TomB From United States of America, joined Nov 2006, 77 posts, RR: 0 Posted (6 years 6 months 2 weeks 3 hours ago) and read 7108 times:
Normally, when they stretch an airliner, the structural efficiency improves. In comparing the Boeing 747-8I to the B-747-400, the OEW is increasing at a faster rate than the MTOW implying less structural efficiency.
Here are some of the statistics comparing the B-747-400 to the B-747-8I.
Seats - 12.3% increase (from 416 to 467)
Maximum Take Off Weight - 10.9% increase (from 875,000 lb. to 970,000lb.)
Operating Empty Weight - 16.9% increase (from 399,100 lb. to 466,700 lb.)
(source - Page 10 of the 747-8 Airport Compatability Guide on the Boeing
OEW per Seat - 4.2% unfavorable increase (from 959 lb. to 999 lb.)
Fuselage Length - 8.1% increase (from 231' 10" to 250' 8")
Wingspan - 6.2% increase (from 211' 5" to 224' 7")
Max Range - 10.2% increase (from 7260 NM to 8000 NM)
(the range increase primarily reflects the fuel efficiency of the GEnx
Engine Thrust - 7.1% increase (from 62,100 lb. to 66,500 lb.)
Freighter Version OEW - 15.2% increase (from 358,900 lb. to 413,600 lb.)
The GE CF6-80C2B5F engine on the B-747-400 produces 62,100 lb. of thrust and weighs 9,860 pounds. The GEnx-2B67 engine on the B-747-8 will produce 66,500 lb. of thrust. How much does the GEnx engine weigh?
As a non-engineer, I am perplexed as why the OEW on the B-747-8I is increasing at a faster rate than the other parameters perhaps suggesting less structural efficiency. I would like the experts on the Forum to enlighten me on this subject.
RJ111 From , joined Dec 1969, posts, RR: Reply 1, posted (6 years 6 months 2 weeks 3 hours ago) and read 7090 times:
When an aircraft starts to gets quite long you have to reinforce the structure so it can cope with its own length. Imagine a 2m long drinking straw, wouldn't bend quite horribly. This make it heavier than usual thus you need to strenghen more ect ect. This was a problem with the A346. i don't know how much it has effected the 748I.
Also the engines are probably heavier per lb thrust than the former ones. Fans are getting bigger but they're getting much more efficient. Look at the Trent 500 and the RB211-524H/T. Similar power output and design, but the Trent has a larger fan and is heavier by about 1000lb.
SailorOrion From Germany, joined Feb 2001, 2058 posts, RR: 6 Reply 2, posted (6 years 6 months 2 weeks 3 hours ago) and read 7045 times:
This is a difficult question to answer, but lets look at the figures a bit more closely. One of the question is how the seat capacities are measured, or rather: how does the usable floor space develop? For example, LH flies their 747-400s (with new business class) with 330 seats, nowhere near 400.
We add 5.8meters, for 4 economy rows, we need 4.1 meters. This leaves 1.7 meters, or one row of business class seats, plus one row of first class seats. This increases seat count from:
resulting in an increase of:
Overall an increase of 15.5%.
I think that the seat count for the 747-8I is more conservative than the one for the 744. It would for example be interesting to have a look at the increase in usable floor space.
KC135TopBoom From United States of America, joined Jan 2005, 11711 posts, RR: 52 Reply 3, posted (6 years 6 months 2 weeks 2 hours ago) and read 7033 times:
The GEnx-2B67s tip the scales at something over 12,500lbs each. that is a 22% increase over the weight of the CF6-80C2B5Fs. So that accounts for some 10,160 lbs of the weight increase. Increasing the lenght and structual reenforcing of the B-747-800I over the B-747-400 accounts for the rest of the weight.
But, you would really need to compare the OEW of the B-747-400ER/FER to the weight of the B-747-800I/F to be more realistic. These are the two models next to each other (only about 5 yeras apart), where the -400 was a generation ago.