Schweizer Tow Hook Installation

I'm looking for a used Schweizer Release Handle with its Mounting Support Bracket for my Super Cub. A previous owner installed the Schweizer Tow Hook and Mounting Hardware above the tail wheel but was using a homemade release handle. Since I want to occasionally tow glider friends, and they tow me (nothing commerical), I need to get this system certified rather than get rid of it. Once I get all the proper components and documentation, I'll have to go the 337 route with my IA.

But here is maybe some trivia I found out after lots of phone calls for those who may be interested. Later PA-18 Airplane Flight Manuals had as an option in the original equipment list a "Tow Hook Installation per PAC Dwg. #60721." After talking with the folks at New Piper Aircraft, this Dwg. actually referred to the complete Schweizer Tow Hook Installation Kit under Schweizer STC1-349 for PA-18 and 18As. This Kit is installed per Schweizer Drawing #3415D which I obtained from Schweizer for $15. Schweizer apparently no longer has the kits and they will not be making the tow hook apparently because of a policy of the new company that bought Schweizer. However, I see that Wag Aero has the kit for sale in their online catalog. Schweizer will sell the STC if it is a replacement but that is not the case for me.

Anyone have other related information on this installation?

Help in finding a Schweizer handle with its support bracket is appreciated.

Jim

OldCuby: A couple thoughts.

In the context of your original post, at one point Wag Aero purported to have the kit, so you might try them for the release handle. At one point, Bellanca/subsequently American Champion used essentially a modified Schweizer kit on their 7GC/8GC series, including what seemed the same floor release lever, so give them a ping.

Likely, there are some other Supercub tow kits which have been removed for various reasons; maybe some others can post back.

Now the question: What is your intent with this kit? Occasionally towing gliders with experienced pilots? Towing mixed group of glider club, including inexperienced students? Towing banners? Nifty tail tiedown for handpropping? or just making your existing stuff legal.

Personally, I ( and most of the experienced Supercub Tuggies I know) dislike the floor-mounted tow release bracket. Here's why: It requires you to bend down, and with your left hand, somehow find the knob by brail (I used to require a blindfold test before I'd check someone out), and the stock Schweizer doesn't have great mechanical advantage. Yeah, I know, it's 'approved data' per 43.13, and on their STC.

All of this monkey motion tends to happen when the Tuggie has an inexperienced glider pilot kiting up, you've just hit the control stop, you're pointed straight down, and the release force is beyond what a human can do.

This is most likely to happen on any glider towing from a centre-of-gravity (belly) tow hook, which is probably 85% of the 'glass fleet in the US. The UK and some of the rest of Europe is starting take a jaundiced eye on this practice.

You get the idea, not a very good setup (and yes, I've done "a few thousand" tows with that very setup, including quite a few of them on the "other" end of the rope...).

With the Schweizer bracket and hook, a far better setup is the "Dave Johnson" release lever, which is a much longer handle mounted to the lower instrument panel tube, on the left side. Advantage, it's less than a foot from your throttle hand, you keep your head/body up, and much better mechanical advantage. Quicker, more intuitive reaction. More likely to work if you need it in a hurry.

Anyone flying one of those nifty ex-Dave Johnson 180 'Cubs with a Form 337 they'd like to share for that installation?

The Banner Pirates pretty much use variations of the Schweizer, with up to three releases, but they don't have to put up with the 'kiting' issue.

A FAR better setup if you're seriously towing gliders: The Tost release and bracket sold in this country by Tim Mara at www.wingsandwheels.com. VERY spendy (~$1600 parts, plus install $, plus paperwork$). They hold the equivalent of European STC, which SHOULD be "approved data" for a 337 in USA, but most FAA people totally ignorant about this.

The advantage of the Tost is it has the same release force, regardless of glider pitch angle; on a Schweizer, the higher the angle, the higher the Tug release force; at some point it is IMPOSSIBLE to release. Had two friends killed this way.

On the Tost, you still need to figure out a reasonable release handle, which should be close to the throttle hand, NOT on the floor. In service, I've heard rumours of corrosion on the Tost bowden cable, due either to moisture or inactivity, so watch for that. The Tost requires a different tow ring setup, which is a $30 part in lieu of the $20 certified Schweizer part. PLEASE don't even think about using farmstore/horsering grade hardware if peoples' lives might be at sake!

Sorry for the windy reply, this is just the CliffsNotes condensed answer, but the real answer depends on how you intend to use this setup.

Good luck, please feel free to PM me for expansion on this outline.

Thanks. Cubscout

Hey old cuby,there is one on ebay .type in pa-18 under buy now.Looks like some bids already though good luck.P.S. I took one out of a maule years ago,i dont know what i did with it but will look.I have lived with too many women to keep track of all my stuff.I even lost a couple planes when i crashed my relationships.

pzink,
Thanks for the tip. Looks like the whole thing including hooks for banner towing types!

As I told Cubscout in a PM, I only plan on towing friends who I know and have one of them tow me in my glider. I'm aware of the pitfalls for tow pilots and Cubscout has good advice for those who tow gliders especially when the tow pilot does not know much about who he is towing. Professional tow pilots all should be using the Tost setup.

I also of course want all my paper work to be up to date. I just bought this SC last Nov 04 and the purpose is for fun and I've never had so much fun in a powered plane. Soaring gliders has its thrills too!

Jim

When we used to tow in Europe with our L21b's there was a spring loaded hook mounted at the tailwheel hookup (sandwiched between the fuselage tubes and the springs of the tailwheel basically) and the release was done with a cable that was going over a roller mounted underneath the tube by the rear wing mount and the looped/fixed to the tube by the front wing mount. In order to release you took your left (throttle) hand and reached up towards the skylight and just pulled on the release cable that hang there looped on your left side just underneath the skylight. Pretty good setup and you did not have to look down. not sure if I still have pictures of this.

using the Schweizer tow hock pulling gliders if they get to high above you you will not be able to release so be careful on who you let hock up

One on Ebay now...........

http://cgi.ebay.com/ebaymotors/ws/e...=4545296090&rd=1&sspagename=STRK:MEWA:IT&rd=1

tow hook

I've got one I had on my 150 T-Craft. It's the handle, cable, hook assy. I'm looking for a 3200 tailwheel for a project. [/i]

skysigns said:

using the Schweizer tow hock pulling gliders if they get to high above you you will not be able to release so be careful on who you let hock up

Click to expand...

Those Schweizer tow hooks seem dangerous!



I have only seen the Tost releases and in Europe they are definitely the most common. I have never experienced or heard about release problems with those, neither in tow nor in winch launch.

And I can promise you that I made some really high tows during my first hours of gliding...

