Group,
             looking to fit a prop to my P ported renesis and need to
 know what actual HP it will generate and not an enthusiastic guess.
 Would I be safe in aiming for 230 HP?  Apparently if the prop is too big
 nothing works, so smaller seems to be the aim.  Any suggestions ??  It
 will be a fixed catto prop, and as usual craig Catto has been caught
 many times before with HP in engines.  Actual HP not guesses required.
 Neil.

 What gear ratio is your gear box?

 If it is a 2.85 the prop will turn about 2600 and the engine
 will turn about 7400 and make 250 HP plus or minus 10.

 We need to get a group buy together and find somebody to make ground
 adjustable blades for a Warp Drive type hub. That way you can fine tune
 the pitch without buying a new prop.

 Paul Lamar

 Aren't there other factors that have to be right to get 250hp?  Intake,
exhaust..  Can't go too big on the pipes, smooth transitions, no big
restrictions, etc.  A bit of time on a dyno with the complete firewall setup
from the airplane might be money well spent.  Compared to swapping props.

 As for the prop, if pitch or diameter are wrong, it's a bigger project to
add material to the prop than it is to take it away. At least for wood
props, it can be relatively easy to cut the diameter down, or even reduce
the pitch to some extent.  Catto props are composite covered, so it's
probably a bigger hassle to modify than for a straight wood prop.

 How about buy or borrow another prop to try before committing to one in
particular.  If you could find a fixed pitch prop from a local Pitts or RV
or Skybolt, you'll have something to use for a baseline. Many/most of those
airplanes have 180hp engines.

 Another thought is to do prototyping with a wood prop of your own
construction.  If you have gone to the effort of building a whole airplane,
including the powerplant, building a prop may turn out to be that difficult,
by comparison.  There were ads in Sport Aviation for doing this. And online.


 Matt-

I am assuming (possibly incorrectly) that Neil is doing the p-port at least as well as I am doing it and he is using a 2.85:1 gear box.

IMHO the best thing about a welded p-port it is hard to screw up but possible.

I have taken the position that only a ground adjustable prop is worth
fooling with provided you are not using a constant speed or in the air
adjustable. I have come to the conclusion there are too many variations in aircraft drag to recommend anything else. The Warp Drive type adjustable
pitch hub is becoming an industry standard as even Sensenich is supporting it.
Unfortunately Sensenich does not yet have a blade suitable for our use.

Randy told me today that Warp drive now has three different all carbon  blade designs. Ultra Light, LSA and high power. One of them is called Constant Speed Blade Platform. http://www.warpdriveprops.com/

However I am not yet convinced the WD blade plan-form and twist is yet
optimum for  the lower drag AC designs. That I why I would like to see some
other companies get in the biz of ground adjustable.

The high power to weight ratio of rotary powered aircraft and the excess length
of most runways is why I think constant speed props are not worth the money.
Set the pitch for best cruise and let the take off performance be what it is.
We are mostly not building C182's here or cargo aircraft.

IMHO pure wood props will always have less performance than a metal prop
due to the lower modulus of elasticity wood. The high modulus of elasticity in
carbon has yet to be taken advantage of. In other word when the tips are in
the transonic range you want a thin blade as the drag of the tips becomes
a significant consumer of HP. Therefor a stiff thin tip is an advantage.

Paul Lamar