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MV-JimStewart avatar image
MV-JimStewart asked FlyingRaccoon commented

Slow responsiveness of [RECIP ENG DETONATING] simvar? Bug?

While testing out the functionality of the RECIP ENG DETONATING simvar, I've noted that while it does seem to work, it seems quite slow. Is this a bug?

I've set up an engine with the new supercharger with enough top end boost to significantly over-boost the engine at sea level. I've then set the detonation_onset parameter in the engines.cfg file to ensure that detonation happens if the engine is over-boosted enough. This engine does not have any anti-detonation systems.

The end result is successful, more or less - the engine immediately starts to lose power. However, trying to monitor this event seems difficult, since the simvar [RECIP ENG DETONATING] doesn't seem to trigger until a little while after it's already hugely noticeable that something is wrong with the engine.

Ideally, it would immediately trigger the simvar, even a few seconds before the engine failure. This would allow detonation effects such as sounds to be triggered, giving the pilot a warning that something REALLY bad is about to happen.

On the same subject, I've noted a similar behavior with the RECIP ENG NUM CYLINDERS FAILED simvar. After the engine has completely stalled, the number slowly starts climbing until all cylinders have failed. Again, ideally, this would be a metered response - if the engine starts detonating, after X seconds cylinders start failing in a staggered fashion, perhaps allowing the pilot to throttle back, and limp to the nearest airport with only a couple of failed cylinders. If this simvar also was immediately responsive, this would allow the sounds to be adjusted appropriately.

Edit: I should also note that the RECIP ENG DETONATING simvar also only seems to work while 'Engine Stress Damage' is turned on in the Assistance Options. While I can understand that this option should allow for the user to turn on or off engine failures, the effects of detonation is something can could still be monitored and acted upon (via sounds, effects) even if outright engine failures aren't desired by the user.

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FlyingRaccoon avatar image
FlyingRaccoon answered FlyingRaccoon commented

Hello @MV-JimStewart

From what I can see in the code, cylinder detonation will start only once the cylinder health has gone below 60%. And the RECIP ENG DETONATING simvar will return true once at least 2 cylinders are detonating.
That could explain the delay you're observing.

A cylinder will be set to failed state when its health has reached 0% and the health will degrade at a rate that depends on the delta with the detonation_onset parameter.
I'm not sure why this would happen after the engine has stalled. I'll run some tests about this.


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FlyingRaccoon avatar image FlyingRaccoon ♦♦ commented ·
Regarding the cylinders failing after the engine has stopped: the damage evaluation still occurs when combustion has stopped but the manifold pressure should drop back to the ambient pressure in that case.

So the only reason I could see for cylinders failing after the engine stalled is that your detonation_onset parameter is set to a value that is below the ambient pressure but that would be surprising, no?

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