CG hook on aero tows??

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.
And it's good for re-sale since you never know where a glider may go next.

Mark

K.P. Termaat wrote:
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

I've noticed that, on many gliders, both the CG and nose hooks can produce
wind noise. I tape over the hook not in use to make it quiet and keep dirt
out of it.

Bill Daniels

"Mark Zivley" wrote in message
m...
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.
And it's good for re-sale since you never know where a glider may go
next.

Mark

K.P. Termaat wrote:
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

I just read the referenced article, and while its conclusions are
disturbing -- primarily the release failure of the tow plane's
Schweizer hook -- the experiment itself was not well conducted.

First and foremost, identical circumstances were not created to test
the difference between nose hook and cg hook. The K-13 with nose hook
was taken "progressively higher..." while the same aircraft with cg
hook was "pitched up."

As noted in an earlier post, I think all of us are in agreement that a
nose hook is (qualitatively) a safer proposition, but if you're going
to raise an alarm, it should be valid and proportionate.

Chris Rollings has presented us with a compelling demonstration of
what can happen during aerotow. The conclusions based on outcomes for
the two release types, since the maneuvers were not identical, has
been exptrapolated and are weighted to some degree by the knowledge
that the nose hook is preferred. 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.

In the absence of valid statistical or empirical evidence, it's hard
to determine just how critical this problem is. I think most of us are
willing to spend dollars on our well-being, but we'd like to know that
we are, in fact, purchasing something of value. If the record shows
that we're simply buying better handling as opposed to a measurable
increase in safety, then we are looking at a much different
proposition.

Point of reference, I only have a nose hook in my Ventus 2. I am
perfectly content to aerotow gliders with a cg hook if there is no
other choice. And frankly, I'd rather aerotow on a cg hook that winch
launch, which I consider an unreasonable comprimise to safety. It's
all a matter of what you're used to. No tow plane? let's unwind the
winch. But the risk to reward equation is becoming less attractive.

[Apologies if this is a double-post - Google seemed to have lost the
first one. This version is shorter and more to the point anyway.]

Earlier, Ian Strachan wrote:

... If only one hook is fitted then it
will be somewhat forward of the pure
"C of G" position because its location
is a compromise for both air tow
and winch and it will be tested for
both before the initial C of A is
given for the type.

From the perspective of an amateur sailplane developer:

That might have been true some time ago. However, increased demand for
better performance have made such compromises less tenable in the last
generation or two of sailplane.

The way I understand it, there are only two good locations for a tow
hitch: At the stagnation point on the nose of the glider, and aft of
the point of maximum thickness of the fuselage.

With the tow hitch buried in the nose vent at the stagnation point,
there is no particular disruption to the airflow, and you can
reasonably expect to get laminar flow over most of the forward
fuselage. At least, until the air encounters a disruption such as a
canopy separation line or passes the point of maximum thickness and
encounters an adverse pressure gradient.

With the to hitch located aft of the point of maximum thickness, the
airfow will already have tripped over into turbulent flow, and the
extra drag of that flow encountering the tow hitch will be minimal.

However, with the hitch located in the "compromise" area as Ian
suggests, it will almost certainly disrupt the laminar flow there, and
trip it over into draggier turbulent flow. Furthermore, the area of
turbulence will spread laterally at about a 7-degree angle aft of the
disruption. So you end up with a triangular patch of turbulent flow on
the belly with an included angle of about 14 degrees. That means extra
drag and poorer performance.

My own next glider will have a nose hook in the air vent duct at the
stagnation point on the nose of the glider, and a mounting location
for an optional CG hook that will be covered by the landing gear
doors.

Thanks, and best regards to all

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

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.

"Chris OCallaghan" wrote in message
om...

Snip-------------
Point of reference, I only have a nose hook in my Ventus 2. I am
perfectly content to aerotow gliders with a cg hook if there is no
other choice. And frankly, I'd rather aerotow on a cg hook that winch
launch, which I consider an unreasonable comprimise to safety. It's
all a matter of what you're used to. No tow plane? let's unwind the
winch. But the risk to reward equation is becoming less attractive.

Hmmm. After this harrowing discussion of the hazards of airtow, you would
think a winch might seem safer by comparison.

Bill Daniels
(Scared many times on airtow, but never on a winch.)

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.


Following up on my own post -- during aerotow, acceleration is greatest
at the beginning of the takeoff run, where airspeed is low. By the
time that airspeed gets to the point where the glider can fly,
acceleration is minimal. So the pull on the tow line shouldn't have
much effect on longitudinal stability when the glider is near takeoff speed.

I am sure that a glider with a CG hook will be inclined to climb more
steeply once it has a high angle of attack -- this is due to the pivot
point being further aft on the glider. However, in the initial stages
of going to that high angle of attack, does it matter whether the glider
has a CG hook or a nose hook? It is that initial stage that causes
problems on aerotow. Once a glider achieves a high angle of attack, the
towplane is well past the point of no return.

I am not a sufficiently expert statistician to be certain, but I think
the UK data leads to two conclusions about tug upset fatal accidents:

1. There have been too few such fatalities - I think about 6-10 over 30
years - to draw conclusions with a high probablility of being certain of
the correlation - and I can't stipulate how "high" is high;

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.

There have been tugging accidents other than upsets, with nose hooks as
well as belly hooks, but these do not affect such inferences as one can
draw from 1 and 2 above.

By the way, I fly mostly a Ka6E with a belly hook. I am very careful
not to kill my friends who tug, being all too well aware of the danger.
One of the changes was to alter our preferred tow position, as has been
referred to by others, to only just above the prop wash - termed the
"low High-tow" position, IIRC. Before the changes, we normally kept the
glider at or slightly above the tug height once established on tow.

Chris N.

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.

My ASW 28 also has a forward belly hook. If I had a nose hook I would
never have used the cg hook on the ASW 28 for aerotow. Nose hooks,
like exposed CG hooks, are usually easy to hook up and easy to inspect
for proper closure. The same is NOT true for the forward belly hook
fitted on the ASW 28 because it is concealed by a very stiff slotted
plastic cover.

Andy (GY)

Chris,

Your wasting your breath in this thread - just listen
and learn from the wise ones.

John Galloway

At 19:30 07 January 2004, Chris Nicholas wrote:
I am not a sufficiently expert statistician to be certain,
but I think
the UK data leads to two conclusions about tug upset
fatal accidents:

1. There have been too few such fatalities - I think
about 6-10 over 30
years - to draw conclusions with a high probablility
of being certain of
the correlation - and I can't stipulate how 'high'
is high;

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.

There have been tugging accidents other than upsets,
with nose hooks as
well as belly hooks, but these do not affect such inferences
as one can
draw from 1 and 2 above.

By the way, I fly mostly a Ka6E with a belly hook.
I am very careful
not to kill my friends who tug, being all too well
aware of the danger.
One of the changes was to alter our preferred tow position,
as has been
referred to by others, to only just above the prop
wash - termed the
'low High-tow' position, IIRC. Before the changes,
we normally kept the
glider at or slightly above the tug height once established
on tow.

Chris N.