Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
ZapZac1027
Topic Author
Posts: 3
Joined: Sun Feb 16, 2020 8:44 am

Can A Boeing 747-8 Be A Trijet?

Fri Feb 28, 2020 9:58 am

Hey again. Recently I was thinking that with modern technology and powerful engines like the GE90 and GE9X, can the 747-8 be powered by three engines? Although it's definitely not practical to convert it into a trijet because of a big redesign of the wings and vertical stabilizer, do three engines have enough thrust to power a 747-8?
 
User avatar
calstanford
Posts: 70
Joined: Mon Dec 04, 2017 2:16 pm

Re: Can A Boeing 747-8 Be A Trijet?

Fri Feb 28, 2020 10:02 am

With the big hump of the upper deck, no. It wouldn't make any sense. Thrust wise yea sure. 747-8i uses 4x66,500 lbf (296 kN) GEnx-2B67 engines. You could put 3x GE9X at 105,000lbf on theoretically.
 
SpaceshipDC10
Posts: 7014
Joined: Tue Jan 01, 2013 11:44 am

Re: Can A Boeing 747-8 Be A Trijet?

Fri Feb 28, 2020 10:07 am

ZapZac1027 wrote:
Hey again. Recently I was thinking that with modern technology and powerful engines like the GE90 and GE9X, can the 747-8 be powered by three engines? Although it's definitely not practical to convert it into a trijet because of a big redesign of the wings and vertical stabilizer, do three engines have enough thrust to power a 747-8?


I guess it could but would it be worth it? No. Be it to convert or design from the begining a 748-like aircraft with a tail engine means adding lots of structure to support the added tail weight and thrust coming form the engine you want to install there. Also, on the maintenance side, it's less easy and more costly to maintain a tail engine.
 
User avatar
DarkSnowyNight
Posts: 2673
Joined: Sun Jan 01, 2012 7:59 pm

Re: Can A Boeing 747-8 Be A Trijet?

Fri Feb 28, 2020 10:16 am

SpaceshipDC10 wrote:

I guess it could but would it be worth it? No. Be it to convert or design from the begining a 748-like aircraft with a tail engine means adding lots of structure to support the added tail weight and thrust coming form the engine you want to install there. Also, on the maintenance side, it's less easy and more costly to maintain a tail engine.


Also, the CG will shift quite a lot. It will likely need to retain the 744 structure aft of the wings, with a 748 (or longer still) fwd of the LE spars.

It would be beyond the scope of an STC, so it would have to be a new airplane. As a legal matter, I doubt that's actually possible given the amount of exit-structure grandfathering in existing 747s.

Though, and I cannot stress this enough, it would look really, really cool.
"Nous ne sommes pas infectés. Il n'y a pas d'infection ici..."
 
pillowtester
Posts: 150
Joined: Fri Nov 12, 2004 9:44 am

Re: Can A Boeing 747-8 Be A Trijet?

Fri Feb 28, 2020 10:29 am

I feel like I'm seeing so many absurd hypotheticals lately. The trijet layout disappeared in the 90s because it's a maintenance headache. It will never come back, and we shouldn't want it to.

If you want to get excited about the future, let's talk about the incredible engineering feats that go into reducing the industry's carbon footprint (one of the worst) — and further out, speculate about what post-fossil fuel aviation might look like?
MÜVI Patient Education is the first 4K dental patient education video system. If you are looking for patient education videos for dentists or want to play dental videos in your waiting room, discover what MÜVI can do for your practice!
 
VSMUT
Posts: 4483
Joined: Mon Aug 08, 2016 11:40 am

Re: Can A Boeing 747-8 Be A Trijet?

Fri Feb 28, 2020 10:34 am

Only just. With one engine out, the 747-8 generates 200.000 lb of thrust. With one engine out, 2 GE9Xs would deliver 210.000 lbs.
 
djpearman
Posts: 17
Joined: Thu Feb 06, 2020 9:02 pm

Re: Can A Boeing 747-8 Be A Trijet?

Fri Feb 28, 2020 11:50 am

Also, the weight of the tail engine reduces the aircraft's payload by that amount. Since payload is how airlines make their money, this means less revenue.
 
steeler83
Posts: 7700
Joined: Sat Feb 25, 2006 2:06 pm

Re: Can A Boeing 747-8 Be A Trijet?

Fri Feb 28, 2020 1:02 pm

pillowtester wrote:
I feel like I'm seeing so many absurd hypotheticals lately. The trijet layout disappeared in the 90s because it's a maintenance headache. It will never come back, and we shouldn't want it to.

If you want to get excited about the future, let's talk about the incredible engineering feats that go into reducing the industry's carbon footprint (one of the worst) — and further out, speculate about what post-fossil fuel aviation might look like?

Suppose they develop a jet engine that runs on hydrogen - regarding the future of aviation, that's an area where I think aviation is headed. That's a topic for a different discussion.

But... on the subject of 3- and 4-engine aircraft, those days are pretty much history. The 777 killed the DC10/MD11 when it was first launched. Now, when the program was conceived, it was a tri-jet model. Boeing abandoned that idea due to ETOPS; the tail engine was therefore redundant. Improvements and larger variants lead to the demise of the 747/A380 line. Two engines can carry roughly the same amount of people the same distance as a 748. Plus, with the 787 and A350 programs, the airlines can use this equipment to fly more long-haul P2P routes rather than funneling passengers through their "mega" hubs. Plus, airlines favor frequency over capacity.
Do not bring stranger girt into your room. The stranger girt is dangerous, it will hurt your life.
 
User avatar
PatrickZ80
Posts: 4270
Joined: Tue Jul 13, 2010 5:33 am

Re: Can A Boeing 747-8 Be A Trijet?

Fri Feb 28, 2020 5:39 pm

It would be easier to convert the 747-8 into a twin than into a tri-jet. That's essentially the idea of the A330 and A340, where except for the engines it's nearly the same aircraft. An A340 could be converted into an A330 by simply removing the outer engines and replacing the inner ones with larger more powerful ones (and of course a lot of other small modifications). The same could be done with the 747-8.

However adding a third engine in the center would cause a giant problem. If it needs to be mounted on the tail, the whole structure would need to be reinforced in order to support the weight of that engine. Because of that, the wings would need to be re-aligned placing them further to the rear of the fuselage. Such huge adaptions would basically make it a whole new aircraft.

And is a third engine really needed? I suppose not. Engines with near double the power of an existing 747-8 engine can be developed. That would make the 747-8 just as powerful on two of those engines than it is on 4 of it's current engines. If you'd convert it into a twin like the A340 - A330 conversion, this would also mean a lot of the internal wing structure that is needed to support the weight of the outer engines can be removed. That would reduce weight on the aircraft.
 
VSMUT
Posts: 4483
Joined: Mon Aug 08, 2016 11:40 am

Re: Can A Boeing 747-8 Be A Trijet?

Sat Feb 29, 2020 11:22 am

PatrickZ80 wrote:
And is a third engine really needed? I suppose not. Engines with near double the power of an existing 747-8 engine can be developed. That would make the 747-8 just as powerful on two of those engines than it is on 4 of it's current engines. If you'd convert it into a twin like the A340 - A330 conversion, this would also mean a lot of the internal wing structure that is needed to support the weight of the outer engines can be removed. That would reduce weight on the aircraft.


No, doesn't work like that. Remember the single engine out issue. Your 747-8 twin needs a lot more than just twice as powerful engines. Each engine will need the power of at least 3 747 engines.

Which is why this simplistic talk about twin engines being automatically superior is complete nonsense. Bigger engines burn more fuel, regardless of whether or not you use that power under normal conditions, and at some point 4 smaller engines will be superior to 2 massive ones.
 
IADCA
Posts: 2181
Joined: Mon Feb 26, 2007 12:24 am

Re: Can A Boeing 747-8 Be A Trijet?

Sun Mar 01, 2020 6:22 pm

PatrickZ80 wrote:
It would be easier to convert the 747-8 into a twin than into a tri-jet. That's essentially the idea of the A330 and A340, where except for the engines it's nearly the same aircraft. An A340 could be converted into an A330 by simply removing the outer engines and replacing the inner ones with larger more powerful ones (and of course a lot of other small modifications). The same could be done with the 747-8.

However adding a third engine in the center would cause a giant problem. If it needs to be mounted on the tail, the whole structure would need to be reinforced in order to support the weight of that engine. Because of that, the wings would need to be re-aligned placing them further to the rear of the fuselage. Such huge adaptions would basically make it a whole new aircraft.

And is a third engine really needed? I suppose not. Engines with near double the power of an existing 747-8 engine can be developed. That would make the 747-8 just as powerful on two of those engines than it is on 4 of it's current engines. If you'd convert it into a twin like the A340 - A330 conversion, this would also mean a lot of the internal wing structure that is needed to support the weight of the outer engines can be removed. That would reduce weight on the aircraft.


"Near doubled" wouldn't get you there. It would need to be more than doubled because you'd need to be able to take off on only one of them. The 747-8 has a MTOW that's more than 1.25x that of the 777-9, so you'd need something significantly larger and more powerful than the GE9X. And an engine that large (at least with the same bypass ratio as the GE9X) wouldn't fit under a 747 wing - even the 744 carrying the 9X test engine had to be significantly modified for it to take the engine.

Who is online

Users browsing this forum: PERA346 and 35 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos