744F and 744 fuel burn differences for GE engines

[phil@LFPG]

hello guys,

there is a long time before i posted here but here s a good question (on my opinion and i share it...lol)... while i was trying to create a profile for FOC 2003 for 744F and comparing with a 744 already done i was wondering why the 744 and 744F are not burning the same fuel in same time from the books ?

i mean of course same engines for both CF6-80C2B1F same zfw and of course same level and weight

744F
enroute climb tow 390T 19' FL310 120NM and 7900 kgs burnt

744
enroute climb tow 390T 19' FL310 121NM and 8000 kgs burnt

now the cruise

744F
.85 FL 310 380T TAS 499 12716 kgs each hour
LRC .852 FL310 380T TAS 500 12776 kgs each hour

744
.85 FL 310 380T TAS 499 13271 kgs each hour
.86 FL 310 380T TAS 505 13164 kgs each hour
.87 FL 310 380T TAS 510 14010 kgs each hour
LRC .859 FL 310 380T TAS 504 13128 kgs each hour
CI100 .845 310 380T TAS 495 13129 kgs each hour

so we can see the -400 is more burning than the -400F but getting better speed.
in the same time at .85 there is 555 kgs difference.
is the differences due to the upper deck or else ?
why the same burn or close too between LRC and CI100 for the -400 ?

hope this is clear ??

any pilots or engineers to help

truly yours

phil

[Tinstaafl]

Different airframes with different aerodynamics. I believe the F is slightly more efficient due the original, non-extended hump. The original hump is slightly better at area ruling the forward fuselage/wing root region.

[DJohnsen]

Phil... it may very well be the fuselage "profile drag" as pointed out... but what is the PAC or engine bleed flow rate difference between a B744 and a B744F...? I'm just speculating here... but I would assume a "conventional" PAX configuration B744 would have somewhat higher engine bleed flow requirements than a freighter... Could this be the difference in the fuel burn you are seeing...?

Dag

[spannersatcx]

Could be, this is because the 744F has a completely different conditioning system to the PAX a/c. Far too complex to go into here though.

[DJohnsen]

Well... I don’t know the details of the B747 pneumatic system either… and how the PAX configuration differs from the freighter configuration…? I know the KC10’s dropped the “customer bleed” system on the number two engine… due to less ECS demand. "Sick"… when you mentioned 3% fuel burn increase for cargo cooling down to 4 deg C… 3% over what…? Is this a given “Book” value from Boeing…? Is this built into your flight-planning program…? We keep a close eye on the Drag/FF values… especially on the B777’s… to ensure the Drag/FF index in the FMS matches the flight-plan… and these values are updated on a monthly basis to optimize payload… It becomes a challenge when you intermix the conventional GE90’s and the 3D compressor engines… due to substantial difference in fuel burn.

Phil… still no takers here…?

Dag

[Phil Squares]

Tinstaafl hit the nail on the head with his answer. All things being equal, the difference in the fuel burn is the parasite drag from the extended upper deck. When compared to the original upper deck the extended deck has a little bit more drag.

One of Boeing's designs for the -400 was a completely extended upper deck. That resulted in slightly less drag than the original upper deck. However, one of the requirements for the -400 was to have it fit in the same footprint as the classic. If the upper deck was extended completely, a new wing would have to be designed. As it was, the winglets were added to handle the increase weight without increasing the footprint.

[phil@LFPG]

hello guys,

thanks for your answers and explanations.
i have to say that datas are from boeing books (jar)...!!! so this is not the planning program...

no i dont know about aerodynamics but i think this is more the bleed system as i m talking in norm cruise not specific transport...

now i can say that is from a classic side (i just dig from others manuals) that boeing made a good design for -300 but the weight is worst (more metal is more to carry...)


742 GE 320/.82
climb 370T fl 310 27' 10150 kgs 167 nm
cruise 360T .84 14272 kgs/hr 492 tas tat -15

743 GE 330/.83
climb 370T FL 310 25' 9800 kgs 154 nm
cruise 360T .84 13508 kgs/hr 492 tas tat -15

so with same result but inverse we can extrapolate that this is ccertainly some engine extraction that can cause this difference as the speed is better for LRC on the -400 versus -400F ???!!!

thanks for your attention and more help

truly yours

phil

[CR2]

Hi Phil.
As far as I'm aware, the -300 has a different (more efficient) wing than the -200. I think the last -200s to be built had the -300 wing.
I'll ask our Tech Pilot if he has any ideas for you.
rgds CR2

[Phil Squares]

The -300 had some improvements made to the wing/body fairing area. Not quite as extensive as the -400, but they were enough to lower the fuel burn a little when compared to the -400. I am not sure the wing is changed from the -200 as such, but improvements were also made in the structure and there might be a little less drag from improvements there.