Hardy,
I am not seeing the fuel temperature fall toward the TAT as quickly as this representative graph from Boeing suggests, neither have I seen it fall at the rate at which the post I have linked would also suggest.
(https://i.imgur.com/AeN0S6Ll.png?1)
http://aerowinx.com/forum/topic.php?id=2327
On my current flight (ICN-ANC) the fuel was pumped in at +18'C, enroute the TAT started off at approx -18'C at FL330 & has fallen as I have climbed to -23'C (SAT -55'C) at FL370. Some 6hrs 50mins into the flight the Fuel Temperature is sitting steadilly at +2'C.
I have never seen a temperature reduction or 'fall' rate as depicted in the Boeing illustration, which seems to indicate a fairly rapid initial reduction in temperature, before a slower reduction toward a 'stabilisation' approx 3'C above the TAT.
Without becoming an absolute PITA could it be time to perhaps revisit/refine the Fuel Temperature reduction/lapse rate?
I can send you the whole Boeing document via e-mail if you wish.
Best
Please not again ...
These are approximations. What are you expecting?
The most critical point is the fueling. How do you know the airport fuel temp was 18° and not 30°?
I just retested it: My fuel temp drops by 50° after 3000 nm. E.g. when starting with 30°, I get -20° after 3000 nm. Your example starts at 5 and ends at -45. It's the same.
Here's the above quoted thread in the new forum software (in use since 2015). Please ignore the old forum software; it doesn't show texts that contain any non-ASCII characters (e.g. the degree character).
http://aerowinx.com/board/index.php?topic=2327.0
An aside:
These fuel temp threads remind me of supersonic aircraft and their very different issues re fuel temperature. I hope this isn't too far off-topic.
Below is a map of the Concorde's skin temperature:
(https://upload.wikimedia.org/wikipedia/commons/thumb/2/2d/Concorde_-_airframe_temperatures.svg/634px-Concorde_-_airframe_temperatures.svg.png)
---------------------
Perhaps the solution to the 747's low fuel temp concerns would be to redesign it for supersonic speeds!
CC
We use the Boeing Fuel Temp Prediction Program in our Flight Planning System at work. The FTPP models how fuel lies within and flows from the tanks to the engines and is detailed to aircraft type. Some factors for fuel temp is how much of the internal tank structure is exposed to the very low TATs at altitude, and of course those TATs at altitude. Also, you never use an FTPP prediction for an aircraft type it wasn't designed for.
The chart shows that after 4-5 hours in flight, resulting fuel temp isnt really affected by the fuel temp as it was loaded - it has reached an equilibrium temp, and is now more affected by the air temps outside the aircraft.
The FTPP will throw an alert if the temp is predicted to get within 3 degs C of the fuel freeze point temp, which requires the dispatcher to adjust the flight thru the area of the cold fuel (either adjust the altitude, increase speed, or in some cases both). Also, with the trop at a low altitude, it may be better to increase the altitude to get to warmer air aloft. We also require the flight plan to be remarked so the crew is aware of what was done. Our dispatchers will do something when the FTPP alerts as min fuel temp is an Airplane Flight Manual Chapter 1 limitation.
Quote from: DougSnow on Sun, 22 Jul 2018 16:25
The chart shows that after 4-5 hours in flight, resulting fuel temp isnt really affected by the fuel temp as it was loaded ...
Yes,
after 4 to 5 hours. But in the
initial phase the reduction rate is higher if the difference is higher; this is modelled in PSX and is shown on that Boeing chart. I'm just saying that these empirical values in the initial phase are
approximations. 5 hours are 25% more than 4 hours.
Developing and testing a simulation of this stuff is very time consuming as it has to be flown in real time; the time acceleration function in PSX may influence the result because of the normal rounding and time frame granularity combined with those tiny temperature changes along extreme distances.
Perhaps I was misunderstanding what Steve wrote. Did the fuel temp
stay at 2° for the remainder of the flight while the TAT was -23°? That would be a difference of 25°. If so, we're talking about the time
after the initial phase. The difference should then slowly decrease to less than 5°. If not, something's wrong.
|-|ardy
Ahhhhhhhhhhh!!!!!!!!!!! It's not just me!!!
@Hardy: correct - the temperature delta between TAT and fuel temp REMAINS 20 degrees or more above TAT.
