Thanks for your input John. I value your time and experience in this great sport of Indoor Free Flight. You sent me a very good analysis for calculating F1M moments a few months ago. I have saved those notes and will use them for any event I build for.
I have decided that the best event for me to focus on for the next couple of years is F1L. I plan to build many models and as many props as I can. Yes, I would love a copy of the spreadsheets you mentioned.
I will follow your advise and concentrate more on blade angle than pitch. I would also welcome your thoughts on how to build uniform prop spars. They seem to be very important.
Sincerely,
James Alderson
To: Indoor_Construction_at_yahoogroups.com
From: john.barker783_at_ntlworld.com
Date: Tue, 10 Sep 2013 12:01:02 +0100
Subject: RE: [Indoor_Construction] Re: Bernard Hunt EZB Pitch Specifications
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_at_yahoogroups.com [mailto:Indoor_Construction_at_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 AldersonTo: Indoor_Construction_at_yahoogroups.com
From: mkirda_at_sbcglobal.net
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_at_yahoogroups.com, James Alderson <aldershine_at_...> 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_at_..." <mkirda_at_...> 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 Wed Sep 11 2013 - 20:33:37 CEST