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Mosquito Fuel Management


Helles Belle

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I am no way an expert of this and like a lot of people I am still learning.

 

The fuel system on the Mosquito is obviously a bit different to what we have used before – a total of 13 tanks if we count wing drop tanks and long range tanks.

 

I’m not sure the long range tank is even operative. I thought I saw the gauge at full with full internal fuel loaded when I first used it, but now whenever I take full fuel the gauge reads zero.

 

No offence to the developers as the game supplied manual is still a work in progress and is also derived from the actual Mosquito FB6 Manual. (I’ll refer to this manual as the FB6 manual to avoid confusion later on). But I believe a more rigid checklist structure needs to be produced to help understand what to do to manage the fuel system.

 

From reading both manuals, (the original FB6 manual goes into it a bit further), I came to the conclusion of how the fuel system ‘should’ be managed.

As I said earlier I could be wrong & am more than happy for correct advice to be given.

 

I’ll start as if wing drop tanks are being used and work down from there.

 

WING DROP TANKS usage:

After take-off

          Fuel Transfer Cock................... *OPEN

When OUTER tank level drops

          Fuel Transfer Cock........................ OFF

 

*HOWEVER from the FB6 Manual re: the Fuel Transfer Cock:

‘If Mod. 613 is incorporated, the cock is marked ON FOR AUTO TRANSFER and it may be left on whilst using fuel from the outer tanks. Transfer will then be automatic until the wing drop tanks are empty when the gauge will show a fall in the contents of their respective outer tanks.'

 

Ours is labelled JETTISON TANKS FUEL TRANSFER.

 

Therefore from the FB6 Manual:

‘If the transfer is not automatic this cock is marked JETTISON TANKS FUEL TRANSFER ; in this case the outer tanks must be nearly emptied before transferring, or fuel will be lost by venting to atmosphere.’

‘If automatic transfer is not provided, sufficient fuel must be used from the outer tanks before attempting to transfer, or fuel may be lost through the atmospheric vents. To transfer fuel, change to main supply and turn on the transfer cock. When the outer tanks are full, turn off the transfer cock and revert to outer tanks. Repeat the sequence until the wing drop tanks are empty.


Therefore for our aircraft I believe the correct procedure when using wing drop tanks is:

 

Empty the OUTER Tanks, then:

Fuel Tank Selector.......................................... MAIN

Fuel Transfer Cock.......................................... OPEN

          When the OUTER tanks are full:

                   Fuel Transfer Cock.......... CLOSE

                   Fuel Tank Selector.......... OUTER

          Repeat until Wing Drop Tanks are empty.

 

If Wing Drop Tanks are NOT loaded but all internal tanks are full:

 

OUTER TANKS usage:

Fuel Tank Selector............................. OUTER

Fuel Transfer Cock............................. CLOSE

Fuel Tank Pressure.............................. ^OFF

Immersion Fuel Pump........................... OFF

^doesn’t appear to be required ON when using the OUTER tanks as it only pressurises the INNER & CENTRE tanks

 

LONG RANGE TANK usage:

Fuel Tank Selector............................... MAIN

Fuel Tank Pressure.............................. #OFF

Immersion Fuel Pump............................ ON

When pump pressure light comes ON

          Immersion Fuel Pump................. OFF

          Fuel Tank Pressure........................ ON

 

#From the FB6 Manual:

‘When Mod. 443 is incorporated the pressure venting cock is usually wired in the ON position because the pressurising is then extended to the long-range tank. When this modification has not been incorporated it is advisable to turn the cock OFF whilst actually using the long-range tank because the immersed fuel pump might not be able to overcome pressurising in the fuel collector box sufficiently to ensure a supply of fuel from the long-range tank.'

 

Continue on MAIN – CENTRE & INNER TANKS.

 

Please correct me if I am wrong and I will modify the above procedures.


Edited by Helles Belle
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We don't have the long range tank, (No 12), fitted in the bomb bay.

It will read zero on the gauge, when 100% fuel is carried.

 

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Thanks @Holbeach I thought that might be the case

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2 hours ago, Holbeach said:

We don't have the long range tank, (No 12), fitted in the bomb bay.

It will read zero on the gauge, when 100% fuel is carried.

 

..


thats useful - couldn’t work out why the one gauge read 0 when the a/c was fully fuelled

 

I am struggling to work out which gauges are for which tanks though🤔  

It doesn’t help that the tank numbering on Fig 18 dong match the a/c tank numbers shown on the gauges…! 🙄

 

from forward to rearward, I assumed the starboard gauge panel read:

 

- first pair, inner wing tanks, 146 gallons per wing, one gauge per wing… tanks 2&3 from Fig 18??

- second pair - no logic here as the RH gauge is the non fitted long range tank. First gauge is only for 53 gallons - both tank 1 centre tanks from Fig 18??

- rear pair - outer tanks, excluding drop tanks, which matches the 58 gallon per wing capacity on Fig 18

 

I can confirm that the transfer pump dumps fuel out of the aircraft… thought I’d been hit as I had two plumes of fuel streaming behind…!

