Jet engines capped at 100% CN1

[MSFS 2024] Bug Reports Aircraft
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1

Version: Any

Frequency: Consistently

Severity: High
Similar MSFS 2020 issue: https://devsupport.flightsimulator.com/t/is-there-a-planned-fix-for-corrected-n1-being-capped-at-100/5832

Bug description:

The first major bug is that CN1 is capped at 100%. From a flight model standpoint, we need to go past 100% CN1 at high altitudes to be able to maintain a stable indicated N1, which is what happens in reality.

In FSX -which uses the same Corrected method as MSFS- we were able to go past 100% N1 as we climbed and therefore, we could keep N1 consistent throughout different altitudes. In MSFS Corrected N1 is capped at 100%, meaning that with full throttle the indicated N1 will decrease with altitude.

We can programmatically override the TURB ENG N1 variable, but that is an extra step that shouldn’t be needed as the engine simulation is correct, other than that cap at 100%.

Repro steps:

Take the Grand Caravan, 737 MAX or PC-12NGX and set it to full power and climb from sea level to 15000ft without moving the throttle. You will notice that indicated N1 will drop with altitude. IRL it should be stable, meaning that Corrected N1 should increase with altitude.

COMMENT:

The base sim already has the correct mathematics in it and Corrected Fuel Flow sets Corrected N1 already. If the clamp is removed from CN1, all developers have to do is adjust their fuel flow to achieve higher N1 with altitude and their engines will work perfectly, without external programming.

If a 3rd party developer does not update their fuel flows after this is fixed, their plane will work exactly the same as before, so no problems will be caused.

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I can’t say for the others but with the C208 the corrected N1 is NOT capped. It stops at 100% only because the fuel_flow_max is set the same as high_fuel_flow.

If I set fuel_flow_max higher then high_n1 then CN1 will go happily over 100%. You can also map GENERAL ENG THROTTLE LEVER POSITION to go past 100% and CN1 will flow.

But ye it would be much much easier if we could just set high_n1 lets say 110 and be done with it.
For example:
high_fuel_flow = 607
fuel_flow_max = 900

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I am aware of that, but it still involves feeding an Avar through code. Throttle shouldn’t go past 100% if we are looking at realistic ops.

In my tests, setting max fuel flow to a high value works but the CN1 will settle at 100% again.

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I can confirm this issue exists for helicopter engines as well. With throttle at 100% I can only get the N1 above 100% for a short moment instead of consistently.