Why did larger airliners move away from tail mounted engines?

[Tantalum]

Engineering is about compromises.

Tail-mounted engines allows the airplane to sit lower. This works well for smaller airplanes and for giving easier access for stairs and baggage loading. You also have the thrust vector closely aligned with the longitudinal (i.e. through the CG) which virtually eliminates pitching moments from thrust changes. The primary disadvantages have to do with weight and structure.

Under-wing engines are supported directly by the wing. That means that the load for supporting the weight of the engines does not have to be transferred to the fuselage through the wing attach structure. You can also have a simpler tail structure as a T-tail is not required. Engine maintenance is also facilitated by the engines being closer to ground level.

...and then you have the DC-10 / MD-11 / L-1011 that creates a worst of both worlds! At least on the L1011 the engine replacement for #2 was less of a PITA

 

[X3 Skier]

At least on the L1011 the engine replacement for #2 was less of a PITA

Except for the poor toad who had to go down the S Duct for FOD inspections

Cheers

 

[flyingron]

MD didn't build the DC-3, Douglas did. Not much of the old company survived once they merged in the sixties.

Oh God.. you just described Boeing

No, I didn't. No Boeing plane other than the MD stuff they inherited that had that harebrained system.

 

[Tantalum]

MD didn't build the DC-3, Douglas did. Not much of the old company survived once they merged in the sixties.


No, I didn't. No Boeing plane other than the MD stuff they inherited that had that harebrained system.

So MD is the death knell for planes then.. Boeing's recent issues with the 767 tanker and the Max debacle would suggest that the Boeing of today is not the Boeing that gave us 747/757/767/777.. pretty soon we will see that it's taking longer for Boeing to fix the issue with the Max than it did for Juan Trippe to meet with them and have the 747 built and flying

 

[flyingron]

You'd have to as Ron W about internal Boeing turmoil.

 

[nauga]

So MD is the death knell for planes then..

Other airplanes, maybe.

Nauga,
from a world where experience matters more than opinion

 

[wanttaja]

You'd have to as Ron W about internal Boeing turmoil.

I retired three years ago. Other than a short temporary loan to the P-8 program (mentoring a young engineer), and a short dalliance with a UAV in the '90s, I never worked a Boeing airplane program (and the UAV was subcontracted to Schweizer). In addition, we were a "skunk works" sort of organization that was as isolated from the Boeing bureaucracy as we could manage.

Did catch the by-blow from Boeing policies, of course. Saw more emails urging us to enhance stockholder value than to generate good products. Fortunately, the stockholders (and 99% of the upper management) didn't know about us.

Ron Wanttaja

 

[Tantalum]

Other airplanes, maybe

I forget who mentioned it, but someone on one of the Max threads quipped "MD bought Boeing with Boeing's money" - it was in response to the mess the Max has apparently been, suggesting that post MD when Boeing moved to Chicago, the culture shifted


..
separate, I did find this peculiar early 747 concept that had a tail mounted engine:

http://www.boeing-747.com/boeing_747_family/

I also found this Argentine concept for a five engined tail mounted concept:

https://en.wikipedia.org/wiki/FMA_IA_36_Cóndor

 

[nauga]

I forget who mentioned it, but someone on one of the Max threads quipped "MD bought Boeing with Boeing's money" - it was in response to the mess the Max has apparently been, suggesting that post MD when Boeing moved to Chicago, the culture shifted

That quote was around long before the 37 Max was a thing. I first heard the phrase relating to the fallout from Macair's loss and Boeing's 'win' in the JSF downselect leading to the acquisition. For those keeping score, the downselect was in 1996 and the acquisition 1997. The quote is ~20 years old and there's still bad blood over it, further irritated by the HQ move from nearby one business unit (of several) to a more central location.

Nauga,
hopefully not doomed to repeat

 

[Ghery]

Not having worked for Boeing, what I hear is just rumor and other stuff, but it sounds to me that it's MD operating as Boeing. Kind of like Continental Airlines operating as United (and I have over 1.4 million miles riding on UA). Not good for Boeing and not good for UA. Of course, I could be wrong.

 

[Tantalum]

Bloomberg had an article recently blaming the move to Chicago. When you remove the executives from the company it's not usually a good move

Also, not picking Mullaly was just plane idiotic

 

[X3 Skier]

It is difficult to “manage by walking around” when the work getting done is 1000 or more miles away.

Cheer

 

[nauga]

It is difficult to “manage by walking around” when the work getting done is 1000 or more miles away.

So which business unit should HQ be based closest to so that MBWA will work across a global company? Boeing is far more than Puget Sound and Boeing Commercial HQ is still in Seattle.

