break-in props for 91&1.20 fs's?
03-03-2007, 10:54 AM
#1
Thread Starter
break-in props for 91&1.20 fs's?
been away from the hobby for 15 years.
have 2 planes i'll be flying, GP Super Skybolt and GP Super Stearman.
bought the 91 II surpass with pump and the 1.20 III surpass with pump for these birds.
going off of OS's website specs for break-in props calls for a 12x11 and 14x9 respectively for these 2 engines.
problem is that i don't see anything in this size listed.
a little background on me, i have been a competition free flighter most of my years and dad and i dabbled in RC off and on since the late 60's.
whenever we broke-in engines, we normally took a prop that was 2 sizes over and then chopped off around 3-4 inches of the diameter and ran them rich for ring engines, and just breaking the 2 cycle for ABC engines. always got great HP out of all our engines, but i realize we are talking about four strokes now, and yes, time they do change.
i want to break these 2 engines in to get the best performance..........with that, what nitro %, and what prop for break-in will be best?
have 2 planes i'll be flying, GP Super Skybolt and GP Super Stearman.
bought the 91 II surpass with pump and the 1.20 III surpass with pump for these birds.
going off of OS's website specs for break-in props calls for a 12x11 and 14x9 respectively for these 2 engines.
problem is that i don't see anything in this size listed.
a little background on me, i have been a competition free flighter most of my years and dad and i dabbled in RC off and on since the late 60's.
whenever we broke-in engines, we normally took a prop that was 2 sizes over and then chopped off around 3-4 inches of the diameter and ran them rich for ring engines, and just breaking the 2 cycle for ABC engines. always got great HP out of all our engines, but i realize we are talking about four strokes now, and yes, time they do change.
i want to break these 2 engines in to get the best performance..........with that, what nitro %, and what prop for break-in will be best?
03-04-2007, 10:32 AM
#2
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RE: break-in props for 91&1.20 fs's?
os 91 fsII pumped i started w/master airscrew 14x6, good overall, but not enough verticle. tried 14x8, too much big, excessive vibration, about low 9k's. apc 14x6 was the best, close to 10k, definitely the best choice.
120 fsIII pumped i ran a 16x4w, about 9900 rpm. i beleive it should be a 16x6. as i said, use apc. os are the easiest engines to break in and adjust the ls.
break in w/the same prop. these are ringed engines; break in sloppy rich to keep the cylinder cool for about 40 minutes, then lean out. do it in 10 minute runs at a time, all at full throttle, opening the needle valve to lower the rpm. run for 10 minutes at 4-5k, stop it, allow to cool to ambient temp, this heat cycles it (as much as 30 minutes), do it several times. then after the forth start to close the needle valve a bit and up the rpm. begin to lean out toward peak and check idle and transistion, should be good, looking at this time for around 2800 rpm idle, that means that the ring is wearing in. then set your HS then LS, keep checking the HS everytime you adjust the LS.
whatever you do, don't run it long at a peak needle setting, it will get too hot on the ground, no more than 30 seconds at peak needle setting, open 1 turn for 30 seconds or so to cool it down.
for non ringed; you have to get them hot, the cylinder is tapered and expands when it gets hot. if you run it rich, it will score the piston and cylinder. what i do is bring it to near peak to heat it up for about 30 seconds, then open the needle one turn to cool the cylinder for about a minute, then keep repeating for 10 minute run times (ending w/a 30 second rich cool down), do this 3 times.
the prop can be the regular flight prop or just 1 less on pitch (not dia.) to lighten the load.
jon b
120 fsIII pumped i ran a 16x4w, about 9900 rpm. i beleive it should be a 16x6. as i said, use apc. os are the easiest engines to break in and adjust the ls.
break in w/the same prop. these are ringed engines; break in sloppy rich to keep the cylinder cool for about 40 minutes, then lean out. do it in 10 minute runs at a time, all at full throttle, opening the needle valve to lower the rpm. run for 10 minutes at 4-5k, stop it, allow to cool to ambient temp, this heat cycles it (as much as 30 minutes), do it several times. then after the forth start to close the needle valve a bit and up the rpm. begin to lean out toward peak and check idle and transistion, should be good, looking at this time for around 2800 rpm idle, that means that the ring is wearing in. then set your HS then LS, keep checking the HS everytime you adjust the LS.
whatever you do, don't run it long at a peak needle setting, it will get too hot on the ground, no more than 30 seconds at peak needle setting, open 1 turn for 30 seconds or so to cool it down.
for non ringed; you have to get them hot, the cylinder is tapered and expands when it gets hot. if you run it rich, it will score the piston and cylinder. what i do is bring it to near peak to heat it up for about 30 seconds, then open the needle one turn to cool the cylinder for about a minute, then keep repeating for 10 minute run times (ending w/a 30 second rich cool down), do this 3 times.
the prop can be the regular flight prop or just 1 less on pitch (not dia.) to lighten the load.
jon b
03-05-2007, 11:51 AM
#3
My Feedback: (11)
RE: break-in props for 91&1.20 fs's?
For your FS-91 Surpass engine, you can use a 12 x 10 prop for initial running. You want the engine to be able to turn in the mid-to-high 9,000's when it's finally leaned to just rich of peak RPM...after some initial running. Any propeller that will allow you to fly the airplane and turn that RPM is fine.
For the FS-120, use a 15 x 8 prop, and target the mid-9,000's for your peak RPM.
For fuel, use the same fuel in both engines, with at least 18% oil content and 5%-15% nitro. The higher nitro fuel will help idle and throttle transition, but you won't see a lot in the power department.
For the FS-120, use a 15 x 8 prop, and target the mid-9,000's for your peak RPM.
For fuel, use the same fuel in both engines, with at least 18% oil content and 5%-15% nitro. The higher nitro fuel will help idle and throttle transition, but you won't see a lot in the power department.
03-05-2007, 12:00 PM
#4
RE: break-in props for 91&1.20 fs's?
I break my engines in with a similar prop that I am going to be flying with. On my os 120 w/o pump I used a 16x8 to break in because I thought I was going to be using that prop but then had second thoughts and went down to a 16x6 on the third tank and i am getting aroung 9500 rpm a little rich. Me personally I would say a 16x6, 15% cool power omega. this is on a Gee Bee too. Running real stroke rich so I can not wait to lean it up some more.
