Moderators: jsumali2, richierich, ua900, PanAm_DC10, hOMSaR

 
mjoelnir
Posts: 9411
Joined: Sun Feb 03, 2013 11:06 pm

Re: How come quads outlasted trijets?

Sun Sep 23, 2018 11:53 pm

trnswrld wrote:
Someone above mentioned the A300.... Can anyone explain to me why the A300 didn't seem to do anywhere near as well as the 767? I know the A300 came out first, but what made the 767 more successful? I know it was early off in the game for Airbus, did that have anything to do with it? My understanding is that neither the A300 or the early 762 models had spectacular range. Did the A330 come along soon enough to where that was more or less Airbus' answer for their own airplane? Just looking for a little more info on that subject.


The A300/310 did not do to bad. It was quite a bit older frame than the 767 and was already replaced by the A330, when the 767 sold in numbers.
 
Dominion301
Posts: 2894
Joined: Wed Jul 20, 2016 1:48 pm

Re: How come quads outlasted trijets?

Mon Sep 24, 2018 3:54 am

neomax wrote:
So everyone talks about fuel efficiency as the reason for downsizing to twins from quads. But twins are a relatively new phenomenon and even then, there is still a healthy number of pax quads flying around but zero pax trijets. By that logic, shouldn't quads have disappeared first? Trijets are more efficient than similarly sized quad counterparts so what gives? A340's, 747's, and A380's are rare but not that rare. But DC10's, L1011's, and 727's by comparison are a thing of the past and almost seem to have disappeared too quickly. Is it just me or have trijets vanished before the true end of their usable lifespan?


Actually pax carrying 727s are not yet a thing of the past. You can still catch a couple in Iran with Iran Aseman...probably for at least a couple more years now that the US embargo is back.

Also, aren’t there a couple of YAKs still kicking around Russia?...along with the charter TU-154 ops hanging on by a thread.
 
User avatar
seahawk
Posts: 9852
Joined: Fri May 27, 2005 1:29 am

Re: How come quads outlasted trijets?

Mon Sep 24, 2018 7:21 am

A quad is nice for the bending moments in the wing and the wingbox, a Trijet is bad for the structure in the fuselage.
 
SpaceshipDC10
Posts: 7054
Joined: Tue Jan 01, 2013 11:44 am

Re: How come quads outlasted trijets?

Mon Sep 24, 2018 10:51 am

chornedsnorkack wrote:
Why were DC-10 and Tristar ever invented as trijets in the first place? Couldn´t a small widebody quadjet like Il-86 (but with better engines!) have worked?


To be some sort of an air bus, that is a large widebody airplane but still smaller than the 747. From the back of my brain I remember reading that McDonnell Douglas proposed their DC-10 to be a twinjet but AA really wanted a trijet. Back then it was still a cheaper option than having either an oversized 747 or multiple 707s plying on a route. Then the Europeans launched their air bus, the A300, with a capacity of 300 seats to serve on trunk routes, hence the Airbus name.
 
Max Q
Posts: 8631
Joined: Wed May 09, 2001 12:40 pm

Re: How come quads outlasted trijets?

Mon Sep 24, 2018 11:26 am

spacecadet wrote:
A lot of people have hit on reasons that I think are valid - it wasn't just one thing. But I think you also have to consider that every trijet was its own unique animal. They weren't all retired en masse, they were retired one by one, for their own reasons, but usually because a more efficient replacement came along. And in the case of existing trijets, those replacements came in the form of twinjets, which are pretty much always going to be more efficient.

That recalibrates the question a little bit to "why didn't new trijets replace old quads?" And the answer there is still mainly "because those quads were replaced with twins", although in some cases, they were replaced with newer quads either because four engines were needed for performance reasons (the A380) or because it was cheaper to adapt an existing design (the later 747 variants) than to create a new twin of the same size.

