[rebel-builders] More prop questions

[Walter Klatt]

John, whether you are on amphibs or wheels, you want a prop to maximize the
power of your engine. So for starters, you want a prop that will be near max
rpm (2700 for the 320) at full throttle straight and level. Anything less,
and you are not getting the most out of your engine for the money and
weight. My 320 on amphibs maxed out at 2720 rpm which was just about
perfect.

Then you want a prop that gives you the highest static or take-off rpm and
climb but still within the max rpm at top speed. Again, my old Sensenich
with the 320 excelled there as it gave me 2500 on take-off, to help with
water take-off performance.

On wheels, you will have a greater speed range, so will likely need a pitch
that brings your take-off rpm down to about 2450, if you don't want to
exceed max rpm at top speed. With the Sensenich that means about 2 inches
more pitch.

So, whether wheels or amphibs, you want a prop that will get the highest
take-off rpm, without exceeding your top speed max.

Once you have the right size prop for your engine, the rest is all about
thrust, for the speed range profile of your aircraft. For that, I only trust
side by side take-off and flight comparisons with identical planes. And
don't get sucked in by some of the BS the custom prop makers give you about
how their prop can do it all. I just don't believe it, especially after some
of the crap that I have seen happen.

Personally, though, I would probably just keep the same prop as I have with
the amphibs. You may run at a higher rpm in cruise, but you will not be
sacrificing fuel consumption if that is what you are worried about. That was
another myth that I proved wrong when I was testing different props and
pitches with my plane. I found that if you fly the same speed, but at a
different pitch and rpm with the same prop (I used to have a ground
adjustable Warp, too), your fuel consumption remained the same. I have a
fuel monitor to one decimal place, so had some pretty accurate measurements.
Drag, weight, and even c of g (aft is better) had a greater impact on fuel
usage. The biggest effect was your flaperon position. Reflex definitely gave
you much lower fuel consumption at the same speed.

Again, JMHO.
Walter

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of John
R. Davidson
Sent: Sunday, December 04, 2011 5:47 AM
To: Rebel List
Subject: [rebel-builders] More prop questions


First, thanks for all the winter flying suggestions. Much food for thought.

Next, does anyone have contact information for Jason Brownell? I've sent a
couple of e-mails to the address he uses for this list with no response. His
spam detector may not recognize my address.

Finally, does anyone have recommendations for a prop for the Rebel on
wheels?

Thanks,

John




-----------------------------------------------------------------
List archives located at: https://mail.dcsol.com/login username "rebel"
password "builder"
Unsubscribe: rebel-builders-unsubscribe@dcsol.com
List administrator: mike.davis@dcsol.com
-----------------------------------------------------------------






-----------------------------------------------------------------
List archives located at: https://mail.dcsol.com/login
username "rebel" password "builder"
Unsubscribe: rebel-builders-unsubscribe@dcsol.com
List administrator: mike.davis@dcsol.com
-----------------------------------------------------------------