Boeing767-300 From Australia, joined Sep 2001, 659 posts, RR: 0 Posted (12 years 3 weeks 4 days 23 hours ago) and read 3389 times:
After browsing through the Aircraft data section on this site it would appear that the A380 is somewhat underpowered. By dividing the MTOW by the total amount of thrust(lbs)
A380 800 MTOW 590 000kg with 4 x 72000lb Trent 900s equals 2.12 Kgs per lb thrust
Proposed 777 300X MTOW 341000kg with 2 x GE 115 000lb equals 1.47 kgs per lb of thrust
747 400 MTOW 396 895kg with 4 x GE CF680C2b1Fs at 61500 Lbs each equals 1.61
737 300 MTOW 56740kg with CFM56-3B2s at 22000lb equals 1.27 kgs per lb of thrust.
2.12 kgs per lb of thrust compared to a 744 of 1.61 is quite significant. about 25 to 30 percent less power to weight. I think it will be a little underpowered but then I'm sure more powerful engines will end up being fitted.
I guess the A380 will be about as exciting to watch taking off as an A340 300 which at MTOW 275000 and 4 x CFM5653C at 32550 lbs equals 2.11 kgs per lb of thrust almost the same as the A380.
Seagull From United States of America, joined Jun 2001, 340 posts, RR: 1 Reply 1, posted (12 years 3 weeks 4 days 22 hours ago) and read 3130 times:
I think you need to convert your 747 thrust numbers to Kg or the weight to pounds and try your math again, you'll be in for a surprise!
The twins can't be compared as the thrust requirement is based on the minimum climb after an engine failure, so losing half your thrust is the scenario as opposed to losing 25% of it. Twins have to be overpowered for that reason.
SQ325 From Germany, joined Jul 2001, 1441 posts, RR: 8 Reply 4, posted (12 years 3 weeks 4 days 21 hours ago) and read 3062 times:
@ Marc Kobaissi
Ever saw an A340-300 fully loaded taking off.
God bless there is the curvature of the earth.
That 's not a joke, I know a A340 Captain he told me that this Airbus climbs more slowly as a overloaded C152.
Seagull From United States of America, joined Jun 2001, 340 posts, RR: 1 Reply 6, posted (12 years 3 weeks 4 days 19 hours ago) and read 3038 times:
OK, I see you mixed pounds and kg in all cases, which is a bit odd. However, what you're also missing is the wing design and high lift devices which may change some of your assumptions on climb rate quite a bit!
Cedarjet From United Kingdom, joined May 1999, 7808 posts, RR: 54 Reply 7, posted (12 years 3 weeks 4 days 19 hours ago) and read 3033 times:
Seagull is right, an airliner flies on the wing, not on the engine thrust. This isn't the F104 Starfighter (aka Widowmaker) we're talking about. Compare square foot of wing surface to weight, 744 vs A380. Most important is the actual shape of the wing.
There are things about Boeing I prefer to Airbus, but few would dispute the fact that Airbus wings (designed by the British) are the best in the world.
By Underpowered what you really mean is Efficient.
fly Saha Air 707s daily from Tehran's downtown Mehrabad to Mashhad, Kish Island and Ahwaz
WhiskeyNovembr From , joined Dec 1969, posts, RR: Reply 9, posted (12 years 3 weeks 4 days 16 hours ago) and read 3001 times:
No, Cedarjet, what we mean by underpowered is, indeed, underpowered. As a passenger and as a pilot, I feel a heck of a lot more comfortable in an airplane that has enough excess thrust/climb ability to get out of sticky situations such as microbursts and wind shear. When you hit severe shear, firewall the throttles, and hang on for dear life while the stickshakers are going off, "efficiency" isn't going to save hundreds of lives. That's how I feel whether I'm in an A-340 or a C-152.
