Are Weak Links really Necessary for Aero Tow?

[[email protected]]

A lot of the clubs here tow with thickish (5/8 inch and some 1/2inch)
poly and nylon ropes, without weak links, and pilots with years of
experience say that no load exerted by the glider can damage the tug -
and in the worst of cases even a 5/8 rope will break before damaging
the Tug (Most often a supercub)

Comments from knowlegable people please ---

Thanks and kind regards

JS

[Stewart Kissel]

There was a recent thread on this topic...a search
of the archives should turn it up. FWIW 1/2' poly
typically is 1,000lb strength new, which allows it
to be used here in the USA for most gliders without
weak links.

[Doug Haluza]

I think this is really ignorant and misguided thinking. Yes, absolutely
the glider can damage the tug. The tail structure of most airplanes was
not designed to handle the load of a glider on tow. It was only
designed to handle aerodynamic and landing loads. Considering that the
breaking strength of a 5/8" rope is greater than the weight of the
towplane, it's not hard to imagine that it is certainly strong enough
to damage the tail. A 1000 lb glider can deliver well over 6000 lb of
pull before it's wings come off.

We have had an ongoing problem with stress cracking of the longerons
near the tail on our Super Cub towplane. It has been dsicovered from
time to time over the years during annual inspections because we have a
very good IA who knows how to look for this. And we tow with a 5/16"
poly rope, 1/4 the breaking strength of a 5/8" rope.

There have been a number of towplane upsets that would have resulted in
accidets had the tow rope not broken. The rope will not break when the
glider pulls the towplane's tail up, because the forces are not that
great. But after the upset, the forces are much greater, and if the
rope breaks, the towpilot has a chance to recover if there is enough
altitude remaining.

Most tow hook installations in the US are supposed to be placarded for
1200 lb breaking strength maximum. Most gliders also have maximum
breaking strength limits on their tow hooks as well (check your
manual). As has been pointed out in another thread, if you conduct
operations outside these limits, your insurance could deny coverage for
any resulting accident, especially since there will be a causal
relationship.

wrote:
> A lot of the clubs here tow with thickish (5/8 inch and some 1/2inch)
> poly and nylon ropes, without weak links, and pilots with years of
> experience say that no load exerted by the glider can damage the tug -
> and in the worst of cases even a 5/8 rope will break before damaging
> the Tug (Most often a supercub)
>
> Comments from knowlegable people please ---
>
> Thanks and kind regards
>
> JS

[Doug Haluza]

1/4" poly rope is between 1000 and 1200 lbs breaking strength when new,
not 1/2" which is much too strong. Note that the breaking strength will
reduce with use, so you would not want to use 1/4" poly to tow a double
seater or motorglider with water ballast.

Stewart Kissel wrote:
> There was a recent thread on this topic...a search
> of the archives should turn it up. FWIW 1/2' poly
> typically is 1,000lb strength new, which allows it
> to be used here in the USA for most gliders without
> weak links.

[Stewart Kissel]

At 20:36 16 September 2006, Doug Haluza wrote:
>1/4' poly rope is between 1000 and 1200 lbs breaking
>strength when new,
>not 1/2' which is much too strong.

My bad...yes you are correct, I had my numbers wrong.

[[email protected]]

If the towrope has a breaking strength more than twice the maximum
certificated operating weight of the glider being towed, a safety link
has to be installed at the point of attachment of the glider and the
tow plane with the following breaking strength requirements.
Safety Link (Weak Link) Requirements
Safety link (Weak Link) at the glider end:
o Minimum Strength = 80 percent of the glider maximum certificated
operating weight
o Maximum Strength = twice the maximum certificated operating weight
Safety link (Weak Link) at the tow plane end:
o Strength Requirements = Greater, but not more than 25% greater than
that of the safety link on the glider end, and not more than twice the
maximum certificated operating weight of the glider

[[email protected]]

Typical Rope Strengths in Pounds
Diameter Hollow Braid Polypropylene Polypropylene
Nylon Dacron Polyethylene Monofilament Multifilament
3/16 " 960 720 700 800 870
1/4 " 1,500 1,150 1,200 1,300 1,200
5/16" 2,400 1,750 1,750 1,900 2,050

[KM]

Doug Haluza wrote:
> I think this is really ignorant

No need to call people names here.I think the guy was just looking for
an honest opinion.

> The tail structure of most airplanes was
> not designed to handle the load of a glider on tow. It was only
> designed to handle aerodynamic and landing loads. Considering that the
> breaking strength of a 5/8" rope is greater than the weight of the
> towplane, it's not hard to imagine that it is certainly strong enough
> to damage the tail. A 1000 lb glider can deliver well over 6000 lb of
> pull before it's wings come off.

This is maybe true at high airspeeds.But at typical towing speeds, the
glider would probably stall before it could exert 6Gs of load.Most
towing is done well below the max maneuvering speed of a
sailplane.Therefore, it would stall well before the wings came
off.Another thing to consider (those of you who auto tow or winch
launch can relate), The tailplane would probable stall before you could
exert 6K load on tow.

>
> We have had an ongoing problem with stress cracking of the longerons
> near the tail on our Super Cub towplane.

Do you know for certain this is caused by towing?I flew for a company
with a fleet of tow ships, some with 8000 hours of nothing but tows and
we didnt have this problem.Check to see what your tow pilots are doing
on the way down.

> The rope will not break when the
> glider pulls the towplane's tail up, because the forces are not that
> great. But after the upset, the forces are much greater, and if the
> rope breaks, the towpilot has a chance to recover if there is enough
> altitude remaining.

Now you are contradicting yourself.You just wrote that a sailplane can
apply 6000 LBS of pull, and here you say the force is not that
great.Why would the forces increase after an upset.

> Most tow hook installations in the US are supposed to be placarded for
> 1200 lb breaking strength maximum.

This depends on the type of hook.Also, I think this guy was posting
from another country.Also, he was aking about tow ROPES and not hooks.


Fly Safe,
KMU

[Doug Haluza]

KM wrote:
> Doug Haluza wrote:
> > I think this is really ignorant
>
> No need to call people names here.I think the guy was just looking for
> an honest opinion.

I was not referring to the poster, I was referring to the supposedly
experienced people he was quoting.

> > The tail structure of most airplanes was
> > not designed to handle the load of a glider on tow. It was only
> > designed to handle aerodynamic and landing loads. Considering that the
> > breaking strength of a 5/8" rope is greater than the weight of the
> > towplane, it's not hard to imagine that it is certainly strong enough
> > to damage the tail. A 1000 lb glider can deliver well over 6000 lb of
> > pull before it's wings come off.
>
> This is maybe true at high airspeeds.But at typical towing speeds, the
> glider would probably stall before it could exert 6Gs of load.Most
> towing is done well below the max maneuvering speed of a
> sailplane.Therefore, it would stall well before the wings came
> off.Another thing to consider (those of you who auto tow or winch
> launch can relate), The tailplane would probable stall before you could
> exert 6K load on tow.

