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
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