airliner fuel tanks heating

[Guest hfghfghfgh]

Does airliners have fuel tanks heating?I know that PMDG manuals mentioned that b747 has temp probe in each tank and that EICAS warning message is created if fuel temp gets below -37

[Lord Farringdon 494]

Hi hfghfghfgh That's a very interesting topic actually. There is far more to it than FSX simulates. This site: www.airliners.net/aviation-forums/tech_ops/read.main/140073/1/#26 (can't hyperlink due forum restrictions), may have a more tech information than you want but take what you need. I'm sure you'll find it interesting. If you want to learn more on this topic then do a few more searches on the tech ops forums. There is huge wealth of real world info there. CheersTerry

[ZachLW 37]

Many times hydraulic lines and/or pumps are placed very close to the fuel tanks, heating the fuel.I can think of one particular aircraft that had some growing pains because of lack of heated fuel. What I affectionally call the "Mitsubishi Hawker Beechjet Jet" had a few incidents/accidents because of dual flame outs-- caused none other than by frozen/nearly frozen fuel lines. These aircraft require fuel additives (ie Prist) to lower the freezing point.Especially on larger aircraft, fuel is typically (not always) heated in the tanks. I'm no expert (as you can tell) but this is an interesting topic! Get your hands on a copy of an air carrier's operating hand book. It will put these sytems into English so a pilot can understand. :( The 727s have an interesting and simple way of fuel tank heating. Some others are a little more complicated.

[michal 44]

This is done via fuel to engine oil heat exchanger, but is the fuel in tanks heated?

I don't think so. The fuel is of course naturally heated because of jet's high speed and air-friction (roughly by about 20C) . It is further (naturally) heated when it is close to entering the engine by a heat exchanger from the generators. But I never heard that the main body of the fuel be somehow artificially heated - it would require way too much energy. You only really have to worry about fuel temperature when flying on those extreme Polar routes and pilots do use special procedures before/during such flights.

[Guest hfghfghfgh]

I don't think so. The fuel is of course naturally heated because of jet's high speed and air-friction (roughly by about 20C) . It is further (naturally) heated when it is close to entering the engine by a heat exchanger from the generators. But I never heard that the main body of the fuel be somehow artificially heated - it would require way too much energy. You only really have to worry about fuel temperature when flying on those extreme Polar routes and pilots do use special procedures before/during such flights.

Based on my knowledge there is no such think as natural heated fuel. You are right that friction increases kinetic energy of molecules, but this will only increase temp of wings leading edges and certainly not to 20

[michal 44]

and certainly not to 20

[Guest hfghfghfgh]

Read exactly what I said .. I said BY 20 C, I never said TO 20 C, a big difference. For nitpickers I also said roughly about, so maybe it is closer to 15, I don't recall. And I stand by what I said - friction is constant and it creates a constant heat flow from the skin of the wing/underbelly (NOT ONLY its leading edge as you imply - basis physics of friction) to the fuel. So yes, in fact the friction acts as a natural fuel heater increasing its temperature by _____ (fill in the blanks) degrees. If this heating did not take place no jet could fly at higher flight levels where air temperature is routinely below jet fuel freezing point.Ouchh.. this is really, really BAD, BAD physics but lets not go there ... :(

You are not reading my post in a context. Of course air molecules hit or touch or kiss wings surface or however you wana call it, but they don't hit the upper and lower surface at the 90

[Murmur 3,941]

Leaving aside the fuel heating issue:

air stream must increase at the upper side because it has to make a longer distance than at the lower side. This increase in speed reduces the pressure. The other factor of lift is inpact lift - this is created whenever angle of attack is greater than 0. This lift force is generated because air molecules are directed downwards and thus by physics law of action and reaction "push" the plane up. Inpact lift is greatly boost when flaps are in down position. Hope we agree on that.

Those are two common myths on the mechanics of lift generation, and they are wrong.Air molecules do not "have to" speed up because the upper surface of the wing is longer than the lower surface.Infact, a cambered (curved) thin airfoil will produce lift at zero AoA even if upper and lower surfaces have the same length.Regarding what you call "impact lift", the air is indeed deflected downward every time lift is produced, but the mechanism (in un-stalled, subsonic conditions) is different from what your description would seem to suggest. In other words, it's not that air molecules hit the lower side of the airfoil like bullets and get deflected downward, the mechanics are much more complicated and involve the upper surface of the wing as well.Marco

[michal 44]

how come "clean" air stream on wings creates such a high differences BY 20?