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@Helles Belle you're understanding of the fuel system is bang on from what I read in your post.

 

Talking of the external fuel transfer I've been doing a bit of testing with it. I jumped onto a server in a Mossie with 100% fuel. I defueled the aircraft to 76% on the fuel slider in the ground crew options, see NOTE below before doing this!!, which empties the outer tanks. If you switch on the main battery switch you can see this happening on the outer tank gauges. I then fitted 50 GAL drop tanks to the aircraft and went flying. Once in the air, with mains selected (as the outers are empty from the defuel), I opened the transfer valve. The fuel transfers into the outers ok, takes a while, but what I found is I can only get 30 GAL into the outer tanks as seen on the gauges. I thought the tanks hold 50 GAL which should almost fill the outer tanks (58 GAL capacity) on each side. Similar thing happened with the 100 GAL tanks. Can anyone else confirm this or am I missing something? (other than the missing fuel! lol). 

 

NOTE :- if you defuel a full aircraft to under 76% I found it tries to take some fuel out the main tanks and there currently seems to be a bug where the fuel sound loops, the fuel never comes out the mains and you're basically stuck in a dead aircraft as the ground crew won't prime the engines for engine start while they are busy with the defuel which is stuck in the never ending loop! only thing to do is abandon it and jump into another aircraft. So if you defuel a full (100%) aircraft DON'T go past 76% on the fuel slider, this will effectively empty the outer tanks only.


Edited by bart
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9 hours ago, bart said:

Once in the air, with mains selected (as the outers are empty from the defuel), I opened the transfer valve. The fuel transfers into the outers ok, takes a while, but what I found is I can only get 30 GAL into the outer tanks as seen on the gauges. I thought the tanks hold 50 GAL which should almost fill the outer tanks (58 GAL capacity) on each side. Similar thing happened with the 100 GAL tanks. Can anyone else confirm this or am I missing something? (other than the missing fuel! lol). 

Might be worth saving a track and reporting that as a bug.

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Re: what fuel gauge shows what.

I have used the diagram from the FB6 manual (it’s easier to understand for me)

@rkk01 hope this helps.

 

@bart I did the same thing with transfer of wing tanks. (50 gal drop tanks)
although I started with full outer tanks, used the fuel down to 10 gal, then transferred the fuel.

it took a while but same thing, the gauge stopped at 40 gal. Which tells me it only transferred 30 gal.

I’ll try the same with the 100 gal drop tanks and see what happens.

 

interesting what happened with the de-fuel, sounds like a bug.

I only tried starting with about 40% fuel then went up in by 10% at a time.

Everything seemed to ‘fill up’ ok.

I was even impressed that the centre tank was filled last, which is the expected behaviour.

 

image.png

 

 


Edited by Helles Belle
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11 hours ago, bart said:

NOTE :- if you defuel a full aircraft to under 76% I found it tries to take some fuel out the main tanks and there currently seems to be a bug where the fuel sound loops, the fuel never comes out the mains and you're basically stuck in a dead aircraft as the ground crew won't prime the engines for engine start while they are busy with the defuel which is stuck in the never ending loop! only thing to do is abandon it and jump into another aircraft. So if you defuel a full (100%) aircraft DON'T go past 76% on the fuel slider, this will effectively empty the outer tanks only.

 

 

+1 can confirm this is true.

 

If you try to de-fuel below 76% it gets stuck.

 

I'm not sure what the standard procedure was in 1942.

But it re-fuels the centre tank last. While this appears to be correct, to keep the weight on the wings. I would expect if you don't need fuel above 76%  i.e. 2x59 gals which = the total amount of the outer tanks. Then you'd be better having the inner tanks & centre tanks full instead of the outer tanks in case you get an engine failure, as you can then use all available fuel.

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8 hours ago, Helles Belle said:

I'm not sure what the standard procedure was in 1942.

But it re-fuels the centre tank last. While this appears to be correct, to keep the weight on the wings. I would expect if you don't need fuel above 76%  i.e. 2x59 gals which = the total amount of the outer tanks. Then you'd be better having the inner tanks & centre tanks full instead of the outer tanks in case you get an engine failure, as you can then use all available fuel.

 

All WW2 aircraft were open line refuel (as opposed to the pressure refuel system used on modern jets) which is basically like refuelling your car. You take the fuel cap off, use a nozzle similar to what you get in a fuel station but bigger, and fill up the tank until it's full. Replace the cap and go to the next tank. There was a sequence to do it in. I was always taught (Ex RAF) to refuel open line tanks from the centre out, and I did this countless times on all sorts of aircraft, so my logic says the centre tanks should be filled first followed by the inner wing tanks, then the outer wing tanks and lastly the externals if they are fitted. By not filling the centre tank but the inner wing tanks first that may be another bug, but I'm not 100% sure. Also IRL if the tanks were at different heights within the fuselage with the centre tanks slightly below the inner wing tanks, if you filled the inner wing tanks and not the centre tanks then the fuel would run down into the centre tanks anyway due to gravity or at least self level after a period of time. I would guess that's why the long range tank that fits into the bomb bay was fitted with a booster pump, as when it was fitted it was below all the other tanks in the system.

