When's the last time you caught a ride in an autogiro?
- By T.A. Heppenheimer
- Air & Space magazine, March 2003
PLENTY OF BLUNDERS AND BLOOPERS SHOW UP IN THE HISTORY OF THE AIRPLANE. Time and again, inventors (and investors) staked their hopes on dreams that never quite came true or on ideas that went nowhere. As some designers created the classic aircraft of the past century, others proceeded through numerous wrong turns, and here are ten of the most memorable.
Inherently Stable Aircraft
The first powered aircraft to fly were not built by the Wright brothers. They were large model airplanes constructed by then-Secretary of the Smithsonian Samuel Pierpont Langley, and they flew, propelled by small steam engines, in May l896. Like models built by hobbyists today, they were inherently stable. With tandem wings canted at a pronounced dihedral and cruciform tails, the “aerodromes,” as Langley called them, were able to fly distances approaching a mile without falling to the side or nosing into the ground. (Langley’s full-scale aerodrome, which dumped his assistant in the Potomac River, was not as successful.)
The Flyer that the Wrights experimented with a few years later could never have flown such distances without the intercession of a pilot. It was an unstable craft equipped with control devices; with them, the pilot could make the biplane climb, descend, and turn.
An early French aeronaut, Henri Farman, followed Langley’s approach. He built a full-scale inherently stable aircraft. In January 1908, he flew it in a complete circle, skidding around corners in wide, level turns by using only a rudder. Later that year, Wilbur Wright, making a demonstration flight at Le Mans, France, warped the wings of his craft to sweep through a series of banked turns, astonishing the audience with his airplane’s precision and agility. Later, a colleague of Farman declared, “Well, we are beaten! We just don’t exist!”
Unstable aircraft, built in the Wright style, flourished into the l930s, when airplanes grew so large and were capable of flying so far that pilots wearied of constantly struggling with controls during long flights. At that point, engineers began building some stability back into large bombers and airliners to ease the pilot’s workload. Even so, no one returned to inherently stable craft and the flat skidding turns of Langley and Farman.
Reinforcing the notion that the Wrights invented the airplane but the Germans invented everything after that, the first aircraft to fly with forward-swept wings was German: The Ju 287 appeared in August 1944. It had already been discovered that aircraft with wings swept back produced less drag at high speed but were difficult to control at low speeds. (Big surprise: The first aircraft with wings swept back was also German.) Ju 287 designer Hans Wocke reasoned that reversing the sweep should continue to reduce drag at faster speeds but would improve control at lower speeds. He was right, but his design was slightly ahead of the materials available to build it. The Ju 287 made it through several test flights, but its aluminum wings flexed upward and created concern that they would break off from the airplane.
(Wocke returned to forward-swept wings during the 1960s. He headed an engineering team at the firm Hamburger Flugzeugbau, which created the Hansa business jet, a modest commercial success. The last one flew in 1987.)
Lighter composite materials, which offered both stiffness and strength, provided another opportunity to experiment with forward sweep. They led to the Grumman X-29, an oddly graceful jet with a patriotic paint job. The U.S. Defense Advanced Research Projects Agency commissioned and tested it at NASA’s Dryden Flight Test Center in California between 1984 and 1992. The X-29 was extremely unstable and therefore highly maneuverable. Its pilot, relying on a digital flight control system, could maneuver at high angles of attack. Air moving over the forward-swept wings tended to flow inward toward the fuselage rather than outward toward the wing tips; as a result, the wing stalled at the roots before stalling at the tips, and the ailerons near the tips continued to function. So why aren’t future fighters showing forward sweep? The X-29 produced too much drag. Designers, including those at the Sukhoi bureau in Russia, have turned to other ways of achieving maneuverability at high angles of attack. Sukhoi’s Su-47, which may be fielded to contend with the F-22 Raptor, first flew as the S-37 in the late 1990s with forward-swept wings. Last year, the Russian military elected to continue its development with conventionally swept wings.
