CG hook on aero tows??

In article , Andy
Durbin writes
Ian Strachan wrote in message
...

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 a previous posting I stated that the CG hook on my ASW 28, and the
only hook on my ASW 19, are in the same place. They are both just
forward of the main gear and inside the gear doors. I think they
would both be considered to be true CG hooks even though they are
forward of the CG.

When you say that "the hook is forward of CG" you seem to imply a static
measurement.

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.

--
Ian Strachan
Lasham, UK

On Tue, 6 Jan 2004 18:39:17 -0000, "W.J. \(Bill\) Dean \(U.K.\)."
wrote:

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?

So that is 4 in 40 years.

I think we've managed to kill that many towplane pilots in Aus in the
last 15 in mid airs. At least one, maybe more would have had a good
chance of survival if he had had a parachute. Something that still
isn't required here.

The common link with the upsets mentioned seems to be high wing wooden
gliders of low wing loading with deep fuselages. These may be prone to
pitch up.

How long were the ropes in these situations?

Were there other circumstances that contributed?

Could they have been compensated for?

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.

You are suggesting that on a winch launch with much higher loads in
the cable that these gliders are not controllable in pitch?

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 once owned an ASW20B. The GFA required the nose hook to be fitted.
The Scheicher factory job on this was pitiful. Nobody who bought
gliders from this batch of 6 put up with it. The releases were taken
out and glassed over. When finishing the area it became apparent that
the skin had been distorted by the additional release bulkheads.
I don't ever recall the 20B having the slightest tendency to pitch up
on aerotow on the belly release.

I have no aversion to properly engineered nose hooks like in
Glasflugel and Schempp gliders but poorly designed retrofits are a bad
idea particularly when no testing has been done on that particular
type to see if indeed the "solution" is effective or even necessary.

The BGA considers 150 foot ropes acceptable. I consider these
dangerously short, 200 feet is more like it with around 240 to 260
being much better.

Now consider this::

The world's politicians and bureaucrats are forever looking for ways
to meddle in our lives to keep themselves in jobs. If we place
requirements on our own operations (Like compulsory nose releases)that
are not firmly founded in proper testing and rational analysis we
weaken our case in resisting the idiot requirements that come in a
never ending stream from these people.

I've yet to meet anyone who has flown on a 250 foot rope who hasn't
admitted it was easier than on shorter ropes. When I aerotow I want to
go soaring for maybe several hours and maybe the enviroment on the
ground was stressful due to heat, humidity etc. I really don't need a
5 minute adrenaline thrill to begin a cross country. I would like
tows to be a non event. Longer ropes and tow pilots who don't try to
thermal or do other sudden manouevers all aid in this.

The scariest tow I ever had was in my Salto (with nose release) behind
a tow pilot who was not paying attention and who pulled back hard on
leaving the ground as we encountered a gust leaving me dangling low
from the end of the rope with decreasing airspeed. Followed by a hard
push just as I was climbing slowly back up into station(low tow)
leaving me very high followed by another hard pull which put me very
low again wherupon I released and did a 180 back to the strip.
Probably my shortest ever aerotow flight, closest to disaster and on
the 130 foot or so ropes that were fashionable at the time. I never
ever want to do this again. It was 30 years ago and I remember it
clearly.
A rope twice as long likely would have made this a non event.

The surprisingly easy tows were at Minden in an ASW20(belly release)
through the rotor behind a 182. Long rope, no problem at all.

Mike Borgelt

Earlier, Mark Zivley wrote:

If someone can afford the cost of
a new glider, it isn't going to break
them to pay for BOTH nose and CG hooks.
I don't see why SH (or any other
manufacturer) would waste the time with
"options" on this subject...

The issue here isn't getting the buyer to pay for both hooks. It's
getting them to pay _more_ for them. That's where the profit margin
is.

A year or so ago, I had the experience of observing a friend select
and purchase a brand-new European racer. Just about everything that
wasn't absolutely required was optional. Even the canopy sliding
window was "optional."

With that experience in mind, I'd say that the factories play the
"option" game for the same reason that car dealers do it: It's a
relatively easy way to make the basic price tag look attractive, while
increasing the profit margin on the typical sale. It's not at all a
time-waster, except perhaps for the purchaser.

For all the relatively high prices the factories charge for new
sailplanes, they are still operating on relatively slender profit
margins. Even high-production types are pretty much hand-built by
skilled workers using some pretty expensive materials. It's hard to
fault them for getting all the market will bear, any way they
reasonably can.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

"Mike Borgelt" wrote in message

Snip------
I don't ever recall the 20B having the slightest tendency to pitch up
on aerotow on the belly release.
Snip------

Mike Borgelt

Mike, I have flown a number of different gliders on air tow using a CG hook.
None of them had a tendency to pitch-up either. My Nimbus 2C tows just fine
with a CG hook. Airtow with a CG hook isn't a problem -- as long as the tow
is flown normally.

