CG hook on aero tows??

At 09:18 07 January 2004, Marc Ramsey wrote:
Chris Rollings wrote:
In launching on a C og G
hook you are risking the tow-pilots life more than
your own, and this I will not defend.

Marc Ramsey wrote
I personally prefer to fly aerotow with nose hooks,
and
both of the gliders I now fly have them. But, I'm
not
convinced that anyone has provided actual evidence
of an
observed safety issue with CG hooks.

Some numbers like these for, say, the past 20 years
in the UK:

How many aerotow operations were there per year?
What percentage of aerotow operations used CG hooks?
How many aerotow upset accidents were there during
that period?
What percentage of the aerotow upset accidents involved
CG hooks?

If these figures aren't available, is the use of CG
hooks being
discouraged based simply on the assumed lack of positive
longitudinal
stability during aerotow?

Marc

I hate to agree with Chris Rollings but he sums it
up quite well.

The questions posed by Marc Ramsey, difficult to obtain
that no one will even try, so they will not get answered.

Whatever we write here, I cannot see the owners of
C of G only aircraft rushing out to retrofit a nose
hook. Having towed on both, the worst being an Olympia
2B with only a C of G hook and a powerful tug, I prefer
the nose hook every time.

Some years ago, mid 1908’s I believe, the Australian
Gliding Association, following a number of tug upsets
produced a very graphic illustration showing the various
stages of a tug being upset by a glider on tow, wherever
the hook. It clearly and simply illustrated the difficulties
this caused the pilots at each end of the combination.


C of G hooks merely increase the likely hood of this
happening with an inattentive pilot.

The short answer is educating the pilots on the particular
hook to be used and hammering home the consequences
of inattention to all.

The Australian poster should be displayed at all gliding
sites.

To try to answer the question that started this thread,
the B4 pilots problems could be solved by asking the
tug to accelerate a little faster from the start, having
due regard to the problems this may cause. IE Things
may go wrong even quicker!

Dave

Flying a Pik-20D some years ago I had to be very cautious in airtows because
the glider:
- had a large tendency of dropping the left wing at low speed (angle of
attack problem because of the large wheel and short fuselage)
- had a large tendency of dropping the right wing because of prop wash
- was quite unstable in pitch during the tow because of the quite backward
position of the CG hook, while no nose hooh available.
Nevertheless the towpilot and I survived very many tows without a serious
problem. However I would not go through this once more; just to risky that
something goes wrong.

After the Pik-20D I flew a DG800S 18m for about 10 years. Only a CG hook and
never a problem. Would do it again this way without hesitation.

Just recently we (my son and I) bought a Ventus-2cxT. Nice glider. My first
flight with it was on airtow. Used nosehook which we paid for seperately. No
tendency of dropping a wing. However very nervous on pitch during the tow.
Not a pleasure and was happy to release. I guess a novice would certainly
have had problems with it.

So one may say that each glider has its own way of being pulled into the
air. Being towed is certainly a safety issue. So I wonder why not everybody
concludes that for airtows nosehooks should be mandatory and CG hooks should
not be allowed. We are talking about money I guess. We spent many thousands
of euros on the glider itself and try to save some euros in not having a
nose hook installed and still like to take off in an airtow. To my humble
idea our lives and especially those of towpilots are to valuable to run an
additional risk of not using a nose hook in air tows.

Karel, NL



"W.J. (Bill) Dean (U.K.)." schreef in bericht
...
There have been several fatal "aerotow upset" accidents in the U.K. where
it seems certain that towing on a hook intended for winch launching was a
factor.

These include:
Lasham new year 1963/4 Auster towing a Ka 6cr or Skylark 2 (I forget
which),
Tug at Aboyne towing a Ka 6e,
Tugs (Super Cubs) towing K 18s at Portmoak and Dunstable (within a few
months of each other), this led to the tests by Chris Rollings, Verdun
Luck
and Brian Spreckley at Booker see
http://www.glidingmagazine.com/ListF...Dtl.asp?id=327 .

Will that do, or how many others do you need?

Any glider which launches well on a cable using the aft launching hook,
will
do the same behind a tug maybe killing the tug pilot in the process. If
you really think that the glider pilot can control or stop this process
once
it starts, READ THE ARTICLE LINKED ABOVE; I suggest that the pilots who
conducted those tests were more experienced, more current and just plain
better than you.

To my certain knowledge it is possible to fit a forward hook for aerotow
to
the ASW 15, 17, ASK 18, ASW 19, 20, and 22 and the Pegase; the ASK 21 and
23
and I think later types were fitted with it as standard. I don't know of
any examples of these in club (as distinct from private owner) use which
have not been modified.

I think you would be very wise to have your ASW 19 fitted with the
approved
forward hook modification before your wife flies it on aerotow.

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


"Andy Durbin" wrote in message
om...


Ian Strachan wrote in message
...


In article , Andy
Durbin writes

snip

LBA certification
prohibits the use of CG hook for aerotow


Does not that tell you something, then?


1. With over 1500 hours in the ASW 19 I am very familiar with aero
tow
with CG hooks.


So I have no doubt also thought the glider pilots who got out of
position and killed the tug pilot.


If you have data on those accidents I would be interested in seeing
it. I used to be a tug pilot (2 USA clubs and 1 UK club). The only
tug pilot fatalities I am familiar with that resulted from glider
being too high did not involve a cg hook.


Just do not come to my club and expect to tow on your aft hook, or
anywhere where I am towing. I would have thought where
life-and-death
was concerned you could be a tad more humble about your undoubted
handling abilities. But perhaps unlike the rest of us, you never
have
an off-day ......


One of the reasons I included the forward hook in my order was the
slim chance that I would return to UK.

What should I do with my ASW 19? I had planned to transition my low
time wife to it but perhaps the risks are just too great. Is there an
approved forward hook modification?

Andy (GY)

Chris Rollings wrote in message
...

SNIP
Let's look at the numbers. I will use the UK as an
example, since I have a fairly accurate knowledge of
the statistics there, but the pricipals are the same
for any of the World's gliding nations.
SNIP

Chris

I learnt to fly at an all aerotow operation back in 1967 at the old
Leicestershire club at Rearsby. Training was on a Slingsby Capstan and
pupils were then sent solo in an Olympia 2b, (in my case after twenty seven
flights). These of course like virtually all gliders of that time had only
CoG hooks.

What do the accident statistics say when comparing that period with the
present day ?

Don Brown

Karel,

I think you may have paid the extra for the belly hook
not the nose hook. I am on the Schempp-Hirth waiting
list at present and when I enquired about the cost
of adding a nose hook I was told that all gliders had
the nose hook as standard and that the additional cost
option was for a belly hook. They would build a glider
with the belly hook only for no extra cost on special
request but it would be placarded as not certified
for aerotowing.

John Galloway

At 10:30 07 January 2004, K.P. Termaat wrote:
Just recently we (my son and I) bought a Ventus-2cxT.
Nice glider. My first
flight with it was on airtow. Used nosehook which we
paid for seperately. No
tendency of dropping a wing. However very nervous on
pitch during the tow.
Not a pleasure and was happy to release. I guess a
novice would certainly
have had problems with it.

So one may say that each glider has its own way of
being pulled into the
air. Being towed is certainly a safety issue. So I
wonder why not everybody
concludes that for airtows nosehooks should be mandatory
and CG hooks should
not be allowed. We are talking about money I guess.
We spent many thousands
of euros on the glider itself and try to save some
euros in not having a
nose hook installed and still like to take off in an
airtow. To my humble
idea our lives and especially those of towpilots are
to valuable to run an
additional risk of not using a nose hook in air tows.

Karel, NL

Yes John, you are right.
I looked through the papers and found that the belly hook is the option
indeed. So SH does it it in the right way and tries to convince pilots to
use the nose hook when on an airtow. Probably the LBA has forced them to do
so.

Karel, NL

"John Galloway" . uk
schreef in bericht ...
Karel,

I think you may have paid the extra for the belly hook
not the nose hook. I am on the Schempp-Hirth waiting
list at present and when I enquired about the cost
of adding a nose hook I was told that all gliders had
the nose hook as standard and that the additional cost
option was for a belly hook. They would build a glider
with the belly hook only for no extra cost on special
request but it would be placarded as not certified
for aerotowing.

John Galloway

At 10:30 07 January 2004, K.P. Termaat wrote:
Just recently we (my son and I) bought a Ventus-2cxT.
Nice glider. My first
flight with it was on airtow. Used nosehook which we
paid for seperately. No
tendency of dropping a wing. However very nervous on
pitch during the tow.
Not a pleasure and was happy to release. I guess a
novice would certainly
have had problems with it.

So one may say that each glider has its own way of
being pulled into the
air. Being towed is certainly a safety issue. So I
wonder why not everybody
concludes that for airtows nosehooks should be mandatory
and CG hooks should
not be allowed. We are talking about money I guess.
We spent many thousands
of euros on the glider itself and try to save some
euros in not having a
nose hook installed and still like to take off in an
airtow. To my humble
idea our lives and especially those of towpilots are
to valuable to run an
additional risk of not using a nose hook in air tows.

Karel, NL

Chris,

It's very hard to argue with your point of view. There is absolutely
no doubt that a nose hook should always be preferred to a cg hook
during aerotow for safety reasons. As you note, resistance to
regulatory change on this issue is based on cost. Retrofitting a
glider designed with only a cg hook will be high. And as is often the
case, a balance must be found between cost and improved safety. Which
gets to my point. You've offered an overview of why individual,
anecdotal experience should not be trusted, but you've given us
nothing quantitative to work with. Can you show that PIO related (as
opposed to control failure) aerotow take-off accidents involved a
disproportionate number of gliders with cg hooks? What is the current
ratio of such use among launched glider (not the whole fleet, but
those flying actively)? What is the cost of retrofitting an LS-4 or
Discus or other appropiate model?

I'll reemphasize that we're in agreement regarding the preference for
a nose hook, but if you are going to discount our collective
experiece, give us some real numbers.

Andreas Maurer wrote in message . ..
On Mon, 5 Jan 2004 21:58:53 +0000, Ian Strachan
wrote:

In article , Andy
Durbin writes

snip

LBA certification
prohibits the use of CG hook for aerotow

Does not that tell you something, then?

Unfortunately the above is wrong.
LBA certification prohibits the use of the CG hook in these cases:

- no use of CG hook for aerotows of student pilots
- no use of the CG hook if a nose hook is available
- retro-fitting of nose hook NOT required.

- according to the Gliding Operation Handbook (SBO) of the German Aero
Club (DAeC) a pilot is required of doing at least three aerotows on a
nose hook before he can do aerotows on a glider equipped only with CG
hook.

...

Bye
Andreas


Hi Andreas,

The initial statement is correct because it was with reference to *my*
ASW 28 which I chose to have fitted with both books. (clause 2 of your
reply).

Andy (GY)

In article , Andreas Maurer
writes
On 6 Jan 2004 08:21:29 GMT, Ray Payne
wrote:

ASW 27B is only certificated for aerotow operation when the forward tow
release is used!

This is correct.
And an ASW-27 where no nose hook is installed is certified for aerotow
operation on the CG hook.

A point I made in an earlier contribution to this thread seems to be
being missed but I think is important. That is, where a glider has two
hooks, the rear hook can be placed close to the true C of G position.
With only one hook, the position will normally be somewhat forward of
the C of G position and will be a compromise rather than a true C of G
hook.

In other postings people talk generally about "CG hooks" without making
the above distinction, which could be critical to handling on the
launch. "Belly hook" might be a better term, and many will not be true C
of G positions unless a nose-hook is also fitted.

