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Engine primed even though the fuel lever is off


Redglyph
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DCS 1.5.5.60338.212

 

The fuel pressure indicator goes off and the engine is primed even when the main fuel lever is off. Is this normal?

 

Procedure below:

 

- pushed the throttle forward to switch the undercarriage indicator on, and so the fuel pressure warning indicator on

- throttle to about 1 inch of idle

- (main fuel valve lever is off)

 

(A) - pump booster on for 30 seconds

=> the fuel pressure indicator immediately switches off (which is unexpected)

or

(B) - about 10 strokes on wobble pump

=> the fuel pressure indicator eventually switches off (which is unexpected)

 

© - main fuel valve on

or

(D) - main fuel valve remains off

 

- both magnetos on

- start and booster coil covers off

- start + booster coil buttons depressed

- mixture rich when the engine catches

 

=> engine has started

 

In conclusion:

- should the fuel pressure indicator reveal an increase of pressure when the fuel valve is off?

- should the engine start without proper priming?

- should the engine start when the main fuel valve remains off?

 

Also of note: when the engine is running, switching the fuel valve to off has those effects:

- after a few seconds, the fuel pressure indicator lights up

- quickly after, the engine shuts off


Edited by Redglyph

System specs: Win7 x64 | CPU: i7-4770K | RAM: 16 GB | GPU: GTX 980 Ti 6 GB | Thrustmaster HOTAS | MFG rudder pedals | SATA3 SSD | TrackIR

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There is a similar topic. It looks like it works as it supposed to: https://forums.eagle.ru/showthread.php?t=179467

F/A-18, F-16, F-14, M-2000C, A-10C, AV-8B, AJS-37 Viggen, F-5E-3, F-86F, MiG-21bis, MiG-15bis, L-39 Albatros, C-101 Aviojet, P-51D, Spitfire LF Mk. IX, Bf 109 4-K, UH-1H, Mi-8, Ka-50, NTTR, Normandy, Persian Gulf... and not enough time to fully enjoy it all

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The thread you mention is about the fuel cock lever, and I suppose by default (not mentioned in the first post), the wobble pump.

 

By the way, I see a possible error in the position of the fuel cock too, in the DCS manual. Normally it's in series with the wobble pump, not in parallel (Pilot's Notes), though that may differ with the hybrid wobble/booster pump we get, perhaps? But normally item 10 is a non-return valve, necessary because of the wobble pump, otherwise it wouldn't work.

 

So I'm not convinced it works as it's supposed to, but I'm not sure so I'll try to dig into more documentation about this.

 

 

Anyway, here I'm talking about the main fuel valve lever (see figure 82 pg 119 vs bottom figure without number page 122/item 60), the fuel booster pump, and optionally a very short delay for the fuel pressure to set when using that one.

 

I don't see how the fuel could go through a closed valve, even if the pump was active, it would give in under the pressure.


Edited by Redglyph

System specs: Win7 x64 | CPU: i7-4770K | RAM: 16 GB | GPU: GTX 980 Ti 6 GB | Thrustmaster HOTAS | MFG rudder pedals | SATA3 SSD | TrackIR

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...I don't see how the fuel could go through a closed valve, even if the pump was active, it would give in under the pressure.

I might be taking too far going assumption but looking on the diagram (page 81) it seems that the wooble pump (15) is bypassing the main cut-off valve in a way that it is taking the fuel before it and feeding the fuel line after it.

 

EDIT: I think it's actually described this way in manual:

A hand wobble pump is mounted on the starboard side of the cockpit of early aircraft powered by a

Merlin 66 engine. The pump draws its supply from the fuselage lower tank and delivers into the main

fuel supply line at a point between the main fuel cock and the non-return valve. Designed to fill the

aircraft's supply pipeline, drive pump and the carburetor before starting the engine. It can also be used

as an emergency pump in case of drive pump failure.


Edited by firmek

F/A-18, F-16, F-14, M-2000C, A-10C, AV-8B, AJS-37 Viggen, F-5E-3, F-86F, MiG-21bis, MiG-15bis, L-39 Albatros, C-101 Aviojet, P-51D, Spitfire LF Mk. IX, Bf 109 4-K, UH-1H, Mi-8, Ka-50, NTTR, Normandy, Persian Gulf... and not enough time to fully enjoy it all

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I might be taking too far going assumption but looking on the diagram (page 81) it seems that the wooble pump (15) is bypassing the main cut-off valve in a way that it is taking the fuel before it and feeding the fuel line after it.

 

EDIT: I think it's actually described this way in manual:

 

I suppose we should interpret that as the non-return valve being between the supply and the return of the wobble pump, and the main fuel cock being further down the line. The figure 41 only shows the bottom non-return valve, so it's hard to be sure how they modelled that in this intermediate version.

 

attachment.php?attachmentid=153733&d=1482142944

(figure from AP 1565I Pilot's Notes for Spitfire IX,XI & XVI)

 

This main fuel valve, though, must be located elsewhere... from the DCS manual, "The main fuel valve is mounted to the right of the compass. This valve shuts off the flow of petrol from the tank to the engine dispensing pump.".

 

EDIT: This on/off lever IS the fuel cock lever, not sure why I was lead to believe there were two levers. Disregard my rantings about that :p

 

=> But so the model clearly is malfunctionning, since closing this valve should cut the fuel from the carburettor, where the fuel pressure indicator samples the pressure, and yet this indicator switches off and the engine starts.

 

It does work once the engine is running, but not when it's starting.


Edited by Redglyph

System specs: Win7 x64 | CPU: i7-4770K | RAM: 16 GB | GPU: GTX 980 Ti 6 GB | Thrustmaster HOTAS | MFG rudder pedals | SATA3 SSD | TrackIR

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I test this and I am able to pressurize tanks and start engine with fuel cock off.

 

But soon the fuel pressure drops and engine stop, and now is not more possible pressurize tanks, if don't open fuel cock.

 

Suggest that initially the fuel in lines is sufficient for engine start.

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Hmm, I let it run a few seconds, based on how fast it shuts down when the engine is running and the valve is closed. Perhaps it wasn't long enough, but those delays should be similar, or even shorter when starting.

 

Thanks for the info! :)

 

The whole model should still be checked and fixed for the pumps that should have no influence on the pressure indicator, for instance. Probably just a few missing flags in a verification ;)

System specs: Win7 x64 | CPU: i7-4770K | RAM: 16 GB | GPU: GTX 980 Ti 6 GB | Thrustmaster HOTAS | MFG rudder pedals | SATA3 SSD | TrackIR

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