Fatal crash Arizona

Someone wrote:
"Turns do not cause stall/spin accidents. In fact, the steeper the turn, the greater the stall margin. That's because elevator authority is progressively used up making the glider turn as the bank gets steeper until the angle of attack can't be raised above stall. Try it. You'll find many gliders will run out of up elevator before they can be stalled at bank angles over 45 degrees."

Any comments on the above statement. Steep turns offer a greater stall margin--really?

On 5/7/2014 6:00 PM, 150flivver wrote:
Someone wrote: "Turns do not cause stall/spin accidents. In fact, the
steeper the turn, the greater the stall margin. That's because elevator
authority is progressively used up making the glider turn as the bank gets
steeper until the angle of attack can't be raised above stall. Try it.
You'll find many gliders will run out of up elevator before they can be
stalled at bank angles over 45 degrees."

Any comments on the above statement. Steep turns offer a greater stall
margin--really?


We're really drifting away from this thread's initial topic, but if some folks
learn a useful thing or two from so doing, then maybe thread drift ain't
always so bad!

I think I can relate to the (presumed on my part) bemusement underlying the
question...it took some cogitation on my part when first exposed to the
concept, too.

My short form answer to the question is: Yes.

Assuming a still atmosphere, consider what constitutes a wing stall, what
control is used to drive the wing to stalling angle of attack, and what that
control has to be doing to get/sustain the glider into a constant speed bank,
and the light bulb may begin to glimmer.

And if you're a glider pilot with access to a glider capable of stalling the
wing in steady, 1G flight, go try it out at a safe height (e.g. steep
thermalling)...and ponder some more. Remember, it's not the speed, it's the
angle (of attack)...glider pilots are just used to using speed in the pattern
as a proxy for AoA.

Bob W.

P.S. I am not a lawyer nor have I ever played one on TV, but do keep in mind
two things: 1) all free instruction is worth exactly what you paid for it; 2)
the reader assumes all risks involved in testing any advice they may presume I
may be offering... :-)

On Thursday, May 8, 2014 12:00:45 PM UTC+12, 150flivver wrote:
Someone wrote:

"Turns do not cause stall/spin accidents. In fact, the steeper the turn, the greater the stall margin. That's because elevator authority is progressively used up making the glider turn as the bank gets steeper until the angle of attack can't be raised above stall. Try it. You'll find many gliders will run out of up elevator before they can be stalled at bank angles over 45 degrees."



Any comments on the above statement. Steep turns offer a greater stall margin--really?

Sure.

If you have a glider that stalls at 35 knots then in a 60º banked turn (2 Gs) at 49.5 knots your turn radius is about 38m.

If your glider has 6m (20ft) between the wing and the tailplane then they are 9 degrees around the circle from each other and will see 9º different angle of attack to each other compared to straight and level flight. That 9º comes off your available back elevator movement.

In a corresponding 5G turn the numbers are 78.46º of bank, 78.3 knots, 33..8m radius and over 10 degrees of difference between wing and tailplane airflow. Plus you're going to need a lot more back elevator to pull those Gs.

Can you stall your glider in straight and level flight if you don't use the last 9 or 10 degrees of elevator deflection?

Another factor is that in a high G steep turn the two wingtips are seeing more more nearly the same airspeed and same angle of attack. So even if you do manage to stall, the spin tendency is much less and the merest easing of back pressure will stop it instantly.

"Why is anyone aero towing with a tow hook that will back release?"

Some of us don't have much of a choice. For example the two ASW-19's and two ASW-15's at my field all have both a C of G hook AND a forward mounted aerotow hook. The forward hooks have a back release function as well. Short of engineering, building, installing and getting an STC from Transport Canada for a completely redesigned forward hook mechanism there's not much we can do about this.

At 04:02 08 May 2014, wrote:
"Why is anyone aero towing with a tow hook that will back release?"