Nauga,
geographically dispersed

 

[Tantalum]

I found the article I was talking about, it's an opinion so grain of salt but it's a little more comprehensive than "move to Chicago"

https://www.bloomberg.com/opinion/articles/2020-01-16/boeing-lost-its-way-on-a-wall-street-detour

 

[X3 Skier]

So which business unit should HQ be based closest to so that MBWA will work across a global company? Boeing is far more than Puget Sound and Boeing Commercial HQ is still in Seattle.

Nauga,
geographically dispersed

If it were I, I would have the HQ in the location of the largest revenue source where final assembly takes place. This way the CEO and President of the enterprise could remove their posteriors from the Ivory Tower once in a while to see what problems may or may not be happening preventing delivery of a quality product on time. Periodic visits to other places to do the same thing would be useful. If the major revenue source changes over time, move the HQ, The basic idea is to get eyes on the product, not on death by slides on a screen.

It’s one thing to get a report and a jumble of numbers on a screen vs talking to a mechanic who points out the number of rivets that have to be drilled out and reinstalled from a supposedly quality supplier of a wing, be it internal or external, or listening to the actual repeat squawks from an acceptance test pilot. Whenever I was dragged down to a Wing or Command HQ for an a** chewing session, I always took time to visit the wrench turners to see what they needed fixed or the ready room to see what the aircrew wanted improved.

If the CEO or President have no real feel for what’s happening on the floor, s*** happens because nobody thinks they care. But if money reports are the only thing that matters, sooner or later, the quality slips and the money starts leaking out.

Must be my time on the shop floor seeing it at various companies and Squadrons because it sure wasn’t being in the Executive Suite being served tea and crumpets that makes me a believer.

Cheers

 

[nauga]

If the CEO or President have no real feel for what’s happening on the floor, s*** happens because nobody thinks they care. But if money reports are the only thing that matters, sooner or later, the quality slips and the money starts leaking out.

Must be my time on the shop floor seeing it at various companies and Squadrons because it sure wasn’t being in the Executive Suite being served tea and crumpets that makes me a believer.

Were you an enterprise CEO? MBWA starts lower, as your own post indicates, and moving Boeing Global HQ to Chicago did not inhibit the CEO of BCA, located much closer to the BCA workforce, walking the floors in any way. How many times were you in a squadron when the commander in chief practiced MBWA? Think whichever one visited, if any, really had a good idea of the day-to-day issues?

While there's one guy at the top of the org chart, I don't think the one guy who was there a few weeks ago is single-handedly responsible, nor do I think the location of his office has anything to do with the issues they're facing now.

For a different perspective, which major US A&D companies have headquarters collocated with their largest revenue source? I can't think of any off the top of my head.

Nauga,
so moved

 

[Tantalum]

nor do I think the location of his office has anything to do with the issues they're facing now

For curiosity sake, what would be your perspective on the root cause of the issues being faced?

 

[kyleb]

While there's one guy at the top of the org chart, I don't think the one guy who was there a few weeks ago is single-handedly responsible, nor do I think the location of his office has anything to do with the issues they're facing now.

I believe the proximity of senior level of management to the shop floor (whatever that might be) is important because of informal information sharing. Peon's talk to their supervisors. Some of that gets passed up to department managers, then to mid level managers, high, and senior level managers. Kind of an osmosis process via the water cooler, impromptu meetings in the hallway, and comments made at lunch. At some point, the issue will become apparent to senior management IF there is a path where osmosis can occur. But if there is a firewall (or a thousand miles) between the CEO and the shop floor, it is much harder for the information to reach the CEO.

 

[nauga]

But if there is a firewall (or a thousand miles) between the CEO and the shop floor, it is much harder for the information to reach the CEO.

In a large global organization there is no base where the CEO can be less than 1000 miles from every major worksite.

Nauga,
who gets left out in the rain

 

[X3 Skier]

Were you an enterprise CEO?

How many times were you in a squadron when the commander in chief practiced MBWA? Think whichever one visited, if any, really had a good idea of the day-to-day issues.

For a different perspective, which major US A&D companies have headquarters collocated with their largest revenue source? I can't think of any off the top of my head.

Nauga,
so moved

a) Nope, just an Engineer in charge of development and production technical stuff.

b) From that perspective, I guess the POTUS never did. But I know from walking around Charleston AFB with CinC Transcom and Langley AFB with ACC/CC, they did. One of my more “interesting” experiences was in TAC/CC’s Conference room where the table was arrayed with broken parts he had collected personally from maintenance shops. He’s also the guy who more or less invented the Borescope inspection of hot sections when he took the Command Surgeon with a proctoscope over to the engine shop to look at turbines or so I was told. So the idea of The Head of Boeing Commercial in Seattle is equivalent, I suppose.

c) Not sure but I think before Lockheed became LockMart + GD, They had their HQ moved to Marietta where the C-130 and F-22 were being done. After production of the F-22 moved to Ft Worth and the mergers, HQ moved to DC IIRC which is often not true.

Cheers. X3 Skier
Who has stopped “leaving no answers unquestioned” when he retired.....again.

 

[kyleb]

In a large global organization there is no base where the CEO can be less than 1000 miles from every major worksite.

Nauga

No doubt. OTOH, how much of Boeing's operation is in the Seattle area compared to the Chicago area and isn't it likely the CEO would have a better feel for the corporate pulse if he was on the ground in Washington instead of Illinois?

Kyle

who's flown around the world checking the corporate pulse. ;-)

 

[nauga]

c) Not sure but I think before Lockheed became LockMart + GD, They had their HQ moved to Marietta where the C-130 and F-22 were being done. After production of the F-22 moved to Ft Worth and the mergers, HQ moved to DC IIRC which is often not true.

Yeah Lockheed used to, but so did Boeing.
Currently (from memory, also suspect):
Boeing - Chicago IL
LM - Bethesda MD
NGC - Northern VA
Raytheon - Boston MA

I've missed a few

Nauga,
well-traveled

 

[flyingron]

Lockheed's CORPORATE headquarters remained in Calabasas, California I believe to the end. They did shutter the Burbank plane and move all the airplane manufacturing management to Marietta, Georgia in 1990. By the way, the Marietta in the "Martin Marietta" is actually Marietta, Ohio.

American Asphalt (Chicago) and the Marietta (Ohio) Paint and Color merged to form American-Marietta. This merged with the Glenn L. Martin Aircraft Company (Baltimore) to form Martin Marietta.
Martin Marietta (Bethedsa, MD) which merged with Lockheed.

I worked with these guys who were in Gaithersburg who started out as the IBM Federal Systems Sector/Division (that changed over time). They got bought out by Loral, then Martin-Marietta got Loral and then they became LockMart. And I thought I had a hard time the five years I worked for the Army and I couldn't hardly get through a box of business cards before a reorg made the information obsolete (In one instance, it changed while they were still at the printer).

 

[genna]

How about one of these

I always thought that tail mounted engines make aircraft more susceptible to an often unrecoverable flat spin due to weight distribution. No idea if this is actually correct though(vs design/loading issues specific to aircraft). Or still valid with modern designs.


Edit: or maybe it was that they are harder to recover from spins in general.

 

[Tantalum]

How about one of these

I always thought that tail mounted engines make aircraft more susceptible to an often unrecoverable flat spin due to weight distribution. No idea if this is actually correct though(vs design/loading issues specific to aircraft). Or still valid with modern designs.


Edit: or maybe it was that they are harder to recover from spins in general.

As much I love Soviet era planes, the VC-10 is a much prettier example of a four engine tail mounted airliner

 

[genna]

As much I love Soviet era planes, the VC-10 is a much prettier example of a four engine tail mounted airliner

Hard to tell them apart actually

 

[Spring Ford]

As much I love Soviet era planes, the VC-10 is a much prettier example of a four engine tail mounted airliner

??????? They look like clones to me.

 

[genna]

And even more fun

Ok, i'm pretty sure this is fake.

 

[Tantalum]

??????? They look like clones to me.

Something about the nose

 

[neon]

The engines mounted close to the tail move the center of mass of a big airplane to its rear side. It is as if you have a tail heavy arrow.

 

[kontiki]

Designers want to keep an airplane as light as possible. High strength structure is heavy. There are flight loads, and landing loads. In a mid wing airliner the high strength inner wing spar supports the cabin, and landing gear. With engines on wing pylons, that same structure supports engine weight on landing and thrust loads.

Move the engines to the aft fuselage and now the fuselage needs to be strengthened to carry loads from engine thrust and landing loads. Having weight back there may help performance because horizontal stabilizer tends to hold the aft end of the airplane down aerodynamically which creates a drag penalty.

There are just trades. We only need two engines any more, decades ago, we needed three or more for thrust and reliability. That's what aerospace engineers do, Balance trade offs to optimize a design for specific mission or market.

 

[Larry in TN]

The engines mounted close to the tail move the center of mass of a big airplane to its rear side. It is as if you have a tail heavy arrow.

The wing is moved slightly aft on airplanes with tail-mounted engines to account for the weight of the engines on the tail.

The RJs with tail mounted engines (CRJs and ERJs) often need ballast in the aft cargo compartment when full to bring the CG into the allowable envelope. I've been denied the cockpit jumpseat on a full CRJ-200 because the station didn't have enough ballast.

 

[kontiki]

Some MD11s and A300s have active CG management systems that transfer fuel in and out of tanks in the tail as fuel burn from swept wings shifts the CG, to keep the airplane within some percentage of the optimal CG. There are a lot of possibilities.

 

[Larry Vrooman]

Eh? There's no such thing as ETOPS operations with other than two engines.

The ETOPS term also applies to 3 and 4 engine aircraft, although cargo aircraft are exempt from most of the requirements. The FAA rejected the proposed LROPS terminology for 3 and 4 engine aircraft.

-----

In regard to the OP's question on why tail mounted engines fell out of favor, ETOPS has a lot to do with why three engine designs fell out of favor. Three or more engines were necessary for over water routes back in the day when the loss of an engine (piston or turbine) may have resulted in the aircraft being unable to maintain flight when fully loaded to the closest diversionary airfield.

Several years ago when I noted my flight to HI was on a 737-700 I did some research into the old 90 minute ICAO rule dating from 1976, ETOPS 120 dating from 1985 (along with the 15% extension to ETOPS 138 under adverse weather conditions), ETOPS 180 dating from 1988 (along with the 15% extension to ETOPS 207), and ETOPS beyond 180 which kicked off in 2009 with the A330 receiving an ETOPS 240 certification.

Most North Atlantic routes are flyable under the 120 minute diversion rule, with the 15% extension to 138 minutes. About 95% of the routes on the planet fall under the ETOPS 180 rule with the extension to 207 minutes.

The ideas behind the revised ETOPS rules were that turbine engines are extremely reliable, and powerful enough for a twin engine airliner to maintain flight with a full load on one engine for the required number minutes to a diversion airfield. However, the engines' ancillary systems are potentially less reliable, so ETOPS certification hinges on ancillary system reliability and redundancy built in at certification.

Engine reliability also matters for both the aircraft and for the airline. ETOPS 120 requires an engine shut down rate for both aircraft and airline of no more than 1 in 20,000 hours. With ETOPS 180 that increases to 1 in 50,000 hours and for ETOPS beyond 180 that increases to 1 in 100,000 hours. If an airline short fails on maintenance and doesn't meet the required standard, their ETOPS will be downgraded or eliminated.

With that in mind, the regulatory need for 3 engine jet airlines started going away as far back as 1976, was largely gone by 1985, and by 1988 was all but dead on 95% of the routes flown by major airlines. Those previous engine out requirements were the main selling point for a three engine airliner and they offset the increased structural weight, increased maintenance difficulty, and in many cases decreased efficiency of a centerline tail mounted engine.

 

[Tantalum]

The ETOPS term also applies to 3 and 4 engine aircraft, although cargo aircraft are exempt from most of the requirements. The FAA rejected the proposed LROPS terminology for 3 and 4 engine aircraft.

-----

In regard to the OP's question on why tail mounted engines fell out of favor, ETOPS has a lot to do with why three engine designs fell out of favor. Three or more engines were necessary for over water routes back in the day when the loss of an engine (piston or turbine) may have resulted in the aircraft being unable to maintain flight when fully loaded to the closest diversionary airfield.

Several years ago when I noted my flight to HI was on a 737-700 I did some research into the old 90 minute ICAO rule dating from 1976, ETOPS 120 dating from 1985 (along with the 15% extension to ETOPS 138 under adverse weather conditions), ETOPS 180 dating from 1988 (along with the 15% extension to ETOPS 207), and ETOPS beyond 180 which kicked off in 2009 with the A330 receiving an ETOPS 240 certification.

Most North Atlantic routes are flyable under the 120 minute diversion rule, with the 15% extension to 138 minutes. About 95% of the routes on the planet fall under the ETOPS 180 rule with the extension to 207 minutes.

The ideas behind the revised ETOPS rules were that turbine engines are extremely reliable, and powerful enough for a twin engine airliner to maintain flight with a full load on one engine for the required number minutes to a diversion airfield. However, the engines' ancillary systems are potentially less reliable, so ETOPS certification hinges on ancillary system reliability and redundancy built in at certification.

Engine reliability also matters for both the aircraft and for the airline. ETOPS 120 requires an engine shut down rate for both aircraft and airline of no more than 1 in 20,000 hours. With ETOPS 180 that increases to 1 in 50,000 hours and for ETOPS beyond 180 that increases to 1 in 100,000 hours. If an airline short fails on maintenance and doesn't meet the required standard, their ETOPS will be downgraded or eliminated.

With that in mind, the regulatory need for 3 engine jet airlines started going away as far back as 1976, was largely gone by 1985, and by 1988 was all but dead on 95% of the routes flown by major airlines. Those previous engine out requirements were the main selling point for a three engine airliner and they offset the increased structural weight, increased maintenance difficulty, and in many cases decreased efficiency of a centerline tail mounted engine.

Thanks! An unusually informative and a well-written post