Below is some technical information for this first generation shut-off system for F2D-combat.
Hopefully it can help somebody else to develop other types of shut-off systems.
You are always welcome to contact me if you need more information.
- Normal line tension:
- The theoretical line tension for a 450 g combat model flying at 42 m/s is 45 N.
- 42 m/s is equal to 150 km/h or 24.0 sek. for 10 laps. 45 N is equivalent to the force needed to lift 4.5 kg
- This is a theoretical value. I have not yet been able to measure the line tension for a flying model
- Minimum line tension:
- The minimum line tension to keep the fuel line open on this system is 15-17 N
- Theoretically, a 450 g model would just be able to keep the fuel line open at 24 m/s (85 km/h).
- It has been possible to fly with this adjustment in very strong wind without any problems.
- At the World Cup in Karlskoga, Sweden, I even managed to make small loops up against a strong wind without any problems.
- In Bitterfeld I try to fly half a model after a mid air collision, but after some time the shut-off killed the engine (video).
- Activation: More info here
- The line tension that activate the shutoff system is 25-35 N
- At this line tension a small spring is released and the shut-off system becomes active.
- At a normal start I feel a click from this activation in the handle after one quater of a lap.
In the next generation of the system I will go for a higher value. Probably 60-70 N.
The pilot will then have to give a hard pull at the lines to activate the shut-off, but it would make it much easier for the mechanics to handle the models.
- The total extra weight of this system is 20 g
- o This also includes the extra fuel line and the modifications to the model.
- Known problems:
- In some situations it is not possible to fly with a shut-off system activated by line tension.
- If your model gets so damaged by a mid air collision that it can not obtain enough flying speed to generate the necessary line tension.
- You can not fly a model with a very poor engine performance. Bad fuel adjustment, damaged prop, etc.
- Normally it is possible to fly a half model. The reduced speed and weight will make it impossible with a shut-off
- It takes some time for the mechanics and the pilot to get used to a starting procedure where the lines must not be pulled.
- The shut-off system might cause some confusion when the mechanic removes or puts on the streamer.
- Hard landings in an inverted flight might damage the shut-off system.
I have done some "tests landings" in these competitions without any problems.
- General problems:
- It is very easy to block the system so it will not stop the engine. This would prevent mall functions of the shut-off in competitions (but also block the function in the case of a fly away).
- It is not possible to check if the system is active during the flight. It would only be possible to demonstrate the function by cutting the lines and that is far too dangerous.