Cadillac commercial accident?

On Oct 16, 8:40*am, ContestID67 wrote:
*Someone check my math.

For constant acceleration the average speed for a run that starts with
zero speed is half the end speed. The Escalade does 0-60 in under 10
seconds I think. Assume 10 seconds and add 25% for the extra mass of
the glider and that gives a ballpark zero to 60 mph distance of
88*12.5/2 ft = 550ft. That leaves enough room to get down and
stopped. However, if the goal really was a turn back, I'd assume the
intention would have been to be at winch limit speed with as much
altitude as possible. Guessing winch redline at 90mph that would use
up about 825ft. Still enough to get down and stopped but not a
situation where I'd be tempted to try a turn back.

However, If the run reached winch redline at the point where the tow
truck had to start maximum braking to stop before the end, then the
runway available for a turn back looks much better. At winch redline,
and with say 100ft of altitude, the available energy is looking
comparable to an aerotow rope break at 200ft. (Ballpark you have half
the potential energy but over 2 times the kinetic energy). Someone
knowing the winch redline and the normal aerotow speed could run the
numbers.

Not saying I'd want to try a turn back under those conditions but the
idea may not be as stupid as some are suggesting.

Andy

On Oct 16, 4:41*pm, Andy wrote:
On Oct 16, 8:40*am, ContestID67 wrote:

*Someone check my math.

For constant acceleration the average speed for a run that starts with
zero speed is half the end speed. *The Escalade does 0-60 in under 10
seconds I think. *Assume 10 seconds and add 25% for the extra mass of
the glider and that gives a ballpark zero to 60 mph distance of
88*12.5/2 ft = 550ft. *That *leaves *enough room to get down and
stopped. *However, if the goal really was a turn back, I'd assume the
intention would have been to be at winch limit speed with as much
altitude as possible. *Guessing winch redline at 90mph that would use
up about 825ft. *Still enough to get down and stopped but not a
situation where I'd be tempted to try a turn back.

However, If the run reached winch redline at the point where the tow
truck had to start maximum braking to stop before the end, then the
runway available for a turn back looks much better. *At winch redline,
and with say 100ft of altitude, the available energy is looking
comparable to an aerotow rope break at 200ft. (Ballpark you have half
the potential energy but over 2 times the kinetic energy). *Someone
knowing the winch redline and the normal aerotow speed could run the
numbers.

Not saying I'd want to try a turn back under those conditions but the
idea may not be as stupid as some are suggesting.

Andy

I've done many auto tows with an aero tow rope but never in a scenario
like this. My tows were to just so I could glide down a long taxiway
to the ramp and stop in front of a hangar saving the walk back. The
climb was very shallow with a slack rope release when I thought I had
enough height - usually about 170' AGL. Then never a turn more than
30 degrees until touchdown. It was fun and safe.

This was obviously neither. I'm afraid it was one of those, "It can't
be that hard" situations. Excellent, in depth training is the key
to safe ground launch operations. Given that training, winch launch
can be safer than aero tow judging by the German experience. DIY
training can be deadly as we've seen.

Most ground launch accidents don't involve the launch - more than 80%
are landing accidents where the pilot gets safely airborne but can't
manage a safe landing. Usually, it's because the pilot had no plan if
the launch didn't go as expected. A launch failure doesn't mean a
safe landing is impossible - or even difficult.

The best this pilot could have hoped for is to be at 170 feet AGL
2000' down the runway then try for an aero tow-like turn to a downwind
landing. Doable? Maybe, by an experienced pilot - but with no safety
margin whatsoever.

On Oct 16, 12:58*pm, Peter Scholz wrote:

A rough graphical calculation that I just did shows that the Tost CG
hook will probably release at about 100 ft height above ground, perhaps
even earlier, depending on the climb angle.


That answer does not seem reasonable since it implies a limiting cable
angle of 30 degrees to the horizontal. Anyone who has observed a
winch launch knows the normal cable angle at top of the launch greatly
exceeds 30 degrees. If the limiting cable angle is conservatively
assumed to be 60 degrees then a 200ft rope would give 173 ft of
altitude if the climb profile was flown correctly.