 

10 hours ago, No1sonuk said:

Might be worth saving a track and reporting that as a bug.

 

I could try but it would be a rather large track file. I tried to post tracks here on the forums before and with the limit of 5MB it's been an issue in the past. Still I'll give it a go later and see what happens.

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20 minutes ago, bart said:

All WW2 aircraft were open line refuel (as opposed to the pressure refuel system used on modern jets) which is basically like refuelling your car.

 

The inner tanks in the Mosquito could be pressure refuelled via the fuel gallery in the bomb bay (the collector box on the diagram). It also contained non-return valves that prevented fuel from flowing between the tanks uncommanded. 

 

I'm not sure why all manuals I've seen state that the engines should be started from the outer tanks. It may be that they are higher than the engines, so the gravity assists in priming and starting. It may be that the fuel return lines from the engines go to those tanks, so there has to be some extra room or you're overfill them. Maybe both reasons. 

Other than that, the outer tanks should be used first and filled last, because they are unpressurised, and because of the droptanks feeding them (which also should be emptied asap). For the inner wing and center tanks, I don't think much distinction was made between them, they work the same way and can be used/filled in any order. 

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1 hour ago, some1 said:

The inner tanks in the Mosquito could be pressure refuelled via the fuel gallery in the bomb bay (the collector box on the diagram). It also contained non-return valves that prevented fuel from flowing between the tanks uncommanded. 

Interesting, I didn't know this.

So what was the reason for pressure refuelling the inner tanks only? and why were the other tanks not refuelled in this way?

All the warbirds I ever refuelled at station air shows were open line. One occasion I was refuelling a Grumman Avenger and it air locked and spat fuel out of the tank filler point all over the wing, it even ran down into the cockpit floor! The pilot didn't bat an eyelid, he just said "ach don't worry about that, does it all the time! it'll soon evaporate" and it did. AVGAS is stinky volatile stuff.


Edited by bart

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It's simply because the inner tanks are connected to the common manifold, while the outer tanks are not. The outer tanks can be connected only to the engine in the same wing and that's it. 

A color picture from DCS manual

Screenshot 2021-10-13 110653.jpg

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3 minutes ago, some1 said:

It's simply because the inner tanks are connected to the common manifold, while the outer tanks are not. The outer tanks can be connected only to the engine in the same wing and that's it. 

 

Yeah, I see that. But why pressure refuel these tanks and not open line them?

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You could if you wanted to, or didn't have the hardware for pressure refuelling available. 

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On 10/13/2021 at 10:39 AM, some1 said:

 

The inner tanks in the Mosquito could be pressure refuelled via the fuel gallery in the bomb bay (the collector box on the diagram). It also contained non-return valves that prevented fuel from flowing between the tanks uncommanded. 

 

I'm not sure why all manuals I've seen state that the engines should be started from the outer tanks. It may be that they are higher than the engines, so the gravity assists in priming and starting. It may be that the fuel return lines from the engines go to those tanks, so there has to be some extra room or you're overfill them. Maybe both reasons. 

Other than that, the outer tanks should be used first and filled last, because they are unpressurised, and because of the droptanks feeding them (which also should be emptied asap). For the inner wing and center tanks, I don't think much distinction was made between them, they work the same way and can be used/filled in any order. 

The engines are started on the least important tanks, the outer ones, where it's safe.

Then the engine run up is on the next important tanks, the inner ones.

The critical stage, taxi and take off, on the more important centre tanks, which will service both engines.

This ensures all fuel systems are checked.

Next, when a safe height is obtained, go back to outer tanks and when some has been used, start transferring from drop tanks, to outer tanks.

When these are full, stop transfer until more space has been made. Repeat until drop tanks are empty.

Use remaining outer tanks before starting on main tanks.

(From the MK 6 manual).

..


Edited by Holbeach

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My engineer brain tells me using the outer tanks first may be a flight performance thing.
My theory behind this:
If you have weight out that far, the roll rate will be lower than if it was all in the centre.
Using that fuel in transit to the target means you'll reduce that weight at a distance from the fuselage so that you'll have better performance when you need it - over the target and egress.

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All the other tanks are pressurized to prevent fuel vaporization at altitude, but outer tanks are not. 

Also if one of your engines dies in flight, you can't use the fuel from that outer tank to feed the other engine, you just have a dead weight. 

These are the reasons why the outer tanks should be emptied first. 

It also looks like the engine priming system is connected to the outer tanks, but that seems to be a separate line bypassing the pilot's selector, at least on ED's diagram. 

 

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  • 10 months later...

Starting on outer tanks is a good way to test that they satisfactorily feed the engines in a safe environment. You don't want to learn about fuel tank feed problems mid flight. This also removes some fuel from the outer tank system so later drop tank transfer is less likely to vent fuel overboard. There also may be some benefit (requirement?) to ease of engine starting as priming uses the outer fuel system. Warming up on main fuel may be an early check of that system.

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