Calculations

[David Gundling]

Message text written by INTERNET:discussion at nsrca.org
>On 1/23/05 11:31 AM, "Ron Van Putte" <vanputte at cox.net> wrote:

>  
> On Jan 23, 2005, at 7:22 AM, Amram Privat wrote:
> 
>> Does someone has an experience and can advise me on a good software for
>> calculating thrust based on motor output (electric), prop size and
pitch,
>> speed weight etc etc..
>  
> Go to; http://www.motocalc.com/.  They have a program which does
everything
> you mentioned and more.  You can download  the program and use it free
for 30
> days.  If you decide it's what you want/need, you can pay them for it and
use
> it from then on, after they give you an unlocking code.
> 
> Ron Van Putte 
> 

Thrust is measured in pounds, yes even thrust from a propeller driven
aircraft.  The way full scale aircraft and engines measure thrust is on a
test stand there the engine is mounted on a movable stand that is anchored
with a force transducer calibrated in pounds.  The engine is ran up and the
resultant trust is measured.

Apply the same principle to our smaller model engines.  You could make a
stand on wheels (to minimize friction) and anchor it with a spring scale
Mount the engine with a small tank on the stand and chose an appropriate
size prop.  Run the engine up, record the RPM and the resultant trust from
the scale.  Now you can see the effect of many different variables, fuel,
prop size, mixture settings, even glow plug heat ranges.

With all of the data you can collect you should be able to really fine tune
your engines/fuel/props for maximum performance<

Possible alternate approach

There is an alternate method. Buy the Astro Flight "Electric Motor
Handbook".
In it, I think you will find most of the answers you are looking for. It
has a whole table on the amount of power absorbed by 
various size props at various RPMs. As for thrust, if you check old issues
of R/C Report you will find that
the engine test reports give thrust readings for various sizes of props at
various RPMs. The info should put you very close to what you are looking
for.

Good luck.

Dave

Dave
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