Page 240 - Understanding Flight

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Aerodynamic Testing 227

conditions can then be determined by analysis. The predictive abilities
are so good today that there are rarely surprises in performance when
the airplane goes for its flight test.

Climbing and Turning

In the previous chapter it was shown that climbs and turns require
power and thrust. So climbing and turning tests are nothing more than
determining the available power. The difference between the power
available and the required power is the excess power. The bottom line
is that the power and thrust available is the only test required to deter-
mine climb and turn performance.
To measure the available power, the procedure is to push the
throttle to a specific setting and measure the acceleration. The
acceleration times the mass of the airplane is the net thrust. Since the
required power and thrust can be calculated from a previous flight
test, the available thrust, and available power, can be determined.

Flight Test Accidents
Unfortunately, flight test accidents do not leave much to talk
about. Today, there is rarely a crash of a commercial airplane
Lt. Thomas Selfridge was the first
in flight testing. With military aircraft it happens on rare occa-
casualty of a powered airplane
sions, but nothing like during the rapid development period of
crash. He was assigned by the
the 1940s to 1960s. Today even military aircraft performance
U.S. Army to ride with Orville
is so well predicted that there are few surprises. But, in gen-
Wright. A cable snapped,
eral, the riskier business of military flying will lead to more
breaking a propeller, leading to
flight-test accidents. The bottom line is that flight testing
the crash.
occurs all the time with very few accidents.

Wrapping It Up

Testing is an integral part of any airplane development program. It is
an expensive part too. The days are long gone when testing can be
used in place of detailed analysis to develop an airplane design. Test-
ing is now used mostly for refinement and validation.
This book has taken you through a complete course in aeronautics.
We hope that you have achieved an intuitive understanding of flight.