Not sure what "living wing" is but the 787 does have aerodynamic enhancements like aileron droop and cruise flap droop, but it's seemless to the pilot.

Erwin,

I've never heard the wing referred to as 'living,' but it's as good a description as any. It does deploy flaps above 25,000' if it thinks it needs to. LOL, it's apparently got a mind of its own! Seriously, the flight control system is so good, you have to check the engine instruments to see which engine is not running during engine failures (in the sim, of course, since I haven't heard of one quitting on line... yet). It's astonishing how well the auto flight system is as well. Like I said... it's a nice flying airplane, easy to manage, quiet as a mouse up front (the windows don't open... it has an escape hatch) and just flat out good looking!

Isn't this a simple thrust-to-weight ratio problem?

747 = thrust 63,000 lbs/ea
MTOW 875,000 lbs

3.47 aircraft lbs per thrust lb

https://sciencebasedlife.wordpress.com/ ... oeing-747/

787 = thrust 70-76,000 lbs/ea
MTOW 500,000 lbs

3.28 aircraft lbs per thrust lb

http://www.geaviation.com/engines/docs/ ... t-genx.pdf

So the 787 has less weight per pound of thrust (MTOW, biggest engine). Additionally, I just did some overseas travel (as pax) in a 787 and a 747. Subjectively, the 787 really accelerated down the runway.

Nate,

Not really... Although I get lost in the engineering details, basically transport airplanes are kind of designed backward in the performance area. They have to do certain things with an engine inop at a critical time. V1, takeoff decision speed. At that point the airplane has to be able to either stop in the remaining runway or continue and clear the obstacles at the end of the runway by 35 feet. All of us pilots here on BT can find plenty of things that make that scenario not work as well... like wet conditions (stop distance increases), hotter than standard temp (slower acceleration)... you get the picture. Runways can be made longer, but there are considerations like obstacles miles away that affect takeoff weight. There's runway limited takeoff weight, climb limited weight, temperature limits, icing penalties, performance penalties too numerous to list. And every runway we operate off of has its own numbers... even if its only a few hundred feet from a seemingly identical runway.

Anyway, almost everything cuts into the performance envelope. So, what do we do? Well, if the weight is so much for given conditions and the plane won't comply with the 35 ft rule, we don't take as much weight. Less passenger load, less fuel, less cargo, whatever it takes, maybe even a fuel stop has to be planned. There's nothing like a sea-level airport, departing out over the water with a nice cool temperature!

What this all comes down to is utility. Not much different than any of us working to balance our useful load and trip length. The lighter the empty weight on Max's Bonanza, the more weight he can carry. We all know of airplanes that can only carry 2 people if full of fuel. Not a bad thing knowing they can carry 6 on a shorter trip. The 787 is no different. When I fly it 15-16 hrs with a full load of people and cargo, it simply doesn't have room for full fuel tanks. It will go much farther, but at the expense of revenue. These 15 hr trips are its sweet spot. Bad weather at the other end? Cut some cargo and take more fuel. Only plan shorter trips so revenue is always maximum? You're losing $$ on all the good days. It's a wonder airlines make money when you think about it. At $200 million a copy and 100 on the way, you do the math. Crazy.

Back the the original question: do 78's take less runway than 74's? Yep, because they have a wider operating envelope, more modern engines and efficient designs. That's really their only advantage. Believe me, if a 787 would cross the fence on takeoff and get to 36 ft instead of 35 ft, Boeing would increase the takeoff weight. That's how it really works.

PS. Twin jets are snappier on takeoff than 3 and 4 engine planes because of the need to meet that pesky 35 ft rule on half their power rather than 66 or 75%. So 3 and 4 engine airliners seem underpowered in normal operations. But they all do the same job when one quits at V1. Clear as mud?

PSS. If this is boring the tar out of everyone, I apologize. This stuff has always fascinated me, but I can just picture all the 3000 ft stares while reading this. lol

Not boring at all Jeff. That is what I love about BT, so much to read, so much to learn.

Great explanation, Jeff - thank you for taking the time to put that together!

- Martin

Thanks Jeff! That was fairly nerdy but I enjoyed it! I had no clue about all of that. Thanks for the details!

Well done Jeff !

A better comparison between 787 and 777 would be when you compare the 777-200 to the 787.

The 777-300 is a bit of a dog in climb but the -200 does good.

When they stretch the 787 then compare it to the 777-300. More apple to apples comparison.

I was a Boeing flight test engineer for 43 years and would suggest a fairly simple answer to the original question comparing 747 and 787 takeoffs. As Jeff touched on earlier, the biggest factor for takeoff runway length is the thrust to weight ratio. We experience the same relationship when we take off in our Beech airplanes at different altitudes, weights or power settings. Most modern heavy transports have similar stall speeds, which define their takeoff speeds, so wing differences are secondary and have less effect. The transport certification regs (FAR 25 in the U.S.) require transport airplanes to achieve specific takeoff climb gradients (angles) at max gross weight with one engine inop. Twins therefore have at least twice that legally required thrust in normal all-engine operations, three-engine planes like the 727 or DC-10 have 50% more and 4-engine planes like the 747 have 33% more. Even at max weights the twins will have better acceleration down the runway, so they will take off sooner and in less distance than birds with more engines at their max weights. Once airborne the twins can climb faster for the same reason. And, just like or Beech airplanes, all are affected by different temperatures, altitudes, weights and power settings.

Other things equal twins also offer better fuel economy and cost less to operate and maintain (fewer expensive engines, less drag from engine nacelles, fewer expensive parts and spares needed, etc.) Historically the main reasons for more engines on big airplanes were issues of engine reliability and power. Early turbojets were much more reliable and powerful than piston engines but their performance, the regulations and airline experience mandated 4 engines for the early large transcontinental jets like the 707. Modern engines are even more reliable, powerful and efficient and their proven operating histories justified regulatory changes - primarily relating to ETOPS - that permit the heavy twin jets we use so routinely today.

What I said 20 something posts ago . . . I'm a Boeing contract 777/787 flight instructor and have been teaching performance and dispatching issues to most foreign pilots since I retired. As I said earlier two engine planes are the performance beasts. I used to hate taking off behind a 747coming back to the states from Asia. We'd be held down for the first 2 - 4 hours, 'till the routes split or they'd burn down fuel. Airbuses' a totally different deal . . .

Burns,

Please continue your thoughts on Airbuses. Curiosity is killing me!

Ed

They are called flying Renaults

Jeff Rowland: You answered the original question in the 1st "P.S."
Thanks.

Nice video , unpacking the new KLM Boeing 787

[youtube]https://youtu.be/N2MUsayyAgU[/youtube]