geeter

My Feedback: (110)

hey guy's, i just built a fun p-51 profile fuse kit from great planes. simple plane. my power was a super tigre 51, a few months old. after three flight the engine started to run rough at idel. i would speed it up above 1/4 throttle and it would be ok. thinking it was the engine i looked at it for bad bearings etc.........nothing everything good. still at 1/4 throttle the engine would start running rough and quit. checked fuel tank an all nothing. put in my 48 o.s four stroke. does the same thing. some how vibration is getting into the engine, not foaming the tank either, witch is foam padded. it vibrates through the profile fuse right to the wings and engine and makes the engine run sick. everything is solid on the plane. it has to idel to fast to land now or the engine will shut down. never ,ever, had this problem before in any plane. everything is in balance to it makes a funny humming noise too. under 4000 rpm's forget it. what the heck is causing this ?..........any help out there?...thanks in advance. should i rubber mount the motor ?...........RON

gene6029

You stated you checked your fuel tank & lines, how old is your fuel? The humming noise may be a resonateing noise comming from the plane at a certain rpm....Gene

geeter

My Feedback: (110)

gene, you got that right, thats exactly what it is. how do i get rid of it? try rubber mounting the motor. like putting rubber fauset washers behind the motor i thought might help. not o rings i mean the hard rubber kind that already have a hole in them for the bolt. some are tapered a little and come in a box of assorted sizes at home depot. any ideas.......thanks............RON

WacoNut

Ron,
If you are getting a frequency vibration form the airframe I would 1st look at your prop balance. Another thing you can do is change the frequency of the airframe. This can be accomplished by simply adding some tail braces to the stab. I would try from the bottom of the fuse to the bottom of the stab. I am not a fan of soft mounting small engines.

I built and test flew one of these planes for a friend with a Supertigre .51(I believe) and had no such issues. The plane is a blast to fly.
Good Luck!!
Anthony

geeter

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thanks for the info. maybe i'll try that. yes it is fun to fly and is the 80- 85 mph range with the tigre and a 10x7 apc prop. i never had probelms with this either......but iv'e never had a profile fuse plane either. my fuel is fine. i flew the same stuff saturday in my twister, and no probelm. it is definately the air frame causing this. you can here it through the wings etc.........thanks i'll fix it ,i always do. just needed some advice on the probelm i have never had before...........thanks...HAPPY LANDINDS .......RON

geeter

My Feedback: (110)

i took the motor out and put it in my test stand. runs perfect. it idels down very well without a shake or anything at all. it is the plane doing it. i'll do some things to correct it. it's a cool plane to fly soooooooooo.......thanks........again..........RON

Lnewqban

I believe the rubber washers will do nothing to help.
If you leave them loose, they will break the bolts.
If you press them hard, there is no cushion effect.
Note that real rubber isolators do not have a bolt all the way across.

Try to make the fuse more stiff in the weakest directions, which are sideways and twisting along the fuse.
Those are the ways in which the engine-prop vibrations tend to deform any profile fuse.

geeter

My Feedback: (110)

thanks all, and thanks for the diagram. that explanes alot........HAPPY LANDINGS.............RON