Pick any airliner flying today: It’s probably powered by turbofan engines. With their gaping intakes and enormous, multi-blade fans, turbofans revolutionized aviation during the late l960s, propelling aircraft of undreamed-of size: the Lockheed C-5A and Boeing 747. They were able to do so because the great size of the fans—some are as large as 10 feet in diameter—enabled them to move huge quantities of air, increasing the engines’ thrust.
The turbofan also offers superb fuel economy. Most of the air pushed rearward by the fan bypasses the engine’s combustion chamber and flows at relatively slow speed, increasing the engine’s effective thrust without burning additional fuel. But after l980, when the price of oil had climbed higher than the aircraft it fueled, General Electric sought to develop engines that would push the fanjet’s efficiency still further.
Existing versions enclosed the fan within a cylindrical housing, or cowl. The cowl slowed the airflow to prevent the tips of the fan blades from rotating faster than the speed of sound, a condition that would have made the engine unacceptably noisy. Just as supersonic aircraft create sonic booms, fan blades spinning supersonically would cause their own loud disturbances in the air.
The cowl also held thrust reversers, clamshell-like structures that reversed the flow of the jet exhaust, directing it forward so it could be used for braking during landings. Making the fans larger would have also required larger cowls, which would have been heavy and difficult to install and would have needed even heavier thrust-reversers.
GE thus put its hope in an unducted fan—a fan without a cowl. Its blades were swept back to reduce the drag from supersonic rotation, and, like reversiblepitch propellers of earlier days, the fan blades swiveled to direct thrust forward during landing. The GE 36 UDF engine produced 15,000 pounds of thrust and weighed only three tons.
In NASA-sponsored ground tests, the engine consumed 20 percent less fuel than the standard turbofan, but flight tests showed that the unducted fan was unacceptably noisy, even in versions scaled down in power for the modest-size airliners of the McDonnell Douglas MD-80 series. For larger aircraft, the noise problem would have been far worse. What really killed the unducted fan, however, was the fall in oil prices in the mid-1980s.
Biplanes flew for decades with great success, but fell by the wayside when they failed to match the speed of monoplanes. The autogiro, a rotary-wing aircraft, suffered a similar fate. A Spanish inventor, Juan de la Cierva, flew the first of them in 1923 and introduced an entirely new mode of flight.
The autogiro was based on the conventional monoplane: It sported stubby fixed wings and a front-mounted engine, but it had a large, unpowered rotor, which turned in the craft’s slipstream and yielded additional lift. An autogiro could fly with a short takeoff run and land nearly vertically, its rotor whirling like a pinwheel as it descended.
Cierva formed a partnership with U.S. airplane builder Harold Pitcairn, who also ran a lucrative airmail route (which he sold to a business that developed it into Eastern Airlines.) Amelia Earhart flew one of the Pitcairn-Cierva craft and praised its safety and ease of control.
But another aircraft was under development in the 1930s that would outshine the autogiro, and by the end of the decade, Igor Sikorsky had mastered its design. A helicopter, which had a powered rotor, could hover, take off and land vertically. Even though the autogiro was faster, the helicopter’s eventual success in military operations proved to be so sweeping that the autogiro vanished entirely.
Custer Channel Wing
There’s something valiant, if clown-like, about the Custer Channel Wing. The semi-circular troughs on either side of its fuselage are suggestive of the oversized ears on Disney’s cartoon elephant, Dumbo. But these channels, through which air was sucked at high speeds by propellers, also created enough lift to bestow on the aircraft Dumbo’s amazing capability for short takeoff and landing (STOL). The aircraft could take off in as little as 150 feet.
The Channel Wing was the lifelong obsession of Willard Custer, a distant relative of the general who died fighting the Sioux at Little Big Horn. Custer flew his first version in 1942 and submitted it for military evaluation, but the Army saw no reason to pursue it. Undaunted, Custer sought backers for a civilian aircraft. A 1953 version flew successfully at speeds as low as 22 mph, and actually hovered in an 11-mph wind, but Custer proved a more talented inventor than financial manager. Although his aircraft never went into production, Custer does have a place in aviation history. His first Channel Wing is in the collection of the National Air and Space Museum, and his third can be seen at the Mid Atlantic Air Museum in Reading, Pennsylvania.
Since The Man with the Golden Gun’s Scaramanga fled James Bond in a custom fastback-cum-airplane, villains everywhere have patiently awaited a production model. Unfortunately for them, manufacturers have been unable to sustain enthusiasm for the concept.
Convair, a major wartime manufacturer, crafted prototypes of its ConvAirCar in the late 1940s (one was reported to have circled San Diego for over an hour), but the effort ended after one of them crashed and another was lost in a fire.
Two models, Robert Fulton Jr.’s Airphibian and Moulton Taylor’s Aerocar, eventually won certification from the Civil Aeronautics Administration, the Federal Aviation Administration’s predecessor, but it was the public, not the government, that needed to be convinced. Taylor, dean of the so-called “roadable” airplane, came close to getting his craft into production in 1961, after it had been featured in a popular 1950s TV show starring Bob Cummings. The firm of Ling-Temco-Vought promised to build 1,000 Aerocars if Taylor could persuade 500 enthusiasts to each plunk down $1,000. He rounded up little more than half that number, and the venture died.
Fulton’s Airphibian also hit a dead end; after 200,000 miles of driving and 6,000 successful flights, it lost its financial backers. They pulled out of Fulton’s company, Continental, Incorporated, and took with them eight production Airphibians meant for CAA inspectors.
Little has been done in the past 40 years to resurrect the always-intriguing concept. The reason: A winged car is too heavy to be a good airplane.
During the heyday of the autogiro in the early ’30s, Gerald Herrick invented an aircraft that fused elements found in autogiros with those found in conventional airplanes. The Vertaplane employed a two-blade rotor: It could be left to spin freely in order to dramatically shorten takeoff rolls, or it could be locked into place before takeoff to form a second wing. Fixed as an additional wing, the rotor effectively converted the aircraft to a biplane, which was faster than an autogiro. Once in flight, the rotor could be unlocked to allow the aircraft to land vertically (the rotor could not be stopped and locked in mid-air).
Initial flight tests were promising, but the aircraft suffered from excessive drag and was too underpowered to lift more than a single pilot and a small amount of fuel. When a lack of funding ended further research and development, Herrick’s aeronautical oddball was put out of its misery.
Convertiplanes reappeared during the l950s, this time as hybrids trying to combine the speed of fixed-wing aircraft and the vertical capabilities of rotary wings. The McDonnell XV-l of l954 took the shape of a helicopter with wings, using a single engine to drive both the rotor and a pusher propeller. It topped speeds of 200 mph, but by 1957, when the Pentagon ended its development, it was clear that helicopters would soon be capable of such speeds. Three companies followed with new designs. The Hiller X-18 mounted engines on a tilting wing; the Curtiss Wright X-19 used tilting rotors. Both were flat failures. The Bell Textron V-22 has been flying for over a decade, but on the question of whether the tilt-rotor is a viable design, the jury’s still out.
Ramjet- andRocket-Powered Aircraft
Aviation entered World War II with a single practical powerplant, the reciprocating piston engine, and emerged with three new ones: the turbojet, ramjet, and rocket. All three promised speed, but only the fittest would survive.
During World War II, Germany developed a rocket-powered interceptor, the Messerschmitt Me 163. Radar systems of that era lacked the range to give enough warning for propellerdriven airplanes, which took precious time struggling up to the altitudes where bombers flew. The Me 163 was capable of an ultra-quick ascent (it could reach nearly 40,000 feet in just three and a half minutes), but it ran out of fuel only minutes after takeoff, had a tough time targeting much slower bombers, and was vulnerable during descent, when it was unpowered. The Luftwaffe chose to place its bets on turbojet Me 262 fighters instead.
