But silhouettes mask details and size, and a closer look reveals how the massive Hughes XF-11 was a vastly different aircraft—with a vastly different fate.

The size of the XF-11 isn’t readily apparent in most photos. Only when a person or automobile is positioned next to it does the scale really sink in. At over 101 feet, the wingspan is greater than that of an early Boeing 737, and at over 58,000 pounds, it’s heavier than a 50-passenger regional jet.

The scale of the engines is equally impressive. Compared with the 1,600 hp Allison V-12s fitted to the P-38, the XF-11 utilized massive Pratt & Whitney R-4360 Wasp Major 28-cylinder radials—the same engines found on the Convair B-36 Peacemaker. Unlike the Peacemaker, however, each of the XF-11’s engines was designed to turn two four-bladed contra-rotating propellers.

The XF-11’s long, thin, high-aspect-ratio wing and powerful engines provide clues to its intended purpose. Capable of reaching 42,000 feet with a 5,000-mile range, it was positioned as an ideal solution for photo reconnaissance work—a task that became increasingly necessary during World War II. With so many Japanese enemy bases positioned so far away from U.S. bases, top military officials saw value in developing a purpose-built aircraft for the task.

Although the XF-11 proposal beat out competing ones from Boeing, Lockheed, and Republic, Hughes soon found themselves struggling with production and logistics issues. A number of major components, such as the wing and the engines, were delayed by as much as seven months, placing the program well behind schedule. Adding to the company’s woes, other components, such as the propellers, were consistently problematic—a problem that led to the loss of one of the two XF-11s that were ultimately produced.

On July 7, 1946, Howard Hughes himself took the controls for the first official flight of the XF-11. Despite the right-side propeller exhibiting mechanical issues prior to the flight, Hughes elected to continue with the flight. He also elected to extend the duration of the flight considerably beyond the original 45-minute plan. 

Just over an hour into the flight, the right-side propeller lost oil pressure and changed pitch. This drastically increased drag on that wing. Control inputs to counter this deployed the left-side roll-control spoilers, further increasing the aircraft’s overall drag.

Unable to maintain altitude, Hughes attempted to make an off-field landing at a golf course in Beverly Hills, California. He was unable to extend the glide that far, however, and crashed into a neighborhood. He struck several houses, causing the aircraft to burst into flames and leaving him with multiple severe injuries.

The Hughes Corporation continued developing the second prototype. In an effort to eliminate the cause of the first aircraft’s crash altogether, they opted against using the original contra-rotating propellers and fitted it with simpler, standard four-blade propellers instead. This aircraft went on to undergo further testing at other air bases, but when the program was terminated in 1949, it was scrapped.

The photo-reconnaissance role for which the XF-11 was designed was ultimately filled by far more cost-effective modifications of existing airframes, such as the Boeing RB-29. Ironically, another such replacement was the F-4 and F-5 photo-reconnaissance versions of the P-38 Lightning, of which over 1,300 were manufactured and flown.

The post The Hughes XF-11, a Behemoth That Never Made It Out of Testing appeared first on FLYING Magazine.

It would entail multiple powerplants, long drive shafts, and pusher propellers mounted on the extreme aft end of an aircraft. Well-stocked from the war effort with a robust team of engineers and faced with a dwindling number of military contracts, the company tasked a team to investigate and develop the concept.

• READ MORE: Cessna 407: Full Steam Ahead, Right Up Until the End

The company’s first attempt at integrating the new design resulted in the XB-42 “Mixmaster”—an experimental military bomber with twin contra-rotating propellers mounted to a common drive shaft. Although the company built and flew two examples, the military quickly lost interest in piston engines, and Douglas pivoted, ultimately reworking the XB-42 into the jet-powered XB-43. Neither aircraft would advance beyond the development stage.

Undeterred, Douglas unveiled a proposal for the same twin-powerplant, pusher-propeller concept in 1945, which was applied to a conceptual airliner. Called the Douglas DC-8 “Skybus,” it would utilize the same Allison V-12 engines as in the XB-42, this time buried in the forward fuselage section and linked to the aft propellers with a series of shafts that extended nearly the entire length of the 77-foot aircraft. The Skybus never left the drawing board.