That just leaves the loose end of why those individual trijet designs were each dead ends while we're still getting updated 737's and 747's, and that question is covered by some of the earlier answers regarding maintenance and other things. One thing I've not yet seen mentioned is that the larger trijets often had/have weight restrictions on various runways at various airports because of that rear center-mounted engine, which concentrates the weight in the center of the airplane. I'm not sure if this could have been overcome in time with different gear designs, but I know that at least at some airports, a much heavier 747 could land with no restrictions whereas an L-1011 could only land at something like 511,000 lbs. or less. And this is also why the later DC-10 variants had that center gear, to spread and carry the weight a bit more evenly. So this is at least a concern with trijets that doesn't exist with quads or twins.




That makes no sense, the entire
weight of an aircraft is transmitted
to the ground through its landing gear


No matter where that weight is situated.
Now certain airports have pavement
restrictions that limit how much weight
can be imposed by each wheel or axle


That would explain lower limits for some
L1011 models with its twin bogie gear
configuration at a few airports
(LGA was one )


The 747 with its quad bogies and weight
spread over sixteen main wheels and two
nose wheels has a big advantage here


The heaviest DC10’s were quite a bit heavier than even the -500 version of
the Tristar and needed that center
gear to spread the load


It had nothing to do with engine
location
The best contribution to safety is a competent Pilot.


GGg
 
WIederling
Posts: 9580
Joined: Sun Sep 13, 2015 2:15 pm

Re: How come quads outlasted trijets?

Mon Sep 24, 2018 11:46 am

"And this is also why the later DC-10 variants had that center gear, to spread and carry the weight a bit more evenly. So this is at least a concern with trijets that doesn't exist with quads or twins."

The A340 has a third (middle) MLG leg too.

But "not taking the forces for a walk" is good engineering.

The wing already is designed to carry lots of load.
Why would you want to walk the forces from a tail engine through the
hull and into the wingbox when you
could hang a pair ( or 4 ) from the wings _and alleviate flight loads
on the wing_ in the process?

engines mounted away from the wings allows a more ideal design
for the basic wing and especially for high lift devices. ( unbroken flap line vs thrust gate.)
( But you can achieve that with wing hung engines too: See the Airbus wingdesigns.)
Murphy is an optimist
 
B8887
Posts: 457
Joined: Sun Sep 30, 2012 9:47 pm

Re: How come quads outlasted trijets?

Mon Sep 24, 2018 6:30 pm

Because the performance of twins made trijets themselves quickly obsolete as they are now.

I've started a thread many moons ago called "Not Enough Credit Given To The GE90?"... as I also think this is an interesting question.

Regards.

B8887

..
 
Max Q
Posts: 8631
Joined: Wed May 09, 2001 12:40 pm

Re: How come quads outlasted trijets?

Tue Sep 25, 2018 7:37 am

WIederling wrote:
"And this is also why the later DC-10 variants had that center gear, to spread and carry the weight a bit more evenly. So this is at least a concern with trijets that doesn't exist with quads or twins."

The A340 has a third (middle) MLG leg too.

But "not taking the forces for a walk" is good engineering.

The wing already is designed to carry lots of load.
Why would you want to walk the forces from a tail engine through the
hull and into the wingbox when you
could hang a pair ( or 4 ) from the wings _and alleviate flight loads
on the wing_ in the process?

engines mounted away from the wings allows a more ideal design
for the basic wing and especially for high lift devices. ( unbroken flap line vs thrust gate.)
( But you can achieve that with wing hung engines too: See the Airbus wingdesigns.)




That is good perspective and
very well put
The best contribution to safety is a competent Pilot.


GGg
 
Armadillo1
Posts: 582
Joined: Thu Apr 20, 2017 5:14 pm

Re: How come quads outlasted trijets?

Tue Sep 25, 2018 8:26 pm

the question of this topic actually still is why a380 not a trijet. (not a twin because of small market for engine)
and posts above not uncover this for 100%

few years ago airbus guy says tail engines not as bad as common thinks, as it helps to make nose longer with same rotation angle. even after 346 they still think its a good idea
380 wing with 4 trust gates not as good as other airbus wings, in addition for lower aspect ratio

also, 380 still fliyng over north pole where 777 cant
 
GalaxyFlyer
Posts: 6708
Joined: Fri Jan 01, 2016 4:44 am

Re: How come quads outlasted trijets?