After an upset, the towplane will enter an unrecoverable dive, and if
the rope does not break, the speeds will quickly increase beyond
maneuvering speed.

> > We have had an ongoing problem with stress cracking of the longerons
> > near the tail on our Super Cub towplane.
>
> Do you know for certain this is caused by towing?I flew for a company
> with a fleet of tow ships, some with 8000 hours of nothing but tows and
> we didnt have this problem.Check to see what your tow pilots are doing
> on the way down.

They are stress cracks, probably from a combination of vibration,
landing, and towing loads. They are not doing tail slides on the way
down.

> > The rope will not break when the
> > glider pulls the towplane's tail up, because the forces are not that
> > great. But after the upset, the forces are much greater, and if the
> > rope breaks, the towpilot has a chance to recover if there is enough
> > altitude remaining.
>
> Now you are contradicting yourself.You just wrote that a sailplane can
> apply 6000 LBS of pull, and here you say the force is not that
> great.Why would the forces increase after an upset.

Because the airspeed will increase.

> > Most tow hook installations in the US are supposed to be placarded for
> > 1200 lb breaking strength maximum.
>
> This depends on the type of hook.Also, I think this guy was posting
> from another country.Also, he was aking about tow ROPES and not hooks.

The rope and the hooks on both end work as a complete system. All of
the parts must work together. And they will work the same in any
country--the laws of Physics know no political boundaries.

[KM]

Doug Haluza wrote:
> Considering that the
> > > breaking strength of a 5/8" rope is greater than the weight of the
> > > towplane, it's not hard to imagine that it is certainly strong enough
> > > to damage the tail.

Are you telling us that the tail can only handle its own weight?You are
using apples and oranges here because you used the FLIGHT loads of a
sailplane and the actual weight of the tow plane.In other words, if a
towplane can sustain 4.4Gs (In the utility category) shouldnt the tail
of said towplane ALSO sustain 4.4Gs.


> After an upset, the towplane will enter an unrecoverable dive, and if
> the rope does not break, the speeds will quickly increase beyond
> maneuvering speed.

Where do you come up with this?I have NEVER flown an airplane that
could not be pulled out of a dive.Another thing to consider is that the
tow pilot would just release by this point.The tost hook will release
at vitually any angle, and even if the plane had a Schweitzer hook, by
forcing the tail up you will change the angle on the rope and the pilot
could then release it.

> They are stress cracks, probably from a combination of vibration,
> landing, and towing loads. They are not doing tail slides on the way
> down.

Are you a metalurgist?When you say "Probably" it kinda implies that you
are guessing.If your Cub has Jack screw trim, take a look at what the
tail is doing on the take off roll.Also, I never mentioned a tail
slide.There has been a tow pilot or two who thinks acro wont hurt a
plane as long as you are carefull.How long have you been hanging out at
gliderports?

> The rope and the hooks on both end work as a complete system. All of
> the parts must work together. And they will work the same in any
> country--the laws of Physics know no political boundaries.

Boy you are a sharp one Doug!I would have never guessed (G).What I
actually meant was that the laws in this pilots country could be more
conservitive than the US.Take a look at the rules in germany (Where
most of our gliders come from).
Happy Landings
KMU

[baron58y]

KM wrote:

> Doug Haluza wrote:

>> After an upset, the towplane will enter an unrecoverable dive, and if
>> the rope does not break, the speeds will quickly increase beyond
>> maneuvering speed.
>
> Where do you come up with this? I have NEVER flown an airplane that
> could not be pulled out of a dive.

Then you haven't flown tow planes much (if at all), if you can't imagine
that scenario.


Jack

[KM]

baron58y wrote:
>
> > Doug Haluza wrote:
>
> >> After an upset, the towplane will enter an unrecoverable dive, and if
> >> the rope does not break, the speeds will quickly increase beyond
> >> maneuvering speed.
> >
> > Where do you come up with this? I have NEVER flown an airplane that
> > could not be pulled out of a dive.
>
> Then you haven't flown tow planes much (if at all), if you can't imagine
> that scenario.

Jack, Why dont you go back and read my post?I never said I could not
imagine ANY senario.Are you just trying to be stupid?Doug wrote that a
sailplane could impose a 6000 LB. load on the tail of a towplane.Now if
you want to split hairs THAT would be a scenario I would have a hard
time imagining.Jack, with all your experience towing, have YOU ever
seen such a thing?
> Jack
With Warmest Regards,
KMU

[baron58y]

KM wrote:

> Are you just trying to be stupid?

Sorry, KM, I'm just too stupid to tell when you mean what you write and
when you don't. I'll try harder, I really will.


> Doug wrote that a sailplane could impose a 6000 LB. load on the tail
> of a towplane....

> Jack, with all your experience towing, have YOU ever
> seen such a thing?

I don't know if a sailplane can impose a 6000 lb load on a tow plane.
I have just enough experience towing to know it takes only a fraction
of that loading for the tow plane to run out of pitch control, and it
didn't take much experience to find that out.


Jack

[KM]

baron58y wrote:
> Sorry, KM, I'm just too stupid to tell when you mean what you write and
> when you don't. I'll try harder, I really will.

What?Jack, I think you and I are arguing about two different things
here.I took exeption to you questioning whether I had any
experience.Now I am gonna be honest with you, I dont have much
experience in soaring.I have about 450 hours of towing, and about 200
hours in sailplanes, half of which is in an ASW20 that I own.In
reference to Doug's post,and using my 20 as an example, I dont see how
I could pull 6Gs while on tow.Also, in reference to Dougs post, If a
tow pilot was losing pitch authority, why wouldnt he just pull the
release?I know I would, in fact, some tow pilots I know keep their free
hand on the release till they are through pattern altitude.Now Jack,
lets get back to this experience thing.I notice from your nickname that
you fly a Baron.And that you have to make sure everyone is aware of
this ;).Why dont you fly that Baron down to Atlanta and we can get into
the cockpit of my 737-800 and talk more about this experience thing;).
Or better yet, lets just get back to the post that started this
thread.And the short answer is; Keep a week link in the cockpit of your
sailplane and use it, and two, a sailplane, given a pretty extreem (And
remote) scenario could cause damage to a tow plane.
> I don't know if a sailplane can impose a 6000 lb load on a tow plane.
> I have just enough experience towing to know it takes only a fraction
> of that loading for the tow plane to run out of pitch control, and it
> didn't take much experience to find that out.
>
>
> Jack
Best Wishes, KMU

[baron58y]

KM wrote:

> I dont see how
> I could pull 6Gs while on tow.

Fair enough -- I don't either, but I'm not going to argue about it.
Unless I find some reliable info that states otherwise, Doug might be
right. Got some?


> Also, in reference to Dougs post, If a tow pilot was losing pitch
> authority, why wouldnt he just pull the release?

