Re: [Flightgear-devel] FGPiston patch RFC

[Ron J. <wi...@je...>]

On Fri, 2008-12-19 at 23:28 -0700, John Denker wrote:
> An alternative approach is diagrammed at
>   http://www.av8n.com/fly/throttle.htm#fig-x1xt
>
> This is more plausible in terms of the physics of the situation, and
> more consistent with everyday Real World pilot experience.

Here is a dynamometer test report of an engine intended for use in an
aircraft:
http://members.cox.net/alg3/Dynamometer%20test%20report.htm

Please note especially the RPM v. Manifold Pressure chart at the end:
http://members.cox.net/alg3/Dynamometer%20test%20report_files/image005.jpg

The shape of this curve is the reverse of the curves you've postulated
in your figure 3.  It also remains above 28 inHg to nearly 5000 RPM.
Your proposed model appears unable to duplicate this feat, as your full
throttle line is below 0.94 (28 inHg / 29.92 inHg) MAP by 0.07 RPM.

While we're at it, please consider this dyno picture
http://aagearinc.com/supercharged_na.gif
Yes, its a motorcycle engine not an aircraft engine, but both function
according to the same principles and studying one will lead to
understanding of both.
The red line is a normally aspirated engine.  You can clearly see the
power peak and fall off.
The blue line is the same engine with boost.  It produces linear power
to the top of the RPM run because it can breathe.

Thanks,

Ron