the X-14 and invited pilots and engineers from abroad to participate, thus supporting the development of what ultimately became the VTOL Harrier attack jet. As the X-14’s first chapters of testing drew to a close, NASA took interest. The Apollo program was about to begin, and officials recognized the need for specialized astronaut training. While Gemini had proven astronauts could get to and from space, NASA now needed to train astronauts to precisely maneuver the lunar lander to a predetermined point on the moon’s surface. 

Lacking easy access to a training environment with limited gravity, they employed the X-14, reasoning that the bleed air maneuvering system bore a reasonably close resemblance in practice to the thrusters used to maneuver the Lunar Module. After shipping the X-14 to the Ames Research Center at Moffett Field, California, astronaut flight training commenced. NASA also utilized the X-14 to help develop a more comprehensive training platform, the Lunar Landing Research Vehicle (LLRV).

Among the numerous pilots to fly the X-14 was Neil Armstrong. He put the aircraft through its paces, learning to “perch on a bubble of hot air,” as he reportedly described the hover. Armstrong also reportedly claimed the X-14 was the only aircraft in which he could execute a zero-radius loop, flopping around its center of mass “by deft manipulation of the throttle, nozzle control, and stick.”

All such maneuvers were conducted directly above the airfield of origin, as the total fuel capacity of 110 gallons resulted in as little as 20 to 30 minutes of endurance. Armstrong reportedly ran the tanks dry on more than one occasion, and he compared its glide characteristics to that of a Cessna 206. With Beechcraft wings, the handling would have indeed seemed docile, particularly compared to the F-104 and the hypersonic X-15 he had been flying.

After the X-14 had served its purpose with NASA, it was entrusted to a government entity that initially had plans for restoration but ultimately placed it into long-term storage. Decades of being disassembled to various degrees and moving from place to place took a toll. Sections of the airframe were damaged, the brightly-polished aluminum skin became weathered and dull, and when it ultimately began to resemble a pile of discarded scrap, the entire thing was eventually sent to a scrapyard. 

When an aircraft arrives at a civilian scrapyard, it typically doesn’t take long for it to be erased from existence completely. Fortunately for aviation enthusiasts and historians, however, a man named Rick Ropkey learned about the X-14 before it succumbed to that fate. In the late 1990s, upon learning of its condition and of the plan for it to be scrapped, he purchased it and arranged for it to be trucked to his family’s military history museum in Indiana, the Ropkey Armor and Aviation Museum. 

Ropkey was not satisfied with rescuing only the aircraft itself. He also managed to locate and salvage a massive amount of materials related to the X-14, including large-scale blueprints, various forms of test data, and boxes of manuals, some of which had been initialed “N.A.” Familiar with the aircraft’s history, Ropkey reached out to an old fraternity brother who knew Neil Armstrong personally and eventually got in contact with the legendary astronaut. Before long, Ropkey and Armstrong were on a first-name basis, and Ropkey was able to gather unique, first-hand accounts of the X-14’s history.

Over the years, Ropkey and his son Noble gradually worked through the restoration process, restoring one part at a time while keeping the X-14 on display in their museum. When Ropkey’s father died in 2017, the museum was forced to relocate. Presently, plans are afoot to display the X-14 again, and the restoration is nearly complete. 

While the family has no intention of ever flying the X-14, they are striving to complete a full restoration and share it with the public. Presently, the most significant challenge is sourcing parts for the GE J85 engines, and Ropkey hopes to find a source willing to donate surplus engine parts. “It’s been a labor of love for the last three decades,” Ropkey said, and added, “It’s going to be in the Ropkey hands for a long time.” 

After surviving 24 years of operation with no major accidents or serious injuries, and after countless landings by astronauts-in-training, aviation and history enthusiasts alike are fortunate that the unique X-14 has landed in the hands of a family with a strong appreciation for it and its legendary history.

The post How NASA’s Unconventional Bell X-14 Almost Landed in the Scrapyard appeared first on FLYING Magazine.

Throughout the late 1980s and early 1990s, McDonnell-Douglas was struggling to secure contracts for the production of tactical military jets. In 1986, after submitting multiple proposals for the USAF’s Advanced Tactical Fighter (ATF) program, the company was excluded from the running. Later, it partnered with Northrop Grumman to develop the YF-23, only to lose to the F-22 in 1991.

