Re: Re: Analysis of the new F1D rules

From: Nick Ray <lasray_at_gmail.com>
Date: Wed, 16 Apr 2014 21:58:57 -0400

Assuming the power for level flight remains constant, how does one drive a
19.2" prop with a smaller cross section of rubber than was previously
required to drive the smaller prop? I know prop efficiency increases as the
diameter increases, but I thought this was proportional to the sink rate as
a glider times (larger prop diameter divided by the smaller prop diameter)
raised to the 0.1 power?

This would mean the prop efficiency would increase by 0.5% in the example
used above. I wouldn't think this would actually effect required power for
level flight noticeably.


On Wed, Apr 16, 2014 at 4:04 PM, <ykleetx_at_gmail.com> wrote:

>
>
> I promised to provide further analysis on the following:
>
> 2a. keeps the overall flight weight the same as before, at 1.8 g. This
> means that the model would fly at the same speed, have the same sink rate,
> and experience the same aerodynamic loads. In addition, the 2/3 reduction
> in motor weight would translate almost directly into a 1/3 reduction in
> flight times.
>
> 2b. would decrease the overall flight weight to 1.6g. This means that the
> model would fly at a slower speed, have lower sink rate, and experience
> less aerodynamic loads. This is a higher performing model than before.
> The overall flight time would be reduced, but not by less than 1/3. (I
> will provide the prediction in a follow up post.)
> 2a. Same size prop, rubber cross section, flight time reduction would be
> 33.3%. In the Mine, this would be a 18.3" prop.
>
> 2b. I estimate that a larger prop would be used with a thinner cross
> section. In the Mine, this would be a 19.2" prop. Flight time reduction
> would be 16.5%.
>
> These are based on my possibly flawed estimates that are based on a
> possibly flawed simulation. I think they are in the ball park, though.
>
>
>
Received on Wed Apr 16 2014 - 18:58:58 CEST