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Guest balt

B744F Fuel temperature problem

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Guest balt

Hi all,I'm currently flying over northern canada in the PMDG 744-F, with an SAT of -88

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>I would expect at this point to >>1) Fall out of the sky with jellied up Jet A-1 in my fuel>injectors>2) Get a Fuel Temp Lo EICAS message.>>Neither happens. Why?Balt,No offense but I think you are expecting a little to much of a $50 simulator. I don't think dynamic fuel viscosity or temperature is simulated if at all possible.Hope it helps,


Mats Johansson
PMDG Flight Test Dept
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You could be right Mats, but maybe the simulator knows that the fuel is not common JetA but probably the civilian equivalent of what the Air Force puts in the tanks for polar flights.. I think they call it JP5 (vs JP4, which is similar to JetA). I do know from being retired military now working around refineries that there are many different blends, in fact there was a special one for the SR-71 called JP8 (I think) that wouldn't explode at the high temperatures that it was exposed to in the wet wing at Mach 3+. The stuff was also pretty thick at "normal" temps when the wings would weep, a condition that went away at "cruise" speeds when the high temps expanded the wing components thus closing the weep holes.


Dan Downs KCRP

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Guest balt

The "Fuel Temp Low" message is in the manual. Given the other functionalities that have been modeled with great accuracy, proper fuel temp behaviour is peanuts... so no, I don't think that's asking too much of a $50 sim... however, we do get a LOT for $50 already!

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Wow that is one #### of a low SAT. I have struck -75 in that region.The EICAS low temp message is predicated around JET A fuel and not JET A1 which freezes about 3 degrees lower.If you are assuming that JET A is loaded then when the warning light comes on you need to think about doing something. Descending is the most effective. You can increase the MACH speed but it has to be by a large margin to make a big difference. Both is even better. In the RW I have found wing anti ice to be quite effective.As long as the warning is correctly modelled then that should be enough. No real world pilot would let the fuel temp get any lower so why model the consequences of not doing so?


Cheers

Steve Hall

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Guest balt

Hmm, I don't think you read my post... The trouble is I do NOT get a warning. The fuel has a temp of -60

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>same reason the consequences of a stall are modelled.Sorry, you can't equate a stall with fuel freezing. They belong to completely different class of predictability and have completely different cause-effect relationship. For the same reason no one is expecting to see proper modelling of ice formation on the wings, engine, nor effects of wet runways, etc. There are way too many factors to model such events properly.Michael J.


Michael J.

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Well If the fuel temp was that low I don't expect them to fully model the consequences (although it would be nice) but I would have thought atleast the warning light (which is there and mentioned) would come on, oh well doesn't matter. :)Jay


Jay Vorkapic

 

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Guest balt

ah no? given the consequences of either it should be modelled. Same as icing as well as ice patches/slush on the runway. We have been simulating that stuff in full flight sims for decades, running on hardware that could barely count to two (and still filled rooms). Funny how the computers that controlled the UPS's were more advanced than the mainframe the simulation was running on.To explain briefly: in order to simulate ice/slush on the runway, you simply substitute the friction coefficients for dry with those of ice/slush/water. Aquaplaning included. It's really not that complex. Same goes for airframe icing. Changes Cl and drag, that provides an excellent simulation input. Let it rock and roll at 30 hertz and you're good to go...

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