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Shut-off for F2D-Combat
Valves with no moving parts!

Cool Shut-off - Hot Shut-off - Nitro Shut-off

Any electronic shut-off will need some kind of actuator to stop the engine.
This actuator should be able to react on an electrical signal from the electronic circuit and it must be very robust.
The environment is very rough on a combat model in action: vibrations, high temperature, water, mud, dust, high G-forces in maneuveres, even higher G-forces in hard landings or mid air collisions and, worst off all, pitmen working under stress.

What we ultimate are looking for is an electric valve that doesn't need cleaning, has a low weight, a low price and dosen't get blocked by dirt or oil.
A simple valve with no moving parts would be nice.
Does a valve with no moving parts sound impossible to you?
To me it sounds just right, so let's se how it can be done.

Here is three wild idea's for a super robust electrical valve with no moving parts: Cool Shut-off, Hot Shut-off and Nitro Shut-off


Cool Shut-off

In this first example we will use low temperature to restrict the fuel flow.
This flow resistance of the fuel will vary with the viscosity. If we lower the temperature the viscosity of the fuel will rise. With a very low temperature the viscosity will be so high that we get a very low flow. We don't necessarily need to completely stop the flow; a reduction that will kill the engine is enough.

An electronic device called a Peltier element will cool down on one side and heat up on the other side when it is connected to a power supply. A typical Peltier device is here shown on top of a Fora engine.

Fora and Peltier device

Fora with a Peltier element

The fuel should be lead through a tube with a small opening on the cold side of the Peltiere element.
The Pelitere element will need a lot of cooling so it must be fitted with some sort of cooling plate. An engine bearing could be an effective cooling plate. In a computer model it would look like this.

Fora and Peltier device

CAD model of a Fora with a Peltier shut-off
More 3D engines

A little research on Peltier elements and the heat capacity of fuel shows that the electric power needed to cool down the fuel will be a problem and this type of device will probably not be able to react fast enough for a shut-off in combat.


Hot Shut-off

- or the "Molotov shut-off"

The next idear for a shut-off valve with no moving parts is to block the flow by creating a gas bubble in the fuel line.
A heating element in the fuel line shuld be able to boil some fuel and create a gas bubble. If the boiling can continue for a couple of seconds it should be enough to kill the engine.
The pressure from the boiling fuel will press the fuel back in the latex tube and press some of gas thrugh the needle valve. Only gas will be able to pass the heater.

At athmospheric pressure Methanol will boil at 65 °C and Nitromethane at 100 °C but with the pressure from the latex tube the boiling temperature for the Methanol will probably be around 80 °C. Castor oil will boil at a temperature higher than 313 °C

To test the idea I built a simple system with some brass tube and a piano spring. I sat up an experiment with some fuel in a latex tube and an old needle valve. As I turned up the power the heater started to boil the fuel and the flow was stopped. The power needed to block the fuel flow was approximately 20 Watts.

This experiment suddenly became more thrilling than expected when I realized that the piano spring was glowing inside the fuel line!
This device has the potential to transform a fly-away model into a free flying Molotov cocktail!

Molotov-ShutoffHeating element

A fuel line with an electric boiler. The piano wire spring was burned in the first test!

This winther I took the experiment to the flying field and gave it a try on a real engine.
You can see the result on this video clip.

Anders Kudst with a Molotov-cocktail

A test of the the "Moloto shut-off" on a running engine. See the video.

To improve the system I also made a smaller heater with the steel tube from a syringe needle. I never tested this device but with the smaller mass it should be able to block the flow with less power than the piano spring version.

Next generation

A smaller heater with a steel tube from a syringe needle

The power for the heater could come from a Supercapacitor.
A MOSFET transistor in a TO-220 package could be used to regulate the heating. The power loss in the transistor will probably be so big that the transistor can be used as fuel heater. If the transistor comes with an internal heat protection the system could be made just as a simple short circuit!

Supercapacitor from Wima and Heter and the TO-220 packages


Nitro Shut-off

An even wilder idea for a valve with no moving parts could be to combust some of the fuel in the fuel line to generate a gas bubble.

A spark or a hot catalysator in the fuel line might crack some of the Nitromethane and give free oxygen. This oxygen could feed a small combustion of the fuel and result in a gas bubble in the fuel line.

Nitromethane could be decomposed by Pyrolysis or Thermolysis in the high tempature of the spark
I'm not strong in chemistry and don't know if this is possible but the fuel could be an alternative source for energy to activate a shut-off valve.


- I actually don't think that any off these ideas will be a practical solution for a shut-off valve, but it is my hope they can inspire others pilots to come up with new ideas.

Henning Forbech


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