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Speed,Combat,Scale,Racing => Speed Talk => Topic started by: Bob Reeves on July 05, 2010, 10:05:27 AM
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Tried to get the DynaJet in the air over the weekend but everytime it got airborne it would quit. It would start and run on the ground just fine, roll out and lift off but almost as soon as it broke ground it would flame out. Wondering if anyone with expierence with these things could give us a few hints on what might be the problem.
This is a photo of the airplane, was a kit one of our members had. Already know it leaves a little to be desired but it is what we have to work with and it's just for fun and to make noise. Wasn't much room for a fuel tank, I cut the back of a Fox profile tank down to clear the engine and replaced the 1/8 tubes with the next size up.
Help.....
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Hi Bob,
Please fill me in on the following:
What fuel? What metering orifice? Any baffles in your fuel tank? Is starting quick and easy, or is there a lot of popping?
Will Stewart
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Thanks Will..
Starts fairly easy, discovered it starts easier by lifting the nose but no popping just go or no-go. Using regular unleaded gas right from the pump. Am pretty sure I didn't put the baffle back in when I reworked the tank. Not sure what orifice, whatever one comes with it. From my limited research it seems as though the only way to get a different size is to make it. Remember going to the DynaJet web site and seeing them listed as no longer available.
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Bob,
Gasoline has a narrow flammibility range. The gasoline of today is often spiked with ethanol or MTBE or whatever which would require a slightly larger metering jet than the #4 you probably have installed.
I would try Coleman fuel (like used in camp lanterns and stoves). There may also be corrosion in the brass metering orifice which would reduce the ID and roughen it, reducing flow. I'd try to ream the orifice, without removing any metal. If it still cuts, try enlarging the orfice by a couple of thou.
As an alternative, methanol with 20% nitromethane and a metering jet drilled to 0.055-inch ID should get you into the air. Flo-jector holes might have to be enlarged slightly with this fuel. Make sure that the holes in the flo-jector are top and bottom. Alcohol fuel (Followed by a light spray of WD-40 on the reed after flying) should let the reed last indefinitely. With gasoline, reed life is considerably shorter.
Good luck, Will
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Is there a possibility the flame-out is being caused by the tank feed changing as a function of the build-up in centrifugal force? What is the internal plumbing configuration?
Bill
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Thanks guys, when we get a chance we'll try some of the suggestions..
Bill, tank is pretty much stock except with larger tubing and no baffles. Speed isn't changing that much from just before liftoff to liftoff. Wouldn't think CF is a big factor but who knows, I sure don't.
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Bob,
If the cut comes just after the ship clears the ground, recognize that with rolling resistance gone, the airplane increases acceleration. This can lean the mixture to where it won't ignite- tho the engine would run fine when finally up to speed. This is one of the problems of running gasoline. Try the Coleman fuel, or ream the metering jet a few thou.
Will
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Just my 2 cents worth it sound like a tank vent issue.. how is the vent placed in the tank???
Robert Bolton
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Just my 2 cents worth it sound like a tank vent issue.. how is the vent placed in the tank???
Robert Bolton
Inside top corner. Will pick up a gallon of Colman fuel, seems to be the easiest thing to try.
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the vent should be aft = 45 degress down aft.
Not into the wind, can't tell by the photo.
Patrick
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yep that will be the problem the vent needs to be pointing backwards unless you have a uniflow vent.. Its one of the problems we faced when we first started to play with sidewinders etc..
Robert
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Vent is pointed into the wind (forward).. Could this be causing it to go too rich on take off?
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Yes this will be your problem... The vent needs to be pointing backwards out of wind.... The engine will run on the ground but once let go will soon die rich...
Robert
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Ok guys lets look at the picture its an upright .. The vent should face forward however if the vent is too large it will flood out .. If you could tell me what the pick up and vent sizes are I can figure this out .. Yes I agree Colemans is the better way to go.., Jet Bill