|Jan 21, 2013, 11:02 PM|
United States, NV, Gardnerville
Joined Jan 2013
OS 4 Strokes
I am thinking of using either an OS 72-a or 81-a in a Top Flite P039 Airacobra that i"m building. anyone having any experiance with these engines I would appreciate your comments.
|Jan 22, 2013, 01:38 AM|
United States, MI, Clarkston
Joined Mar 2007
I had a OS72 in the TF P39 and found it was very marginal for power especially on takeoff. I replaced it with an older OS90 like Datsunguy used and found that it had plenty of power. I believe that the old OS90 rear cam motor was more powerful than the newer OS 91's. I do not think you will be happy with the 72 or 81.
My opinion only!
|Jan 27, 2013, 04:17 PM|
Yep... I have that P-39 and I put an OS 91 four stroke in it
I installed the engine on its side, that way the exhaust blew
down and away from the fuselage.
Mine has the air retracts too.
The 91 flew it pretty good but the plane was so heavy that
you have to land it really hot or it will stall.
It sure is pretty though...
|Jan 28, 2013, 09:31 PM|
Joined Jun 2011
That was exactly the problem with mine. It would stall and snap roll at the drop of a hat at low speeds. You had to land going lickity split. Always exciting. The old 90 was more than enough power though.
|Jan 30, 2013, 05:32 PM|
United States, NY, Ithaca
Joined Sep 2007
I think you'd be fine with the .81. I don't understand why the OS 72 even exists. The 81 is essentially the same but more powerful. It is only down from an OS 91 Surpass by a couple hundred rpm on standard props (I cannot believe the old 90 FS was more powerful than the Surpass; If it seemed so then the prop on the Surpass was not optimal).
So just be careful about weight as you build, always a good idea; if the old 90 FS will fly it then I'm sure the 81 would also.
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