Would, if he could -- if he didn't wait too long.


> ...some tow pilots I know keep their free
> hand on the release till they are through pattern altitude.

Pretty smart. So, whatever the g-load of which a sailplane might be
capable while on tow, it's more than enough to upset the tow plane.


> ...lets get back to this experience thing. I notice from your nickname that
> you fly a Baron.

Yet another unfounded assumption on your part. I fly a 1-26.


> ...we can get into the cockpit of my 737-800 and talk more
> about this experience thing.

Oh, excellent! A "mine is bigger than yours" retort. We rarely get those
on r.a.s. -- unlike most of the rest of USENET. When we do it's usually
just some lurking wannabee.

There are probably some folks here whose aviation careers could put both
mine and yours to shame, if we wanted to talk about experience -- so
let's not embarrass ourselves. If "my 737-800" means you own it,
congratulations are in order! But if Delta just pays you to fly it, I
ain't that impressed.


> Or better yet, lets just get back to the post that started this
> thread.

First smart thing you said. What was that post all about? Oh yeah, here
it is:

wrote: "A lot of the clubs here tow with
thickish
(5/8 inch and some 1/2inch) poly and nylon ropes, without weak
links, and pilots with years of experience say that no load exerted
by the glider can damage the tug - and in the worst of cases even a
5/8 rope will break before damaging the Tug (Most often a supercub)

Comments from knowlegable people please ---

Thanks and kind regards

JS


So civil, not contentious at all -- what a guy that JS is.

So, what do you think KMU -- now that you have reviewed the original post?



Jack

[Ian Johnston]

On Sat, 16 Sep 2006 20:32:50 UTC, "Doug Haluza" >
wrote:

: 1/4" poly rope is between 1000 and 1200 lbs breaking strength when new,
: not 1/2" which is much too strong.

If by "poly" you mean polyester, those numbers seem a bit low. For
their prestreched stuff, Marlow quote average breaking loads of 2584lb
for 6mm and 7826lb for 12mm.

http://www.marlowropes.com/public/pageManager.cfm?page_id=130

Ian
--

[Ian Johnston]

On Sun, 17 Sep 2006 00:54:22 UTC, "KM" > wrote:

: Where do you come up with this?I have NEVER flown an airplane that
: could not be pulled out of a dive

Started vertically downwards at an altutude of 300 feet?

Ian
--

[Doug Haluza]

Oh, my, where to start?

KM wrote:

> Are you telling us that the tail can only handle its own weight?You are
> using apples and oranges here because you used the FLIGHT loads of a
> sailplane and the actual weight of the tow plane.In other words, if a
> towplane can sustain 4.4Gs (In the utility category) shouldnt the tail
> of said towplane ALSO sustain 4.4Gs.

No, I'm saying the airplane was designed to handle flight and landing
loads, based on it's max gross weight. These loads on the tail are only
a fraction of it's weight. The glider can transfer most of the lifting
force developed by the wing to the rope if a C.G. hook is used for
aerotow. An aircraft with a design load limit of 4.4 G's will have an
ultimate load limit >6.6 G's so a glider with a 1000 lb gross weight
could deliver over 6000 lb of force, before the glider's wings failed.

> > After an upset, the towplane will enter an unrecoverable dive, and if
> > the rope does not break, the speeds will quickly increase beyond
> > maneuvering speed.
>
> Where do you come up with this?I have NEVER flown an airplane that
> could not be pulled out of a dive. Another thing to consider is that the
> tow pilot would just release by this point.The tost hook will release
> at vitually any angle, and even if the plane had a Schweitzer hook, by
> forcing the tail up you will change the angle on the rope and the pilot
> could then release it.

You can't pull out of the dive if the glider is still attached to your
tail by a rope that won't break. And if you have a Schweizer hook on
the tail, it may not release after the upset because the pull is
greater and may no longer be straight back. There have been several
cases of upset where the tow pilot could not make the hook release, and
the dive would have been unrecoverable if the rope did not break.

Even if you tow with a Tost hook, you still need to react and operate
the release, and this will take more time than a rope needs to break.
If the glider pulls your tail up fast enough, you could be in negative
G's which will take your hand off the knob. How fast can you find and
operate the corect knob when the stuff hits the fan? That time could be
the difference between a low recovery and a splat.

[Stealth Pilot]

On 16 Sep 2006 13:30:15 -0700, "Doug Haluza" >
wrote:

>I think this is really ignorant and misguided thinking. Yes, absolutely
>the glider can damage the tug. The tail structure of most airplanes was
>not designed to handle the load of a glider on tow. It was only
>designed to handle aerodynamic and landing loads. Considering that the
>breaking strength of a 5/8" rope is greater than the weight of the
>towplane, it's not hard to imagine that it is certainly strong enough
>to damage the tail. A 1000 lb glider can deliver well over 6000 lb of
>pull before it's wings come off.
>

my old auster J1b which is under a long slow restoration was used for
towing gliders at on stage of its life by the Narrogin Gliding Club in
Western Australia. You can clearly see a weld repair to the bottom two
longerons just in front of the tailpost where a glider did its
damndest to tear the back end out of the aircraft.

no weak link seems on evidence to warn of a funeral in the making.
Stealth Pilot
Oz

[Papa3]

wrote:
> A lot of the clubs here tow with thickish (5/8 inch and some 1/2inch)
> poly and nylon ropes, without weak links, and pilots with years of
> experience say that no load exerted by the glider can damage the tug -
> and in the worst of cases even a 5/8 rope will break before damaging
> the Tug (Most often a supercub)
>
> Comments from knowlegable people please ---
>
> Thanks and kind regards
>
> JS

Been there, done that (damaged a towplane). I got my CFI-G ticket in
2-33s and had about 100 hours instructing in these. Then, I
volunteered with another club that used Grob 103s for training. A very
different animal from the 2-33. Things get out of whack much faster.
On my second flight with a fairly new student, I let her get a fairly
impressive PIO going in both pitch (vertical position) and roll
(lateral position). On about the 3rd oscillation, she had a huge loop
develop and, before I could reach the release, she applied full
opposite stick. A godawful sproingggg and we were in free flight. I
noticed the towplane (an L-19) in a fairly impressive rolling dive to
the left and saw the rope trailing free from the towplane end (ie.
attached to the glider) . Once I got my nerves under control, we
dropped the remaining rope over the airport and had an uneventful
landing...

.... Uneventful, that is, until the towpilot came walking over. It
didn't take a genius to figure out that he was not in the best of
moods. I noticed he was carrying something in his hand. The
something was the mangled release mechanism. We had broken it from
the towplane at the mounting bolt; it stayed attached only thanks to
the release cable.

So, in answer to your question, it is possible to damage a towplane
with a glider. At this operation, they used 5/8 braided poly with
Schweizer rings for the main rope. The club which owned the G103 used
"adapters" for the Tost release. I believe (can't recall for sure)
that these were also 5/8.

