Prop size ??

[Steve Agrella]

How do you know what prop size to use for a given combination.
 Is there a formula, or a chart or just experience

[Balsa Butcher]

Experience, experimentation, personal preference, and the recommendations of others. There is some good info above this subject in the "Tell us your LA-46 setup" thread and in any thread that is posted by Randy Smith. There are also a lot of experienced modelers in your area who fly at the Sepulveda Basin and/or Whittier Narrows. I'd contact one of them, possible through the Knights of Round Circle or Circle Burners Clubs and get some assistance with your early flights. It will make the learning curve less steep and the experience more fun.

[Tim Wescott]

Ditto on what Randy Smith says.  Brett Buck, if he speaks up on an engine topic, is saying something worth listening to.

When I have some specific engine that I don't have experience with I ask here and hope that neither Brett nor Randy say "oh, that one's never been tried -- let us know how it works out", or worse "that's a good RC engine but it doesn't do well for CL stunt".

It's very helpful if you state the plane you're flying, your expected weight (well, what you expect the plane to weigh), and the engine you plan on using.

Sometimes, it's even more helpful to state the plane and the expected weight and then to ask what engine to use, or tell us what nifty new engine you've acquired and ask what size plane should go with it.

[Terry Caron]

Hi Steve -

Here's a chart that gives basic recommendations for various engine sizes, taken from published  information.
Specific prop can vary depending on many factors, but more often than not, one of the props shown will work well enough to get you going.

Terry

[Steve Agrella]

Thanks very much Terry for the chart, just what I was looking for

[Terry Caron]

You're very welcome Steve.
Here's another chart giving a bit different range.

Terry

[Brett Buck]

You're very welcome Steve.
Here's another chart giving a bit different range.

Terry

   In both cases, I think these are more applicable to older engines than to anything made in the last 30 or so years. For stunt, you want something in the range of 4" of pitch, not 6" as this suggests in many cases. This will permit/require the engine to run in the 12000 rpm range in the air, where it has a chance to make decent power with decent fuel suction without modifications.

    Brett

[Chris Wilson]

How do you know what prop size to use for a given combination.
 Is there a formula, or a chart or just experience

Does not the manufacturer give some details?

I know that my PAW 40 likes 7" of pitch and some four strokes are the same, as are RCV geared engines (some have a 2:1 reduction drive built in).

I know that these are exceptions but they are made within the last 30 years.

But please, give us the 'combination,'

[Motorman]

Generally speaking diameter/blade area has to do with the size of the airplane and pitch has to do with the rpm range of the engine.

MM

[bob whitney]

 the Deisel wants more pitch than a glo. Brett is right ,but the split needs to be cross flo Baffle ,and schnule (spelling ) the cross flo wants more pitch, 5,6,7,in. the schnully less pitc ,4,5,6,in