Tue Sep 25, 2018 8:30 pm

Triple 7s certainly do fly polar routes.

GF
 
Armadillo1
Posts: 582
Joined: Thu Apr 20, 2017 5:14 pm

Re: How come quads outlasted trijets?

Tue Sep 25, 2018 8:54 pm

you can see at f24 emirates 380 DXB-LAX through Iran-pole and Qatar 777 DOH-LAX through Murmansk
 
User avatar
flyingclrs727
Posts: 2678
Joined: Thu Apr 19, 2007 7:44 am

Re: How come quads outlasted trijets?

Wed Sep 26, 2018 5:48 am

What I don't understand is why McDonnell Douglas never developed a twin engined derivative of the DC-10. There were proposals to do just that. Such a plane would have benefited from commonality and economies of scale with the trijet version. It would have been positioned to take advantage of the improvements in high bypass engine technology. A twin DC-10 derivative could have eventually evolved into a 777 type role.
 
User avatar
flyingclrs727
Posts: 2678
Joined: Thu Apr 19, 2007 7:44 am

Re: How come quads outlasted trijets?

Wed Sep 26, 2018 6:01 am

Armadillo1 wrote:
the question of this topic actually still is why a380 not a trijet. (not a twin because of small market for engine)
and posts above not uncover this for 100%

few years ago airbus guy says tail engines not as bad as common thinks, as it helps to make nose longer with same rotation angle. even after 346 they still think its a good idea
380 wing with 4 trust gates not as good as other airbus wings, in addition for lower aspect ratio

also, 380 still fliyng over north pole where 777 cant


What are you talking about? There plenty of polar 777 routes. With ETOPS-330, the only part of the world off limits to twins is the interior of Antarctica. There is no commercial reason to overfly the middle of Antarctica anyway.
 
Armadillo1
Posts: 582
Joined: Thu Apr 20, 2017 5:14 pm

Re: How come quads outlasted trijets?

Wed Sep 26, 2018 12:59 pm

Ok, let it be about qatar issue only
 
GalaxyFlyer
Posts: 6708
Joined: Fri Jan 01, 2016 4:44 am

Re: How come quads outlasted trijets?

Wed Sep 26, 2018 2:09 pm

No, let it be that ULRs have daily variations in routing depending on winds, ETOPS availability, flight planning engines having different parameters, national bilaterals, etc.

GF
 
User avatar
NameOmitted
Posts: 929
Joined: Sun Oct 23, 2016 7:59 pm

Re: How come quads outlasted trijets?

Wed Sep 26, 2018 3:17 pm

A similar question might be why no more rail mounted engines? There are many reasons for wing mounted engines, and if you've made that choice, it's logical to design in pairs.
 
USAirKid
Posts: 739
Joined: Mon Jun 13, 2016 5:42 am

Re: How come quads outlasted trijets?

Wed Sep 26, 2018 6:57 pm

NameOmitted wrote:
A similar question might be why no more rail mounted engines? There are many reasons for wing mounted engines, and if you've made that choice, it's logical to design in pairs.


Last I checked there were still rail mounted engines. Here's a photo of one.

Image
 
User avatar
NameOmitted
Posts: 929
Joined: Sun Oct 23, 2016 7:59 pm

Re: How come quads outlasted trijets?

Wed Sep 26, 2018 7:42 pm

USAirKid wrote:
NameOmitted wrote:
A similar question might be why no more rail mounted engines? There are many reasons for wing mounted engines, and if you've made that choice, it's logical to design in pairs.


Last I checked there were still rail mounted engines. Here's a photo of one.


:D Of course. And how could I forget Bombardier’s jet train, based around the PW-150?

