Necigrad From United States of America, joined Sep 2001, 183 posts, RR: 0
Reply 3, posted (10 years 8 months 3 weeks 5 days 19 hours ago) and read 5856 times:
Don't see noise being a problem. But how about wing loading? Ground clearance? A 747 engine put's out what? 50,000 pounds of thrust? The 777 engines are good for 90,000. So you've got the increased weight, increased drag, and increased thrust all pulling on the wing in differnet directions. The structural MTOW probably wouldn't change, although I think the performance MTOW might benefit. It would wreck hell with the landing weight limit though.
Thrust From United States of America, joined Sep 2003, 2690 posts, RR: 10
Reply 4, posted (10 years 8 months 3 weeks 5 days 14 hours ago) and read 5483 times:
I actually suggested this idea in several other posts. Now that I think about it, Necigrad makes several good points about the issues of having four 777 engines for a 747 aircraft. 90,000 lbs. of thrust is a ridiculously high amount of thrust for each of the four engines on a 747 unless this aircraft is an absolute monster like the future A380. Also, the wings would have to be incredibly strong to hold two GE90s on each wing. Those engines are the heaviest ones available in service. Fuel economy and noise I don't see as a problem, considering how quiet the 777 engines are for their power and size. The GE90 is very fuel-efficient. Really, all the 777 engines are fuel efficient. By the way, Necigrad, the 747 could use the engines on the domestic 777s, like the PW 4077s instead of 90,000 lbs. of thrust. That might make a bit more sense for fuel efficiency. MTOW would be a problem. The combination of the crushing weight of the current 747s combined with the enormous weight of four 777 engines would sink right through the tarmac. Maybe Boeing will find a way though. For a response to the A380, in my opinion, the answer lies within the 747.
HlywdCatft From United States of America, joined Jan 2001, 5321 posts, RR: 6
Reply 6, posted (10 years 8 months 3 weeks 5 days 13 hours ago) and read 5394 times:
When Boeing orriginally planned the 747-500X 600, etc in the late 90s it was supposed to have four 777 engines and also triple axle landing gear (6 wheels) on the wing landing gear struts while the under fuselage gear would still be the double axle.
Slamclick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 7, posted (10 years 8 months 3 weeks 5 days 13 hours ago) and read 5309 times:
I'd rather see two CFM-56 on a BAe-146 and use the outer pylons for external fuel tanks or ski lockers.
Most factory engineers are pretty smart guys. If you hang too-powerful engines on an airplane they will cheerfully push it up higher than the wings can then carry it. Even the B-727-200 with -17 engines had a little problem with this. If you have access to the performance data, check out "Cruise Capability" charts against "Maneuver Capability" charts for the same altitude and weight. Get up near the coffin corner and you will see what I mean.
Happiness is not seeing another trite Ste. Maarten photo all week long.
Navigator From Sweden, joined Jul 2001, 1208 posts, RR: 14
Reply 8, posted (10 years 8 months 3 weeks 5 days 13 hours ago) and read 5243 times:
You would have to reconstruct the whole engine mountings to the wings. The 777-engines simply won´t fit a 747 without a major reconstruction of the plane. I doubt it is at all realistic. The diameter of an 777 engine is far greater than that of a regular 747 engine. So this is simply not a realistic option for the 747. Ground clearence without mods would be nothing or the plane would be resting on it´s engines if you don´t also reconstruct the landning gear...
Alessandro From , joined Dec 1969, posts, RR:
Reply 12, posted (10 years 8 months 3 weeks 5 days 12 hours ago) and read 4831 times:
First, Airliner777, the B744-Beluga is a new project but probably not what you
Anyway I think the cost to re-design of the B747 would be too much, especially when it´s a low wing design. I would suggest a 4 engined GE90
AN225 instead of the current 6 Progress engines, the high wing design of
the AN225 makes it easier to put on bigger engines...