Reeling from these losses, company leaders decided they needed to make up lost ground. Recognizing that stealth technology and affordability were key elements in future success, they launched a program in 1992 to develop their capabilities. This program entailed the design, manufacture, and testing of a cutting-edge research aircraft that would become known as the Bird of Prey.

Named after a Klingon spacecraft from Star Trek and given the designation ‘YF-118G,’ the jet incorporated dramatic design inside and out, albeit in very different manners. The fuselage, wing, and exterior were designed to explore multiple facets of stealth technology above and beyond, minimizing the radar cross section (RCS). While the RCS is estimated to be as small as a mosquito, engineers also buried the engine deep within the fuselage to minimize the infrared signature and even carefully designed the paint shading to visually mask the actual fuselage shapes in daylight—a measure not utilized by other stealth aircraft such as the F-117 and B-2.

Less visible but no less significant were the efforts made toward the company’s goals of streamlining the design and assembly processes and ultimately improving affordability. By utilizing rapid prototyping techniques through the use of computer programs and 3D rendering, engineers were able to simulate the performance of individual parts and systems aboard the aircraft, thus minimizing the need to continuously produce and test multiple iterations of physical parts. These efforts even extended to making tooling easier and more affordable to manufacture.

A parallel effort was made to reduce the cost of the aircraft itself through the use of off-the-shelf components wherever possible. By selecting an off-the-shelf business jet engine, landing gear from Beechcraft turboprops, an ejection seat from a Harrier, and cockpit controls from various existing tactical jets, the team scavenged scrap yards and kept the balance sheet under control. Ultimately, the entire program reportedly cost $67 million, less than the cost of two new 737s at that time.

When the Bird of Prey made its maiden flight in September of 1996, it quickly became clear that the aircraft, with its highly-swept, 23-foot-span wing, did not exhibit good flying performance. Fortunately, it didn’t need to. With an airframe that placed far greater value on low observability than on aerodynamic performance, the speeds, altitudes, and handling characteristics were less than impressive.

The Pratt & Whitney JT15D engine, basically the same engine as used by the Cessna Citation V and Beechcraft Beechjet, produced 3,190 pounds of thrust. Maximum takeoff weight was 7,400 pounds, producing a similar thrust-to-weight ratio as those jets. The optimization for stealth performance, however, resulted in an “operational speed,” as reported by an official Boeing press release, of 260 knots and a maximum operating altitude of 20,000 feet. A Pilatus PC-12 can fly both higher and faster.

Nevertheless, the Bird of Prey went on to fly 38 test flights between 1996 and 1999, and the program was successful enough to survive the Boeing acquisition of McDonnell-Douglas in 1998. After the program was publicly unveiled in late 2002, the aircraft was given to the National Museum of the United States Air Force in Dayton, Ohio, where it remains on display today.

Despite being put on display, one curiosity remains—an apparent lack of any publicly-available photos of the cockpit or instrument panel. While it’s unlikely these are still officially classified, the jet currently hangs at a height that keeps them well out of view. Additionally, the cockpit windows of the similarly spooky Tacit Blue stealth testbed were painted black for display in the museum, also preventing any views into the cockpit.

Whether these efforts are coincidental or intentional, they certainly lend an air of mystery to aircraft that themselves were shrouded in secrecy from the beginning.

The post Boeing Bird of Prey Shrouded in Secrecy Still appeared first on FLYING Magazine.

When designing a single-engine jet, there are only so many places one can mount the engine. To avoid asymmetric thrust, it must be mounted on the centerline of the fuselage, and doing so introduces new challenges. Something must be done to provide the engine with clean, undisturbed air for the intake, for example, and the design must somehow prevent the hot exhaust from damaging tail surfaces.

In mid 2007, when many manufacturers were developing new designs for the newly-identified very light jet (VLJ) category, Piper began development of their own VLJ with the goal of finding the simplest solution possible. They decided against housing the engine within the fuselage, as this would present complex challenges with regard to ducting airflow cleanly through inlets. Additionally, an engine housed within the fuselage must be engineered to minimize the risk to the occupants in the event of an uncontained compressor blade or disk failure.

