Re: propellor and rubber of a F1D model

From: kevin_f1m <kevin1990__at_hotmail.com>
Date: Tue, 11 Mar 2008 10:13:41 -0000

Thanks for all help.

I will measure the angle at 3/4 of the radius. I allready find out
that I need to make new propblades, but for know I will find a
compromise with an angle of 32-36 at 3/4 radius towards the tip.

I will tell you next week about my progress and probably ask for more
help.

Kind regards,

Kevin Lamers


--- In Indoor_Construction_at_yahoogroups.com, "John Barker"
<john.barker783_at_...> wrote:
>
> Kevin
> I am not clear what your propeller block is like and how you are
using it
> but I think it is easier to ignore it for the moment. You mention
that at a
> radius of 50 mm you have a blade angle of 64 degrees. The sums are
correct
> but is the angle calculated from an assumed pitch of 650 mm or is it
> measured?
>
> In any case the blade angle so close to the hub is not a good
reference
> point. The significant factor in propeller performance is the
blade angle
> at the radius three quarters of the way out towards the tip. I
think with a
> modern F1D that you will find this angle is usually about 32 – 36
degrees.
> That is the place to check your propeller and by measuring the
angle, not by
> some guessing at what the prop block may give.
>
> It is a pity that pitch has such a hold in model stuff. (in
propeller design
> text books it is rare to see the term mentioned.) It is imprecise
and
> virtually impossible to measure and is usually assessed by a
calculation
> from the blade angle, so why not just stay with the blade angle.
>
> Le Roy
> Kevin and Bill Gowen have already explained very well the benefit of
> specifying rubber as grams per metre but I would like to add a
further
> point. When using rubber width to define the motor it is common
for people
> to assume the thickness is standard at the manufacturers 0.04".
This is not
> the case and difference of 0.002" are not uncommon. As an example
of the
> effect of thickness variation take the case of the 0.6g motor made
from 1.3
> g/m rubber that I gave in an earlier post.
>
> The motor was 1.3 g/m it made up into a loop 9.1" long and took
1594 turns.
>
> If the rubber had been 0.002" thicker then the g/m would have been
higher
> with the following result.
>
> Motor 1.365 g/m would make a loop 8.7" long and would take 1482
turns.
>
> A turns formula based on g/m takes care of these variations much
more
> easily.
>
> John
>
>
>
>
> [Non-text portions of this message have been removed]
>
Received on Tue Mar 11 2008 - 03:13:45 CET