CG hook on aero tows??

On Thu, 8 Jan 2004 10:16:04 UTC, Chris Rollings
wrote:

: In the tests on the
: Ka8, it seemed to me to be (almost?) impossible to
: stop it, once the pitch angle exceeded about 30 degrees.

My Pirat does the rotation all by itself on a winch launch, regardless
of pilot input. I'd never even dream of aerotowing it with that hook.

Ian

PS The manual says it's fine to winch it with the nose hook!

--

On 8 Jan 2004 11:02:45 GMT, "Ian Johnston"
wrote:

My Pirat does the rotation all by itself on a winch launch, regardless
of pilot input.

Does this mean that if you push the stick forward, you are unable to
stop the rotation (in other words - the pilot in a Pirat has no pitch
control during the winch launch)?

Hard to believe I have to admit.



Bye
Andreas

Andreas Maurer wrote in message . ..
On 8 Jan 2004 11:02:45 GMT, "Ian Johnston"
wrote:

My Pirat does the rotation all by itself on a winch launch, regardless
of pilot input.

Does this mean that if you push the stick forward, you are unable to
stop the rotation (in other words - the pilot in a Pirat has no pitch
control during the winch launch)?

In my experience, yes, but only during the initial rotation, and it
only happens at a reasonable speed. In the climb it's fine. And a very
gentle initial acceleration avoids the earlier problems, mostly.

Ian

(Ian Johnston) wrote in message . com...

In my experience, yes, but only during the initial rotation, and it
only happens at a reasonable speed. In the climb it's fine. And a very
gentle initial acceleration avoids the earlier problems, mostly.

Sorry to follow up to myself but ...

The reson, I think, is that the Pirat has quite a high-set wing and a
belly hook as low as it can get. As a result, the lever arm, and
therefore upwards pitching moment from the winch cable about the wing
is relatively high compared to the typical glass glider with mid-set
wing and belly hook offset and up a bit. So with a good fast winch
launch, yes, this moment can overcome anything the elevator is trying
to do.

However, this is an intrinsically stable situation. As the cable angle
relative to the glider's longitudinal axis increases, the lever arm
reduces (by approximately 50% when the glider is 30 degree nose up and
the cable is 30 degrees down). So as the glider pitches up the effect
of the cable reduces, the effect of the elevator (all other things
being equal) stays the same and a point of equilibrium is reached. To
put it simply:

Nose down: winch pulls it up again.

Nose up: elevator pushes it down again

That, I think, is why a good winch launch - "it's like going up on
rails" is so easy and comfortable: the glider is much more stable in
pitch than it is in free flight. I'd expect this to be more marked as
the hook-wing distance increases.

I know, by the way, that I have omitted things like the effect of the
changing AoA on the lift and drag (secondary effects in this case, I
think) and the slingshot effect of a short rope and the relatively low
tow forces behind a tug.

Ian

On 8 Jan 2004 10:16:04 GMT, Chris Rollings
wrote:

will it carry on pitching
further up of its own accord, stay it the attitude
it has reached, or start to pitch back down of its
own accord?

Check this (and use Babelfish for a rough translation - the sketches
should be self-explanatory even for non-German speakers).
http://www.daec.de/se/faq/fschlepp/dlr.htm






Bye
Andreas

'2. Notwithstanding 1. above, as far as I know 100
percent of UK tug upset fatal accidents in the last
30 years happened with belly hooks. We changed our
procedures and recommendations before we could gather
more data and satisfy statistical pedants with some
more fatalities which might have improved the correlation
calculations. Since the changes, fatal tug upsets have
almost entirely disappeared from the UK fatal accident
reports.

Interesting thread! The only Accident that I have personal
knowledge of is one that happened at Turf Soaring in
95 and that particular one involved a SGS-2-33 and
a Pawnee 235 tow plane. The Student Gilder pilot saw
the tow plane go through a dust devil at about a 100-200
feet and when it hit him he was not prepared for it.
They were using a 200 foot rope and the tow plane was
fitted with SGS hook. Niether the tow pilot or the
glider pilot released and the rope broke 4 feet behind
the tow plane. But not before the tow plane was upset
enough not to be able to recover and he 'pancaked'
in to the ground killing himself. The glider pilot
was able to return to the field and land safely. Afterwards
they summarized that the towpilot could not have released
do to the forces on the release. Since then they have
redesigned andgotten FAA aproval to invert the SGS
hook and eliminate this problem. This happened with
a Nose hook and student pilot. I believe that the most
important factor in this disscussion is the lack of
experience not wether or not it is a nose or belly
or cg hook!

Come on people, is the gliding world turning into a
nannie state?

As a glider pilot for some 40 odd (some very odd) years
and a tug pilot for 30 I can't believe some of this
drivel.

Launching of any description on any hook is not a problem
if the gowk at the back has had it properly drummed
into him to keep his hand on the release and thus be
able to throw the launch away instantly in the event
of a dropped wing or the tug disappearing from sight.

"Z Goudie" wrote in message
...
Come on people, is the gliding world turning into a
nannie state?

As a glider pilot for some 40 odd (some very odd) years
and a tug pilot for 30 I can't believe some of this
drivel.

Launching of any description on any hook is not a problem
if the gowk at the back has had it properly drummed
into him to keep his hand on the release and thus be
able to throw the launch away instantly in the event
of a dropped wing or the tug disappearing from sight.

Agreed.

Bill Daniels

"Z Goudie" wrote in message
...
Come on people, is the gliding world turning into a
nannie state?

As a glider pilot for some 40 odd (some very odd) years
and a tug pilot for 30 I can't believe some of this
drivel.

Launching of any description on any hook is not a problem
if the gowk at the back has had it properly drummed
into him to keep his hand on the release and thus be
able to throw the launch away instantly in the event
of a dropped wing or the tug disappearing from sight.

Agreed.

Bill Daniels


If anyone decides to modify their experimental glider to
be towed tail first on a tailhook, I guess we have two
volunteers to be the tow pilots...

In article 3ffee053$1@darkstar, Mark James Boyd
writes

snip

If anyone decides to modify their experimental glider to
be towed tail first on a tailhook, I guess we have two
volunteers to be the tow pilots...

The main question is, in how many seconds would it be being towed
tail-first ......

Another question would be insurance, but we are in "reductio ad
absurdum" land, here, aren't we?

--
Ian Strachan
Lasham, UK