Avoiding such constraints necessitated an engine positioned outside of the fuselage, and to ease cabin access with shorter, lighter landing gear, this meant on top. Piper needed to protect the tail surfaces from the aforementioned hot engine exhaust, but they wanted to avoid the use of relatively heavy and complex designs like some competitors were using. The Eclipse 400 Concept Jet, for example, utilized a V-tail that required a separate engine pylon, and Adam Aircraft opted for a massive twin-boom design for their A700.

Perhaps drawing inspiration from the McDonnell Douglas DC-10 airliner, the team opted to integrate the engine with the vertical stabilizer. This configuration offered several significant advantages. Chief among them, the engine would be provided with clean, undisturbed airflow, and there would be no concerns about hot engine exhaust affecting the airframe.

The simplicity of this configuration provided some ancillary benefits, as well. Because the fuselage was relatively conventional, existing components could be used. For the proof-of-concept aircraft, the team repurposed a Meridian fuselage. The wing was also conventional and didn’t require any significant engineering beyond that of existing aircraft. Compared to an entirely clean-sheet design, these factors would reduce the complexities of certification and production.

This would also enable the team to focus on the unique engineering challenges introduced by the tail-mounted engine…and after the aircraft’s first flight took place in July of 2008, they discovered several to address. The most significant was identified early on in the design program – the high thrust line. Because the engine was placed so far above the aircraft’s center of gravity, the application of thrust would result in a nose-down pitching moment, and a thrust reduction would result in a nose-up pitching moment.

This thrust/pitch coupling could be addressed in several ways. Various systems like vectored thrust and active trim could be utilized, but systems like these introduce weight, complexity, and additional points of failure. Piper instead developed a simple and clever fixed nozzle system that produced a variable thrust angle. 

The nozzle did so through the Coanda effect, in which air clings to a surface and can thus be aimed via this air pressure alone. At low speeds, the Coandă effect was pronounced and created a greater thrust vector that effectively countered the high thrust line. At high speeds, the effect was minimal and resulted in a 2.2 percent geometric loss of thrust, which was considered acceptable. 

This system was a success. Even with the high thrust line, go arounds could be accomplished hands free, a rare handling characteristic even among more conventional designs. Test pilots reported power changes had a less pronounced effect than propeller-driven aircraft. 

The team encountered another challenge when they discovered that the use of full flaps could produce a tail-plane stall. This would result in an uncommanded pitch down, which is obviously an undesirable characteristic. The issue was resolved by altering the horizontal stabilizer, increasing its span, increasing the elevator size, and adding 30 percent of sweep, which moved the aerodynamic center aft and solved the problem.

With significant engineering accomplishments under their belt and 180 pre-orders for the $2.2 million aircraft, Piper moved forward with development of a new version called the Altaire. The Altaire would incorporate a larger, roomier cabin, and projected performance of a 35,000-foot maximum cruise altitude, a 360-knot maximum cruise speed, and a 1,200- to 1,300-nm maximum range.

Despite the numerous engineering accomplishments and an optimistic initial outlook, the PiperJet program ultimately succumbed to market conditions. Economic and market forecasts became bleak, and rather than risk the company on a single new aircraft subject to the projected market downturn, Piper put the program on indefinite hold.

When it became clear the program would progress no further, the Smithsonian expressed an interest in acquiring the sole prototype, with the caveat that Piper include the first Piper/Taylor E-2 Cub ever sold. The Florida Air Museum in Lakeland also expressed an interest in acquiring the prototype but included no such contingencies and ultimately received the aircraft. 

There, the sole PiperJet remains on display for the public and future generations to admire.

The post The Rise and Stall of the Piper PA-47 PiperJet Program appeared first on FLYING Magazine.

Postwar aircraft development, particularly throughout the 1960s and 1970s, was an interesting chapter in general aviation. Light singles saw a wide variety of new and creative designs launched and tested, ranging from small experimental aircraft like the Rutan Quickie to larger-sized design studies like the Cessna XMC. Some of these more unique types like the pressurized Mooney M22 Mustang even reached limited production.

