I am modeling a Le Rhone9J and according to wiki to get higher speeds with a
low rpm like 1,300 they add a heavy flywheel. I have been trying to figure out
a way to increase the overall speed with a low rpm and not drop the drag for
the airframe. How can I do this? Also for some reason with the engine cfg set
to fixed prop and only at 1,300 rpm fixed_pitch_beta is not making any
difference. I have never seen this before. Not sure it’s because of the low
rpm. Usually this the overall aircraft speed change.
https://en.wikipedia.org/wiki/Le_Rhône_9J
Hello @Flysimware Either your engine does not
output enough power, or the propeller does not convert it into enough thrust
or the frame produces too much drag. You seem to eliminate the drag and I
assume you are pretty confident about the engine power output? So that leaves
us with prop config only to make adjustments, is this right? Do you have any
reference thrust to compare to or this is empirical and you want to increase
thrust until you have the proper speed? Also, I understand you only want to
change performances at low RPM but you are happy with mod/high RPM? That’s a
lot of questions, but I need to make sure before we can advise a parameter to
adjust. Regarding the fixed_pitch_beta parameter having no influence, I’ll run
some tests. Regards, Sylvain
1. You seem to eliminate the drag and I assume you are pretty confident about
the engine power output? Yes. 2. So that leaves us with prop config only to
make adjustments, is this right? Yes. 3. Do you have any reference thrust to
compare to or this is empirical and you want to increase thrust until you have
the proper speed? Proper speed. 4. Also, I understand you only want to change
performances at low RPM but you are happy with mod/high RPM? There is no high
rpm. This may be the BIG issue. I posted more info below. thrust_scalar for
props solves the issue but why does the fixed_pitch_beta make no change. I
wonder if low rpm is an issue. Never seen this before. i would prefer to use
1.0 for thrust_scalar and have more bite for the fixed_pitch_beta and
increase the engine power for the extra bite. But something is wrong and it
may be the low rpm or low compression. I mean pitch for the prop is
everything. Right? How can this make no change?
What I also did to get 1,300 rpm in high altitude while not going above 1,300
rpm in low altitude was adjust the engine_mechanical_efficiency_table so there
is less efficiency above 1,300 rpm. This helped a lot. I currently have auto
mixture on for testing only. Later this will get turned off as there is a
mixture. Better to test with it on. But since the critical_altitude = 12000 we
should not be losing performance at 6K feet. So normally I would not have to
do this trick. So I am just overall confused as this low rpm engine is
throwing me for a loop as I normally do not have these issues. I am hoping I
made a simple mistake but so far all seems correct.
Hello @Flysimware I tracked the fixed_beta_prop
issue and it appears we have a problem similar to what’s described here:
https://devsupport.flightsimulator.com/t/4955 We have a set of propeller
parameters that are not supposed to be mandatory but that will trigger an
airfile reading and overwrite your own config when not being explicitly set in
the cfg file. Here’s the list of parameters: propeller_type
propeller_diameter propeller_blades propeller_moi beta_max beta_min
min_gov_rpm prop_tc gear_reduction_ratio fixed_pitch_beta
low_speed_theory_limit Make sure they’re all defined in your cfg file, even
if just set to default values. We will change the documentation and Aircraft
Editor to reflect this. I assume this will allow you to solve your problem.
Come back to us if that’s not the case. Regards, Sylvain
Adding these 2 entries fixes the issue. The fixed_pitch_beta does nothing as
the sim is reading the beta_max instead. I found I can put zero for the
two other entries and it proves the sim uses the beta_max as the
fixed_pitch_beta . So now I know I was not going crazy. Thanks for solving
this @FlyingRaccoon and I am glad to help
point this out. beta_max=45 beta_min=0 fixed_pitch_beta = 0
Hello @Flysimware I’m not sure what you mean
here… I tested adding beta_min and beta_max but the beta ends up
being the one defined in fixed_pitch_beta in my case (visible in engine
debug view) 
Regarding the AE
removing those parameters, you can temporarily edit the
FileDefs_AircraftEditor.xml file in the base packages and remove the
ValueControl sections:
Regards, Sylvain
I will check and see what this shows on the simvars.
beta_max=45 beta_min=0
fixed_pitch_beta = 0
I tried a bunch of different arrangements and I think I had something similar
and it failed as I got 1 degree for pitch when using this arrangment. But
maybe if the beta_max is higher than fixed_pitch_beta then it reads
fixed_pitch_beta .
beta_max=1 beta_min=1
fixed_pitch_beta = 24
For the AE removing the entries I had removed this quote as it actually does
not remove them. So all ok there. Thanks.
I was right until fixed the beta_max is what is being used. When I change
the fixed_pitch_beta values not only is the simvars not changing for the
prop beta:1 but the airspeed only changes when changing the beta_max.
I am also not sure what tool you used but the airspeed tells me what is being
used. Thanks again for solving this. Looking forward to a fix.
Hello @Flysimware I don’t reproduce this
behavior. I always get the value set in fixed_pitch_beta. Can you provide
me with your package so I can check a context related issue? Regards, Sylvain
But when testing do you see the airspeed changing? Because this is what tells
me which is being used. Will post the current project below.