I have NEVER had a flight where fuel temp remotely became an issue, even when I set the OAT to ISA-20.
For me, it typically reaches about +3 deg. C and doesn't drop any lower. TAT is -25 deg. C or lower. The fuel temp never gets close to TAT at all.
If you search the forum, you will find posts by me on this issue previously.
Your last post I found on this subject is from 2014:
http://aerowinx.com/board/index.php?topic=2327.msg23144#msg23144
We're now in 2018 and there have been a zillion updates.
When you're writing "Ahhhhh!!!!" -- is this a mental flashback to version 10.0.0 from 2014, referring to an effect that has been updated in PSX but not updated in your memory? Such mental effects happen sometimes to everyone of us. Or are you referring to the latest PSX version? If so, I need exact data so that I can try to reproduce the effect. Please understand that I can't work with vague phrases like "I never had ..." etc.
In my PSX code I see this:
The target fuel temp is always TAT + 1 + X.
X is a thrust dependent parameter and varies between circa 3 and 4.
So the target fuel temp is always TAT plus 4 or 5.
And here's the closure rate:
When delta is 60° or higher, the rate is maximum.
At delta 40° or higher, it's 50% of maximum rate.
At delta 20° or higher, it's 33% of maximum rate.
At delta 10° or higher, it's 25% of maximum rate.
Below delta 10° it's 20% of maximum rate.
The result should be a curve similar to that on the above Boeing diagram (which doesn't show any TAT, by the way).
|-|ardy
I did some further tests and noticed my curves are similar to the green curve on that Boeing diagram -- if the initial fuel temp is already low. If it's higher initially, my curve should be steeper at the start -- indeed. In that part the original PSX version 10.0.0 wasn't that bad. The compromises thereafter were not perfect. I'll try to tune this stuff a bit further ...
Regards,
|-|ardy
Initial part of the curve is now steeper in PSX 10.41:
http://aerowinx.com/board/index.php?topic=4191.0
Regards,
|-|ardy
Hardy,
Thanks for taking another look at this .... the faster temperature reduction rate with a warmer initial fuel temperature looks much better now.
Best
Steve
I'll check later! I wasn't aware it had been updated (I do read most of the release notes, though not all).
I fly PSX quite often, so my observations are through various versions, not just the initial release. :)
Hardy,
Just resurrecting this old thread from the distant past after watching an interesting new piece of footage of the Upper/Lower EICAS from a CargoLogicAir flight from EGSS to KATL:
https://youtu.be/oOYVYJAhPaU
At the beginning of the footage the aircraft is just reaching Circa F340 with approx 93.1t of fuel remaining.
The SAT is -25'C, OAT -57'C & the fuel temp -16'C.
At the end of the footage the aircraft is still at F340, there is 80.3t of fuel remaining according to the Upper EICAS.
This would indicate that the aircraft has been airborne for circa 65-75 minutes since the previous set of Upper EICAS readings seen in the footage, having consumed approximately 13t of fuel.
The temperature readings at this stage are as follows:
The SAT is approx -23'C, OAT approx-54'C & the fuel temp has now reduced to -23'C.
I'm never seeing a fuel temperature drop of that magnitude in that timeframe & the fuel temperature always seems to "hover" at a temperature circa 5-10'C above the SAT whatever the flight time duration. The simulation of "cold soak" also seems to let the fuel temperature rise quickly again in the descent into warmer air.
Without trying to sound irritating would you consider a revisit of the fuel temperature cooling curve to perhaps increase the rate of fuel cooling & decrease the rate of fuel warming for a future update?
I'm also using wind corridors & a live real world source (not PFPX or a third party flight planning software program) to populate the wind corridor data box, correct in real time for the flight I am doing when making my comparisons inside PSX.
Quote from: G-CIVA on Thu, 18 Feb 2021 10:10
Without trying to sound irritating would you consider a revisit of the fuel temperature cooling curve to perhaps increase the rate of fuel cooling & decrease the rate of fuel warming for a future update?
I'm sorry, this video is just one random example of zillions of random examples. I certainly won't use this single random example as a main reference; we don't even know the external influences there. The stuff is highly interactive and complex. My current model refers to various real-world observations and Boeing documentations, and provides reasonable average values in all kinds of flight scenarios. I won't change it.
Regards,
|-|ardy