Light piston twins saw considerably less variety and experimentation than singles. While a few less-conventional examples like the Piper Aerostar and Angel 44 made their marks, the scene was dominated by relatively conservative designs like the Piper Seneca, the Beechcraft Baron, and Cessna’s 300 and 400-series cabin-class twins.

Among the more obscure and unique specimens was the Burns BA-42. Launched by businessman Sam Burns in 1963, the program was a product of a collaborative design effort from a group of engineers and students at the Mississippi State University’s Department of Aerodynamics. One member of the group was none other than Al Mooney, and as one might expect from Al, much effort was focused on the aerodynamic cleanliness of the airframe.

The BA-42 is a compact aircraft, with an understated presence that would be overshadowed by even a Beechcraft Duchess. The mid wing provides for a low-slung appearance, and the relatively long fuselage enables the use of a compact vertical stabilizer. Looking at it from across a ramp, one might not guess that it is a 4,300 pound, six-place airplane.

Examine the BA-42 up close, and additional details shed light on the goals of the design team. Flush riveting indicates strong concern for drag reduction, as is the lack of any major flat surfaces on the airframe. Such design elements place emphasis on performance rather than cost-effective manufacturing.

One of the most striking aspects of the airframe is the positioning of the 210 hp Continental IO-360-D engines. In an attempt to minimize Vmc (the speed below which aircraft control cannot be maintained if the critical engine fails), the engines are placed as close to the aircraft’s centerline as possible. Only two fingers can be placed between the prop tips and the fuselage, and one wonders just how loud the cabin would be at high power settings.

The effectiveness of this engine placement is unclear. Early press about the BA-42 touts Vmc being below stall speed, but a look at the airspeed indicator in the aircraft itself suggests otherwise. If the white arc on the airspeed indicator is to be believed, the stall speed is 76 mph. Additionally, the FAA type certificate data sheet (TCDS) and the red line on the airspeed indicator both define the BA-42’s Vmc as 95 mph.

The BA-42 first flew in 1967, four years after initial design work commenced. Very little information is available regarding the airplane’s performance, but one early review mentioned a 218 mph cruise speed at 75 percent power. If accurate, this would have been impressive, besting comparable Cessna and Beechcraft models with 50 fewer horsepower per engine. The company claimed that the BA-42 has less frontal area than a Cessna 182. If this is indeed the case, such a cruise speed might be plausible. 

Burns had high expectations and equally high optimism for the airplane. The circular fuselage cross section was chosen in part for the ability to more easily adapt pressurization in future derivations. More powerful engines were anticipated, as well, including turboprops that would greatly increase cruise speed and service ceiling.

As is all too common among new aircraft manufacturers, however, the project died in 1973. The market for light twins was relatively crowded at that time, and although the BA-42 was granted FAA type certification, weight and balance issues emerged. Specifically, the type certification was predicated upon a limitation to only four seats as opposed to six as originally planned.

Two BA-42s were ultimately built. After the initial corporation ended the program, it was later purchased in whole by the Mael Aircraft Corporation in Portage, Wisconsin. A family-owned company, Mael put further effort into completing certification for the six-place design and has reportedly entertained multiple proposals over the years to put the airplane into full-scale production. To date, however, none have come to fruition.

Presently, both BA-42s are being kept in Portage, Wisconsin. The example being kept outside shows considerable wear from the elements, but a representative from Mael reports that the second aircraft has been preserved indoors and could be returned to an airworthy state with relatively little effort.

With any luck, this little-known Al Mooney design will one day take to the skies again.

The post The Short Run of the Burns BA-42 appeared first on FLYING Magazine.

Most aircraft engineers, tasked with designing a new STOL aircraft, wouldn’t opt to drill 160,000 holes in the wing and utilize two piston engines to drive a single pusher propeller. 

But then again, most engineers aren’t Jim Bede. 

While still enrolled in the aeronautical engineering program at Wichita University, Bede designed an aircraft that would incorporate a number of unique technologies. His vision was to integrate these technologies to provide superior performance to existing designs. Integrating new systems and complexity into an entirely new aircraft design, however, would prove to be challenging even for him. 