Because it does. You are underestimating friction forces my friend. You think that unless it hits at 90 deg it ain't much. SR-71's skin heats up to over 300 C while flying at Mach 3 at 85000 ft, all at 'zero degree angle'. SR-71 pilots have to wear special cooling vests otherwise they would cook inside their aircraft - all because of friction. You are also confusing friction with air compression effects that also generate heat). So if at Mach 3 you get delta T of +300 C how come a mere 20 C is such a big deal for you at Mach 0.85?. What is so difficult to comprehend here? Again, by your own admission fuel can freeze at around -40 C yet passenger aircraft fly every day when outside temperature is -55C. So what is your explanation for that? There are no fuel heaters that would do the job so what kind of magic is involved here?(Not sure what purpose serves your tirade about lift generation - we are talking about friction/heating and not lift generation).

[RobertVA 0]

Because it does. You are underestimating friction forces my friend. You think that unless it hits at 90 deg it ain't much. SR-71's skin heats up to over 300 C while flying at Mach 3 at 85000 ft, all at 'zero degree angle'. SR-71 pilots have to wear special cooling vests otherwise they would cook inside their aircraft - all because of friction. You are also confusing friction with air compression effects that also generate heat). So if at Mach 3 you get delta T of +300 C how come a mere 20 C is such a big deal for you at Mach 0.85?. What is so difficult to comprehend here? Again, by your own admission fuel can freeze at around -40 C yet passenger aircraft fly every day when outside temperature is -55C. So what is your explanation for that? There are no fuel heaters that would do the job so what kind of magic is involved here?(Not sure what purpose serves your tirade about lift generation - we are talking about friction/heating and not lift generation).

I'm thinking -55

[Bob Scott 7,721]

I'm thinking -55

[mgh 89]

Because it does. You are underestimating friction forces my friend. You think that unless it hits at 90 deg it ain't much. SR-71's skin heats up to over 300 C while flying at Mach 3 at 85000 ft, all at 'zero degree angle'. SR-71 pilots have to wear special cooling vests otherwise they would cook inside their aircraft - all because of friction. You are also confusing friction with air compression effects that also generate heat). So if at Mach 3 you get delta T of +300 C how come a mere 20 C is such a big deal for you at Mach 0.85?. What is so difficult to comprehend here? Again, by your own admission fuel can freeze at around -40 C yet passenger aircraft fly every day when outside temperature is -55C. So what is your explanation for that? There are no fuel heaters that would do the job so what kind of magic is involved here?(Not sure what purpose serves your tirade about lift generation - we are talking about friction/heating and not lift generation).

Most of the heating occurs because of adiabatic compression of the air - not becuase of skin friction. Adiabatic compression is what cause a bicycle pump to get hot.

[Guest hfghfghfgh]

Murmur:I really don't know why I allways read about inpact lift and airshape generated lift if these two things are a myth. I agree airflow mechanic are very complex, can't really be calculated since model simunaltions give better results, but still I think lift is generated from these two main things. Inpact lift or downforce lift is allso generated on F1 car rear and front spoiler by same principle. But I see I'll have to visit technical library to search for some reading - since I don't know much about. michal:OK I believe what you claim since I see you are an expert. So heat isn't generated sollely from friction but also from air commpression? Does bellow equation describe this?Just a word about simulated PMDG B747. In upper EICAS at the right bottom corrner you have also data about fuel temperature - probably average from all the tanks. The reading is nearlly same as TAT reading an it changes in matter of seconds - is this PMDG error or what?

[michal 44]

Most of the heating occurs because of adiabatic compression of the air - not becuase of skin friction. Adiabatic compression is what cause a bicycle pump to get hot.

Could be. In SR-71 for example skin heating alone accounts for 600 F, of course in the nose of the aircraft when you have additional significant compression effects it gets up to 800 F. The end effect is that you get temperature increases throughout the fuselage of the aircraft - in some places more and in other places less and all are result of some combination of friction and compression effects.

[michal 44]

The reading is nearlly same as TAT reading an it changes in matter of seconds - is this PMDG error or what?

Don't expect they spent a lot of time on simulating fuel temperature or that they claim a lot of precision in this area.But since they had many real life 747 pilots advising them - they probably did just enough with the info they had.