I have problem. I correct the aileron the wrong way at takeoff

On Jan 19, 6:58*pm, bildan wrote:

You guys can't believe how nasty a ground loop can be when a wing tip
catches and the glider is being pulled with he CG hook. *A nose hook
will help keep you straight if a tip digs in. *A CG hook will just
accelerate the ground loop. *If it happens with enough speed (or power
in the case of a winch launch), you'll likely end up inverted - and
dead.

I'd guess from your reply that your glider has both CG and nose
hooks. Many pilots have flown hundreds of aerotows without incident
despite the fact that their gliders only had CG hooks.

I had a few wing drop incidents with aerotow using a CG hook but those
were all when using a wing runner. Most I immediately released, one or
two I recovered and completed the takeoff. As a general rule I'll
release as soon as the wing drops.

At the start of an aerotow takeoff the probability of a high energy
ground loop is very low since the ground speed is low and the
acceleration is fairly low. The risk of a high energy ground loop is
later in the takeoff roll and is there whether a wing runner is used
or not. It is a very different situation for a winch launch.

The yaw restoring moment of the tow rope is directly related to the
distance from the main wheel, or from the CG once airborne. A typical
CG hook is forward of both the main gear and the CG, so the moment of
the tow rope is in the same sense as for a nose or belly hook and,
although smaller, is still stabilizing rather than destabilizing.
Given that, can you please explain why you believe a CG hook will
accelerate a ground loop.


Andy

On Jan 20, 9:04*am, Andy wrote:
On Jan 19, 6:58*pm, bildan wrote:



You guys can't believe how nasty a ground loop can be when a wing tip
catches and the glider is being pulled with he CG hook. *A nose hook
will help keep you straight if a tip digs in. *A CG hook will just
accelerate the ground loop. *If it happens with enough speed (or power
in the case of a winch launch), you'll likely end up inverted - and
dead.

I'd guess from your reply that your glider has both CG and nose
hooks. *Many pilots have flown hundreds of aerotows without incident
despite the fact that their gliders only had CG hooks.

I had a few wing drop incidents with aerotow using a CG hook but those
were all when using a wing runner. Most I immediately released, one or
two I recovered and completed the takeoff. *As a general rule I'll
release as soon as the wing drops.

At the start of an aerotow takeoff the probability of a high energy
ground loop is very low since the ground speed is low and the
acceleration is fairly low. * The risk of a high energy ground loop is
later in the takeoff roll and is there whether a wing runner is used
or not. *It is a very different situation for a winch launch.

The yaw restoring moment of the tow rope is directly related to the
distance from the main wheel, or from the CG once airborne. *A typical
CG hook is forward of both the main gear and the CG, so the moment of
the tow rope is in the same sense as for a nose or belly hook and,
although smaller, *is still stabilizing rather than destabilizing.
Given that, can you please explain why you believe a CG hook will
accelerate a ground loop.

Andy

Andy you assume too much. I don't have a nose hook.

I wrote, "If it happens with enough speed (or power in the case of a
winch launch)". I think that makes the distinction between aero tow
and winch launch.

So, how would a CG hook accelerate a ground loop? If a wing tip
catches the ground loop pivot point is now the wing tip. The pull at
the CG hook will rapidly accelerate the other wing so it lightens up
the weight on the main wheel. Basically, it's a Frisbee launch.

Yes, it could happen with either nose or CG hooks but the CG hook will
produce a more violent ground loop. If it's violent enough, the
glider will roll inverted.

The wing tip doesn't have to actually catch and stop. If it is
retarded enough by ground friction, the pivot point shifts toward that
tip enough to amplify the ground loop.

On Jan 20, 8:42*am, bildan wrote:
On Jan 20, 9:04*am, Andy wrote:



On Jan 19, 6:58*pm, bildan wrote:

You guys can't believe how nasty a ground loop can be when a wing tip
catches and the glider is being pulled with he CG hook. *A nose hook
will help keep you straight if a tip digs in. *A CG hook will just
accelerate the ground loop. *If it happens with enough speed (or power
in the case of a winch launch), you'll likely end up inverted - and
dead.

I'd guess from your reply that your glider has both CG and nose
hooks. *Many pilots have flown hundreds of aerotows without incident
despite the fact that their gliders only had CG hooks.

I had a few wing drop incidents with aerotow using a CG hook but those
were all when using a wing runner. Most I immediately released, one or
two I recovered and completed the takeoff. *As a general rule I'll
release as soon as the wing drops.

At the start of an aerotow takeoff the probability of a high energy
ground loop is very low since the ground speed is low and the
acceleration is fairly low. * The risk of a high energy ground loop is
later in the takeoff roll and is there whether a wing runner is used
or not. *It is a very different situation for a winch launch.

The yaw restoring moment of the tow rope is directly related to the
distance from the main wheel, or from the CG once airborne. *A typical
CG hook is forward of both the main gear and the CG, so the moment of
the tow rope is in the same sense as for a nose or belly hook and,
although smaller, *is still stabilizing rather than destabilizing.
Given that, can you please explain why you believe a CG hook will
accelerate a ground loop.

Andy

Andy you assume too much. *I don't have a nose hook.

I wrote, "If it happens with enough speed (or power in the case of a
winch launch)". *I think that makes the distinction between aero tow
and winch launch.

So, how would a CG hook accelerate a ground loop? *If a wing tip
catches the ground loop pivot point is now the wing tip. *The pull at
the CG hook will rapidly accelerate the other wing so it lightens up
the weight on the main wheel. *Basically, it's a Frisbee launch.

Yes, it could happen with either nose or CG hooks but the CG hook will
produce a more violent ground loop. *If it's violent enough, the
glider will roll inverted.

The wing tip doesn't have to actually catch and stop. *If it is
retarded enough by ground friction, the pivot point shifts toward that
tip enough to amplify the ground loop.

Interesting point - I would think it would depend on the relative
stabilizing moment along the hook-to cg pivot (inertial) and the hook-
to wheel pivot versus the destabilizing moment from the wing tip to
wheel pivot and the wing tip to hook pivot. Unless your wing tip hits
a ton of friction (not so likely with the tip wheel Andy describes) or
a relatively immovable object I doubt the glider would totally pivot
around the tip. If the tip did really dig in a 25 foot moment arm is
going to matter a lot more than the inches of difference between a
belly hook and a cg hook for the first 15 degrees or so of rotation
that are going to decide your fate. I agree that there is a bigger
restoring moment arm the further forward the hook is, but it would be
a pretty narrow set of circumstances where the tow rope force helps
more than it hurts with the tip totally dug in.

THis line of thinking does raise a question in my mind on whether
tapping the wheel brake would help pull the nose straight in a wing
down situation - it slows your acceleration so it's a bit of a
tradeoff. I'm normally on the divebrakes until I have positive aileron
control - partly for improved aileron effectiveness (not sure this has
ever been proven but it doesn't seem to hurt) and partly to have them
unlocked in case I need to pull the plug and get stopped. From
experience I will say if the wing goes down (tip skids, not wheels)
and you are on a typical asphalt runway you will have only a 2-count
to get it back up before your are sure to end up in the weeds - be
ready and don't try to save it - once you get 15-degrees off runway
heading you just won't get it straightened out in time.

Excellent point on wing running technique - I always tell wing runners
to let the wing go up or down in response to the force they feel - a
foot or two so I can notice and correct, but not all the way to the
ground. They don't always get it. If you don't trust your wing runner
consider your options. One day last year I had a choice between three
wing runners - one in flip-flops, one with a bad hip and one who'd
never run a wing before. Who would you choose?

9B

I see nothing in your reply that convinces me that making a wing low
aerotow retrieve from a paved runway using a wing tip wheel and a CG
hook is an unacceptable risk.

Andy

Although slightly off-topic, the gyro effect of the wheel on bicycles
and motorbikes is not nearly as important as most people think. Check
out tests run with a contra-rotating wheel attached to the front wheel
of a bicycle:

http://www2.eng.cam.ac.uk/~hemh/gyrobike.htm

Mike

Bad hip; has better judgment than flip-flop artist. He is expecting a fall
and is prepared to let go.

At 17:46 20 January 2009, wrote:
On Jan 20, 8:42=A0am, bildan wrote:
On Jan 20, 9:04=A0am, Andy wrote:



On Jan 19, 6:58=A0pm, bildan wrote:

You guys can't believe how nasty a ground loop can be when a wing
tip
catches and the glider is being pulled with he CG hook. =A0A nose
hoo=
k
will help keep you straight if a tip digs in. =A0A CG hook will
just
accelerate the ground loop. =A0If it happens with enough speed (or
po=
wer
in the case of a winch launch), you'll likely end up inverted -
and
dead.

