HOME

TheInfoList



OR:

The McDonnell Douglas YC-15 is a prototype four-engine short take-off and landing (STOL) tactical transport. It was
McDonnell Douglas McDonnell Douglas Corporation was a major American Aerospace manufacturer, aerospace manufacturing corporation and defense contractor, formed by the merger of McDonnell Aircraft and the Douglas Aircraft Company in 1967. Between then and its own ...
' entrant into the
United States Air Force The United States Air Force (USAF) is the Air force, air service branch of the United States Department of Defense. It is one of the six United States Armed Forces and one of the eight uniformed services of the United States. Tracing its ori ...
's Advanced Medium STOL Transport (AMST) competition to replace the
Lockheed C-130 Hercules The Lockheed C-130 Hercules is an American four-engine turboprop military transport aircraft designed and built by Lockheed Corporation, Lockheed (now Lockheed Martin). Capable of using unprepared runways for takeoffs and landings, the C-130 w ...
as the USAF's standard
STOL A short takeoff and landing (STOL) aircraft is a fixed-wing aircraft that can takeoff/land on short runways. Many STOL-designed aircraft can operate on airstrips with harsh conditions (such as high altitude or ice). STOL aircraft, including tho ...
tactical transport. In the end, neither the YC-15 nor the Boeing YC-14 was ordered into production, although the YC-15's basic design would be used to form the successful McDonnell Douglas (later Boeing) C-17 Globemaster III.


Design and development

In 1968, the USAF started work on a series of prototype proposals, which would lead to both the AMST project and the Light Weight Fighter. The official Request for proposal (RFP) was issued in January 1972, asking for operations into a semi-prepared field with a payload and a mission radius.Norton 2001, pp. 6–7. For comparison, the C-130 of that era required about for this load. Proposals were submitted by
Bell A bell /ˈbɛl/ () is a directly struck idiophone percussion instrument. Most bells have the shape of a hollow cup that when struck vibrates in a single strong strike tone, with its sides forming an efficient resonator. The strike may be m ...
,
Boeing The Boeing Company, or simply Boeing (), is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, and missiles worldwide. The company also provides leasing and product support s ...
,
Fairchild Fairchild may refer to: Organizations * Fairchild Aerial Surveys, operated in cooperation with a subsidiary of Fairey Aviation Company * Fairchild Camera and Instrument * List of Sherman Fairchild companies, "Fairchild" companies * Fairchild ...
,
McDonnell Douglas McDonnell Douglas Corporation was a major American Aerospace manufacturer, aerospace manufacturing corporation and defense contractor, formed by the merger of McDonnell Aircraft and the Douglas Aircraft Company in 1967. Between then and its own ...
and the Lockheed/
North American Rockwell North American Aviation (NAA) was a major American aerospace manufacturer that designed and built several notable aircraft and spacecraft. Its products included the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the F- ...
team at this stage of the competition. On 10 November 1972, the two top bids (from Boeing and McDonnell Douglas) were selected. The companies were awarded development contracts for two prototypes each. McDonnell Douglas' prototype was designated YC-15.Kennedy 2004, pp. 8–11. McDonnell Douglas's design incorporated a supercritical wing, the result of
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
research carried out by the already famous Richard Whitcomb. This wing design dramatically lowers
transonic Transonic (or transsonic) flow is air flowing around an object at a speed that generates regions of both subsonic and Supersonic speed, supersonic airflow around that object. The exact range of speeds depends on the object's critical Mach numb ...
wave drag In aeronautics, wave drag is a component of the aerodynamic drag In fluid dynamics, drag, sometimes referred to as fluid resistance, is a force acting opposite to the direction of motion of any object moving with respect to a surrounding flu ...
by as much as 30% compared to more conventional profiles, while at the same time offering excellent low-speed lift. Most contemporary aircraft used
