Okay, I know if you change the pitch of the prop, smaller pitch will give you more power, larger pitch will give you more speed.

What about length? If the pitch is the same what difference will be made from changing length, say 15X6 vs 14X6?

Thanks for any info,
Tim

That usually slows your engine down.

Jim

If you go down 1in pitch , go up 1in. in diameter. That will keep the prop rpm in the same ballpark.

What Jim is trying to convey is that if you go from 14x6 to 15x6 your engine will not be turning as many rpm's. More pitch and less diameter is associated with speed, and the converse for more acceleration. For instance, I like to fly some of the smaller profile fun fly type planes. For a .40 size engine we usually use more diameter, say an 11x4 instead of a 10x6. This gives more rpm, better throttle transition and better hovering ability and slower flight speeds when we need them. Sort of like a helicopter, a long flat blade. What particular plane, engine, prop and plug are you flying?

I just finished a Sig Hog Bipe with a YS-91-AC engine an OS-F plug, using 20% nitro 20% oil. I have 4 flights on it so far. Engine runs great, lots of power and sounds good too. This is my second 4 stroke engine.

I like to fly SLOW and low, most of my flight time so far has been less than 1/2 throttle. I would like to slow the plane down some without fear of over revving when I do go full throttle.

I am still running a little on the rich side being still new about 8000 rpms. It leaves a nice smoke trail. The prop that I have been using is a Zinger 15X6-10. This is a prop that has a 10 pitch in close to the hub and tappers out to 6 pitch at the tip.

Any tips would be appreciated.

Thank,
Tim

Tim,

You might try a 15-6 APC. You may have to order it? Tower doesn't carry it. I never cared for the dual pitch props. I'm old fashioned. The dual props didn't catch on in the U.S. like they did in Europe.

If you take a regular 6" pitch prop and measure it on a pitch gauge, it will only measure 6" pitch from about half way on out on the blade. From half way on in it will get down to about 4" pitch. To look at the 6" pitch prop, this doesn't look correct because anyone can planely see that the angle gets greater as you get closer to the hub? Yes, the angle does get greater, but not greater enough. If you are good at math and do some calculations about the blade angle 1/4 the way out you will find that the 6" prop doesn't have 6" pitch there.

Anyway, the 6" prop will let the 91 stay closer to 9000 and you can develop more power and have better climb when you need it. The prop will also act as a brake at low idle.

Enjoy,

Jim

Ok guys, thanks for the info.
I will try the 15X6 next.

Tim