I'd guess from your reply that your glider has both CG and nose
hooks. =A0Many pilots have flown hundreds of aerotows without
incident
despite the fact that their gliders only had CG hooks.

I had a few wing drop incidents with aerotow using a CG hook but
those
were all when using a wing runner. Most I immediately released, one
or
two I recovered and completed the takeoff. =A0As a general rule
I'll
release as soon as the wing drops.

At the start of an aerotow takeoff the probability of a high energy
ground loop is very low since the ground speed is low and the
acceleration is fairly low. =A0 The risk of a high energy ground
loop
i=
s
later in the takeoff roll and is there whether a wing runner is used
or not. =A0It is a very different situation for a winch launch.

The yaw restoring moment of the tow rope is directly related to the
distance from the main wheel, or from the CG once airborne. =A0A
typica=
l
CG hook is forward of both the main gear and the CG, so the moment
of
the tow rope is in the same sense as for a nose or belly hook and,
although smaller, =A0is still stabilizing rather than destabilizing.
Given that, can you please explain why you believe a CG hook will
accelerate a ground loop.

Andy

Andy you assume too much. =A0I don't have a nose hook.

I wrote, "If it happens with enough speed (or power in the case of a
winch launch)". =A0I think that makes the distinction between aero
tow
and winch launch.

So, how would a CG hook accelerate a ground loop? =A0If a wing tip
catches the ground loop pivot point is now the wing tip. =A0The pull
at
the CG hook will rapidly accelerate the other wing so it lightens up
the weight on the main wheel. =A0Basically, it's a Frisbee launch.

Yes, it could happen with either nose or CG hooks but the CG hook will
produce a more violent ground loop. =A0If it's violent enough, the
glider will roll inverted.

The wing tip doesn't have to actually catch and stop. =A0If it is
retarded enough by ground friction, the pivot point shifts toward that
tip enough to amplify the ground loop.

Interesting point - I would think it would depend on the relative
stabilizing moment along the hook-to cg pivot (inertial) and the hook-
to wheel pivot versus the destabilizing moment from the wing tip to
wheel pivot and the wing tip to hook pivot. Unless your wing tip hits
a ton of friction (not so likely with the tip wheel Andy describes) or
a relatively immovable object I doubt the glider would totally pivot
around the tip. If the tip did really dig in a 25 foot moment arm is
going to matter a lot more than the inches of difference between a
belly hook and a cg hook for the first 15 degrees or so of rotation
that are going to decide your fate. I agree that there is a bigger
restoring moment arm the further forward the hook is, but it would be
a pretty narrow set of circumstances where the tow rope force helps
more than it hurts with the tip totally dug in.

THis line of thinking does raise a question in my mind on whether
tapping the wheel brake would help pull the nose straight in a wing
down situation - it slows your acceleration so it's a bit of a
tradeoff. I'm normally on the divebrakes until I have positive aileron
control - partly for improved aileron effectiveness (not sure this has
ever been proven but it doesn't seem to hurt) and partly to have them
unlocked in case I need to pull the plug and get stopped. From
experience I will say if the wing goes down (tip skids, not wheels)
and you are on a typical asphalt runway you will have only a 2-count
to get it back up before your are sure to end up in the weeds - be
ready and don't try to save it - once you get 15-degrees off runway
heading you just won't get it straightened out in time.

Excellent point on wing running technique - I always tell wing runners
to let the wing go up or down in response to the force they feel - a
foot or two so I can notice and correct, but not all the way to the
ground. They don't always get it. If you don't trust your wing runner
consider your options. One day last year I had a choice between three
wing runners - one in flip-flops, one with a bad hip and one who'd
never run a wing before. Who would you choose?

9B

On Jan 20, 10:46*am, wrote:
On Jan 20, 8:42*am, bildan wrote:

Excellent point on wing running technique - I always tell wing runners
to let the wing go up or down in response to the force they feel - a
foot or two so I can notice and correct, but not all the way to the
ground. They don't always get it. If you don't trust your wing runner
consider your options. *One day last year I had a choice between three
wing runners - one in flip-flops, one with a bad hip and one who'd
never run a wing before. Who would you choose?

