| Summary: | The C-17 military transport aircraft is being developed for the Air Force by the McDonnell Douglas Corporation, Douglas Aircraft Company. It is being designed to carry the full range of military cargo directly into small, austere airfields, a capability that distinguishes the C-17 from other airlift aircraft, such as the C-5, C-141, and C-130. Direct delivery is key to achieving the full potential benefits of the C-17. Direct delivery capability is provided by a set of interrelated flight characteristics and design criteria incorporated in the C-17 that enables it to approach runways at much lower speeds and steeper descents than conventional aircraft. It can thus land in very short distances with very heavy cargo loads. One of these flight characteristics is powered lift, which involves a unique use of flaps. A flap is a movable attachment to the trailing edge of the aircraft's wing that increases the lift of the aircraft. Powered lift is the result of extending the flaps into the engine exhaust to deflect the exhaust stream. This deflection converts the engine thrust into lift, which permits reduced approach speeds for landing and changes the normal techniques required for aircraft flight path and airspeed control. Standard flaps do not interact with the engine exhaust stream. Because flap performance is vital to the C-17, the General Accounting Office reviewed the results of temperature and acoustic testing to determine whether Douglas Aircraft Company had demonstrated that the flap would achieve the required 30,000-hour life expectancy.
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