swept wing A swept wing is a wing angled either backward or occasionally forward from its root rather than perpendicular to the fuselage. Swept wings have been flown since the pioneer days of aviation. Wing sweep at high speeds was first investigated in Ge ...
s to lower wave drag, but this led to poor low-speed handling, which made them unsuitable for STOL operations. The design team also chose to use externally blown flaps to increase lift. This system uses double-slotted flaps to direct part of the jet exhaust downwards, while the rest of the exhaust passed through the flap and then followed the downward curve due to the
Coandă effect The Coandă effect ( or ) is the tendency of a jet (fluid), fluid jet to stay attached to a surface of any form. ''Merriam-Webster'' describes it as "the tendency of a jet of fluid emerging from an orifice to follow an adjacent flat or curved s ...
. Although the effects had been studied for some time at NASA, along with similar concepts, until the introduction of the
turbofan A turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft engine, aircraft propulsion. The word "turbofan" is a combination of references to the preceding generation engine technology of the turbojet and the add ...
the hot and concentrated exhaust of existing engines made the system difficult to use. By the time of the AMST project, engines had changed dramatically and now provided larger volumes of less-concentrated and much cooler air. The YC-15 prototype was the first jet powered aircraft to use externally blown flaps. For later prototypes, there were several modifications including a computer on the YC-15 was devised that would calculate the best flap angle for various flight conditions given the current gross weight. Together these modifications offered a reduction in approach speed of 10 kn. For the YC-15, four engines were used, versions of the Pratt & Whitney JT8D-17 widely used on the
Boeing 727 The Boeing 727 is an American Narrow-body aircraft, narrow-body airliner that was developed and produced by Boeing Commercial Airplanes. After the heavier Boeing 707, 707 quad-jet was introduced in 1958, Boeing addressed the demand for shorter ...
and
Douglas DC-9 The McDonnell Douglas DC-9 is an American five-abreast, single-aisle aircraft designed by the Douglas Aircraft Company. It was initially produced as the Douglas DC-9 prior to August 1967, after which point the company had merged with McDonnell ...
. The YC-15 borrowed components from other McDonnell Douglas aircraft, with its nose gear coming from the
Douglas DC-8 The Douglas DC-8 (sometimes McDonnell Douglas DC-8) is an early long-range Narrow-body aircraft, narrow-body jetliner designed and produced by the American Douglas Aircraft Company. Work began in 1952 towards the United States Air Force's (USA ...
and the nose section and cockpit being derived from the Douglas DC-10. Parts borrowed from other aircraft included the Universal Aerial Refueling Receptacle Slipway Installation (UARRSI), taken from a Fairchild A-10, anti-tipover stabilizer struts from the Lockheed C-141 Starlifter, pumps taken from the
McDonnell Douglas F-15 Eagle The McDonnell Douglas F-15 Eagle is an American twin-engine, all-weather fighter aircraft designed by McDonnell Douglas (now part of Boeing). Following reviews of proposals, the United States Air Force (USAF) selected McDonnell Douglas's desi ...
,
Lockheed C-5 Galaxy The Lockheed C-5 Galaxy is a large military transport aircraft designed and built by Lockheed Corporation, Lockheed, and now maintained and upgraded by its successor, Lockheed Martin. It provides the United States Air Force (USAF) with a heavy ...
, DC-9 and C-141 and actuators taken from the C-5 Galaxy and DC-10. In addition, the environmental cooling system was composed of components taken from the DC-9, C-141 and
Boeing KC-135 The Boeing KC-135 Stratotanker is an American military aerial refueling tanker aircraft that was developed from the Boeing 367-80 prototype, alongside the Boeing 707 airliner. It has a narrower fuselage and is shorter than the 707. Boeing gav ...
. The YC-15 interior cargo hold was large, with dimensions 47 x 11.8 x 11.4 feet. The YC-15 was the first aircraft to offer pilots a heads up display. It was especially designed to help with short field landings, showing the pilot the horizon, flight path scale, airspeed indexer and touchdown point.


