Engine Stall in Steep Dive

sgtmike74 · May 21, 2013

I have a question for those in the know. I had dropped my last bomb over on the 104th server and was heading back home. I was at 20,000ft with a big old white contrail behind me when I just got the urge to flip inverted and pull into a steep dive. I got up to about 300+ knots when I started to ease back on the stick (she was getting very squirrely) leveled at 8200ft. The entire maneuver only took a few seconds, when I heard the all too familiar sound of an engine spooling down. My right engine flamed out on me but I was able to restart it with no problems using the APU.

I know if you are inverted for a prolong period of time, you can starve an engine of fuel and it will shut down on you. This time,however, I was only in the dive for a few seconds. A few very fast (by A10's standards) seconds. Can excessive speeds lead to a flameout? What is actually happening to the engines in those extreme moments?

Just curious.:joystick:

Nealius · May 21, 2013

Would you happen to have been inverted for 10 seconds or longer?

FreeFall · May 21, 2013

I think you don't have to be inverted for that 10 seconds, negative G will do the same thing.

Kaiza · May 21, 2013

Did you chop the throttles back quickly? I think it is more likely that it was a compressor stall. If you pull the throttles back quickly at high airspeeds the compressor will stall and your engines will flame out. Be nice and gentle.

I dont know if this happens in RL, I thought the fuel control would be able to handle things like that, however perhaps not?

Edited May 21, 2013 by Kaiza

Dejjvid · May 21, 2013

Steep dives with low throttle will cause a flameout. I don't know the exact cause.

If you dive with 50% throttle your ok.

sgtmike74 · May 21, 2013

Im pretty sure it wasn't longer than a few seconds. I'm gonna look at the track again and see, just to make sure.

I did chop the throttle as I pulled from inverted into the dive and I was up there at 20+. I didn't know chopping the throttle at high altitudes would cause a compressor stall.

It is pretty neat that something like that is modeled.

Dejjvid · May 21, 2013

I don't think the altitude has anything to do with it, except your aircraft gain speed.

It think it's something with high IAS - AoA - idle engines. Maybe disrupted airflow or something.

We need Yo-Yo here :D

ericoh · May 21, 2013

I would expect that the airflow causes flamout cause theres not enought fuel feeding in when diving fast without throttle.

ralfidude · May 21, 2013

I would like to know as well.

I have noticed that the G indicator in steep dives is close to 0, but the boost fuel pumps should be able to handle that for a good 10 seconds or so.

It's something else.

This happens at variable speeds, I have been able to get both engines out at 360 kts, and I have also been able to keep them ON past 420 kts.

So it's something else.

sgtmike74 · May 22, 2013

I looked through the track and posted it on youtube (cut down to the flameout). Sorry for the quality, I don't have fraps and recorded off of my iphone.

Let my know what your hypotheses are.

Teej · May 22, 2013

Haven't flown A-10 for a while, but isn't 20,000 kinda low for a contrail?

Were you hit?

sgtmike74 · May 22, 2013

When I replayed the video, I was actually at 24,500 with the contrail. I'm not sure at what altitude contrails begin though.

I wasn't shot at or anything. The only thing around me was a friendly F15, and a sa6 that was well out of range from me.

So from the responses so far an engine stall could be from, "increase airflow from excessive speed combined with reduced fuel flow from idle throttles", or "inability of fuel pumps to provide adequate flow in prolong dive".

ENO · May 22, 2013

That's interesting to know... so I guess if you've got to enter a dive you have a decision to make... lose your wings or lose your engines.

ralfidude · May 22, 2013

I mean a lot of us here have watched the real gun run HUD tape of an A-10 power diving for a gun run at 80 degrees and 460kts and he was just fine... so....

Teej · May 23, 2013

That's interesting to know... so I guess if you've got to enter a dive you have a decision to make... lose your wings or lose your engines.

Hmmm. Someone will have to do some power dive testing. I'd think holding a low percentage throttle...like 10-20%...would greatly reduce / eliminate the problem....don't think you'd have to go into the dive balls to the wall. :D

sgtmike74 · May 23, 2013

Hmmm. Someone will have to do some power dive testing. I'd think holding a low percentage throttle...like 10-20%...would greatly reduce / eliminate the problem....don't think you'd have to go into the dive balls to the wall. :D

I took your advise and did a little non-scientific testing. I posted five short tracks of the tests. two were at 0% throttle, one at 25%, 50% and finally 100%.

Both times with the throttle at idle, both engines cut out at about 450kts.

The other three times with throttle settings between 25%-100%, I had no issues with the engines. So, I'm guessing with high speeds, a low throttle setting is the culprit, or at least a major contributor to the flame outs.