Boeing YC-14

Boeing YC-14
The first prototype of the Boeing YC-14 in flight
Type:	Tactical transporter
Design country:	United States
Manufacturer:	Boeing
First flight:	August 9, 1976
Commissioning:	Flight tests ended in 1977
Production time:	Was never mass-produced
Number of pieces:	2

The Boeing YC-14 was an experimental transport aircraft of the United States Air Force built by the US aircraft manufacturer Boeing . The two built prototypes as well as the two competing McDonnell Douglas YC-15s were tested from 1976 to 1977 as possible replacements for the C-130 Hercules as part of the Advanced Medium STOL Transport (AMST) program. The test program of the shoulder- wing aircraft was ended in the summer of 1977; after the entire program was discontinued, there was no longer any series production.

history

development

In 1971 the United States Air Force laid down the requirements for a new aircraft to replace the C-130 Hercules transporter, which was almost 20 years old at the time. Nine manufacturers were involved in the tender, from Bell , Boeing , Fairchild , Lockheed and McDonnell Douglas bids had been received by the end of the tendering phase on March 31. On November 10th, McDonnell and Boeing received orders to build two test models. After a further study phase in which the requirements for the aircraft were slightly reduced, the development of the aircraft began on January 10, 1973 under the internal model number 953. Boeing received a budget of 96.2 million US dollars. At the turn of the year 1973/74, the continuation of the AMST program was uncertain, the work at Boeing and McDonnell for a short time almost stood still because they had to wait for new funds from the Department of Defense. Boeing's development budget was increased to $ 105.9 million after the program was approved.

In order to achieve the short take-off properties required in the tender, the Boeing designers relied on the “Upper Surface Blowing” concept, in which the exhaust gas jet from the two engines was guided over the upper side of the wing using the Coandă effect . In tests in the wind tunnel of NASA in Langley , this concept had proven to be promising. Antonov took a similar approach with his An-72 transport aircraft , which flew for the first time in 1977.

In the summer of 1975, the assembly of the wings and fuselage began. Marconi-Elliot's Avionics System delivered the first electronic flight control system in February 1976, used in Seattle for laboratory testing. The systems for the first aircraft followed in March. Also in February, testing of a wing section and the CF6 engine began in Tulalip Bay , north of Seattle. During the tests, various flap positions and thrust forces were tested, and the results were incorporated into the flight control. The engines were assembled on the first prototypes in March 1976, and the rollout finally took place on June 11, 1976 at Paine Field in Everett near Seattle in front of 2000 invited guests.

testing

After the rollout, the extensive test program began with the aircraft. After the first refueling tests and electronics checks, the CF6 engines were started for the first time on June 21. On July 7th, testing of the electronic flight control began, after further tests for electromagnetic compatibility, which had ended on July 21st, the machine with the USAF license plate 72-1873 took off on the afternoon of August 9th, 1976 from Boeing Field on the maiden flight. The machine was controlled by test pilot Raymond L. McPherson from Boeing and Major David Bittenbinder from the US Air Force. During the one and a half hour flight, during which mainly the electronic systems and the flaps were tested, the aircraft reached a speed of 300 kilometers per hour and a summit height of around 4500 meters. During the test flights in September, the lifting aids of the YC-14 were tested and the landing flaps were tested in flight.

The measurement data were recorded by a network of 1125 measuring points, the recording devices were located in the hold of the aircraft. Test engineers were also on board for later test flights so that the measurement results could be evaluated directly.

The second prototype in 1976 at Andrews AFB

The second aircraft (72-1874) was completed in September 1976; the maiden flight took place on October 21st. After completion of the factory tests, during which minor defects in the machines had been eliminated, the two prototypes were relocated to Edwards Air Force Base in California on November 12th after about 60 hours of flight , where further testing was to take place. The first successful short landing was carried out on February 2, 1977, and by April 1977 both machines had completed a total of 950 short landings, 60 of them on unpaved runways. When unloaded, the machines only needed about 180 meters of take-off distance. Attempts to drop pallets and parachute dummies from high and low heights also took place during the period. After further loading attempts, which took place in Yuma , the second prototype went on a large demonstration tour to Europe on May 21, 1977. In the United Kingdom , Germany and France , a total of 177 short landings were carried out in 78 demonstrations, including at the Paris Air Show . A 50-ton M60 main battle tank was also brought on board during loading demonstrations .

After completing the "European tour", four NASA pilots were trained on the aircraft in August 1977, who were later to fly the Quiet Short-Haul Research Aircraft (quiet short-haul test aircraft).

End of the project

The second prototype, stored at Davis-Monthan Air Force Base

After Jimmy Carter was elected president in 1977, the military budget was cut drastically, which should lead to the end of the AMST program. The election of a winner of the AMST program, originally planned for autumn 1977, was initially postponed to spring 1978, but then ceased completely when the project was discontinued. The official end of the project came on December 10, 1979, the two aircraft had previously been leased by Boeing for improvements and demonstrations for a short time.

Both aircraft still exist today, the first prototype is in the Pima Air & Space Museum near Tucson , Arizona ( 32 ° 8 ′ 16.3 ″  N , 110 ° 52 ′ 2.8 ″  W ); the second is in the neighborhood in the 309th Aerospace Maintenance and Regeneration Group on Davis-Monthan Air Force Base ( 32 ° 10 ′ 18.6 ″  N , 110 ° 50 ′ 50.8 ″  W ).

technology

hull

The 40.13 meter long fuselage with a circular cross section measuring 5.44 meters was constructed using conventional frame construction. It is planked with aluminum panels, and composite materials are used in the rear area. The wings attached to the shoulder ( shoulder wing ) with a wingspan of 39.32 meters had a continuous wing spar . The cladding consisted of 30-meter-long metal sheets with integral stiffeners, which reduced the number of parts by 50 percent. The wing area was 163.7 square meters. There was enough space at the rear of the fuselage for a large cargo hatch under the high-mounted T-tail. The cargo hold was 18.66 meters long, 3.50 to 3.55 meters wide and a maximum of 3.66 meters high. The loading capacity was up to 36,740 kilograms, with a short start it was still possible to load 12,245 kilograms.

The landing gear had a steerable nose wheel with twin tires, the short main landing gear, each with two twin-tire axles, was attached to the side of the fuselage and could absorb impacts of up to 4.5 m / s.

The first prototype was left unpainted, the second was given the camouflage that was typical of the United States Air Force, which consisted of large spots in light brown, light green and olive gray.

Drive, control and electronics

The drive of the aircraft is provided by two General Electric CF6-50D - turbofan engines with a thrust of 214.6 kN. The engines were mounted very close to the fuselage in front of the wings, which gave the aircraft a very characteristic appearance. The thrust jet of the turbine was directed directly onto the wing surface through a narrow nozzle that was adjustable in width by flaps. To reverse thrust , the engines had a large guide flap on the top, which diverted the thrust flow very effectively.

Directly behind the engines were large double slotted flaps that could be extended up to 70 degrees. Due to the Coandă effect , the engine flow remained “stuck” to the flap surface, which resulted in very high lift coefficients. The landing flaps , which were also designed as double slotted flaps , could be extended from 36 to 58 degrees and supported the lift in slow flight or short take-off. This was supported by five fold-out spoilers and extendable slats that extend over the entire width of the wing . At the same time, engine bleed air could be blown out at the wing leading edge in order to stabilize the boundary layer. Overall, an increase in the lift coefficient of around 20 percent was achieved.

A large, three-part and double-articulated rudder increased maneuverability, as an engine failure in particular would have caused severe yaw and an asymmetrical lift distribution. The horizontal stabilizer was set very high above the vertical stabilizer with a negative V position . The ailerons attached to the outer wing end could also be lowered slightly to increase lift.

The electronic flight control system from the British manufacturer Marconi-Elliot Avionics System was designed with triple redundancy to ensure the greatest possible safety. The cockpit had a heads-up display that showed the pilot important aircraft data directly in the field of vision when approaching. In addition, when visibility was poor, a television image from a camera in the aircraft's nose could be displayed on a screen in the cockpit with flight guidance symbols displayed.

Thanks to the special buoyancy aids, the aircraft reached approach speeds of 160 kilometers per hour and managed with 360 meters of taxiing distance. When loaded (77,110 kg total mass), the take-off run was 305 meters. The maximum take-off mass was 104,500 kilograms, the landing mass was slightly lower at 102,000 kilograms. The maximum speed of the Boeing YC-14 was 810 kilometers per hour (Mach 0.74), the normal cruising speed was 723 km / h. The service ceiling was 13,716 meters, the maximum rate of climb 32 m / s. The aircraft had a maximum transfer range of 4,815 kilometers and an operational radius of 740 kilometers.

Technical specifications

Three-sided tear

Parameter	Data of the YC-14
length	40.13 m
span	39.32 m
height	14.7 m
Wing area	163.6 m²
Empty mass	53,297 kg
Max. Takeoff mass	113,852 kg (77,111 kg for STOL )
Payload	36,740 kg (12,245 kg for STOL )
Top speed	810 km / h
Cruising speed	723 km / h
Max. Altitude	13,715 m
Climb performance	32 m / s
Use radius	740 km
Range	4815 km
Engines	two General Electric F103 (CF6-50D11) with 214.6 kN thrust each

See also

• List of aircraft types

literature

• Karl Schwarz: Short start with Coanda effect in FlugRevue Edition: Aviation classics 2/07 . Motor Presse Stuttgart, Stuttgart 2007.

Web links

Commons : Boeing YC-14  - collection of images, videos and audio files

• Pictures of the Boeing YC-14 at airliners.net (English)
• The homepage of the Pima Air & Space Museum (English)

Individual evidence

1. ↑ ^{a b} FlugRevue Edition: Classics of Aviation 2/07 . Motor Presse Stuttgart, Stuttgart 2007. p. 55
2. ↑ ^{a b} FlugRevue Edition: Classics of Aviation 2/07 . P.56

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This version was added to the list of articles worth reading on March 2, 2007 .