Takeoff roll longer at heavier weights?

[Robini]

Hello,
Every pilot always tries to use FLEX to save some engine years and money...
This about performance is very interesting but quite hard subject...
The REAL problem for me for the moment is following:
I have seen many TKF: s in my life and EVERY one uses a lot of runway when they
are heavy...
Here are some examples:
A332 360 pax and flight time of 3 h. The plane is far away from MTOW (The weight use to be around 180T)and FLEX
probably almost to the max...Doesn't matter, it still shouting of the runway like h**l and
is in the air after only 1300 m.

A332 370 pax and flight time of 5 h. The plane weighted about 190T and was
a bit under MTOW...Used much FLX again and was in the air after 1800m...

BUT here the real dicey one come...

A333 400 pax and flight time of 6 h...It's of course MAX PAYLOAD and fuel
use to be max at 45T.
MZFW is 173T
Fuel 45T
MTOW (wich should be possible): 218T
This flight rolls for about 2400-2500m EVERY TIME!!!!

The plane only weights 218T....Saw a movie about an Austrian flight from PEK to VIE. The flight time was 10 h 17 min and they were at MTOW.
Temp was 8C
QNH was 1009
Wind...almost nothing...
They took of from the 4000 m runway with FLX 41.They used about 2500 m of the
runway, wich is quite a lot for being ROLL distance.

You can clearly se above that the weight (example A332) made a difference in roll.
But if you look at the last 2 ones. The A333 examples. You se that they have the
same roll distance...And if calculated it right the difference between the planes is
12T and 0 Metres in dif!!! How is that even possble?
Can the A333 go with MTOW anyway even if the MZFW is 173 T?


Thanks!!

//Robini

[Chris Scott]

Hey Robini,

A long time ago I used to watch aeroplanes at airports like you do, but must admit I never tried to compare take-off rolls as carefully as you seem to be doing.

Of the Airbuses, I've only flown the A310 and A320, and I'm not getting reliable weight figures for A330 from a quick internet search. But I'm not entirely happy with all the figures you are quoting. There seem to be a number of different MTOWs (structural) and maximum ZFWs for the various models of A330, as I would have expected. I think your maximum fuel figure of 45T is much too low: if my memory hasn't failed me after 22 years, we carried more than that even on the A310.

You are puzzled by the two A333 distances being the same. If the weight difference is indeed only 12T, that is not a large difference. Different winds and/or temperatures and/or runway slopes could explain it. And the reduced thrust (higher FLEX temperature) on the lighter aeroplane will reduce the difference if all the other parameters are the same. But can you tell me how you are so sure that the aeroplane on the film at Beijing used the same distance as the ones you are watching for real, presumably at Arlanda or Landvetter?

Cannot answer your last question, "can the A333 go with MTOW anyway even if the MZFW is 173 T?", but no doubt someone else will do so later on. It's a good one, because many aeroplanes cannot fill the tanks at MZFW without exceeding MTOW (structural). But I think your figure of 218T for MTOW is on the low side.

Hope this gives you some food for thought until an A330 expert picks up the thread.

Chris

[spannersatKL]

Believe the A333 can have MTOW of around 230 tons, and fuel weight of around 78 tons.......look at the Type Certificate Data SHeets for the aircraft....on the EASA web site.

[lederhosen]

Improved climb could also account for significant differences in runway length used.

Put simply if the runway length is not the limiting factor but the terrain or obstacles around the airfield, then we accelerate to a much higher speed on the runway. We then use this additional speed to allow us to climb better once airborne.

There can be 30 knots or so of additional speed at rotation. This can be quite uncomfortable on some runways where the surface is not all it might be, Moscow springs to mind.

There is therefore no simple link between weight and takeoff distance. As others have pointed out there are many factors and many companies now use laptops to produce this performance data. This can take the pilots one step further out of the loop, which in turn can contribute to other problems such as the MK 747 crash at Halifax. But that is another debate!

[Robini]

How much fuel you can have with you totally depends on your ZFW.
I didn't say that the plane are CERITIFIED to max 45T, these numbers only
shows the fuel that USELY max are on these flights. :}

Yes Chris Scott surely i can tell how i can see it.:ok:
Yep, i use to see it at GOT. How can i know these distance so surely?
The simple answer is GOOGLE EARTH.

And this with MTOWS.
A332 3 H flight was flown with NVR MTOW: 233T
A332 5H flight was flown with NVR MTOW: 233T
A332 10H flight was flown with AUA MTOW:230T
A333 6H flight was flown with MYT MTOW: 230T

[411A]

One example, from long ago.

B707-320
JT4A-17 engines.
Max weight.
Max thrust...(these engines, when applicable, used a fixed derate, not flex).

Flaps 20....distance used, 11,600 feet
Flaps 30....distance used, 9,550 feet.

So, we see that the larger flap setting yields the shorter takeoff run required (obstacles permitting, of course).

Another example.
L1011-100
Weight 474,000 pounds.
Max thrust.