It is after the glider gets seriously out of position that the problems
arise. With a CG hook, it is easier to get out of position through pilot
inattention, and once there, the situation can very quickly become
unrecoverable. It is difficult to believe how fast things can go from
seeming normal to horribly wrong unless you have been there and done that.
It is so dangerous that no instructor would deliberately subject a tow
pilot, a student and himself to it just for training.

I encountered this once more than 40 years ago. I was a young student
pilot flying a glider known for it's challenging flight characteristics. At
the time, no weaklinks were required in the 200 foot, 9/16" nylon rope.
Note that I don't claim that this would not have happened anyway with a nose
hook, but it wouldn't have happened as easily.

I was inattentive, lulled into complacency by the smooth air. Instead of
watching the tug, I was watching the scenery. Sudden G forces woke me up as
the glider soared above the tug and to the right. Both the gliders and the
tug's releases jammed under the stress. The tug dove to the left and
pulled me it into the dive after it.

It was only because the aerodynamically clean glider could outdive the tug
that the rope went slack and both releases functioned simultaneously. We
both landed safely, but I bought beer for that tug pilot for several years
afterward. Had this occurred under 1000 feet, we both would have died. I
never looked at air tow the same way again.

The concern about airtow with CG hooks is for a condition that lies well
outside the experience of 99% of glider pilots. If you airtow with a CG
hook, keep in mind that a dragon lurks outside the normal airtow box. Don't
go there.

Bill Daniels

On Wed, 7 Jan 2004 19:06:40 -0700, "Bill Daniels"
wrote:


The concern about airtow with CG hooks is for a condition that lies well
outside the experience of 99% of glider pilots. If you airtow with a CG
hook, keep in mind that a dragon lurks outside the normal airtow box. Don't
go there.

Bill Daniels


I completely agree Bill.

I'm a long rope fan because the normal box is larger. In fact I think
it is not a linear function of rope length as the first 100 feet of
rope is probably counts for little due to pilot/sailplane
perception/reaction times.

There are other dragons which have happened in Oz. Get too low on low
tow, put a large bow in the rope and have it catch in the aileron/wing
gap. Good reason to have a weak link at *both* ends of the rope.

Having once done a cross country tow in low tow on a 130 foot rope and
then discovered that the towplane exhaust system was about to fall off
makes me not a low tow fan.

I worry about the "we've required nose tow releases so we've fixed
that problem" thinking. The problem didn't get fixed because nobody
had the gumption to require a retrofit on ALL gliders. Politically
impossible because when the chips were down it would be impossible to
justify. Instead just stick the owners of new gliders with the cost
because if they are buying a new glider they can afford it.

The LBA/BGA/GFA/insert your civil aviation bureaucracy name here
bureaucracy get to feel good because they have "improved" safety and
can boast about this, most of the glider pilots don't care one way or
the other as they are unaffected and tow pilots are at just as much
risk as before as the fleet replacement only occurs slowly. Great!

Requiring longer ropes would have been cheaper and would give
immediate benefits but here we are still thinking 150 feet is
adequate. Wonderful.

Meanwhile we've had one mid air on tow in Oz. One side benefit of 250
foot ropes is that you do have time to look around while on tow
instead of maintaining station with all your attention.

Anybody who hasn't towed on a 250 foot rope I suggest you try it. It
took one tow in 1982 for me to be a convert.

Meanwhile realise as the tow pilot opens the throttle that you are
potentially less than a minute from proving that youve thought about
the low altitude tow emergency enough to carry it out successfully.
It could be a rope break, engine failure or getting out of station or
any one or more of quite a number of other things. Tom Knauff had a
good article about this that I saw in Gliding Kiwi.

Mike Borgelt

The Australian Poster Dave refers to was actually line
drawings of the photo's taken of the tests I described.

Chris Rollings

At 10:30 07 January 2004, Dave Martin wrote:
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

The Capstan and Olypia 2 really have 'compromise' hooks,
halfway between nose hook and C of G hook. Not quite
so good for winch launching but not as wildly unstable
on aerotow as a true C of G hook.

Not sure about the accident statisics for those days,
my close involvement only began when I started work
at Booker in 1970 - certainly there were aerotow accidents
back then.

Chris Rollings

At 10:48 07 January 2004, Silent Flyer wrote:

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

Todd is right in every respect, at least one of the
aerotow upset fatals involved a largly winch launch
experienced pilot and the cicumstances he surmised.

Chris Rollings

At 15:06 07 January 2004, Todd Pattist wrote:
Eric Greenwell wrote:

The US might have less trouble with CG hooks than a
country where aero
tow isn't as common.