tOW HOOKS

F
rom Chris Rollings, Former Chief Instructor, Booker Gliding Club, UK
Aerotow ?Upset? Accidents.
R
ecent discussions concerning the fatal aero-towing accident at the US Air Force Academy last
year, made me think that it was possible worth giving wider publicity to the information which I
provided to the investigators of that accident, regarding the experiments we conducted some
years back into the nature of these accidents.
W
hilst I was Chief Instructor at Booker Gliding Club, we conducted two series of tests on the
phenomenon variously referred to as ?Kiting?, ?Winch Launching behind the Tow-Plane? and
?Sling-Shot Accident?, one in 1978 and one in 1982; my memory of them is quite vivid.
Airplanes used were a Beagle Terrier (a side by side, two place, high wing, tail-dragger), fitted
with an Ottfur Glider hook for towing (very similar to the Tost hook, dissimilar to the Schweitzer
hook) with a 160 hp Lycoming engine for the first series of tests, and for the second series a
PA18-180 with a Schweitzer hook. Gliders used were a Schleicher Ka 8b and ASK 13. Tow
rope initially used was a heavy (4000 lb) rope with a thinner rope weak link at the glider end
(nominally 900 lb, but a well worn specimen could break at as little as 200 ? 300 lbs ? laboratory
tests, not opinion), the second series of test used the same heavy duty rope with ?Mity? links at
each end, 1100 lbs at the Tow-Plane end and 900 lbs at the Glider end ? these links use metal
shear pins, one under load and a second unloaded, which takes over if the first one fails. This
eliminates failure due to fatigue and means that the links always fail at close to their nominal
load even after some time in service ? again laboratory tested, not just subjective opinion. Rope
length was around 180 feet in all cases.
I was the Glider Pilot on all the tests, Tow-Plane Pilot was Verdun Luck (then my deputy Chief
Instructor) for the first series of tests and Brian Spreckley (then Manager of Booker GC) for the
second. The object of the tests was to try to reproduce the ?Kiting? under controlled
circumstances, with a view to developing a Tow-Plane release mechanism that would
automatically release the glider if it got dangerously high above the Tow-Plane. All tests were
conducted at about 4000 feet agl.
First test: Terrier Tow-Plane and ASK 13 on nose-hook. At about 4000 feet I took the glider
progressively higher above the tow-plane, eventually reached about 100 feet above tow-plane
(i.e. rope angle more than 45 degrees above horizontal). At about this point, the tow pilot, who
had been using progressively more back stick, ran out of back stick and the Tow-Plane began to
pitch nose down but not excessively violently. I released at that point. It took a very positive
control input on my part to achieve the displacement, we both felt it was something unlikely to
occur accidentally, even with an inexperienced glider pilot, and there was plenty of time for
either party to release if it did occur.
Second test: Terrier Tow-Plane and ASK 13 on C of G hook. I pitched the glider about 25 ? 30
degrees nose up ? the weak link broke immediately! Tow pilot reported a sharp jerk, but no
significant change to flight path.
T
hird test: Terrier Tow-Plane, K 8b on C of G hook. I pitched the glider about 25 degrees nose
up. The glider continued to pitch up fairly rapidly (as at the start of a winch launch) and
substantial forward movement of the stick only slightly slowed the rate of pitch. The glider
achieved about 45 degrees nose up, speed increased rapidly from 55 knots to about 75 knots and
the glider was pulled back towards level flight (again as at the top of a winch launch). I released
at that point. The entire sequence of events occupied a VERY short period of time (subsequently
measured as 2 - 3 seconds). The Tow Pilot reported a marked deceleration and start of pitching
down which he attempted to contain by moving the stick back, this was followed immediately by
a very rapid pitch down accompanied by significant negative ?G?. The tow-plane finished up
about 70 degrees nose down and took about 400 feet to recover to level flight. We both found
the experience alarming, even undertaken deliberately at 4000 feet. Our conclusion was that the
combination of the initial pitch down and the upward deflection of the elevator caused the
horizontal stabilizer/elevator combination to stall and the abrupt removal of the down-force it
provided caused the subsequent very rapid pitch-down and negative ?G?.
O
ur first conclusion was that, in the event of this sequence occurring accidentally as a
result of an inadvertent pitch up by the glider pilot, there was effectively no chance that
either the glider pilot or tow-pilot would recognise the problem and pull the release in the
available time.
Attempts to produce a tow-plane hook that would release automatically were unsuccessful for
reasons that became apparent later.
T
hese tests were repeated a few years later with a PA18 ? 180 as the tow-plane, Brian Spreckley
flying it. The third test described above was repeated and photographed from a chase plane
using a 35 mm motor drive camera on automatic (this took a frame every half second ? video
camcorders of small size were not readily available then). The photo sequence started with the
glider in a slightly low normal tow position and starting to pitch up, the second frame has the
glider about 30 degrees nose up and about 20 feet higher than previously in the third frame it is
about 45 degrees nose up and has gained another 30 feet or so, the tow-plane is already starting
to pitch down, in the fourth frame the glider is about 100 feet higher than its original position and
the climb is starting to shallow, the tow-plane is about 50 degrees nose down, the final frame
shows the tow-plane about 70 degrees nose down and the glider almost back in level flight ,
almost directly above it (that was about the point that I pulled the release).
Sufficiently alarmed by events, Brian Spreckley had been trying to pull the release in the
tow-plane earlier and found that it would not operate until my releasing at the glider end
removed the tension from the rope. Subsequent tests on the ground showed that the
Schweitzer hook fitted to the tow-plane, whilst perfectly satisfactory under normal loads,
was jammed solid by the frictional loads when subject to a pull of around 700 lbs with a
slight upwards component ? not something that a normal pre-flight check would reveal.
We solved that problem on our tow-planes by replacing the bolt that the hook latches onto with a
small roller bearing. So far as I know, no one has tested the Schweitzer hook as fitted to a glider,
but I would not be surprised if it exhibited the same characteristics at high loads.
T
he photo sequence also showed that at no time was the glider at an angle greater than 30
degrees above the tow-plane?s centre-line. However, of course once the glider has pitched up,
considerable extra lift is generated by the wings and that extra lift provides extra load on the
rope. With a large, heavy glider it is easy to exceed weak link breaking strains and with a lightweight
machine the tension can easily rise to 700 lbs or so. With that much load on the rope,
quite a small upward angle provides enough of a vertical component to produce the results
described.
T
hat of course is the reason that attempts to produce a hook that released if an certain angle was
exceeded were unsuccessful. The quite small angle needed to trigger the ?Kiting? when the
glider is pitched significantly nose-up is not much greater than the amount of out of position
commonly experienced in turbulent conditions. We did build an experimental hook and tried it,
but, set to an angle that prevented ?Kiting? it occasionally dumped an innocent glider in
turbulence, and set to an angle that prevented that, it didn?t prevent the ?Kiting?. What was
needed was a hook that responded to the vertical component of the load, not the angle at which it
was applied, and that problem we decided was beyond us (at least in a form robust and foolproof
enough to be attached to the rear end of a tow-plane).
Our conclusions for preventing ?Kiting? were:
Don?t aerotow gliders, especially lightweight, low wing-loading gliders on C of G hooks
intended for winch launching (I think the JAR 22 requirement for nose hooks to be fitted to
new gliders for aerotowing was at least in part a result of these tests). I didn?t do any
experiments with the 2-33 along those lines, so I?m not sure how to categorise its hook position
nor could I predict how ?well?? it would ?Kite?. If you feel tempted to experiment, bear in mind
that you are effectively going to wind up doing a winch launch at way above the maximum
winch launch speed, and most of the 2-33?s around are very old and tired.
Don?t use short ropes. The speed at which things happen varies directly with the length of the
rope.
Don?t let inexperienced pilots fly at anywhere near aft C of G.
Don?t let inexperienced pilots fly solo in turbulent conditions.

