buzzard bait

I received the manual from Hobby Services...very quick, friendly service.

I'd like a little clarification on props. I can't find any mention of rpm to shoot for on the ground, and the prop recommendations seem like the same as people are using on 91s, i.e., 14x6, 14x7. I'm thinking I might get more thrust with a bit less load on the prop, but don't want to over-rev.

I'm more interested in low speed thrust than going fast, so I'm wondering if the APC 14x4W would be too little load for this engine. I've been running my 70 FS on that prop, and also a Zinger 14x4, and those work well and run in the mid to upper 9s. I'd expect the 81 to be in the lower 10s on those props.

I'm also thinking about getting a Zinger 14x5 (or Xoar in that size if it is available).

Haven't run it up yet; expect to use same prop for break in. Appreciate advice.

Thanks,
Jim

MetallicaJunkie

youll get better performance in that prop range out of apc 14x4w quality or quantity

Bax

My Feedback: (11)

You want to prop the engine so that it's running in the mid-9,000's or so. Then, whatever prop will give you the performance you want is the "correct" propeller. Shoot for the RPM range first. Select a prop that will turn that RPM and see how the airplane flies. O.S. suggests large propellers to keep noise down, but you do lose performance. Their recommended range is 13x7-9 or 14x6-7.

buzzard bait

Thanks Bax. I thought I might be able to go a little higher than mid 9s with this engine, but I do understand that rpm in flight will be higher.

Jim

Bax

My Feedback: (11)

Yes, tach it on the ground for the mid-9,000's or so and then see how it flies. The actual RPM won't be particularly critical, but it's how the model performs that you want to watch.