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National Advisory Committee for Aeronautics, Report - Summary of Scale Model Thrust Reverser Investigation

An investigation was undertaken to determine the character-
istics of several basic types of thrust reverser. .Models of three
types, target, tailpipe cascade, and ring cascade, were tested
with unheated air. The efiects of design variables on reverse-
thrust performance, reversed-flow boundaries, and thrust-
modulation characteristics were determined.

Values of reverse-thrust ratio as high as 84 percent could be
obtained if the gas were turned far enough and permitted to
attach to the eaternal fairing. Without reversedj‘low attach-
ment and with controlled reversed—flow patterns, all three types
of reverser gave reverse-thrust ratios over 40 percent. The ring
type with a 7° external fairing gave 41 percent, the target type
with a 7° fairing gave 49 percent, and the tailpipe-cascade type
with a 0° fairing gave ’73 percent. All three types had satis-
factory thrust-modzdation characteristics and were capable of
producing desired reversed-flow patterns. It was, thus, con—
cluded that the seledion of a reverser type may be based pm;
marily on installation considerations rather than on per-
formance characteristics.

With the landing speeds of jet aircraft ever increasing, the
required landing distances are becoming prohibitively long.
Landing speeds are high for two reasons: first, aerodynamic
reasons such as high wing loadings and low maximum—lift
coefficients, and second, the necessity for making the final
approach at a relatively high engine speed in preparation for
a possible wave-off.

The effectiveness of reducing the landing run by the appli-
cation of several braking methods has been computed, and
the results are compared in figure 1. The methods consist of
the use of wheel brakes alone, wheel brakes plus a drag
parachute, and wheel brakes plus 40— and 80-percent thrust
reversal. These methods were assumed to be effective at
the instant of touchdown, and no braking or thrust spoilage
was applied until that time. Thus, figure 1 shows that
thrust reversal plus Wheel brakes is superior to the other two
methods as an after-touchdown braking device, even if only
40-percent reversal is attained. ’

Thrust reversers and drag parachutes can also effectively
reduce the landing roll by reducing the approach speed.
The thrust reverser has the advantage of providing the re-
quired reduced or reverse thrust (at rated engine conditions)
with the assurance that full forward thrust can be regained
rapidly if the need arises.