Hey guys. problem.. my plane dies when flying inverted. I have a Sig-Mayhem with a OS 70-Surpass engine. The plane flies great in rolls, spins, loops etc.. but, any invert for more than a second or two and the motor dies..???? any ideas? It also will siphon gas if I let it sit. The breather line is kind of long as the engine is inverted and it must run over the motor then back down through the cowling and out the bottom. Thanks for any tips or tricks...

G'day Mate,
The motor doesn't care which direction it is running, as long as it has a glow plug that keeps glowing & fuel air mix.
You say it stops when the plane is inverted, so the engine is upright, so it is running out of fuel, ie, your mixture is too lean, because your tank level is too high, & so it is low when the plane is inverted. Tank centre line should be level with or no more than 3/8" below the fuel nipple on the carby. Adjust as needed, & see the difference.
A high tank level will also cause the fuel syphoning.

Another thing to look at is your pickup line in the fuel tank. If it doesn't move freely in the tank, is stuck at the bottom of the tank because the fuel line is too long, then when the plane inverts the clunk will no longer be in the fuel and the engine will die. This would explain why simple rolls or loops it doesn't die, because there is enough fuel in the line for you to come back upright and the pickup can now get fuel, but when you invert it dies.

Hope this helps

Ken

G'day Ken,
I agree, but I mentioned the tank height because of the fuel syphoning problem.
How's the weather over there Ken, Bloody hot here, & finally no wind, so we had a great days flying.

I agree on they syphoning too, but since you brought it up I didn't need to say it again!!

Ugly weather here. Overcast, cold, and windy today and tomorrow. Been almost a month since we got fly. [:@] Gonna have to fire up the 777 and come down your way for a visit!!

Ken

G'day Ken,
If you have Google Earth, these are the coordinates for our field, Manning Model Aero Club. Lat, 31°51'17.82"S
Longitude, 152°22'59.43"E
Come on over & see us sometime, there will be a Giant Scale event on 9, 10 June this year.
But that is our winter, cool days, not below 18C during the day, that's why we fly all year round, terrible, but we manage.

hey thanks a ton guys. I really appreciate all the advise... all sounds sound to me... Here in South Carolina its been beautiful but, suppose to rain any minute so flying is out.. good day to work on the planes... thanks again for the advise..

I guess I disagree with the majority.
You can have problems flying inverted or with an engine mounted upright or inverted if you don't make sure the centerline of the tank and the centerline of the carburetor's spray bar is on the same line or VERY close to it. Check this first. If there is more than 3/8 of an inch between the two, then I would change how the engine/tank is mounted to get them in line.

Geistware, I appreciate any and all advice or angles on solving a problem. This is a great site with much help and many friendly people. I've been riding dirt bikes for about 35 yrs and finding a hobby to ween me off of it but, keep the thrills going has been a blast. Being more of a newbie than a novice I really thank everyone for the help.