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JSBSim: P-Factor gives no effect?

Good sims require good FDMs (the "thing" that makes an aircraft behave like an aircraft).

JSBSim: P-Factor gives no effect?

Postby dany93 » Mon Jun 11, 2018 1:45 pm


Prior to disturbing the JSBSim developers, I'd like to be more certain of not doing a mistake.

In the propeller file, the
Code: Select all
    <p_factor> number </p_factor>

seems having no effect, even at high RPM and AoA angles. (I've done tests on two different single-engine aircraft, having different propeller files)

I've tried p_factor values up to 10000, which should give a very exaggerated yaw effect, at no avail.

An excerpt of my file:
Code: Select all
<propeller name="NACA 640 (5868-9) 76-inch 20deg Two-Blade Propeller" version="1.01">

    <ixx> 1.67 </ixx>
    <diameter unit="IN"> 76.0 </diameter>
    <numblades> 2 </numblades>
    <p_factor> 60 </p_factor>

    <table name="C_THRUST" type="internal">
            0      0.1040
            0.1      0.1040

    <table name="C_POWER" type="internal">
            0      0.0660
            0.1      0.0650


I could not find a property which would enable me to check the effect in-sim.

I tried understanding it by doing the math calculation (based on velocity-vector additions) for a pure AoA disorientation but, very possibly due to my more than basic knowledge of C++, I couldn't understand the FGPropeller.cpp code at (lines 254 - ).
The only thing that is clear: "the effect is simulated by a shift of the acting location of the thrust".
After that, it should be proportional to the aircraft velocity, propeller RPM, AoA (small angle approximation).

Thank you if you can.


[EDIT, 14 jun 2018]
No response, posted a ticket (#120) on JSBSim FDM, Bugs
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