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A B747 With 4 777´s Engines  
User currently offlineLugonza_2001 From Spain, joined Oct 2001, 315 posts, RR: 1
Posted (10 years 3 months 3 weeks 5 days 11 hours ago) and read 6058 times:

Hi!

how would a B747 fly if you change its natural engines, for 4 GE 90 engines? How fast could it climb and fly?

Have you ever wondered?

 Smile/happy/getting dizzy

22 replies: All unread, jump to last
 
User currently offlinePerthGloryFan From Australia, joined Oct 2000, 751 posts, RR: 0
Reply 1, posted (10 years 3 months 3 weeks 5 days 11 hours ago) and read 5996 times:

Actually I haven't (wondered) until you've just mentioned it.

That would be one gruntmiester - would the wing structure cope with that?
Probably not, but as this a hypothectical question that doesn't matter.

Climb & cruise would be interesting - MTOW & range/fuel consumption & capacity would be another issue though.

PGF


User currently offlineMog From , joined Dec 1969, posts, RR:
Reply 2, posted (10 years 3 months 3 weeks 5 days 11 hours ago) and read 5876 times:

I think it would also make a lot of noise and not be permitted at many airports.

User currently offlineNecigrad From United States of America, joined Sep 2001, 183 posts, RR: 0
Reply 3, posted (10 years 3 months 3 weeks 5 days 10 hours ago) and read 5778 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.

User currently offlineThrust From United States of America, joined Sep 2003, 2686 posts, RR: 10
Reply 4, posted (10 years 3 months 3 weeks 5 days 5 hours ago) and read 5405 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.

--Thrust




Fly one thing; Fly it well
User currently offlineLugonza_2001 From Spain, joined Oct 2001, 315 posts, RR: 1
Reply 5, posted (10 years 3 months 3 weeks 5 days 5 hours ago) and read 5337 times:

"For a response to the A380, in my opinion, the answer lies within the 747."

I agree with this 100%.




User currently offlineHlywdCatft From United States of America, joined Jan 2001, 5321 posts, RR: 7
Reply 6, posted (10 years 3 months 3 weeks 5 days 5 hours ago) and read 5316 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.

User currently offlineSlamclick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 7, posted (10 years 3 months 3 weeks 5 days 4 hours ago) and read 5231 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.
User currently offlineNavigator From Sweden, joined Jul 2001, 1144 posts, RR: 14
Reply 8, posted (10 years 3 months 3 weeks 5 days 4 hours ago) and read 5165 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...

Oh no...



747-400/747-200/L1011/DC-10/DC-9/DC-8/MD-80/MD90/A340/A330/A300/A310/A321/A320/A319/767/757/737/727/HS-121/CV990/CV440/S
User currently offlineDan2002 From United States of America, joined Dec 2002, 2055 posts, RR: 5
Reply 9, posted (10 years 3 months 3 weeks 5 days 4 hours ago) and read 5096 times:

As a matter of fact, GE has N747GE and uses it as a flying testbed for GE engines.


View Large View Medium
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Photo © David Matyas



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Photo © Georg S.






-Dan



A guy asks 'What's Punk?'. I kick over a trash can and its punk. He knocks over a trash can and its trendy.
User currently offlineKorg747 From United States of America, joined Mar 2003, 549 posts, RR: 6
Reply 10, posted (10 years 3 months 3 weeks 5 days 4 hours ago) and read 4943 times:

I think the GP7000 OR TRENT900 would be a better choice than the heaver GE90.


Please excuse my English!
User currently offlineAirliner777 From United States of America, joined May 2000, 493 posts, RR: 0
Reply 11, posted (10 years 3 months 3 weeks 5 days 4 hours ago) and read 4843 times:

I think that after the B7E7 starts flying, Boeing will continue a B747-XX project.


My 0.02 cents......
Adel


User currently offlineAlessandro From , joined Dec 1969, posts, RR:
Reply 12, posted (10 years 3 months 3 weeks 5 days 3 hours ago) and read 4753 times:

First, Airliner777, the B744-Beluga is a new project but probably not what you
thought of?
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...


User currently offlineGigneil From United States of America, joined Nov 2002, 16345 posts, RR: 86
Reply 13, posted (10 years 3 months 3 weeks 5 days 2 hours ago) and read 4553 times:

At any rate, what would be the point?

The engines on the 747 are optimized for it. Replacement engines would include the not-yet-in-service Trent 600, or optimizations of thei other engine designs.

N


User currently offlineThrust From United States of America, joined Sep 2003, 2686 posts, RR: 10
Reply 14, posted (10 years 3 months 3 weeks 5 days 2 hours ago) and read 4525 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.


Fly one thing; Fly it well
User currently offlineKGAI From United States of America, joined Dec 2003, 120 posts, RR: 0
Reply 15, posted (10 years 3 months 3 weeks 5 days 1 hour ago) and read 4414 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.


User currently offlineUnited4ever From United States of America, joined Dec 2003, 291 posts, RR: 2
Reply 16, posted (10 years 3 months 3 weeks 5 days 1 hour ago) and read 4390 times:

Perhaps it could use the outer two as boosters for take off and climbing (a la Trident) and to circumvent ETOPS rules, but cruise as a twin?

Mike


User currently offlineGigneil From United States of America, joined Nov 2002, 16345 posts, RR: 86
Reply 17, posted (10 years 3 months 3 weeks 5 days ago) and read 4305 times:

It really isn't necessary. Planes are intentionally not overpowered.

Larger engines definitely don't cause a faster cruise flight.

Carrying the extra two engines turned off would be a huge aerodynamic drag and substantial weight. Its better to cruise with their 4 less powerful ones.

N


User currently offlineB2707SST From United States of America, joined Apr 2003, 1369 posts, RR: 59
Reply 18, posted (10 years 3 months 3 weeks 5 days ago) and read 4210 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.

NASA diagram:



--B2707SST



Keynes is dead and we are living in his long run.
User currently offlineDufo From Slovenia, joined May 1999, 792 posts, RR: 4
Reply 19, posted (10 years 3 months 3 weeks 4 days 23 hours ago) and read 4083 times:



not bad!
(with all respect to the photographer).

Regards



I seriously think I just creamed my pants without any influence from any outside variables.
User currently offlineBronko From United States of America, joined Jul 2001, 810 posts, RR: 12
Reply 20, posted (10 years 3 months 3 weeks 4 days 23 hours ago) and read 4010 times:

That's the first time one of my pics has been photoshopped...  Smile

Sorry for the poor picture quality, I was very new to photography at the time, and the lighting conditions were not that great.

Also, the 777-300ER, with the most powerful of GE90's, is VERY quiet. I stand maybe a hundred yards from it taking off at BFI, and I swear the old learjets are louder. It is an amazing engine.



Jet City Aviation Photography
User currently offlineKGAI From United States of America, joined Dec 2003, 120 posts, RR: 0
Reply 21, posted (10 years 3 months 3 weeks 4 days 19 hours ago) and read 3766 times:

Clearance would be a problem for sure. When GE flew the 747 testbed for the GE90-115, they landed on the right gears first in order to avoid an engine strike.

User currently offlineCha747 From United States of America, joined Dec 2003, 781 posts, RR: 6
Reply 22, posted (10 years 3 months 3 weeks 4 days 14 hours ago) and read 3500 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
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