CG hook on aero tows??

A few seconds into take-off roll today in a Pilatus B-4, while applying left stick to correct for a dipping right wing, the right wing suddenly dipped all the way into the ground. The glider lurched to the right, and a second or two later popped up into the air, a good 20 feet up and 30 or more feet out to the side. By that time I had full left rudder in addition to full left aileron, so the glider recovered rather quickly, and I was able to bring it to normal take-off position right about the time the tow plane started to climb. I was amazed he had maintained his heading directly down the runway. The winds were light and variable. It was my ninth flight on the B-4.

After landing, the tow pilot apologized, saying it was his fault -- something about the wake turbulence. But I'm still puzzled about what, if anything, he did wrong; it looked like a completely normally take-off roll to me.

I had thought that maybe a sudden tail wind had reversed the effective correction of my aileron deflection during take-off, causing the right wing to dip harder instead of leveling off. Does this make sense to anyone with more experience on an aircraft like the B-4?

Also, I'm curious to know how much the CG hook location on the B-4 contributed to the squirrelly sequence of events after the right wingtip hit the ground. How many 15+ meter gliders have CG-only hooks? Are such exciting events more commonplace with CG hooks?

Other than the wobbly tows, I'm loving the B-4, it's the first 15-meter single-seater ship I've flown, and the first with retractable gear...

~tw

CG vs Nose hooks.. the Nose hook will help pull the glider to center "some".. not much early in the run.. or resist a tendency to pull towards a dropped wing..

A dropped wing will create more drag on grass or gravel than on pavement.. a dropped "draggy" wing will cause more deviation from center with a CG hook. Large moment arm with no counter resistance. Consider a "crack the whip" effect like when water skiing.

As for the "tow pilots fault".. SOMETIMES.. a quick "Burst" application of power will create a spiraling propwash effect that as a tendency to drop a wing.. as opposed to a smooth increase in power.. where wing runner runs farther.. and slower for your ailerons to become effective.

Does not take much "tail wind" effect to decrease the effectiveness of controls.. a new owner of a Speed Astir learned that even 3knts was enough to make his rudder ineffective in the early stages of the take off.

A "loss of control" on takeoff resulting from a dropped wing and CG hook was evident in the launching accident at the Nationals a couple of summers ago at Tonopah NV. Wing heavy with water was dropped as power applied, down wing pulled the glider well off the runway where the wing then struck an airport maint worker.

Some gliders only have the CG hook, some only the nose.. and some both.. we mostly use the nose hook for the Grob 103, easier for the ground crew to get to. But we require those checking out in the LS-4 to have at least 3 rides with the Grob 103 (w/CFIG) using the CG hook.

BT
"Ted Wagner" wrote in message newsI1Kb.17587$7D3.9225@fed1read02...
A few seconds into take-off roll today in a Pilatus B-4, while applying left stick to correct for a dipping right wing, the right wing suddenly dipped all the way into the ground. The glider lurched to the right, and a second or two later popped up into the air, a good 20 feet up and 30 or more feet out to the side. By that time I had full left rudder in addition to full left aileron, so the glider recovered rather quickly, and I was able to bring it to normal take-off position right about the time the tow plane started to climb. I was amazed he had maintained his heading directly down the runway. The winds were light and variable. It was my ninth flight on the B-4.

After landing, the tow pilot apologized, saying it was his fault -- something about the wake turbulence. But I'm still puzzled about what, if anything, he did wrong; it looked like a completely normally take-off roll to me.

I had thought that maybe a sudden tail wind had reversed the effective correction of my aileron deflection during take-off, causing the right wing to dip harder instead of leveling off. Does this make sense to anyone with more experience on an aircraft like the B-4?

Also, I'm curious to know how much the CG hook location on the B-4 contributed to the squirrelly sequence of events after the right wingtip hit the ground. How many 15+ meter gliders have CG-only hooks? Are such exciting events more commonplace with CG hooks?

Other than the wobbly tows, I'm loving the B-4, it's the first 15-meter single-seater ship I've flown, and the first with retractable gear...

~tw

Ted Wagner wrote:
I had thought that maybe a sudden tail wind had reversed the effective
correction of my aileron deflection during take-off, causing the right
wing to dip harder instead of leveling off. Does this make sense to
anyone with more experience on an aircraft like the B-4?

You had probably just barely reached flying speed. When you deflect an
aileron, it increases the effective angle of attack of that wing. The
tip probably stalled, and since the other wing was still flying, the tip
you were trying to pick up, instead dropped to the ground. The lesson
you should learn from this is that until you are at a reasonable speed
(i.e., able to pick up the tail and roll on the mainwheel), use opposite
rudder to pick up a dropping wing tip, not aileron...