Image
 
User avatar
lightsaber
Moderator
Posts: 20903
Joined: Wed Jan 19, 2005 10:55 pm

Re: How come quads outlasted trijets?

Wed Sep 26, 2018 8:08 pm

GalaxyFlyer wrote:
trnswrld wrote:
Someone above mentioned the A300.... Can anyone explain to me why the A300 didn't seem to do anywhere near as well as the 767? I know the A300 came out first, but what made the 767 more successful? I know it was early off in the game for Airbus, did that have anything to do with it? My understanding is that neither the A300 or the early 762 models had spectacular range. Did the A330 come along soon enough to where that was more or less Airbus' answer for their own airplane? Just looking for a little more info on that subject.


The 767 had more growth potential than the A300 in terms of rangefor one thing. The A300 was designed to be a “ regional” jet, the region being high traffic intra-Europe routes, so it didn’t have the range that the 767 has. Also, until the -600; there was an engineer required.

GF

I would add the following:
1. 757, A320 and 737NG limited the market for a regional widebody. It wasn't just the 767, it was an attack from below (cost) and above (range).
2. Yes the cost of a 3rd pilot was a handicap.
3. The A310 cost to much for the payload. Shrinks tend to have short sales lives as PIPs reduce the cost of the stretches more (e.g., engine overhaul span, range increase for the stretch such as A333 to 5,700nm then 6,200nm reducing the A332 market quickly).
4. The engine improvements gave the 763ER enough extra range to be that much more flexible.

The same with trijets. The 757 doomed the 727. The 763ER and A300/310 doomed the DC-10 and L-1011. The 77E/A333 doomed the MD-11.

Then the 77W just smashed the trijet business case and the A332 finished off what little was left.

Drag is mostly at the wing. Transferring thrust to the wing adds weight. The third engine adds, in a widebody, 6+ tons of weight minimum versus a twin. Three engines will have worse cruise TSFC than a twin and the tri requires more thrust! There are scaling factors in engines (larger engines are just more efficient as there is less proportional tip losses, less internal drag area over thrust area and less mass per unit of thrust).

The A300 had the right idea, just not enough payload at range to take advantage of the cargo volume and not long enough to carry enough people to optimize the cross section. In many ways, the A330 is the A300NEO...

Now there is hope for a trijet: Boeing and Airbus favor Trijets for BWBs. Twin BWBs have issues NDAs prevent me from discussing. It is tri or quad (favored by other Airframers as the maintenance is simpler podding the engines in pairs).

Lightsaber
I cannot wait to get vaccinated to live again! Warning: I simulated that it takes 50%+ vaccinated to protect the vaccinated and 75%+ vaccinated to protect the vac-hesitant.
 
GalaxyFlyer
Posts: 6708
Joined: Fri Jan 01, 2016 4:44 am

Re: How come quads outlasted trijets?

Wed Sep 26, 2018 9:28 pm

Yes, twin take-off performance dictates relatively higher thrust engines which can become an advantage upon reaching cruise where the power comes back into the TSFC “bucket”. Where a tri and a quad are operating at higher thrust levels and further up the TSFC curve. A significant advantage to twins.



GF
 
User avatar
aerolimani
Posts: 1329
Joined: Tue Jun 18, 2013 5:46 pm

Re: How come quads outlasted trijets?

Wed Sep 26, 2018 10:55 pm

Didn't the A300-600 and the A310, with their two-man cockpits, both enter service within a year of the 767? There are a number of reasons (already stated by others) why the 767 did better, but I don't think it had much to do with the three-man cockpit of the original A300's.
 
Max Q
Posts: 8631
Joined: Wed May 09, 2001 12:40 pm

Re: How come quads outlasted trijets?

Thu Sep 27, 2018 2:23 am

Main reason is the 767 had
far superior range
The best contribution to safety is a competent Pilot.


GGg
 
KICT
Posts: 815
Joined: Fri Jun 16, 2017 11:54 pm

Re: How come quads outlasted trijets?

