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Question: Why were the wings coming off
T-34s?
Answer:
There were a
total of 3 crashes where the aircraft experienced a structural
failure. All 3 accident aircraft were in owned and operated by
companies conducting “Air Combat for hire” and the aircraft were
used for “dogfighting”. These aircraft had thousands of hours of
high g cycles in addition to the many thousands of hours that they
had already experienced in normal operations. There were also some
indications that the g limits were exceeded by the operators and one
of the accident aircraft had exceeded a mandatory inspection. More
information is available on the accident aircraft on our
Airworthiness Issus page.
The T-34A has g
envelope of +6 / -3 clean and a “rolling” G limit of +4 / -2. The
gear g limits are +3 / -1 and the flap down g limits are +2 / -0.
Many people do
not know about or respect the +4 / -2 “rolling g” limits. These
limits are very easy to exceed when “dogfighting” which often
involves high airspeed, high g, rolling maneuvers. In the early
1950’s the Air Force had a spate of accidents in the T-33 jet
trainers. As they would begin their pitchups for overhead approaches
they would lose a wing. This phenomena is due to the fact that while
rolling one wing coming up is producing more lift (more load) than
the descending wing. This asymmetrical load factor can exceed the +6
g symmetrical load limit although the pilot (and g-meter) are
experiencing less. For the T-34, Beech determined that with maximum
stick deflection a load of +4 g’s would be within the symmetrical
load limit of +6. The recommended and currently taught method in
both aerobatics and upset recovery is to “roll then pull or pull
then roll, but never pull and roll together”. If you have to “put
your stick in the corner”, your g-meter MUST be below 4 g’s. Anytime
the airspeed is at or above approximately 120 KIAS you have enough
elevator authority to reach the +4 g “rolling” limit.
Many people also
do not realize just how much “g” is available at pretty low
airspeeds. At 105 KIAS there is 3 g’s available. Anytime the
airspeed is at 149 KIAS or above you can exceed the +6 g limit of
the aircraft will full aft stick deflection. You can exceed the +9 g
ultimate load factor anytime you are at or above approximately 185
KIAS.
It is extremely
important to operate the aircraft within its certified envelope and
to become thoroughly familiar with ALL of the recommended operating
techniques and respect the manufacturers limits.
Aerobatic
instruction in the T-34 is highly recommended prior to aerobatic and
formation flying.
There is a great
article about g and aircraft life here:
What is ACM
Anyway?
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