Airbus A346 Climb Performance

[T.Z]

I am an engineering student in the middle of writing my Diploma thesis. As a part of it I need to model a flight of the A340-600 from a performace persperctive and distinguishing between the different segments (T/O, CLB, CRZ, DES, HLD, LDG).

What I am having problems with is modelling the climb phase. Specifically I don't know how the thrust is regulated.

For all my calculations I am assuming ISA conditions (15*C & 1013hPa@MSL) and T/O at MTOW (365t)
I have assumed climb with constant IAS (250KIAS bellow 10000ft, then 320KIAS and M0.82 until TOC)

To be able to calculate the thrust I need to know another given variable for the climb phase, so my first questions is:

>> 1. Besides a given speed, what else do you have given? Is there a constant climb rate in feet/min or a constant pitch that you climb with?

If someone has access to some performance chart

>> 2. How long would the following climbs take or what climb rate could you expect assuming the conditions above

a) 1500' -10000' at 250KIAS
b) 10000' - 26500' at 320KIAS
c) 26500' - 29000' at M0.82 (or to a TOC you think would be suitable)

>> 3. What would suitable initial cruise altitude be?

>> 4. Roughly how much fuel do you use for T/O and climb, (I know it depends on a lot of things, but is it closer to 5, 10, 15, 20t?)


I'm greatfull for all any and help, even if it might not be directly revelent to the questions it might help on my way getting there.

If you need any more info on anything I will gladly provide you with it.

[divinehover]

The thrust in the climb will always be at Climb Thrust. Normally 250kts is maintained until FL100 and then normal climb speed until initial Cruise Alt. 320 kts is fine for an estimate but it may vary according to the cost index. The pitch angle and rate of climb will all depend on the weight and atmospheric conditions. What I mean is for the given weight and atmospheric conditions at 320kts the rate of climb will be X. The constants will be speed and thrust settings and the variables will be pitch and rate of climb. A normal initial cruise alt will be between FL300 and FL320 depending on ISA deviation.

There is the option of using a derated thrust climb to save some money but the same principles apply just with less thrust set. It saves the engines but uses a bit more fuel and takes longer to climb.

[T.Z]

Thanks for the answer!!

While the thrust lever is at the climb detent, are you sure that thrust output is constant. Do you by any chance remember how the gauges (N1, EGT, EPR - not sure which one you would use) change during the climb. Are they constant, increasing, decreasing?

The availabe power from the engines will decrease with increase in altitude (decrease in density), I am not sure if the A/C will try to compensate for this.



Happy new year!!!

[Coldbear]

Hi,

I cannot answer for the A346, but I do have some data from the A320

with the thrustlevers in the Climb Gate the N1 will, for a constant TAT, increase. The N1 will however decrease, at a constant altitude, for a decrease in TAT.

Hope this helps in anyway.

Regards,

Martin

[Remus T]

I have access for the entire A340-642 FCOM and performance handbooks...but obviously the whole lot has a size of around 2GB...:zzz:

[mustafagander]

When in climb mode, most big jets use CLB thrust and pitch for speed, that is to say the attitude changes to hold the speed selected.

In cruise it's fixed attitude (for the short term anyway) and thrust for speed.

Descent is pitch for speed generally with thrust idle.

[9.G]

T.Z here is some data for A 346 for 360 tons till FL 290 with your schedule:
time 21 min, 6900 kg fuel burn, 128 nm, TAS 365 kts. the rest is as described in previous posts. :ok:

[T.Z]

Thanks a lot guys for the answers!!

@9.G: any chance you could break down the numbers to the three segments. Also, I didn't really understand how, when, where the TAS is 365kts.

The values I get now are bellow, but here I have made some pretty rough estimations for how much thrust the engines are putting out.

CLB FL15->FL100
Time: 3.3m Dist: 15.0nm Fuel: 1599.2kg Weight: 358.4t

power setting: 55%

ACC 250KIAS->320KIAS
Time:1m Dist:5.2nm Fuel:383.8kg Weight:358.0t

power setting: 50%

CLB FL100->FL290
Time: 9.7m Dist: 71.5nm Fuel: 2999.8kg Weight: 355.0t

power setting: 40-50%

================================
time: 14min Dist: 91.7nm Fuel: 4982.8kg



My goal is to figure out how much thrust the engines are putting out in each stage of the climb.


thanks again and a happy new year to all :)

[9.G]

T.Z happy new year to you mate and best of luck with your work. Ok, data obviously depends on engine type as well. I'm giving you RR Trent 500 data. Regarding the power settings you should be more specific N1, N2, N3 or EPR?
In any case 55% power settings appears to be way too low. Usually we're talking bout N1 in the range of 81% with EPR of 1.35. Anyways here's the breakdown of data:
CLIMB 250/320/.82 from brake release point with TOW 360T, ISA, CG 30%, Anti Ice OFF, AC normal.

BR till 1500 ft: 2 min, 6 NM, FB 1099 kg, TAS 146 kts.
BR till FL 100 : 6 min, 23 NM, FB 2595 kg, TAS 223 Kts
BR till FL 290: 21 min,128 NM, FB 6890 kg, TAS 465 Kts.
Obviously you need to subtract those figures from each other to find out data for each segment as it's always from brake release point. You need the TAS to determine distance bearing in mind in wind calm. How else do you wanna find out distance you covered during climb? Maximum thrust: 56000 lbf (249 kN) on RR trent 500 :ok:

[divinehover]

The A346 only came with RR Trent 500 engines

[T.Z]

Would I be correct in assuming that % N1 and % of maximum thrust are closely related?

If yes would this be MCT or max. certified T/O thrust? (is MCT about 100% N1?)