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Tow Plane Upsets......



 
 
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  #11  
Old April 24th 17, 01:31 PM posted to rec.aviation.soaring
Charlie M. (UH & 002 owner/pilot)
external usenet poster
 
Posts: 1,383
Default Tow Plane Upsets......

Sounds great to me! In the US, high tow is predominate although low tow is taught.
Our club is one of 2(?) in the US that predominantly use low tow although we also teach high tow.
We have tested "going too low" and the towplane still has elevator available whereas going to high runs the towplane out of elevator.
If the glider pilot gets way out of position, the time difference is not much between the 2 tow types in my opinion.

Not trying to start a "conversation regarding which to use", just noting what we do. This can turn ugly fast, even worse than US contest rules discussions.......

PS, lost a friend during tow a couple decades ago while he was towing with a "known squirrel" on the glider end. The towplane was a L19 and went in from about 300' when the glider went too high in front of a couple dozen onlookers.
Not sure low tow would have helped.
  #12  
Old April 24th 17, 01:35 PM posted to rec.aviation.soaring
Chris Rollings[_2_]
external usenet poster
 
Posts: 133
Default Tow Plane Upsets......

A large proportion of the tow-plane upsets, including most of the fatals,
happen very shortly after take-off, before there is an opportunity to get
into low tow. Also, descending into the prop-wash can be a trigger to the
momentary loss of control that leads to the upset, if the glider is on a C
of G hook.

At 12:05 24 April 2017, wrote:
In Australia we do low tow only with the aim of reducing tug upsets. It
int=
uitively makes sense to me that kiting upsets are much more likely and
much=
worse than 'diving' upsets (do these even happen?), and low tow offers
muc=
h more time to react.
It's also much harder to lose sight of the tug, it's right there in your
fi=
eld of view.

On Monday, 24 April 2017 01:43:12 UTC+1, Walt Connelly wrote:
I have been towing for about two and a half years and have logged over
6,500 tows. Having recently experienced a couple of rather violent
glider kiting incidents, one at about 300 feet AGL I decided to
investigate the experiences of other tow pilots in these

circumstances.=
=20
I have spent several hours reading posts about gliders kiting and
upsetting the tow plane, many of the posts deal with creating an
automatic release that will recognize the actions of the glider and
release without input from the tow pilot. Nice idea, some really
creative approaches and the bottom line is anything can be done if you
have enough money and can get the FAA to buy into it and give
approval.
=20
Lots of opinions and ideas as to why these things happen. Bottom line
is that they do happen, they have resulted in loss of tow pilot lives
and the causes are well known.=20
=20
Of my two most recent experiences one was with a 67 year old licensed
private pilot, glider only, no other pilot ratings who at 2000 feet
tried to release, =E2=80=9Cslipped back in the seat pulling back on the

s=
tick
and going vertical.=E2=80=9D I took a stab at the release to no avail,

t=
he
pressure was too great and I soon found myself at about 75 degrees nose
down at full power. The natural instinct at this point is to pull back
the power and try again to release. He managed to release before I
could try for a second time and I recovered. If this has to happen to
you, 2000 feet is a good place to be. My understanding is that this

was
his first tow in more than a year. Something to think about. =20
=20
My second experience in the same week was with a 15 year old student on
her 3rd solo pattern tow. At about 250 to 300 feet I started a turn
from the downwind drift to the right. I felt a tug on my tail pulling
my nose to the left. After a few seconds I tried again to turn to the
right knowing that she was behind me to the right. Could not see her,
no mirror on the right. (much easier if she was a little to the left)

=20
The second time the pull of my tail to the right and nose to the left
was a bit more violent=E2=80=A6..followed by a very hard tug of my

tail
=
UP and
to the right. We could not have been much more than 300 feet when I
found myself nose down and trying to release=E2=80=A6.again the

pressure
=
was too
much to overcome and I needed to retard the throttle. Before I could
make a second attempt at release I heard a loud BANG as the rope broke,
I regained control and recovered just above the trees. (glad that I

had
made a pit stop before I started towing). She made it back to the

field
and didn=E2=80=99t seem at all concerned=E2=80=A6=E2=80=A6I shall

withhol=
d my comments at this
point. =20
=20
I had to straighten out the Schweizer hook which was off to the right
about 30 degrees before I could make the last 8 tows of the day.
=20
While I have concerns with both of these pilots my major concern is

that
the difficulty of actuating the release when the glider kites is well
documented. To make matters worse, the release in the tug I was

flying,
although a bit more manually accessible than the other two I fly
requires that the pilot pull it back and push down to fully actuate the
release. Not an easy thing to do under the circumstances. The other
two release handles are down on the floor to the left and for someone

of
my height, sitting on a cushion and trying to grab the release is very
difficult. It would seem to me that an easy fix would be to simply

make
a longer handle curved up so one could both see and feel for it in an
emergency. A longer handle would also provide a bit more mechanical
advantage although having read many of the posts I am not sure this
would overcome the pressure on the Schweizer hook. Of course I hear

all
the noise about needing to apply for a 337 and get FAA

approval=E2=80=A6.=
next I
will need approval to put a cushion on the seat or to have an

inspection
after washing the airplane. =20
=20
So, the fixes appear to be going to a Tost hook or inverting the
Schweizer hook which I understand can be done with an available STC.

=20
In my case I would also like to see a more accessible release
handle=E2=80=A6would (or should) an STC be required for this? This

wou=
ld be
the short term fix I would like to see. If the handle was made from

the
same stock as the current device, just a foot or so longer it would

seem
that this should be able to be done without a long drawn out approval
process. =20
=20
I love flying, enjoy the gliderport environment and people but I am NOT
willing to give up my life. When the glider kites things happen very
fast. Unless your hand is on the handle (not feasible in my
circumstances) you will not be able to release before the pressure gets
too great. If it happens much lower than I experience it will be

lights
out. So remember my glider pilot friends=E2=80=A6.fly

well=E2=80=A6.the
=
life you save
might be your tow pilot.
=20
Walt Connelly
=20
=20
=20
=20
--=20
Walt Connelly



  #13  
Old April 24th 17, 02:16 PM posted to rec.aviation.soaring
Bruce Hoult
external usenet poster
 
Posts: 961
Default Tow Plane Upsets......

On Monday, April 24, 2017 at 3:45:05 PM UTC+3, Chris Rollings wrote:
A large proportion of the tow-plane upsets, including most of the fatals,
happen very shortly after take-off, before there is an opportunity to get
into low tow. Also, descending into the prop-wash can be a trigger to the
momentary loss of control that leads to the upset, if the glider is on a C
of G hook.


Do these upsets *only* happen with a C of G hook?

I've done a fair bit of flying in a C of G hook Janus, including on days with wave and pretty bad rotor. Never had a problem.

Does an upset really happen because the glider pilot simply flies out of position? It seems unlikely to me. You need not only to be high but also with significant pull on the rope. All the times I've gotten high it's because the towplane suddenly ran into sink (of at least out of lift), and the result has been a slack rope, not the tight rope required for an upset. Simply maintaining station (even though high) until the slack starts to come out, and then descending back into position with a constant amount of bowing (i.e. low tension but not slack as such).

Without having actually been there myself, I suspect that upsets may be caused not by being out of position, but by having a slack rope suddenly come tight. With a C of G hook this causes a reasonably large nose up pitching moment which may not be able to be countered by the elevator. The glider can get significant angle of attack and lift and upwards and (as the angle increases) backwards acceleration. If you're towing at 68 knots (or more) with a stall speed of 40 knots then you can generate 3 G of acceleration. With 3 G of acceleration you've only got to get to 10 degrees nose up to tension the rope to half the glider's weight, 20 degrees nose up to put a full 1 G of force onto the rope, and 30 degrees for 1.5 times the glider's weight in tension.

The glider being out of position is most likely the very quick *result* of the glider going into winch launch mode, not the cause of it.

I can't see that low tow would make any significant difference to this. Slack being taken out violently (but not quite enough to break the rope) will have exactly the same effect as in high tow.
  #14  
Old April 24th 17, 02:20 PM
Walt Connelly Walt Connelly is offline
Senior Member
 
First recorded activity by AviationBanter: Aug 2010
Posts: 365
Default

Quote:
Originally Posted by Dave Springford View Post
Walt,

Our Pawnees have Tost releases. Schweizer hooks were removed about 30 years ago after an upset accident. The release cable is within a few inches reach of the throttle lever.

The release cable runs along the floor near the flap handle to a pulley attached to the floor that turns the cable 90 degrees upwards and then it attaches to the bottom of the instrument panel directly in front of the throttle quadrant. Reach forward and pull the cable, the glider is gone.

Release handles mounted to the floor are an accident waiting to happen, as are Schweizer hooks. As you have now experienced!
Thank you for your input Dave....it is quite obvious that this problem is well known and that there are things that can (AND WILL) be done to mitigate the difficulty of releasing in an emergency. While nothing is fool proof our current situation is FOOLISH. Until you experience it, until you try to pull the handle it will not be obvious to you. It is now beyond obvious to me. The discussions going forward will be what we can do and why....NOT what we can't do. It CAN be corrected...It WILL be corrected. I love aerobatics, just not at 200-300 feet AGL in a non aerobatic airplane.

Walt
  #15  
Old April 24th 17, 02:24 PM
Walt Connelly Walt Connelly is offline
Senior Member
 
First recorded activity by AviationBanter: Aug 2010
Posts: 365
Default

Quote:
Originally Posted by View Post
Walt, I "feel your pain". It has been long reported that a Schweizer hook is difficult if not impossible to release under abnormal situations such as yours. A lot of tow pilots claim if that if the stick hits a stop, pull the release now! Another item I've always been acutely aware is the co-location of the flap handle and the release handle. Do you in a stressful time have the ability to grab the release NOW! Perhaps a Tee handle on a heavy cord in your lap would be quicker and provide more leverage. I like Dave's comment in favor of switching to Tost releases
Wes,

There will be Tost hooks and release handle modifications post haste on all three of our tugs or I will commence my full retirement. There is NO logical reason why a longer handle cannot be fabricated and installed....FAA or NO FAA.

Walt
  #16  
Old April 24th 17, 02:29 PM
Walt Connelly Walt Connelly is offline
Senior Member
 
First recorded activity by AviationBanter: Aug 2010
Posts: 365
Default

Quote:
Originally Posted by Charlie M. (UH & 002 owner/pilot) View Post
Sounds great to me! In the US, high tow is predominate although low tow is taught.
Our club is one of 2(?) in the US that predominantly use low tow although we also teach high tow.
We have tested "going too low" and the towplane still has elevator available whereas going to high runs the towplane out of elevator.
If the glider pilot gets way out of position, the time difference is not much between the 2 tow types in my opinion.

Not trying to start a "conversation regarding which to use", just noting what we do. This can turn ugly fast, even worse than US contest rules discussions.......

PS, lost a friend during tow a couple decades ago while he was towing with a "known squirrel" on the glider end. The towplane was a L19 and went in from about 300' when the glider went too high in front of a couple dozen onlookers.
Not sure low tow would have helped.
Charlie, a big part of the problem here were the squirrels but the inadequacy of the release in the tug is just as much my concern. I am a student of body language and facial expression and emotion. I do not believe some people should be allowed to fly, their head is not in it, they are mechanical, they are not seat of the pants, hard wired into the situation. In the future I will reserve the right to NOT tow someone.

Walt
  #17  
Old April 24th 17, 02:38 PM posted to rec.aviation.soaring
Roy B.
external usenet poster
 
Posts: 304
Default Tow Plane Upsets......

Does anybody have actual experience or testing with the McFarlane product that uses a roller bearing instead of a mechanical connection between the latch and the finger? Again - I am looking for actual experience - not opinions.
See: http://www.mcfarlaneaviation.com/new.../march2007.htm
ROY
  #18  
Old April 24th 17, 03:13 PM posted to rec.aviation.soaring
Charlie M. (UH & 002 owner/pilot)
external usenet poster
 
Posts: 1,383
Default Tow Plane Upsets......

"Time to get to low tow"?!?!
You're doing it wrong.

Towplane and glider start rolling, glider lifts off and stays a few feet off the ground in ground effect, towplane lifts off and climbs out, when sight picture looks correct, glider starts climbing.
The propwash is not really a factor since it has not quite come together yet with normal ropes, maybe felt a bit on rather short ropes. By the time the turbulence has come together, it's over the glider.

BTW, I am not an AandP or IA, just an ex CFIG, long time glider pilot with some power time.

As to a release with a roller, any roller is better than a sliding surface, although keeping it rolling while operating on grass or dirt may be an issue.
On a sliding type release, at least make sure the edges of the hook where it goes into the release are smooth, not mushroomed out. A flat file now and then to smooth it out helps this.
Also some lube on release cable guide rollers, inside guide tubes and release pivots helps out a bit.
  #19  
Old April 24th 17, 03:34 PM posted to rec.aviation.soaring
Papa3[_2_]
external usenet poster
 
Posts: 753
Default Tow Plane Upsets......

As mentioned elsewhere in the thread, this topic comes up every few years. As I've posted in the past, I actually sat in a lab with John Campbell and built/tested a rig to measure release forces on the Schweizer release mounted on our PA-18 Supercub. We used various towropes, a simple protractor and a strain gauge.

I can't for the life of me find the handwritten notes and mimeographed (!!) handout that we created, but the conclusion is very clear.

- It only takes a fairly small amplitude kiting event to load up the Schweizer hook to a point where the release forces are significant. Don't quote me, but I believe the magic angle was less than 20 degrees above the longitudinal axis of the release hook with a relatively low load (100lbs IIRC)

- Beyond that point, the pilot in the towplane couldn't apply enough force on the release cable to effect a release. Compounding the problem is the fact that the routing of the release cable drastically reduced the effective force that was applied at the release point (cable bowed and routed around several pulleys). We had a separate version of the release we used for auto tows, and that one had a direct pull with a lever that actually worked under much higher loads.

