Conversion Matrix for SPEED, THRUST & HP


Unobtainium Member
May 21, 2006
Columbia, SC
Air Command Tandem w/ Arrow 100hp; GyroBee w/ Hirth 65hp; Air Command Tandem w/ Yamaha 150hp
Total Flight Time
It is fun to play with numbers and power output for our power plants, so here is a nifty little conversion table I have been using for a few years that others might want in their reference folder. With this, you can determine things like
  1. Theoretical top speed, with known static thrust (tied up to a scale on the ground) and HP
  2. True crankshaft HP developed, with known static thrust at any given ERPM and air speed realized at that same ERP
  3. True thrust developed at a known true airspeed and crankshaft HP
  4. Prop efficiency, given true airspeed, known thrust and HP
You'll also need to know testing air density ratio, with MSL = 1.0 and estimated prop efficiency until you pin down your true prop efficiency number. I was surprised to learn one day a few years back that the 68" 3-blade Warp Drive props I am a dealer for produce and very respectable 90% efficiency, while the Ivo on my Honey Bee was no better than 85% at best.

If you want the working Excel spreadsheet with the working formulas installed (all you do is plug in your known values and it produces your desired unknown) then...

Please email [email protected] - and keep me in mind for all of your Yamaha power plant conversion kits, parts, needs & info, Warp Drive propellers and RK400 clutches for all engines.

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Convert Thrust to HP.png



Gold Supporter
Apr 21, 2008
San Diego, CA. USA
Piper Archer, Aviomania G1sb
Total Flight Time
Not sure over 10,000+ logged FW, 260+ ultralights, sailplane, hang-gliders
Thanks, I'll create one of these for PRA library.