Fuel system and in-flight re-starting

[Kodoss]

The other problem could be that you can't fly inverted for longer than that 30 seconds (as in the report given), because the electric pump is not a flexible submerged pump but a static submerged pump.

 

The Bf 109 G-K has a the electric fuel pump 8-4544-K from DBU. An internet search delivered me a 8-4544-H.

But if you look into the manuals of the 109, for pictures, even the E-series had a static pump.

 

Fuel tank attachments of the Bf 109 E

[Crumpp]

The other problem could be that you can't fly inverted for longer than that 30 seconds (as in the report given), because the electric pump is not a flexible submerged pump but a static submerged pump.

 

No claim is being made the aircraft can fly inverted.

 

The electric booster pump was not turned on in the accident. The purpose of that pump is to clear any air trapped in the fuel lines and act as a back up to the mechanical fuel pump.

 

The engine would have had a much better chance of restarting if it even quit at all with the booster pump engaged.

 

The air in the lines from flying inverted would have have most likely just cleared.

Edited March 28, 2015 by Crumpp

[IIIJG52_Otto_]

The other problem could be that you can't fly inverted for longer than that 30 seconds (as in the report given), because the electric pump is not a flexible submerged pump but a static submerged pump.

 

The Bf 109 G-K has a the electric fuel pump 8-4544-K from DBU. An internet search delivered me a 8-4544-H....

Good job Kodoss !!:thumbup: Thank you very much, I've been looking for information for weeks about this, without success.

This device 8-4544-K from DBU is the key to explaining why the Bf-109 can fly inverted, almost a minute.

 

 

No claim is being made the aircraft can fly inverted.

.

Excuse me, but I'm claiming from the beginning that the Bf-109 can fly inverted at least 34 seconds before the engine stops.

[I.ZG15_FALKE]

From the referenced page, this pump is described to be an emergency fuel dumping pump.

Kraftstoff-Ablasspumpe / für Schnellablass

:music_whistling:

Since this is the only source given, I highly doubt if this pump is able to deliver sufficient fuel flow if 109 K is inverted - or if it was it´s purpose at all.

Other than internal MW50/Fuel tank I have no info on a fuel dumping device for maintank of Bf109.

Edited March 30, 2015 by I./ZG15_FALKE

[iFoxRomeo]

Good job Kodoss !!:thumbup: Thank you very much, I've been looking for information for weeks about this, without success.

This device 8-4544-K from DBU is the key to explaining why the Bf-109 can fly inverted, almost a minute.

 

 

 

 

Excuse me, but I'm claiming from the beginning that the Bf-109 can fly inverted at least 34 seconds before the engine stops.

Otto, this is a fuel dumping pump. It is described as such on the page where these pictures are from.

 

Its use was to dump fuel in case the aircraft was hit and had to perform an emergency landing. So the danger of a fire was reduced.

 

Fox

[IIIJG52_Otto_]

From the referenced page, this pump is described to be an emergency fuel dumping pump.

Kraftstoff-Ablasspumpe / für Schnellablass

:music_whistling:

Since this is the only source given, I highly doubt if this pump is able to deliver sufficient fuel flow if 109 K is inverted - or if it was it´s purpose at all.

Other than internal MW50/Fuel tank I have no info on a fuel dumping device for maintank of Bf109.

 

Otto, this is a fuel dumping pump. It is described as such on the page where these pictures are from......

 

Bf-109 have not emergency fuel dumping pump, (it has the fuel dumping by gravity) and if the info given by Kodoss is true, the P/N matches, except for the letter after The dash.

Probably, the electric fuel pump P/N: 8-4544-x from DBU. has multiple applications and variations, depending of the P/N letter after the dash.

But this is my assumption, because i work in aviation. and is a common practice of spare part vendors, and manufacturers.

Edited March 31, 2015 by III/JG52_Otto_+

[iFoxRomeo]

Bf-109 have not emergency fuel dumping pump, (it has the fuel dumping by gravity) and if the info given by Kodoss is true, the P/N matches, except for the letter after The dash.

Probably, the electric fuel pump P/N: 8-4544-x from DBU. has multiple applications and variations, depending of the P/N letter after the dash.

But this is my assumption, because i work in aviation. and is a common practice of spare part vendors, and manufacturers.

