prop
 

what is the practical prop size for a webra .61

RE: prop
 

11x7, 12x8 would be good places to start based on other engines of the same size I would imagine[8D]

RE: prop
 

I have an FS .70 Surpass II, what would be the best prop for the break in, and what would be the best prop for the plane, a U-CAN-DO 3D? I've seen reference to a 14X4 but that seems too big! HELP![:@]

RE: prop
 

Check this out. Click on it,then click "file", then click "print".

RE: prop
 

For the O.S. FS .70... 14X4 is a bit large. 13X4 would be better. I use a 13X6, 14X4 or 14X6 on my O.S. FS .91. (mostly the 14X4...)

For the U-Can-Do to give maximum 3D performance, you want the longest lowest pitch prot appropriate for the engine. Static thrust rules for 3D. (thus the 13X4 should be very good)

The Webra .61 2-stroke should turn 11X6, 11X7, 11X8 , 11X9 or 12X5, 12X6, 12X7, 12X8 or 13X4, 13X5, 13X6 Depending on what aircraft it is on.

If trying for speed... the Webra engine is a good choice... and can turn a 10X10 if you can find one. (use that on a LIGHT 50 to 55 inch span P-51. ;) )

RE: prop
 

I have a World Models Sky Raider Low Wing I used for a first time build experience. I am putting a 40 on it to just get used to the low wing tail dragger type plane. Should I use a 10-6 or 11-5 prop.

Thanks for the replys

Ray

RE: prop
 

I just found the Sky Raider... looks like a typical trainer style aircraft. I would start with the 11X5... or maybe an 11X4 with the .40 engine.

Which engine? The .40 LA or weaker end of the line .40 ci engines (most bushing bearing ones), I would use the 11X4. The TT Pro 40 or high power end of the .40's (most ball bearing ones) I'd use the 11X5.

RE: prop
 

Simplify.
Check out my previous post, download, and print for your shop.

Jetts

RE: prop
 

I don't have an OS .70FS Surpass, but I do have an old OS .61FS (pre-surpass, it's an oldie). I use a 13x6 on it, and have tried 14x5 and 14x6 props, which worked fine (but at a noticeably lower RPM). I never had a 14x4, and I don't think it had enough pitch for my application, so I never tried it. But based on my experiences with my .61, a 14x4 would not be too much prop for a current generation .70 4-stroke. 4-strokes can turn bigger props than 2-strokes.

Many 4-strokes (espeically my .61, but I've seen it with others) have a max RPM that they will run. My .61 would tach exactly the same on a 12x6 and a 13x6 APC. The level flight speed was the same as well (same unloading in the air). But the 13x6 pulled a lot harder, for much better climb. The engine simply would not go faster on the smaller prop. (fwiw, it was turning at around 10k on those props, 8.5k with the 14x6, if I recall. That engine just will not go faster than about 10.5k).

Maybe the .70 is ported differently and set up for higher RPMs and would benifit from a smaller prop, but I kind of doubt it (the smaller prop bit, I'm sure it's ported a bit differently). Also, many 4-strokes get in to valve float problems much over 10k anyway. I don't know if the OS .70 has that problem or not though.

Anyway, get a range of props and try them, that's the only way to know for sure what works best. Start with what's in the engine manual, listen to what other guys say, and don't be affraid to try things just to see how it goes, even if someone else says it won't work. If you go a little at a time, you won't hurt the engine.