On Sunday, April 24, 2011 05:41:43 PM Ron Jensen wrote:

> On Sunday 24 April 2011 15:00:41 Pavel Cueto wrote:

> > Hello to all

> >

> > I'm developing with a friend the PZL M18B "Dromader" in JSBSim, doing

> > this first with aeromatic generated data; and now, we are mixing them

> > with real aircraft data from very reliable sources. However, the engine

> > behavior seems very different in numbers compared with what we expect

> > from it:

> >

> > Engine: ASz-62IRM18

> > Max.RPM: 2200 / Min.RPM: 550

> > Constant speed propeller


snip


>

> > "Volumetric efficiency"

>

> VE controls how much air goes through the engine at a given RPM. You can

> use it to fine tune fuel flow at a given manifold pressure/rpm setting.

> Its partner, BSFC, is the amount of power the engine produces per unit of

> fuel consumed. Use it to tune the power produced.

>

> Both are on the property tree under /fdm/jsbsim/propulsion/engine/ so you

> can control them at run-time.



For an example of how to do this at run time have a look at the Systems/Propulsion.xml file for the p51d.


The supercharger model used by JSBSim assumes a turbo charger so the power and fuel consuption curves are incorrect for an engine driven supercharger where more horse power (and fuel) are used to drive the supercharger. Using functions to set VE and BSFC at runtime gives you a way to get fuel consumption and power curves close to correct but it does take a lot of effort to get these functions tuned.


snip


> > How can i to adjust the cooling factor to avoid engine overheating?

>

> The latest code has two properties that can be set in the xml file. Cooling

> factor can also be controlled at runtime via property tree

> under /fdm/jsbsim/propulsion/engine/cooling-factor.

>

> cylinder-head-mass controls how fast the engine heats up and cools off. So

> if you have a '5-minute' limit on a power setting you can adjust this

> value so the engine just starts to overheat at the end of the given time

> frame.

>

> cooling-factor controls how much 'air' flows over the engine to cool

> it. Raising the value makes the engine run cooler. This can be used to

> simulate cowl flaps, for example.


For an example of how this might be used the p51d uses this in an "autopilot" (PID controller) to simulate the automatic cooling system doors of the P-51D. For manual cowl flaps this should be fairly easy to setup since you would only need to do some tuning to figure out the cooling-factor for the closed and open cowl flaps and then write a simple function to vary the cooling-factor with the clowl flap control position.