Page 239 - Understanding Flight
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CH08_Anderson 7/25/01 9:02 AM Page 226
226 CHAPTER EIGHT
Fig. 8.24. VMU test with a tail skid on the airplane to prevent damage. (Used
with the permission of the Boeing Management Company.)
can look as if the airplane is on fire, as shown in Figure 8.24. Usually
little damage is done to the airplane. For flight testing, a small tail skid
is placed on the airplane to prevent damage.
The maximum-braking test demonstrates that the airplane can
abort takeoff and stop on the runway without risking the passengers.
What makes this test exciting is that all of the kinetic energy of the
airplane is transferred to the brakes. So the brakes get extremely hot,
as discussed in the previous chapter. The test requires that the
airplane be able to remain on the runway without help for a certain
period of time. You have to understand that the tires are probably
melting and exploding. The heat from the breaks may be radiating to
the underside of the fuel tanks. The test ensures that if a maximum-
breaking abort is required, the airplane can survive until fire trucks
can arrive on the scene to cool down the brakes.
Takeoff and landing tests must be performed in a variety of
configurations. These are demonstrating the “what happens if?”
scenarios. Tests with one engine out, flaps in various positions, different
gross weights, and at different atmospheric conditions must be
performed.
Although the first supersonic
As computer models get more and more accurate, some
flight did not occur until 1947,
flight testing is being replaced by careful calculations. So,
Ernst Mach photographed the
rather than having to test every possible condition, which is
shock waves on a supersonic
very expensive, a few key conditions can be tested in flight
bullet in 1887.
and used to validate the calculations. The rest of the