Marc

"Ted Wagner" wrote in message
newsI1Kb.17587$7D3.9225@fed1read02...
A few seconds into take-off roll today in a Pilatus B-4, while applying left
stick to correct for a dipping right wing, the right wing suddenly dipped
all the way into the ground. The glider lurched to the right, and a second
or two later popped up into the air, a good 20 feet up and 30 or more feet
out to the side. By that time I had full left rudder in addition to full
left aileron, so the glider recovered rather quickly, and I was able to
bring it to normal take-off position right about the time the tow plane
started to climb. I was amazed he had maintained his heading directly down
the runway. The winds were light and variable. It was my ninth flight on
the B-4.

After landing, the tow pilot apologized, saying it was his fault --
something about the wake turbulence. But I'm still puzzled about what, if
anything, he did wrong; it looked like a completely normally take-off roll
to me.

I had thought that maybe a sudden tail wind had reversed the effective
correction of my aileron deflection during take-off, causing the right wing
to dip harder instead of leveling off. Does this make sense to anyone with
more experience on an aircraft like the B-4?

Also, I'm curious to know how much the CG hook location on the B-4
contributed to the squirrelly sequence of events after the right wingtip hit
the ground. How many 15+ meter gliders have CG-only hooks? Are such exciting
events more commonplace with CG hooks?

Other than the wobbly tows, I'm loving the B-4, it's the first 15-meter
single-seater ship I've flown, and the first with retractable gear...

~tw

It could have been a wake encounter. If there was a slight right crosswind,
the majority of the tug's prop blast would have drifted to the left and hit
the B-4's left wing, causing it to rise. I usually expect to encounter the
tug's wake after I have rolled about 2/3rds of the rope length. Sometimes
tuggies will advance the throttle more slowly in these conditions so as to
minimize the effect. That might be what your tug pilot was talking about.
I'm always ready to stuff in some fast downwind aileron at the wake
encounter.

As for the CG hook, well, it didn't help your situation. CG hooks aren't
much of a problem for airtow UNTIL you are way out of position and then
things can go really bad, really fast. I always remind myself before each
takeoff roll that this is a CG hook and to release if things start to go
bad. I won't accept a downwind takeoff with a CG hook.

I have done many training flights with pilots planning to fly a single
seater with a CG hook. The unfortunate result of many such flights is that
the trainee comes away thinking that airtow with a CG hook is no big thing.
It isn't a big thing -- until things get out of hand and most training
flights don't dare go there.

There's a BGA write-up on CG hooks and pitch-up incidents that should be
required reading for anyone contemplating airtow with a CG hook. Maybe one
of our British friends can provide a link to it.

Bill Daniels

There is an article in the archives of Gliding & Motorgliding International
on Aerotow "Upset" Accidents by Chris Rollings which may be found at:
http://www.glidingmagazine.com/ListF...Dtl.asp?id=327 .
All tug pilots, and glider pilots who launch by aerotow, should read this
article.

For the U.K. the B.G.A. give advice to be found in "Laws and Rules for
Glider Pilots" 14th edition June 2003 (cannot be read on-line):

Under "Recommended Practices":

RP12. The minimum length of aerowtow rope recommended is 150ft. However,
under special circumstances a short rope may be used. 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.

RP13. After releasing the cable, the glider should turn away so that the
tug aircraft pilot can see clearly that the glider is free.

Under "Operational Regulations":

4.16 The sum of tows made by the tug pilot and the glider pilot, in their
respective capacities, shall not be less than six.

My own opinion is that if a forward aerotow hook is fitted it should always
be used for aerotowing. If the glider does not have an aerotow hook, but
can be fitted with one as a modification then this should be done if it is
to be launched by aerotow.

It is quite normal for tug pilots to refuse to launch a glider if the rope
is on the aft hook when an aerotow hook is available.

I cannot think of any circumstance when the use of the forward hook rather
than the aft one for aerotow launching could cause a problem.

The longer the rope the easier the flying is for the glider pilot (except
perhaps in violent rotor?). The 150 ft rope is a compromise between safety
and operational convenience which has been found to be satisfactory in
practice in the U.K.

The above BGA recommendations and my opinions are based on the assumption
that the glider pilot has been properly trained and checked for currency
etc. The requirements etc. are to be found in the BGA Instructors' Manual
(which is not available to be read on-line).

