ST 90
 

:eek: :eek: I have a ST 90 Farley new and in good shape. I want to put it on a sport scale 82" Eindecker. I am building the Eindecker out of scrap parts (SR Telemaster wing etc) and want to use stuff I have laying around (OK I am a cheap skate). The question is --- What is the pinility of over propping the ST 90. For scale reasons I want to swing an 18 x 6 prop instead of a 13 x 6. I looked for a 18 x 4 but they don't seem to exist.

By the way in other post people complain about buying bad engines. I sell stuff and I have 100% positive feedback. So look at the feedback. If there is any complents run!!!! Also their is a lot of stuff for sale on this site. Is all this stuff also for sale because it is no good. I have found that in the RC airplane comunity most folks are good people!

RE: ST 90
 

Hi,
I would say you would not get away with running an 18 inch prop on a 90. The engine would overheat from too much load. I have not had any experience with this engine, but that size prop seems far too big....
I would say a 15x6 would be about the maximum, but then again I have not run this engine myself so I cannot be sure.

Stefan

RE: ST 90
 

I run a 14x8 APC so I am sure that a 15x6 would be ok, and it probably would handle a 15x8 but that would not be a very efficient set-up. I would think 16x6 would be max.

Clair

RE: ST 90
 

Thanks all, I will try the 15-6. The good news is that it don't cost that much. As a stand off scale the 15" should look OK.:D

RE: ST 90
 

Actually, you can use any prop that will allow your SuperTigre 90 to turn about 12,000 RPM when on the ground. Any prop that will allow the engine to turn that RPM and fly the model the way you want it to fly is the correct propeller. Running a prop that bogs the engine down too much only causes heat and extra wear.

We normally use a 12 x 8 prop for testing, so you could logicially go to a 13 x 7 or 14 x 6. Getting up to a 15-incher may cause too much load, even with smaller pitches because of the sheer weight of the bigger props.

The SuperTigre S-90, S-90K, and G-90 are all ported to run at higher RPM than other engines of similar size. 12K static RPM is a good number to shoot for when leaned to just rich of peak RPM.

For scale models, use the propeller that flies the airplane the best, and ignore scale appearance. For scale appearance, substitute a display propeller when you're not flying. When the engine's running, the prop's pretty much invisible, especially once the model's off the ground.

RE: ST 90
 

;)Great mindes think alike!! I had already considered this approach and it is probbaly the only one that makes any sense.

RE: ST 90
 

I realize Mr. Baxter does this sort of thing for a living, but I respectfully disagree that you have to turn the ST 90 at 12000 on the ground to successfully fly it. That may well be where the specs say it will develop maximum horsepower (not that H.P. means much with model airplane engines), but that will not necessarily be the best engine/airframe combination.

As an example, we used to fly the OS FSR or VF engines with 11x7 to 11x7.5 props, with tuned pipes, in the old "go fast" pattern style. These 61 engines would turn around 14500 to 15000 on the ground, probably coming close to the 17000 in the air that OS showed as the rpm to produce the HP figures in the specs. We found that we could use longer tuned pipes and go to 12x10 through 12x12 props, which quieted the noise down (noise rules came in) and the performance surprised most of us. OS did come out with long-stroke engines which may have turned the longer props even better, but the short-strokes did a admirable job. And they didn't fall apart from this use either.

With noise problems losing RC fields across the country, it makes some sense to turn lower rpms and cut the noise down. No desire to flame anyone here, just an honest difference in opinion based upon a long acquaintance with model airplane engines.

Clair

RE: ST 90
 

Actually, you can run an engine wherever it gives you good throttle response. The RPM I mentioned above is where the SuperTigre 90's tend to give the best all-around performance, with good idle and acceleratioin, as well as developing good top-end power. It's just how they're ported.

Peak horsepower is developed at about 15K for most of the SuperTigre 90's. You'll lose low-end performance if you try to run it that high.

RE: ST 90
 

I have run my S90K for years on a Zinger 15x6 prop... so I can safely say than using a prop this big will not hurt the engine. It runs just excellent... it may even handle a 16x6 if you don't mind losing some power. Just make sure you have adequate cooling and the engine is set up correctly. I mean, use the right plug, don't run 20% nitro through it... that kinda stuff.

Can't speak for the G90 though, since I don't have one... but it shouldn't be all that different.

RE: ST 90
 

I like an APC 14X6 on mine, fast enough and slows well for landing.