--------------------

In more detail:

Gliders with only one tow hook:

The hook will be under the belly rather than in the nose, so that it can
be used for both winch/auto tow AND air tow.

Test and certification. The hook will be tested for both wire and air
tow launches before the initial C of A is granted for the design.
Testing will be at a number of glider C of G positions, the most
critical being the aft CG case because it is the least longitudinally
stable.

The hook is unlikely to be aft enough to be strictly a "C of G"
position, so that natural longitudinal stability while on air tow is
maintained. This is rightly a certification requirement.

During a winch or auto tow launch, a positive pull force will be needed
to keep the right climb angle. With some gliders this pull force can be
quite high, but at least is safe in the sense that if the cable breaks,
the nose falls quickly as soon as back-pressure on the stick is relaxed.


Gliders with two tow hooks:

Front hook, for air tows. Straightforward. Better longitudinal
stability while on tow, more directional stability before takeoff. Less
tendency for a "tug upset". Better all round for air tow.

Winching on a nose-hook. One of my early clubs (RAF Swinderby, near
Lincoln, UK) had an old Cadet Mark 1 glider which only had a nose hook.
It also had no instruments! We used to winch launch it and were lucky
to get 600 feet. The back-pressure on the stick to get even this low
height, was considerable. How did we know that it was 600 ft? The CFI
borrowed an altimeter from the RAF Instrument Section and we carried it
in a pocket, consulting it when off the wire. Those were the days !

Rear hook.
Because there is a front hook, the rear hook can be placed close to the
true C of G position. That is, where the vector of the pull of the wire
during the main part of a winch or auto-tow passes close to the glider C
of G. This minimises the hard pull force otherwise necessary to climb on
a wire launch, and maximises the launch height.

Flight Manual and Testing. Such a hook may not be included in the
flight manual conditions for air tow and may not have been tested on air
tow during initial certification testing.

Back pressure during launch. During a winch launch there should be a
pull force, but not a large one.

At aft CG, little if any pull force may be needed on the winch and such
a condition can even be neutrally stable longitudinally (relax stick
pressure during the launch and the pitch angle hardly changes). Under
these conditions it is easy to climb too steeply and break the wire,
particularly with a heavy glider. Answer, look sideways at the angle
that a wing is cutting the horizon to judge pitch angle. At aft CG it
is easy to enter a spin, so careful handling is needed on cable break
recovery.

--
Ian Strachan
Lasham, UK

Chris Rollings wrote in message ...
Under JAR 22 (Glider Certification Rules), a glider
is required to have postive (or at least neutral) longitudinal
stability. Put simply, if you move the nose up (or
down) a bit and then leave it alone, it should tend
to move back towards where it started from, or at least
stay where it is, not continue to pitch further up
(or down).

It is quite possible (easy in most cases) to learn
to handle a glider that does not have this stability,
but it requires CONSTANT vigilance on the part of the
pilot. A failure in concentration of only one or two
seconds can result in a massive divergence of the flight
path with catastrophic consequences.

Both my ASW 19 and my ASW 28 exhibit positive pitch stability for
small disturbances when aero towed on the cg hook. Both gliders will
fly hands off on aerotow for several seconds and will return to the
trimmed pitch attitude following small upsets.

You tests on kiting used very large pitch upsets and they were
determined to be unrecoverable. Was any testing done to determine the
largest recoverable pitch upset?

Now that most gliders in UK have both aerotow and CG hooks, is there
any intention to repeat the test series to compare the characteristics
of the same glider with each hook?


Andy

Todd Pattist wrote:

Of course, despite those comments, we also experience too
many towing accidents. The CG hook can be implicated in more
than the kiting accidents, and I know several pilots who
have purchased or retrofitted the nose hook after a loss of
directional control during the initial roll on a CG hook
aerotow launch.

That is exactly what prompted me to have a nose hook installed; I mean,
as long as it was in the shop anyway, getting the damage from the loss
of directional control fixed...

--
-----
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Eric Greenwell
Washington State
USA