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 Alderson
_____
To: 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 Tue Sep 10 2013 - 04:01:06 CEST