RJMAZ wrote: You just got it wrong again.
No, I didn't.
RJMAZ wrote:
Engine to aircraft centreline
787-9/10 973cm
a350-900 1050cm
I used the number for the 787-10 in the Boeing ACAPS for the 787: 9.71 m
You're just making things up and taking the value for the 787-8 (9.73 m) as gospel and using it for the 787-9/-10
Boeing's official ACAPS numbers for fuselage centre-line to engine centre-line:
787-8: 9.73 m
787-9: 9.91 m
787-10: 9.71 m
Now, I tend to believe that the fuselage centre-line to engine centre-line is the same on the 787-8/-9/-10 and, therefore, two out of the three numbers are wrong. However, unless you work for Boeing, you have no idea which number is correct -- yet, you have chosen 9.73 m to be right number while saying that I'm wrong. Go figure!
In contrast to Boeing's seemingly erroneous numbers in the 787 ACAPS, the fuselage centre-line to engine centre-line on the A320ceo family and A320neo family is identical (i.e. 5.75 m); on the A330ceo and A330neo it is identical (9.37 m); and on the A350-900 and A350-1000 it is identical (10.5 m).
What would the 787 gain in efficiency by not having identical engine positions for the 787-8/-9/-10?
If, in fact, the 787 does have three unique engine positions for each of the 787-8/-9/-10, the certification costs would not only have been higher than for one common engine position, but the manufacturing costs would increase as well.
RJMAZ said: Now if we assume an equal maximum bank angle of 7 degrees the ground clearance of the engine can be the following.
787-9/10 67cm
A350-900 75cm
So the 787 engines can be 8cm closer to the ground than the A350 with the same risk of engine hitting the ground.
This is getting ridiculous.
The point of attachment of the pylon box to the aircraft wing box is more than 60 cm closer (24 inches) to the ground on the 787 than on the A350 and 777X. That's by far the most important metric in order to determine the growth potential in engine size for the 787 and A350.
And it's a matter of fact that the 787 engines are hung much higher on the wing than the engines on the A350 -- you can just take a look at the drawings in the 787 and A350 ACAPS documents and see the difference and that the A350 engine is hung significantly lower with respect to the wing.
Once you combine this with the fact the 787 needs smaller engines with 80% less thrust they both have now equal ability to fit similar tech 14:1 bypass ratio engines.
Why do you keep comparing the engine thrust requirements for the 787 with the A350-1000 and not with the A350-900?
The 787 (-10) has 10 percent less thrust than the A350-900.
And once again, you seem to be unable to grasp that the point of attachment of the pylon box to the aircraft wing box is more than 60 cm closer (>24 inches) to the ground on the 787 than on the A350 and 777X.
Also, you've not answered my question why Boeing decided to move the engines on the 777X further outboard.
As I've already pointed out, the 777X nacelle diameter is 174 inches (4.42 m) and as the "ground clearance" for the point of attachment of the pylon box to the aircraft wing box is similar on the A350 and 777X, the fan diameter for new engines on the A350 can be more than 20 inches wider than what would be possible for a re-engined 787.
That's why the current 787 would be extremely vulnerable to a new A360X familyThe exact argument could be used to say how vulnerable your A360 would be to the much lighter 797. The 797 would have only 50,000lb thrust engines and the largest version will be quite close to 787-8 in size. Optimising for lower range produces a significantly lighter aircraft and gives a huge efficiency boost up to that design range. Your A360 numbers are also completely unrealistic.
The A360X family would replace the A330neo and primarily compete with an upgraded 787 family.
The 797 family would have much less range than an A360X family. The 797 family would also have much less cargo capability than the A360X family. In conclusion: Two very different aircraft serving different markets requirements (i.e. Asian airlines do seem to like LD-3 capable cargo holds on short and medium range routes, North American airlines, not so much).
As for weight estimates, the fact of the matter is that Boeing dramatically overshot their weight targets for the 787 as can be seen in this document:
Airbus dossier: 787 Lessons Learnt (October 2008)
https://www.slideshare.net/aergenium/b787-lessons-learnt-presentationOn page 12 in the document:
Design________Key Date_____MZFW*___MTOW*____MWE*____Range**
7E7 stretch____July 2003_____163.8_____219.8______93.8______7500
7E7-9_________June 2004____167.8_____230.0______98.5______7970
787-9_________April 2008_____181.4_____247.2_____108.4______6810
*Weights in metric tonnes
** Range in nautical miles
Take your A360-1000. The 787-10 has 299m2 vs 290m2 of the A350-900. So you just proposed a 2 metre stretch of the A350-900 but with a 220t MTOW. You've reduced MTOW by 20%. A normal A350-900 would have a range of only 4000nm with a normal load taking off at 220t. Even with 10% improved engines the range would struggle to exceed 5000nm. 7000nm is absolutely ridiculous.
The A360 wing would have a 25 percent smaller wing area than the A350 and 10 percent smaller wing area than the 787. The wingbox could be designed with a maximum fuel capacity of, say, 95,000 litres -- vs. 126,400 litres on the 787 and 165,000 litres on the A350. Less fuel volume means less weight, right? The A360-900X would be designed to fly for no more than 15 hours (maximum). In contrast, the current A350-900 can be in the air for nearly 20 hours.
However, the A360 wing would have the same span as the current A350 wing (64.8 m), so the aspect ratio of the A360X wing would be 30+ percent larger than the A350 wing; but still, only a 12 percent larger aspect ratio than the A330neo wing, which BTW has a higher wing aspect ratio than any other wide body. That's quite ironic, isn't it, when considering the fact that the A330 wing is not a composite wing.
Since the wing assembly typically accounts for up to 40 percent of MWE, it's obvious that the A360 wing would weigh significantly less (>10 metric tonnes) than the A350 wing, while being 10+ percent more efficient (i.e. significantly less induced drag). Add a smaller horizontal tail plane, smaller and lighter landing gear (etc.) optimised for a 220 metric tonnes MTOW and a 10 percent lower TSFC for the smaller and lighter engines -- and with a rule-of-thumb that a reduction in fuel consumption on long range aircraft of about 0.75% results from each 1% reduction in weight -- you would have an A360-900X (same size as the 787-9) burning some 30 percent less fuel per trip than the current A350-900. Since fuel weight typically accounts for 50 percent of the MTOW for long range wide-bodies -- that's 15 percent lower MTOW than the A350-900 right there (i.e. in a first order approximation).
In fact, my MWE estimates for the A360X are quite similar to the early MWE weight estimates for the 7E7/787; the difference being, of course, some 20 years of advances in technology separating the launch of the 787 and the A360X (i.e. assuming an A360X launch in 2025).
It would be crazy for Airbus to launch the A360-1000 that had a larger cabin than their A350-900. The next Airbus aircraft family will probably be 50-100m2 smaller than the A350-900. The A330 cross section is perfect for this size
As I've earlier indicated; the best-seller of the A350neo family would be the A350-800neo (i.e. A350-1000 length) and the A350-2000neo.
What Airbus could do, though, with the A350neo, is to significantly improve the efficiency of its wing. The wing outboard of the engines could be re-designed in order to increase wing span to 75 metres. That would increase the aspect ratio by 25 percent. Of course, in order to maintain Category E requirements, the re-designed wing would be designed with 2 x 5 metre long folding wing tips. So, with new UltraFan engines and a much improved wing, the A350neo would lower fuel consumption by more than 15 percent over that of the current A350.
An extra bonus with the much higher aspect ratio wing would be lower take-off thrust requirements (due to the significantly lower induced drag at take-off). Hence, the thrust required for an A350-2000neo at a MTOW of 325 metric tonnes should be no more than the 97,000 lbf of thrust on the current A350-1000. Similarly, the maximum take-off thrust of the current A350-900 would be reduced to less than 80,000 lbf of thrust.
