Ju-88 A-4 fuel tank logic wrong?!

[FTC_DerSheriff]

Hello!

While researching for a video I needed to look up how the fuel indicators have to be read in the Ju-88. TL;DR at the end.
 

I couldn't figure it out by just looking at the gauges, I read things up in official handbooks which are available online in german.

Primarily this one:

http://1.airwar.z8.ru/transfer/manual/[aviation]%20-%20[manuals]%20-%20Ju%2088%20A-1%20Betriebsanleitung.pdf
But this as well:
http://www.allworldwars.com/Ju-88-Flying-Operations-Manual.html

 

Our Ju-88 ingame is the A-4, which features 4 wing tanks. Two inner tanks and two outer wing tanks.

In the mentioned manual its stated that the fuel tanks are linked and that pumps are feeding fuel from the outer wing tanks to the inner wing tanks. Only the inner wing tanks are used to feed the engines with fuel. "Entnahmebehälter"

Paraphrased:
"Because the inner Wingtanks are only setup to feed the engine [...] they need to be refilled with the other tanks when a warning light lights up"

 

The fuel amount for the wing tanks can be read with the two indicators on the right side in the cockpit. The indicators show the amount of the inner and outer wing tanks in dependence of the position of that selector switch in the middle.

Ingame that selector switches automatically between fuel tanks 2 and 3.
2 are the outer tanks, 3 are the inner.

I tried now the Ju-88 and tested how the fuel tanks get used. Only to be puzzled, since the ur Ju-88 consumes all the fuel from the inner fuel tanks first, only then to proceed to use up the fuel in the outer tanks. The inner tanks are kept completely empty. To my knowledge this should lead to fuel starvation!

So my FM/Model/Bugreport/TL;DR:
To my knowledge the fuel tank indicators are either showing the wrong tanks or the engines are using fuel from the wrong fuel tanks.

I am happy if somebody could prove me wrong, or can confirm this. To my knowledge nothing changed with the fueltanks from A-1 to A-4 which would explain this.
Cheers.
 

Edited February 19, 2018 by DerSheriff

[Pail]

Bah ! Who looks at fuel gauges anyway.....?

[xvii-Dietrich]

To my knowledge the fuel tank indicators are either showing the wrong tanks or the engines are using fuel from the wrong fuel tanks.

 

I am happy if somebody could prove me wrong, or can confirm this.

You're second deduction is correct. It is using fuel from the wrong tanks, first using the inner tanks, then the outer ones.

 

There is no complex engine management here, so there are going to be discrepancies between the historic manuals and the in-game experience. In this case, the fuel is simply subtracted from one set of tanks, then the other. You have no option to pump fuel about between tanks for balance, mitigating leaks or even just getting fuel from the correct tank. And the fuel indicator switch just clicks back and forth automatically; you can't leave it on the inner tanks and thus get your current fuel at a glance.

 

[Dakpilot]

With the planned update to fuel management across the board, things should improve regarding this, and many other issues

 

Cheers, Dakpilot

[FTC_DerSheriff]

You're second deduction is correct. It is using fuel from the wrong tanks, first using the inner tanks, then the outer ones.

 

There is no complex engine management here, so there are going to be discrepancies between the historic manuals and the in-game experience. In this case, the fuel is simply subtracted from one set of tanks, then the other. You have no option to pump fuel about between tanks for balance, mitigating leaks or even just getting fuel from the correct tank. And the fuel indicator switch just clicks back and forth automatically; you can't leave it on the inner tanks and thus get your current fuel at a glance.

 

 

As I recall the Ju-88 does do some fuel pumping. But it pumps the fuel out of the inner to the outer. But I can't test this atm.

[Sgt_Joch]

There may be an issue, but it does not have a practical impact in game.

 

I have been flying the JU88 a lot lately in a PWCG campaign. The JU88 already has a huge range relative to the map sizes (i.e  3.8 hours flight time). I usually just calculate how much fuel I need beforehand, plus a safety margin and do not worry about it in flight. There is a low fuel warning light when only 10% fuel is left, but that still leaves you with 20-25 minutes flying time.

 

The gauges are hard to understand anyway since the AI keeps cycling from tank to tank every few seconds.