Bede started with an entirely clean-sheet design. Envisioning an eventual family of multiple aircraft varying in size and passenger capacity, he began with an experimental prototype of the Bede BD-2, which he called the XBD-2. Intended as a proof-of-concept and testbed and first flown in July of 1961, it was boxier and more utilitarian than the sleek, streamlined concepts he endeavored to build, but it would function well for its intended purpose.

At first glance, even an experienced pilot or engineer might not guess the XBD-2 is a twin-engine aircraft. But it is, and two 145 horsepower six-cylinder Continental O-300s are snugly nestled in the aft fuselage, stacked one above the other. While such an engine configuration is decidedly unconventional, Bede was of the opinion that it offered several advantages.

Most obviously, housing the engines within the fuselage provides for a clean wing, undisturbed by engine nacelles and far more aerodynamically efficient. From a controllability perspective, an engine failure would be a non-event, as there would be no risk of asymmetric thrust. The lack of engine nacelles helped to reduce overall drag, enabling an 18:1 glide ratio. 

A system of 10 belts and multiple clutches enabled operation at any combination of engine power, and the pilot could shut one engine down completely to maximize endurance. Bede even mounted each engine on a slide-out rack, a design he claimed enabled an engine to be removed in only 30 minutes. Presumably, little time was required to decouple an engine from the system of drive belts.

It was a complex system, but Bede wasn’t finished. With the assistance of Mississippi State University’s aerophysics department, he introduced further complexity to the aircraft by integrating a Boundary Layer Control, or BLC system, into the design. Utilizing 160,000 strategically-placed pinholes in the upper wing and aileron surfaces—holes roughly 30-50 percent as large as those in a typical air hockey table—the system would draw air into the wing to create additional lift. By causing the boundary layer to stick to the wing at high angles of attack, the system effectively increased lift and lowered the stall speed.

The BLC system drew air into the wing via a pump driven by the propeller shaft. So long as the propeller was being turned by at least one engine, the BLC system would operate. Ingested air was ducted back to the engines to provide additional cooling. The system proved to be effective, lowering the stall speed from 64 mph to only 42 mph—an impressively slow speed for an airplane with a gross weight of 3,300 pounds. Bede even claimed that the system would be undeterred by rain.

The most visually notable feature of the XBD-2 is the shrouded propeller. Bede was of the opinion that the aerodynamics at the tips of a standard propeller was one of the greatest sources of inefficiency, and he claimed his testing found that “a correctly-designed shroud” would increase the static thrust of a given propeller by over 100 percent. While many would be interested in seeing figures to back up this rather extreme claim, his other claim that a shroud greatly reduces propeller noise is perhaps more palatable and easy to accept.

The basic performance figures of the XBD-2 are impressive. At 9,000 feet, max cruise speed was said to be 179 mph at 16 gallons per hour. Max rate of climb at maximum gross weight was listed as 1,050 feet per minute with both engines operating and 720 feet per minute with one engine shut down, and the service ceiling was 21,000 feet on two engines and 14,500 feet on one. 

Takeoff distances were similarly impressive. While the company didn’t specify at what weight the numbers were achievable, they claimed only 300 feet was required for the takeoff roll, and 500 feet was required to clear a 50-foot obstacle. 

Ultimately, the XBD-2 logged approximately 50 hours of flight time before being permanently retired. No further derivatives were ever produced, and neither the BLC system, the coupled twin engine configuration, nor the shrouded propeller would make an appearance in any of Bede’s subsequent designs. Today, the sole XBD-2 is on display at the Manitowoc County Airport in Manitowoc, Wisconsin.

The post Bede XBD-2: Experimental Prototype for Unique Technologies appeared first on FLYING Magazine.

During the 1960s and 1970s, many aircraft companies developed twin-engine derivatives of their existing single-engine offerings. Piper produced the Seneca, which was essentially a Twin Cherokee Six. Cessna produced the Skymaster, which could be considered a twin 210. And Grumman created a twin-engine version of the single-engine Tiger called the Cougar.

Whether the demand for twins was a function of a real or perceived lack of engine reliability, or whether it was simply a sign of the industry taking advantage of robust demand for aircraft across all categories is unclear. But what is clear is that aircraft owners and operators had twin fever, and in the rush for market share, even smaller, more specialized companies like Helio responded to the demand and began designing twins.

