CG hook on aero tows??

CG hooks on tow do not create a problem for competent pilots. It is only
necessary to fly the towed glider, as in close formation flying, without
depending on the tow hook to do a lot of the work for you. Of course, very
short tow ropes can make any tow difficult. Both my own glider, a Phoebus
A-1, and the DG-101 I frequently fly in my club, have only CG hooks. With
reasonable tow-rope length I have never found CG hooks to present any
problems. But, do keep the trim full down on take-off.

Ed

C of G hooks do not create a problem on tow - for anyone
who does not find himself with a significant degree
of pitch up (sorry can't give a figure in degrees,
it will vary according to type) relative to the tow-plane's
flight path.

I agree that competent pilots (whatever that means)
are less likely to find themselves in that position.
However, given that it takes less than 0.5 seconds
for the necessary amount of pitch up to occur, and
that pitch up can be caused by either a gust, an inadvertant
elevator input by the glider pilot, or an unexpected
attitude change by the tow-plane, I don't think anyone
is 'competent' enough to guarantee that it can never
happen to them.

Changing the subject just slightly; the use of 'low'
high tow, refered to several times in this thread,
does not really help because:

1. The 'few feet lower' position adds less than half
a second to the time the 'upset' takes (given a 'normal'
lenght rope of just under 200 feet); usually not enough
to make any difference to the outcome.

2. The slight upward angle of the force on the rope
increases the instability of the situation and means
that a slightly smaller pitch angle is needed to set
the whole thing off.

3. The close proximity to the tow-plane's prop wash,
and occasional indvertant excursions into it, may well
provide the trigger mechanism that causes the unwanted
pitch movement.

I will post no more on this subject until and unless
someone actually comes up with some new flight test
reports.

However, I am prepared to offer my services as an expert
witness, to the estate of any tow-pilot who is killed
in a 'tug upset' accident whilst towing a glider on
a C og G hook.

Chris Rollings

At 03:18 09 January 2004, E. A. Grens wrote:
CG hooks on tow do not create a problem for competent
pilots. It is only
necessary to fly the towed glider, as in close formation
flying, without
depending on the tow hook to do a lot of the work for
you. Of course, very
short tow ropes can make any tow difficult. Both my
own glider, a Phoebus
A-1, and the DG-101 I frequently fly in my club, have
only CG hooks. With
reasonable tow-rope length I have never found CG hooks
to present any
problems. But, do keep the trim full down on take-off.

Ed

Chris Nicholas wrote in message ...

Chris you listed the following 6


"The operators' attention is drawn to the following factors which may
cumulatively contribute to a hazardous situation:

(a) Low experience of glider and/or tug pilot
(b) Gliders fitted with C of G hook only
(c) Glider's C of G towards the aft limit
(d) Turbulent air in the take-off area
(e) Rough ground in the take-off area
(f) Significant cross-wind component."

Then stated, almost as an aside,


We have almost
eliminated tug upset accidents in the UK since this and the "Low
High-tow" standardisation,

I suspect that condition 7 may be more significant in reducing tug
upsets than any of the 6 in the primary list.

As a US instructor I have flown with many pilots that received their
initial training from other instructors. I have often been surprised
at the tow position taken by such pilots. I usually urge them to keep
lowering the tow position until they feel the wake, then to move just
high enough that the wake is not a factor. That tow position may be
10 or 15 ft lower than that initially used.

A pilot flying a high high tow has less time to react to a potential
upset than one flying the UK recommended low high tow. The fact that
US pilots seem to be trained to use high high tow may explain why tug
upsets continue to happen even when a nose or forward hook is used.


Andy (GY)

"Andy Durbin" wrote in message
om...
Chris Nicholas wrote in message
...

Chris you listed the following 6


"The operators' attention is drawn to the following factors which may
cumulatively contribute to a hazardous situation:

(a) Low experience of glider and/or tug pilot
(b) Gliders fitted with C of G hook only
(c) Glider's C of G towards the aft limit
(d) Turbulent air in the take-off area
(e) Rough ground in the take-off area
(f) Significant cross-wind component."

Then stated, almost as an aside,


We have almost
eliminated tug upset accidents in the UK since this and the "Low
High-tow" standardisation,

I suspect that condition 7 may be more significant in reducing tug
upsets than any of the 6 in the primary list.

As a US instructor I have flown with many pilots that received their
initial training from other instructors. I have often been surprised
at the tow position taken by such pilots. I usually urge them to keep
lowering the tow position until they feel the wake, then to move just
high enough that the wake is not a factor. That tow position may be
10 or 15 ft lower than that initially used.

A pilot flying a high high tow has less time to react to a potential
upset than one flying the UK recommended low high tow. The fact that
US pilots seem to be trained to use high high tow may explain why tug
upsets continue to happen even when a nose or forward hook is used.


Andy (GY)

I've seen the same thing, Andy.

Bill Daniels

On 8 Jan 2004 11:37:23 -0800, (Chris
OCallaghan) wrote:

thanks for the link. I'll do my best to get it translated. We've some
willing German speakers at the club, but it's unlikely I'll see any of
them before March!

I am pretty sure that there is an English version somewhere out
there... unfortunately I haven't found it yet...
Bye
Andreas

Mind you, if it was a type which was often aerotowed on a belly hook,
and if the pilot knew what s/he was in for, and had suitable
experience, then it wouldn't worry me greatly.

The same holds true for aerotowing an L-13 by the tail tie down.

I suppose it may be possible to install a tow release in the tail
or tie a towrope on the tail tie down, and then aerotow an L-13
tail first. If someone had tried this in a wind tunnel first,
and had lightning quick reflexes, and adjusted to a suitable
CG, perhaps he could reliably fly it on aerotow tail first, facing
rearward, and upon release, do a horizontal hammerhead type
manuever and then fly normally.

If you saw someone do this a dozen times, you might conclude
and if the pilot knew what s/he was in for, and had suitable
experience, then it wouldn't worry me greatly.

With the appropriate training, conditions, and experience,
one can fly an L-13 tail first, or fly the Wright flyer. This
is trivially true. Of more interest is the relative ease
of towing forward vs. rearward (front vs. CG hook) and the
associated things to be cautious about.

I'm waiting for someone to post that aerotowing with a CG hook is
easier and requires less training and experience than towing
with a nose hook. As yet I haven't seen this claim...

As usual, there have been several outstanding posts of firsthand
CG tow experiences, and I've been most appreciative for these...

"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...

Andy Durbin wrote:

As a US instructor I have flown with many pilots that received their
initial training from other instructors. I have often been surprised
at the tow position taken by such pilots. I usually urge them to keep
lowering the tow position until they feel the wake, then to move just
high enough that the wake is not a factor. That tow position may be
10 or 15 ft lower than that initially used.

Where is the towplane, relative to the horizon?

A pilot flying a high high tow has less time to react to a potential
upset than one flying the UK recommended low high tow. The fact that
US pilots seem to be trained to use high high tow may explain why tug
upsets continue to happen even when a nose or forward hook is used.

10 or 15 feet doesn't sound like it would give much extra time, not like
the low tow position Australia uses.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

"E. A. Grens" wrote in message ...
CG hooks on tow do not create a problem for competent pilots.

That's true, by definition: "A competent pilot is one for whom CG
hooks on tow do not cause problems." The trouble is - as my club has
found out - is that many pilots don't know whether or not they are
competent in this regard. We do some very wild towing in primary
rotor: even with a nose hook the tow can be a testing experience!

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