Some of us don't have much of a choice. For example the two ASW-19's and
tw=
o ASW-15's at my field all have both a C of G hook AND a forward mounted
ae=
rotow hook. The forward hooks have a back release function as well. Short
o=
f engineering, building, installing and getting an STC from Transport
Canad=
a for a completely redesigned forward hook mechanism there's not much we
ca=
n do about this.=20

I had for a time an ASW17 which has the same release arrangement as the
ASW15,19,and 20. There was a wooden block attached to the rear of the
aerotow release aperture which prevented operation of the back release. It
never crossed my mind that this was not how it was built. It was
effective.
In the days of yore it was common practice to use bodge tape to prevent the
operation of the back release when aerotowing.

Well, we have plenty of opinions about what to do after the rope suddenly releases, lets take a quick check on how to keep the rope firmly attached until we decide to release it. When you hooked up the rope, did the 'pull' feel normal? If it didn't take much of a pull, one of the springs in the over-center mechanism may have failed. Did the cable return all the way back into its tube? If not, broken cable strands may be flaring out and preventing the tow hook from returning all the way back to its fully closes and locked position. I have seen low altitude releases caused by both of these malfunctions.
Condolences to the family,
JJ

On Thursday, May 8, 2014 7:00:00 AM UTC-6, JJ Sinclair wrote:
Well, we have plenty of opinions about what to do after the rope suddenly releases, lets take a quick check on how to keep the rope firmly attached until we decide to release it.

It is interesting how this discussion has become a data geek's exchange about the physics of a turn back. If the rope had stayed attached he would likely not have tried to turn back, if indeed that is what he tried to do. Apparently no one saw it.

I was always told a Superior pilot uses his superior judgment to keep himself out of situations where his superior piloting skill are needed. The superior judgment in this case would be to not use a back releasing tow hook for aero tow.

When you hooked up the rope, did the 'pull' feel normal? If it didn't take much of a pull, one of the springs in the over-center mechanism may have failed.

JJ, the "Zuni towhook" does not use an over center system. This one of the problems with it. Unlike the Tost hook the force to actuate it is proportional to the tow rope tension.

I am very interested in knowing if there is an obvious malfunction of any part of the tow release system, that was not caused by the actual crash.

Robert Mudd

This discussion clearly indicates one of the fundamental reasons gliding safety is far worse than it should be. Issues such as rope breaks (PT3) have been discussed over and over again, for many years, and this thread demonstrates the wide variation of knowledge of procedures of this and other common launching emergencies.

Also, one must wonder how many pilots flying gliders with the Tost tow hook have ever returned them to the factory for the required periodic overhaul.

Considering who the glider community is - intelligent, well educated, well to do individuals, you must wonder why most simply go out of their way to avoid the simple educational process which will allow safe flight.

Tom Knauff

At 14:42 09 May 2014, Tom wrote:
This discussion clearly indicates one of the fundamental reasons gliding
sa=
fety is far worse than it should be. Issues such as rope breaks (PT3)
have
=
been discussed over and over again, for many years, and this thread
demonst=
rates the wide variation of knowledge of procedures of this and other
commo=
n launching emergencies.

Also, one must wonder how many pilots flying gliders with the Tost tow
hook=
have ever returned them to the factory for the required periodic
overhaul.

Considering who the glider community is - intelligent, well educated,
well
=
to do individuals, you must wonder why most simply go out of their way to
a=
void the simple educational process which will allow safe flight.

Tom Knauff


Not for the first time, I find myself in complete agreement with you Tom.

Chris Rollings

At 16:33 09 May 2014, Chris Rollings wrote:
At 14:42 09 May 2014, Tom wrote:
This discussion clearly indicates one of the fundamental reasons gliding
sa=
fety is far worse than it should be. Issues such as rope breaks (PT3)
have
=
been discussed over and over again, for many years, and this thread
demonst=
rates the wide variation of knowledge of procedures of this and other
commo=
n launching emergencies.

Also, one must wonder how many pilots flying gliders with the Tost tow
hook=
have ever returned them to the factory for the required periodic
overhaul.

Considering who the glider community is - intelligent, well educated,
well
=
to do individuals, you must wonder why most simply go out of their way
to
a=
void the simple educational process which will allow safe flight.

Tom Knauff


Not for the first time, I find myself in complete agreement with you Tom.

Chris Rollings

Me too