Noone said the 109 had a fuel dumping pump. The description of this particular pump and webpage says that this is a fuel dumping pump for combat aircraft. Bf109 is not mentioned in the description.

 

Yes, you´re right, manufacturers use similar parts.

 

But how does this pump explain what you claim?

 

Fox

[iFoxRomeo]

:doh:

 

Sorry Otto, I didn´t understand the problem. I had a vapor lock in my head...

 

 

The moment the pilot of the D-FWME went inverted he sealed the aircraft´s fate.

It didn´t matter how long he flew inverted.

It only mattered that he cut the fuel supply by flying inverted.

From this moment onward, the engine was only supplied by the remaining fuel in the fuellines that go from the tank to the engine. And this fuel was followed by the air sucked into the lines because of the inverted flight.

So if he flew 1 second or 30 seconds inverted, it wouldn´t change the outcome (just looking at the fuel only). After 34 seconds at this powersetting the fuellines will run dry. I guess it misfired only because of fuel starvation as the injection system itself overcomes the problems of G forces pointing in any direction.

As the electric pump was off, there was nothing that could overcome the air in the lines.

 

So the question is:

Why does the DCS Bf109-K4 misfire 5-8 seconds after going inverted and therefore cutting the fuel supply of the fuellines at 2300rpm and 1.3ata?(could someone recheck this time value? I´m for a few days away from my gaming machine)

 

That would mean that the K4 engine consumes within 5-8 seconds the same amount of fuel that is sufficient to run the G6 Engine for 34 seconds

 

That is an increase in fuel consumption by the factor 4,25(considering the 8 seconds)

 

Or was the fuelline of the K4 shortened so that the fuel amount inside the lines got reduced significantly?

 

Or does the DCS Bf109K4 (by mistake/bug) not take the 1,9l fuel in the fuelline into account?

 

Why does it instantly resume normal operation on rolling back to normal? Shouldn`t it misfire till the electric pumps resumed full fuel pressure in the fuellines by removing the ingested air?

 

 

Fox

Edited April 7, 2015 by iFoxRomeo

[I.ZG15_FALKE]

It didn´t matter how long he flew inverted.

It only mattered that he cut the fuel supply by flying inverted.

From this moment onward, the engine was only supplied by the remaining fuel in the fuellines that go from the tank to the engine. And this fuel was followed by the air sucked into the lines because of the inverted flight.

So if he flew 1 second or 30 seconds inverted, it wouldn´t change the outcome (just looking at the fuel only).

 

Again it´s not that easy. It depends on how tolerant the engine driven pumps will be to air in the fuel line.

 

If there is air in the line and the airplane is put into a normal flight situation it might be that the air in the fuel line is no problem because the suction of the pump is able to overcome the uncompressing air in the line.

 

Only if the volume of air in the fuel line is to high the pump fails to overcome the degrading suction (by the expanding air in the line) so in the end the flow of fuel is interrupted.

 

Looking at the given system the timeframe of 5-8 seconds of possible inverted flight /neg G maneuver

variing with the amount of throttle seems plausible to me.

Edited April 7, 2015 by I./ZG15_FALKE

[Siegfried]

I just test the 109 in lastest DCS World beta version.

 

The time since total inverted to engine fail is about 8 seconds at 1.4 ata and 15 seconds at 1.1 ata with automated RPMs.

 

Can you confirm that?

[Ala13_ManOWar]

I said in another post.

 

http://forums.eagle.ru/showpost.php?p=2370067&postcount=30

 

S!

[I.ZG15_FALKE]

Very nice results! So I think this issue is ironed out.:thumbup:

[Kurfürst]

I am not sure if its ironed out completely... with current version, if I do a negative G bunt, the engine stutters (fuel pressure is lost) like a BoB-era Hurricane, only that its not immidiate but with a couple of seconds of delaz. When leveled out, the fuel pressure comes back.

 

I am not sure if its correct or not, surely the fuel systems have their limits, but certainlly it is a odd match with historical accounts. Perhaps its partly a control-related issue, since control forces were implemented and perhaps its only indirectly caused by the negative gs being present longer than before, due to relative control ineffectiveness.

 

With negative G dives being the Luftwaffe's favourite escape manouvre through the war and all that. I am sure some of them would notice the caughing of the engine at the beginning of the dive.

Edited January 2, 2017 by Kurfürst