External fuel tank hold too much fuel?

[outbaxx]

As the topic says, I believe the tank hold too much fuel. If I choose a clean ac with x-tank and set the internal fuel to 51% I get 99% in the pit. It should read about 79%.

Full internal is about 107% and with x-tank about 133% according to SFI.

If I set 100% internal with xt I read 135% in pit but it stay at 135 long after take off.

If I set internal to 0% I will read 46% in pit.

 

107-133=26 so I think it holds about 20% too much fuel. Or it should be reduced by about 45% depending how you count.

Edited February 6, 2017 by outbaxx

[outbaxx]

It's kinda weird, if you read the SFI pt2 for the AJ it says that 5525 liters is 100% and in SFI pt2 for the AJS it say 5525 liters is 107%.

The AJ external tank hold 1320 liters and the AJS 1250 liters.

It says 1250 liters is 26% but I get it to about 24% (if 5525 is 107% 9600lbs, 100% is about 5163 liters 9000lbs)

 

How come that 5525 liters became 107% for AJS when it was 100% for the AJ?

 

Anyhow, the external tank in sim seem to hold between 2375-2540liters, about 1000-1200 liters too much. Unless the fuel gauge has an error.

[renhanxue]

They changed fuels between the AJ 37 and AJS 37 to a new one with slightly different density, IIRC. That's why there's a red sticker in the cockpit next to the fuel gauge that says (if memory serves) FLYGFOTOGEN 75 or MC 75 or something to that effect. Yes, it's basically an "unleaded fuel only" sticker ;V

[microvax]

The needle stays indeed for quite some time at 135%, but iirc the 11minutes of zon3 I get out of it X-Tank and internal at SL are correct with the X-Tank. Could be mixing up burner times with the mirage here though.

[outbaxx]

They changed fuels between the AJ 37 and AJS 37 to a new one with slightly different density, IIRC. That's why there's a red sticker in the cockpit next to the fuel gauge that says (if memory serves) FLYGFOTOGEN 75 or MC 75 or something to that effect. Yes, it's basically an "unleaded fuel only" sticker ;V

 

 

Ah, but isn't 1 liter = 1 liter? Is the % based on weight then? And perhaps that is why the external tank hold less liters for AJS as the weight increase with the new fuel?

[microvax]

Weird thing i notices though, If you set your AC to start in the air in the Mission editor the fuel gauge doesnt start at 135... But something like 132 and starts going down instantly.

 

 

Just checked my fuel tests. Full zon3 on internal is roughly 9 minutes, with external tank that is 11.

So seems to match with the +25% fuel.

 

I think something with the gauge is off.

Edited February 8, 2017 by microvax

[outbaxx]

I have only started in "parking hot" yet. Will start my cold start training tonight, but yes, if it's ok in air start then perhaps the gauge get weird in hot start?

[razo+r]

with cold start, my needle was about 125 or so, with hot start it was maxed out

[renhanxue]

Ah, but isn't 1 liter = 1 liter? Is the % based on weight then? And perhaps that is why the external tank hold less liters for AJS as the weight increase with the new fuel?

 

A liter is a liter yes - not sure what's up with the drop tank, though.

 

As I understand it, the new fuel had a slightly different capacitance, which made the fuel meter show higher values (the fuel sensors are basically capacitors which chance their capacitance and therefore AC resistance depending on the fuel level in the tank). This is all hearsay from the Viggen FB group though, I don't have a source on this and it's not in the SFI as far as I know.

Edited February 8, 2017 by renhanxue

[scaflight]

By the way, if you guys are testing this -- AFAIK you can, while in midair, go to the ground radio menu to rearm and refuel, and that'll tell you the precise weight or quantity of fuel aboard at any time.

[Goblin]

As I understand it, the new fuel had a slightly different capacitance, which made the fuel meter show higher values (the fuel sensors are basically capacitors which chance their capacitance and therefore AC resistance depending on the fuel level in the tank).

 

This may very well be the case, but should be possible to calibrate.

The MC75 is a heavier fuel (higher density=more energy per liter). This could be why you essentially get 7% extra "energy" compared to the older fuel? I don't know. Just speculating. :)

[QuiGon]

I just revisited this issue with the following results:

 

- Air start without tank: 102,5%
- Air start with tank: 126%
- Ground start without tank: 102,5%
- Ground start with tank: 126%
- Ground start with tank but no internal fuel: 22.5%

So seems like the external tank doesn't hold too much fuel anymore, but the internal tanks are a bit too small (according to posts above it should be 107% instead of 102,5%).