Flameout in a dive

[primus_TR]

Hello,

 

I've had both engines flameout during a steep dive (~30 deg) for a strafing run with both throttle levers at idle position. Initially I thought I was shot, but checking the mission log I saw it was not the case. There was no indication that I was targeted nor shot at by any unit, but there was a peculiar radar altimeter error failure report (perhaps from the power off due to flameout?). Not sure tho.

 

So, is flameout to be expected during a steep dive with idle throttle?

 

Thanks

[sobek]

Do you still have the track? This is pivotal in reporting it as a bug.

[primus_TR]

I didn't mean this to be "bug report" per se, since I am new to this sim, so I didn't care to keep the track. But I'll try to reproduce it this evening and make sure I post the track.

 

So, am I correct in understanding that experiencing a flameout during a steep dive at idle throttle is not normal?

[ralfidude]

In my experience with this, it just "might" be caused by the fact that the engines are fed by fuel that work with the help of gravity. So there is a special pump that activates to pump fuel if gravity is no longer doing the job for about 10 seconds.

 

Try flying upside down for that long, you will experience engine loss.

 

Anywho, I figured this was the problem when i tried to fly upside down, and immediately pushed my stick forward to keep the nose level with horizon, so in about 3 seconds of inverted flight, my engines cut off due to the excessive negative Gs i was putting my aircraft through where the pumps could no longer pump fuel to the engines.

 

My suspicion is that it is the same culprit.

 

Did you dive on your target by simply pushing the nose of the plane down, or did you roll the aircraft inverted, push back on the stick, and roll back when you were close to your dive angle? That's the way it's supposed to be.

[macedk]

If you exceed maximum speed the engines can flameout.

 

For the technical stuuf you have to ask somone with that knowledge :)

[primus_TR]

I appreciate the feedback guys,

 

 

@Ralfidude

It was indeed a negative G dive for a few seconds (I pushed the nose down). It may well be the reason for the flameout.

 

Thanks for pointing it out. I wasn't aware of this A10c limitation (it is not fitted with a Spit MK1 carb I hope :D).

 

I'll mind negative Gs from now on. :thumbup:

 

@macedk

I never came near the maximum speed limit (~400 kts) throughout.

[ralfidude]

Engines work fine until you exceed 450 knots. Im pretty sure he cannot be doing 450 knots with engines idle.

 

It took me a 90 degree dive angle with full engines to achieve that kind of speed when I stalled out from overspeed.

[shagrat]

So, is flameout to be expected during a steep dive with idle throttle?

 

Thanks

 

As far as I can tell, yes! I had this more than once.

 

If you go into a steep dive and pick up speed you should not lower the throttle to idle!

Use the speedbrake at 30-50% (unfortunately no indication, so use gut feeling or a look over the shoulder) to maintain speed below 380...

 

EDIT: You may go faster, but it is problematic to execute a break turn at 1500 ft when going at 400+ ...at least I have problems keeping here from flipping over.

 

I'm no expert, but I guess the wind pushing through the fan is "blowing" the burning fuel away from the fuel pumps outlet so it no longer self-ignite ?! :dunno:

 

In any case this is reproducable. If it should not be the case (technically), there, might be a bug.

But I guess is intentional and reason of the superb systems modeling...

Edited December 5, 2011 by shagrat

[primus_TR]

Good advice, thx :thumbup:

[Gypsy]

Well, glad to see my question has been answered 3 years before I even asked it, just had it happen to me for the first time today too, so I hit the forums. Didn't help that I was in the middle of the mountains, so by the time i got my engines restarted there was no hope.

[StrongHarm]

I worked on aircraft engines a bit in the Navy but it was cross training, not my primary area of expertise. Although I have limited knowledge on the matter (where's an AD or 2A6X1 when you need them) I do have a few theories about why ED may have modeled engine stall under the circumstance (if it's not a bug).

 

1. Turbofan shaft lost momentum and angle of attack prevented sufficient air into the combustion section to maintain mix.

2. If speed was high enough and angle of attack allowed a high flow of air through the inlet, a combination of compression section overpressure and low shaft RPM caused flame out.

 

I'm really grasping at straws.. hopefully there's an expert on hand that will have concrete information that's better than my wild theories.

 

Snoooooopy?! Put on your crewchief cape and swoop in to save our brains!

 

Check out this wonderfully horrible video I found about turbo fan engines!

[fltsimbuff]

I played around with this yesterday pulling engines to idle and diving at various angles. I was only able to do this from over 20,000 feet in about a 35-45 degree dive when I hit 450kts at about 8,000 feet. I shallowed my dive to about 10-15 degrees and they relit when I started moving the throttle forward.

 

I don't know much about the mathematics and physics of a turbofan engine, but maybe bad things happen if the speed of the air moving into/around the engine exceed the air velocity exiting the exhaust? Going 450kts in a dive with engines at idle might also ram too much air into the engine for the amount of fuel. I was trying to test this via NASA's enginesim, but can't find the right parameters for a TF34.

[Gypsy]

20,000 feet, 35-45 deg dive was what I did when it happened. I just didn't have the room to maneuver or recover in time.