Flaps 10....distance for takeoff run, 12.650 feet
Flaps 18....distance for takeoff run, 10,600 feet
Flaps 22....distance for takeoff run, 9,960 feet

One more.

L1011-500, RB.211-524B402 engines
Max weight, 510,000 pounds
Airfield, JNB

Flaps 4....distance for takeoff run, 13,900 feet
Flaps 14...distance for takeoff run, 11,950 feet

Performance, 101

[Denti]

Groundroll is pretty much a useless figure nowadays. You can change it a lot by using intersection data, reduce to the max and improved climb speeds etc. For example with a lightweight B737-700 (around 55t) i can comfortably use up to close to 3000m on a 4000m runway if i use everything at my disposal (derate 2, assumed temperature, improved climb with a Vr close to 170kts). I can also get into the air and 35 ft within quite a bit less than 2000m with the same weight (around 1500 unreduced iirc).

[Robini]

YOU DID WHAT??!!!
I have flown with the B737-700 once...Very lightweight of course.
We were in the air within 800 m and a N1 at around 90%...
But if the light aircrafts use so much of the runway as you said, then i would see
it too,right? But i have never seen an big aircraft with light load using up so much runway...never...Well Well.

No one here has still not answer my question about if it's possible to go with MTOW
on a flight when you have 45T fuel and MZFW of 173T...
Someone knows if it's possible?

Thanks!!

[lederhosen]

Robini this is all getting a bit autistic. You asked an interesting question about the relationship between weight and takeoff roll. You (an apparent 15 year old spotter) have had some reasonable answers from people who know what they are talking about. The answer is, it depends on a number of factors.

If this particular example is really so important to you then provide the runway used, weather and aircraft registration and no doubt some kind soul will look it up for you.

I am pleased you have flown on the NG and seem to have enjoyed it. There are conditions when we takeoff using unreduced thrust but they are relatively few and far between (winshear et.). There are of course cowboy outfits that still operate in the dark ages. As an example we were horrified when we got one of our aircraft back from a lease to discover that it had been regularly going unreduced at great cost to engine life.

Believe me the guys who are using more of the runway are doing things right.

[Robini]

.................

[Pugilistic Animus]

Noone hates you Robini ---it just that we tend to be very emotional people---comes with the environment --I guess at time we are all 'hated'

[SKYWRITER1]

Understanding take off performance is the key. The idea of take off performance is not to use the least amount of runway and get airborne! Many factors are taken into account. Runway length - Yes, but also obstacles close in, terrain further out, then all these again with one engine! The idea is then to take the worst case scenario, with that days weather conditions. Finally, if your take-off weight is less than the calculation says is the maximum, you can then flex/ derate or use assumed temp etc. to simulate that weight.

The point you leave the runway is irrelevent, what really matters is that before V1 you can stop and after V1 (as you must go) you will clear all obstacles and terrain and have enough runway to get to the speed to achieve that.

Finally dont forget, an extra 50 people weigh about 5 tonnes. Not very much change for an A330 I would guess (I drive little 73's) You could take several extras tonnes of fuel if your first alternate is out!

Many variables to consider.....

[Robini]

I'm at the end of my project now ( wich should be finished latest 15 Nov...)...
So could anybody just answer this qucik last question:

Is it possible to go with MTOW (230T) if the flight include following:
MZFW: 173000 kg
Fuel: 45000kg

Logically wouldn't the TOW be 218T? Or can it be 230T? And if it can, HOW?

Thanks so much for the one that helps me.......:}

//Robini

[bfisk]

Given MTOM=230, AZFM=MZFM=173 and Fuel on board = 45, the following applies:

AZFM=<MZFM, ie. this is ok.
ATOM=173+45=118
ATOM<MTOM, ie this is ok.

So you could go.

(What you have to consider is the most limiting weight; stuctural take-off mass, performance limited takeoff mass (could be runway, climb or obstable limited), zero fuel mass and landing mass (again either structural or performance limited), and of the three, the most limiting will be your limit.

In plain text in your example, you could go, and you could add weight, however, all weight above MZFM must be fuel, so you could fuel up, but not add cargo etc. This is all based on there not being any performance limiting factors.

[Chris Scott]

Quote from Robini:
Is it possible to go with MTOW (230T) if the flight include following:
MZFW: 173000 kg
Fuel: 45000kg
Logically wouldn't the TOW be 218T? Or can it be 230T? And if it can, HOW?
[Unquote]

Robini, your English is 1000 times better than my Swedish, but I'm sorry to say I still do not fully understand your question. I agree with what bfisk has just posted, so I hope that gives you the information you wanted. Just in case it doesn't, however, I am going to risk insulting you by spelling out what is probably the obvious...

In the way you phrase the question, the only answer is that 173T + 45T = 218T (not 230T). The weight (bfisk correctly calls it the "mass") of an aircraft is, by definition, the actual ZFW plus the current FOB (fuel on board). If the aeroplane is loaded already up to a maximum ZFW of 173T, the ony legal way of increasing the actual TOW to 230T is to load more fuel on board, so that you have 57T FOB at the start of the take-off run. [And you have to prove that the RTOW for all the prevailing conditions is 230T or more.]

All the best for your project,

Chris

[Robini]

Thanks so much guys :ok:
I still find this subject VERY interesting, i just can't leave it :ugh:

//R

[Robini]

''If this particular example is really so important to you then provide the runway used, weather and aircraft registration and no doubt some kind soul will look it up for you.''

I really hope so :ok:

Well here are my ''approvements''...
I can take 2 examples:

http://i236.photobucket.com/albums/ff119/Airbus330/LandvetterRWY03.jpg

Here runway 03 was in use. The runway has a slope is +0,3% and is on a
elevation of 478ft (146m). The runway has 1 obstacle. Wich is 3580 m from
brake release point and has an height of 14 m.

When runway 03 is in use NO HEAVY use intersection takeoffs (just small ones).
And so the case with this flight to. He taxied the whole way to runway 03, lined up
set TKF power. I have lived with this airport in my whole life so i know almost
EXACTLY how many meters that went when passed XX taxiways.
When he passed the taxiway that is exactly 2000 m from runway 03 he didn't even
lift the nose from the ground. Some seconds later after 2200 m passed he started
to lift the nose and very soon he was up in the air...After almost EXACTLY 2500m
used runway.
As many of you know im a real perf nerd :ok: So of course i went to the check in
BEFORE the check in desks closed. I calculated 404 adults and 24 infants.
So it was 100% cabin factor (as almost every time)...I did this BEFORE the takeoff
, so you know.
I actually been writing down the most of the weathers when the A333 is about to depart. So i remember it quite well.
Following:
Temperature: 10C
QNH: 1023
Visibility: VERY good
Wind: 010/12 knt ( so almost headwind)

The registration on this flight was OY-VKG with MTOW of 230T.

Here you have example number 2.

http://i236.photobucket.com/albums/ff119/Airbus330/LandvetterRWY21.jpg

Here the takeoffs are from runway 21 ( TORA,TODA,ASDA of 3299m).
The runway has a slope of -0,3% but an elevation of 506ft (154m).
At this runway there are no obstacles so you can just gently float out after
departing :ok:
To see exact were the airplanes is leaving the ground is X-Tremly hard but i can say
for sure it's lifting the nose at a taxiway ( at this time also is 2000m but from rwy21)
and lifting off the nose at around the same time. So you can safely assume that is use
to be around that amount of runway too.
The registration of this flight was this time OY-VKH with an MTOW of 230T.
As usually i saved the weather.
Following:
Temperature: 4C
QNH: 1027
Visbility: Good
Wind: 250/15 knt

So it's almost headwind for runway 21.

So PLEASE someone, i have searched many years and i DON'T want to continue.
But i can't change subject before i really understand this with performance.
So could someone help me with this, i would appreciate it moore than anything else..

Thanks!!

//Robini

[Mshamba]

Well, so if you checked all these datas you still don't know 90% of all factors for the takeoff performance calculation.

Just some examples.
- which takeoff performance program for calculation did they use?
- how much cargo did they have?
- where is the c.g.?
- improved climb yes/no?
- does this acft in particular has the alternate forward c.g. option available?
- what was the ZFM?
- how much fuel?
- takeoff configuration? (bleed air etc.)
- technical defects? (e.g. antiskid inop)
- intersection takeoff calculation?
- did they calculate with the real weather data or did they calculate with some "margin"? (e.g. choosing less or no headwind component)
- and which captain was flying and how's his preferences for takeoff calculation? (same airport, same situation, different captain = different t/o calcs, like "no flex temp, no improved climb, no alternate forward c.g. option")

So its just always the same answer - you don't know, you cannot know, you will most probably never know. best would be: maybe you can manage one day to join a flight in the cockpit and join the takeoff calculations?

Anyway, enjoy spotting!

[lederhosen]

Robini, if I have understood you correctly, you are interested in why some A330s are using more runway than others.

Unfortunately the take off calculations do not tell us how much runway we will use before lifting off. Therefore I think it unlikely that anyone will easily be able to answer the question to your satisfaction.

Our performance calculation for Gothenburg gives V1/Vr speed for flaps 1 around 160 knots for both runways. So we are accelerating to a higher speed than the minimum we could use to get airborne, which would be around 130 knots using full thrust and flaps 5 on the 737NG.

Other posters have indicated that there are many factors which can make a difference. Going back to your original comparison of the A330 200 and 300 you have spotted an interesting difference.

Maybe you should target you question at Mytravel pilots on the Nordic forum. But again I am not confident you will get much further.

[mutt]

The information can be found in the Electronic AFM, however I suggest that you get your hands on "Airbus getting to grips with performance" so that you can educate yourself about the methodologies that they use.

Mutt