Andy

Am 17.10.2011 18:59, Andy wrote:
On Oct 16, 12:58 pm, Peter wrote:

A rough graphical calculation that I just did shows that the Tost CG
hook will probably release at about 100 ft height above ground, perhaps
even earlier, depending on the climb angle.


That answer does not seem reasonable since it implies a limiting cable
angle of 30 degrees to the horizontal. Anyone who has observed a
winch launch knows the normal cable angle at top of the launch greatly
exceeds 30 degrees. If the limiting cable angle is conservatively
assumed to be 60 degrees then a 200ft rope would give 173 ft of
altitude if the climb profile was flown correctly.

Andy

You have to add the rope angle and the plane angle (measured against the
ground), the resulting angle is the angle between the rope and the
plane. The shorter the rope, the earlier you get to a resulting angle
that gets near 90°. Typically, a Tost hook will release a bit earlier
than 90°.

In a typical winch launch, with rope length more than 2000 ft at the
beginning, and more than 1000ft at the end of the launch, increasing the
angle of the plane does not release the Tost hook in the climb phase,
because the rope angle is much smaller than in the 200ft example that we
have here.
--
Peter Scholz
ASW24 JE

On Oct 17, 12:13*pm, Peter Scholz wrote:
Am 17.10.2011 18:59, Andy wrote:

On Oct 16, 12:58 pm, Peter *wrote:

A rough graphical calculation that I just did shows that the Tost CG
hook will probably release at about 100 ft height above ground, perhaps
even earlier, depending on the climb angle.

That answer does not seem reasonable since it implies a limiting cable
angle of 30 degrees to the horizontal. *Anyone who has observed a
winch launch knows the normal cable angle at top of the launch greatly
exceeds 30 degrees. *If the limiting cable angle is conservatively
assumed to be 60 degrees then a 200ft rope would give 173 ft of
altitude if the climb profile was flown correctly.

Andy

You have to add the rope angle and the plane angle (measured against the
ground), the resulting angle is the angle between the rope and the
plane. The shorter the rope, the earlier you get to a resulting angle
that gets near 90°. Typically, a Tost hook will release a bit earlier
than 90°.

In a typical winch launch, with rope length more than 2000 ft at the
beginning, and more than 1000ft at the end of the launch, increasing the
angle of the plane does not release the Tost hook in the climb phase,
because the rope angle is much smaller than in the 200ft example that we
have here.
--
Peter Scholz
ASW24 JE

So the answer is clear. To achieve maximum altitude on a short rope
auto tow do not use high pitch attitudes. The original question was
- what is the greatest altitude that could be reached with a 200ft
rope. My answer of about 173 feet is close to the experience
reported by Bill Daniels. Assuming a back release angle of 85 deg and
a rope angle of 60 deg gives a release pitch attitude of 25 deg. The
climb could be made at much less than 25 deg pitch.

As I said in my first answer "if the climb profile was flown
correctly". Auto tow does not require an aggressive climb profile to
reach maximum altitude as long as the runway length is not limiting.
Unlike winch launching the rope length remains constant.

Andy

On Tue, 18 Oct 2011 06:28:45 -0700, Andy wrote:


As I said in my first answer "if the climb profile was flown correctly".
Auto tow does not require an aggressive climb profile to reach maximum
altitude as long as the runway length is not limiting. Unlike winch
launching the rope length remains constant.

To me, auto-launching on a 200 ft rope sounds uncomfortably like aero-
towing on a CG hook except that now you're *trying* to get above the
'tug'. This sounds to me like a recipe for getting into the
uncontrollable sling-shot region that upsets tugs. Further, it seems to
me that if you do that to a rear-wheel drive vehicle your problems will
be compounded by a loss of acceleration due to loss of traction as the
rope tension reduces the weight on the driving wheels.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Oct 18, 6:28*pm, Martin Gregorie
wrote:
On Tue, 18 Oct 2011 06:28:45 -0700, Andy wrote:

As I said in my first answer "if the climb profile was flown correctly"..
*Auto tow does not require an aggressive climb profile to reach maximum
altitude as long as the runway length is not limiting. Unlike winch
launching the rope length remains constant.