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


"Bill Daniels" wrote in message
hlink.net...

snip

There's a BGA write-up on CG hooks and pitch-up incidents that should be
required reading for anyone contemplating airtow with a CG hook. Maybe
one of our British friends can provide a link to it.

Bill Daniels

"W.J. (Bill) Dean (U.K.)." wrote in
message ...
| There is an article in the archives of Gliding &
Motorgliding International
| on Aerotow "Upset" Accidents by Chris Rollings which may
be found at:
|
http://www.glidingmagazine.com/ListF...Dtl.asp?id=327 .
| All tug pilots, and glider pilots who launch by aerotow,
should read this
| article.
|
| For the U.K. the B.G.A. give advice to be found in "Laws
and Rules for
| Glider Pilots" 14th edition June 2003 (cannot be read
on-line):
|
| Under "Recommended Practices":
|
| RP12. The minimum length of aerowtow rope recommended is
150ft. However,
| under special circumstances a short rope may be used.
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.
|
| RP13. After releasing the cable, the glider should turn
away so that the
| tug aircraft pilot can see clearly that the glider is
free.
|
| Under "Operational Regulations":
|
| 4.16 The sum of tows made by the tug pilot and the
glider pilot, in their
| respective capacities, shall not be less than six.
|
| My own opinion is that if a forward aerotow hook is fitted
it should always
| be used for aerotowing. If the glider does not have an
aerotow hook, but
| can be fitted with one as a modification then this should
be done if it is
| to be launched by aerotow.
|
| It is quite normal for tug pilots to refuse to launch a
glider if the rope
| is on the aft hook when an aerotow hook is available.
|
| I cannot think of any circumstance when the use of the
forward hook rather
| than the aft one for aerotow launching could cause a
problem.
|
| The longer the rope the easier the flying is for the
glider pilot (except
| perhaps in violent rotor?). The 150 ft rope is a
compromise between safety
| and operational convenience which has been found to be
satisfactory in
| practice in the U.K.
|
| The above BGA recommendations and my opinions are based on
the assumption
| that the glider pilot has been properly trained and
checked for currency
| etc. The requirements etc. are to be found in the BGA
Instructors' Manual
| (which is not available to be read on-line).
|
| W.J. (Bill) Dean (U.K.).
| Remove "ic" to reply.

In Australia, all new gliders and any gliders which change
ownership must be fitted with a nose hook if aero tow is to
be used. C of A not valid otherwise.
John G.

"Ted Wagner" wrote in message news:pI1Kb.17587$7D3.9225@fed1read02...
A few seconds into take-off roll today in a Pilatus B-4, while applying
left stick to correct for a dipping right wing, the right wing suddenly
dipped all the way into the ground. The glider lurched to the right, and
a second or two later popped up into the air, a good 20 feet up and 30
or more feet out to the side.

How many 15+ meter gliders have CG-only hooks? Are such
exciting events more commonplace with CG hooks?

Other than the wobbly tows, I'm loving the B-4, it's the first 15-meter
single-seater ship I've flown, and the first with retractable gear...

~tw

--

My 2 cents worth is that you should have used the 2 seconds to pull
the release before you left the ground. You may have been hit by a
thermal.

A cg hook will give less directional stability during the early part
of the takeoff roll, particulary in a cross wind, but should have no
influence on wing drop tendency.

I have flown the last 15 or so years with aerotow on a cg hook. My new
ASW-28 has forward and CG hooks but I have never used the forward
hook.

Andy (GY)

In article , Andy
Durbin writes

snip

I have flown the last 15 or so years with aerotow on a cg hook. My new
ASW-28 has forward and CG hooks but I have never used the forward
hook.

What you have been doing in your ASW-28 would not be allowed at Lasham
and many other clubs (or if I were towing you!). If you have a forward
hook (often called the air tow hook), at most gliding organisations with
which I have been associated, you must use it for air tows except for
well-controlled exercises to show the difference. A true CG hook
position is for winch launching.

Normally, if both hooks are fitted the rear one will be "really rear"
because the manufacturer will assume that it will only be used for winch
or auto-tow. What does it say in your flight manual?

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.

The reason not to use a CG hook for air tows if a front hook is
available is not so much directional stability while on the ground, but
the potentially much more dangerous "tug upset" which can, and has,
killed tug pilots in the past.

I think that the tug pitch-upset situation has been extensively covered
before on this newsgroup. If the glider becomes high enough behind the
tug, the tow pilot pulls back on the stick to counter the nose-down
pitch and can run out of back-stick. The tug's tailplane (horizontal
stabilizer) can then stall, leading to a sharp and uncontrollable steep
nose-down pitch which, if near the ground (say 600 ft or less) is often
fatal for the tug pilot.