Starting with their successful short takeoff and landing (STOL) Courier, Helio engineers removed the original engine and placed two 250 hp Lycoming O-540 engines on the wing. With nothing remaining in the nose, they cleverly solved one common challenge among taildraggers—poor forward visibility—by incorporating a helicopter-style bubble window in the nose.

To improve forward visibility even further, they also shrunk the instrument panel, relocating many gauges, switches, and the throttle quadrant to an overhead panel. This had the added benefit of placing engine-related controls and gauges closer to the engines themselves. When combined with the glass nose, the tiny panel afforded pilots outstanding forward visibility.

To maintain the single-engine Courier’s utility in challenging, off-airport operations, they retained the tailwheel configuration as well as the traditional Helio wing design. Utilizing large flaps and slats for better performance at high angles of attack, the wing also incorporated roll control spoilers that deployed with the ailerons to improve roll response at low airspeeds. Helio added a thin, slotted airfoil spanning the two engine nacelles to later models, reportedly to improve boundary layer control over the center section of the wing.

First flight took place in April 1960, and it quickly became evident the engineering worked. Helio touted a 320-foot takeoff distance over a 50-foot obstacle, though it is unclear upon what weight this was predicated. A 1964 evaluation flight by Air Progress, however, reported a takeoff ground run of only 250 feet at a light weight with a 7 mph headwind.

Other performance specs were similarly impressive. The FAA type certificate data sheet lists a single-engine minimum control speed (Vmc) of 59 mph, and Helio claimed a minimum speed of 35.7 mph. Rate of climb with both engines operating was said to be 1,600 fpm, and single-engine rate of climb, 310 fpm. Range was listed as 808 miles.

FAA type certification was awarded June 11, 1963, and Helio gave the Twin Courier a designation of H-500. Foreseeing military use, the U.S. Air Force assigned the designations U-5A and U-5B to the naturally-aspirated and turbocharged versions, respectively. But despite the certification and preparation, only seven examples would ever be produced.

The operational history of these seven aircraft is as unique as their appearance. While Helio publicly stated that all Twin Couriers were delivered to the CIA, they would go on to operate in clandestine operations under various entities of the U.S. military and government. Over their operational lives, some would be given USAF markings, while others would wear civilian paint schemes and civilian registration numbers. The N-numbers were registered to entities speculated to be shell companies for the CIA.

Tracing their operating missions, locations, and agencies is no small feat. Dr. Joe F. Leeker of the University of Texas, Dallas, has compiled what might be the most comprehensive history of the Twin Courier. In it, he traces the progression of each airframe through its respective history, noting that they saw service in Nepal, Bolivia, Peru, and the U.S. before being transferred to—and disappearing in—India. From there, the trail goes cold, and no Twin Couriers are known to exist today.

We can speculate, however. Given the rugged, remote areas in which the aircraft were known to operate, demanding airstrips and conditions likely claimed more than one aircraft. It’s plausible that one or more examples went down in inhospitable terrain and were swallowed by nature and the elements. Others were probably cannibalized for their rare parts. And given their shadowy history, it’s also possible that every trace of the type was intentionally scrapped and concealed from public view.

Considering the clever engineering and intriguing history of the Twin Courier, it’s unfortunate none exist today to be admired in person by future generations. Despite being certified by the FAA, it’s unlikely more will ever be built. In the meantime, we’re left with a small handful of photos, tiny scraps of unclassified U.S. government documentation, and a five-second cameo in the 1965 Jean-Paul Belmondo film, Up to His Ears.

Ultimately, the Twin Courier was an example of the long-standing effort to blend rotary-wing utility and fixed-wing speed, able to operate into and out of tiny, unimproved clearings while still providing relatively brisk cruising speeds. Today, tiltrotors fill the role admirably, but had the Twin Courier been given more of an opportunity to prove itself, it’s possible it would have provided similar functionality in a smaller and considerably less expensive package.

The post The Clandestine Legacy of the Helio Twin Courier appeared first on FLYING Magazine.

The late 1950s were an exciting time for Cessna. Demand for general aviation aircraft was robust, and thus, the company invested significant resources into identifying and pursuing emerging markets. One such market during that time was corporate travel.

