Tow Release Location

[Ib Jensen]

I am currently building an older Multiplex ASW-22 kit. The tow release is shown mounted on the right side of the nose two inches back from the tip. The mechanism is a simple rod in tube type with a side notch, so a slot would be cut in the nose for the tow line. Being new to airo-tow and this being my first large scale glider I was wondering what the advantages and disadvantages of the to release locations might be.

My thoughts are:
1. Side location: Less chance of dirt entering the mechanism.
2. Nose mount: Scale appearance, center line force vector.
3. Bottom Location: Scale appearance.

My experience with full size gliders of several vintages has included CG side hooks with Y harness, CG at wheel well, under the nose and in the nose tip.

Before I cut the nose to install anything I would appreciate comments from the experienced pilots here.

All were designed so that if the glider ever over flew the tow plane, or had to land with the tow line attached due to tow release failure, a backward tension on the line would cause the release to open. I have not seen any model tow release mechanism with this feature, but it could be done.

Ib

[fabrice]

Hi Ib,
I had the same tow release system on my MPX Flamingo Contest and was pretty happy with it: simple, reliable, cheap.
At some point I was even using the ruder servo to release the tow line and never had any problem although the release looked funny. A good friend decided to instal the same system on his ~2.2 m (Djinn) sailplane and never experienced any problem to release even when I was flying the tow plane not really according text books: under powered 6.5 cc engine with no landing gear... hand launched tow… Big thrill every time but a lot of fun :D :D Of course the Flamingo is smaller (2.8m for 2.3 kg) than your ASW-22 but with a stiffer stainless steel rod smoothed at the end, tube guides on both sides of the opening slit and a nice loop on the tow line plus some lubricant once in a while and it will be just fine.

Fabrice

[kevin kavaney]

Ib.. having used both a nose mounted release and the type suggested by multiplex, I have to say the side mounted system is a whole lot easier to use in the field.. no need to pick up the glider to peer down the tube, just watch the wire close up around the weak link line clearly in sight on the side of the glider.
kevin kavaney

[bie]

Ib,

all the described tow-release-options do work!

I checked them all out with various semi-scales and non-scale-gliders and never had a problem during aero-tow with the location of the tow-release-mechanisms, be it installed in the nose (like in my L-213A, Ventus2c), at the side (Pilatus-B4) or on the bottom (LF-107 Lunak).

[scalesoar]

The only commercial release that realy is a pain and does not work so well is the old wanticheck type ball and socket with spring. too many parts to loose.

The nose release with a cam wheel is the most commonly used type on larger over 4 meter planes, and you do not have to peer down the release to engage, simply pinch the loop, insert relative to the axis of the cam and switch closed. It sometimes takes a try or two until you get used to it.
The cable and wire side mount is fine as well. but not so scale on a modern ship design if that is a factor for you.
Pick your poison, but put a powerful servo on your release in case of a bad situation with tension on the line.

JD

[Ib Jensen]

Thanks for the nice pictures. It appears that in the above cam type of release the servo is required to hold the cam closed. This would seem to be the safest type possible since high tension would tend to help the servo open the cam. The wire slide type would be hindered by friction of the loop around the release wire and require higher torque.
Am I seeing this correctly?

Ib

[scalesoar]

Thanks for the nice pictures. It appears that in the above cam type of release the servo is required to hold the cam closed. This would seem to be the safest type possible since high tension would tend to help the servo open the cam. The wire slide type would be hindered by friction of the loop around the release wire and require higher torque.
Am I seeing this correctly?

Ib

Ib:
Almost...
It is easy to over analyze this thing, the fact remains for normal conditions, (an easy tow up and release), all release types work fine. (especially on smaller lighter ships).
What we sometimes forget is that often you need to release in an emergency mode when there is quite a bit of tension on the line. This is what separates a good release from an average one. Again, the size and weight of the sailplane enters into the picture.

The cam type does not rely on servo power at full closed. The idea is to have no load on the servo at full engagement. The advantage of the cam type is that the inclined cam facilitates release the second the servo moves off center position. It's all downhill.
The ramp and cross bar type of release, (multiplex et al) while simple and clever, requires more servo power to disengage if there is a problem, and you, for whatever reason find yourself dangling from the tow line. It puts a lot of pressure on the wire causing it to be more difficult to release the more tension is on the line.
I have used all types of releases and have found the above to be the case from actual experience. I have 4.3 meter broken up Fox wings leaning up in a corner of my shop to remind me :-} It was a spectacular comedy of errors resulting in a 100 mph straight in approach. The pilot was never recovered at the crash site, his head was in the rear of the fuse, and his body was 18" underground buried with the broken tow line still attached to the release.

This was not intended to be a scare tactic, and for smaller planes under 4 meters there is little practicle difference. The most single important factor is to have excess servo power on any release you install, regardless of type.

JD