Hey, we realized that our aircraft (FBW 320) produces quite some forward
thrust in the reverser range, which seems to be caused by the direct
THROTTLE LEVER POSITION”. So only at full reverse, we do get full nozzle
depoloyment and appropriate reverse thrust. We did try setting
“min_throttle_limit” to very low values (i.e., -0.01), which did lead us into
the right direction but scales the “TURB ENG REVERSE NOZZLE PERCENT” simvar
and goes to 2000% in full reverse leading to very hard backwards acceleration
(-20 throttle pos leading to 2000% nozzle). Ideally, we would be able to write
to this variable. But of course, other suggestions are welcome as well.
Attempts to scale the thrust using “reverser_available”. Were unsuccessful, it
seems like values below 1 are being ignored, I couldn’t observe a reduction in
thrust. Thanks, Saschl

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Hello @saschl When you say “quite some forward thrust”, do you mean more
forward thrust than in idle position?

Hi @FlyingRaccoon thank you for the reply. No, it’s less than idle but still
producing forward thrust. See the following picture with thrust at idle:

And here on Reverse idle
(Throttle is negative but thrust still positive):
Our goal would be to have
“negative” thrust starting with Throttle below 0. Currently it needs position
around -15 until thrust goes below 0lbs, which is not correct for the plane.

Hello @saschl First, some info about how our reverse are modeled (inherited
from FSX). The reverser nozzles are extended linearly on the reverse range and
this is not configurable or controllable through simvars or key events.
Reverse thrust scalar is applied to current turbine thrust and is computed as:
1 - ( 1 + 0.375 * reverser_available ) * (throttle_lever_pos /
I have investigated your issue on our own A320 and
noticed similar behaviour. Here are some total thrust values I plotted,
changing values of reverser_available and min_throttle_limit

As reverser nozzles are extended
linearly (which I think is not the case on the A320 neo), it adds another
delay in the reverse efficiency. So we even have a slight increase of thrust
compared to idle. I think the problem could be solved by adding some config or
events to control how the nozzles are deployed and I’ll review the subject
with designers. Also, from my understanding of cold stream reversers, at low
RPM it can end up in a situation where the amount of reverse thrust is
inferior to the thrust still being produced by the combustion chamber. Are
you sure you are supposed to have negative thrust as soon as you go in reverse
mode? Regards, Sylvain

Hi @FlyingRaccoon , thank you very much for the detailed answer. That supports
my observations made, especially the effect on thrust of min_throttle_limit.
“As reverser nozzles are extended linearly (which I think is not the case on
the A320 neo)”:
I think you nailed it here. Would be really nice if you could
check and add a setting or event to control the Nozzle deployment, as to my
knowledge it is fully deployed on the 320 on any reverse setting (as you
observed); so not dependent on the throttle position. That way we might
already have enough flexibility to improve reverse thrust modeling. " Are
you sure you are supposed to have negative thrust as soon as you go in reverse
No, I’m actually not sure, I do not have numbers right now but I can
check with the team :slight_smile: Again thanks for the answer and investigation, really
appreciate it! Cheers, Sascha

Hi, is there an update on this issue?

We still seem to not have gotten any additional way to influence the reverser deployment. This makes simulating accurate reverser behaviour on most turbine engines impossible.

Is there any solution on the horizion? Like being able to set the amount of reverser deployment or modifying a time constant for the deployment?