To me, auto-launching on a 200 ft rope sounds uncomfortably like aero-
towing on a CG hook except that now you're *trying* to get above the
'tug'. This sounds to me like a recipe for getting into the
uncontrollable sling-shot region that upsets tugs. Further, it seems to
me that if you do that to a rear-wheel drive vehicle your problems will
be compounded by a loss of acceleration due to loss of traction as the
rope tension reduces the weight on the driving wheels.

--
martin@ * | Martin Gregorie
gregorie. | Essex, UK
org * * * |

Yep, but so far as I know, no one has yet upset a tow car. If the
rear end is light, the rear wheels can spin on low traction surfaces
but the solution is to fill the back end of the tow vehicle with
rocks.

In Europe we now have EASA to protect us from ourselves. I am sure there is
already, or will be very soon, an EASA edict to say that we cannot launch
anything behind a car without 12 hours of training of both driver and
pilot, a written exam on the maths involved, a practical test (with annual
renewal), and a fee to pay too.

This is a shame. Many years ago a venerable pilot at my club was told by
the CFI that it was much too windy for him to fly his K6 on the local ridge
and was refused a launch.

So he hitched his trailer up to his Ford Cortina and drove to a field at
the top of the ridge. He rigged and his mate then towed him with said
Cortina towards the ridge using a standard aerotow rope. This was so
successful he did it again the next day. This sort of derring-do was what
gliding was made of then.

Unfortunately in EASA land gliding is becoming a paperwork exercise and is
getting boring. You do not know how lucky you are in the land of the free
that you are still allowed to put yourself in danger.

Jim


At 00:28 19 October 2011, Martin Gregorie wrote:
On Tue, 18 Oct 2011 06:28:45 -0700, Andy wrote:


As I said in my first answer "if the climb profile was flown
correctly".
Auto tow does not require an aggressive climb profile to reach maximum
altitude as long as the runway length is not limiting. Unlike winch
launching the rope length remains constant.

To me, auto-launching on a 200 ft rope sounds uncomfortably like aero-
towing on a CG hook except that now you're *trying* to get above the
'tug'. This sounds to me like a recipe for getting into the
uncontrollable sling-shot region that upsets tugs. Further, it seems to
me that if you do that to a rear-wheel drive vehicle your problems will
be compounded by a loss of acceleration due to loss of traction as the
rope tension reduces the weight on the driving wheels.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Oct 18, 10:53*pm, Bill D wrote:
On Oct 18, 6:28*pm, Martin Gregorie
wrote:









On Tue, 18 Oct 2011 06:28:45 -0700, Andy wrote:

As I said in my first answer "if the climb profile was flown correctly".
*Auto tow does not require an aggressive climb profile to reach maximum
altitude as long as the runway length is not limiting. Unlike winch
launching the rope length remains constant.

To me, auto-launching on a 200 ft rope sounds uncomfortably like aero-
towing on a CG hook except that now you're *trying* to get above the
'tug'. This sounds to me like a recipe for getting into the
uncontrollable sling-shot region that upsets tugs. Further, it seems to
me that if you do that to a rear-wheel drive vehicle your problems will
be compounded by a loss of acceleration due to loss of traction as the
rope tension reduces the weight on the driving wheels.

--
martin@ * | Martin Gregorie
gregorie. | Essex, UK
org * * * |


So, putting this thread together it seems we have another plausible
scenario: the glider does a "ground tow" using a short rope, but
following a climb profile, with the plan being to release and then
land straight ahead. The rope breaks or back-releases with the glider
still pointing up at about 175 feet. At this point it's nearly
impossible to recover. The glider stalls and spins, resulting in the
nose-down turn reported by the observers. That's a much more common
scenario than spoiler malfunction.

It would seem easy to use a 200 foot rope to just get up to speed,
getting to no more than 50 feet and then overflying the car. Using it
to get altitude, flying a regular climb profile but doing in 200 feet
what you normally do in 1000 feet, could easily lead to the surprise
rope break or back release while still climbing, as the moment to nose
over and release would come very fast and you can't see the car.

I presume those of you who have tried auto towing behind short ropes
(not me!) were basically just getting up to speed, say to do a modern
bungee launch from the top of a hill, not trying to get to the
standard 60 degrees or so maximum altitude release point.

At least it's more plausible than a plan to do a 180 turn from 200
feet!

Presumably at least the NTSB will get to see the video and we will
know what really happened.

John Cochrane

On Oct 19, 8:49*am, John Cochrane
wrote:
On Oct 18, 10:53*pm, Bill D wrote:









On Oct 18, 6:28*pm, Martin Gregorie
wrote:

On Tue, 18 Oct 2011 06:28:45 -0700, Andy wrote:

As I said in my first answer "if the climb profile was flown correctly".
*Auto tow does not require an aggressive climb profile to reach maximum
altitude as long as the runway length is not limiting. Unlike winch
launching the rope length remains constant.

To me, auto-launching on a 200 ft rope sounds uncomfortably like aero-
towing on a CG hook except that now you're *trying* to get above the
'tug'. This sounds to me like a recipe for getting into the
uncontrollable sling-shot region that upsets tugs. Further, it seems to
me that if you do that to a rear-wheel drive vehicle your problems will
be compounded by a loss of acceleration due to loss of traction as the
rope tension reduces the weight on the driving wheels.

--
martin@ * | Martin Gregorie
gregorie. | Essex, UK
org * * * |

So, putting this thread together it seems we have another plausible
scenario: the glider does a "ground tow" using a short rope, but
following a climb profile, with the plan being to release and then
land straight ahead. The rope breaks or back-releases with the glider
still pointing up at about 175 feet. *At this point it's nearly
impossible to recover. The glider stalls and spins, resulting in the
nose-down turn reported by the observers. That's a much more common
scenario than spoiler malfunction.

It would seem easy to use a 200 foot rope to just get up to speed,
getting to no more than 50 feet and then overflying the car. Using it
to get altitude, flying a regular climb profile but doing in 200 feet
what you normally do in 1000 feet, could easily lead to the surprise
rope break or back release while still climbing, as the moment to nose
over and release would come very fast and you can't see the car.

I presume those of you who have tried auto towing behind short ropes
(not me!) were basically just getting up to speed, say to do a modern
bungee launch from the top of a hill, not trying to get to the
standard 60 degrees or so maximum altitude release point.

At least it's more plausible than a plan to do a 180 turn from 200
feet!

Presumably at least the NTSB will get to see the video and we will
know what really happened.

John Cochrane

John,

Not quite...

If he really got to 170' AGL before the rope break, the glider's
attitude would have been fairly level. It's only possible to get the
nose way up early in the launch. The "CG hook" is actually slightly
ahead of the actual CG so the rope's pull will bring the nose down as
the glider reached the top of the auto tow even with full-up
elevator. Also, if the rope angle is near 70 degrees, the automatic
"back release" function of the Tost CG hook will activate. Given
enough room and a knowledgeable pilot, there is nothing inherently
dangerous about an auto tow with a 200' rope.

It may have gone like this. The pilot rotates prematurely into a very
steep climb right after liftoff with the stick full back having been
trained that way launching old gliders with a nose hook or a
"combination hook". He may not have been prepared for how
aggressively a DG1000 with a true CG hook flown solo responds to full
up elevator. When the rope breaks, full-up elevator causes the nose
to "pop-up" so now the nose is up 60 degrees at low altitude. Only
airspeed and quick reactions could have saved him.

Calculations done by one of our winch engineering group show if the
glider had at least 60 knots at the break, and the pilot reacted by
pushing over at 0 G within .2 seconds, (Healthy human reaction time.)
he could have recovered straight ahead at Vs x 1.3 with a height loss
of only about 25 feet suggesting even this extreme event was
potentially recoverable if the recovery started above 25' AGL.

However, the pilot, surprised by the rope break, is unable to get the
nose down before the glider stalls. A wing drops in an incipient spin
but, being extremely spin resistant, the glider transitions into a
spiral dive almost immediately. The pilot reacts late to the
incipient spin applying spin recovery controls with the glider in a
spiral dive. The result is a turning dive into the ground.