B1C17L1011 From United States of America, joined Jun 2001, 96 posts, RR: 0 Reply 10, posted (12 years 3 weeks 4 days 16 hours ago) and read 2992 times:
The wings of the A330/A340 have many trailing devices on the rear of the flaps (I don't know what they are called) campared to about half as many on a 777. So I would say that the 777 wing is a cleaner and more efficient design.
SailorOrion From Germany, joined Feb 2001, 2058 posts, RR: 6 Reply 11, posted (12 years 3 weeks 4 days 16 hours ago) and read 2992 times:
First of all, one cannot say that Wing X is more efficient than Wing Y when comparing wings of different airplanes. By the way, traditionally Boeing is doing lighter wings and Airbus is doing wings with less drag. It doesn't matter. Both are VERY efficient, otherwise we wouldnt fly for less then 1000 bucks around the globe. PERIOD.
Now, for the computations. I'll get the data off the web pages, and calculate thrust-to-weight ratio (TWR).
I will only compare 4-engined airplanes, because of the reason mentioned by Seagull.
STSL Thrust / MTOW:
605 kN / 2696 kN = 0,22
997 kN / 3579 kN = 0,28
1247 kN / 5494 kN = 0,23
1126 kN / 3894 kN = 0,29
Now Seagull here's one thing that you forgot. Apart from the very beginning of the flight (until you reach about 50ft) lift does NOT make an airplane climb. Thrust does. Which means, an aircraft with a higher TWR is ABLE to climb faster. Now please to consider these points:
1) Climb ratio does not have anything to do with safety.
2) Very few takeoffs do take place with maximum takeoff power.
3) Very few takeoffs are in fact performed at MTOW
Yes, an A380-800 will climb about as fast as a A340-300. But what does underpowered mean?
AA737-823 From United States of America, joined Mar 2000, 5542 posts, RR: 11 Reply 13, posted (12 years 3 weeks 4 days 12 hours ago) and read 2947 times:
Okay folks, think about it a minute.
No matter how high-tech a wing is, that doesn't make the plane move faster. What gets a plane rolling down the runway is THRUST. I had no idea that the 380 would be as bad as the 340.
Additionally, it doesn't matter if the conversions are made or not, so long as the math is right you can compare numbers even if it's apples to MGTOW or peaches to LBS thrust.
So, I guess that y'alls point would be that the 380 has a much higher lift wing and therefore leaves the ground at, say, 120 knots??? Didn't think so.
Thrust also gets you out of the way in event of a go around procedure, not lift. During these situations, like takeoff, you need thrust to go up quickly, not lift alone. You're trying to ACCELERATE. The 340... doesn't do that well.
Additionally, you CAN compare twin to quad jet IN THIS CASE. That's because- whether they are overpowered or not- both types use full thrust on takeoff or go around situations. And we're talking about thrust to weight, not cruising power.
You're right, the A380 makes the A340 look spritely! The interesting thing is the A380 seems to be working on aerodynamic magic, with its very high wingloading. I don't understand how AI can claim to have so much magic with this plane - but I'm not the engineer.
With such low thrust ratios & high wing loadings, the A380 would have very low initial cruise altitudes. It must have a very special wing to be able to have significant performance.
Just remember one fact, you always have more power after losing one engine in a quad, than a twin - because quads have to make higher climb gradients without one engine, than twins.
DC10Tony From United States of America, joined May 2001, 1012 posts, RR: 0 Reply 16, posted (12 years 3 weeks 4 days 9 hours ago) and read 2924 times:
I think all Boeings are a little overpowered and Airbuses may be a little underpowered, here's why.
Boeing 767-300: MTOW ~415,000 lbs.
thrust per engine ~63,000 lbs.
Airbus A330-200: MTOW ~510,000 lbs.
thrust per engine: ~72,000 lbs.
The Airbus weighs like 100,000 pounds more than the 763, yet each engine only makes 10,000 lbs. of thrust more.
