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A333 Vs A343 Takeoff Distance  
User currently offlinethenoflyzone From Canada, joined Jan 2001, 2358 posts, RR: 12
Posted (1 year 4 months 3 weeks 1 day 5 hours ago) and read 2615 times:

Takeoff distance for an A333, MTOW (235t), at sea level, in ISA conditions, with RR engines, is roughly 11,000 feet.

http://www.airbus.com/fileadmin/medi...h_data/AC/Airbus-AC_A330_Dec11.pdf

Takeoff distance for an A343, MTOW (276.5 t), at sea level, in ISA conditons, with highest rated engines (CFM56-5C4) is roughly 10,200 feet.

http://www.airbus.com/fileadmin/medi...C/Airbus-AC_A340-200_300_Dec11.pdf

Now here is what is puzzling. How come the A343, with 40 more tonnes of payload, has better takeoff performance than the A333, considering the fuselage and wing area are identical, and so is the engine thrust total for both aircraft (If anything, the A333 (142,000 lbf) has a few thousand more lbf of thrust compared to the A343 (136,000 lbf total).

The only answer i can see based on the sources i provided is the flap setting on takeoff. For the A343, we can see on the charts that Flaps 3 must be selected for sea level takeoffs. There is no flap indication whatsoever on the charts for the A333. Does that imply that a no flaps takeoff is the norm for the A333?

If not, what is a typical flap setting for the A333? I read on another post that flaps 1, 1+F, or 2 are standard. Does the A333 ever need flap 3 for takeoff?

Thanks in advance.

Thenoflyzone

[Edited 2013-02-19 07:08:03]


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5 replies: All unread, jump to last
 
User currently offlineMir From United States of America, joined Jan 2004, 21423 posts, RR: 56
Reply 1, posted (1 year 4 months 3 weeks 1 day 5 hours ago) and read 2586 times:

Quoting thenoflyzone (Thread starter):
ow here is what is puzzling. How come the A343, with 40 more tonnes of payload, has better takeoff performance than the A333, considering the fuselage and wing area are identical, and so is the engine thrust total for both aircraft (If anything, the A333 (142,000 lbf) has a few thousand more lbf of thrust compared to the A343 (136,000 lbf total).

I'd figure it has something to do with the extra thrust that the 343 has over the 330 after an engine failure at V1. That'll get you to rotation speed faster, which gets you off the ground in a shorter distance.

-Mir



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User currently onlinevikkyvik From United States of America, joined Jul 2003, 9700 posts, RR: 27
Reply 2, posted (1 year 4 months 3 weeks 1 day 4 hours ago) and read 2564 times:
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I agree with Mir. You have to have enough runway + clear zone to clear all obstacles after an engine failure.

Quoting thenoflyzone (Thread starter):
Does that imply that a no flaps takeoff is the norm for the A333?

Doubt it.



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User currently offlinethenoflyzone From Canada, joined Jan 2001, 2358 posts, RR: 12
Reply 3, posted (1 year 4 months 3 weeks 1 day 4 hours ago) and read 2538 times:

Makes perfect sense. Thanks Mir.


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User currently offlinePapaChuck From United States of America, joined Aug 2010, 136 posts, RR: 0
Reply 4, posted (1 year 4 months 3 weeks 1 day 4 hours ago) and read 2532 times:

Keep in mind that the Airbus performance tables show generic performance based on standard aircraft capabilities in standard conditions. A real world scenario would consider winds, obstacles, and a host of other factors.

That being said, this is a classic discussion about twin versus quad takeoff performance with an engine failure. Takeoff performance is not simply based on the distance between the point of brake release and the point the wheels leave the ground. If that were the case, the A330 would always have the shorter takeoff distance at MTOW due to the superior thrust to weight ratio. More thrust, less mass, better acceleration, less runway used.

Now consider the decision speed during the takeoff roll. In a twin, that speed will tend to be higher compared to a quad. If a twin loses an engine after decision speed, it still has to continue to accelerate to takeoff speed and climb out safely on the remaining engine. Continuing to accelerate on half of your original thrust is dicey at best, so the decision speed tends to be fairly close to rotation speed. Lose and engine, let's hurry up and get airborne. Accelerating to a higher decision speed requires more runway. A quad can accelerate and climb better on three out of four engines, so the decision speed can be a little slower.

Now consider aborting takeoff just before you reach V1. In a quad, you're not going quite as fast and have used less runway to get to that speed, so you will need less runway to stop. A twin, traveling at a higher velocity just before V1, needs more room to stop.

PC



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User currently offlinePihero From France, joined Jan 2005, 4383 posts, RR: 76
Reply 5, posted (1 year 4 months 3 weeks 1 day 3 hours ago) and read 2510 times:
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Quoting thenoflyzone (Thread starter):
The only answer i can see based on the sources i provided is the flap setting on takeoff. For the A343, we can see on the charts that Flaps 3 must be selected for sea level takeoffs

As a matter of fact, these graphs follow the same presentation : They both include a "continuous" performance line with CONF 1, 2 and 3 (... and yes, the 330 can use CONF 3 as a takeoff setting. Never seen it, though )
Be also very careful that inside these graphs, one might well find the 1.15 TOD (N) for dry runway as it could be longer than the TOD (N-1) limitation.
Twins are more sensitive to climb performance than quads and CONF 3 is rather draggy, not good for climbing. That's the reason we use CONF 1 and 2 for most cases.
In general speaking, Mir is quite right... for identical Takeoff weights.



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