Bottom line is that the towpilot was very unlikely to be able to release once the glider got significantly outside of normal tow envelope.

Erik Mann (P3)

On Sunday, April 23, 2017 at 8:43:12 PM UTC-4, Walt Connelly wrote:
I have been towing for about two and a half years and have logged over
6,500 tows. Having recently experienced a couple of rather violent
glider kiting incidents, one at about 300 feet AGL I decided to
investigate the experiences of other tow pilots in these circumstances.
I have spent several hours reading posts about gliders kiting and
upsetting the tow plane, many of the posts deal with creating an
automatic release that will recognize the actions of the glider and
release without input from the tow pilot. Nice idea, some really
creative approaches and the bottom line is anything can be done if you
have enough money and can get the FAA to buy into it and give
approval.

Lots of opinions and ideas as to why these things happen. Bottom line
is that they do happen, they have resulted in loss of tow pilot lives
and the causes are well known.

Of my two most recent experiences one was with a 67 year old licensed
private pilot, glider only, no other pilot ratings who at 2000 feet
tried to release, “slipped back in the seat pulling back on the stick
and going vertical.” I took a stab at the release to no avail, the
pressure was too great and I soon found myself at about 75 degrees nose
down at full power. The natural instinct at this point is to pull back
the power and try again to release. He managed to release before I
could try for a second time and I recovered. If this has to happen to
you, 2000 feet is a good place to be. My understanding is that this was
his first tow in more than a year. Something to think about.

My second experience in the same week was with a 15 year old student on
her 3rd solo pattern tow. At about 250 to 300 feet I started a turn
from the downwind drift to the right. I felt a tug on my tail pulling
my nose to the left. After a few seconds I tried again to turn to the
right knowing that she was behind me to the right. Could not see her,
no mirror on the right. (much easier if she was a little to the left)
The second time the pull of my tail to the right and nose to the left
was a bit more violent…..followed by a very hard tug of my tail UP and
to the right. We could not have been much more than 300 feet when I
found myself nose down and trying to release….again the pressure was too
much to overcome and I needed to retard the throttle. Before I could
make a second attempt at release I heard a loud BANG as the rope broke,
I regained control and recovered just above the trees. (glad that I had
made a pit stop before I started towing). She made it back to the field
and didn’t seem at all concerned……I shall withhold my comments at this
point.

I had to straighten out the Schweizer hook which was off to the right
about 30 degrees before I could make the last 8 tows of the day.

While I have concerns with both of these pilots my major concern is that
the difficulty of actuating the release when the glider kites is well
documented. To make matters worse, the release in the tug I was flying,
although a bit more manually accessible than the other two I fly
requires that the pilot pull it back and push down to fully actuate the
release. Not an easy thing to do under the circumstances. The other
two release handles are down on the floor to the left and for someone of
my height, sitting on a cushion and trying to grab the release is very
difficult. It would seem to me that an easy fix would be to simply make
a longer handle curved up so one could both see and feel for it in an
emergency. A longer handle would also provide a bit more mechanical
advantage although having read many of the posts I am not sure this
would overcome the pressure on the Schweizer hook. Of course I hear all
the noise about needing to apply for a 337 and get FAA approval….next I
will need approval to put a cushion on the seat or to have an inspection
after washing the airplane.

So, the fixes appear to be going to a Tost hook or inverting the
Schweizer hook which I understand can be done with an available STC.
In my case I would also like to see a more accessible release
handle…would (or should) an STC be required for this? This would be
the short term fix I would like to see. If the handle was made from the
same stock as the current device, just a foot or so longer it would seem
that this should be able to be done without a long drawn out approval
process.

I love flying, enjoy the gliderport environment and people but I am NOT
willing to give up my life. When the glider kites things happen very
fast. Unless your hand is on the handle (not feasible in my
circumstances) you will not be able to release before the pressure gets
too great. If it happens much lower than I experience it will be lights
out. So remember my glider pilot friends….fly well….the life you save
might be your tow pilot.

Walt Connelly




--
Walt Connelly


  #20  
Old April 24th 17, 04:10 PM
Walt Connelly Walt Connelly is offline
Senior Member
 
First recorded activity by AviationBanter: Aug 2010
Posts: 365
Default

Quote:
Originally Posted by George Haeh View Post
It seems to require a dead towpilot before a club gets rid of Schweitzer
tow
hooks.
George, we are a commercial operation, not a club. BUT if there are not three Tost hooks ordered tomorrow when we open for business and arrangements made to properly position the release handle I will terminate my employment.

Walt
 




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