#120 P-Factor gives no effect?

[Daniel Dubreuil]

Hi,

Sorry, I'm not sure that the subject of my question is a bug (hard to believe), but I don't know where to place it. The problem seems so simple that I can't put it in "Support Requests".
Prior to disturbing you, I've posted in the FG forum (Development ‹ Aircraft ‹ Flight dynamics model) to insure that I was not doing a mistake but I've had no response.
https://forum.flightgear.org/viewtopic.php?f=49&t=34376

In the propeller file, the
<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 test file (c172p):
(attention: the c172p already has a spiralling propwash effect, which preferably should be cancelled to isolate this P-Factor effect. Property: /fdm/jsbsim/aero/coefficient/spiral-propwash-coeff)

File excerpt:

<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">
    <tableData>
        0      0.1040
        0.1    0.1040
        (etc...)
    </tableData>
</table>

<table name="C_POWER" type="internal">
    <tableData>
        0      0.0660
        0.1    0.0650
        (etc...
    </tableData>
</table>

</propeller>

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

Thank you if you can help.

Dany

[Bertrand Coconnier]

Hi Daniel,

The JSBSim project has moved to GitHub, could you please post your issue there ?
https://github.com/JSBSim-Team/jsbsim

Thanks.

Bertrand.

[Bertrand Coconnier]

Addressed in issue #64 on GitHub