fuel pumps always working

[leafer]

So I was wondering how long the engine would run for if I shut off the fwd and aft fuel pumps. Well, they kept working long after I shut them off. So I shut down the cross feed valve and they quit within seconds.

 

So the fuel pumps don't do anything?

[Yo-Yo]

Try to start the engines without them. If the engines run their own pumps suction is sufficient to feed the engines. But at high altitude steam bubbles can interrupt fuel flow because of pressure loss at suction.

[leafer]

Ok. I figured it might be the suction thing. But why did turning off the cross feed instantly killed the turbines?

[Yo-Yo]

I have no idea. Frankly speaking it can be a bug. Sorry...

I wonder if our testers performed this combinations of clicks.

And where had you been until patch was not closed? :)

Edited July 13, 2009 by Yo-Yo

[AlphaOneSix]

I just tried it, and shutting off the crossfeed valve didn't cause my engines to shut down. I tried it both with the fuel pumps running and with them shut off.

[Yo-Yo]

I just tried it, and shutting off the crossfeed valve didn't cause my engines to shut down. I tried it both with the fuel pumps running and with them shut off.

 

Mmmm... we did see it twice. Run engine at AUTO, shut off both tank pumps, wait 1-2 minutes and then open crossfeed valve. Unfortunately it works... :)

[Yskonyn]

It works, as in it shuts down? Or 'it works' as in: the engines keep running as designed?

[leafer]

After shutting down the fuel pumps, I flew for about ten minutes before turning off the crossfeed valve. Maybe it was a coincident the turbines decided to quit when I turned off the crossfeed? I'm away from home for a week so I can't test this.

 

I am so qualified to be on the A-10 beta tester team. :D

[joey45]

I am so qualified to be on the A-10 beta tester team. :D

 

would rather do the apache thanx...

 

I think the crossfeed has something to do with the feul tanks.. xfeeding feul from both tanks instead of just one so the heli isn't off balance.

you need the fuel pumps on when starting to pump the feul into the engines then the suction from the engines takes over.

[EinsteinEP]

No matter how precise you manufacture a jet engine, each one consumes fuel at its own rate. Cross-feed pumps generally make sure that both tanks have the same amount of fuel in them, even though one engine is sucking more fuel than the other. Cross-feeds really come in handy if one engine is shut down. As the engine pulls fuel from only one tank, the cross-feed pumps fuel from the unused tank to the tank being emptied by the engine, ensuring the pilot can use all the fuel he has, not just what happens to be in one tank.

[starbird]

The manual shows that the forward tank feeds the left engine and rear feeds the right. So if one engine is shutdown, you'll run only one of the tanks dry. Opening the crossfeed will let one engine consume both tanks fuel. Its not normally open in the Ka according to the checklists. the APU runs off of the rear tank.

 

I think I read something about a maximum fuel imbalance for flight, but I can't find it now.

 

There are some nice schematics and other stuff in the printed manual. I don't think these diagrams were in the pdf.

[moggel]

How does one turn crossfeed on/off? I assumed it's on by default since I've never needed to bother?

[PE_Tigar]

The one good reason to close the crossfeed would be to isolate a ruptured tank or a ruptured fuel line. I don't know how the real Ka-50 SOPs go, but in large jets crossfeed is usually closed, unless there's significant fuel imbalance. I don't know why, probably not to loose all the fuel if there was a large leak in fuel lines on one side. To me it seems that there are two things to consider - whether you want to keep the fuel balance and have to do another task when the fuel tank is ruptured or the engine shut down (on by default, xfeed clsd when tank ruptured) or you want to continuously check for fuel imbalance, but have more safety for the ruptured tank scenario (xfeed clsd, open only when needed). In large jets it makes sense keeping it closed, because there's seldom such imbalance that requires actually opening the crossfeed. Again, I may be wrong, because I know it only in theory, haven't got any type ratings yet :).

Edited July 14, 2009 by PE_Tigar

[SNAFU]

If the engines run their own pumps suction is sufficient to feed the engines.

 

Is that sure? Are you talking about suction at the injection needles or to the shaft/gear attached pumps, and the switches in the cockpit are only for the prime booster pumps?

 

I don´t believe a high performance axial jet turbine without proper injection of fuel into the flamechamber (only suction due to hydrodynamic pressuredifferenz in the chamber) will provide enough power to keep a 11ton helicopter flying. Not to mention the difficulties in governing the turbine and compressor revolutions and available power output at the shaft, without any effective meaning of controlling the amount of fuel provided to the flamechamber.

Edited July 14, 2009 by SNAFU

[Yskonyn]

It is. Modern engines like the CFM56 (737NG series) function similar. They provide enough suction to keep a positive feed of fuel from the tanks.

Fuel pumps are redundant as far as fuelfeed is concerned. They provide means to empty the tanks and they provide enough pressure in the fuel lines for non-normal situations.

