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CG hook on aero tows??



 
 
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  #1  
Old January 5th 04, 12:53 AM
Ted Wagner
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Default 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

  #2  
Old January 5th 04, 01:34 AM
BTIZ
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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

  #3  
Old January 5th 04, 01:47 AM
Marc Ramsey
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Default

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
  #4  
Old January 5th 04, 02:10 AM
Bill Daniels
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Default

"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

  #5  
Old January 5th 04, 05:55 AM
Andy Durbin
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Default

"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)
  #6  
Old January 5th 04, 07:21 AM
Mike Borgelt
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Default

On Sun, 4 Jan 2004 16:53:58 -0700, "Ted Wagner"
wrote:

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


How long was the rope?

Most of the towplane wake turbulence or whatever problems go away if
you use a 250 foot rope. Lots more time in the event of a pitch up and
less likely anyway due to lower energy in the wake turbulence.

I once saw three gliders damaged in one day at Waikerie(all unflyable
the next day) due to aero retrieves out of fields with short ropes and
nose hooks. Problem with a nose hook is that if things get out of hand
and you release they instantly get a lot worse.

Short ropes are deadly. It is the angle that counts. Longer rope =
smaller angle = recoverable situation. I find this so bleeding obvious
after observation, experience and thinking about it that if I was an
insurance company I'd refuse all claims for ground loops or towplane
upsets that used a shorter than 250 foot rope.

Anyway I gave up aerotowing and bought a TOP.

Mike Borgelt
  #7  
Old January 5th 04, 07:46 AM
BTIZ
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Default

we use a 200ft rope as standard.. we had 230ft ropes.. great for training..

160ft ropes really get your attention..

BT

"Mike Borgelt" wrote in message
...
On Sun, 4 Jan 2004 16:53:58 -0700, "Ted Wagner"
wrote:

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


How long was the rope?

Most of the towplane wake turbulence or whatever problems go away if
you use a 250 foot rope. Lots more time in the event of a pitch up and
less likely anyway due to lower energy in the wake turbulence.

I once saw three gliders damaged in one day at Waikerie(all unflyable
the next day) due to aero retrieves out of fields with short ropes and
nose hooks. Problem with a nose hook is that if things get out of hand
and you release they instantly get a lot worse.

Short ropes are deadly. It is the angle that counts. Longer rope =
smaller angle = recoverable situation. I find this so bleeding obvious
after observation, experience and thinking about it that if I was an
insurance company I'd refuse all claims for ground loops or towplane
upsets that used a shorter than 250 foot rope.

Anyway I gave up aerotowing and bought a TOP.

Mike Borgelt



  #8  
Old January 5th 04, 12:04 PM
Peter Seddon
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"BTIZ" wrote in message
news:HK7Kb.46875$m83.26542@fed1read01...
we use a 200ft rope as standard.. we had 230ft ropes.. great for

training..

160ft ropes really get your attention..

BT


The only bad take off I had in my Pilatus was at HusBos, it was downwind and
slightly cross, plus I was towed by a not very powerful Chipmonk. All other
takeoffs with our supercub are fine though these are all into wind as we
have three runways to play with. Its a great aircraft with few vices, and
can outclimb some newer glass ships.

Peter S

DLA
lakesgc.co.uk


  #9  
Old January 5th 04, 01:15 PM
Ian Strachan
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Default

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


  #10  
Old January 5th 04, 01:52 PM
Wojciech Scigala
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Default

05-01-2004 06:46, BTIZ:

we use a 200ft rope as standard.. we had 230ft ropes.. great for training..
160ft ropes really get your attention..

In Poland 200ft ropes are used for training, but pilots prefer shorter,
130ft ropes. For tows in very turbulent air (like tows for wave flying)
the ropes are even 60ft long.

Longer ropes gives more time for reaction to tug's turns, but shorter
ones are less springy, which makes easier to maintain steady speed
during tow. Especially if the tug is not so powerful.

--
Wojtus'.net __|__
FidoNet: 2:484/47 `--------o--------'

 




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