I am beginning to think that weight, or, maybe more accurately, wing loading, is the important thing in determining power needed.  It is not the only factor, of course.  10 oz for a 207 square inch wing CL airplane sounds fine for something like a TD 049. I think it would need to be a couple oz lighter for a Black Widow.  As to the relative power to weight of a Black Widow vs a Torp 19, I couldn't say as I don't have appropriate engine reviews at hand.  I've flown both engines CL and find them difficult to compare.  The Torp 19 is a powerful engine (held the A CL speed record at one time).  I think the one I had would have easily flown the stunt pattern on a large Flitestreak. 

The Aquabat might need more power to get off the water.   I think a 20 oz large Flitestreak with a Torp 19 would fly very well. but I would think the Aquabat more a sport model. Also, a 250 square wing is almost 25% larger than a 207 square wing. 

Thinking about it, I'd probably take each airplane as an individual situation and do very little comparison with other airplanes.   

Hi Tim,

There is so much to consider like Jim and Dave say.  The RM 207 was expressly designed with 1/2A power in mind.  Drag (the different types I don't know much about), wing loading, and other factors I am less knowledgeable about, all must be considered when picking an engine for a model.

I do know that many times a smaller "modern" engine will fly a model designed for a larger one.  And people will always work out ways to put larger engines into smaller models.

(personally, I feel that the McCoy/Testors .049 will be a touch small on the RM207)

BIG Bear
RNMM/AMM

This may belong in the 1/2 A forum.  But I'll ask it here, anyway.

I just got a recommendation that a Pat Johnson Ringmaster 207 (with a 207 square inch wing) would work well with a McCoy or Cox Black Widow 049.

Yet, I have a plan from 1954 for a CL flying boat that calls out a K & B 19, and has a 250 square inch wing.

Why such a small difference?  Is it just that the predicted weight of the RM 207 is around 10 oz, while the Aquabat looks like it'll be around 20oz all up?  Or is a Black Widow all that more powerful size-for-size than the K & B?

Or what?

     Or what, mostly. Pat's is a stunt plane, the flying boat may have been touted as a "stunter" but that might mean it can do a loop.  1/2A's at the time had incredibly feeble power compared to something like a Black Widow. All of the Cox engines were an amazing improvement over the Infant Torpedo and the like.

    Brett

Ah, I will take a stab at this and will try not to be too technical.  To make a gallon of fule last over the winter, live somewhere North where there is a lot of snow, is really windy and really cold.  Another solution is to not fly very much in the winter.

Or switch to electric!