About Fuel Temp...

[DrumsArt 270]

Hi,During a flight (+- 2hours and half) the fuel temperature decreased at -3 degrees C.Problem : during descent and after landed the temperature is always at -3C.... I waited a long time with the plane parked but the temperature does not rise.NGX W 800 SP1Outside Temperature=15CWhen I reinstalled the plane I deleted all save, panel state files, deleted also all ref in fsx.cfg about the ngx.Someone from PMDG ?Thank you in advanceRegards,Richard Portier

[Paul Deemer 13]

The NGX is the first aircraft to accurately simulate fuel temperature changes. In other planes whatever the temperature outside was that would be the fuel temp and it happened instantly. If you take off in a warm place in the NGX and fly at high alititude it will take a long time for your fuel temps to drop. So I would imagine it will take a long time for it to warm up as well.

[DrumsArt 270]

So I would imagine it will take a long time for it to warm up as well.

May be you are right but I'm not sure about that. Let us suppose that the temperature of fuel decreases dangerously during flight, it's supposed to increase speed or/and decrease altitude to address this problem. So, with what you say it would not be possible ? I flied the 747PS1 from aerowinx for +1000 hours, I've never seen that. Sure the 737 is not 747 but.....Regards,Richard Portier

[scandinavian13 5,192]

Even at 15 degrees temp on the ground, you have to keep in mind that if it was a two hour flight that put the temp down to -3, you've chilled the fuel and the aircraft is cold soaked, so now they're in somewhat of a cycle of cooling. The cool airframe isn't warming the fuel, and the cool fuel isn't warming the airframe. Furthermore, the fuel heat (hyd cooling) comes from the hydraulics, and if your aircraft is shut down, those aren't exactly moving around much to generate too much heat.

[Paul Deemer 13]

Did not say it would not be possible. What I said is it is not an instant thing like some planes. It takes awhile. If your flying way up north at night and in the winter time the temps can get down to -40 or lower up there. The solution is fly at a lower altitude and the fuel would gradually rise in temperature, but it takes time.

[Paul_Smith 92]

I think it was PMDG's MD-11 that was the first to accuratly simulate fuel temperature effects (including freezing). If it took 2 hours with outside temp of about -50C and airspeed of 450knots to cool the fuel from +15 to -3, then you would expect it to take 2 hours with outside temperature of +65C and airspeed of 450knots to heat it back up to +15C.

[FLEX1978 373]

The NGX is the first aircraft too accurately simulate fuel temperature changes. In other planes whatever the temperature outside was that would be the fuel temp and it happened instantly. If you take off in a warm place in the NGX and fly at high alititude it will take a long time for your fuel temps to drop. So I would imagine it will take a long time for it to warm up as well.

I wouldn't be too sure about that, quite a few addons out there replicate fuel temps accurately.And his fuel should not remain at -3 after landing, you can affect fuel temp by descending lower into warmer air or increasing speed and TAT, why would you think it would be realistic to land at 15c and still have fuel at -3 after a prolonged descent?In extreme cases the lag between TAT and fuel temp can be up to an hour but normally you are looking at a 15 minute lag at most

[Paul_Smith 92]

...And his fuel should not remain at -3 after landing, you can affect fuel temp by descending into lower air or increasing speed and TAT why would you think it would be realistic to land at 15c and still have fuel at -3 after a prolonged descent?

The fuel can only warm up by absorbing the energy from the air actually touching the surface of the wing, but once that air is cooled, there is no energy left to transfer. During the approach, or even by just flying at a lower altitude, the airflow replaces that cooled air with warm air. Once on the ground, the airflow is next to zero so once the air in contact with the wings is cooled, it stays cold.You can see this in real life when you take some meat from the freezer. If you just leave it on the counter, even though you have a nice warm house, it will still take a long time to defrost, and that is only warming from -4 to +4. Put the same piece of meat in front of a fan, even one blowing cold air, and it will thaw much faster.

[FLEX1978 373]

Hey Paul,Yes correct if the aircraft magically went from cruise to the ramp. The OP had a TAT of -3 in cruise and through the whole descent and landing not a even a 1c change in temp? I am not saying PMDG coded the system wrong since they got it right on all other products, it is probably a glitch on his setup.Regards

[Guest]

I tend to agree with the fact that from -3 when descending and when on ground above all the temperature should have raised of several degrees, f.i. around 1-2 when descending and around 10-12 when on ground.

[willywonka 36]

Remember that rate of heating/cooling is also dependent on mass, so it won't be constant as you burn up fuel through out the flight.Also, even if the temperature outside (SAT) is -50C or so, your fuel temp will only go down to the airframe's temperature (TAT) of around -24C, "well above" the freezing point of fuel of -40C (I think).

[Guest]

Remember that rate of heating/cooling is also dependent on mass, so it won't be constant as you burn up fuel through out the flight.Also, even if the temperature outside (SAT) is -50C or so, your fuel temp will only go down to the airframe's temperature (TAT) of around -24C, "well above" the freezing point of fuel of -40C (I think).

You are right, anyway do you concur about the issue highlighted from the thread's starter ? I think yes.

[DrumsArt 270]

Effectively the temperature is lowered at the parking gate after almost 2 hours. Thank you for the explanation in previous post. It's ok on the ground...But during phase descent the temperature remained at -3C. From the FCTM Chapitre 4.11 "Low Fuel Temperature" page 157 there is :"

It takes from 15 minutes to one hour to stabilize the fuel temperature. In most cases, the required descent would be 3,000 to 5,000 feet below optimum altitude. In more severe cases, descent to altitudes of 25,000 feet to 30,000 feet might be required. An increase of 0.01 Mach results in an increase of 0.5° to 0.7° C total air temperature."

I would other test... That said, not a big deal... I was just surprised of that

Regards,

Richard Portier

[flygarn1 0]

As DrumsArt spells it: it is the compressibility of the air that warms the fuel a little bit.On decent and landning you loose altitude BUT the speed decreases also so the big cold energy that was on cruise altitude doesn't exist on decent and approach.In the case of cold fuel on warm ground/fuselage you will expect a phenomene that is called: "cold soked fuel". which means that the moisture in the air freezes on the wings when there is cold fuel inside (if fuel temp is below the dew point it will condence and if it is below zero it will condence and freeze), and you actually may need to de-ice before take-off depending on were the ice is on the wing.A cold white wing on the tarmac will not heat up in a rapid phase because white or similare colours will send the sunrays back into space!

[kevinh 409]

In extreme cases the lag between TAT and fuel temp can be up to an hour but normally you are looking at a 15 minute lag at most

A 15 minute lag for that amount of liquid? If you boil a kettle it will much take longer than 15 minutes to cool down to ambient, and that's only a small volume of water. Fuel tank temp lags much slower than 15 minutes. The less the fuel in the tanks the less the lag of course. Also in flight with a lot of cold air flowing over the wings reduces the lag.Kevin Hall