 

Crossfeed is normally closed in many fuel configs, however on the 737NG we do have a few situations where we open the X-feed valve;

 

-Emptying the center tank (to prevent imbalance in the wing tanks while scraping the last drops out of the center tank). We do it when the fuel in the center tank is 1000kg or less.

 

-Also, quite logically, to prevent -or fix- and imbalance between the left and right tank. (Think of fuel leak, one engine inoperative, etc).

[AlphaOneSix]

It is important to note here that the Ka-50 does not have a crossfeed system that allows the fuel tanks to "share" or equalize fuel. There is no crossfeed pump on the aircraft. There is only a single crossfeed valve that allows an engine to pull fuel from either tank.

[Feuerfalke]

X-feed doesn't have an effect on my engines, neither with active or inactive fuel-pumps under normal conditions.

 

Maybe you were damaged? I could imagine that a damage to the tank of fuel-lines that causes bubbles in the fuel-lines could kill the suction effect and stall the engine.

[Cp]

Feuerfalke, try this:

 

1. Create a mission where you start on the runway.

 

2. Shut off both fuel pumps.

 

3. wait 30 seconds and then open the X-feed valve.

 

4. the engines should shut off within 20 seconds.

 

 

At least that works to replicate this for me.

 

[Feuerfalke]

Roger that. I didn't wait for 20 seconds. So at least switching them back on prevent the engines from dying. I will try and wait for 20 seconds later.

[Yo-Yo]

Is that sure? Are you talking about suction at the injection needles or to the shaft/gear attached pumps, and the switches in the cockpit are only for the prime booster pumps?

 

I don´t believe a high performance axial jet turbine without proper injection of fuel into the flamechamber (only suction due to hydrodynamic pressuredifferenz in the chamber) will provide enough power to keep a 11ton helicopter flying. Not to mention the difficulties in governing the turbine and compressor revolutions and available power output at the shaft, without any effective meaning of controlling the amount of fuel provided to the flamechamber.

 

 

What things are you talking about??

Engine own PUMPS suction - I only meant that the pumps that provide high pressure to feed the combustor provide enough suction to feed themselves without boost pumps assistance. It works but at high altitude the lack of pressure in pipelines can cause fuel vapourizing and vapour lock.

[AlphaOneSix]

Feuerfalke, try this:

 

1. Create a mission where you start on the runway.

 

2. Shut off both fuel pumps.

 

3. wait 30 seconds and then open the X-feed valve.

 

4. the engines should shut off within 20 seconds.

 

 

At least that works to replicate this for me.

 

 

I got the failure to occur by following these steps. Oddly enough, if I restart the engines, I am unable to get it to happen again.

[Cp]

Thats odd, I can restart the engines and recreate the failure as many times as I want it seems.

 

heres a track of me recreating it 3 times in a row:

Xfeed-failure-x3.trk

[SNAFU]

It is. Modern engines like the CFM56 (737NG series) function similar. They provide enough suction to keep a positive feed of fuel from the tanks.

 

What things are you talking about??

Engine own PUMPS suction - I only meant that the pumps that provide high pressure to feed the combustor provide enough suction to feed themselves without boost pumps assistance. It works but at high altitude the lack of pressure in pipelines can cause fuel vapourizing and vapour lock.

 

Ok, but you have mechanically attached pumps and the pumps you control via the pumps switches in the cockpit are only booster pumps and not the only means for fuel flow. I don´t know the fuel system of the Ka50, that´s why I am asking. ;)

 

And sure you don´t want any cavitation in the fuel lines, especially with high flammable jet fuel.

[Feuerfalke]

I got the failure to occur by following these steps. Oddly enough, if I restart the engines, I am unable to get it to happen again.

 

Same here. Odd. I will repeat the tests later today under different circumstances.

 

I also had the idea, if x-feed is activated and fuelpumps are offline, it may suck fuel from external tanks, too, so I also repeated the procedure with 4 external tanks. It had the same effect, though. The engines died after less than 10 seconds.

[Druid_]

For ED. Is it a cross feed fuel pump or a cross feed valve. I would of thought the latter.

 

To transfer fuel or run engines from a certain tank you would open the x-feed fuel valve, switch 1 (say fwd) fuel pump OFF and switch the other (in this case aft) ON. Fuel 'should' then transfer due to a difference is differential pressure between the tanks.

 

I only use the x-feed for

1) very low fuel states - x-feed open with both tank pumps ON

2) fuel balancing (to obtain the same amount of fuel in both tanks)

3) for a fuel leak (which if my thinking of the ka50s fuel system is correct, does not work correctly in BS)

 

Oh and btw, most modern fuel systems and engines will "gravity feed" the fuel isn't "sucked" out as such. The fuel tanks are also pressurised by conditioned bleed air from the engines which aids the process. Obviously, any hard manoevering may cause a flameout, especially at low fuel states.

Edited July 16, 2009 by Druid_