Winch Launch - Fatal

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

At 02:30 15 December 2016, wrote:
Having the tailwheel rolling along the ground with=20
the mainwheel several feet in the air is not, and never should be,=20
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.


Not really. Where you go wrong is assuming that the tailwheel is the centre
of rotation -
it isn't, it's an arm hitting a limit.

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
onlya 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 Sunday, December 18, 2016 at 9:45:10 PM UTC-7, B4soaring wrote:

Not really. Where you go wrong is assuming that the tailwheel is the centre
of rotation - it isn't, it's an arm hitting a limit.

Same difference. When an arm hits a limit, the center of rotation shifts to the contact point.

On Tuesday, December 6, 2016 at 6:15:05 AM UTC-8, Jock Proudfoot wrote:


When I started flying a 19meter Kestrel years ago (on aerotow) I quickly found I could not reliably keep my wings level at the start of the aerotow launch if I looked straight ahead, because the ailerons were so inneffective at low speed. So when we started to move, I looked directly left or right towards one wing, for the first few seconds. That made it much easier to keep the wings level, although it usually needed full aileron inputs initially.. My tailwheel Kestrel would initially roll straight ahead wth the tailwheel on the ground, so there was no need to look ahead. It just needed a few seconds to gain reasonable aileron effectiveness, then I could look ahead again.

On Thursday, December 15, 2016 at 10:30:28 AM UTC-7, wrote:
On Tuesday, December 6, 2016 at 6:15:05 AM UTC-8, Jock Proudfoot wrote:


When I started flying a 19meter Kestrel years ago (on aerotow) I quickly found I could not reliably keep my wings level at the start of the aerotow launch if I looked straight ahead, because the ailerons were so inneffective at low speed. So when we started to move, I looked directly left or right towards one wing, for the first few seconds. That made it much easier to keep the wings level, although it usually needed full aileron inputs initially. My tailwheel Kestrel would initially roll straight ahead wth the tailwheel on the ground, so there was no need to look ahead. It just needed a few seconds to gain reasonable aileron effectiveness, then I could look ahead again.

OK, now that we're off on tangents, here's another.

I once flew with a pilot checking out on winch launch who always applied full-right aileron as soon as the acceleration set in - often to the point the right tip nearly dragged. I asked why he was doing that. He replied that he "felt" the left wing was dropping. Video of the takeoff showed the wings level until he slammed the stick over to the right. He was baffled still insisting he "felt" a strong left wing drop.

Eventually, an AME found this individual had a left-right asymmetry in his vestibular organs which, apparently, caused him to experience a sensation of roll under linear acceleration.

This story shows why one must use visual cues and not "feel" to keep the wings level. It also shows the value of making videos of takeoffs.