Thu Sep 27, 2018 2:41 am

I could be wrong, but maybe it had something to do with Lockheed nearly going out of business and McDonnell Douglas being bought out by Boeing?
People are saying. Believe me.
 
GalaxyFlyer
Posts: 6708
Joined: Fri Jan 01, 2016 4:44 am

Re: How come quads outlasted trijets?

Thu Sep 27, 2018 2:49 am

Lockheed California did go out did out of business —no more Lockheed commercial planes. Douglas was on the road to Chapter 11 when they were bought by McAir, so Boeing was the second rescue.

GF
 
User avatar
hOMSaR
Moderator
Posts: 2363
Joined: Tue Jan 19, 2010 4:47 am

Re: How come quads outlasted trijets?

Thu Sep 27, 2018 3:46 am

KICT wrote:
I could be wrong, but maybe it had something to do with Lockheed nearly going out of business and McDonnell Douglas being bought out by Boeing?



Not really. If the trijet was a good design/configuration, Boeing and/or Airbus would be building them.
I was raised by a cup of coffee.
 
KICT
Posts: 815
Joined: Fri Jun 16, 2017 11:54 pm

Re: How come quads outlasted trijets?

Thu Sep 27, 2018 3:53 am

hOMSaR wrote:
Not really. If the trijet was a good design/configuration, Boeing and/or Airbus would be building them.

You're absolutely right. Three engines is a horribly unsuccessful aircraft design with no future...




Image

https://boomsupersonic.com/
People are saying. Believe me.
 
LH707330
Posts: 2402
Joined: Fri Jun 15, 2012 11:27 pm

Re: How come quads outlasted trijets?

Sun Sep 30, 2018 10:46 am

When I was reading Norris and Wagner's book A340/330, they discuss the tradeoffs and bring up many points as to why Airbus selected the quad layout for the 340 when it did. Basically, it was structurally and aerodynamically better to do it that way, which contributed to the 340 killing the MD-11 in the market (so too did the fact that the MD-11 wing was outdated).

This raises the point: why were the DC-10 and L-1011 not designed as mini-A340s? The answer lies in who the initial customers were, what their mission spec was, and how big the market was. Both designs started out as transcon WBs that needed to be LGA-capable, so they were able to compromise on three engines. For those shorter hauls, the structural penalty of the three-holder design probably mattered less than the maintenance savings from 3 vs 4 engines, especially considering fuel prices back then. Moreover, I also wager that the engine OEMs were wary of doing an engine that couldn't be repurposed to other designs, considering that the market was smaller. The DC-10-30 and the 747-200B were near contemporaries, PW and GE were both putting their latest tech into boosting the thrust on their engines to increase the MTOW for these designs, and amortized the costs over both lines.
 
LH707330
Posts: 2402
Joined: Fri Jun 15, 2012 11:27 pm

Re: How come quads outlasted trijets?

Sun Sep 30, 2018 11:18 am

KICT wrote:
hOMSaR wrote:
Not really. If the trijet was a good design/configuration, Boeing and/or Airbus would be building them.

You're absolutely right. Three engines is a horribly unsuccessful aircraft design with no future...




Image

https://boomsupersonic.com/

I'm assuming your post was meant to be humorous, those trijets are all bizjets, where efficiency is much less important...
 
WIederling
Posts: 9580
Joined: Sun Sep 13, 2015 2:15 pm

Re: How come quads outlasted trijets?

Sun Sep 30, 2018 12:30 pm

Armadillo1 wrote:
380 wing with 4 trust gates not as good as other airbus wings, in addition for lower aspect ratio


There is no thrust gate on the A380. ( IMU none on any Airbus designed wing )
https://en.wikipedia.org/wiki/Flap_%28a ... rust_gates
( though the reasoning there is partly off ( to go from inboard double to single slotted outboard
and to allow for the inboard aileron fixup.)
with the low/no bypass tightly mounted jet engines the thrust gate was a must.
hot fast engine exhaust would have burned its own path otherwise :-)
Murphy is an optimist
 
User avatar
JBo
Posts: 1779
Joined: Wed Jan 05, 2005 7:23 am

Re: How come quads outlasted trijets?

Sun Sep 30, 2018 3:29 pm

Quads have outlasted trijets mainly because trijets are inherently more complicated and expensive to maintain due to the added complexity of the tail-mounted engine, so you either have the added maintenance complexity of a fourth engine, or you have the added maintenance complexity of a tail-mounted engine.

Past that, technology has improved such that most trijet airliners have been replaced by large twins with the same performance capability. Quads exist where the additional engine performance is needed (747, A380; the A340 has largely been rendered obsolete by newer twins).

Yes, there are still three-engined business jets, but it's also an entirely different situation when a corporation has a single (or select few) aircraft to maintain versus when an airline has an entire fleet to maintain.

Despite everyone's opinions on here, the answer is a practical fact: Trijets are unnecessarily complex from a maintenance standpoint when either large twins or smaller quads can get the job done just as well.
I'd take the awe of understanding over the awe of ignorance any day.
 
User avatar
lightsaber
Moderator
Posts: 20903
Joined: Wed Jan 19, 2005 10:55 pm

Re: How come quads outlasted trijets?

Sun Sep 30, 2018 5:59 pm

LH707330 wrote:
KICT wrote:
hOMSaR wrote:
Not really. If the trijet was a good design/configuration, Boeing and/or Airbus would be building them.

You're absolutely right. Three engines is a horribly unsuccessful aircraft design with no future...




Image

https://boomsupersonic.com/

I'm assuming your post was meant to be humorous, those trijets are all bizjets, where efficiency is much less important...

Another thought, most business jets do not get a custom engine. If more thrust is needed and two engines of sufficient thrust are not available, a tri-jet goes forward.

Boom is different, very few engines are candidates for supersonic. The fact GE is doing a custom low spool... surprises me (to be honest). But only of an existing in production engine that already has a variety of low spools available. 3 engines are required for an economic airframe.

But commercial, Western airframes had the success of the 727, L1011, and DC10/MD11.
727 was replaced by the 757 and now A321.
L1011 & DC10/MD11 were replaced by the 777, A330, and later 787/A350.

But the Falcon 9X is rumored to be a twin. Mainly as taking the 5X, errr... 6X to a larger level it is too complicated to create a new trijet. Let us see what happens. But everyone wanted part of RR's business jet market. Actually, no, GE and Pratt wanted the entire large business jet market. Pratt has the PW816 (so far all applications are derated a little) and the PW812 (which is getting a big boost thanks to Silvercrest issues). GE now has the high end (Passport of GE7500). RR has the Pearl defending the next tier down with competition from the *finally* certified G500 (and soon G600). The BR700 set the standard for owning a market, which in a way perpetuated the trijet due to the price premium RR was able to command (there never would have been a 7X if BR710 engines were less costly in my opinion).

Lightsaber
I cannot wait to get vaccinated to live again! Warning: I simulated that it takes 50%+ vaccinated to protect the vaccinated and 75%+ vaccinated to protect the vac-hesitant.
 
LH707330
Posts: 2402
Joined: Fri Jun 15, 2012 11:27 pm

Re: How come quads outlasted trijets?

Mon Oct 01, 2018 3:27 am

Another thought on trijets concerns the layouts: the Falcons and 727 are less disadvantaged relative to their same-config twin competitors, because all of those designs need to deal with the problems of tail-mounted engines, so it's a trade of maintenance and weight versus field performance (due to OEI limitations).

It's the DC-10/L10-11 layout that's really the most disadvantaged trijet from a structural standpoint.
 
MatthewDB
Posts: 172
Joined: Wed Oct 25, 2017 6:33 pm

Re: How come quads outlasted trijets?

Mon Oct 01, 2018 4:11 am

JBo wrote:
Past that, technology has improved such that most trijet airliners have been replaced by large twins with the same performance capability. Quads exist where the additional engine performance is needed (747, A380; the A340 has largely been rendered obsolete by newer twins).


Did the A380 have to be a quad? When the 747 came out, it had to be a quad because there were not engines big enough to make it a triple. The A380 might have been possible as a tri-jet, but the massive duct or tail structure (if they went DC-10 style) would certainly have been a difficulty. It think it was more about the troubles of a tri-jet that forced the A380 to be a quad, plus the possibilities of a stretch.
 
User avatar
flyingclrs727
Posts: 2678
Joined: Thu Apr 19, 2007 7:44 am

Re: How come quads outlasted trijets?

Mon Oct 01, 2018 6:30 am

MatthewDB wrote:
JBo wrote:
Past that, technology has improved such that most trijet airliners have been replaced by large twins with the same performance capability. Quads exist where the additional engine performance is needed (747, A380; the A340 has largely been rendered obsolete by newer twins).


Did the A380 have to be a quad? When the 747 came out, it had to be a quad because there were not engines big enough to make it a triple. The A380 might have been possible as a tri-jet, but the massive duct or tail structure (if they went DC-10 style) would certainly have been a difficulty. It think it was more about the troubles of a tri-jet that forced the A380 to be a quad, plus the possibilities of a stretch.


Boeing was considering a trijet configuration for the 747SP, but Pan Am wanted the SP sooner. If the SP had been built as a trijet, I'm sure Boeing would have considered larger trijet 747 versions. Imagine a 747 with 3 GE-90's borrowed from the 777.
 
User avatar
SomebodyInTLS
Posts: 1888
Joined: Wed Jun 15, 2016 12:31 pm

Re: How come quads outlasted trijets?

Mon Oct 01, 2018 11:40 am

Tri-jets were basically a solution for a regulatory environment that no longer exists.

If a twin was not allowed across oceans but a quad was too much engine => tri-jets.

ETOPS means twins now fill that role. Quads are still a solution where the amount of power you need would be impractical for a twin. Engines for an A380 twin would have to be huge (expensive, difficult to mount under the wing), unique to that aircraft (expensive, not worth the investment) and a step up in thrust (expensive, not worth the investment)... and did I mention expensive?
"As with most things related to aircraft design, it's all about the trade-offs and much more nuanced than A.net likes to make out."
 
RetiredWeasel
Posts: 816
Joined: Sat Jul 05, 2014 8:16 pm

Re: How come quads outlasted trijets?

Mon Oct 01, 2018 1:52 pm

SomebodyInTLS wrote:
If a twin was not allowed across oceans but a quad was too much engine => tri-jets.

Yes. Which is why the manufactures of the DC-10 and L-1011 thought and rightly so, that those tri-jets would be /more profitable than a quad on certain over the water flights Otherwise the airlines would have just stuck with quads. That doesn't answer the TA's question, but at the time (before ETOPS) the tri-jet widebodies filled a niche revenue gap for airliners who did long haul.
 
GalaxyFlyer
Posts: 6708
Joined: Fri Jan 01, 2016 4:44 am

Re: How come quads outlasted trijets?

Mon Oct 01, 2018 2:56 pm

Another thought, most business jets do not get a custom engine. If more thrust is needed and two engines of sufficient thrust are not available, a tri-jet goes forward.


Well, except Dassault was the only builder that went to tris. Reason being that the “marketing” portfolio at DA has always been efficiency in operational cost—light frame weights, smaller fuselage diameters, efficient wings with sophisticated, for the market, high lift systems. All aimed toward excellent field performance and low fuel burns. The G550/650 and Globals are 95,000#+ planes were the 7X is around 72,000# MTOW.

To your point, once they lifted the frame size, engines producing the right thrust for that size plane weren’t available. For them, it was either the 731 derivatives or a leap to the BR710. Now, the PW 800-series and the Honeywell 7000-series provides a nice step up in thrust.

Sorry for the drift.

GF

Who is online

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