Erik Mann
LS8-18 (P3)

[Papa3]

Doug Haluza wrote:
> Oh, my, where to start?
>
> KM wrote:
>
>
> > > After an upset, the towplane will enter an unrecoverable dive, and if
> > > the rope does not break, the speeds will quickly increase beyond
> > > maneuvering speed.
> >
> > Where do you come up with this?I have NEVER flown an airplane that
> > could not be pulled out of a dive. Another thing to consider is that the
> > tow pilot would just release by this point.The tost hook will release
> > at vitually any angle, and even if the plane had a Schweitzer hook, by
> > forcing the tail up you will change the angle on the rope and the pilot
> > could then release it.
>
> You can't pull out of the dive if the glider is still attached to your
> tail by a rope that won't break. And if you have a Schweizer hook on
> the tail, it may not release after the upset because the pull is
> greater and may no longer be straight back. There have been several
> cases of upset where the tow pilot could not make the hook release, and
> the dive would have been unrecoverable if the rope did not break.
>
>

I recall that John Campbell did a detailed analysis of this issue
(loads on a Schweizer towplane release mechanism) when he was a
postDoc. There were a couple of pretty sobering conclusions IIRC:

1. There is a critical angle (not a particularly steep one) beyond
which the vertical component of the force applied by the towrope will
overcome the force available from the emergency release cable on the
towplane side. In other words, once the glider kites up to a certain
angle, the towpilot may (probably won't) be able to release. Anyone
who has ever eyeballed the Schweizer release will immediately be able
to see why this is the case.

2. The force required for this was significantly less than the
breaking strength of a typical towrope. I could probably rough out
the numbers for this, but it is intuitively makes sense.

Maybe somebody has a copy of this analysis handy?

P3

[Papa3]

Papa3 wrote:
> Doug Haluza wrote:
> > Oh, my, where to start?
> >
> > KM wrote:
> >
> >
> > > > After an upset, the towplane will enter an unrecoverable dive, and if
> > > > the rope does not break, the speeds will quickly increase beyond
> > > > maneuvering speed.
> > >
> > > Where do you come up with this?I have NEVER flown an airplane that
> > > could not be pulled out of a dive. Another thing to consider is that the
> > > tow pilot would just release by this point.The tost hook will release
> > > at vitually any angle, and even if the plane had a Schweitzer hook, by
> > > forcing the tail up you will change the angle on the rope and the pilot
> > > could then release it.
> >
> > You can't pull out of the dive if the glider is still attached to your
> > tail by a rope that won't break. And if you have a Schweizer hook on
> > the tail, it may not release after the upset because the pull is
> > greater and may no longer be straight back. There have been several
> > cases of upset where the tow pilot could not make the hook release, and
> > the dive would have been unrecoverable if the rope did not break.
> >
> >
>
> I recall that John Campbell did a detailed analysis of this issue
> (loads on a Schweizer towplane release mechanism) when he was a
> postDoc. There were a couple of pretty sobering conclusions IIRC:
>
> 1. There is a critical angle (not a particularly steep one) beyond
> which the vertical component of the force applied by the towrope will
> overcome the force available from the emergency release cable on the
> towplane side. In other words, once the glider kites up to a certain
> angle, the towpilot may (probably won't) be able to release. Anyone
> who has ever eyeballed the Schweizer release will immediately be able
> to see why this is the case.
>
> 2. The force required for this was significantly less than the
> breaking strength of a typical towrope. I could probably rough out
> the numbers for this, but it is intuitively makes sense.
>
> Maybe somebody has a copy of this analysis handy?
>
> P3

Here's a very good analysis: http://home.att.net/~jdburch/Towstudy.htm

[Doug Haluza]

Oh, now why did you have to inject facts into the discussion? ;-)

A very good analysis. The AC 43.13-2 referenced can be found at:

http://tinyurl.com/25oz7

The information on tow hook installatioin is at the end.

Papa3 wrote:
> Here's a very good analysis: http://home.att.net/~jdburch/Towstudy.htm

[Doug Haluza]

Papa3 wrote:
> ... Uneventful, that is, until the towpilot came walking over. It
> didn't take a genius to figure out that he was not in the best of
> moods. I noticed he was carrying something in his hand. The
> something was the mangled release mechanism. We had broken it from
> the towplane at the mounting bolt; it stayed attached only thanks to
> the release cable.
>
You are lucky you broke the tow hook attachment bolts. This engaged the
tow hook release by pulling on the release cable from the other end.
That is why the hook stayed attached to the towplane, and the rope
stayed attached to the glider (and the tail stayed attached to the
towplane).

P.S. I saw a similar failure on an L-19 tow hook installation due to
metal fatigue. A bolt broke, and the tow hook released during a normal
tow. It happened early in the tow, so no accident. But it showed an
obvious design flaw with that installation. The hook was mounted
directly to the leaf spring with two plates on either side, all
sandwiched together by two 1/4" bolts. The plates were separated by the
spring thickness, and put a lot of shear loading on those tiny bolts,
both of which are critical. I would rather see a 4-bolt installation,
so you get a chance to catch a broken bolt on pre-flight.

[KM]

baron58y wrote:
> KM wrote:
>
> > I dont see how
> > I could pull 6Gs while on tow.
>
> Fair enough -- I don't either, but I'm not going to argue about it.

Dude!We agree on something!But I do think you want to argue about it or
you wouldnt keep posting marginally coherent responses:).

> Unless I find some reliable info that states otherwise, Doug might be
> right. Got some?

Well consider this.If you take a look at the report (Elswhere on this
thread) about Shchweitzer tow hooks, it states that there were 3
accidents in this 12 year period that were caused by loss of pitch
control.During this same time frame there were at least 4 accidents
where tow planes came apart during aerobatics after the release of the
sailplane.So you have to ask yourself, What causes more damage to
towplanes? I hope you are reading this Doug.
I was flying in So Cal back in the 90s, and right at release the tow
pilot applied (What appeared from my vantage point) full left rudder
and snap rolled the tow plane upside down.He then split S'ed out the
bottom (With a Pawnee).Now I know alot of people on this list are gonna
counter that this wont hurt a towplane if you are slow enough, but I
beg to differ.I used to fly for an aerobatics flight school, and the
types of cracks Doug is descibing showed up on planes that were NEVER
used for towing.I have no idea why Doug had to make a silly remark
about tailslides.You have to also consider that most of our tugs are
tired old ships to begin with.

>
> > Also, in reference to Dougs post, If a tow pilot was losing pitch
> > authority, why wouldnt he just pull the release?
>
> Would, if he could -- if he didn't wait too long.

Jack this is an excellent point, and I would ad that if this happened
low to the ground, a weak link would not matter.

> Yet another unfounded assumption on your part. I fly a 1-26.

Now Jack you silly goose!You cant sign yourself "Baron 58Y" and not
have people assume you fly a Baron.

> Oh, excellent! A "mine is bigger than yours" retort. We rarely get those
> on r.a.s. -- unlike most of the rest of USENET.>
> There are probably some folks here whose aviation careers could put both
> mine and yours to shame, if we wanted to talk about experience -- so
> let's not embarrass ourselves. If "my 737-800" means you own it,
> congratulations are in order! But if Delta just pays you to fly it, I
> ain't that impressed.

Jack, you would be even less impressed if you saw my paycheck
lately;).But more to the point, I threw this in because you had to make
a "unfounded assumption" about my experience level.Now once again I
will be the first to acknowlege that 9/10s of this list has more time
in tow planes and sailplanes than I do.
>
>
> > Or better yet, lets just get back to the post that started this
> > thread.
>
> First smart thing you said. What was that post all about? Oh yeah, here
> it is:
Jack, was that a compliment? Iam touched!

> So civil, not contentious at all -- what a guy that JS is.
>
> So, what do you think KMU -- now that you have reviewed the original post?

???? Once again for you and Doug.Keep a week ling in your plane.And if
your tow pilot is pulling any shenanigans, kindly ask him or her to
knock it off.
>
> Jack

Your Pal,
KMU

[KM]

Doug Haluza wrote:
> Oh, my, where to start?

How about with your condisending tude?

> No, I'm saying the airplane was designed to handle flight and landing
> loads, based on it's max gross weight. These loads on the tail are only
> a fraction of it's weight. The glider can transfer most of the lifting
> force developed by the wing to the rope if a C.G. hook is used for
> aerotow. An aircraft with a design load limit of 4.4 G's will have an
> ultimate load limit >6.6 G's so a glider with a 1000 lb gross weight
> could deliver over 6000 lb of force, before the glider's wings failed.

OK now focus here Doug, the math is not in dispute. The question is
whether a glider could exert this force while on tow.
>
> > > After an upset, the towplane will enter an unrecoverable dive, and if
> > > the rope does not break, the speeds will quickly increase beyond
> > > maneuvering speed.

But what makes you think the dive would be "Unrecoverable" just because
the tow plane is past its manurering speed?

> You can't pull out of the dive if the glider is still attached to your
> tail by a rope that won't break. And if you have a Schweizer hook on
> the tail, it may not release after the upset because the pull is
> greater and may no longer be straight back. There have been several
> cases of upset where the tow pilot could not make the hook release, and
> the dive would have been unrecoverable if the rope did not break.

Completely true statement.But, as the nose of the tow plane drops, this
would change the angle on the release would it not?A couple of local
pilots tried this (At altitude of course) and found this to be the
case.Now at low altitudes, all bets are off of course.This is the
beauty of the tost hook.
>
> Even if you tow with a Tost hook, you still need to react and operate
> the release.

Doesnt this go without saying?
I have to take issue with your previous post where you implied that a
pilot could get away with aerobatics in a Super Cub as long as he wasnt
doing "Tailslides".To coin your phrase this is "Ignorant Thinking".You
should read my response to Baron 58Yankee on this one.I think that any
aerobatics in a Super Cub should be discuraged.
Most Respectfully Yours,
KMU

[John Smith]

A simple question to all the participants in this thread
- How many off you have actually experienced piloting
a tow plane when the glider has kited behind you?
As a tow pilot who has had it happen at 500 feet agl
and did survive I can state that it is not just the
angle of the rope but also the highloads imposed that
prevent release of the rope by the tow plane. This
affects all types of release. You have a tow plane
trying to dive at a steep angle and a glider virtually
winch launching of the back of it - quite a high loading
I can assure you and one that decellerates the tow
plane rapidly. Secondly the upset occurs because of
the upwards load from the glider overcoming the maximum
down load able to be applied at the tow planes tailplane.
This effectively stalls the tailpane in an inverted
sense and the tow plane is actually pitched rapidly
nose down with very little acceleration and indeed
speed. If the rope breaks or releases it is actually
necessary to accelerate the tow plane in its nose down
attitude to gain sufficient speed to pull out of the
nose down attitude.
And NO, I really don't want to experience it again.
With reference to the original question I would strongly
advise the fitting of weak links to all glider tow
ropes regardless of the supposed breaking strength
of the rope used.
PS I do operate at both ends of the tow rope.




At 16:30 17 September 2006, Km wrote:
>
>Doug Haluza wrote:
>> Oh, my, where to start?
>
>How about with your condisending tude?
>
>> No, I'm saying the airplane was designed to handle
>>flight and landing
>> loads, based on it's max gross weight. These loads
>>on the tail are only
>> a fraction of it's weight. The glider can transfer
>>most of the lifting
>> force developed by the wing to the rope if a C.G.
>>hook is used for
>> aerotow. An aircraft with a design load limit of 4.4
>>G's will have an
>> ultimate load limit >6.6 G's so a glider with a 1000
>>>lb gross weight
>> could deliver over 6000 lb of force, before the glider's
>>wings failed.
>
>OK now focus here Doug, the math is not in dispute.
>The question is
>whether a glider could exert this force while on tow.
>>
>> > > After an upset, the towplane will enter an unrecoverable
>>>>dive, and if
>> > > the rope does not break, the speeds will quickly
>>>>increase beyond
>> > > maneuvering speed.
>
>But what makes you think the dive would be 'Unrecoverable'
>just because
>the tow plane is past its manurering speed?
>
>> You can't pull out of the dive if the glider is still
>>attached to your
>> tail by a rope that won't break. And if you have a
>>Schweizer hook on
>> the tail, it may not release after the upset because
>>the pull is
>> greater and may no longer be straight back. There
>>have been several
>> cases of upset where the tow pilot could not make
>>the hook release, and
>> the dive would have been unrecoverable if the rope
>>did not break.
>
>Completely true statement.But, as the nose of the tow
>plane drops, this
>would change the angle on the release would it not?A
>couple of local
>pilots tried this (At altitude of course) and found
>this to be the
>case.Now at low altitudes, all bets are off of course.This
>is the
>beauty of the tost hook.
>>
>> Even if you tow with a Tost hook, you still need to
>>react and operate
>> the release.
>
>Doesnt this go without saying?
>I have to take issue with your previous post where
>you implied that a
>pilot could get away with aerobatics in a Super Cub
>as long as he wasnt
>doing 'Tailslides'.To coin your phrase this is 'Ignorant
>Thinking'.You
>should read my response to Baron 58Yankee on this one.I
>think that any
>aerobatics in a Super Cub should be discuraged.
>Most Respectfully Yours,
>KMU
>
>

[John Smith]

The document at the following reference may be of interest
- in particular pages 28 - 30

https://www.gliding.co.uk/bgainfo/clubmanagement/documents/aerotow
notes.pdf

also see my edit re the tow plane diving

At 17:24 17 September 2006, John Smith wrote:
>A simple question to all the participants in this thread
>- How many off you have actually experienced piloting
>a tow plane when the glider has kited behind you?
>As a tow pilot who has had it happen at 500 feet agl
>and did survive I can state that it is not just the
>angle of the rope but also the highloads imposed that
>prevent release of the rope by the tow plane. This
>affects all types of release. You have a tow plane
>'most likely at full power' trying to dive at a steep
angle and a glider virtually
>winch launching of the back of it - quite a high loading
>I can assure you and one that decellerates the tow
>plane rapidly. Secondly the upset occurs because of
>the upwards load from the glider overcoming the maximum
>down load able to be applied at the tow planes tailplane.
>This effectively stalls the tailpane in an inverted
>sense and the tow plane is actually pitched rapidly
>nose down with very little acceleration and indeed
>speed. If the rope breaks or releases it is actually
>necessary to accelerate the tow plane in its nose down
>attitude to gain sufficient speed to pull out of the
>nose down attitude.
>And NO, I really don't want to experience it again.
>With reference to the original question I would strongly
>advise the fitting of weak links to all glider tow
>ropes regardless of the supposed breaking strength
>of the rope used.
>PS I do operate at both ends of the tow rope.
>
>
>
>
>At 16:30 17 September 2006, Km wrote:
>>
>>Doug Haluza wrote:
>>> Oh, my, where to start?
>>
>>How about with your condisending tude?
>>
>>> No, I'm saying the airplane was designed to handle
>>>flight and landing
>>> loads, based on it's max gross weight. These loads
>>>on the tail are only
>>> a fraction of it's weight. The glider can transfer
>>>most of the lifting
>>> force developed by the wing to the rope if a C.G.
>>>hook is used for
>>> aerotow. An aircraft with a design load limit of 4.4
>>>G's will have an
>>> ultimate load limit >6.6 G's so a glider with a 1000
>>>>lb gross weight
>>> could deliver over 6000 lb of force, before the glider's
>>>wings failed.
>>
>>OK now focus here Doug, the math is not in dispute.
>>The question is
>>whether a glider could exert this force while on tow.
>>>
>>> > > After an upset, the towplane will enter an unrecoverable
>>>>>dive, and if
>>> > > the rope does not break, the speeds will quickly
>>>>>increase beyond
>>> > > maneuvering speed.
>>
>>But what makes you think the dive would be 'Unrecoverable'
>>just because
>>the tow plane is past its manurering speed?
>>
>>> You can't pull out of the dive if the glider is still
>>>attached to your
>>> tail by a rope that won't break. And if you have a
>>>Schweizer hook on
>>> the tail, it may not release after the upset because
>>>the pull is
>>> greater and may no longer be straight back. There
>>>have been several
>>> cases of upset where the tow pilot could not make
>>>the hook release, and
>>> the dive would have been unrecoverable if the rope
>>>did not break.
>>
>>Completely true statement.But, as the nose of the tow
>>plane drops, this
>>would change the angle on the release would it not?A
>>couple of local
>>pilots tried this (At altitude of course) and found
>>this to be the
>>case.Now at low altitudes, all bets are off of course.This
>>is the
>>beauty of the tost hook.
>>>
>>> Even if you tow with a Tost hook, you still need to
>>>react and operate
>>> the release.
>>
>>Doesnt this go without saying?
>>I have to take issue with your previous post where
>>you implied that a
>>pilot could get away with aerobatics in a Super Cub
>>as long as he wasnt
>>doing 'Tailslides'.To coin your phrase this is 'Ignorant
>>Thinking'.You
>>should read my response to Baron 58Yankee on this one.I
>>think that any
>>aerobatics in a Super Cub should be discuraged.
>>Most Respectfully Yours,
>>KMU
>>
>>
>
>
>
>

[W.J. \(Bill\) Dean \(U.K.\).]

Note that the drawing on p.28 of the document referenced by John Smith was
taken from a series of photos taken with a motor drive camera during a
deliberate upset of a Supercub towing a K8 during trials many years ago.
Note that the rope angle to the tug hardly changes.

See http://www.glidingmagazine.com/FeatureArticle.asp?id=327 , where Chris
Rollings who was flying the K8 describes what happened. The PA18-180 was
being flown by Brian Spreckley.

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

>
> "John Smith" >
> wrote in message ...
>
> The document at the following reference may be of interest
> - in particular pages 28 - 30
>
> https://www.gliding.co.uk/bgainfo/clubmanagement/documents/aerotownotes.pdf .
>
> also see my edit re the tow plane diving
>
>>
>>At 17:24 17 September 2006, John Smith wrote:
>>
>>A simple question to all the participants in this thread
>>- How many off you have actually experienced piloting
>>a tow plane when the glider has kited behind you?
>>As a tow pilot who has had it happen at 500 feet agl
>>and did survive I can state that it is not just the
>>angle of the rope but also the high loads imposed that
>>prevent release of the rope by the tow plane. This
>>affects all types of release. You have a tow plane
>>'most likely at full power' trying to dive at a steep
>>angle and a glider virtually winch launching of the back of it - quite a
>>high loading I can assure you and one that decelerates the tow
>>plane rapidly. Secondly the upset occurs because of
>>the upwards load from the glider overcoming the maximum
>>down load able to be applied at the tow planes tailplane.
>>This effectively stalls the tailplane in an inverted
>>sense and the tow plane is actually pitched rapidly
>>nose down with very little acceleration and indeed
>>speed. If the rope breaks or releases it is actually
>>necessary to accelerate the tow plane in its nose down
>>attitude to gain sufficient speed to pull out of the
>>nose down attitude.
>>And NO, I really don't want to experience it again.
>>With reference to the original question I would strongly
>>advise the fitting of weak links to all glider tow
>>ropes regardless of the supposed breaking strength
>>of the rope used.
>>PS I do operate at both ends of the tow rope.
>>
>

[Doug Haluza]

KM wrote:
> OK now focus here Doug, the math is not in dispute. The question is
> whether a glider could exert this force while on tow.

If both aircraft are in a steep dive from a high altitude upset, and
the glider pilot panics and pulls the sitck, it certainly can. But it
really doesn't matter--using a dockline as a tow rope means it won't
break before one of the aircraft does.

> But what makes you think the dive would be "Unrecoverable" just because
> the tow plane is past its manurering speed?

The dive after an upset will be unrecoverable as long as the glider
stays attached to the towplane.

[Don Johnstone]

A very good friend of mine died several years ago in
a tug upset.
He was aero-towing I believe a Ka6 out of a wave site
when turbulence caused the glider to loose sight of
the tug at about 300ft. The glider pilot did not release
and the tug pilot could not as his inertia reel harness
had locked and he was unable to reach the release (conclusion
of the AAIB). The uspet was so bad that the tug was
hanging vertically from the glider before the rope
broke. The resulting dive was irrecoverable and the
pilot died when the tug hit the ground, the glider
pilot of course survived.

