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Strange engine behaviour ?


0xBlb

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First of all, this is using DCS World 1.2 and corresponding A-10C addon.

 

I was experimenting with engine start the other day, when I found this... my questions are: is it normal, if yes could you please explain such behavior, if not is it a known bug already?

 

I followed my usual engine start procedure. After starting both engines, I stood on the brakes, increase throttle to 100% L&R engine power, and cut electrical power (see track for details). Basically at this point, APU is off, APU gen is off, L&R gen are off, inverter is off, battery is off and both engines happily run at full power. Tried to pull L&R engine T-handles hoping it would cut fuel to both engines, but no... both engines still run quite happily at full power.

 

Why is this?

 

It is only when I switch battery power back to on than both engine "die".

 

Is this correct? I remember seeing fuel system schematics on these forums. T-handles should cut fuel, but is fuel cut by an electrical mean or through manually pulling the T-handle?

 

btw, I cannot find a way to restart my engines after this, are they broken, can you restart them, what am I doing wrong?

 

track attached...

a10_strange_engines.trk

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According to A-10A manual, "...fire detection and fuel/bleed air shutoff functions requre auxiliary DC essential and DC essential bus power." The T-handles cut off fuel and bleed air to the effected engine. The fuel shutoffs are motorized and on the DC essential bus. So turning off all generators and battery immobilizes them.

 

The engines will suction feed fuel from the main tanks, so once started they will stay running even without the ac or dc boost pumps running.

 

Bleed air shutoffs are also electrical and on the DC essential bus.

 

When you turned battery back on the fuel and bleed air valves closed killing the engines.

 

I noticed though even with no power the engine core RPM gauges worked. I'm not sure how those are driven.

 

I only shutoff one engine with the Tee handle and was able to restart it only when I brought the uneffected engine to full power then move effected engine to full power when rpm hangs again. Not sure why engine start cycle is hanging on engine that tee handle was cycled, but normal on other engine.


Edited by doright
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Is this correct? I remember seeing fuel system schematics on these forums. T-handles should cut fuel, but is fuel cut by an electrical mean or through manually pulling the T-handle?

 

 

Yes this is correct, the fuel is cut electrically so if there is not DC power from the battery bus or otherwise the fuel can't be cut and thus the engines will continue to suck fuel from the tanks even without the boost pumps activated.

 

About the restarting thing i'm not sure, it's possible that the valve being close when pulling the T-handle can't be reset during flight and thus needs to be reset by an engineer once on the ground, this makes sense to me since reseting it in flight could well cause the fire to reignite when fuel is once again fed to the engine. :-)

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  • 3 weeks later...

The left engine can be started without the boost pumps as there is a DC fuel pump that supplies the APU and left engine. The right engines requires the boost pumps to start.

 

Once running both engines will suction feed it the pumps fail.

 

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I noticed though even with no power the engine core RPM gauges worked. I'm not sure how those are driven.

 

I haven't had the pleasure of working on the TF-34, but it usually works like this...

 

For core RPM, a tachometer generator mounted on the accessory drive (which is mechanically linked to core) directly powers the gauge.

 

The fan spool, on the other hand, is not linked to anything (besides it's turbine) so RPM is sensed by a magnetic pickup and a toothed wheel. This design does not generate it's own power, so it requires aircraft power.

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It takes a bit over 12 hours to drain the tanks with the engines sucking the fuel. I was curious about this, too, so I left the jet running overnight.

 

Once the engines did die, just for fun I switched on the APU and it ran for about 30 seconds and then died of fuel starvation. Pretty neat modelling, me thinks, to have the APU use up its last few drops of fuel in the line before shutting down, too.

 

WC

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It takes a bit over 12 hours to drain the tanks with the engines sucking the fuel. I was curious about this, too, so I left the jet running overnight.

 

Once the engines did die, just for fun I switched on the APU and it ran for about 30 seconds and then died of fuel starvation. Pretty neat modelling, me thinks, to have the APU use up its last few drops of fuel in the line before shutting down, too.

 

WC

 

 

LOL...........You most certainly desurve a +1 for your dedication to this "Sim" Sir. Now you're a 3. :)

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