[Haza]

Gents,

 

I always found this one helpful playing CLOD, although it is an A-1, I'm sure that it is still helpful!

 

http://www.raafsquad.com/cliffs/ju88/JU-88A-1%20Tech%20Brief.pdf

 

 

Regards

[Royal_Flight]

The gauges are hard to understand anyway since the AI keeps cycling from tank to tank every few seconds.

This is one of the stupidest deliberate features of BoX. It's even worse on the Spitfire, which only shows the fuel amount when a button is pressed which the AI only does briefly every twenty seconds or so, meaning you can generally only ever find out the fuel amount by accident.

It's infuriating.

Hopefully it gets fixed in the future.

[Plurp]

I believe there is an easy fix to take care of the most glaring problem.  All that needs to be done is switch the switch, 2 to 3, 3 to 2.

 

@ 20% fuel, there is fuel only in the inner tanks, reading #2 on the switch atm.  This runs until empty with V lights on.  Should read 3 on the switch.

 

@ 22% fuel, less fuel in the inner 2 (3) with ~60l per outer tank 3 (2) V lights on and immediate pumping until outer tanks empty.

 

@ 40%  `280 per inner tank and `60 per outer.  fuel drains inner tanks until V on gauge, V lights come on, fuel pumping begins `5 mins later until outer tanks empty.

 

@60%  `240l per inner tank 2(3) and `250 per outer tank 3(2) :  Pumping for some reason begins immediately until inner tanks full, green L's come on.  Acts as @ 40% from here on.

 

@80%  `240 per inner, full outer:  immed pumping.

 

@100%   All tanks full, green L's on:  Pumping switches on, but no pumping occurs until V is hit:  pumps until green L's on, switches turn off.

 

So, fuel to the engines only happens from one set of tanks, currently 2, should be 3 on the switch.  All pumping occurs at various times, but just to feed the other 2 tanks, never the engines.  

[GridiroN]

Strange that it's designed to use the inner tanks completely first...

 

On modern airliners, the inner tanks are used until the sum of the inner tanks is below the outter tanks, at which point, the outter tanks crossfeed to the inner tanks, until the outter tanks are empty, but the inner tanks are not. 

 

Either way, I agree that the fuel system needs a quick overhaul. I thought it would come with 3.002 but I guess it was too big for that. I think it should be done before a lot of newer bodenplatte planes get rolling as many of them have self-sealing tanks. 

 

At the very least, I'd like to be able to manually check my tanks. 

Edited May 6, 2018 by GridiroN

[Plurp]

23 hours ago, GridiroN said:

Strange that it's designed to use the inner tanks completely first...

 

On modern airliners, the inner tanks are used until the sum of the inner tanks is below the outter tanks, at which point, the outter tanks crossfeed to the inner tanks, until the outter tanks are empty, but the inner tanks are not. 

 

Either way, I agree that the fuel system needs a quick overhaul. I thought it would come with 3.002 but I guess it was too big for that. I think it should be done before a lot of newer bodenplatte planes get rolling as many of them have self-sealing tanks. 

 

At the very least, I'd like to be able to manually check my tanks. 

It doesn't drain the inner tanks completely if you switch the switch (2 to 3, 3 to 2).  Whether 40% fuel or 100%, the inner tanks (currently #2) that feed the engines drain down to about 180 liters per tank, the V light comes on and about 5 mins later the pump switches come on.  The pumps will stay on until the outer tanks are empty or the inner tanks are full (green L)

Edited May 7, 2018 by Plurp

[Yogiflight]

2 hours ago, Plurp said:

It doesn't drain the inner tanks completely if you switch the switch (2 to 3, 3 to 2).  Whether 40% fuel or 100%, the inner tanks (currently #2) that feed the engines drain down to about 180 liters per tank, the V light comes on and about 5 mins later the pump switches come on.  The pumps will stay on until the outer tanks are empty or the inner tanks are full (green L)

So it works the same way as in the 110 (front/rear tanks). I guess the way it currently is modelled is, when you take 60% fuel, the system handles it, as if 40% were already used. So the 40% that are missing, are missing from the tanks, the engines get the fuel from. Therefore the rear tanks in the 110 and the outer tanks in the 88 (and 111?) are full and the remaining fuel is in the inner/front tanks.