bdelmonte

My Feedback: (4)

After 10 tanks of fuel, my OS 70 Surpass II has been leaned to 2300 RPM idle and will reach approximately 9000 RPM at full throttle.

How does this sound (figuratively) for this engine?

carrellh

what prop?
what nitro %
what oil %

my 70 surpass 1 turns around 9400, not peaked
MA 13X6 K Series
10% nitro
20% oil

bdelmonte

My Feedback: (4)

what prop? TF Power Point wood 13 x 8
what nitro % Omega 10%
what oil % Omega has 17% oil blend of Castor/Synthetic

I was expecting closer to 12000 RPM based on the OS 70 II Surpass manual.

Bryan

Harry Lagman

That sounds like about par for this engine. A 13x8 is a bit much prop for a .70 four-stroke. I would go down to 13x6 or 12x8.

A Surpass II .70 I recently set up did just under 10K with an APC 12x8 and 10,900 rpm with an MA 12x8 K series.

Don't expect to do the manufacturer's recommended maximum 12,000 rpm as a matter of course. To do 12,000 with a 13x8 prop would require more than 2.5 horsepower - about what a YS 1.40 would put out.

Prop the engine so it does somewhere between 9,500 and maybe 10,500 rpm static.

bdelmonte

My Feedback: (4)

Thank you for this information.

I am using the 13x8 prop, at the suggestion of my flight instructors after first using a 13x6 prop, which I was flying too fast for a trainer. I have the OS 70 Surpass II installed on a moderatley light Super Flying Model Eindecker (monoplane) semi-scale training designed for 46 engine. I can go likely back to the 13x6 after I am certified for solo flying or ask my instructors to proceed with this change now.

Twice today, I took off, flew (only one required turn-over to instructor) and landed my Eindecker.

After the first flight, it was difficult to hand start and then started in reverse rotation. I was told that I had flooded the engine, which caused this reverse rotation. Using a starter, I went back to normal rotation and flew fine at about 1/2 throttle for training patterns.

speedster 1919

My Feedback: (3)

I have the same EINDECKER and it flies great with a 48 MDS and 11x5 Nexstar prop. Your 70 is too much engine for that plane , but you can tame it down. The SFM Eindecker has small rudder and elevator and will go fast , but then lacks a little control. You could try this---- With a 13" prop your about out of ground clearance. 13x5 or 12x5 MAS and set your WOT with EPA to 10,000 RPM. You now have slowed the plane and won't blow the engine on too high RPM. You'll have great power when you need it.

bdelmonte

My Feedback: (4)

Great to read about another SFM Eindecker, which I am leaving now to fly!

I will shortly move to a 13x6 prop and check the RPM's.

Bryan

bdelmonte

My Feedback: (4)

Forum administrator,

You can close this subject, as I have not received any replies here in one month.

Bryan

KC36330

just to keep it alive a bit longer, my 70 surpass was bought new in 99 but has only been brought to life recently, i use 30% cool power in all my glow engines and with a 10x10 APC i keep it richened to 10K, it'll turn about 800 more leaned out. it's on an ultra sport 40 ARF and performance is outstanding.

kc

bdelmonte

My Feedback: (4)

Why did you choose a 10x10 APC prop, while O.S. recommends a 11x8-9, 12x7-8, 12.5x6?

KC36330

it's what gives me the preferred flight performance from the engine/plane combination. any prop that loads the engine as it's intended to be is an acceptable prop, you just have to find the one that gives you what YOU want out of the engine and stay in that loaded state. other size props didn't give me the speed i wanted out of it, the 10x10 was perfect and loads the engine to the recommended RPM range that OS recommends. it also gives impressive vertical on top of the high speed flat and level flight.

it's only by testing with your own combination of plane/prop that you find which one is best for you in your application. the MFG recommendations are only a starting point. let's say you use a 13x6 wood by Top Flight, a 13x6 of another MFG isn't going to give you the same RPM nor the same flight characteristics, there is no 'set in stone' this prop is for this engine. also a prop/engine combo that works great on plane #1 may not be acceptable on another plane. it's always trial and error with any setup.

kc

bdelmonte

My Feedback: (4)

Thank you for this detailed explanation, as my 13*8 or 13*6 are also not in the recommended range, but helping keep me slower for training certification. Your 10*10 must get you going considerable faster!

KC36330

for elaboration, on my 1/4 scale Extra, it has a 50cc gasser, with a wood MSC 20x8 prop it turns at 7000 RPM, with a Bolly 20x12 carbon i can get almost 800 more RPM, it's a bigger diameter prop and has more pitch then the MSC but turns more RPM, has more forward speed and vertical climb/acceleration. don't get fixed that you have to run what the MFG states on their instruction sheets. my 50s instructions have choices from an 18x8 up to a 22x12, that is a whole lotta prop difference for the unlimited different combinations of setups this engine may be installed into.

as for the going faster with the 10x10, yes it gets impressive speed equal to a pipped 46 2 stroke with allot less noise and fuel consumption. back years ago i had another of the same plane and ran a 36 size 2 stroke with a 9x7 on a pipe, it turned up to 16000, had it clocked with gear up at 102 mph but it took allot of runway to get it off the ground and touch and goes could of used allot of low speed power, it wasnt a plane for the inexperienced. i later popped a thunder tiger 91 4-stroke in with an impressive pitched prop (cant recall the exacts but it was about a 13x13) and it hauled butt as well as had a ton of low speed power, vertical take offs after a short 5' roll out and would even hand launch with a simple toss.

kc

buzzard bait

On the other end of the scale, I'm running my older OS .70 on a 14x4w (wide) APC on my Four Star 60. Rpms seem low, peaking at only about 9300. Maybe it's the wide blades. Coolpower 4-stroke fuel, 15%.

This prop is slow and makes landings very easy, while providing really good vertical. Kind of claws it's way up.

Jim