Here's how it goes, if what your looking for is good sport performance and engine longevity...

Our engines in the 40 size range (46 included) generally perform well and live long in the 10000-13000 rpm range. We try to prop them for that. Racers and other performance folks will happily run them much faster than this, but they buy more engines than you and I.

I'm not intimately familiar with the Royal engine, but the OS and ST .46's I've run have tached in the 13K range with 11x6. Way too fast on 10x6 (14K or better!). An 11x6 running 13K static will give better than 80mph in the air with a sleek airframe, and pulls about 7# static.

If you wanted more speed, or more thrust, you'd change both the diameter and the pitch. If the aim was speed, I'd suggest trying 11x7, 10x8, 9x9. If it over or under revs with any one, change the diameter to correct this. If the aim was thrust, then something like a 12x4 or 12x5 might be in order.

Noone can tell ya what prop is best for your plane, buy a variety in the size ranges I mentioned, and try'em! You'll find one you love!

Be sure to re-tune the hs needle with each prop...

J