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.

Among the two dozen or so individual models that have been built over the years, only a few types have been produced in quantities of more than two or three. Fewer still were both manned and powered, and the small Horten HX-2 is a member of that exclusive group.

There are several reasons for the rarity of flying wings. Airliner versions never caught on due to their size and overall footprint—a flying wing capable of carrying 50-plus passengers would generally be too large to utilize traditional taxiways, ramps, and ground infrastructure. Most passengers in the voluminous structure would be seated far away from the extremely limited number of windows. Additionally, effectively evacuating a large number of passengers from such an airframe presents several daunting challenges.

• READ MORE: The Hiller Hornet and its Ill-Fated Ring of Fire

This leaves only a few categories in which flying wings make sense. They’ve succeeded in a number of military applications, as their unique advantages of internal volume, aerodynamic and structural efficiency, and stealth benefits outweigh the negatives. They’ve had some limited success in the glider and UAV categories. And while they haven’t caught on in other applications, they have potential in applications requiring smaller airframes and fewer seats, such as business and private aviation.

For a modern prototype, the HX-2 has a unique and deep lineage. Like aircraft manufacturer Flight Design, Horten is a subsidiary of Lift Air, itself part of the large Lindig Group based in Germany. But unlike most other upstarts in aviation, Horten has direct ties to early aviation pioneers—specifically, Reimar Horten. A designer of several flying wings, including the jet-powered Ho-229 fighter/bomber, Reimar contributed to the design of the HX-2’s predecessors in the late 1980s and early ’90s. 

• READ MORE: The Unfulfilled Promise of the Fairchild T-46

With a 32-foot span, a 100 hp Rotax 912iS, and a fuel capacity of 63 gallons, the two-seat HX-2 is a far cry from World War II-era bombers. Indeed, the basic stats place it in a category consisting of modern LSAs and legacy two-seaters like the Grumman AA-1 and Cessna 150. But the unique, flying wing configuration offers some similarly unique advantages in a private GA application.

Efficiency is perhaps the most compelling attribute of the HX-2. Initial testing demonstrated a cruising speed of 87 mph while burning less than 2.65 gph. This equates to an impressive 32.8 mpg.

The design has other inherent benefits. Although internal volume is plentiful and could easily be utilized for cargo and baggage, there would be very little center of gravity (CG) variance. Accordingly, the HX-2 would be difficult or even impossible to load outside of the CG limits. The flat profile has also reportedly demonstrated excellent handling qualities during crosswind takeoffs and landings.

When Horten actively marketed the HX-2 prior to 2020, the company presented it as the initial version of a family of aircraft. Horten planned a kit version, buildable by individuals or in concert with the manufacturing facility, as some manufacturers do today. From there, the company envisioned a four-place version optimized for short-range air taxi operations.

A more distant goal was a hydrogen-powered version. The voluminous design of the HX-2 was particularly suited to this, as large-volume hydrogen storage has always been a significant hurdle for more traditional aircraft designs. According to Horten, the aircraft would have been able to achieve a 1,000 nm range with hydrogen power.

One of the company’s most recent efforts was to position the HX-2 as an ideal platform for unmanned operations. With relatively few modifications, it could provide a range of 2,175 miles or an endurance of 20 hours. Although Horten never actively marketed the HX-2 as a manned military aircraft, it observed that the two-seater has sufficient internal space for the installation of a toilet and a bed.

• READ MORE: Horten HX-2 Takes Flight in Germany

When we visited Horten’s facilities adjacent to Lift Air near Eisenach, Germany, in 2019, and studied the HX-2 in person, the construction appeared to be first rate without sloppy details inherent in some prototype and proof-of-concept aircraft. The two-seat cockpit was indeed spacious, with comfortable seating.

While visibility was decent in most directions, downward visibility was effectively zero, a natural side effect of sitting within the wing. Cockpit access was impossible without a ladder, and one wonders how Horten might have developed stowable, built-in steps to address this.

Unfortunately, while the Horten website is still live and touts the HX-2, development and marketing efforts appear to have stalled since 2020. But the presence of the website nevertheless offers hope that with another round of investment, the program could pick right back up from where it left off.

With any luck, the convergence of funding and market conditions will breathe new life into the HX-2 so that it may take flight once again. 

The post The Untapped Potential of the Horten HX-2 appeared first on FLYING Magazine.

Had they asked the pilots a few additional questions, however, the complete picture would have been revealed. They’d have learned that the aircraft type in question was a tiny helicopter called the Hiller Hornet. It utilized two ramjet engines to achieve a top speed of just 62 knots and had a maximum range of less than 30 miles. While perhaps not as flashy as the aforementioned supersonic interceptors, some might argue that it took more guts to fly the Hornet.

The impetus behind the general design of the Hornet was torque. When power is applied to a stationary main rotor on a traditional helicopter, the fuselage naturally wants to spin in the opposite direction. The traditional tail rotor acts as a lateral propeller, enabling the pilot to push the tail left or right to counteract this torque effect precisely.

The Hornet’s designers attempted to eliminate the torque effect. They reasoned that controllability would be improved if the main rotor could somehow be powered by an engine or engines that did not apply any torque to the fuselage. Additionally, the relatively complex tail rotor assembly and associated drive shafts and linkages could be eliminated.

They brought the concept to fruition by placing two 11-pound ramjet engines on each tip of the two-blade main rotor. Each engine generated 31 pounds of thrust by drawing fuel up from a fuselage tank and through lines buried within its respective blade. Interestingly, these engines had no moving parts and could burn several different fuel types. They had a projected service life of 500 hours and were touted as being replaceable for only $200 each, amounting to $2,454 in 2024 dollars.

Unfortunately, while the torque effects were eliminated, the new design came with several very serious inherent drawbacks. Chief among them was the high fuel burn of the ramjets, which amounted to 600 pounds per hour at higher power settings. With a 300-pound fuel capacity, endurance was minutes rather than hours. 

Autorotations were also a problem. The tip-mounted engines introduced drag and inertia to the rotor, making it difficult for pilots to increase rotor RPM in the event of a power loss and then accurately convert that RPM to lift when slowing the descent rate to touch down.

While the Hornet’s design eliminated the need for a tail rotor mechanism, it did require a small gasoline engine for starting purposes. This engine spun the main rotor to an RPM sufficient for the starting of the ramjets. So, while the complexity of a tail rotor was eliminated, much of the weight saved was reintroduced with the addition of the starting engine.

The military took an interest in the Hornet and conducted an evaluation process. Although the helicopter was indeed flyable and controllable without a tail rotor, the military decided they preferred the additional yaw control that a tail rotor provides. Subsequent models of the Hornet, therefore, incorporated a small tail rotor to satisfy this requirement. The tail rotor used was small in size and was powered by the starter engine. It was unique, as well, utilizing just one blade and a counterweight as opposed to a traditional, two-blade design.

The military discovered some additional problems with the Hornet. The combination of the helicopter’s small size and the droop of the rotor blades meant that it could not be approached while the rotors were turning. This limited the usability in the field. 

Additionally, the ramjet engines created vivid, flaming exhaust trails. This produced what appeared to be a brightly illuminated ring at night. Tactically, this made the Hornet very easy for enemies to spot in the night sky, and in peacetime operations, it reportedly resulted in an overabundance of UFO sightings.

Ultimately, a total of 18 Hornets were built, and while the Army and Navy evaluated the type, no production orders resulted. Today, approximately eight Hornets are in storage and on display at various museums across the U.S.

The post The Hiller Hornet and its Ill-Fated Ring of Fire appeared first on FLYING Magazine.

It fulfilled primary trainer duties for more than 20 years and was modified to serve as a light ground attack aircraft in the form of the A-37 Dragonfly. However, as the 1980s approached, so did the end of the T-37’s projected life cycle, and military leaders determined a more modern replacement was needed.

Among the items on the Air Force’s wish list were cabin pressurization, increased range, lower fuel consumption, increased power, and updated avionics. In 1981, a request for proposal (RFP) was issued for a replacement. Several companies responded, but ultimately, Fairchild was chosen, and its proposed aircraft was given the designation T-46.

• READ MORE: The Bold, Bulbous Douglas Cloudster II

Compared to the T-37, the T-46 was nearly identical in external dimensions with similar empty and maximum weights. The most significant visual differences were the T-46’s high wing and the “H” tail, with twin vertical stabilizers mounted to the ends of the horizontal stabilizer that strongly resembled those of the company’s previous jet, the A-10 Thunderbolt II.

The selection of twin vertical stabilizers for the T-46 is an interesting one. Historically, this tail configuration was intended to provide a clear area for jet exhaust, add redundancy to aircraft anticipated to sustain battle damage, or increase yaw authority by placing the rudders within the prop wash of wing-mounted engines. None of these concerns applied to the T-46, and one wonders whether Fairchild simply aimed to save money by repurposing its former engineering efforts in the A-10 program for its new aircraft.

Before any conforming examples took flight, Fairchild contracted with a third party to fabricate a smaller, 62 percent scale proof of concept. The concept, called the Model 73 NGT, was then flown by Burt Rutan’s company in Mojave, California, for the initial test flights. The NGT served its purpose and is on display at the Cradle of Aviation Museum on Long Island, New York.

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

When the initial, full-scale T-46 prototypes took flight, a number of problems arose. As outlined in a U.S. General Accounting Office (GAO) report, the aircraft’s drag was too high, it did not provide adequate stall warning, the primary flight controls had trim problems that affected stability, and the speedbrakes created unacceptable buffet levels. Additionally, the T-46’s weight ballooned to a figure of 900 pounds higher than projected. 

While the Air Force observed that many of these problems were common among new types and could likely be remedied, Fairchild was also found to be struggling with cost, schedule, and contract difficulties. At least one source suggested that the rising development costs of the Saab-Fairchild SF340 commuter turboprop were eating into Fairchild’s budget for other projects and stretching its resources thin. 

In March 1987, with three prototypes flying and 10 additional examples in various stages of assembly and some 17 months after the first flight, the T-46 program was canceled. Most attribute the decision to a combination of the aforementioned internal struggles at Fairchild as well as a strong motivation for the U.S. Congress to cut costs across the board. 

• READ MORE: The One, Brief Life of the Twin Cat

For an aircraft type that generally showed promise, it was unfortunate. The T-46 stood to follow in the T-37’s footsteps, with potential armed export versions on the horizon that could have kept Fairchild in business for many years. In theory, the company could have even modified the cabin to accommodate passengers, as Cessna did with its full-scale mock-up of the model 407.

Today, all three T-46 prototypes survive. One is in storage at the Pima Air & Space Museum in Arizona, one is on display at the Air Force Flight Test Museum at Edwards Air Force Base in California, and one is undergoing restoration at the National Museum of the United States Air Force in Dayton, Ohio.

The post The Unfulfilled Promise of the Fairchild T-46 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.

The “Twin Cat” of the late 1970s and early ’80s was one such example. A development of the 1950s-era, purpose-built Grumman Super Ag Cat biplane, it replaced the Ag Cat’s single 600 hp Pratt & Whitney R-1340 radial engine with two 310 hp Lycoming TIO-540 flat-6 engines.

Rather than being offered as a complete, factory-built aircraft, the Twin Cat was a modification offered in the form of a supplemental type certificate (STC). The Twin Cat Corporation targeted Ag Cat operators wishing for more easily serviceable engines with increased overhaul intervals and multiengine redundancy, and the company offered to travel to the customer for on-site modification of their Ag Cats.

The company had some impressive experience at the helm. The president had overseen the development of a turboprop conversion of the Grumman Albatross and was assisted by the former chief test pilot at the general aviation division of Rockwell International. Most of the test flights were flown by Herman “Fish” Salmon, retired chief engineering test pilot of Lockheed. Salmon had conducted spin testing of the P-38 Lightning and had flown the first flights of the L-188 Electra, P-3 Orion, YF-104A Starfighter, and XFV-1 turboprop VTOL fighter. 

When designing the Twin Cat, one of the top priorities was to minimize asymmetric thrust in the event of an engine failure. The team did so by utilizing an unconventional engine layout in which the engines were mounted on either side of the nose with only approximately 3.5 feet between the propeller tips. The engines were also canted slightly outward to further minimize the effects of asymmetric thrust during single-engine operations.

The company touted benefits beyond the engines’ 2,000-hour TBO and better parts availability. While the engines were rated at 310 hp each, a sales manager said in an industry presentation that they derated them “with a pencil” and that the full 350 hp was available if needed. The Twin Cat’s total fuel consumption was the same as that of the single-engine radial Ag Cat. They also claimed the new layout improved forward visibility, prop clearance, and spray dispersion. 

When the time came for flight testing, the team got to see whether the new design could deliver the performance that backed up predictions. While the Twin Cat’s empty weight was the same as the Ag Cat’s, at 3,500 pounds, the maximum takeoff weight was 2,000 pounds higher, at 6,500 pounds. A load jettison function enabled the pilot to dump 2,000 pounds of payload if needed.

The new engine layout worked. With both engines operating, the Twin Cat’s takeoff distances were approximately 20 percent shorter than the Ag Cat. Asymmetric thrust was so effectively minimized that a sales manager claimed the Twin Cat could even take off with one engine shut down and then climb at 400 feet per minute at sea level. The company marketed this feature as a useful solution to ferry an aircraft with an inoperative engine to a location where maintenance could be performed.

In the air, the maximum cruising speed was 130 knots. By canting the engines slightly downward, the stall speed was remarkably low, at a claimed 49 knots for power-off stalls and 43 knots for power-on. A brochure claimed that the Twin Cat had “no V_MC,” which would have enabled flight all the way down to stall speed without controllability concerns. 

One account of the airplane’s flight characteristics suggests that it needed more refinement, however. It reportedly lacked any kind of rudder trim, and with an engine shut down, a pilot claimed he ran out of rudder and had to reduce power on the good engine to maintain control. It’s unclear whether the company planned to introduce rudder trim in future aircraft.

In the end, only three examples of the Twin Cat were rumored to have been completed and flown, and few photographs exist. One reportedly crashed, and the others presumably returned to their original single-engine configuration when the company decided against pursuing the concept any further. 

The post The One, Brief Life of the Twin Cat appeared first on FLYING Magazine.

It’s also rare for an airplane to be optionally piloted—capable of flying both with a pilot aboard and also as an unmanned aerial vehicle. However, the Interstate TDR incorporated all these unique characteristics to fit a correspondingly unique set of mission requirements, specifically the ability to operate as a remotely piloted flying bomb. The “TD” portion of the designation signified “Torpedo Drone,” and the “R” was an arbitrary letter assigned to the Interstate Corporation.

• READ MORE: Cessna’s O-2TT Was Designed for Forward Air Control Missions

Compared to other manufacturing priorities during the war effort, the development of a relatively small fleet of unusual kamikaze machines was a low one. A previous attempt had been made with the Naval Aircraft Factory TDN, but it was reportedly found too expensive to manufacture and operate. Accordingly, the Interstate Corporation decided to tackle the project, aiming to find ways to improve upon the TDN.

The company got creative, awarding a contract for 200 tubular steel fuselages to the Schwinn Bicycle Company. It awarded a contract for the fabrication of wooden components to the Wurlitzer Company, a logical choice given its significant experience with manufacturing wooden pianos and guitars.

Interstate equipped the TDR with two 220-horsepower Lycoming O-435 horizontally-opposed, 6-cylinder engines. Later, three examples were fitted with more powerful Wright R-975 Whirlwind radial engines. Considering the TDR’s mission, it’s doubtful that multiengine redundancy was a primary factor in the decision to make it a twin. More likely, this layout was chosen to make room in the fuselage for the hundreds of pounds of radios and servos that enabled remote operation. Additionally, the lack of a nose-mounted engine makes that space available for a forward-looking camera.

Performance would have been modest, considering the TDR’s size and relatively low power. With a 48-foot wingspan and a maximum weight of 5,900 pounds, the airplane was comparable to the Beechcraft Twin Bonanza, yet had 150 fewer horsepower. Cruise speed was reportedly 140-150 mph with a 425-mile range. The TDR lacked brakes entirely, and thus, the takeoff procedure was rather unique. After lining up the airplane on the departure runway, ground crews would tether it to a stationary object such as a car or truck. After the pilot commanded takeoff power, the ground crew would cut it loose. 

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

Although the landing gear was nonretractable, there was a way to eliminate landing gear drag entirely. For one-way missions that would result in intentional crashes into the enemy, the gear would be jettisoned immediately after takeoff, extending both speed and range. This would have opened a decidedly unique job position for ground crews—searching for and retrieving all the jettisoned TDR landing gear for use in future missions.

As part of a top-secret operation, Interstate brought in RCA’s chief scientist to adapt television technology to the aircraft. This enabled pilots to control the TDR remotely from airborne Grumman TBF Avengers. By referencing small TV screens, these pilots could fly the TDRs to targets several miles away and conduct attacks from the safety of their Avengers.

While the TDR proved capable of executing its remotely piloted flying bomb missions for approximately one year in 1944, its accuracy was less than impressive, and persistent developmental problems plagued the program. These issues, combined with the overall effectiveness of conventional weapon systems, ultimately led to the cancellation of the TDR after 195 examples had been built. 

• READ MORE: Flaris LAR 01 Still Has Potential

Interestingly, one TDR-1 was acquired by a private operator in Tulare, California, in 1959 with the apparent goal of utilizing it as an air tanker to help fight forest fires. This operator fitted a 200-gallon external tank on the belly of the fuselage and registered it with the civil designation N7790C. Its ultimate fate is unknown. Today, only one intact example survives, and it is presently on display at the National Naval Aviation Museum in Pensacola, Florida.