Operational history

Two YC-15s were built, one with a wingspan of (#72-1876) and one of (#72-1875). Both were long and powered by four
Pratt & Whitney Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of RTX Corporation (formerly Raytheon Technologies). Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially ...
JT8D-17 engines, each with of thrust. The first flight was on 26 August 1975. The second prototype followed in December. They were tested for some time at McDonnell Douglas as the Boeing entry was not ready until almost a year later. In November 1976, both designs were transferred to
Edwards Air Force Base Edwards Air Force Base (AFB) is a United States Air Force installation in California. Most of the base sits in Kern County, California, Kern County, but its eastern end is in San Bernardino County, California, San Bernardino County and a souther ...
for head-to-head testing, including lifting heavy loads like tanks and artillery from dirt airfields at Graham Ranch, off the end of Runway 22. In Phase II of the flight test program, a "refanned" Pratt & Whitney JT8D-209 was tested in No. 1 nacelle of 72–1876, and a
CFM International CFM56 The CFM International CFM56 (U.S. military designation F108) series is a Franco-American family of high-bypass turbofan aircraft engines made by CFM International (CFMI), with a thrust range of . CFMI is a 50–50 joint-owned company of Safran ...
was tested in the No. 1 nacelle of 72–1875. In addition, a new wing with increased chord and span was flown on 72–1875. The YC-15 met specifications under most, but not all, conditions. It was a very good STOL plane for its size. At a gross weight of 149,300lbs, the YC-15 flew short landing approaches at only 87 kn at a 6 degree glide slope yielding a sink rate of 15.4 feet per second, compared with normal approaches that were made at about 127 kn with a typical 8-12 feet per second sink rate. For short landings, the touch down aim-point was only about 300 feet from the runway end. Pilots of the YC-15 tested both no-flare and with-flare landing techniques in STOL mode. Because of slow actuation of the thrust reversers, testing at Edwards AFB showed the plane was unable to consistently stop in “hot-and-high” conditions in the required 2000 feet. However, the seeds of the AMST program's demise had already been sown. In March 1976, the Air Force Chief of Staff, Gen. David C. Jones, asked the Air Force Systems Command to see if it was possible to use a single model of the AMST for both strategic and tactical airlift roles, or alternatively, if it was possible to develop non-STOL derivatives of the AMST for the strategic airlift role. This led to a series of studies that basically stated that such a modification was not easy, and would require major changes to either design to produce a much larger aircraft. The increasing importance of the strategic vs. tactical mission eventually led to the end of the AMST program in December 1979.Kennedy 2004, pp. 12–19. Then, in November 1979, the C-X Task Force formed to develop the required strategic aircraft with tactical capability.Kennedy 2004, pp. 19–24. The C-X program selected a proposal for an enlarged and upgraded YC-15 that was later developed into the
C-17 Globemaster III The McDonnell Douglas/Boeing C-17 Globemaster III is a large military transport aircraft developed for the United States Air Force (USAF) between the 1980s to the early 1990s by McDonnell Douglas. The C-17 carries forward the name of two previ ...
.Norton 2001, pp. 12–13. The
Lockheed C-130 Hercules The Lockheed C-130 Hercules is an American four-engine turboprop military transport aircraft designed and built by Lockheed Corporation, Lockheed (now Lockheed Martin). Capable of using unprepared runways for takeoffs and landings, the C-130 w ...
would be further improved into the
C-130J The Lockheed Martin C-130J Super Hercules is an American four-engine turboprop military transport aircraft. The C-130J is a comprehensive update of the Lockheed C-130 Hercules, with new engines, flight deck, and other systems. The C-130J is th ...
and remains in service. After the flight test program, the two aircraft were stored at the
AMARC The World Association of Community Radio Broadcasters (, AMARC) is the international umbrella organization of community radio Broadcasting, broadcasters founded in 1983, with nearly 3,000 members in 110 countries. Its mission is to support and c ...
, located at Davis-Monthan Air Force Base. One aircraft (72-1875) was subsequently moved to the nearby
Pima Air & Space Museum The Pima Air & Space Museum is an aerospace museum in Tucson, Arizona, US. It features a display of nearly 400 aircraft spread out over on a campus occupying . It has also been the home to the Arizona Aviation Hall of Fame since 1991. Overv ...
in 1981,Norton 2002, p. 174. but was returned to flying status by McDonnell Douglas in 1996; it was first reflown on 11 April 1997. On 16 April 1997, the aircraft was ferried to
Long Beach, California Long Beach is a coastal city in southeastern Los Angeles County, California, United States. It is the list of United States cities by population, 44th-most populous city in the United States, with a population of 451,307 as of 2022. A charter ci ...
to support the C-17 program. On 11 July 1998, the aircraft suffered a massive failure of the No. 1 engine during flight and made an emergency landing at Palmdale, California. On inspection, the aircraft was deemed too expensive to repair and was stored at Palmdale.Norton 2002, pp. 202–206. In 2008, the aircraft was moved by road to Edwards AFB, where it is now on display at the Air Force Flight Test Center Museum's "Century Circle" display area, just outside the base's west gate. The other airframe (72–1876), which had remained on Celebrity Row at the AMARC for many years, was destroyed in place in April 2012.


Specifications


See also


References


Notes


Bibliography

* Green, William. ''The Observer's Book of Aircraft''. London: Frederick Warne & Co. Ltd., 1976. . * Johnson, E.R. ''American Military Transport Aircraft Since 1925''. Jefferson, North Carolina: McFarland & Company, 2013. . * Kennedy, Betty R. ''Globemaster III: Acquiring the C-17''. McConnell AFB, Kansas: Air Mobility Command Office of History, 2004. . * Norton, Bill. ''Boeing C-17 Globemaster III''. Minneapolis, Minnesota: Specialty Press, 2001. . * Norton, Bill. ''STOL progenitors: The Technology Path to a Large STOL Transport and the C-17A''. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2002. .


External links


Edwards AFB: A Pair of Most Unusual Transports
(Internet Archive)


McDonnell Douglas YC-15 (part 1) on The Lexicans
{{DEFAULTSORT:Mcdonnell Douglas Yc-15 1970s United States experimental aircraft 1970s United States military transport aircraft C-015 Quadjets High-wing aircraft T-tail aircraft Aircraft first flown in 1975 Aircraft with retractable tricycle landing gear