I used to work on the groundcrew and have seen both take off, the 763 really gets on it quickly and takes of very fast while the A330 is slow off the start and takes off a bit slower than the 763. If you're all gonna say well it weighs more, bla, bla, bla... When I saw DC-10s take off, they were almost as fast as a 763 and it weighs like 580,000 lbs., so it wasn't underpowered for takeoff. My preference is that I'd rather be in the overpowered aircraft, so it's Boeing for me (if I can help it) .
SailorOrion From Germany, joined Feb 2001, 2058 posts, RR: 6 Reply 17, posted (12 years 3 weeks 4 days 6 hours ago) and read 2899 times:
When comparing aircraft about go-around situations, it is required to compare MLW (maximum landing weights) not MTOWs. Under these circumstances, you really need any little m/s² of acceleration you can get out of the plane, therefore usually N1 can be above 100%, and thrust can be higher than the actual value.
Boeing767-300 From Australia, joined Sep 2001, 659 posts, RR: 0 Reply 18, posted (12 years 3 weeks 4 days 1 hour ago) and read 2868 times:
They are only mixed up because as far as weight is concerned lbs means nothing to me in the metric world (USA excluded) but thrust is like height and although Engines are also quoted in KNs, but being in the transition generations it means more in lbs , a bit like 6ft tall means something and 1.83m does not.
But regardless of that, the result is the same, kilos per pound of thrust. They were all done the same.
Donder10 From Canada, joined Oct 2001, 6659 posts, RR: 23 Reply 19, posted (12 years 3 weeks 4 days 1 hour ago) and read 2868 times:
''When you hit severe shear, firewall the throttles, and hang on for dear life while the stickshakers are going off, "efficiency" isn't going to save hundreds of lives. That's how I feel whether I'm in an A-340 or a C-152.''
OSCAR AWARD OF THE DAY!!!!
WhiskeyNovembr From , joined Dec 1969, posts, RR: Reply 21, posted (12 years 3 weeks 3 days 21 hours ago) and read 2860 times:
XXXX10, you suggest that giving a design more power than it needs will make it inefficient. Having excess power may make it LESS efficient...but not necessarily INefficient. Remember that just because you have the power doesn't mean you have to use it. If, for example, everyone drove their cars around with the accelerator floored, using all available power all the time, efficiency (ie: mileage) would obviously suffer. When driving normally, efficiency is on par with most other cars. Sure, a 3-cylinder Geo Metro would be more efficient, but 99.9% of us opt for a more functional and comfortable vehicle that can actually make it up large hills. That's how I feel about airplanes. To me (and most pilots), a feeling of safety, security, and peace of mind is worth a little more fuel burn.
By the way, I'm not trying to prove you wrong or anything...just offering my point of view on the whole "efficiency vs. power" discussion. Have a good one!
Prebennorholm From Denmark, joined Mar 2000, 6131 posts, RR: 55 Reply 23, posted (12 years 3 weeks 3 days 13 hours ago) and read 2815 times:
There are a few more variables than previously mentioned. First of all practically all airliners come with different engine types or subtypes with different thrust ratings. For instance a 340 comes with three different CFM56 engines with ratings from 31.2 to 34k lbs.
The 340 is no sportscar. But those of you who witnessed a very slow 340 climb, did you remember to check the engine type plate before take off?
The 744 has a relatively short span wing, very little more than a 340 which is so much lighter. Wing span means the most for efficiency at slow speed at take off. The 744 must compensate for its short wing span with powerful engines in order to gain its higher take off speed on the same runway.
The 380 has a 50 feet wider wing span compared to the 744. So the 380 - like the 340 - has a quite generous wing span, therefore relatively slow take off speed.
Sure Airbus quad buyers don't pay much attention to climb ability at MTOW. And they are probably right that it doesn't show up on the bottom line if their planes spend 5 or 10 minutes more or less going from zero to 30,000 feet on a 10-15 hours flight. What counts is the overall economic performance.
