Fire in the hole
 

I have a wren supersport that I have in a plane with a jetpipe. The engine is full autostart and it is starting the prolem I have is as follows:

1. Turbine spins up and gas valve opens. The gas only ignites when the spinning has almost stopped or on the second spin.

2. This results in a fuz full of gas and when it pops I have a gas flame in the fuz which burns before the turbine spins up and gets going

3. Once it spins up again all is well and she runs fine.

4. I will replace the glow plug and try controlling the gas by hand as a first try.

Anyone have any ideas

Thanks

Bert

RE: Fire in the hole
 

Too much propane. Try using a pressure regulated valve on your propane bottle. Dreamworks sells a good one.

RE: Fire in the hole
 

On most, if not all the gas start turbines I have had. I only open the propane a little tell the gas ignites, then open up a few turns more. You have way to much propane going to the turbine when trying to start.

RE: Fire in the hole
 

Agreed about too much gas. Also check that you have the coils sticking far enough out of the plug and check that it is bright enough.

I'm guessing that a very bright glow and only a tiny breath of gas will solve the problem.

RE: Fire in the hole
 

Thanks chaps I am thinking along the same lines

RE: Fire in the hole
 

Bertie,

Above responses are spot on!!

RE: Fire in the hole
 

I have the supplied gas regulator connected to the gas valve on the out side of the valve. How many turnes out is the standare setting for this screw

Bert

RE: Fire in the hole
 

Didn't know you had a SS Dennis Bigplumbs. What aeroplane is that in?

RE: Fire in the hole
 

I start it at 1/4 then after ing. I open to two turns

RE: Fire in the hole
 

I believe the valve on your propane bottle controls flow only and does not regulate pressure. It is very easy to put too much propane in. YOu will need to just crack open the valve until it ignites then open it up further.

RE: Fire in the hole
 

are you starting on propane, or mixed gas? Propane has a much higher presure, and you need a regulating valve (as Gary mentioned). Mixed gas you can get away with a screw valve.......

RE: Fire in the hole
 

In the UK we almost exclusively use mixed gas and not propane.

It sounds to me like Bertie is talking about the onboard adjustable valve (and not an offboard gas bottle valve). Once set, this is a fixed position and shouldn't need to be opened and closed for engine start.

I don't know the standard position but there are 2 ways I would go about setting it.

[ul][*] Close the valve completely and then open it a small amount (maybe 1/4 turn). Try a start and see what happens. If it doesn't start then open it a bit more and try again.
[*] Or, if you can get to the valve easily, bypass the solenoid and plug your gas bottle into the 'in' port on the screw valve. Put a tube on the 'out' port and direct it somewere that you can feel the gas escaping (your hand or, if you're careful, your face). Close the onboard screw valve completely and open the gas tap on your offboard tank fully. Open the onboard screw valve until you can JUST feel gas coming out of the pipe. Reconnect everything, try a start and then fine tune from there.
[/ul]

RE: Fire in the hole
 

Many thanks for all your help. I have several things I can now try. I have lined the area of the fuz that could get burned with litho plate to protect the servo wires above so I am good to go with a few experiments. First of all I am going to change the glow plug as I think this might be old and maybe not have the element pulled out enough.

Sicklick you are correct I was talking about the on board regulating valve which one set is usually fixed in position. And yes I am using mixed gas

Bert

RE: Fire in the hole
 

My SS had exactly the same problem.

After a repair & bearing change it no longer does this, it just seems to accelerate in the start with no pause at all now.

I don't know if it was an ECU parameter change or just more free spinning bearings so that the engine does not slow down as much after the initial, first spin of the starter.

Wren may be able to advise. - John.

RE: Fire in the hole
 

Typically , the propane needle valve is set to 1.5 turns. Do make sure this valve is installed after the solenoid. As for the issue of the motor spinning down prior to ignition, once you get the flow correct, some of this will go away. However, if you have the Fadec program and the data cable, you can go in to the autostart function and set the minimum rpm to connect the starter and rpm before ignition parameters to improve the start.
First parameter is starter voltage , and this should be 39%
Second parameter can be set to 2000 rpm
Third parameter set to 3000 rpm

Hope this helps!