OS FP, FSR

[Gerald Arana]

I know what FIRE stands for (front intake, rear exhaust) but what does "FP" or FSR" stand for?

Does anyone know?

Thank you, Jerry

[Mike Ferguson]

FSR: Front Intake/Side Exhaust/Rotary Valve

Not sure about FP.

[David Hoover]

Front intake/Plain bearing?

[Gerald Arana]

Mike and David, that sounds about right! I forgot about the plain bearing.

Motorman, It's got to stand for something.....

Thanks for the answers guys.

Cheers, Jerry

[Brian Hampton]

What makes things uncertain is that, before the FSR, OS had the 40 SR which was their very first Schneurle ported engine (maybe why the "S"?) and it was intended for Racing (rat race and/or pylon) but it was also Rear induction. My bet would be on Schneurle ported Rear induction as indicated by the SR under the exhaust port. I think it was about 2 years later that the exact same crankcase casting was used to make a front induction version which was then called the FSR where the F could only have meant Front induction and the R was simply a carry over from using the same crankcase. FSR then became common for all similar designs of different sizes. Later still there was a small range of rear induction engines called RSR, mainly for either marine or ducted fan use.

Front induction and plain bearing sounds logical for the FP series but where does that leave something like the FX or LA? I'm guessing only the factory knows and they're not telling .

[John Rist]

Not sure where the thought came from but I thought FSR meant Front Schneurle Rotter.   I bought new, around the time it first came on the market, and still have an OS Max 50  FSR.  Flew it on a Dirty Birdy 40.

[Steve Helmick]

So....what does the "LA" stand for on the fab LA series engines? "Lay About", maybe?  Steve