Welcome to This Date in Aviation History, getting of you caught up on milestones, important historical events and people in aviation from December 12 through December 14.
December 14, 1984 – The first flight of the Grumman X-29. Aside from a few notable experiments, the majority of aircraft up until the 1930s followed the example of the Wright Brothers’ 1903 flyer and utilized a straight wing, perpendicular to the fuselage. A straight wing allows for relatively simple construction, and provides good handling at lower speeds, particularly during landing. Some of the earliest experiments with swept wings, notably those built by Briton J.W. Dunne, attempted to use a swept wing to create a tailless aircraft, or flying wing. Though other manufacturers took up the concept before WWII, the exigencies of wartime aircraft production meant that proven straight-wing designs took precedence over swept wings, at least in large volume production.
The idea that swept wings might be useful in supersonic flight was proposed in 1935 by German aerodynamicist Adolf Busemann. The swept wing has the benefit of producing less drag at transsonic and supersonic speeds, though no aircraft were available at the time that could fly at such speeds. Later in WWII, with the arrival of the operational jet engine, the Germans worked at the forefront of swept wing technology, with both experimental and operational swept wing aircraft. The Messerschmitt Me 262, the world’s first operational jet fighter, employed a wing that was swept by 18.5 degrees.
But along with their work in swept wing aircraft, German scientists also worked on the concept of a forward-swept wing, along with others in Poland and the United States. Perhaps counterintuitively, the forward-swept wing has the same drag-reducing properties of a traditional swept wing, with the added benefit of improved stall characteristics, since the air that is swept along the wing concentrates at the wing root rather than the wing tip. Additionally, the spar box, which supports the wing, can be placed farther aft, opening up more space inside the fuselage. The Germans actually built a large bomber with forward-swept wings, the Junkers Ju 287, but they soon learned that the stresses placed on the wings and fuselage, particularly during high-speed turns, were too great for the materials of the day, and a phenomenon known as aeroelastic flutter threatened to tear the wings off the aircraft.
Experiments with the concept of forward swept wings continued after the war, and the design was utilized on the HFB 320 Hansa Jet, an otherwise traditional business jet with forward-swept wings. But the Hansa Jet was never designed to fly beyond the speed of sound, and the structural problems associated with aeroelastic flutter remained unsolved. What was needed was a material that was strong enough to handle the stresses of supersonic flight, while remaining light enough so as not to hinder the aircraft’s performance. By the 1980s, those materials were finally available in the form of carbon-fiber composites and graphite epoxy, and Grumman put both of to use in the construction of the X-29.
In order to save money, the two X-29s were built using the nose and forward landing gear taken from a pair of Northrop F-5A Freedom Fighters, and control actuators and main gear from the General Dynamics F-16 Fighting Falcon. It was powered by a single General Electric F404 turbofan, the same engine found on the McDonnell Douglas F/A-18 Hornet. With its wing swept forward at more than 33 degrees, the X-29 was one of the most unstable aircraft ever built. Without constant corrections provided by the triple-redundant flight computer through its fly-by-wire controls, the X-29 would have been unflyable. But that instability also meant that the X-29 was extremely maneuverable, and inherent instability, or relaxed instability, with computer assistance is a component of many current fighter aircraft.
When the X-29 took to the air, it was only the third jet-powered aircraft to fly with forward-swept wings. The two experimental aircraft made a total of 242 test flights over a seven-year program that ended in 1991. The second aircraft was fitted with a rescue parachute in case of an unrecoverable stall while carrying out flight tests that explored high angles of attack, and achieved as much as 45 degrees AOA, more than any contemporary fighter. The X-29 was also the first forward-swept wing aircraft to exceed Mach 1 in level flight. Though the test program did not demonstrate the overall reduction in drag thought possible, its use of pioneering construction materials and computerized flight control have had a far-reaching influence over subsequent aircraft design. Both X-29s have since been retired, and they are currently on display at the National Museum of the United States Air Force and the Armstrong Flight Research Center.
December 12, 1985 – The crash of Arrow Air Flight 1285, a chartered Douglas DC-8 (N950JW) that was carrying eight crew members and 248 soldiers of the US Army 101st Airborne Division returning to Fort Campbell, Kentucky after serving in a peacekeeping mission in the Sinai Peninsula. On the final leg of the flight, the DC-8 crashed shortly after takeoff from Gander, Newfoundland, killing all on board. The investigation concluded that the crash was caused by the accumulation of ice on the wings, as well as incorrect weight calculations. However, some investigators dissented, saying that a fire or explosive device likely caused the crash. The accident remains the deadliest single peacetime loss of life in the history of the US Army and the worst crash on Canadian soil.
December 12, 1979 – The first flight of the Sikorsky SH-60B Seahawk, a navalized variant of the Sikorsky UH-60 Black Hawk utility helicopter originally developed for the US Army. Also known as the Sea Hawk, the SH-60B was developed to replace the Kaman SH-2 Seasprite, and it shares 83% commonality with its Army predecessor, with the most significant structural difference being a hinged tail for on-deck storage. The Seahawk also differs by the addition of oleo main gear struts, the shifting forward of the tail wheel, and a more powerful engine. Able to operate from any air-capable ship, the Seahawk is designed for anti-submarine warfare, anti-surface warfare, naval special warfare, search and rescue, vertical replenishment, and medical evacuation. Further variants have replaced the Sikorsky SH-3 Sea King and Boeing CH-46 Sea Knight.
December 12, 1951 – The first flight of the de Havilland Canada DHC-3 Otter. With the DHC-2 Beaver, de Havilland Canada had built a reputation for rugged aircraft that were capable of taking off from short or unimproved airstrips, and the DHC-3 Otter was designed to be a larger and more powerful aircraft that could perform the same mission. Originally called the King Beaver, the DHC-3 is longer and heavier than the DHC-2, and can seat 10-11 passengers. Originally fitted with a Pratt & Whitney R-1340 geared radial engine, some Otters have been upgraded with a turboprop engine and are known as the Turbo Otter. The Otter is capable of operating from land, from sea with floats, or from snow with skis, and 466 Otters were produced from 1951-1967.
December 14, 1979 – The first flight of the EA-7 Edgley Optica, a light observation aircraft designed to be a low-cost alternative to helicopters. The unique design features a glazed bubble canopy set well forward which provides excellent visibility, a twin boom tail, and tricycle landing gear. The original Optica was powered by a Lycoming IO-320 engine driving a ducted, fixed-pitch propeller, an arrangement that resulted in very quiet operation. Production of 22 aircraft was followed by numerous changes in Edgley’s ownership, and financial difficulties led to a halt in production. However, the transportation consulting and finance firm InterFlight Global is investigating the possibility of restarting production in 2018 or 2019.
December 14, 1977 – The first flight of the Mil Mi-26, a heavy lift helicopter designed for civilian and military use and the largest and most powerful helicopter ever to enter production. Powered by two Lotarev D-136 turboshaft engines and fitted with an eight-bladed main rotor, the Mi-26 is capable of lifting 44,000 pounds and was designed to replace the Mi-6 and Mi-12 heavy-lift helicopters. The Mi-26’s main purpose is to move extremely heavy equipment between Russian military bases, such as armored personnel carriers and mobile ballistic missiles, with some payloads weighing as much as 29,000 pounds. A total of 316 Mi-26s have been built, and the helicopter remains in production.
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