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convair880mfan
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Was the McDonnell Douglas MD-90 a good airplane?

Tue Aug 24, 2021 4:06 pm

I've heard that the MD-90 production line was eliminated once Boeing took over McDonnell Douglas because it was competing with the Boeing 737. Was the MD-90 just the right plane at the wrong time? If McDonnell Douglas had been able to survive, do you think there would still be MD-90's out there? What are you thoughts and feelings about the plane?
 
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1337Delta764
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Tue Aug 24, 2021 4:14 pm

The MD-90 was essentially McD's response to the A320 and 737NG. While the fuel economy was good, it was hampered mainly by its lack of range compared to its competitors. With Boeing offering the 737NG (specifically the 737-800), there was no need for Boeing to continue offering it.
 
UA444
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Tue Aug 24, 2021 7:32 pm

MD90-50 would've been the transcontinental version.
 
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PatrickZ80
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Tue Aug 24, 2021 8:02 pm

UA444 wrote:
MD90-50 would've been the transcontinental version.


Actually the MD90-50 was developed as the MD-95 and later renamed into the Boeing 717. Far from transcontinental, more like a competitor for the regional jets at the time. Specially the Fokker F-100 which it showed many similarities with.

The MD-90 was a good short range aircraft for it's time, technically there was nothing wrong with it. It was just not what the airlines desired.

The DC-9 series, on which it was based, has always been a short haul series. Of course during the times of the DC-9 this was no problem because the competition (737-100/200) didn't do much better. However the 737 Classic (737-300/400/500) had significantly more range and the competing MD-80 series started to lose ground. The 737NG meant the final death of the DC-9 continuations. And with Boeing acquiring McDonnell-Douglas it didn't make sense to continue the type. Only the 717 was continued for some time but it wasn't exactly successful either.
 
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Boeing757100
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Tue Aug 24, 2021 8:28 pm

I have heard that the MD-90 could make it from MSP to nearly the whole continental US. I guess that's why it appealed more to DL than others. But, the big issue for most was, in addition to range, the orphan engine type.
 
Yflyer
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Tue Aug 24, 2021 10:25 pm

PatrickZ80 wrote:
UA444 wrote:
MD90-50 would've been the transcontinental version.

Actually the MD90-50 was developed as the MD-95 and later renamed into the Boeing 717.


But wasn't MD planning an entire "MD-90 family" that would have included a longer range variant? Essentially an MD-90ER, although I don't know if that's what they actually called it? Of course it never got built after the merger since it would have been a direct competitor to the 737-800.
 
UA444
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Wed Aug 25, 2021 8:26 pm

PatrickZ80 wrote:
UA444 wrote:
MD90-50 would've been the transcontinental version.


Actually the MD90-50 was developed as the MD-95 and later renamed into the Boeing 717. Far from transcontinental, more like a competitor for the regional jets at the time. Specially the Fokker F-100 which it showed many similarities with.

The MD-90 was a good short range aircraft for it's time, technically there was nothing wrong with it. It was just not what the airlines desired.

The DC-9 series, on which it was based, has always been a short haul series. Of course during the times of the DC-9 this was no problem because the competition (737-100/200) didn't do much better. However the 737 Classic (737-300/400/500) had significantly more range and the competing MD-80 series started to lose ground. The 737NG meant the final death of the DC-9 continuations. And with Boeing acquiring McDonnell-Douglas it didn't make sense to continue the type. Only the 717 was continued for some time but it wasn't exactly successful either.

The MD-90-50 was a proposed longer range version of the -30.
 
classicjets
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Thu Aug 26, 2021 1:35 am

Boeing757100 wrote:
I have heard that the MD-90 could make it from MSP to nearly the whole continental US. I guess that's why it appealed more to DL than others. But, the big issue for most was, in addition to range, the orphan engine type.
Though they had an MD-90 fleet long before they had an MSP hub. However their interest in topping up the fleet with used frames could be explained by this.

Sent from my ELE-L29 using Tapatalk
 
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CarlosSi
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Thu Aug 26, 2021 3:39 am

I think I agree with the above comments, not being too knowledgeable about the MD90.

From what I heard the wing wasn't really upgraded very much either if at all.

Much as people say that airlines will complain an airplane is "too big or too heavy" for its operations, they always end up buying the most capable airplanes. AA doesn't seem to think the 788 is too much airplane for those Northeast US to Europe routes. If the MD90 was a good a320 competitor, it might've garnered more orders. That and if MDD stayed in business.
 
DeltaMD95
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Fri Aug 27, 2021 9:20 pm

PatrickZ80 wrote:
UA444 wrote:
MD90-50 would've been the transcontinental version.


Actually the MD90-50 was developed as the MD-95 and later renamed into the Boeing 717. Far from transcontinental, more like a competitor for the regional jets at the time. Specially the Fokker F-100 which it showed many similarities with.

The MD-90 was a good short range aircraft for it's time, technically there was nothing wrong with it. It was just not what the airlines desired.

The DC-9 series, on which it was based, has always been a short haul series. Of course during the times of the DC-9 this was no problem because the competition (737-100/200) didn't do much better. However the 737 Classic (737-300/400/500) had significantly more range and the competing MD-80 series started to lose ground. The 737NG meant the final death of the DC-9 continuations. And with Boeing acquiring McDonnell-Douglas it didn't make sense to continue the type. Only the 717 was continued for some time but it wasn't exactly successful either.


No, he’s correct - there was the planned MD90-50 and -70 variants. Just as was also planned for the MD95. -30 was the baseline, -50 extended range and -70 a stretch, if memory serves me correctly. In either event, in researching McDD extensively for years, the plan just before Boeing’s merger was to have 3-4 variants for each the MD90 & MD95 (varying in either gw, range, or capacity). This would in essence covered the bases between 736-739 or A318/321.
 
DeltaMD95
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Fri Aug 27, 2021 9:28 pm

convair880mfan wrote:
I've heard that the MD-90 production line was eliminated once Boeing took over McDonnell Douglas because it was competing with the Boeing 737. Was the MD-90 just the right plane at the wrong time? If McDonnell Douglas had been able to survive, do you think there would still be MD-90's out there? What are you thoughts and feelings about the plane?


I think of McDonnell Douglas had stayed in business, we probably would have seen at least the same number built as MD80s (approx 1200). McDD had some big MD90 orders from the likes of DL and others that were cancelled when the merger was announced. Also, the MD90 had really cornered the EM markets of China, Taiwan, so those numbers would have likely grown. Lastly, there was a 737NG/A320 order explosion in the mid 2000s, as airlines rapidly retired 737 classic, MD80/DC9s, Fokkers, etc and just by sheer volume of demand, the -90 would have benefitted from that as well, given its relative competitive fuel burn compared to its peers.
Last edited by DeltaMD95 on Fri Aug 27, 2021 9:33 pm, edited 2 times in total.
 
DeltaMD95
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Fri Aug 27, 2021 9:29 pm

DeltaMD95 wrote:
convair880mfan wrote:
I've heard that the MD-90 production line was eliminated once Boeing took over McDonnell Douglas because it was competing with the Boeing 737. Was the MD-90 just the right plane at the wrong time? If McDonnell Douglas had been able to survive, do you think there would still be MD-90's out there? What are you thoughts and feelings about the plane?


I think if McDonnell Douglas had stayed in business, we probably would have seen at least the same number built as MD80s (approx 1200). McDD had some big MD90 orders from the likes of DL and others that were cancelled when the merger was announced. Also, the MD90 had really cornered the EM markets of China, Taiwan, so those numbers would have likely grown. Lastly, there was a 737NG/A320 order explosion in the mid 2000s, as airlines rapidly retired 737 classic, MD80/DC9s, Fokkers, etc and just by sheer volume of demand, the -90 would have benefitted from that as well, given its relative competitive fuel burn compared to its peers.
 
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Fri Aug 27, 2021 10:48 pm

It was a tired old platform, basically the ultimate warmed up DC9 with lots of compromises and shortcomings compared to more modern aircraft


Developing it further was pointless
 
DeltaMD95
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Sat Aug 28, 2021 11:40 pm

Max Q wrote:
It was a tired old platform, basically the ultimate warmed up DC9 with lots of compromises and shortcomings compared to more modern aircraft


Developing it further was pointless


737MAX: hold my beer
 
blandy62
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Sun Aug 29, 2021 2:04 am

Max Q wrote:
It was a tired old platform, basically the ultimate warmed up DC9 with lots of compromises and shortcomings compared to more modern aircraft


Developing it further was pointless


overall that way MDD problem with both the narrow and wide body products
 
DeltaMD95
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Sun Aug 29, 2021 6:59 pm

blandy62 wrote:
Max Q wrote:
It was a tired old platform, basically the ultimate warmed up DC9 with lots of compromises and shortcomings compared to more modern aircraft


Developing it further was pointless


overall that way MDD problem with both the narrow and wide body products


For proper perspective, the DC-9 platform was not even 30 years old at the time of the MD90’s first flight. Quite equal to the A320’s age when the design was reused for the NEO. And strategically, to scrap the platform on heals of the greatest success the commercial line ever had (the MD80) would have been fiscally irresponsible. The C Series is great innovation but it also lead directly to Bombardier’s liquidation.

All the MD90 needed was a budget that equaled the 737NG. That’s where McDD truly went wrong.
 
CowAnon
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Mon Aug 30, 2021 5:31 am

It seems to me that the MD-90 model that was launched was a huge Delta order in November 1989 was nearly the same as what MDD had proposed in March 1984: a 57-inch stretch of the MD-80 with new V2500 engines. So if McDonnell Douglas had proceeded with that concept at the time, they would've had over 5-1/2 years more time to promote that model, and would've gained many more sales. Instead, MDD first tried to sell UDF/propfan derivatives of the MD-80, which failed. I can't say that I wouldn't have made the same choice, though.

    McDonnell-Douglas studying MD-80 airliner derivative, Financial Times, 3/16/1984 (page 6)

      McDonnell-Douglas of the U.S. is studying a possible new derivative of the highly successful MD-80 twin-engined airliner, as an answer to competition to the recently launched 150-seat European Airbus A-320.
      ...
      With continued product improvement in mind, McDonnell-Douglas is now studying a new version, the MD-88, which would seat up to 164 passengers and would use the projected new international V-2500 engine.
      ...
      The MD-88 would have a 57-inch "plug" built in to stretch the fuselage to give more seats and in addition to the V-2500 engines, it would have a new flight deck with cathode ray tube displays, an improved tail, wing leading edges and make greater use of lightweight materials.

    (Note - the proposed MD-88 concept mentioned here isn't the same as the MD-88 model that was later produced.)

    Delta Places $10-Billion Order for 260 Jetliners : Aviation: The airline will buy Douglas MD-90s and Boeing 737s. Long Beach firm now has a huge backlog., Los Angeles Times, 11/15/1989

      The McDonnell Douglas order will enable that company to begin development of the new MD-90 series of airliners at its Douglas Aircraft unit in Long Beach, Calif.
      ...
      Douglas’ Wolf said that development of the MD-90, which is derived from the older Douglas MD-80, would begin immediately and cost “less than $400 million.” The company expects to obtain government certification of the aircraft and to begin deliveries in 1994.
      ...
      The new MD-90 family will differ from the MD-80s primarily in the use of the new International Aero Engines V2500 turbo jet engine, which is built by an international consortium that includes the American manufacturer Pratt & Whitney and the British firm Rolls-Royce. Other participants in the project include West German, Italian and Japanese firms.
      ...
      The MD-90’s fuselage will be 57 inches longer than the MD-80’s, which will allow 10 additional passenger seats.

Was a conversion to fly-by-wire cockpit or a rewing to a 36-meter span ever seriously considered in the 1980s?
 
CowAnon
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Mon Aug 30, 2021 5:44 am

Another interesting thing about the plane ... McDonnell Douglas had planned an MD-90-40 derivative that was 52.3 meters long (almost 8 meters longer than the A321, and nearly 10 meters longer than the 737 MAX 10). It would've held 170-180 passengers in three-class seating, or 217 passengers in single class!

http://web.archive.org/web/201712070833 ... 203788.PDF
 
LucaDiMontanari
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Mon Aug 30, 2021 12:17 pm

This might be an inconvenient opinion, but I dare to say, that the MD-90 was a superb aircraft, an industry benchmark and years ahead of its competitors - but 15 years late...

Beside the new engines and a slight stretch to comply with those new and heavier engines, the MD-90 is mostly unchanged to the MD-80. But they could have had that at the end of the seventies. Imagine it's 1979 and MD rolls out their first MD-80 prototype, but with CFM56 engines instead of the JT8D-200 blow torches. They knew that engine, they had their hands on it, they already worked with it and even the early versions were far more economical than the Pratt's. I'm pretty sure, a CFM-powered MD-80 would have changed the world of aviation quite a bit, eating up a notable portion of the 737 classic orders and probably even early A320's at around 1990, when lots of former loyal MD customers switched to Airbus, since in our reality MD wasn't able to present a capable successor at that point. Those might have stayed with MD for at least a little longer, Air Canada for example.

Next mistake:

CowAnon wrote:
Was a conversion to fly-by-wire cockpit or a rewing to a 36-meter span ever seriously considered in the 1980s?


No. And this was another nail in the coffin. Not a FBW (737 hasn't it neither) or a wing stretch itself, but not touching the wing at all for the MD-90, when the A320 already made obvious, that supercritical airfoils are gonna be the next big thing in aerodynamics and will be crucial to build a successful airliner in future. The MD-90 program started almost two years after the A320's maiden flight and its first flight took place four years ahead of Boeing's 737NG series. They could have done this and build a good aircraft, competitive to this day to A32S CEO's and 737NG's. And nowadays they would have no issues with fixing large LEAP's under their wing, when designing an MD-90NEOMAX. Instead they built something that was loosely capable to compete with the 737 classics, because in St. Louis no one was really interested in building civil airliners...
 
CowAnon
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Tue Aug 31, 2021 6:43 pm

LucaDiMontanari wrote:
This might be an inconvenient opinion, but I dare to say, that the MD-90 was a superb aircraft, an industry benchmark and years ahead of its competitors - but 15 years late...

Beside the new engines and a slight stretch to comply with those new and heavier engines, the MD-90 is mostly unchanged to the MD-80. But they could have had that at the end of the seventies. Imagine it's 1979 and MD rolls out their first MD-80 prototype, but with CFM56 engines instead of the JT8D-200 blow torches. They knew that engine, they had their hands on it, they already worked with it and even the early versions were far more economical than the Pratt's. I'm pretty sure, a CFM-powered MD-80 would have changed the world of aviation quite a bit, eating up a notable portion of the 737 classic orders and probably even early A320's at around 1990, when lots of former loyal MD customers switched to Airbus, since in our reality MD wasn't able to present a capable successor at that point. Those might have stayed with MD for at least a little longer, Air Canada for example.

Next mistake:

CowAnon wrote:
Was a conversion to fly-by-wire cockpit or a rewing to a 36-meter span ever seriously considered in the 1980s?


No. And this was another nail in the coffin. Not a FBW (737 hasn't it neither) or a wing stretch itself, but not touching the wing at all for the MD-90, when the A320 already made obvious, that supercritical airfoils are gonna be the next big thing in aerodynamics and will be crucial to build a successful airliner in future. The MD-90 program started almost two years after the A320's maiden flight and its first flight took place four years ahead of Boeing's 737NG series. They could have done this and build a good aircraft, competitive to this day to A32S CEO's and 737NG's. And nowadays they would have no issues with fixing large LEAP's under their wing, when designing an MD-90NEOMAX. Instead they built something that was loosely capable to compete with the 737 classics, because in St. Louis no one was really interested in building civil airliners...

Thanks for the reply Luca, your posts are always interesting. The concept of a CFM56-engined MD-80 seems so obvious that I just assumed there was some technical or legal issue that prevented the tie-up. Especially since GE/SNECMA went about 5 years without a CFM56 order in the 1970s. you'd think they would've had salespeople camping out at MDD headquarters begging for an order. Seems like the MD-80 still did pretty well even without the CFM56, but if MDD had that engine, they could've just skipped the V2500 engine "upgrade" and just worked on a new wing instead for the MD-90.
 
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DocLightning
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Thu Sep 02, 2021 5:53 pm

DeltaMD95 wrote:
Max Q wrote:
It was a tired old platform, basically the ultimate warmed up DC9 with lots of compromises and shortcomings compared to more modern aircraft

Developing it further was pointless


737MAX: hold my beer


I think a bit of historical context is appropriate here. Both the DC-9 and the 737 were designed in the 1960s. At the time there were a lot of small airports with semi-prepared runways and no belt loaders. Mounting the engines at the rear allowed the DC-9 to a) avoid FOD into the engines on semi-prepared fields and b) lowered the fuselage very close to the ground where the hold could be loaded/unloaded manually. This same design consideration worked into the 727, which was designed with South American/high-altitude airports in mind, which also could be quite small and have limited handling equipment.

But rear-mounted engines raise a lot of issues. a) The lack of a heavy engine on the wing means that the wing has to carry the full weight of the entire aircraft at its root with no bending relief from an engine, so it needs to be stronger (heavier). b) Wing-mounted engines can serve as anti-shock bodies and assist with the area-ruling of the overall aircraft. c) Rear-mounted engines require extra fuel lines and strengthening of the fuselage to both carry the weight and thrust d) Rear-mounted engines are more difficult to service and e) Rear-mounted engines tend to lead to increased overall length.

Boeing developed a competing 737. This aircraft used the same cabin cross-section of the 707 and the same nose. This decreased development costs, but also the 3+3 seating is the most efficient seating pattern in an aircraft, giving a ratio of six seats to one aisle. No widebody comes close to that, and nor does the 2+3 DC-9. To get around the problem of serving airports with minimal ground equipment, Boeing tucked the relatively narrow engines right up under the wing with no pylon. This, when combined with the wing dihedral, allowed the fuselage to sit about as close to the ground as the DC-9 family. FOD ingesting was the only remaining issue, but Boeing developed a gravel kit for serving semiprepared airfields, and so-fitted 732s still carry cargo to remote airfields in northern Canada to this day.

For the 737 Classics (300/400/500) and NG (600/700/800/900), Boeing was able to mount a larger engine by extending the MLG and nose gear as much as was practical. Both of these models were outstandingly successful.

As for the DC-9 family, by the mid-1980s, just about any airfield with commercial service had a paved runway and a belt loader at least. So the two main advantages of the DC-9 design had been mooted. McD was struggling and didn't really have the resources to design a clean-sheet replacement, and then the merger happened. Boeing had committed to a certain production run of the 717 (nee MD-95), but then canned the program, hoping to sell their 737-600, instead (which was foolish; the 737-600 sold terribly).
 
LucaDiMontanari
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Fri Sep 03, 2021 10:07 am

DocLightning wrote:
But rear-mounted engines raise a lot of issues. a) The lack of a heavy engine on the wing means that the wing has to carry the full weight of the entire aircraft at its root with no bending relief from an engine, so it needs to be stronger (heavier). b) Wing-mounted engines can serve as anti-shock bodies and assist with the area-ruling of the overall aircraft. c) Rear-mounted engines require extra fuel lines and strengthening of the fuselage to both carry the weight and thrust d) Rear-mounted engines are more difficult to service and e) Rear-mounted engines tend to lead to increased overall length.


As we all know, aircraft are just a loose aggregation of bad trade-offs and all your arguments have their counter-arguments:
a) the existence of an engine on the wing disturbs its airflow and thus its aerodynamic efficiency, which asks for an overall larger wing. Hence the "clean wing" advertising for the DC-9 and 727. And larger engines need higher/longer main landing gear struts, which need larger gear bays, which increases the area of weakened wing structure, which asks for strengthening the wing structure, which both increases weight. And also with longer legs, the engines have to be placed farther out, which affects one engine out directional controllability, which asks for a larger, read heavier vertical stabilizer. These issues become even bigger with every engine diameter increase. Which was the case in the past and will be on the next generation of engines.

b) this might have been true on the old turbojets and low bypass turbofans. I learned at some point, that an ideal engine pod is positioned 3/4 of its length ahead of the wing leading edge and the engines longitudinal axis should be one engine pod diameter below the chord line of the wing, as a rule of thumb. Everything closer disturbs airflow between pod and wing too much, everything farther out will make the engine pylon too heavy for no notable gain. The 737 was bad from the beginning in this respect, while the A320ceo was also already sub par. But if you look at an A32S NEO, the upper side of the fan case is also almost as high up as the leading edge of the wing. This is prone for interference drag with the wing and out-rules any anti-shock capabilities by far. Placing the engines farther away from the wings means placing them further ahead of the wing or lower below it. Both increase engine pylon size and thus weight, the latter also ask for even longer gear struts which become heavier and, well read a).

c) an argument that becomes invalid, when someone installs an aft trim tank. Oh, and with aft engines, the fuel lines never need to cross the turbine disk layer, as the combustion chamber is ahead of it.

d) you need a ladder, rather than a footstool when topping up engine oil? For an engine change, you'll need special equipment anyway, since forklifts are inadequate for such tasks as we learned sometime around 1979. Sure, it is a totally different story, when a third engine, buried deep in the fuselage, is involved.

e) so what? Use this space for things that don't ask for windows. Toilets, galleys, avionics, cargo, aft trim tank, you name it.

Don't get me wrong: the recent developments show, that your arguments are in favor at the moment. What I think is a very interesting question from a technical view, is, if there is a tipping point, where Turbofans become just too large in diameter to fit under wings. An A320 NEO is maxed out with the actual gear struts, the 737 honestly already beyond that point. The latest artist impressions of the new Embraer turboprop concept shows an interesting outcome of such considerations. And to find the way back to the MD-90, it is an interesting question, how such a bird would perform in a todays technology iteration. Especially as an actual 103kN rated PW1500G is about the same weight as a 98kN rated JT8D-219 (2177kg to 2125kg), so no need to further increase fuselage length just for W&B issues.

DocLightning wrote:
For the 737 Classics (300/400/500) and NG (600/700/800/900), Boeing was able to mount a larger engine by extending the MLG and nose gear as much as was practical. Both of these models were outstandingly successful.


And MD could have had that in airline service without even touching the MLG by 1980. They didn't, so they failed in the long term. This is my opinion, which means it's not a fact 8-)
 
a320fan
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Sat Sep 04, 2021 2:24 pm

CowAnon wrote:
Another interesting thing about the plane ... McDonnell Douglas had planned an MD-90-40 derivative that was 52.3 meters long (almost 8 meters longer than the A321, and nearly 10 meters longer than the 737 MAX 10). It would've held 170-180 passengers in three-class seating, or 217 passengers in single class!

http://web.archive.org/web/201712070833 ... 203788.PDF

Thats only 2 meters shorter than a 757-300. Would have been a really impressive aircraft to actually see in the flesh. Incredibly awkward looking I imagine.
 
DeltaMD95
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Re: Was the McDonnell Douglas MD-90 a good airplane?

Mon Sep 06, 2021 8:06 pm

LucaDiMontanari wrote:
DocLightning wrote:
But rear-mounted engines raise a lot of issues. a) The lack of a heavy engine on the wing means that the wing has to carry the full weight of the entire aircraft at its root with no bending relief from an engine, so it needs to be stronger (heavier). b) Wing-mounted engines can serve as anti-shock bodies and assist with the area-ruling of the overall aircraft. c) Rear-mounted engines require extra fuel lines and strengthening of the fuselage to both carry the weight and thrust d) Rear-mounted engines are more difficult to service and e) Rear-mounted engines tend to lead to increased overall length.


As we all know, aircraft are just a loose aggregation of bad trade-offs and all your arguments have their counter-arguments:
a) the existence of an engine on the wing disturbs its airflow and thus its aerodynamic efficiency, which asks for an overall larger wing. Hence the "clean wing" advertising for the DC-9 and 727. And larger engines need higher/longer main landing gear struts, which need larger gear bays, which increases the area of weakened wing structure, which asks for strengthening the wing structure, which both increases weight. And also with longer legs, the engines have to be placed farther out, which affects one engine out directional controllability, which asks for a larger, read heavier vertical stabilizer. These issues become even bigger with every engine diameter increase. Which was the case in the past and will be on the next generation of engines.

b) this might have been true on the old turbojets and low bypass turbofans. I learned at some point, that an ideal engine pod is positioned 3/4 of its length ahead of the wing leading edge and the engines longitudinal axis should be one engine pod diameter below the chord line of the wing, as a rule of thumb. Everything closer disturbs airflow between pod and wing too much, everything farther out will make the engine pylon too heavy for no notable gain. The 737 was bad from the beginning in this respect, while the A320ceo was also already sub par. But if you look at an A32S NEO, the upper side of the fan case is also almost as high up as the leading edge of the wing. This is prone for interference drag with the wing and out-rules any anti-shock capabilities by far. Placing the engines farther away from the wings means placing them further ahead of the wing or lower below it. Both increase engine pylon size and thus weight, the latter also ask for even longer gear struts which become heavier and, well read a).

c) an argument that becomes invalid, when someone installs an aft trim tank. Oh, and with aft engines, the fuel lines never need to cross the turbine disk layer, as the combustion chamber is ahead of it.

d) you need a ladder, rather than a footstool when topping up engine oil? For an engine change, you'll need special equipment anyway, since forklifts are inadequate for such tasks as we learned sometime around 1979. Sure, it is a totally different story, when a third engine, buried deep in the fuselage, is involved.

e) so what? Use this space for things that don't ask for windows. Toilets, galleys, avionics, cargo, aft trim tank, you name it.

Don't get me wrong: the recent developments show, that your arguments are in favor at the moment. What I think is a very interesting question from a technical view, is, if there is a tipping point, where Turbofans become just too large in diameter to fit under wings. An A320 NEO is maxed out with the actual gear struts, the 737 honestly already beyond that point. The latest artist impressions of the new Embraer turboprop concept shows an interesting outcome of such considerations. And to find the way back to the MD-90, it is an interesting question, how such a bird would perform in a todays technology iteration. Especially as an actual 103kN rated PW1500G is about the same weight as a 98kN rated JT8D-219 (2177kg to 2125kg), so no need to further increase fuselage length just for W&B issues.

DocLightning wrote:
For the 737 Classics (300/400/500) and NG (600/700/800/900), Boeing was able to mount a larger engine by extending the MLG and nose gear as much as was practical. Both of these models were outstandingly successful.


And MD could have had that in airline service without even touching the MLG by 1980. They didn't, so they failed in the long term. This is my opinion, which means it's not a fact 8-)


Signore LucaDiMontanari, this was one of the most intelligent and insightful posts I have read on these forums in a long time. Grazie mille, molto interessante!
 
DeltaMD95
Posts: 606
Joined: Sun Aug 24, 2014 5:37 am

Re: Was the McDonnell Douglas MD-90 a good airplane?

Mon Sep 06, 2021 8:22 pm

a320fan wrote:
CowAnon wrote:
Another interesting thing about the plane ... McDonnell Douglas had planned an MD-90-40 derivative that was 52.3 meters long (almost 8 meters longer than the A321, and nearly 10 meters longer than the 737 MAX 10). It would've held 170-180 passengers in three-class seating, or 217 passengers in single class!

http://web.archive.org/web/201712070833 ... 203788.PDF

Thats only 2 meters shorter than a 757-300. Would have been a really impressive aircraft to actually see in the flesh. Incredibly awkward looking I imagine.


Would have been fascinating to see an alternative design continue to progress and make it to market.

Aviation today would be a lot more interesting with another big player contributing some non-monotonous/copy-cat R&D to the pool. (Understanding there is a business case for such decisions today).
 
MEA-707
Posts: 3882
Joined: Mon Nov 15, 1999 4:51 am

Re: Was the McDonnell Douglas MD-90 a good airplane?

Sun Sep 26, 2021 5:40 pm

a320fan wrote:
CowAnon wrote:
Another interesting thing about the plane ... McDonnell Douglas had planned an MD-90-40 derivative that was 52.3 meters long (almost 8 meters longer than the A321, and nearly 10 meters longer than the 737 MAX 10). It would've held 170-180 passengers in three-class seating, or 217 passengers in single class!

http://web.archive.org/web/201712070833 ... 203788.PDF

Thats only 2 meters shorter than a 757-300. Would have been a really impressive aircraft to actually see in the flesh. Incredibly awkward looking I imagine.

Can someone make a drawing or photoshop? That must be a flying needle, with its 5 abreast seating making even a 757-300 or DC-8-63 look stubby in comparison.
 
DeltaMD95
Posts: 606
Joined: Sun Aug 24, 2014 5:37 am

Re: Was the McDonnell Douglas MD-90 a good airplane?

Sun Sep 26, 2021 7:06 pm

MEA-707 wrote:
a320fan wrote:
CowAnon wrote:
Another interesting thing about the plane ... McDonnell Douglas had planned an MD-90-40 derivative that was 52.3 meters long (almost 8 meters longer than the A321, and nearly 10 meters longer than the 737 MAX 10). It would've held 170-180 passengers in three-class seating, or 217 passengers in single class!

http://web.archive.org/web/201712070833 ... 203788.PDF

Thats only 2 meters shorter than a 757-300. Would have been a really impressive aircraft to actually see in the flesh. Incredibly awkward looking I imagine.

Can someone make a drawing or photoshop? That must be a flying needle, with its 5 abreast seating making even a 757-300 or DC-8-63 look stubby in comparison.


I second that and would buy our creative content design friend a drink if I could!

But why stop there? Let’s see the whole theoretical family of MD-90 & MD-95 variants.

Ideally in modern Delta widget colors; as IMO if it ever had occurred pre-97 merger gentlemen’s agreement, & during the MD-loyal Ron Allen era, Delta would have been the most fathomable.

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