Winch Launch - Fatal

At 01:59 14 December 2016, wrote:

Don, you brought up the old pitch-up myth so I'll go there.

Pitch-up on acceleration can only happen with the tailwheel in the air
and
=
that can only happen if the glider is slowly dragged into the air with
feeb=
le acceleration and THEN strong acceleration applied. It can't happen if
s=
trong acceleration is applied at the very start of the ground roll and
main=
tained until the glider reaches the normal airspeed for rotating into the
c=
limb.

I could go on at length about this but I wrote a long paper on it
available=
here https://dl.dropboxusercontent.com/u/...celeration.pdf
Rather
=
than take my word for it, I very strongly suggest the BGA and other
nationa=
l clubs do their own investigation using tension loggers. What you will
se=
e may terrify you.


Hi Bill. If you follow URAS you will see that Don, whilst old and wise,
doesn't speak for the UK gliding community.

Originally Posted by

On Tuesday, December 6, 2016 at 7:15:05 AM UTC-7, Jock Proudfoot wrote:


You're right, relying on the pilot pulling the release doesn't work simply because it takes too long for the pilot to react.

I think there is just one cause of ground roll accidents and it's very simple - inadequate acceleration.

A glider just wants to fly and with the wing incidence angle at about 10 degrees with the tailwheel on the ground it will do so in about 2 seconds at 1G. Unless things are badly set up beforehand, the wings will stay balanced for at least that long. Once airborne. there is no risk of a ground roll accident.

The acceleration which worked with old wooden glider just doesn't get a heavy glass glider to aileron control speed and then airborne quickly enough.

Don, you brought up the old pitch-up myth so I'll go there.

Pitch-up on acceleration can only happen with the tailwheel in the air and that can only happen if the glider is slowly dragged into the air with feeble acceleration and THEN strong acceleration applied. It can't happen if strong acceleration is applied at the very start of the ground roll and maintained until the glider reaches the normal airspeed for rotating into the climb.

I could go on at length about this but I wrote a long paper on it available here https://dl.dropboxusercontent.com/u/...celeration.pdf Rather than take my word for it, I very strongly suggest the BGA and other national clubs do their own investigation using tension loggers. What you will see may terrify you.

Hi Bill

An excellent paper and one that I will be sharing. It tallys with my own observations from watching multiple higher acceleration winch launches of a PW-5. In all cases the tail wheel hit the ground with the acceleration and with the stick neutral the glider lifted off in a shallow climb with a slow controlled rotation with increasing speed till it was in the full climb at around 150'

As described in your paper, the most dangerous winch launches I have seen and experienced have been ones with slow acceleration

Regards
Colin

At 09:19 14 December 2016, Jim White wrote:
At 01:59 14 December 2016, wrote:

Don, you brought up the old pitch-up myth so I'll go there.

Pitch-up on acceleration can only happen with the tailwheel in the ai
and
=
that can only happen if the glider is slowly dragged into the air with
feeb=
le acceleration and THEN strong acceleration applied. It can't happen
if
s=
trong acceleration is applied at the very start of the ground roll and
main=
tained until the glider reaches the normal airspeed for rotating into
the
c=
limb.

I could go on at length about this but I wrote a long paper on it
available=
here https://dl.dropboxusercontent.com/u/...cceleration.pd
Rather
=
than take my word for it, I very strongly suggest the BGA and
other
nationa=
l clubs do their own investigation using tension loggers. What you will
se=
e may terrify you.


Hi Bill. If you follow URAS you will see that Don, whilst old and wise
doesn't speak for the UK gliding community.

Hi Bill,

The theory may be correct but I can assure you that a K18 ALWAYS needs the
application of almost full forward stck after lift off to prevent over
rotation. This is using a powerful V8 winch with about 2 seconds of ground
roll. Yes the accleration is still happening after lift off. With a narrow
steel drum throttle response is never instantaneous due to inertia of the
drum, even with the powerful (300 hp+) V8.

At 10:30 14 December 2016, Terry Walsh wrote:
At 09:19 14 December 2016, Jim White wrote:
At 01:59 14 December 2016,
wrote:

Don, you brought up the old pitch-up myth so I'll go there.

Pitch-up on acceleration can only happen with the tailwheel in
the ai
and
=
that can only happen if the glider is slowly dragged into the air
with
feeb=
le acceleration and THEN strong acceleration applied. It can't
happe
if
s=
trong acceleration is applied at the very start of the ground roll
and
main=
tained until the glider reaches the normal airspeed for rotating
int
the
c=
limb.

I could go on at length about this but I wrote a long paper on it
available=
here
https://dl.dropboxusercontent.com/u/...cceleration.pd
Rather
=
than take my word for it, I very strongly suggest the BGA and
other
nationa=
l clubs do their own investigation using tension loggers. What
you will
se=
e may terrify you.


Hi Bill. If you follow URAS you will see that Don, whilst old and
wise
doesn't speak for the UK gliding community.

Hi Bill,

The theory may be correct but I can assure you that a K18
ALWAYS needs th
application of almost full forward stck after lift off to prevent ove
rotation. This is using a powerful V8 winch with about 2 seconds
of groun
roll. Yes the accleration is still happening after lift off. With a
narro
steel drum throttle response is never instantaneous due to inertia
of th
drum, even with the powerful (300 hp+) V8.

I believe there is a solution to this, one which no one will like, but
which would reduce the frequency of the accidents, unfortunately it
may also very expensive and difficult to achieve on existing aircraft
and would result in a reduction in winch launch height. Move the
launch hook forward.

It is pointless to enter into any sort of winch launching discussion here that is based on decades of experience by thousands of European pilots.

At 09:35 14 December 2016, Ventus_a wrote:

;934125 Wrote:
On Tuesday, December 6, 2016 at 7:15:05 AM UTC-7, Jock
Proudfoot wrote:


You're right, relying on the pilot pulling the release doesn't wor
simply because it takes too long for the pilot to react

I think there is just one cause of ground roll accidents and it's
ver
simple - inadequate acceleration.

A glider just wants to fly and with the wing incidence angle at
about 1
degrees with the tailwheel on the ground it will do so in about
seconds at 1G. Unless things are badly set up beforehand, the
wing
will stay balanced for at least that long. Once airborne. there is
n
risk of a ground roll accident

The acceleration which worked with old wooden glider just
doesn't get
heavy glass glider to aileron control speed and then airborne
quickl
enough

Don, you brought up the old pitch-up myth so I'll go there

Pitch-up on acceleration can only happen with the tailwheel in
the ai
and that can only happen if the glider is slowly dragged into the
ai
with feeble acceleration and THEN strong acceleration applied.
It can'
happen if strong acceleration is applied at the very start of the
groun
roll and maintained until the glider reaches the normal airspeed
fo
rotating into the climb

I could go on at length about this but I wrote a long paper on i
available her

https://dl.dropboxusercontent.com/u/...celeration.pdf
Rathe
than take my word for it, I very strongly suggest the BGA and
othe
national clubs do their own investigation using tension loggers.
Wha
you will see may terrify you

Hi Bil

An excellent paper and one that I will be sharing. It tallys with m
own observations from watching multiple higher acceleration winc
launches of a PW-5. In all cases the tail wheel hit the ground with
th
acceleration and with the stick neutral the glider lifted off in
shallow climb with a slow controlled rotation with increasing speed
til
it was in the full climb at around 150

As described in your paper, the most dangerous winch launches I
hav
seen and experienced have been ones with slow acceleratio

Regard
Coli




--
Ventus_a


The tailwheel hitting the ground is normal for all gliders that sit on
a nosewheel and happens because the CofG is higher than the
winch hook. It has nothing to do with the rate of acceleration.
Taking off into a shallow climb with the elevator neutral is what I
would call normal acceleration.

Bill's pdf shows something completely different. The pilot is holding
the stick too far back in the early stages of launch & the elevator is
pushing the tailwheel down on to the ground even after the
mainwheel has taken off. That's just poor technique & usually
happens because the pilot is behind the aircraft & blindly pulling
back after the glider starts moving.

Bill's pdf shows something completely different. The pilot is holding
the stick too far back in the early stages of launch & the elevator is
pushing the tailwheel down on to the ground even after the
mainwheel has taken off. That's just poor technique & usually
happens because the pilot is behind the aircraft & blindly pulling
back after the glider starts moving.

A Discus is a "taildrager" which normally sits tailwheel-down.

At 22:45 14 December 2016, wrote:
Bill's pdf shows something completely different. The pilot is holding
the stick too far back in the early stages of launch & the elevator is
pushing the tailwheel down on to the ground even after the
mainwheel has taken off. That's just poor technique & usually
happens because the pilot is behind the aircraft & blindly pulling
back after the glider starts moving.

A Discus is a "taildrager" which normally sits tailwheel-down.


Of course it is.

If a Discus pilot follows the technique recommended in the flight
manual then the tailplane will raise the tailwheel off the ground before
the glider takes off. Having the tailwheel rolling along the ground with
the mainwheel several feet in the air is not, and never should be,
considered a normal winch launch.

Having the tailwheel rolling along the ground with
the mainwheel several feet in the air is not, and never should be,
considered a normal winch launch.

Absolutely true, but counter-intuitively, the only way this could happen is with low acceleration. High acceleration means high rope tension which acts to pull the nose down if the tailwheel is still rolling.

If you look at videos of winch launch takeoffs frame-by-frame you'll find that it's not unusual to see the main wheel a few centimeters off the ground while the tailwheel is still rolling on the runway. The ASK-21 photo in the paper is typical of this. The duration of a "spur roll" is usually only a few frames of video so it's very hard to catch with a still camera.

One can get these videos with a YouTube downloader. Then, the file can be played back frame-by-frame.

On Wednesday, December 14, 2016 at 6:30:11 PM UTC-8, wrote:
Having the tailwheel rolling along the ground with
the mainwheel several feet in the air is not, and never should be,
considered a normal winch launch.

Absolutely true, but counter-intuitively, the only way this could happen is with low acceleration. High acceleration means high rope tension which acts to pull the nose down if the tailwheel is still rolling.


....Or perhaps any acceleration with C/G near the aft limit?
Experienced a "good looking" start if you didn't notice the stick full forward until airborne.
Still enjoy winch launching. We should do more of it.
Jim