CG hook on aero tows??

A pilot might aerotow on an aft hook when a forward hook is fitted if:

a/ The forward hook is unserviceable,
b/ The forward hook is taped over:
to increase performance,
to reduce noise,
to reduce drafts.

I think that the tug pilot or the organisation providing the tow would be
fully justified in refusing to tow the pilot in any of these circumstances.

If there were to be an accident, there might be a problem in claiming on the
insurance, and any investigation is likely to be adversely critical, even if
the tow hook position was not a factor in the accident.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.


"Ian Johnston" wrote in message
news:cCUlhtvFIYkV-pn2-LTEljpyteDPd@localhost...


On Wed, 7 Jan 2004 03:01:17 UTC, (Mark James Boyd)
wrote:

Are you guys telling me the manual says that if it has only a CG hook,
you can aerotow with it, but if both hooks are present, the manual
prohibits aerotow on the CG hook for the ASW-27?


Under what circumstances would one tow with a CG hook when a nose hook
was available?

Ian

On 7 Jan 2004 09:53:55 -0800, (Chris
OCallaghan) wrote:

A good next step would be to repeat
the experiment, this time putting emphasis on measuring the loads and
effects of identical maneuvers using a nose vs. cg hook.

This is exactly what has been done by the German LBA and DLR,
resulting in the regulations that a nose hook must be installed in any
newly produced glider.

This is the result paper of the experiments:

http://www.daec.de/se/faq/fschlepp/dlr.htm

(unfortunately only in German, I haven't found an English version yet)


In the absence of valid statistical or empirical evidence, it's hard
to determine just how critical this problem is.

http://www.daec.de/se/faq/fschlepp/unfallzahlen.htm

(number of accidents during winch launch and aerotow)

Not hard evidence... but the decrease in accident numbers in aerotow
is significant - maybe caused by the fact that more and more gliders
are equipped with nose hooks?


Bye
Andreas

On Thu, 8 Jan 2004 10:18:37 UTC, "W.J. \(Bill\) Dean \(U.K.\)."
wrote:

: A pilot might aerotow on an aft hook when a forward hook is fitted if:
:
: a/ The forward hook is unserviceable,

That would be ruled out by my " ... is available"

: b/ The forward hook is taped over:
: to increase performance,
: to reduce noise,
: to reduce drafts.

And that would be sheer stupidity - the cause, I reckon, of 90% of all
gliding accidents.

: I think that the tug pilot or the organisation providing the tow would be
: fully justified in refusing to tow the pilot in any of these circumstances.

Agreed. Or to impose conditions. At my club, any visiting pilot who
wishes to tow with a belly hook has to take a check flight in a
two-seater, towed with the belly hook, before s/he may fly,
regardlessof experience or qualifications. But then, it's a club which
lost one of its tug pilots, elsewhere, to an upset.

: If there were to be an accident, there might be a problem in claiming on the
: insurance, and any investigation is likely to be adversely critical, even if
: the tow hook position was not a factor in the accident.

The latter point worries me a bit. Accident investigations should, I
think, concentrate on what happened and what mattered. They shouldn't
kae side swipes at things the investigator doesn't approve of, if they
are irrelevant. In fact, investigations generally shouldn't be
adversely critical. We can all do that when we see what the cause of
an accident were!

Ian

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 Wed, 7 Jan 2004 23:29:16 +0000, Ian Strachan
wrote:

The static on-the-ground measurement of where the glider GC is with
respect to the belly hook position is not what matters. It is what
happens on a launch (dynamic, not static conditions). What matters is
the angle-of-pull of the cable with respect to the centre of motion and
control effectiveness of the glider in that dynamic launch situation.

If you measure where the CG is statically, that is, on the ground, and
placed a tow hook directly underneath it, I think that you would find
the subsequent launch pretty unstable either on winch or air tow.

The best (static) procedure I know for correctly locating the tow hook
on a free flight model glider (launch for these is equivalent to winch
launch with the controls fixed for a minimum sink glide condition) is
to:

- locate the CG on the wing chord (A)
- draw the wing chord on the fuselage
- draw a perpendicular to the wing chord running through the CG
- a line through the tow hook and point A should slope forward
at an angle of 16 degrees from the perpendicular.

On most models that approximates to 18-20 degrees forward of a
vertical line through the CG. In other words, the optimum winch launch
hook position is in front of the CG by an amount that is related to
the vertical distance between wing and hook.

HTH

Martin

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

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

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

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.


"Ian Johnston" wrote in message
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On Thu, 8 Jan 2004 10:18:37 UTC, "W.J. \(Bill\) Dean \(U.K.\)."
wrote:

A pilot might aerotow on an aft hook when a forward hook is fitted if:

a/ The forward hook is unserviceable,


That would be ruled out by my " ... is available"


NO!

If the forward hook is unserviceable, then the glider is unserviceable for
aerotow.

Would you aerotow your Pirat on the aft hook if the forward hook is
unserviceable?

Would you winch launch a K21 on the forward hook (with no back release!) if
the aft hook is unserviceable? Would you do it if you could make the
forward hook back release? Would you wire launch any glider on the forward
hook (unless the C. of A. papers specifically allowed it) ?.

The glider has two hooks for a reason. If an apparently otherwise
identical glider has only one hook, that is a bad reason for assuming that
you can treat your glider hooks as interchangeable.



b/ The forward hook is taped over:
to increase performance,
to reduce noise,
to reduce drafts.


And that would be sheer stupidity - the cause, I reckon, of 90% of all
gliding accidents.


What seems stupidity to you may be a habit formed at a site where this has
become normal behaviour over the years.



I think that the tug pilot or the organisation providing the tow would
be fully justified in refusing to tow the pilot in any of these
circumstances.


Agreed. Or to impose conditions. At my club, any visiting pilot who
wishes to tow with a belly hook has to take a check flight in a
two-seater, towed with the belly hook, before she/he may fly,
regardless of experience or qualifications. But then, it's a club which
lost one of its tug pilots, elsewhere, to an upset.


If there were to be an accident, there might be a problem in claiming on
the insurance, and any investigation is likely to be adversely critical,
even if the tow hook position was not a factor in the accident.


The latter point worries me a bit. Accident investigations should, I
think, concentrate on what happened and what mattered. They shouldn't
take side swipes at things the investigator doesn't approve of, if they
are irrelevant. In fact, investigations generally shouldn't be
adversely critical. We can all do that when we see what the causes of
an accident were!


It was meant to worry you.

Like it or not, accident investigators tend to enquire, notice and comment
on the whole operation and not just the immediate causes of the particular
accident. And some underwriters are always on the lookout for an excuse
not to pay.

Have you never visited a site, or noticed a particular pilot or syndicate,
and said to yourself "there is an accident waiting to happen" ? Accident
investigators look for this, as well as the particular factors directly
leading to an accident.


Ian

'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.