Member log in
Register
 


        
 
 

| Home >> Forum >> A 747 with 2 engines

0 item in your cart
Search :  

A 747 with 2 engines

Return to the forum index
Post a message for this thread

Share |
   
speedbird9468

Joined:
01 Jan 1970
Number of messages:

  Topic: A 747 with 2 engines - Sent 12 Mar 23:53

I often wonder if a 747 could be developed with 2 engines. My reason is that we see the 777, A350, and in general loads of twin engined ultra long routes being flown. I'm sure the engine makers could come up with something.

User profil Private message Suggest deletion    
   
   
EI-DUB

Joined:
05 Jan 2007
Number of messages:
447
  Topic: A 747 with 2 engines - Sent 12 Mar 1:17

I could be mistaken, but I am fairly sure I heard that a 747 and a 777-300 are basically the same fuselage, obviously without the hump, so you basically have a 747 there with two engines, so the R+D costs probably would prohibit such a development when there is a very close alternative already available.


User profil Private message Suggest deletion  
   
DEMIS

Joined:
16 Jul 2006
Number of messages:
157
  Topic: A 747 with 2 engines - Sent 12 Mar 6:07

I believe from engineering point of view , that such a modification is impossible , since this , probably would mean a redesign from almost scratch paper and thus for a plane that has been around almost 40 years , would mean an unjustifiable feasibility study.
Besides with new models coming out soon (i.e.787-XXX) , I don't think there is such a market share , that a modified 747 could fit in.


User profil Private message Suggest deletion  
   
FLX

Joined:
26 Apr 2007
Number of messages:
2377
  Topic: A 747 with 2 engines - Sent 12 Mar 12:36

This is an interesting question and actually, I hv been trying to figure out exactly why so many major airlines are replacing their 744s with 773s/77Ws. Some key observations:

1. In terms of max cabin width, 747 is wider than 777 throughout most of the maindeck length(e.g. 10abreast vs 9abreast in Y-class) so fuselage design can't be the same. However, 747 nose+tail shapes are much more tapered/curved-in(In other words, more streamlined externally) than 777 and therefore less space.

2. In terms of available cabin floor space/max seats, a 744(Biggest 747 variant today) is still a bit bigger than a 773/77W. EI-DUB is right about the 747 hump(Especially for the older 741/742 which has a tiny upperdeck). Without the upperdeck mini-cabin, a 773/77W has nearly the same cabin space as a 744.

3. The way space is used today on 773/77W is a lot more efficient than in the past on any 747s:
a) Stair connecting both decks on any 747 takes up significant floor space that could hv be used for revenue seats.
b) Unlike any current 747, Boeing has designed the 77W's spacious crown area above the main deck as crew rest areas(A must for extra/ultra long range flights) connected by tiny ladders(Ok for crew) to the maindeck. This is a popular option for many 77W operators as it free-up valuable space on the maindeck.

4. In terms of belly cargo space, any 747 is significantly smaller than 773/77W and only a bit bigger than all 772 variants. It should be noted that air cargo is a much bigger rev$ generator in pax flights today than 40yrs ago when the 1st 747 was under development.

5. Max total thurst of a 744 is about 240,000lbs fm 4 turbofans. Max thurst of a 77W is about 230,000lbs fm only 2 GE90s. Yet in terms of fuel burn, 77W is about 60% of 744 for a typical long range mission.

6. 744 EIS in 89(Even the latest 744ER came out not long after that) while the GE90-115B(The most powerful turbofan in the world) on the 77W debuted in 2004. Such powerful engine was simply not available 15yrs ago.

7. The upcoming 748F/I(2009-10) is a significantly bigger/heavier jet than the current 744 or 77W that requires even higher total max thrust level(Over 280,000lbs). If use only 2 turbofans, it means each must produce at least 140,000lbs - nearly 22% increase over the GE90-115B and well over the design limit of the GE90 family architecture(Already the biggest in the world).

8. GE90 is by far the most costly engine family project GE has ever developed. They started with the GE90-85(Max thrust about 85,000lbs) back in the late 80s for the earlier/smaller 772s and took them over a decade to arrive @ the GE90-115B for the latest/heaviest 77W.

We really hv to appreciate how big/expensive a tech leap is required for a 22% increase in thrust. It can never be acheived by small tweaks of the existing GE90-115B(In many ways, the ultimate GE90). GE has to come up with a completely new family design which can take over a decade to develop and won't meet the development schedule of the next 748F/I. And we can forget about RR and PW. Both are totally tied-up with smaller thrust engine projects(e.g. RR's Trent XWB turbofan for the future A350-1000 is planned not to require as much thrust) and neither has announced projects that will yield thrust level equivalent or higher than GE90-115B.

I think by the time the engine makers come up with something, Boeing will hv abandoned any further 747 development long time ago(When the 748I EIS in 2010, the whole 747 program will be over 45yrs old!).


