Kurfurst fuel gauge, fuel tank and manual

Hi dear Simer,

I note a thing that is difficult to understand to me:

The fuel gauge in the cockpit indicates 400 liters when it's full of fuel.

indeed at the page 111 it is note that this bird have a capacity of 400 liters...

But the manual indicates at the page 49 that the main fuel tank, located behind and under the seat (L Shape) have a capacity of 250 liters. The problem is: there is only one fuel tank on this beast.

(The MW50 tank is 118 liters)

Manual mistake ?

Could you light this contradiction ?

Hi brennus54,

the Bf109 tank capacity is 400 liters, must be an error in the manual.

But the manual indicates at the page 49 that the main fuel tank, located behind and under the seat (L Shape) have a capacity of 250 liters. The problem is: there is only one fuel tank on this beast.

 

 

(The MW50 tank is 118 liters)

 

Manual mistake ?

Could you light this contradiction ?

The manual is wrong, on many accounts, sadly. It seems to be based on varied sources, including Wikipedia... the only 109 that had a 250 liter tank was the 109B, subsequent models progressively enlarged the tank.

The K-4 had a 400 liter main tank, a 115 liter aux. dual-purpose tank (fuel or MW, in latter case, only 85 liter is filled to maintain CoG) mounted in the rear of the fuselage and a 300 liter droptank. Since both of these latter two extra tanks feed into (top) the main tank, you only need one 400 liter gauge (and never have to worry about switching between fuel tanks).

.., a 115 liter aux. dual-purpose tank (fuel or MW, in latter case, only 85 liter is filled to maintain CoG) mounted in the rear of the fuselage...

I understand it this way, that with MW50 the tank was filled completely, while with fuel it was filled completely as well while it only weighed 85kg due to density of fuel (~.75 kg/l). I have never read anything about CoG reasons. Now in theory the MW50 should also have a density below 1, probably something around 0.9 kg/l that would result in a weight of ~106 kg for a full tank.

The engine chart on your site says MW50 consumption at Sondernotleistung is 180 l/h, so 118l would lead to 39,3 min of total usage time. I have always read about 40 min of total MW50 usage time, is that incorrect?

The engine chart on your site says MW50 consumption is 180 l/h, so 118l would lead to 39,3 min of total usage time. I have always read about 40 min of total MW50 usage time, is that incorrect?

In the original german manual of the Bf109K-4, total use of MW50 was 26min.

Racoon, you are right, the manual has been changed, my information came from an older version.

Indeed the actual manual which is located in DCS world/Mods/aircraft/BF-109K/doc indicates 400 liters

Sorry :(

All is alright,

Have a good flight

Ok thanks. I dont have access to my manuals at the moment, so ill trust you on this one. :)

180 l/h = 3 l/min

3 l/min * 26 min = 78 l

78 l * 0.9 kg/l = 70 kg :huh:

85 kg MW50 are enough for ~32 min Sondernotleistung.

Why?! :cry:

I understand it this way, that with MW50 the tank was filled completely, while with fuel it was filled completely as well while it only weighed 85kg due to density of fuel (~.75 kg/l). I have never read anything about CoG reasons. Now in theory the MW50 should also have a density below 1, probably something around 0.9 kg/l that would result in a weight of ~106 kg for a full tank.

 

The engine chart on your site says MW50 consumption at Sondernotleistung is 180 l/h, so 118l would lead to 39,3 min of total usage time. I have always read about 40 min of total MW50 usage time, is that incorrect?

I believe it was for CoG reasons, really there is not much else I can think of why placing a heavier equivalent weight liquid in the same place on an airplane. In practice it probably wasn't followed so strictly, there is a Brit intel report in my site noting they found 100 liters MW in the tank. There were tolerenace on CoG for a reason: human nature. :D

85 liters / 180 lit/h works out to me as 28.3 mins, but its again a bit reserve since the easy-to-remember instruction was to "use for ten mintues at a time, twice at max" and you better have reserve to account for sloppy loading for example, since when MW runs out knocking and detonation could occur with B-4 (less so with C-3) and this could damage the engine. I suppose like fuel tanks, you could probably not use the last liters either.

