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Stop at will for line tension shut-off
Rebuild your old shut-off for forced stop
First published: 8/12 2012 - Last update: 26/12 2012

Line tension shut-off with stop@will

by Henning Forbech

I have been using my line tension shut-off for the last four seasons. They have proven reliable and easy for the mechanics to operate. From next year pilots will have to stop there engines after the match have ended. I would like to continue to use my line tension shut-off systems so I developed a simple "stop swing arm" that makes it possible to stop the engine at will.

The design described here was only a simple setup to test the concept. With more experiments and testing it should be possible to develop a very simple add-on to update existing shut-off systems. If old line tension shut-off systems could be refurbished with a "stop swing arm" it would be easy for many pilots to be ready for the 2013 rules.

Here is some photos and a video showing the function of the stop swing arm
  Line tension shut-off:

The "stop swing arm" is mounted on the top of the bolt that fixes the shut-off to the model. The stop swing arm is free to rotate. The extended pies of thread on the bolt act as a bearing for the quit heavy stop swing arm. A spring loaded steel ball click on to the base of the shut-off.

With a hard pull on the lines this spring lock will release the stop swing arm. The spring load on the ball is adjustable. This is just an easy way to adjust the force it takes to release the stop swing arm. In the future this lock can be replaced by a simple spring.

Ready to take-off. The stop swing arm is locked and the activation swing arm is set to keep the fuel line open

Right after take-off the line tension will move the bellcrak enought to release the activation swingarm

During normal flight the fule line is open and the activation swing arm have been released

If the model fly-away the bellcranck spring will pinch off the fule line

It the pilot give a hard pull to the lines during normal flight the stop swingarm will be released. The bellcranck spring will be in a position that block the movement of the stop swing arm

If the pilot release the line tension for a short moment the bellcrank spring will pinch off the fuel line. In this situation the stop swing arm can swing in behind the bellcrank spring and block it from reopen when the line tension comes back

Here is a video clip with a demonstration of the stop swing arm. You can also see the very first flight with the system.

It takes two steps to stop the engine:
First a hard pull on the lines to activate the Stop Swing Arm.
Next should be a moment of low line tension.
On the video I try to give the model some line but it is not working. Then I fly small loops into the wind and finally loosing enough line tension to activate the shut-off. Once the shut-off is closed the stop swing arm prevents it from reopen.

A model equipped with the stop@will shut-off. After a couple of test flight the rebuild shut-off had demonstrated its ability to stop the engine at the pilots will. The mid-air collision wasn't planed (killed two engines) but now the refurbished shut-off have also passed the shock test.

I have no intension to manufacture or sell this device. You are free to use this concept - the design is freeware.
You are welcome to manufacture and sell "stop swing arms" for retro fitting old line tension shut-off systems.

Rebuild your old ViKo shut-off:

Some years back ViKo Models sold a lot of these line tension shut-off systems.
By adding stop swing arms to these old systems they could be used to stop the engine at the pilots will.

More info on the ViKo shut-off

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