There are a couple of things that might make the U.S.
experience a little different in view of our training
and
operating procedures and the different experience of
our
pilot base. Many/most U.S. pilots are unfamiliar with
winch
launching and are extremely uncomfortable with any
kind of
nose high attitude on launch. I have occasionally
wondered
if some 'kiting on tow' accidents might be related
to the
pilots control response in a situation that is dangerous
for
an aerotow, but not for a winch launch. Another potential
difference is the prevalence of U.S. training in the
venerable 2-33, which typically produces a very high
nose up
attitude as the roll commences and requires a strong
forward
stick to compensate.

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.
Todd Pattist - 'WH' Ventus C
(Remove DONTSPAMME from address to email reply.)

Yes the pull can be enough to affect stability, that
was what the test I descibed demonstrated.

Chris Rollings

At 18:36 07 January 2004, Greg Arnold wrote:
Marc Ramsey wrote:



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?


Is the pull on a CG hook during aerotow ever great
enough to have much
effect on the longitudinal stability of the glider?
I have never
noticed such an effect, so I wonder if pilots who fly
from a winch (very
quick acceleration and doubtless a significant effect
on longitudinal
stability) are unfairly extrapolating their experience
there to the
aerotow situation.

Doubtless a nose hook is better for aerotow, but I
wonder if the alleged
advantages aren't being oversold by some posters to
this thread.

The point is not 'does a Cof G hook cause a glider
to pitch up on tow'. The point is that if something
(an accidental pilot input, or a gust not corrected
for immediately because the pilot in momentarily distracted)
causes the glider to pitch up, 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? If the first of those three, how easy
is it to stop it pitching up? 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.


Don't know about most of the other types mentioned
in this thread. I've flown most of them, but even
I didn't include 'simulated tug upset whilst aerotowing
on C of G hook' in my normal type conversion exercises
- I think I would have found it hard to get a tow after
a while if I had.

Chris Rollings

At 00:00 08 January 2004, Mike Borgelt wrote:
On Tue, 6 Jan 2004 18:39:17 -0000, 'W.J. \(Bill\) Dean
\(U.K.\).'
wrote:

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?

So that is 4 in 40 years.

I think we've managed to kill that many towplane pilots
in Aus in the
last 15 in mid airs. At least one, maybe more would
have had a good
chance of survival if he had had a parachute. Something
that still
isn't required here.

The common link with the upsets mentioned seems to
be high wing wooden
gliders of low wing loading with deep fuselages. These
may be prone to
pitch up.

How long were the ropes in these situations?

Were there other circumstances that contributed?

Could they have been compensated for?

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.

You are suggesting that on a winch launch with much
higher loads in
the cable that these gliders are not controllable in
pitch?

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 once owned an ASW20B. The GFA required the nose hook
to be fitted.
The Scheicher factory job on this was pitiful. Nobody
who bought
gliders from this batch of 6 put up with it. The releases
were taken
out and glassed over. When finishing the area it became
apparent that
the skin had been distorted by the additional release
bulkheads.
I don't ever recall the 20B having the slightest tendency
to pitch up
on aerotow on the belly release.

I have no aversion to properly engineered nose hooks
like in
Glasflugel and Schempp gliders but poorly designed
retrofits are a bad
idea particularly when no testing has been done on
that particular
type to see if indeed the 'solution' is effective
or even necessary.

The BGA considers 150 foot ropes acceptable. I consider
these
dangerously short, 200 feet is more like it with around
240 to 260
being much better.

Now consider this::

The world's politicians and bureaucrats are forever
looking for ways
to meddle in our lives to keep themselves in jobs.
If we place
requirements on our own operations (Like compulsory
nose releases)that
are not firmly founded in proper testing and rational
analysis we
weaken our case in resisting the idiot requirements
that come in a
never ending stream from these people.

I've yet to meet anyone who has flown on a 250 foot
rope who hasn't
admitted it was easier than on shorter ropes. When
I aerotow I want to
go soaring for maybe several hours and maybe the enviroment
on the
ground was stressful due to heat, humidity etc. I really
don't need a
5 minute adrenaline thrill to begin a cross country.
I would like
tows to be a non event. Longer ropes and tow pilots
who don't try to
thermal or do other sudden manouevers all aid in this.

The scariest tow I ever had was in my Salto (with nose
release) behind
a tow pilot who was not paying attention and who pulled
back hard on
leaving the ground as we encountered a gust leaving
me dangling low
from the end of the rope with decreasing airspeed.
Followed by a hard
push just as I was climbing slowly back up into station(low
tow)
leaving me very high followed by another hard pull
which put me very
low again wherupon I released and did a 180 back to
the strip.
Probably my shortest ever aerotow flight, closest to
disaster and on
the 130 foot or so ropes that were fashionable at the
time. I never
ever want to do this again. It was 30 years ago and
I remember it
clearly.
A rope twice as long likely would have made this a
non event.

The surprisingly easy tows were at Minden in an ASW20(belly
release)
through the rotor behind a 182. Long rope, no problem
at all.

Mike Borgelt