User profil Private message Suggest deletion  
   
FLX

Joined:
26 Apr 2007
Number of messages:
2377
  Topic: A 747 with 2 engines - Sent 12 Mar 16:00

Are U guys aware that early 747s sometimes fly with 5 engines?

Early 747s are designed with an extra engine attachment point under the wing and between the fuselage and the 1st portside engine closest to the fuselage. This is for ferrying a spare engine to busy overseas airports located far away fm main op bases. In those days, oversized air freighters and well-stocked spare part centers/bases were uncommon around the world. I hv seen old photos of a NW 741 taking-off with 5 engines on the way fm the U.S. to HND(The old Int'l gateway to Tokyo) and I couldn't believe my eyes!


User profil Private message Suggest deletion  
   
speedbird9468

Joined:
01 Jan 1970
Number of messages:

  Topic: A 747 with 2 engines - Sent 13 Mar 0:50

Ok then what about if a six holer was designed like the An224 i believe. Imagine 4 decks 3 for pax 1 for cargo


User profil Private message Suggest deletion  
   
FLX

Joined:
26 Apr 2007
Number of messages:
2377
  Topic: A 747 with 2 engines - Sent 13 Mar 7:40

Yes, imagine 1hr for boarding/disembarking, extra long queue @ security+immigration+custom, below deck baggage space needed for 3decks of pax, wait upto hrs @ the baggage claim, no room to sit or stand @ the departure gates even in the most modern terminal designs today, etc., all are truly romantic images we can associate with flying on a giant jet into ultra-busy superhubs(The only places where such jet make economic sense for an airline)......

When I was younger, I adored flying on jumbo jets - basically the bigger the better. Remember all those revolutionary cabin feature possibilities(e.g. Gym, lounge, internet cafe, shopping arcade, private mini cabin, etc.) Airbus shown us in the 388 cabin mock-up? In service, only a little of those survived in the ultra-premium F-class on SQ's 388 while the remaining pax continue to fly in a cabin environment, frankly, little different than in a 346,77W or 744. I suspect all other 388 operators(Except may be EK which even industry experts don't exactly know how they breakeven, let alone being profitable) will follow a similar set-up as SQ is already THE benchmark in premium inflight products.

As long as oil prices stay high and airlines continue to focus on short-term profit to keep their stock prices fm falling in the nex financial quarter, ultra-large jet is pretty meaningless to pax like me-the avg Joe.....


User profil Private message Suggest deletion  
   
captain bill

Joined:
07 Oct 2006
Number of messages:
3394
  Topic: A 747 with 2 engines - Sent 13 Mar 17:50

re the first question about 747 with two engines. It would cost a fortune to do as the wing would need to be re-designed which would mean a different spar which would mean a redesign of the section of the fuselage that carries the spar. Then there is all the hydraulics and electronics and uncle Tom Cobbly and all so it would be more cost effective to design and build a new airliner.

Yes I remember speaking with Pan-Am in the late 1960s and they reckoned they could even fit a swimming pool.

Captains log star date 2345 the Star Ship Enterprise is grounded so we can change the chlorine in the swimming pool. beam me up Scottie.


User profil Private message Suggest deletion  
   
FLX

Joined:
26 Apr 2007
Number of messages:
2377
  Topic: A 747 with 2 engines - Sent 14 Mar 12:53

Yes, it would be more cost effective to design and build a new airliner which Boeing did and calls it 77W. In many ways, 77W IS the modern 747 with 2 engines minus the upperdeck. Both do essentially the same type of job.

I'm old enough to remember that the basic 747 concept was originally developed for the USAF ultra-large transporter proposal. The upperdeck cockpit+a nose cargo door was Boeing's solution to meet the quick loading/unloading requirements. After Lockheed C5 won the contract, Boeing converted the concept into a civilian airliner with minimum design changes(e.g. Retaining upperdeck cockpit) to save R&D costs. It was PanAm, not Boeing, which suggested to use the tiny space behind the cockpit as a pax lounge and later for a few more seats(Boeing initially planned to use it for crew rest).

If the 747 program didn't hv a military background, I truly believe Boeing would hv designed it in a structurally simpler single deck layout, again, to save cost+weight and suffer only a tiny lost in cabin space. It would hv looked something like a 77W but definitely with 4 engines. In those days when 747 already struggled for the lack of power+reliability fm 4 engines, any aerospace engineer who dared to propose the crazy idea of 2 engines for such a large jet would probably get fired! Today, thurst produced by a single GE90-115B is equal to the total fm nearly 2.5 engines on early 747 or about 6.8 engines on early 707. The gains in reliability are even more staggering.

Isn't it amazing that after 35yrs, 2 engines are not only possible for a jet of similar capabilities, it's fast becoming critical to hv no more than 2 engines(I feel a bit sorry for the A346)?


