Re: RE: Bernard Hunt EZB Pitch Specifications

From: James Alderson <aldershine_at_hotmail.com>
Date: Sun, 8 Sep 2013 22:07:20 -0700

Hi Leo,

Just read over your response a couple more times. I think I am catching on. Am I correct to say that most of the best F1L fliers mold their blades on pitch blocks about 7.5 inches less pitch than their actual blade setting will be? If so, why is that more efficient than using a pitch block with the same pitch as the setting used to attach the blades? Less drag? More thrust? Better washout? This is all very fascinating to me.

Thanks Leo,

James Alderson

Sent from my iPhone

On Sep 8, 2013, at 5:10 PM, leop_at_lyradev.com wrote:

> Jim,
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> A plane that advances or goes forward 22.5" for each revolution of the prop is said to have a prop with a 22.5" advance ratio (AR). If an EZB prop is built on a 22.5" helical pitch block, has an advance ratio of 22.5" (the as built helical pitch and the AR often do not come out to be the same), and is set at a pitch of 26" at a 5" radius, the prop blade will have an angle of attack (AoA) of 4 degrees along its whole length. How does one get the 4 degrees? The angle of a blade set at 22.5" pitch is 35.6 degrees at a 5" radius. The angle if the blade is set at 26" pitch at a 5" radius is 39.6 degrees. The difference of 4 degrees is the AoA of the blade.
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> An EZB is often a much lighter and slower plane compared to an F1L. The as flown AR's may not be the same so a good EZB prop design may not work well for an F1L. As a point of comparison, my current F1L flies with an advance ratio of about 23" (this is by design and I built the prop on a 23" helical block). I set my blades with an AoA of 7.5 to 8.5 degrees (or a 30" to 31" pitch at a 5" radius). The prop has a 15" diameter. This AoA (or pitch) is similar to many other F1L's, while the AR of my F1L is more than usual. Stan Chliton's Spirit F1L has an AR of just over 20" and a pitch of 26.5" (I do not know the exact radius but somewhere between 4.5" and 5") for his 15" prop. This gives an AoA of about 7-7.5 degrees. The same AR, AoA, and pitch are found on Laurie Barr's CargoLifter F1L (14.7" prop diameter. Both of these planes are among the best F1L's and one cannot go very wrong copying their design parameters.
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> Leo
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> --- In Indoor_Construction_at_yahoogroups.com, <indoor_construction_at_yahoogroups.com> wrote:
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> I am becoming more and more interested in propeller design and construction. Recently I read the following specifications found on Bernard Hunt's EZB plan from the early 1990's. Blades molded on 22.5" pitch block/ Blades rotated to 26" pitch at 5" radius when attached to spar. Am I right in thinking that this would produce a prop with more blade twist that a standard blade formed on a 26" block? More angle of attack at the root and less at the tip? (but standard 26" pitch angle at the 5" radius station?)
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> I'd like to know how I can learn more about these types of adjustments and what they produce.
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> Thanks,
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> James Alderson
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Received on Sun Sep 08 2013 - 22:07:21 CEST