Release Handle design

Any update on this request, I am looking for similar....

OldCuby said:

I'm looking for a used Schweizer Release Handle with its Mounting Support Bracket for my Super Cub. A previous owner installed the Schweizer Tow Hook and Mounting Hardware above the tail wheel but was using a homemade release handle. Since I want to occasionally tow glider friends, and they tow me (nothing commerical), I need to get this system certified rather than get rid of it. Once I get all the proper components and documentation, I'll have to go the 337 route with my IA.

But here is maybe some trivia I found out after lots of phone calls for those who may be interested. Later PA-18 Airplane Flight Manuals had as an option in the original equipment list a "Tow Hook Installation per PAC Dwg. #60721." After talking with the folks at New Piper Aircraft, this Dwg. actually referred to the complete Schweizer Tow Hook Installation Kit under Schweizer STC1-349 for PA-18 and 18As. This Kit is installed per Schweizer Drawing #3415D which I obtained from Schweizer for $15. Schweizer apparently no longer has the kits and they will not be making the tow hook apparently because of a policy of the new company that bought Schweizer. However, I see that Wag Aero has the kit for sale in their online catalog. Schweizer will sell the STC if it is a replacement but that is not the case for me.

Anyone have other related information on this installation?

Help in finding a Schweizer handle with its support bracket is appreciated.

Jim

Click to expand...

If you're thinking about serious glider towing you should call these people and consider a Tost tow hitch system.

https://wingsandwheels.com/e-series-tow-release.html

It can save your skin. As for the release handles, we don't use that system for towing large banners. It's a much longer discussion, but I absolutely won't use the handle system - that;s from 65 years in the banner business The quick explanation is there isn't enough slack to ensure the banner doesn't release by accident, or if there is enough slack, there may not be enough throw in the handle to release at high loads. We dead end the cable overhead. That's the only legal method in Europe where they do a lot of glider towing. Give it a think. Otherwise build your own system and use AC43-13. It's approved data. Costs is low.

While the Tost hook is a good solution, the easier solution is low tow, much safer for all concerned. Over 2000 toes in the front and about 500 in the back done from low tow. Never a rope break, no chance of kiteing.

That said, AC43.13-2B has approved data for your Schweizer tow hook and how to make a release lever.

The Cub I used to use for towing had the lever placed just aft of your left leg. For an immediate release, all you had to do was move your left leg back and actuate the lever with your leg. You could also easily reach it with your left hand.

The TriPacer I had with 4 banner releases just had 3” rings on the end of the cables under the right seat. Just grab the ring and pull to release.


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If still needing release handles I have a few setting on the shelve