Portions of a second TDR also survive, including a large intact fuselage section, and are in the possession of a private individual in the U.S. With any luck, this person will be able to source and fabricate the necessary parts to complete a restoration.

The post Interstate TDR Developed as Unusual Kamikaze Machine 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.

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The USAAC sent bids for such an aircraft to multiple manufacturers. The ensuing competition ultimately came down to three, each building three prototypes in 1939 for the contract. Bellanca responded with the YO-50, a high-wing taildragger with an enclosed tandem cabin powered by a 420-horsepower Ranger inverted V-12. Stinson responded with their L-1 Vigilant, an aircraft of similar design but with a more traditional 295-horsepower Lycoming radial engine.

Ryan’s offering was the YO-51 with a company name of “Dragonfly,” and it incorporated a few unique features that made it stand out from the other two contenders. Rather than being equipped with an enclosed and glazed cabin, the Ryan utilized an open cockpit beneath a parasol wing. While doing away with a cabin altogether makes for an effective observation platform by eliminating a number of blind spots, one wonders how effective the airplane would be in frigid northern climates with cold and fatigued crew members.

The Ryan’s landing gear was quite different from the others but nearly identical in design to the Storch. While the YO-51 differed by integrating the wing strut into the design, both the Ryan and the Storch utilized an extremely wide stance and long-travel suspension. In the case of the Storch, it provided a plush 16 to 18 inches of suspension travel to soak up all but the most violent landings. 

In addition to being a parasol design, the Ryan’s wing incorporated full-span leading-edge devices. Publications differ in their description of them, randomly referring to them as slots, which remain fixed in position, and slats, which move between retracted and extended positions in flight. The publications can perhaps be forgiven, however, as photos exist showing both variants installed on different YO-51s.

Ryan chose full-span Fowler flaps for the trailing edge, a then-revolutionary design utilized by Lockheed on the 14 Super Electra and later on most high-wing Cessna models. Notable for introducing primarily lift in the first segment of travel and then drag at higher settings, these flaps helped to enable exceptional STOL performance, particularly when they make up the entire trailing edge of the wing. To provide roll authority in the absence of traditional ailerons, Ryan equipped the YO-51 with roll-control spoilers.

To the delight of U.S. Army Air Forces (USAAF) maintenance technicians, Ryan eschewed inverted V engines and instead opted to use a common and known engine, the Pratt & Whitney R-985 Wasp Junior radial. Producing 440 horsepower for the YO-51, this engine was also utilized in the Beech 17 and 18 as well as the de Havilland Beaver and Vultee BT-13 Valiant. With almost 40,000 built over the years, Ryan must have touted their engine choice as far more sensible than Bellanca’s.

The three YO-51s, wearing serial numbers 40-703, 40-704, and 40-705, first flew in 1940 and predicted performance was achieved in flight testing. Hard data is sparse, but multiple sources report the 4,200-pound airplane could take off in less than 100 feet and clear a 50-foot obstacle in slightly less than 500 feet. Landing over a 50-foot obstacle reportedly required 400 feet. 

When it came to speed, the complex wing enabled a broad operating range. Stall speed was reportedly only 30 mph, while cruise speed was a healthy 107 mph. These numbers were nearly identical to the Storch…and, perhaps not coincidentally, also nearly identical to the Bellanca and Stinson with which it was competing. 

During some of the first test flights, spectators were wowed by the performance. An article in a Ryan company newsletter reported that during one takeoff, the YO-51 “leaped into the air after a run of only 50 feet, pointed its nose at a 60-degree angle, rose almost vertically and remained virtually motionless over the airport.”

The March 15, 1940, edition of the Air Corps Newsletter described the YO-51’s flight capabilities in an even more colorful manner, observing, “The first model of the YO-51 has been grasshoppering in our midst and is doing things that have reduced our carefully nurtured conceptions of how an airplane flies to a pile of ashes.”

Despite such impressive grasshoppering, the USAAC competition was ultimately awarded to Stinson. During its production run, some 324 examples of the O-49 (later L-1) were built for the U.S. and the Royal Air Force.

Sadly, no trace of the three YO-51s nor the three Bellanca YO-50s remains today. One account reports that the three YO-51s were utilized as “ground instructional airframes,” and it’s likely that all six contenders were ultimately scrapped at some point thereafter. 

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