I agree for the most part. My propeller of choice is the Ikara SO prop that Ray Harlan sells. It was originally designed for the older C division rules that allowed a larger prop (don't remember the diameter - 24cm maybe?). I still use this prop because it has more blade area than anything else available. It also has most of the area in front of the spar where it should be. But the pitch, which I thought was on the high side for the larger diameter, is way too high when cut down for the 2007 rules.
There are folks out there who can run a 2:1 P/D on an SO model and get good times, but I've never had much success going that route. My recommended starting point is 10 pitch which is about 1.4 P/D. My current LittleSquare prop is set at 12 pitch or about 1.7 P/D. I will lower this some for the next time out.
I measured the pitch on a just finished student prop and it was 14. This will be reduced before testing starts on this model.
----- Original Message -----
From: Robert Clemens
To: Indoor_Construction_at_yahoogroups.com
Sent: Sunday, January 21, 2007 10:37 AM
Subject: Re: [Indoor_Construction] Propellor Pitch?
John Barker opined, "...from all I have read it is almost unheard of for
bought propellers too have too much pitch - it is usually the opposite..."
John, you're generally correct with this assumption, but the Ikara plastic
props from the Czech Republic often come with excessive pitch built in.
These propellers are the airscrews of choice for our Wright Stuff Science
Olympiad event whose rules specify the use of "a single two-bladed
commercially made plastic propeller."
Two or three years ago I was helping mentor a team of middle school students
who were to compete in the Wright Stuff event. When their models were
completed we mounted the Ikara props provided in the kits. The pitch was so
high that the props provided almost no useful amount of thrust. On the spot
I took two pairs of pliers and twisted the prop spars for a eyeballed lower
pitch. Voila! The models immediately were flying in a normal and successful
manner.
Bob Clemens
[Non-text portions of this message have been removed]
Received on Sun Jan 21 2007 - 09:14:45 CET
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