RE: RE: Re: Bernard Hunt EZB Pitch Specifications from leop_at_lyradev.com on 2013-09-10 ([Indoor

From: <leop_at_lyradev.com>
Date: 10 Sep 2013 05:29:35 -0700

John,

I was the one who made the mistake in the definition of the advance ratio, not Jim. I apologize to everyone in the group that I defined the Advance Ratio as the numerator (or the "advance") in the ratio and did not divide that distance by the propeller diameter (in my defense, not an excuse, one would need to multiply the AR by the prop diameter to get a useful number in the way I described of looking at props just as one uses pitch rather than P/D to produce a pitch block to form a blade). However, we both emphasis that it is the AoA of the blade that is important. I am sorry for any confusion this may cause.

Leo

--- In Indoor_Construction@yahoogroups.com, <indoor_construction@yahoogroups.com> wrote:

James,

I have had a deep interest in propellers for many years. I am fascinated by the fact that even a poor propeller will speed up or slow down, as if by magic, to suit the operating conditions at least to some extent and make our careful calculations and construction seem a waste of effort.

Please do not be offended if I correct your definition of Advance Ratio. Advance Ratio, usually denoted by J is equal to V/nD where V is the forward speed, n is the rotational speed and D is the diameter. To some extent it is an indication of the angle of attack of the propeller blades. If the forward speed is high relative to the rotational speed then the angle of attack will be high, and vice versa. Personally I don’t find it of great use in design but it comes into its own on comparison testing of test results.

If you want to move further in propeller design I recommend more concentration on blade angle than pitch. The word is very rarely found in text books on propeller design. I have checked every page of my Theodorson and there is not a single mention of the word.

More directly concerned with your questions; I wrote a paper for the 2012 Symposium dealing with Pitch Blocks for forming propellers and offered spreadsheets which dealt with constant angle of attack change, differing angle of attack change at each station and also the pitch distribution that occurred if a blade was moulded on a ‘wrong’ pitch block. Just say if you would like a copy of the spreadsheets.

John Barker - England

From: Indoor_Construction@yahoogroups.com [mailto:Indoor_Construction@yahoogroups.com] On Behalf Of James Alderson
Sent: 09 September 2013 17:16
To: Indoor Construction
Subject: RE: [Indoor_Construction] Re: Bernard Hunt EZB Pitch Specifications

Thanks Mike! I will be looking for the spreadsheet. James Alderson

To: Indoor_Construction@yahoogroups.com
From: mkirda@...
Date: Mon, 9 Sep 2013 14:32:32 +0000
Subject: [Indoor_Construction] Re: Bernard Hunt EZB Pitch Specifications

Hi James.

I got part of the way through rewriting a spreadsheet this morning.
I will post it later. With it you can enter a lower pitch, a rotation angle for the lower pitch and a higher pitch. It will spit out similar data as I posted earlier. I think I will add another column that tells you the delta change between the rotation and actual higher pitch so it will be easier to see.

LeoP's F1L flies slow for F1L. The prop is part of the equation, but is certainly not all of it.

Regards.
Mike Kirda

--- In Indoor_Construction@yahoogroups.com, James Alderson <aldershine@...> wrote:
>
> Thanks Mike! I really value your input. Thanks for the quick response. "Oversimplication" is okay for now. I can get educated as I go along. I already suspected uniform spars and blade flex were crucial factors. I have one 25" pitch block I got from Jake Palmer that I will use for F1L.
>
> Higher Times!
>
> James Alderson
>
> Sent from my iPhone
>
> On Sep 8, 2013, at 8:19 PM, "mkirda@..." <mkirda@...> wrote:
>
> > Here are the numbers.
> >
> > 22.5 26
> > Angle 3.5 Angle
> > 1 74.4 77.9 76.4
> > 2 60.8 64.3 64.2
> > 3 50.0 53.5 54.1
> > 4 41.8 45.3 46.0
> > 5 35.6 39.1 39.6
> > 6 30.8 34.3 34.6
> > 7 27.1 30.6 30.6
> > 7.5 25.5 29.0 28.9
> > 8 24.1 27.6 27.4
> > 9 21.7 25.2 24.7
> > 10 19.7 23.2 22.5
> > 11 18.0 21.5 20.6
> > 12 16.6 20.1 19.0
> >
> > Column one: At each inch station
> > Column 2: 22.5"P helical block
> > Column 3: Same 22.5" blade rotated +3.5 degrees
> > Column 4: 26" helical block
> >
> > Note nearly +2 degrees AoA at 1". Move in a bit and there is a bit of wash-out in the middle of the blade. At around the tip of an F1L prop (7-7.5") there is no difference. Only when you get further out do you see the wash-in again.
> >
> > At the risk of oversimplification, I see someone who has a block that is pretty close in pitch to what they needed, made a blade and mounted it to the spar rotated to the pitch they needed. As you can see, rotating the blade a couple of degrees makes very small differences in AoA over the blade overall.
> >
> > I suspect it will be far more important to have the prop spars with equal torsional rotation when loaded and blades that flex similarly.
> >
> > Regards.
> > Mike Kirda
> >
> >
>

Received on Tue Sep 10 2013 - 05:29:35 CEST