I recall fitting a new rear end to a Tiger Moth that
had been used for glider towing, 3 of the four rear
longerons were almost pulled completely apart. None
of the other Tiger Moths, which were not tugs, serviced
by the same organisation had the same problem. Co-incidentaly
the main pilot of the Tiger Moth was the pilot mentioned
above but he was not flying the Tiger in the incident.

The answer to the original poster is, yes they bl00dy
well are, and you would do well to remember it especially
if you are a tuggie.
Glider pilots always seem to survive tug upsets it's
the tuggie that gets it.

At 21:06 17 September 2006, Doug Haluza wrote:
>
>KM wrote:
>> OK now focus here Doug, the math is not in dispute.
>>The question is
>> whether a glider could exert this force while on tow.
>
>If both aircraft are in a steep dive from a high altitude
>upset, and
>the glider pilot panics and pulls the sitck, it certainly
>can. But it
>really doesn't matter--using a dockline as a tow rope
>means it won't
>break before one of the aircraft does.
>
>> But what makes you think the dive would be 'Unrecoverable'
>>just because
>> the tow plane is past its manurering speed?
>
>The dive after an upset will be unrecoverable as long
>as the glider
>stays attached to the towplane.
>
>

[RL]

This topic is worthy of discussion, so it would be nice to avoid having
it degenerate into the typical RAS morass. I've flown at commercial
operations that use large diameter "tugboat" rope. The explanation
for this is usually something like, "Oh well, we put a knot at the
end that cuts the breaking strength in half", or "We can't afford
to keep changing those little skinny ropes...".

Let's start at the top of the list: Number one - In the US, FAR
Part 91.309(3) seems crystal clear in terms of requirements - A
towline (or weaklink) is required to be not less than 80% of max glider
weight and not more than twice the max operating weight. I am not
aware of any options in the regulations to do something different. In
fact, if you are doing something different I suspect the FAA, your
insurance company, or maybe some plaintiff's attorney might be very
interested should an accident occur.

Doug and Papa3 are right in their assessment and experience that a
glider can damage a towplane. I've seen an overstress failure of a
tow hitch which broke and bent parts in the attachment assembly.
Notwithstanding excess structural loads on the empennage, the very real
danger is the tow plane running out of pitch control in the event of a
kiting incident.

I witnessed a kiting accident caused by a glider elevator misconnect.
The glider climb resembled a winch launch with the tow plane at 50-100
feet off the ground. The tow rope broke at about the same time the
towpilot had the stick on the back stop and was pitching down. This
happened so fast, had the rope not broken as it was designed to it is
very doubtful the towplane could have either released or recovered.
There would have most likely been two fatalities that day if the tow
rope had not been the correct breaking strength.

It would take a foolhardy towpilot to believe: 1) An over-strength rope
would be legal 2) An over-strength rope could not cause structural
damage to the towplane 3) The tow pilot could react quickly enough to
release in a low level kiting incident.

The tow "system" works with multiple layers of protection if the
rope is the proper specification.

Bob

[Papa3]

KM wrote:
>
> Are you telling us that the tail can only handle its own weight?You are
> using apples and oranges here because you used the FLIGHT loads of a
> sailplane and the actual weight of the tow plane.In other words, if a
> towplane can sustain 4.4Gs (In the utility category) shouldnt the tail
> of said towplane ALSO sustain 4.4Gs.
>
>
>> Happy Landings
> KMU

KM,

I think what you're missing here is the difference between the limiting
load factor on the towplane as a system (ie. the 4.4Gs) vs. the
limiting load factor on a component. Typically, the primary
load-bearing components in flight are the wing spars and the
carry-through structure; this is carrying the majority of the load.
The tail section will never sustain anything near those sorts of loads
in normal flight.

Think of this way. Suppose your towplane weights 1,500 lbs (just an
illustration). It's pretty easy to imagine it supporting 6,000 lbs of
sandbags spread along the wings (just think of those impressive ads
showing proof-testing of spars). Now, imagine piling those same
6,000 lbs of sandbags on the empennage (assuming you could find the
space to stack them :-))

Anyway, I can probably come up with some guesstimates on what the tail
section of a typical welded steel cluster could withstand, but why
bother?

P3

[Bill Daniels]

Bob's post below is clear and correct.

I would like to add, however, that at least my reading of accident reports
suggest that a fatal glider accident is more likely when the towline fails
prematurely. For that reason, I like to stay near the stronger end of the
FAR 80% - 200% range.

Actually, reading the POH for several German gliders, I note the weak link
for aerotow is specified as as exact figure. For example, the weak link for
both aero tow and winch for my Nimbus 2C is specified as 600 Kg (1323 Lbs)
or a blue Tost weak link. The tolerance is + or -10%. The US Airworthiness
Certificate specifies that the Nimbus 2C is to be flown as specified in the
Pilots Handbook (POH). Considering the possible flying weights, this ranges
between 95% - 160% which is a narrower range than specified in the FAR's.

Make me wonder if we should be using Tost weak links instead of old bits of
rope.

Bill Daniels

"RL" > wrote in message
ups.com...
> This topic is worthy of discussion, so it would be nice to avoid having
> it degenerate into the typical RAS morass. I've flown at commercial
> operations that use large diameter "tugboat" rope. The explanation
> for this is usually something like, "Oh well, we put a knot at the
> end that cuts the breaking strength in half", or "We can't afford
> to keep changing those little skinny ropes...".
>
> Let's start at the top of the list: Number one - In the US, FAR
> Part 91.309(3) seems crystal clear in terms of requirements - A
> towline (or weaklink) is required to be not less than 80% of max glider
> weight and not more than twice the max operating weight. I am not
> aware of any options in the regulations to do something different. In
> fact, if you are doing something different I suspect the FAA, your
> insurance company, or maybe some plaintiff's attorney might be very
> interested should an accident occur.
>
> Doug and Papa3 are right in their assessment and experience that a
> glider can damage a towplane. I've seen an overstress failure of a
> tow hitch which broke and bent parts in the attachment assembly.
> Notwithstanding excess structural loads on the empennage, the very real
> danger is the tow plane running out of pitch control in the event of a
> kiting incident.
>
> I witnessed a kiting accident caused by a glider elevator misconnect.
> The glider climb resembled a winch launch with the tow plane at 50-100
> feet off the ground. The tow rope broke at about the same time the
> towpilot had the stick on the back stop and was pitching down. This
> happened so fast, had the rope not broken as it was designed to it is
> very doubtful the towplane could have either released or recovered.
> There would have most likely been two fatalities that day if the tow
> rope had not been the correct breaking strength.
>
> It would take a foolhardy towpilot to believe: 1) An over-strength rope
> would be legal 2) An over-strength rope could not cause structural
> damage to the towplane 3) The tow pilot could react quickly enough to
> release in a low level kiting incident.
>
> The tow "system" works with multiple layers of protection if the
> rope is the proper specification.
>
> Bob
>

[Derek Copeland]

The tail loads imposed by a glider during a normal
aero tow are really quite small; probably less than
50lbs. The weak links are only really necessary to
cope with upset situations, or if the rope snags a
tree or power lines on the approach to landing. Obviously
they must break before the tail is damaged, or the
aircraft is slowed down enough to stall in.

Derek Copeland

At 13:36 18 September 2006, Bill Daniels wrote:
>Bob's post below is clear and correct.
>
>I would like to add, however, that at least my reading
>of accident reports
>suggest that a fatal glider accident is more likely
>when the towline fails
>prematurely. For that reason, I like to stay near
>the stronger end of the
>FAR 80% - 200% range.
>
>Actually, reading the POH for several German gliders,
>I note the weak link
>for aerotow is specified as as exact figure. For example,
>the weak link for
>both aero tow and winch for my Nimbus 2C is specified
>as 600 Kg (1323 Lbs)
>or a blue Tost weak link. The tolerance is + or -10%.
> The US Airworthiness
>Certificate specifies that the Nimbus 2C is to be flown
>as specified in the
>Pilots Handbook (POH). Considering the possible flying
>weights, this ranges
>between 95% - 160% which is a narrower range than specified
>in the FAR's.
>
>Make me wonder if we should be using Tost weak links
>instead of old bits of
>rope.
>
>Bill Daniels
>
>'RL' wrote in message
ups.com...
>> This topic is worthy of discussion, so it would be
>>nice to avoid having
>> it degenerate into the typical RAS morass. I've flown
>>at commercial
>> operations that use large diameter 'tugboat' rope.
>>The explanation
>> for this is usually something like, 'Oh well, we put
>>a knot at the
>> end that cuts the breaking strength in half', or 'We
>>can't afford
>> to keep changing those little skinny ropes...'.
>>
>> Let's start at the top of the list: Number one - In
>>the US, FAR
>> Part 91.309(3) seems crystal clear in terms of requirements
>>- A
>> towline (or weaklink) is required to be not less than
>>80% of max glider
>> weight and not more than twice the max operating weight.
>> I am not
>> aware of any options in the regulations to do something
>>different. In
>> fact, if you are doing something different I suspect
>>the FAA, your
>> insurance company, or maybe some plaintiff's attorney
>>might be very
>> interested should an accident occur.
>>
>> Doug and Papa3 are right in their assessment and experience
>>that a
>> glider can damage a towplane. I've seen an overstress
>>failure of a
>> tow hitch which broke and bent parts in the attachment
>>assembly.
>> Notwithstanding excess structural loads on the empennage,
>>the very real
>> danger is the tow plane running out of pitch control
>>in the event of a
>> kiting incident.
>>
>> I witnessed a kiting accident caused by a glider elevator
>>misconnect.
>> The glider climb resembled a winch launch with the
>>tow plane at 50-100
>> feet off the ground. The tow rope broke at about the
>>same time the
>> towpilot had the stick on the back stop and was pitching
>>down. This
>> happened so fast, had the rope not broken as it was
>>designed to it is
>> very doubtful the towplane could have either released
>>or recovered.
>> There would have most likely been two fatalities that
>>day if the tow
>> rope had not been the correct breaking strength.
>>
>> It would take a foolhardy towpilot to believe: 1)
>>An over-strength rope
>> would be legal 2) An over-strength rope could not
>>cause structural
>> damage to the towplane 3) The tow pilot could react
>>quickly enough to
>> release in a low level kiting incident.
>>
>> The tow 'system' works with multiple layers of protection
>>if the
>> rope is the proper specification.
>>
>> Bob
>>
>
>
>

[RL]

Bill, thank you for the addendum - You are right in pointing out that
within the FAA 80%-200% limitation there may be a more restrictive
specification in a glider's POH. That's why, in many cases, private
glider owners carry their own weaklink to be sure the rope doesn't
exceed the manufacturer's requirement.

I also agree that a PT3 caused by a towline failure has a history of
bad endings.... better to be toward the higher side within the limits.

Bob

[Frank Whiteley]

RL wrote:
> Bill, thank you for the addendum - You are right in pointing out that
> within the FAA 80%-200% limitation there may be a more restrictive
> specification in a glider's POH. That's why, in many cases, private
> glider owners carry their own weaklink to be sure the rope doesn't
> exceed the manufacturer's requirement.
>
> I also agree that a PT3 caused by a towline failure has a history of
> bad endings.... better to be toward the higher side within the limits.
>
> Bob

Unfortunately, here's a recent PT3.

http://tinyurl.com/gsp6s

Frank

[Bill Daniels]

"RL" > wrote in message
oups.com...
>
> Bill, thank you for the addendum - You are right in pointing out that
> within the FAA 80%-200% limitation there may be a more restrictive
> specification in a glider's POH. That's why, in many cases, private
> glider owners carry their own weaklink to be sure the rope doesn't
> exceed the manufacturer's requirement.
>
> I also agree that a PT3 caused by a towline failure has a history of
> bad endings.... better to be toward the higher side within the limits.
>
> Bob
>

Bob, as a tow operator, maybe you can answer this.

In consideration of the rule that the tug end weak link must be 25% stronger
than the glider end weak link and that the glider being towed may be
anything from a Sparrowhawk to a fully ballasted ASH 25, how do you insure
that the rope and/or tug end weak link is within the rules?

A partial answer to my own question is that towing at a FAI class contest
the glider weights may be within a narrow range but what about sports class
or just a commercial tow operation?

Bill Daniels

[Al[_1_]]

"RL" > wrote in message
oups.com...
>
> Bill, thank you for the addendum - You are right in pointing out that
> within the FAA 80%-200% limitation there may be a more restrictive
> specification in a glider's POH. That's why, in many cases, private
> glider owners carry their own weaklink to be sure the rope doesn't
> exceed the manufacturer's requirement.
>
> I also agree that a PT3 caused by a towline failure has a history of
> bad endings.... better to be toward the higher side within the limits.
>
> Bob
>
Uh, "PT3" ?

I know what a PT6 is.

Al G

[Jim Vincent]

Premature Termination of The Tow.

Tom Knauff has many examples of causes and preventive measures here:
http://www.eglider.org/newsarticles/aerotowemergencies.htm

Some
"Al" > wrote in message
...
>

>
> I know what a PT6 is.
>
> Al G
>
>

[Derek Copeland]

At 20:18 18 September 2006, Al wrote:
>>
>Uh, 'PT3' ?
>
>I know what a PT6 is.
>
Premature Termination of The Tow (PTTT = PT3)

Derek C

[Al[_1_]]

"Jim Vincent" > wrote in message
...
> Premature Termination of The Tow.
>
> Tom Knauff has many examples of causes and preventive measures here:
> http://www.eglider.org/newsarticles/aerotowemergencies.htm
>
> Some
> "Al" > wrote in message
> ...
>>
>
>>
>> I know what a PT6 is.
>>
>> Al G
>>
>>
Thanks.

Al G