In the late 1940s, Republic Aviation designed the awkward-looking XF-91 Thunderceptor for the newly formed U.S. Air Force. It used rockets for an extra boost into combat, but could carry only enough fuel for a 25-minute flight. As did the Luftwaffe before it, the Air Force found solace in the wings of another turbojet—this time the F–l04 Starfighter. Turbojets triumphed because they used oxygen from the air to burn their fuel; rockets had to carry their own supply of liquid oxidizer—a fundamental disadvantage that could not compensate for the higher speed.
The ramjet had better luck. Invented by Frenchman Rene Lorin in 1913, it dispensed with the turbine’s rapidly spinning blades and instead used the force of air rushing in through its carefully shaped intake to compress air for combustion. It could function, therefore, only after being accelerated by another form of propulsion to very high speeds.
In 1948, Stanley Hiller put ramjets at the tips of helicopter rotors for added power, but several problems grounded his prototypes. The ramjets provided only marginal improvement in performance, consumed excessive fuel, and were highly visible at night because of their luminous exhaust. Republic Aviation incorporated the ramjet into another unsuccessful interceptor, the shark-like XF-103, which was designed to fly with both a ramjet and a turbojet, but when the XF-l03 was canceled in l957, the ramjet died with it—at least for piloted aircraft. Several missiles have employed ramjet propulsion systems.
The Anglo-French Concorde is arguably aviation’s most beautiful blunder. How could such a triumph of engineering qualify for a list of wrong turns? It failed in the marketplace. Airlines, other than the state-owned national carriers of the countries that built it, would not buy it because it carried too few passengers and consumed too much fuel. The Concorde was also limited to water routes—its noise and sonic booms made it too annoying to fly over land—a limitation that further weakened its economic viability. Only 14 entered service.
The Soviet Tu-144 was backed by a government that subsidized fuel and ignored noise, sonic booms, and ozone depletion—three concerns that ended the U.S. effort to build a supersonic transport. The Soviet program survived a horrific crash at the 1973 Paris Air Show and proceeded through an initial production run of 10 aircraft. In 1975, after at least two more crashes, the remaining Tu-144s began a weekly mail route between Moscow and Alma Ata (now part of Kazakhstan). Passenger service began later, in 1977. Operations continued for several years, hobbled by delays and cancellations. More troublesome were problems of high drag and fuel consumption.
Unable to find solutions, Soviet officials grounded the Tu-144 in l978 and, in an act of desperation, approached managers of the Concorde for help with problems that varied from metal fatigue to engine inlet design. When it became clear that the aircraft lacked the range to cross the Atlantic and thus compete for profitable routes, it lost all propaganda value and was deactivated. With it went the last hopes of a major role for an SST in civil aviation.
In the years following World War II, the Pentagon pursued three programs to build fighters that, like rockets, could take off vertically: the Ryan X-13 Vertijet, the Lockheed XFV-l, and the Convair XFY-l Pogo. All three flew during the mid-l950s. The Ryan and Convair craft took off vertically, hovered, and landed on their tails, but were hard to control. Lockheed’s entry was never able to take off or land vertically because the engine the Navy provided lacked power for vertical flight.
Unlike other aircraft on this list, the tail sitters had no devoted champions; it became pretty clear pretty fast that the concept was doomed. Fighters had to be capable of carrying extra fuel and heavy weapons, and the tail sitters’ limited engine power was simply not enough.
The military continued to covet craft with the vertical-takeoff-and-landing capability helicopters and the speed of a fighter jet. The British Harrier fighter fought effectively in the Falklands War of 1982 and served as the first operational fighter of this type. The F-35 Joint Strike Fighter will use downward-deflected thrust from a mainengine-driven lift fan to take off, hover, and land with a full array of weapons—enough to make a tail sitter keel over with envy.