Hi folks!

 

I've got a question: I don't know if it's a generally bug, a problem with my installation (in fact, the pmdg777 runs without problems on my system) or maybe realistic...

 

After the first loading a 777 from the fsx menu, no matter if it is a 77L or 77F, the fuel temperature is approximately near the outside temperature. After reaching higher altitudes and decreasing temperatures, the fuel temp decreases also. So far it seems realistic for me - the fuel temp decreases e. g. to -15° C.

 

After coming back to the ground, the fuel temperature rises very very slowly. Even at e. g. 39°C the fuel temperature rises very slowly. During a usual turnaround, the fuel temp won't come up to a +degree. It only rises from degree to degree - but stays normaly below the freezing point. Even the time-lapse does not make it faster.

 

For my opinion, this can't last so long  and I think, I could not notice such a low increase of the fuel temperature with other products (e. g.PMDG747, Level D 767)

 

So my question: Is it a bug, a problem with my installation or maybe realistic?

 

Regards and thx for answers!

 

 

So my question: Is it a bug, a problem with my installation or maybe realistic?

 

It's realistic.

 

The flight loads close to the ambient temperature because how else would you set it?  Do you set it to behave as if it's been on the ground for a minute?  Five hours?  Two days?

 

Depending on how long the turn is, and the ambient temperature, the fuel may not ever get too warm.  Google "cold soaked fuel" and click on Images and you'll see a few pictures of frost on the wings only around the fuel tanks because the fuel warms much slower than the surrounding air.  Remember that most aircraft wings are silver (or at the very least, light grey), which is reflective.  This reflects a lot of the sunlight that would otherwise warm the wing and subframe, which would then warm the fuel.  The fuel, being pretty cold, takes a lot of energy to heat back up, and not a lot of that energy is making it far enough into the wing to expedite that process.

I agree with Kyle.

 

The only thing that can speed up this process is refuelling!

(not sure how/if that is modelled though)

You're warming up a HUGE block of fluid below 0C... Ever seen how long it takes an ice cube to melt in a glass of luke warm water? Imagine that same process, exponentially enlarged. (And no, I'm not saying there are ice cubes in your fuel tanks...)

So, anyone know (roughly) when fuel temp becomes problematic, and what can be done about it?

So, anyone know (roughly) when fuel temp becomes problematic, and what can be done about it?

Descending into warmer air. Especially on polar routes this is sometimes the case. Speeding up may also help, but there is not much room for it...

So, anyone know (roughly) when fuel temp becomes problematic, and what can be done about it?

Fuel temp warnings will come on according to the temperature limit you set in the FMC. I believe -38C is the default temp limit but can't remember for sure. If you drop below this temperature, a warning light will come on and according to the abnormal checklist you must descend. The actual freezing points for jet fuel are a little higher. http://en.wikipedia.org/wiki/Jet_fuel Jet A-1 freezes at -47c, JetA freezes at -40c. Jet B, used in colder climates, freezes at -60c. Jet A is only available in the United States, and I'm not sure if its used on big commercial jets. The world standard is Jet A-1, so you can make a safe assumption the freezing point of the fuel in your tanks is -47c. So I don't think it would be too dangerous to raise your fuel temp limit in the FMC to -40c to avoid some dash warnings at high cruising altitudes.

JP4 and jet B are prohibited.

 

Yes jet A (USA) is used on the 777. When flying from the USA you have to enter -37C in the FMC. This gives you a warning 3 degrees before freezing point.

 

For jet A1 (used mainly), -44 is entered in the FMC (since it freezes at -47C)

Hey - thanks for your answers.

 

 

Regards!

 

 

Yes jet A (USA) is used on the 777. When flying from the USA you have to enter -37C in the FMC. This gives you a warning 3 degrees before freezing point.

 

Thanks for clarifying. Do you happen to know if there are special circumstances where Jet A or A-1 are used? If they takeoff from KJFK with Jet A to EGLL for refueling, wouldn't they be worried about mixing fuel types? Also, is there any circumstance (such as a long haul over North Pacific or North Atlantic during winter where FL410 has a possibility of being reached) where they will go with Jet A-1 for safety reasons? I am using realistic temps and winds aloft and have hit the temp limit on multiple occasions with it set to default, which has led me always assume Jet A-1 for long hauls/oceanic crossings/high cruising altitudes. Would that be totally unrealistic? 

Guys,

 

I skimmed through the whole post. he is saying the aircraft is on the ground at 39c ambient temp and the fuel temp is still showing below freezing during the turn? This is not right.

 

Apologies if I have misunderstood..

where they will go with Jet A-1 for safety reasons? I am using realistic temps and winds aloft and have hit the temp limit on multiple occasions with it set to default, which has led me always assume Jet A-1 for long hauls/oceanic crossings/high cruising altitudes. Would that be totally unrealistic?

 

You cant choose the kind of fuel. In JFK they only offer jet A and you have to plan your flight level accordingly! If you think Fuel Freezing temp could become a problem than make sure you plan and file for a lower FL.

 

Mixing of A and A1 is no problem but you would use jet A freezing temp to be safe.

Maybe tables exist that let you determain the freezing level of the mixed fuel, but I have never seen them. Or you could interpolate and calculate the new freezing temp yourself....but I dont think that is allowed either.

Guys,

I skimmed through the whole post. he is saying the aircraft is on the ground at 39c ambient temp and the fuel temp is still showing below freezing during the turn? This is not right.

Apologies if I have misunderstood..

Why not?....if you have a lot of cold soaked fuel then it wil take way more than an hour for that to warm up again. Even at 39C!

 

I think with below freezing he means below 0C....not below the freezing temp of the fuel!

Hi Rob,

 

I understand he is not talking about below the fuel freeze point! If he was descending from cruise into a destination with an ambient temp of nearly 40c I. Would not expect to see that kind of a lag, in fact from memory I have never seen that kind of lag, at least on the 330/340.

 

Anyway, I am having a read through the Boeing FTPP so hopefully it will shed some light.

 

To the OP, can you give an actual fuel temp figure on the ground...

 

Btw, the reason I pointed out a potential issue is because this exact same conversation has come up multiple times in the past on the NGX and MD11, turned out to be a corrupt panel state, the fuel never rises above 0 degrees even if you leave the aircraft on the ground for hours.

You cant choose the kind of fuel. In JFK they only offer jet A and you have to plan your flight level accordingly! If you think Fuel Freezing temp could become a problem than make sure you plan and file for a lower FL.

 

Mixing of A and A1 is no problem but you would use jet A freezing temp to be safe.

Maybe tables exist that let you determain the freezing level of the mixed fuel, but I have never seen them. Or you could interpolate and calculate the new freezing temp yourself....but I dont think that is allowed either.

 

ok, not an optional thing then. I will plan with -37c with any flight to/from the United States and -45 to/from anywhere else. The LA-Hong Kong trip will be a bit sketchy, but as you suggested I shall plan accordingly. Thanks again.  

 

BTW, anybody know if fuel starvation due to temperature/freezing point is modeled? It seems like an easy thing to model, but I haven't pushed my luck. 

It should be since fuel freeze is already simulated on the MD11