User profil Private message Suggest deletion  
   
speedbird9468

Joined:
01 Jan 1970
Number of messages:

  Topic: A 747 with 2 engines - Sent 14 Mar 15:05

Me 2 I love that plane and the A345


User profil Private message Suggest deletion  
   
captain bill

Joined:
07 Oct 2006
Number of messages:
3394
  Topic: A 747 with 2 engines - Sent 15 Mar 3:52

I remember during my Rolls Royce days doing tests on the RR Conway that powered the old B.O.A.C. / British Airways Boeing 707-436 and the Rolls Royce RB-211 that powered the 747 and the conclusion was that all 4 RB-211s used the same amount of fuel per hour as did 2 Conway's so the old 707 was using twice as much fuel over the same route as the 747.

Engine technology today is fantastic and with the massive reduction in noise, fuel burn and low maintenance with only two engines the sky is the limit.


User profil Private message Suggest deletion  
   
FLX

Joined:
26 Apr 2007
Number of messages:
2377
  Topic: A 747 with 2 engines - Sent 17 Mar 4:54

captain bill:
My info could be a bit outdated but I think 2 airlines are still running scheduled 707 pax flights. 1 in Argentina(May be Aerolineas or something like that) and the other in Iran(May be Iran Air or something like that).

On one hand, we've VS, CO and others embarking on cutting-edge bio-fuel demo projects to save our planet(Ok, these could be just PR stunts..) and their own bottomlines(Now, that's core Corp objectives..). On the other hand, we've these 707 flights probably 4-6Xs more effective in spilling emissions than a single 777/A333 flight and these 707 operators which obviously got $ to burn QUICKLY or receive free gasoline fm their gov'ts..... Such a diverse avaition world we hv today!

Sometimes I wonder what if the world didn't hv deregulation+national airline privatization or major flag carriers continued to receive subsidies fm gov'ts or oil prices remain low? Would we still see advances in propulsion tech as amazing and as quickly as we've got today? Would Boeing and Airbus be interested in developing 2-engine jumbo jets at all?


User profil Private message Suggest deletion  
   
John in Brisbanw

Joined:
01 Jan 1970
Number of messages:

  Topic: A 747 with 2 engines - Sent 23 May 3:57

The biggest issue I think is single engine performance. The twin version of the 747 would need to be able to continue the flight after an engine failure at the worst possible point of the take off roll and climb to a safe height for a return for landing. As a 4 engine aircraft, losing an engine is a 25% loss of thrust only. As a twin I would imagine that it would need more than the 115K pounds of thrust from the big GE. If that engine has the capacity to produce more power for a limited period of time, maybe it would work. A more realistic option is the 727 or md-10 config triple - there is a fuel and maintenance saving without the need for engines that exceed current tech.


User profil Private message Suggest deletion  
   
FLX

Joined:
26 Apr 2007
Number of messages:
2377
  Topic: A 747 with 2 engines - Sent 26 May 4:22

John in Brisbanw:
Assuming 77W is essentially<The twin version of the 747>, then single engine takeoff performance has been proven & certified as a non-issue. At MTOW, a 77W is significantly lighter than a 744<Less airframe weight, less fuel onboard for similar range/payload performance, etc.>. Yet in terms of max total thrusts, there're only about 4% diff between 77W<230k lbs> and 744<240k lbs>. So @ takeoff, it's easy to image a 77W hv plenty of<surplus> power relative to a 744. All these before we even begin to consider the airfoil lift efficiency gains of basically a 1990 wing design over a 1960 wing design. For these reasons, a 77W hv sufficient power+speed to continue takeoff safely if 1 engine shutdown completely<Losing 50% total max thrust> after V1<i.e. Takeoff abort speed>.

Of course, if U're just talking about a straight-forward re-engining of a 744 fm 4 turbofans to 2turbofans and retaining everything else on the 744, it won't work even with the mightly GE90-115B. However, that doesn't seem like what U're talking about since your proposed option include 727-like or MD11-like tri-jet config which is a much greater/more complex departure from the 747 layout than the 777 family....just ask any ex-MD tailfin structural engineers, they'll tell U how complex/difficult/costly to accomodate a centerline engine design layout on the D10/M11 tail. I STRONGLY believe that because if a tri-jet option is easy or financially realistic, we would hv seen the 380 in that layout sporting 3 GE90-115Bs producing 345k lbs total max thrust that's @ least 25k lbs more than today's most powerful 380 variant in reality.


User profil Private message Suggest deletion  

Acces Restriction

It is not possible to post messages to the forum for the moment



Airfleets.net 2002-2014

[Contact] [Privacy Policy] [Disclaimer] [Advertisement]


The Airport Game - Tourism in Ibiza - Tourisme Ibiza - Tourism in Menorca  
AVIATION TOP 100 - www.avitop.com Avitop.com