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Devices for avoiding VNE?



 
 
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Old March 28th 04, 11:53 PM
John Galloway
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Default Devices for avoiding VNE?

Through the contributions to the avoiding VNE thread
runs the theme of the difficulty of avoiding overspeeding
and/or overstressing some modern designs in accidental
spin recovery. This is made more difficult than in
older composite gliders because they had a little more
drag and a little more (fortuitous) margin in the g
limits.

Is it not blindingly obvious that there is a need for
an emergency drag device that does not reduce the G
limits of gliders? Clearly if we all handled the recovery
from inadvertent spins etc perfectly all would be well
but equally clearly that does not always happen and
it is a shame to lose pilots in this situation.

As the Phoebus pilot pointed out a tail chute is ideal
for this - providing that it can be made to actuate
and jettison reliably. (I found the design used on
the Kestrel particularly good and I never once had
a failure for landing use) On the other hand they
are expensive and inconvenient to replace and there
are several ways that they can fail.

So can anyone think of a better idea than a chute?
The best I can come up with is some sort of flush
fitted rectangular-with the-long-edge-horizontal rear
hinged airbrakes (like old fashioned automobile suicide
doors) located on the fuselge sides somewhere in the
region below or below/behind the wings. If they opened
to about 45 degrees with a spring actuator (and limited
by sliding metal stays that hinge/attach to the front
of the panel and whose inner ends slid along in runners)
then they would provide a lot of drag without any deep
internal mechanism (such as wing airbrakes have).
Once they have done their job the rear end of the brakes
could be released by a spring loaded mechanism similar
to the front end so that the brakes would then instantly
spring to as position set out from and parallel to
the fuselage so that there would be very little drag
- only that provided by the stays at both ends and
the brake panels edge on to the wind. That configuration
would be good enough to fly home with. It would only
be possible to reset these brakes on the ground and
they would not replace conventional wing airbrakes
for approach control - although they could have a secondary
use for emergency approach control.

I am envisaging something the could be included in
new designs although there does not seem to be any
obvious reason why such a device could not be retrofitted
as a fairly major modification. The contours of the
brake panels would be specific to the individual fuselage
type but the mechanism could be generic. The assembly
would be fairly shallow and complete within itself
apart from e.g. a cable release attachment.

I am not advocating a technical solution to this problem
in place of spin recovery practice but I do think that
there must be something that the combined intellects
of the gliding community can come up with other than
observing that if we get into that particular overspeeding/steep
attitude condition we are stuffed.

Anyone got any simpler or better ideas? I am definitely
not an engineer.

John Galloway


 




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