Corporate aviation had existed for decades, but the post-war environment rekindled the segment. A handful of companies converted larger, former military types into executive aircraft, but most new models under development—such as the Aero Commander 500 series and Beechcraft Queen Air—had relatively small cabins. Others, like the Twin Beech, were relatively slow and lacked pressurization. Cessna saw an opportunity.

Launching a massive market research project, Cessna interviewed several hundred executives and corporate pilots who either operated or were interested in purchasing a new corporate aircraft. As Cessna’s marketing team categorized and studied the responses, they identified six very consistent concerns: safety, all-weather capability, comfort, speed, economy, and general utility. Using these themes as guidance, the engineers got to work.

In 1956, the Cessna 620 emerged. Its name derived from having twice as many engines as the 310, the four-engine pressurized corporate aircraft was something altogether different for Cessna as well as for the market as a whole. With a wingspan of 55 feet, a fuel capacity of 535 gallons, and a maximum takeoff weight of 15,000 pounds, it was by far the largest civilian Cessna model to date.

The 620s design and performance reflected the marketing study perfectly. The four-engine configuration was regarded as a significant safety feature compared to existing twins. It was equipped with a Garret turbine auxiliary power unit (APU) that pressurized the cabin, and supercharged, 350 horsepower Continental GSO-526 engines that enabled a service ceiling of 25,000 feet and provided a means of flying above inclement weather.

The 620’s tall cabin enabled comfortable movement within. [Credit: Textron Aviation, Inc, all rights reserved]

Compared to existing 6- to 8-place cabins, the 620’s cabin was massive. The oval cross section provided six feet of height, various seating configurations could be utilized, and niceties such as a lavatory and baggage area were installed for long-distance comfort. Comfort was important, as achieving the maximum 1,700 miles of range at a cruising speed of 260 mph would mean long stints aloft.

The cruise speed was reportedly considered acceptable by the focus group, however. This was fortunate, as it enabled the use of smaller piston engines as opposed to turboprops, which Cessna reasoned would have resulted in an unacceptably high purchase price. Cessna also touted the piston engines as more easily serviceable at out-of-the-way locations than turbines.

Convinced the 620 had a bright future, Cessna constructed a full-size cabin mockup and sent it to trade shows, where it was showcased alongside existing aircraft. Smaller mockups and technical displays accompanied the cabin mockup, touting the 620’s ability to utilize its APU where ground power wasn’t available. The marketing team also displayed individual technical components of the aircraft such as an engine and a propeller.

Cessna’s marketing effort for the 620 was strong, utilizing both miniature and full-sized cabin mockups. [Credit: Textron Aviation, Inc, all rights reserved]

In August 1956, the 620 made its maiden flight. Test pilots reported great handling characteristics, and Cessna began collecting refundable deposits. The price of the 620 had increased substantially above the original target price, however, and had reached $375,000—the equivalent of $3.9 million today.

For perspective, the Learjet 23, which was only about five years away, would initially sell for $489,000. While still a significant premium above the 620, it would be a sign that smaller corporate jets were poised to take over. Additionally, sales numbers of corporate piston aircraft such as the Howard 250 were relatively small, further suggesting the segment’s future would burn jet fuel. 

Cessna President Dwane L. Wallace (left) poses with the 620. [Credit: Textron Aviation, Inc, all rights reserved]

Just over a year later, Cessna made the decision to cancel the 620 program entirely. The single prototype was scrapped, and the company’s largest corporate aviation offerings would be limited to the 400-series twins until 1968, when the Fanjet 500 would make its debut. This, of course, would evolve into the wildly successful Citation series of business jets. 

Whether the 620 would have captured a significant share of the market during that ten-year gap is arguable. It’s possible Cessna could have sold enough of them to create a notable chapter in corporate aviation history. But it’s also possible the development, launch, and manufacture of the unusual four-engine airplane might have robbed critical resources from the development of what would become the Citation, thus hobbling the company for decades to come.

The 620, therefore, is relegated to a curious and unique footnote in the history of corporate aviation, demonstrating what can be accomplished with outside-the-box thinking…and also what can be accomplished by instead opting to pursue more viable alternatives.

The post The Four-Engined Cessna and Its Corporate Mission appeared first on FLYING Magazine.