We have had such fatals in the UK at both Lasham, Dunstable and
elsewhere, hence the universal use of nose hooks for air towing where
such a hook is fitted to the glider.

There was even a debate within the BGA after the last UK fatal tug
upset, on whether gliders with only a CG hook should be allowed to be
air towed at all. The upshot was the present situation combined with
careful briefing and air tow practice concentrating on sitting close on
top of the tug slipstream and never getting high. Tug pilots watch the
rear-view mirror very carefully at and after takeoff and I am quite
willing to dump anyone who gets really high, particularly close to the
ground.

Finally, on rope length I agree with Mike Borgelt. The longer the rope
the easier an air tow is to fly in the glider. Last year I had a tow in
Poland in a Puchatz at their Zar mountain soaring centre on a VERY short
rope, and flying the tow was "very active". The field at Zar is a
respectable length so I do not know why they insist on using such short
ropes. The only reason for a short rope that I can think of is to tow
out of a VERY short field, and in my view even that is questionable, if
the field is THAT short it may not be safe to tow out of anyway.
Finally, Lasham make up air tow ropes to be 50m long (164 ft). From
memory, the BGA minimum tow rope length recommendation is 150 ft.

Andy, I really suggest that you start using your air tow (front) hook
when you take an air tow !

--
Ian Strachan
Lasham Tow Pilot

If I am well informed in Germany CG hooks are not allowed for airtow
anymore.
The exception is that if your glider does not have a nose hook, you may use
the CG hook provided that you can show that you made at least six airtows in
the last three month prior to this occasion (or wordings like this).

Karel, NL



"Ian Strachan" schreef in bericht
...
In article , Andy
Durbin writes

snip

I have flown the last 15 or so years with aerotow on a cg hook. My new
ASW-28 has forward and CG hooks but I have never used the forward
hook.

What you have been doing in your ASW-28 would not be allowed at Lasham
and many other clubs (or if I were towing you!). If you have a forward
hook (often called the air tow hook), at most gliding organisations with
which I have been associated, you must use it for air tows except for
well-controlled exercises to show the difference. A true CG hook
position is for winch launching.

Normally, if both hooks are fitted the rear one will be "really rear"
because the manufacturer will assume that it will only be used for winch
or auto-tow. What does it say in your flight manual?

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.

The reason not to use a CG hook for air tows if a front hook is
available is not so much directional stability while on the ground, but
the potentially much more dangerous "tug upset" which can, and has,
killed tug pilots in the past.

I think that the tug pitch-upset situation has been extensively covered
before on this newsgroup. If the glider becomes high enough behind the
tug, the tow pilot pulls back on the stick to counter the nose-down
pitch and can run out of back-stick. The tug's tailplane (horizontal
stabilizer) can then stall, leading to a sharp and uncontrollable steep
nose-down pitch which, if near the ground (say 600 ft or less) is often
fatal for the tug pilot.

We have had such fatals in the UK at both Lasham, Dunstable and
elsewhere, hence the universal use of nose hooks for air towing where
such a hook is fitted to the glider.

There was even a debate within the BGA after the last UK fatal tug
upset, on whether gliders with only a CG hook should be allowed to be
air towed at all. The upshot was the present situation combined with
careful briefing and air tow practice concentrating on sitting close on
top of the tug slipstream and never getting high. Tug pilots watch the
rear-view mirror very carefully at and after takeoff and I am quite
willing to dump anyone who gets really high, particularly close to the
ground.

Finally, on rope length I agree with Mike Borgelt. The longer the rope
the easier an air tow is to fly in the glider. Last year I had a tow in
Poland in a Puchatz at their Zar mountain soaring centre on a VERY short
rope, and flying the tow was "very active". The field at Zar is a
respectable length so I do not know why they insist on using such short
ropes. The only reason for a short rope that I can think of is to tow
out of a VERY short field, and in my view even that is questionable, if
the field is THAT short it may not be safe to tow out of anyway.
Finally, Lasham make up air tow ropes to be 50m long (164 ft). From
memory, the BGA minimum tow rope length recommendation is 150 ft.

Andy, I really suggest that you start using your air tow (front) hook
when you take an air tow !

--
Ian Strachan
Lasham Tow Pilot

Ian Strachan wrote:


Andy, I really suggest that you start using your air tow (front) hook
when you take an air tow !

I presume you can have an upset incident even with a nosehook. Are
there any statistics that show the safety advantage of a nose hook
compared to a CG hook?

Greg Arnold
330 aerotows with CG hooks, and never any problems except when taking
off without a wing runner