Douglas would try one last time to make the unconventional design work, this time in the form of a 39-foot-long, 5,085-pound, five-passenger GA aircraft. With a large, bulbous forward fuselage section and low wing, the Cloudster II housed two 6-cylinder Continental piston engines behind the passenger compartment. Douglas designed the aircraft around two 250 hp engines but explained in a 1947 press release that it would be flown initially with 200 hp engines until the more powerful ones became available.

As unique as the pusher design was, it was not without precedent. Just two years earlier, Lockheed had built and flown its Model 34 “Big Dipper,” and WACO’s Aristocraft made its first flight only a few months before the Cloudster II. The companies touted many of the same theoretical advantages, including unrestricted visibility from the cabin, no spiraling slipstream effect from a forward-mounted (tractor) propeller, and a quieter cabin. 

• READ MORE: Interstate TDR Developed as Unusual Kamikaze Machine

Moulton Taylor, the designer of the similarly configured roadable “Aerocar” that would fly a couple of years later, added that at idle a propeller mounted to the extreme aft end of the fuselage has the effect of an anti-spin drag chute, adding stability and aiding recovery from spins. Taylor defended the pusher configuration passionately, observing, “Who ever saw a boat with a tractor propeller?”

Another benefit of the design had to do with controllability in the event of an engine failure. Like the Cessna Skymaster, the Cloudster II utilized centerline thrust, meaning that if an engine failed, the remaining engine could power the aircraft without introducing asymmetric thrust and the associated handling challenges. Of course, because the Cloudster II utilized just one prop and drive shaft, a single point of failure of any of these components would leave the aircraft entirely unpowered, illustrating the lack of redundancy compared to a traditional twin.

When the Cloudster II finally flew, it encountered problems that were both predictable and serious. The lengthy drive shafts produced significant vibration through the airframe, a problem that would require careful engineering and multiple isolation units to address. Additionally, the location of the engines mounted side by side, deep within the airframe, introduced cooling issues. While more airflow could be ducted onto the engines easily enough, this would come at the expense of significant drag. 

• READ MORE: The Ryan YO-51 Wowed with STOL Performance

Ultimately, development of the Cloudster II was abandoned in late 1947. Douglas reportedly donated it to a local Boy Scout troop for ground training before it was scrapped sometime after 1958. The concept was then left for WACO to pursue, also unsuccessfully, with its Aristocraft.

In the early 1960s, Jim Bede attempted to make it work with the Bede XBD-2. Later, in the 1980s, the twin-turboprop Lear Fan 2100 attempted to resurrect the concept yet again, but despite building and flying three examples, it once again fizzled out.

The post The Bold, Bulbous Douglas Cloudster II appeared first on FLYING Magazine.

Cessna was no exception, and it took an interesting approach to developing a new model in September 1959. 

Historically, Cessna would modify civilian types for military use. For example, the 310 became the U-3, the 185 became the U-17, and the 172 became the T-41. In the case of the 407, the company reversed the process, using the existing T-37 “Tweet” primary jet trainer as a starting point and modifying it for civilian use. By installing new engines and modifying the cabin section, it aimed to convert the two-place military trainer into a comfortable, four-place personal jet.

There was some precedent for this new category of aircraft. Just seven months prior, French manufacturer Morane-Saulnier introduced the MS.760 Paris, a four-place jet with similar dimensions. With both military contracts and civilian sales secured, Morane-Saulnier appeared to have found multiple markets and would ultimately go on to build more than 200 examples.

Never one to happily cede market share, Cessna observed that it could pursue the blossoming personal jet market and also possibly secure some additional military contracts with minimum investment. By utilizing many of the same components and tooling as the T-37, much of the necessary development work could be avoided. Building a full-scale wooden mock-up and beginning construction of the first prototype, the marketing group began a sales tour, pitching the concept at various locations around the U.S.

Outwardly similar to the T-37, the 407 utilized the same tail section and wing as the jet trainer but repositioned the engine nacelles 9 inches outward to create more internal space. The cabin utilized this additional space to accommodate four passengers and their baggage. Occupants could easily step into the low-slung cabin without the need for separate steps or ladders, a welcome change from the MS.760, which required occupants to climb a stepladder and clamber into the cockpit from above—decidedly unsophisticated for the target customers of luxurious private jets.

