Hi Mike,

I am gonna have to let Don tell us his speeds, but he was at 8000 feet so indicated speed will have to go thru the dreaded calculation as well in order to find the true airspeed..  :>)   since airplanes fly in the air and don’t touch the ground (except occasionally) every speed you see will be some kind of calculation and not a “fact”.

Maybe he has a GPS and can fly some kind of rectangular pattern and find the average (no wind) speed.???

Maybe you can get a copy of Paul’s dyno sheet and take a look at the horsepower he was producing at the lower rpms I mentioned.  I will bet they are very close to the numbers I mentioned.  Mazda used to claim that the Renesis produced 250 @ 7500, but they have since backed it off to, I think, 238 @ maybe 8500.

The point I was trying to make about the rotary was that your HP is based on rpm.  All those high HP numbers are all at really high rpm.  Much higher than we run in the plane, unless, like Mark Steitle, you have a CS prop.

Mark gets (I think I saw him say) 7500 on takeoff and although I haven’t heard him say, I assume he can get the same in cruise as well.

Bill B

Sorry, not buying it Bill. If you are going to quote speeds here, quote speeds, not calculated speeds based on so many variables that the end result is meaningless. That sounds like something we'd see on the other list, not here. As far as I know, Don's best reported speed is 174 IAS (and IAS is not all that meaningful either). Based on performance that Don has actually reported his performance is roughly equivalent to mine (and I'm both prop and gearing limited). His performance may have improved since he reported those numbers. In any case I'd prefer to stick to facts.

Speaking of the other list, Paul has video of a PP Renesis on a dyno  at Mazdatrix cranking out near 250HP @7500RPM. And he had the dyno sheet to prove it. Powersport claimed 210HP at 2700 prop RPM (their reduction ratio was around 2.2; roughly 6000 engine RPM). I believe they also had dyno data to prove it. I'm anxious to hear how Mark Stietle's PP 20B performs.

Mike Wills

Mike,

Don didn’t report speed.  I took his pitch and rpm and figured it.  That speed at cruise is what he would get with no slippage or “lift” from the prop.  Most of the folks with the Catto are actually getting higher speeds than would be calculated which indicates that the prop is producing “lift”, not slippage. 

But his engine rpm with that big prop are higher than any I have seen.  With the rotary, rpm = horsepower.  If you aint making the rpm, you aint making the horsepower.  It doesn’t seem to matter what you have done to the engine…ported, PP, turbo, supercharger.  If you look at the dyno charts that are all over the web, you will see that torque is pretty flat after about 4K, about 150 ft lbs.  The horsepower is around 150 at 6K, maybe 180 at 7K, and 200 at 7.5K.  You can get more horsepower than that, but only if you scream it up to 8K  or 8.5K.  All the charts I have seen are within 10 horsepower of each other at all rpms.  The difference in total horsepower is always a higher max rpm.

We all talk about wanting to cruise at 5800 and make 200 horsepower…it aint happening!  Not with the rotary.

Bill B

Bill,

I went back and looked at Don's previous post. Saw reference to climb performance, RPMs, and temps, but no speed numbers. Has he previously reported cruise speeds over 200? Last post from him that I saw with any speed numbers reported 174MPH IAS at 8000. If he's over 200 now, wow those are good numbers!

Mike Wills

Those are the best numbers I have seen with anyone with a Renesis so far.  In fact, I have not heard of numbers that good on any 13B.  Don is getting over 200 MPH with a cruise prop and climbing at over 1400 fpm with it.  The only way he is going to do better is either with an electric CS prop and/or turbo.  If he shaves the prop off to say, 74”, he will get a couple hundred more rpm, but will probably lose in total thrust.  Diameter is a big determiner in thrust. 

I would like more pictures of Dons intake and exhaust!

Bill B