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Just thinking...The engines sucking in fuel via the inletport of the prime pump.....transfer pumps delivering the fuel from the main tank to the supplytank. Assuming the transfer fuel lines exits situated somewhere on/near the bottom of the supply tank...the fuel flow generated by the transferpumps is way larger than the suction flow to the engine. Is this creating some swirl effect in the supply tank.....when you suddenly stop the supply from the transfer pumps; the swirl will continue for a couple more minutes, creating static pressure drop at the exit of the fuel transfer line, and thus continue pulling fuel from the main tank. The swirl effect slows in time and after some minutes the static pressure drop ceases to exist and the engine starts sucking from the supply tank........ So I think a lot of sucking is involvedhttp://images.ibsrv.net/ibsrv/res/sr...s/embarass.gif so if you did a similar check without switching on the transfer pumps at the beginning of the sequence....no swirl created,.... the supply tanks would start emptying rightaway. (assuming the main tank Qty level is below the overflow channels) skadi |
Sucking fuel for 15 minutes from the main tank to the supply through all that pipeage simply by the pressure difference caused by a swirl that can be reproduced by making a cup of tea …. if only we'd known about this effect before archimedes invented his screw :ok:
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. if only we'd known about this effect before archimedes invented his screw* Yep, because I question things* (also looking forward to your reply on this one) |
Phoinix; We had exactly the same; 159 till 139 after XFER pumps OFF, sucking at it for almost 15' before supply tank indication dropped." |
that's the main reason why I decided to disagree with you on this issue.... p.s. Remember what Viper said about arrogance? Viper |
.. you don't*decide*to disagree. p.s. Remember what Viper said about arrogance? |
I must have missed that Y135, I guess we agree to disagree.
Perhaps there will be some more investigation into this phenomena :ok: |
Yellowbird, I think thats the first plausible explanation since I started this long debate with my simple question... Thanks! With transfer pumps off, Run the supply tanks down until red fuel warning. Shut down the engines. Turn on both transfer pumps, when supply tanks start filling, turn off transfer pumps and monitor the supply tank levels. |
PC,
yep...could be, but I'm not sure whether the suction of a running engine is needed to create this phenomena. I'm not even sure if this actually is the explanation..........I just can't think of anything else. To be honest, I know I have a creative imagination, but I would never have predicted this effect (if it's true) to continue for this long. I think that the boys and girls from Donauwerth might have addressed the "couple of minutes" note in the ASB a little further. I was about to shut down the thing after more than 10 minutes wittnessing the Main tank qty go down, thinking I must have done something wrong.:ugh: Still, I'm almost certain now that this is exactly what happens. |
Donauwörth :}:}
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6 pumps, 4 nrv, 3(4) fuel tanks - still no consensus on how it works - uphill swirl syphoning, I see! certifiable !
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Factory Training
Having read most of the posts regarding this tragic accident there seems to be a great deal of poor understanding of the fuel system.
May respectfully suggest that all crew go on a FACTORY training course ensuring that they fully and correctly understand the systems they are operating. |
..cont from other thread.
I thought you might have been on about transfer pump failures/turned off, with a check valve failure. |
Normal flight ops......use of transfer pumps with low main tank fuel levels.
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brought over from other thread..
AnFI SS - The irony of your post is staggering - the first accident in the AAIB report, you point to, is a double engine stoppage of a twin cause by fuel exhaustion - given that that may also be the case here (and other complete power loss events) it is tempting to conclude that the mathematical assumptions concerning the safety of TWIN ENGINED helicopters is FLAWED - is the rarety of full power loss in twins actually 10^-9 per hour ? Umm, if you care to read the first incident all the way to the end, you'll get to the bit that says, "no action was taken to select an alternative fuel source for the engines after their power loss." Single or twin, if the crew don't switch tanks, the engine will stop :ugh: |
SS
Agree SS
more complexity - more room for human error - more human errors if you have 2 FCL then it is possible to retard the wrong one - if you don't it is not possible.... It is clear that if an 'internet room' full of experts can't work out how a fuel system works that it is probably too complicated - if a system is prone to human failure then it's not totally 'Kosher' to blame pilot's - it's a whole system deal Stats don't support the theory |
I'm really surprised to hear that the fuel system (airframe) is considered complicated, I can imagine people having difficulties (before anyone starts asking......myself included) with the engine fuel system. But a bladder divided in 1 large, 2 small reservoirs, a couple of impeller pumps........how complicated can it be?
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Human factor wise, how is the fuel system being considered complicated?
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yellowbird
I'm really surprised to hear that the fuel system (airframe) is considered complicated, I can imagine people having difficulties (before anyone starts asking......myself included) with the engine fuel system. But a bladder divided in 1 large, 2 small reservoirs, a couple of impeller pumps........how complicated can it be? I thought these are diaphragm not impeller pumps? I'm sure I read that and would seem to me to be the better choice with these low fuel flow rates. |
Fuel system complexity
I total agree that the fuel system is not complicated.
How the system is managed with fuel levels below the weir is where l guess a certain procedure is required. I have asked how you manage the TRANSFER PUMPS to ensure that one is submerged in fuel with the change in pitch attitude with no reply. My understanding is the one pump may be above the fuel and switched off. I thought these are diaphragm not impeller pumps? This is what worries me, if you operated a 135 you should know. Do you not do a tech refresher course. |
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