SparrowHawk Test Flight Facts

David Lawrence's article in the August issue of Soaring magazine "Lord if
You're Up There." teaches us a lesson about the need to be thorough and
prepared whenever we fly. The accident is also a reminder of what can happen
when an aircraft is flown faster than it is designed to fly. But there are
important points in the article about the SparrowHawk glider that need to be
clarified. As mentioned in the article the redline of the SparrowHawk is 123
KEAS (120 KIAS) based on a calculated flutter speed of 158 KEAS. Flutter
speed was exceeded during the flight (162 KIAS ~ 185 KTAS at 7,600 ft) and
resulted in the destruction of the wings due to flutter, not because of a
".2.5 g load." as implied in the article. The data recorder showed that the
SparrowHawk went from 80 KIAS to 162 KIAS in less than five seconds and with
only 1100 FT of altitude loss. It was still accelerating at 15 KTS per
second at 162 KIAS with David pulling 2.8 g's while the nose coming up but
still at 45 DEG nose down. The SparrowHawk is a tough little plane and is
rated at +5.6 g and -4 g using standard safety margins and would not and has
not failed at speeds below redline. High speeds also lead to the failure of
the BRS ballistic parachute, which is rated at a maximum deployment speed of
120 KEAS. The BRS has a decelerator ring which limits the g load at speeds
below redline but had limited effect at the speeds encountered in this
accident. It has been estimated that the rapid opening of the BRS at 162
KIAS caused a load of over 100 g, more than enough stress to destroy the
attachment to the glider and pilot or enough stress to kill the pilot if the
pilot did stay attached in the airframe. The data logs showed that in
previous flights maneuvers up to 5 g's had been done. In addition the
over-speeding of the aircraft was not limited to a single flight or flight
maneuver. It was discovered that many instances of speeds well over redline
had been completed without incident.

High speed and flutter are dangerous threats to an airframe regardless of
which glider we are talking about. The flights at the University of
Mississippi have proven that the SparrowHawk has out-performed its
calculated specifications at high speeds and through high g maneuvers and is
among the most thoroughly tested gliders on the market. In no way does this
mean that this or any other aircraft should be flown over redline speed.
Flutter is an important risk that is not discussed enough in the soaring
community. Modern gliders are so sleek that they can easily fly over redline
even in non-aerobatic flight and the risk of serious flutter is multiplied
at high altitudes when TAS becomes much larger than IAS. Flutter has two
states: flutter, and no flutter, there is no warning other than flying too
fast and once it starts the result is a destroyed airframe and often a dead
pilot. Thank God you are still with us David!

Greg Cole, Designer and manufacturer of the SparrowHawk and Bill Thar,
Eastern USA SparrowHawk dealer

· KTAS is "knots true airspeed", the airspeed of an aircraft
relative to undisturbed air.

· KIAS is "knots indicated airspeed", the speed shown on an
aircraft's pitot-static airspeed indicator.

· KCAS is "knots calibrated airspeed", the indicated airspeed
corrected for position error and instrument error.

· KEAS is "knots equivalent airspeed", the calibrated airspeed
corrected for adiabatic compressible flow for the particular altitude.

Correction, Mississippi State University not The University of Mississippi.

"Bill Thar" wrote in message
...
David Lawrence's article in the August issue of Soaring magazine "Lord if
You're Up There." teaches us a lesson about the need to be thorough and
prepared whenever we fly. The accident is also a reminder of what can
happen when an aircraft is flown faster than it is designed to fly. But
there are important points in the article about the SparrowHawk glider
that need to be clarified. As mentioned in the article the redline of the
SparrowHawk is 123 KEAS (120 KIAS) based on a calculated flutter speed of
158 KEAS. Flutter speed was exceeded during the flight (162 KIAS ~ 185
KTAS at 7,600 ft) and resulted in the destruction of the wings due to
flutter, not because of a ".2.5 g load." as implied in the article. The
data recorder showed that the SparrowHawk went from 80 KIAS to 162 KIAS in
less than five seconds and with only 1100 FT of altitude loss. It was
still accelerating at 15 KTS per second at 162 KIAS with David pulling 2.8
g's while the nose coming up but still at 45 DEG nose down. The
SparrowHawk is a tough little plane and is rated at +5.6 g and -4 g using
standard safety margins and would not and has not failed at speeds below
redline. High speeds also lead to the failure of the BRS ballistic
parachute, which is rated at a maximum deployment speed of 120 KEAS. The
BRS has a decelerator ring which limits the g load at speeds below redline
but had limited effect at the speeds encountered in this accident. It has
been estimated that the rapid opening of the BRS at 162 KIAS caused a load
of over 100 g, more than enough stress to destroy the attachment to the
glider and pilot or enough stress to kill the pilot if the pilot did stay
attached in the airframe. The data logs showed that in previous flights
maneuvers up to 5 g's had been done. In addition the over-speeding of the
aircraft was not limited to a single flight or flight maneuver. It was
discovered that many instances of speeds well over redline had been
completed without incident.

High speed and flutter are dangerous threats to an airframe regardless of
which glider we are talking about. The flights at the University of
Mississippi have proven that the SparrowHawk has out-performed its
calculated specifications at high speeds and through high g maneuvers and
is among the most thoroughly tested gliders on the market. In no way does
this mean that this or any other aircraft should be flown over redline
speed. Flutter is an important risk that is not discussed enough in the
soaring community. Modern gliders are so sleek that they can easily fly
over redline even in non-aerobatic flight and the risk of serious flutter
is multiplied at high altitudes when TAS becomes much larger than IAS.
Flutter has two states: flutter, and no flutter, there is no warning other
than flying too fast and once it starts the result is a destroyed airframe
and often a dead pilot. Thank God you are still with us David!

Greg Cole, Designer and manufacturer of the SparrowHawk and Bill Thar,
Eastern USA SparrowHawk dealer

· KTAS is "knots true airspeed", the airspeed of an aircraft
relative to undisturbed air.

· KIAS is "knots indicated airspeed", the speed shown on an
aircraft's pitot-static airspeed indicator.

· KCAS is "knots calibrated airspeed", the indicated airspeed
corrected for position error and instrument error.

· KEAS is "knots equivalent airspeed", the calibrated airspeed
corrected for adiabatic compressible flow for the particular altitude.