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Is 1910 Static enough? -9a w/ 72x72 Catto

R

Rick of Austin

Well Known Member
Thats what I am seeing as soon as I add full power on the takeoff roll. Its a 160hp RV-9a, recently I went from a climb prop to this very beautiful 72x72 composite prop. I asked for a cruise prop and thats what I have. The cruise is very quiet, super smooth and efficient. It will max at 2675rpm at WOT @ about 3,500. But as you can imagine my takeoff performance is marginal.
My strip is 2,900 feet of grass slightly sloped against my normal takeoff direction.
I used to let it fly itself off then accelerate to maybe 100+ for cooling and to let it spin up to higher hp. Using that technique now makes for a very flat climb out, uncomfortably so, especially for the neighbors in the house off the departure end :)
Would it be better to rotate to the best climb speed (maybe 75) and hold it there for the first couple hundred feet then flatten out? It just doest feel right to do that with only about 2100 rpm though
Thanks Guys
 
Yuck

This strikes me as patently unsafe, not to mention not any fun at all. :eek:
Go get a constant speed prop and get it over with.
 
It sounds like your field situation (grass, uphill, needing to climb out steeply) and your desire for a cruise prop are incompatible. Without a c/s prop, you get climb or cruise - never both.
 
At Best Climb angle?

Well I already know its not as safe as it could be but a 3000' field is not exactly short. A CS prop is out of the question for me.
What do you guys think is best, holding best angle for 500' or a very flat climbout at 110?
Thanks
 
You need to have a prop that maxes at 2700 rpm at 8000' dalt, at least. your static ought to be about 2100-2200. Get another prop!
 
I vote

I vote pitch for 75. Either your energy is in speed or altitude, either one makes little differance. As long as you are making enough power at that airspeed to be comfortable. Will speeding it up a little give you a little better climb? Does the climb prop change best angle due to power available at that airspeed? Or is that purely a function of A.O.A.?
 
I agree with others, your static RPM is way low and you need a different prop. However, given the situation, my answer would be to climb at a better angle initially, as long as it doesn't cause other problems (like overheating).

greg
 
I have an o-320 in my -9. Originally my Catto prop had a static RPM of 2250 and max RPM at 8KDA of 2920 WOT. Yep, you guessed it, wow, was that a climb prop. 2000FPM was no problem at all. Of course cruising around at 2700 RPM sure did make a lot of noise.

So, I sent the prop back to Craig and now my static is right around 2150-2175. My max RPM at 8KDA WOT is 2680. Definitely noticeable climb rate reduction, but still not bad. Maybe 13-1500fpm. Cruising at 2500 rpm will produce about 150KTAS.

Although I am happy with my numbers now, the desire for a constant speed prop is tempting. If anyone would like to donate one to the Tony Phillips Charitable Climb Rate Foundation (C.C.R.F.) that would be awesome. Sorry, no tax deduction however.

For now, I would send your prop back to Catto. He can re-pitch it and get you where you want to be. On his behalf, it's very difficult to pitch props for us RV guys as we all have different engines. Mine is an ECI, which is rated for 164 HP and running dual P-mags, which probably has some HP effect.
 
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66X70 Catto

My 3-blade 66X70 Catto prop on an O320 driven -9A has a static RPM of about 2250 with a full throttle speed of 189 mph at about 2600 RPM. Craig can fine tune the outer few inches of your prop to change the static and full-throttle RPMs.
Leland
 
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