Like the MS.760—but unlike the T-37—the 407 would incorporate a pressurized cabin for passenger comfort. This helped to enable a rather impressive service ceiling of 46,400 feet, some 13,000 higher than that of the French jet. At a more typical cruising altitude of 35,000 feet, the 407’s cabin altitude would have been maintained at a reasonable 8,000 feet.

Performance-wise, Cessna promised some fairly impressive numbers. With a 4,657-pound empty weight and 9,300-pound gross weight, the team boasted a range of 1,380 nm and a maximum level speed of 423 knots. The stall speed was listed as a relatively low 84 knots, making the jet capable of accessing runways of around 3,000 feet in length. 

Ultimately, like some other intriguing concepts from Cessna, the 407 was not to be. The mock-up pictured was, in fact, a T-37 with a wooden cabin section. And while construction of actual cabin sections was underway, the entire 407 project was abandoned in favor of the massively successful Citation family, the first of which flew in 1969. Interestingly, the FAA registry shows that Cessna registered a 407 as N34267, with serial number 627, indicating the project was full steam ahead, right up until the end.

The post Cessna 407: Full Steam Ahead, Right Up Until the End appeared first on FLYING Magazine.

Cessna was no exception. Beginning with the O-1 Bird Dog in 1949, the company went on to manufacture a number of other military aircraft, including the T-37/A-37 jet and military versions of the 172, 185, 310, and 337. In the year following the introduction of the militarized 337, known as the O-2, Cessna spotted an opportunity to create a modified version and wasted no time manufacturing a full-scale mockup.

Known as the Cessna O-2TT, the proposed aircraft was an intriguing blend of design elements collectively focused on forward air control missions. Using the O-2 as a starting point, Cessna replaced the 210 hp piston engines with 317 hp Allison 250 turboprops. This, Cessna predicted, would result in notably improved performance. 

In a November 1968 press release, Cessna listed the performance specs of the 3,220-pound (empty) O-2TT. Cruise speed at 75 percent power was listed as 174 knots and the rate of climb in standard conditions was listed as 2,160 feet per minute. The rate of climb with one engine out ranged from 710-795 feet per minute depending on which engine was shut down, but the specification sheet doesn’t articulate whether this is at the maximum (normal) takeoff weight of 5,000 pounds or the maximum (alternate) takeoff weight of 5,750 pounds. Useful load is listed as 1,780 pounds (normal) and 2,530 pounds (alternate).

More visually notable were the changes made to the fuselage. In an effort to provide the two occupants with unrestricted visibility, Cessna extended the forward fuselage dramatically, positioning each seat forward of the wing. Because the 138-pound Allison turbine engine was less than half the weight of the Continental piston engine it replaced, the repositioning of the forward engine would have been necessary regardless to maintain the proper center of gravity.

With both passengers moved forward, the change opened up ample space beneath the wing. Judging by the mock-up, enough space would be available for a third seat, but as the mission requirements only call for two occupants, it would instead be utilized for equipment and cargo. Given the additional fuel burn of the turbine engines, it could also be utilized for an auxiliary fuel tank to extend range and endurance.

To improve short takeoff and landing (STOL) performance, Cessna proposed modifying the wing as well. By increasing the span by over 4 feet and wing area by nearly 20 square feet, the wing would be notably larger than that of the standard O-2. Additionally, the O-2TT would incorporate high-lift devices to further improve STOL performance including a constant-radius leading edge and drooped ailerons interconnected with single-slotted flaps.

• READ MORE: The Ryan YO-51 Wowed with STOL Performance

The relatively straightforward and well-thought-out modifications used to create the O-2TT concept would likely have resulted in a formidable tool for use in forward air control missions. The improved, unrestricted visibility from each seat would have made the job easier for the occupants, the turbine engines would have improved performance and reliability, and the slow-turning propellers would have made the aircraft less noticeable to enemy units on the ground.

Unfortunately, the O-2TT concept never reached production, and the sole mock-up was presumably destroyed. In late 1969, the North American Rockwell OV-10 Bronco would enter service to fulfill the role—perhaps not coincidentally with twin turboprop powerplants, forward tandem seating with unrestricted visibility, and cargo space behind the two occupants.

The post Cessna’s O-2TT Was Designed for Forward Air Control Missions appeared first on FLYING Magazine.

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.

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.

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.

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.

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.

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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.

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