4-stroke

I haven't written to this group in awhile, but thought I would try and get some info.
I am currently building a Don Smith B-24. Its a joint project on building time and funds.
My question is what engine: Saito 100 or the OS .91 Surpass pumped.
I have done the research and like the Saito 100 for power to weight. My partner thinks the pump would be good for reliability. I have read some threads that indicate a problem with the pump.
Anyway, any solid first hand experience you can share.
Mike

Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:
Go with the Saito. If you, for some unknown reason, are still concerned about "reliability", add Perry pump(s)
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Ted Campanelli wrote:
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I would definitely add the Perry fuel pump on the Saitos. I have flown three of the Saitos and with the Perry pump, they are really solid. They do take a little time to break in, so I would run them for a couple of tanks on the ground or fly them in another plane for a bit before the first flight.
Bob

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I don't have any experience with the pumped O.S. four-stroke, but I do have several Saitos and one O.S. Surpass II. I'd say the pump is something that could REDUCE reliability....
I would not hesitate to fly a twin powered by two Saitos (or non-pumped O.S. four-strokes).
Good flying, desmobob

Have both engines. My pumped OS surpass 91 has never failed & given a one engine database I'd say it has been quite reliable. The Saito was finicky epecially when new. In my opinion if it's reliability that is important to you then OS would be it but for weight and power considerations Saito should be the powerplant.
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Thanks everyone.
I believe I will go with the OS pump.
Mike
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The Senior Pattern Association's most competitive and permitted engine is the OS FS-91 Surpass II/P (pump) engine. The fellows using them claim that they are the best powerplant for powering their planes (30% nitro fuel too!). These fellows are older modelers, on the average, and many are ex pattern pilots. If anyone is critical of an engine, it is pattern pilots, ex or otherwise.
I just bought two of them from Tower myself for SPA usage.
Ed Cregger

30% nitro! I've tried nitro contents up to 20% with my OS 91pump and I've not seen much of a performance benefit beyond 15% nitro. So I ended with 15% nitro (18% oil Power Master fuel) for my flying. I'm curious whether the "Senior Patten Association" have any rpm data with the 30% nitro fuel that they're using. I typically use a Master Airscrew K-series 14x6 prop and my highest recorded engine speed (ground, static) has been 9400 rpm.
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I am just repeating what I have been told. The claim is that throttling is significantly enhanced and the extra nitro lets them pull larger than normal props, although I wouldn't swear to it.
I did buy a case of 30% heli fuel just to try it for myself, after break-in, of course.
Ed Cregger

Ok,
I sorta agree with using 15% max.
So, 14x6 at 9400. I guess a 14x6 3-blade would get 9000.
So 4 os 91 pumps with 14x6 3 blade, 15% nitro 18% oil - common fuel.
I'll keep this group informed on building progress of the Don Smith B-24. Almost got the tail group complete.
Mike
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PowerMaster fuel (18% caster/sysnthetic, 15% nitro is quite common in my neck of the woods). I don't think you can get 9000 rpm for a three bladed 14x6 prop and unless you're after looks why would you? If you need more static thrust you could try a 15x4 wide APC prop instead. I think a three bladed 14x6 prop will bring the rpm way down for the engine to be as effective as it needs to run in the 9000 rpm range.
Ed - please post your findings once you've taken data with the 30% nitro fuel that you have.

Yah,
I agree. I will do a static test on the right props.
Just thinking a three blade would look nice!!!! Actually 4 - 3 blades
13x6?
I will be posting a a build forum on RCuniverse.
Mike
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