Page 106 - Understanding Flight

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Wings 93

Fig. 3.32. Fixed slat. Fig. 3.33. Handley-Page retractable slat.

lift increase with a slipstream, the plane must have engines In 1934, antitrust laws prevented
mounted on the wings with large propellers that generate a airframe manufacturers from
slipstream over a substantial portion of the wing. The wing owning mail-carrying airlines.
must also have a multislotted flap system to deflect the slip- Boeing holdings under United
stream effectively. This technique has not found significant Aircraft and Transport Corp.
commercial applications. became three entities: United Air
The exhaust of a turbofan-powered airplane, which is Lines, United Aircraft (later
described in Chapter 5, can be diverted down to produce renamed United Technologies, of
additional lift at low speeds. One way to produce the diversion which Pratt & Whitney is part),
is to have the flaps extend down into the exhaust when fully and the Boeing Airplane Company.
extended. One problem with this technique is that the flap
extension into the jet exhaust exposed it to very high temperatures,
creating a significant design challenge.
Another way to divert the jet exhaust is to mount the engines on the
top of the wing with the engine exhaust crossing the top of the wing as
in Figure 3.34. Flaps behind the engines use the Coanda effect to divert
the exhaust down when extended. This gives a substantial increase in lift
for takeoff and landing.

Fig.3.34. NASA QSRA STOL research vehicle with deflected jetwash.(Photo Courtesy of NASA.)