Thanks for the answers. The tank was pressurized with around 4 bar overpressure when using MW50, so in this case it should have actually worked to empty it almost completely. You are probably right, a few liters being reserve makes sense.

85kg MW50 are actually ~95 l while 85kg of fuel corresponds to ~115 l. Therefore my confusion in usage time. I really always thought the tanks were filled to the maximum, with both fuel and MW. So how much MW50 is actually modeled in the DCS tank? If it is full it may contribute to the CoG/ pitch up problem..

PS: If the MW pressure on K-4s was produced by the supercharger, it wouldnt really make sense if the pressure was ~4 bar. The 4 bar one was probably the earlier type pressurized by compressed air bottles.

I believe it was told by the devs that, at least in the Fw190 the amount filled into the MW50 tank is proportional to the amount of fuel loaded in the mission.

I believe it was told by the devs that, at least in the Fw190 the amount filled into the MW50 tank is proportional to the amount of fuel loaded in the mission.

Yes, that is what they said.

Oh.. Thats quite a strange way of doing things. :huh:

A slider would be the perfect solution, though I am not sure if that is possible in the model?

Can anybody of ED tell us whats the max fill volume or mass of a full MW tank (well the content) and if weight of MW is according to density? I know for fuel it is.

Thanks for the answers. The tank was pressurized with around 4 bar overpressure when using MW50, so in this case it should have actually worked to empty it almost completely. You are probably right, a few liters being reserve makes sense.

 

85kg MW50 are actually ~95 l while 85kg of fuel corresponds to ~115 l. Therefore my confusion in usage time. I really always thought the tanks were filled to the maximum, with both fuel and MW. So how much MW50 is actually modeled in the DCS tank? If it is full it may contribute to the CoG/ pitch up problem..

Works out 296 kg for the main fuel tank (0,74 kg / lit), 85,1 kg for the rear tank if fuelled with 115 liters of fuel. 85 liters MW in the rear tank should be about 76 kg, if I calculated with a density of 0,896 kg / liter, which seems reasonable since it was a 50/50 mix of water and methanol. Methanol is lighter (0,792 kg/lit) than water, which is 1 kg/liter in SI at +4 Celsius IIRC.

PS: If the MW pressure on K-4s was produced by the supercharger, it wouldn't really make sense if the pressure was ~4 bar. The 4 bar one was probably the earlier type pressurized by compressed air bottles.

Possibly. 4 bars seem to be a bit much anyway - I mean car tires are pressurized to just about 2-2,5 bars and rock solid when they are pumped and strong enough to hold a two ton vehicle. Should not the MW pressure gauge show how much is that pressure actually, iirc something like 1,8...?

P.S.: One of the thing that always amazed me when people talk about how "strong" engines must be if they can withhold such "extreme" manifold pressure like 2 ata at over. In reality it is not that much pressure, even car tires can hold it easily... its the insane power and torque of the engine running at such boost pressures that is hard to contain by the bearings and connecting rods...

Well I didnt go as far as calculating with 3 digits since there is also ~1.5 % Volume of some oil in MW50 which I dont know the density of. :P

Tires have 2.0 - 2.7 bar overpressure, so in absolute pressure (3.0 - 3.7) are not that much different from the 3.5 - 4.5 bar pressure in the early MW tanks. I think the system was adapted for MW from the earlier GM-1 systems, so the tank should be a lot more sturdy and much heavier as well.

Modern charged Diesel aggregates are actually closing in on 200 bar point pressure. Talk about a strong engine right there! :thumbup:

I think when I have the spare time Ill test for how long I can fly with MW50 enabled and this way find out whats the maximum MW fill volume in DCS is.

Hehe, with time lapse its actually no problem.. so the MW50 pressure starts to drop after ~25 minutes, at the 28-29 minute mark the engine starts knocking. Thats a clear sign, at that time point there is no more MW50 injected.

Conclusion in DCS a full MW50 tank contains ~85 l! Perfect!:megalol:

Now if the mission editor would show the MW50 weight, we could check if density is correct. But I suspect it is. :thumbup: