REFLECTOR: Fixed pitch prop info

[Herb Sanders]

Could you tell me if that is a two or three blade prop?  Herb Sanders

From: Geoff Gerhardt 
Sent: Saturday, March 08, 2014 7:07 PM
To: Velocity Aircraft Owners and Builders list 
Subject: REFLECTOR: Fixed pitch prop info

Folks, 

I have two props from Catto for my 173RG.  One, I had Craig build and another is one I got from a Cozy owner who had it laying around.  I have an LIO-360, and he had a left-turning prop from an auto conversion that he was no longer using, so I grabbed it.

The newer Catto prop is a 66" dia x 74" pitch.  This was Craig's recommendation for a 173RG.  The other is a 64" dia x 76" pitch.  So, the newer one is a couple inches larger diameter, but less pitch.  I have been flying with both of them on and off, but other than some seat-of-the-pants numbers, I never really did a good comparison of them to see which actually performs better.  Today, though, I put each on and took it out for a spin following very similar flight profiles and collected the data.

I used an app on my iPhone called CloudAhoy to collect the flight data.  Pretty neat app - I've provided links to the two flights that you can look over.

The newer Catto prop (66x74) has a static of 2150RPM, the older one (64x76) has a static of 2300.  Bottom line is, the smaller diameter, longer pitch prop has a shorter takeoff roll (~1200' vs ~1600'), but they both have about the same cruise speed (~175ktas, LOP, 2750RPM).

Have a look at the two flight profiles (links below).  If you're wondering about the funky pattern at the end of each flight, I did an overhead approach.

Older prop (Catto: 66" dia x 74" pitch - static 2300RPM)
http://www.cloudahoy.com/api/S.cgi?tZdSdTJtntdj2U


Newer prop (Catto: 64" dia x 76" pitch - static 2150RPM):
http://www.cloudahoy.com/api/S.cgi?6vLxFSMb9IQOt4HdC9A8


I would actually like to send the newer prop back to Craig and have him trim it to something like a 64x77.  I can live with the longer takeoff roll if it would give me a bit more on the top end.

Hope this info helps those trying to figure out a fixed-pitch prop to use.

Geoff



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