9B

I'd take any of them but give special instructions.

1. Balance the glider carefully so it takes 5 or 6 seconds for the
wing to drop when released.
2. Don't run, just stand there and let the tip go as the glider starts
to move.

I will carefully center the ailerons so the wing runner can precisely
balance the glider and not move them again until the glider starts to
move and then only if a wing starts down. I'm often airborne before
any serious aileron inputs are needed.

This technique works extremely well and is easy to teach - please give
it a try. The current system doesn't properly divide the task between
pilot and runner and they often fight each other.

Bill Daniels

On Jan 20, 2:07*pm, bildan wrote:
On Jan 20, 10:46*am, wrote:

On Jan 20, 8:42*am, bildan wrote:
Excellent point on wing running technique - I always tell wing runners
to let the wing go up or down in response to the force they feel - a
foot or two so I can notice and correct, but not all the way to the
ground. They don't always get it. If you don't trust your wing runner
consider your options. *One day last year I had a choice between three
wing runners - one in flip-flops, one with a bad hip and one who'd
never run a wing before. Who would you choose?

9B

I'd take any of them but give special instructions.

1. *Balance the glider carefully so it takes 5 or 6 seconds for the
wing to drop when released.
2. Don't run, just stand there and let the tip go as the glider starts
to move.

I will carefully center the ailerons so the wing runner can precisely
balance the glider and not move them again until the glider starts to
move and then only if a wing starts down. *I'm often airborne before
any serious aileron inputs are needed.

This technique works extremely well and is easy to teach - please give
it a try. *The current system doesn't properly divide the task between
pilot and runner and they often fight each other.

Bill Daniels

I should have added some more context to my multiple-choice question:

- 10 kt crosswind with gusting
- 6,000 field elevation
- 90+ degrees F

That's not a circumstance where I recommend just letting go of the
tip. I do always direct wing runners to hold the tip by the trailing
edge so it's hard to push or pull the nose around.

Another decent piece of advice to to have the towplane run the engine
up before releasing the brakes - even if you get a little catapult
from the stretch in the tow rope you'll still get to Vmc more quickly.

9B

On Jan 20, 4:48*pm, wrote:
On Jan 20, 2:07*pm, bildan wrote:



On Jan 20, 10:46*am, wrote:

On Jan 20, 8:42*am, bildan wrote:
Excellent point on wing running technique - I always tell wing runners
to let the wing go up or down in response to the force they feel - a
foot or two so I can notice and correct, but not all the way to the
ground. They don't always get it. If you don't trust your wing runner
consider your options. *One day last year I had a choice between three
wing runners - one in flip-flops, one with a bad hip and one who'd
never run a wing before. Who would you choose?

9B

I'd take any of them but give special instructions.

1. *Balance the glider carefully so it takes 5 or 6 seconds for the
wing to drop when released.
2. Don't run, just stand there and let the tip go as the glider starts
to move.

I will carefully center the ailerons so the wing runner can precisely
balance the glider and not move them again until the glider starts to
move and then only if a wing starts down. *I'm often airborne before
any serious aileron inputs are needed.

This technique works extremely well and is easy to teach - please give
it a try. *The current system doesn't properly divide the task between
pilot and runner and they often fight each other.

Bill Daniels

I should have added some more context to my multiple-choice question:

- 10 kt crosswind with gusting
- 6,000 field elevation
- 90+ degrees F

That's not a circumstance where I recommend just letting go of the
tip. *I do always direct wing runners to hold the tip by the trailing
edge so it's hard to push or pull the nose around.

Another decent piece of advice to to have the towplane run the engine
up before releasing the brakes - even if you get a little catapult
from the stretch in the tow rope you'll still get to Vmc more quickly.

9B

That would take a little more skill from the wing runner but the basic
balancing technique still works better than the traditional way.
10,000' + density altitudes are routine for me as are gusty
crosswinds.

The only change I would make is to ask the wing runner to run a bit.
The glider can be balanced against a crosswind even if it's gusty -
just not as precisely which is why he needs to run a little.

It's frustrating for me as a wing runner to be trying to balance a
glider and the pilot won't let me do it. If they will just put the
ailerons in neutral long enough for me to find the balance point, the
takeoff will go a lot better.

Bill Daniels