RE: Everything Radial Engines
The OS engine specifications are available on their website. Once I had the specs I simply entered them into my ThrustHP calculator. This FREE and excellent little program will tell you how much static thrust an engine will make at a particular RPM with a particular prop. It's pretty darn accurate. More than accurate enough to make purchasing or design decisions.
As far as dragging on the ground I'm running a 24x12 Zinger on my 1/4th Flair PT-17 Stearman and It has plenty of ground clearance. I have posted these links to videos of my Stearman in other threads. I will add them here so you can easily see how BIG a 24x12 prop is on a 1/4h scale Bipe. I don't think you will have any problems with a 22 inch prop on a 1/4th WACO.
The links below no longer work -Moderator...
[link=http://www.cmac.org/phot/videos/pt17_stearman/PT17_1stFlight.wmv]PT-17 1st Flight Video[/link]
[link=http://www.cmac.org/phot/videos/pt17_stearman/BigPlaneFly.wmv]PT-17 BIG Plane Fly-in Video[/link]