Thrust From United States of America, joined Sep 2003, 2690 posts, RR: 10
Reply 14, posted (10 years 8 months 3 weeks 5 days 11 hours ago) and read 4603 times:
While a 747 may be being used as a test-bed for GE-90 engines, the most a modern 747 could stand is one GE-90 per wing. Two GE-90s would rip the wing in half. In fact, there may be an even easier solution to solve this problem. Why not use the 7E7 engines that will be coming. They would be more fuel-efficient, and would make more sense because they would give less MTOW. This would come closer to the current weight limits today, and would save the burden of bearing 4 enormous 777 engines. The GE-90, the PW engines for the 777, and the Trent 800s are far too heavy to make MTOW what we would like. With 7E7 engines, the wing would not need as drastic strengthening, Boeing would save weight, and because of the 9,000 mile range guaranteed for the 7E7, the 7E7 engines would offer greater range than any 777 engine. A 9,000 mile range is well beyond any 777 model that exists right now. No 777 has that great range unless I suppose the 777 was operating empty overseas. The 7E7 engines make far more sense for the 747 than the 777 engines, because they would save weight, offer greater fuel-efficiency (90,000 lbs. of thrust per engine I think is more power than we would need for 4 engines on the A380), and therefore, because of these two factors, the 747 would have greater range.
KGAI From United States of America, joined Dec 2003, 120 posts, RR: 0
Reply 15, posted (10 years 8 months 3 weeks 5 days 10 hours ago) and read 4492 times:
Actually the 7E7 stretch is supposed to have a range of 8300NM, vs 772ER's ~7700NM. The 772LR will fly >9000NM.
Obviously you need major modifications to the 747 to fit 4 777 engines on it. But assuming that's done, the plane would have maybe 50% more power.
So, faster cruise (M0.88-0.90 maybe?) and faster climb. Less range though as the 777 engines drink far more fuel. Unless you stuff the plane full of extra fuel tanks. But then you could do the same with 747 engines too.
You pick the right engines for your plane, beyond that, you're going to get decreasing return with bigger engines.
B2707SST From United States of America, joined Apr 2003, 1369 posts, RR: 59
Reply 18, posted (10 years 8 months 3 weeks 5 days 9 hours ago) and read 4288 times:
It bears repeating that more powerful engines do not necessarily mean a faster cruise speed. The 747's non-supercritical wing was designed 1960s, which means that strong shock waves begin to build up as the wing passes its critical Mach number (the point when airflow over the wing reaches Mach 1). These shock waves create tremendous drag and stress on the airframe and cause a dramatic fall-off in wing efficiency as you approach Mach 1 (the so-called "sound barrier"). Modern supercritical wings both delay the formation of shock waves to higher Mach numbers and reduce their intensity, so aircraft like the 777 can cruise at similar speeds with a lot less sweep than the 747.
More powerful engines might have enough force to push the aircraft faster than Mach 0.86, but the drag and stress involved would almost certainly prohibit sustained cruise at those speeds. The 747Xs were to cruise faster due to a reshaped "semi-supercritical" wing; larger engines were needed just to get a million-pound aircraft off the ground.
In any case, the pictures of GE's engine testbed show that the inboard GE90 has virtually no ground clearance (looks like less than a foot). Fitting another GE90 outboard would, because of its weight, bow the wing downward and further reduce clearance on the inboard engine. Major wing and gear revisions would be needed to fit GE90s to a 747, and as mentioned, there's simply no need for that much thrust.
Cha747 From United States of America, joined Dec 2003, 785 posts, RR: 6
Reply 22, posted (10 years 8 months 3 weeks 4 days 23 hours ago) and read 3578 times:
Here's an article about a problem that the GE testbed 747 had with carrying the 777 engine. The questions are did this fire occur with the 777 engine itself or was it somewhere else (the article isn't clear).
Taken from: http://www.geocrawler.com/archives/3/78/2002/12/0/10267730/
Plane Testing 'World's Most Powerful Engine'
POSTED: 3:24 p.m. HST December 11, 2002
UPDATED: 3:25 p.m. HST December 11, 2002
HONOLULU -- A fire aboard a non-commercial 747 airplane at Honolulu Airport Tuesday night started in the left wing pylon which connects the engine to the wing.
The General Electric plane is in Honolulu testing what it calls "The World's Most Powerful Jet Engine."
Late Tuesday afternoon as the plane landed, witnesses saw thick black smoke pouring out from under the left wing.
Airport crash crews doused the engine area and the 23 people on board evacuated using the inflatable slide.
G.E. said it's testing the jet engine in Hawaii because it is required to test the engine in various types of weather.
The company said the engine did not catch fire.
It hopes to get government approval to install the engines on very large aircraft within the next couple years.
You land a million planes safely, then you have one little mid-air and you never hear the end of it - Pushing Tin