There is another consideration: Especially the 744 at MTOW has problems to clean up its wing at the 250kts. speed limit below 10,000 feet. Long duration flight with flaps extended means a lot of drag and extra fuel burn.
But the reality is that mostly the manufacturers install the power which the customers want. Most large European and Asian airports are close to sea level. It cals for less take off power needed. Things like Denver and Mexico City etc. do not exist on the other side of the pond. So manufacturers selling to American operators will often have to install more power.
There ain't many Airbus quads sold in America. Maybe because they are less powerful. But if one day Airbus sells quads in America, then they will most likely have to install more power, because that's what the customer needs for his operation profile. At least on the 380 that's no big deal since more powerful RR trent engines are on the shelf ready to be installed when the customer wants it so.
Regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs, Preben Norholm
Seagull From United States of America, joined Jun 2001, 340 posts, RR: 1 Reply 24, posted (12 years 3 weeks 3 days 9 hours ago) and read 2803 times:
OK. lots of good points. To the poster above who worries about 250 kts below 10k on the 744, the MD-11 climbs at 289kts below 10k, look at the reg, we can exceed 250 if we need to for operational reasons, we are NOT expected to climb with the slats out!
The rate of climb may be a function of power, but the ANGLE of climb is what is the concern on takeoff and also to a great extent on the windshear escape. The lower speeds of the A-380 will net a better angle, and that's how it easily meets Part 25 performance requirements. Cruise climb at lower airspeeds with less drag to overcome with thrust will help as well. This is all more complex than has been indicated here, and I don't have time to respond to all of the posts above, so I'll leave it at that.
25 Cedarjet: I agree that in windshear the more power the better. But no A340 has ever crashed in windshear (or for any reason) and of course they encounter all fo
26 Megatop: I agree with prebennorholm and Cederjet. To all of you: Have you ever tried to takeoff with all 3 types, A340, B777 and B744. I have tried all 3, on l
27 WhiskeyNovembr: Saying the A340 is perfectly safe simply because none have crashed in windshear/microbursts (yet) is like saying an old, bald, frayed tire is safe bec
28 Blackbird: The comment about the A340 not crashing in windshear is false logic. It can definetly crash, it just has been lucky so far. The L-1011 @ Dallas encou
29 Prebennorholm: WhiskeyNovembr, sure you have got a valid point. But I think that there are a few more variables to take into account. 1. All long haulers are long ha
30 Racko: "Saying the A340 is perfectly safe simply because none have crashed in windshear/microbursts (yet) is like saying an old, bald, frayed tire is safe be
31 WhiskeyNovembr: Hey Racko...you work for the American media, right? I assume so because you incorrectly read my post and then based your argument on the false stateme
32 MiG31: Whats the matter with A380 anyway? First people think it had not enough doors, then not enough power whats next? Kind Regards, I.T.
33 Skystar: MiG31, Didn't you read my post? Not enough wing either Cheers, Justin
34 VC-10: It surpises me that AI ever sell any a/c with all you design "experts" out there. Regarding the unexiciting T.O.'s you are predicting. Exciting T.O.'s
35 VC-10: I saw a 343 take off and I've seen nothing climb slower Ever saw an A340-300 fully loaded taking off. God bless there is the curvature of the earth. D
36 Skystar: VC-10, Irrespective of whether the takeoff is derated, the A340s takeoff performance is quite relaxed. I have not criticised this fact - I like the A3
37 MD-11 forever: VC-10, I agree with you in every single point! to safe the materials with derated take offs and therefore give more on-wing time to the engines is mor
38 Dynkrisolo: I'd like to point out a big difference between the A380 and the A343. The A380 has a much lower wing loading than the A343. So, the A380 does not need
39 Skystar: Here are some wingloading numbers. A340-300 (275t) weight/area 275,000/361.6 =760.51 kg/m2 A380 (560t) weight/area 560,000/845 =662.72 kg/m2 The A380