stunthanger.com
Engine basics => Engine set up tips => Topic started by: Niklas Löfroth on May 19, 2019, 03:28:35 PM
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I have been flying my new model for a while now and I really love the power from the PA75 on Randy CF pipe.
I have a problem though. There is lots of unburned oil on the nose after each flight. It seems to be coming from the venturi. This makes me wonder if maybe the pipe leanght can have anything to do with the problem.
I know other pilots using the PA75 without this oil/fuel problem. I have used other piped engines and I have never had this problem before. I would be grateful for some help in this matter.
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I don't run tuned pipes, but if fuel is getting out of the venturi, how about covering it with some pantyhose material? I do that mainly to keep dirt out, but that should trap any fuel trying to come out.
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I don't run tuned pipes either, but going by what I do know about model engines and engines with expansion chamber pipes, I think your first suspicion may be correct. You do not say what type of fuel and oil content that you are running, and that may have a bearing on what is happening. Randy Smith is the moderator of this section, and the manufacturer of your components, and I'm sure he will see this and answer. He has been out of town at the Joe Nall event but should be catching up on things soon.
In the mean time, I would not run the engine if at all possible, just to make sure the extra oil is not hurting the rod journals or anything else in the top end.
Good luck,
Dan McEntee
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I have been flying my new model for a while now and I really love the power from the PA75 on Randy CF pipe.
I have a problem though. There is lots of unburned oil on the noose after each flight. It seems to be coming from the venturi. This makes me wonder if maybe the pipe leanght can have anything to do with the problem.
I know other pilots using the PA75 without this oil/fuel problem. I have used other piped engines and I have never had this problem before. I would be grateful for some help in this matter.
This is sometimes caused by the pipe being too short. What pipe length and RPM are you running?
Brett
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Here comes some additional information:
I’m using the following setup:
PA75 RE with Bru-Line air filter (green)
CF-pipe (75-size) from Randy
Pipe length: 19 1/4 inches
fuel: 7% nitro, 20% Klotz Super Techniplate, 73% Methanol
Prop: Brian Eather 3-blade, 13.2 x 4.2”
Release rpm: 9000
Model: Slightly modified Trivial Pursuit
Weight: 64oz
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Not 100% sure but when I remove the engine, the engine compartment is basically free from oil/fuel.
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Almost all oil is collected inside the cowling and then flows into the joint between the cowling and the fusulage towards the fuse mounted landing gear.
The engine comsumes 8oz fuel for 6 min, which strengthens my suspicion that all fuel is not combusted.
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Almost all oil is collected inside the cowling and the flows into the joint between the cowling and the fusulage towards the fuse mounted landing gear.
The engine comsumes 8oz fuel for 6 min, which strengthens my suspicion that all fuel is not combusted.
Hi Niklas
Try moving the pipe out a 1/4 inch and see if that reduces the oil flow, if you have the pipe tuned too short it will pump oil out of the front of the engine
Reason is the pressure wave gets back to the engine BEFORE the intake shuts, this just pushes the charge back thru the engine
Randy