B744 fuel flew figures

[Michelmvd]

I know, this is depending heavily on weights, but in order to calibrate my sim as real as it can, I should like to have FF figures for T/O mode, CLB modes CRZ / DES and APP
Based 224t ZFW. 100t FUEL. - engines CF6-80C2B1F
Many thanks for help
Ciao
Michel

[enicalyth]

G'day Michel!!

You wrote

I know, this is depending heavily on weights, but in order to calibrate my sim as real as it can, I should like to have FF figures for T/O mode, CLB modes CRZ / DES and APP
Based 224t ZFW. 100t FUEL. - engines CF6-80C2B1F

Okay Michel I’ll have a go. People are not answering because you are asking quite a difficult general question and no-one is going to give away company confidential information. It is a small industry and despite anonymity it does not take long for everyone to figure out who everyone else is by the nature of little give aways. So I’ll guide rather than answer you and keep it simple to suit the sim. Everyone else don’t flame me for saying you forgot about this or simplified that.

Firstly take-off. Ball park figure 4 x 56000lb thrust at 0.35 lb fuel per lb of thrust per hour = 78400lbs/hr = 36 tonnes/hr. I’m not going to refine it any further than that.

Climb mode. Assume 182 tonnes for aircraft crewed, provisioned, no fuel, nobody else aboard, no bags. Assume 400 pax at 175lbs each plus 45lbs allowance and add extra 5% on top. Yup 42 tonnes so we agree ZFW at 224 tonnes for this trip. Busy flight. 100 tonnes fuel. 324 tonnes brake release. Climb will take 2-2.5% of your weight, say 6.5 tonnes to get to FL330. In an ideal unimpeded world 15-25mins and 100-150nm over the ground. Call it 25 tonnes an hour average in climb if you cover 100 miles in 15 minutes.

100 tonnes fuel. So 324 tonnes at brake release ball park That’s not a lot of fuel you know. You’re going to burn off 90 tonnes ISA still air over 4500nm leaving you 9 tonnes for diversion, legal and company reasons and I tonne for “unaccounted”. But you know where you are going.

Cruise. Ball park figures at your weights suggest that at first cruise you burn 3.4% of your weight every hour and at end of cruise 3.8%. If that looks strange remember that a little percentage of a big figure is greater than a big percentage of a little figure. Remember that at pay increase time!

I’ll now ask you to discover how to work out Lift/Drag. Basically in such a short treatment and at your weights I’m going to simplify everything and have you cruise at FL350 and 255metres per second throughout. Let’s guess the density of air to be 0.38kg per cubic metre. Your weight at top of climb is 317500kg which is 3114675 newtons for “g” = 9.81 metres/sec/sec. Guessing your weight at top of descent at 237500kg is 2329875 newtons. So lift coefficient at ToC is twice weight/(density x speed squared x wing area). Wing area is 541 square metres so the answer for ToC is 0.466. Now for ToD the answer is 0.349. At the risk of being criticised I am now going to say that for the 744 the total drag coefficient is therefore1.06 x (0.015 + (lift coefficient ^2)/20.72). Do the maths and ToC L/D = 0.466/.0272 = 17.13 and ToD L/D = 0.334/0.0218 = 15.65. ToC Drag is therefore 317500/17.13 = 18535kg and ToD drag is 227500/15.65 =15175kg

Assume you consume fuel at 0.57 kg per kg of thrust (drag) per hour. So at ToC you are burning 0.57 x 18535 = 10.6 tonnes per hour and at ToD 0.57 x 15175 = 8.7 tonnes per hour. That latter figure seems low to me but now you know how to do it you can check for mistakes.

Finally descent. I’ll just allow 1.1 tonnes. That’ll do it.


Now that was a rush and some simplification so I’ll invite John Tullamarine and Old Smokey to pull me to shreds and try and justify any assumptions if asked. Mistakes I make plenty so do check the maths and knock yourself up a spreadsheet. If you’re within 3-7% of reality then that is as real as you are going to get in a sim I’d guess and I haven’t broken any company rules I hope.

I forgot approach!! Guess approach L/D to be about 8 because drag with flaps and gear down at least doubles and assume fuel consumption goes up from 0.57 to 0.65 kg per hour per kg of thrust (drag).

Good Luck.

[Tonic Please]

I'd like to pass my thanks for that very time consuming but informative reply :ok:

[Michelmvd]

Hello enicalyth
A very big thank you for your interesting reply on my request.
It will be very useful for my sim.
Ciao
Michel

________________________________________________
My B744 sim project
msn : [email protected]
website B744: users.pandora.be/michel.vandaele/sim1.htm

[Thunderball 2]

Isn't human nature a wonderful thing?

I presume enicalyth was happy to spend time on his post, and hopefully got a buzz out of doing it. He certainly should have - that's a superb framework for analysis of the B744 - or any other aircraft.

Good man:ok: