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



I agree with Matt.  You should be much more conservative with your HP
estimate for the prop maker.  Powersport was only claiming 210 h.p. and
I think that is more in line with what the average p-port builder can
expect.  In aircraft we are seldom able to achieve the same optimum
numbers produced in dynos and on cars.  Largely that is due to our fixed
gear ratio an also by imperfections in the design and fabrication of the
intake and exhaust manifolds, like Matt mentioned.

With reguard to props, I am still mostly an advocate of fixed pitch
composite props for our application.  The MT electric c/s is heavy (like
a lot), expensive (like a REAL LOT), and comes with an RPM limitation
that you would not want to have to live with (can't remember the number
off the top of my head).  The IVO is, well, the IVO... search the
archives.  And Whirlwind, as of the time I called them asking about a
prop 7 years ago, would not make one that turned in reverse direction or
with custom blades. (even in ground adjustable form).  Warp Drive and
Whirlwind both do not make hubs and blades big enough for our application.

So that pretty much leaves fixed pitch.  I disagree that metal props are
always faster.  If this is true, then why are all the top finishers,
indeed most of the fields in the Formula One, Biplane, and Sport classes
at Reno using composite props?  Kevin Eldridge was the odds on favorite
to win the 2010 Super Sport class in his Nemisis NXT when an oil line
blew and overspead his prop causing it to quickly depart the aircraft.
He credits the fact that he had a composite prop and not a metal prop
with saving his life because a metal prop would have taken the engine
with it.  But that's not why he was using a composite prop, he was using
one because it was fast - and he was doing more than 400mph.

If there is a difference in modulus that disadvantages composite props,
then it is so small that it does not overcome the other advantages that
composite props offer in terms of efficiency.  Not to mention ease and
cost of production

Although the Catto has an epoxy layer, it is not difficult to re-pitch.
Craig took a few degrees out of mine in just a couple of days for
minimal cost.  Matt is right, Craig said that it is easier to remove
pitch than to add it.  But still, go with about 210 hp. when having your
prop made.  Getting a loaner would be nice if you can find one.Or,
maybe start with a used prop that you can re-sell for about the same
price that you paid once you get some performance numbers.