Why was 737NG developed?
Why was the NG launched? To compete with the A320, which was taking sales from the 737 in both North America and Europe.
The Classic already had CFM56 engines, so fitting an updated model was no big deal. 61-inch fan on the NG compared to 60 on the Classic.
The big difference was the brand new wing, using aerodynamics from the 777. It's more efficient than the A320's. Plus, as said above, the 737 fuselage is "efficient", with a better ratio of seats to external area than the A320.
The excellent new wing allowed the launch of the -800, a 3m stretch on the -400. The resulting seat-mile costs measured up to the A320's and the rest is history.
More interesting is what was going on in the late 90s/early 2000s. Boeing was developing Project Yellowstone, consisting of the Y1, Y2, and Y3. The Y2 launched as the 787 and the Y1 was intended to replace the 737NG with a plastic jet using 787 tech. But single-aisle sales grew beyond what's possible to mass-produce in CFRP. Then Airbus just fitted next-gen engines to the A320 rather than develop a new, better airframe, knowing that Boeing couldn't do the same. Boeing tried anyway and the rest is... 🙁.
The Classic already had CFM56 engines, so fitting an updated model was no big deal. 61-inch fan on the NG compared to 60 on the Classic.
The big difference was the brand new wing, using aerodynamics from the 777. It's more efficient than the A320's. Plus, as said above, the 737 fuselage is "efficient", with a better ratio of seats to external area than the A320.
The excellent new wing allowed the launch of the -800, a 3m stretch on the -400. The resulting seat-mile costs measured up to the A320's and the rest is history.
More interesting is what was going on in the late 90s/early 2000s. Boeing was developing Project Yellowstone, consisting of the Y1, Y2, and Y3. The Y2 launched as the 787 and the Y1 was intended to replace the 737NG with a plastic jet using 787 tech. But single-aisle sales grew beyond what's possible to mass-produce in CFRP. Then Airbus just fitted next-gen engines to the A320 rather than develop a new, better airframe, knowing that Boeing couldn't do the same. Boeing tried anyway and the rest is... 🙁.
The thing that really killed going to an all new 737 replacement was how long it would take to bring it on-line. Resources were still tight with the 787 and 747-8 just entering service, and not only would it have taken a couple years longer to develop than the MAX, it would have taken another few years to bring the production rate up to the 50/month ballpark. That would have meant conceding something like 3000 narrow body sales to the NEO - something that Boeing saw as untenable (although with the benefit of 20-20 hindsight doesn't look so bad).
Minor point, the NG wing is not 'new' - it was aerodynamically re-profiled (using the same structure as the classic). The new aero bought a little drag but it also bought speed - the NG critical Mach was meaningfully higher than the classic - which given the NG's longer legs was meaningful. Some that had worked on the 737-300 complained that they'd wanted to make similar changes on the -300 but were not allowed to.
The thing that really killed going to an all new 737 replacement was how long it would take to bring it on-line. Resources were still tight with the 787 and 747-8 just entering service, and not only would it have taken a couple years longer to develop than the MAX, it would have taken another few years to bring the production rate up to the 50/month ballpark. That would have meant conceding something like 3000 narrow body sales to the NEO - something that Boeing saw as untenable (although with the benefit of 20-20 hindsight doesn't look so bad).
The thing that really killed going to an all new 737 replacement was how long it would take to bring it on-line. Resources were still tight with the 787 and 747-8 just entering service, and not only would it have taken a couple years longer to develop than the MAX, it would have taken another few years to bring the production rate up to the 50/month ballpark. That would have meant conceding something like 3000 narrow body sales to the NEO - something that Boeing saw as untenable (although with the benefit of 20-20 hindsight doesn't look so bad).
the NG forward section removed the drooped cuff that was placed on the Classic wing profile of the original section. The weight increase of the Classic over the 200 resulted in a need for higher Cl/aoa, gained by the cuff. The NG extended the wing span, removed the cuff, and added a re-profiling of the aft section of the mid and inboard wing providing mild aft loading. The ailerons were increased in span, and reduced in chord which permitted removal of the outboard upper surface VGs, the shockwave remains clear of the hinge line at high speed. Flap system was simplified, and track design removed the residual tracks that the Classic carried over from the JT8 aft nacelle. The thrust gate design of the Classic flap was cleaned up, giving an improvement in flap effect, while mainly avoiding impingement on the flap and associated fatigue issues.
The Classic ran out of goodness around .745 but could be pushed higher if needed at considerable fuel burn. The NG for the same weight is running .785-.795 on lower fuel burns than the classic. To run a Classic at .79 takes a lot of extra gas... and while well within the operating boundary is associated with noticeable buffet from the aileron/shock separation. The NG has relatively high approach speeds, which is a tradeoff of the simplification of the flaps. Randolph's paper on high lift devices covers the tradeoffs well.
The Classic EFIS functioned, but the PFD/ND/EIS is supportable and upgradeable on the NG, the Classic being difficult to upgrade piecemeal. The Classic handles better IMHO, but the NG is a more effective transport aircraft,
As far as the fuselage goes, the double bubble profile precludes underfloor LD3 loading, Airbus picks up freight opportunities from any 737 operators.
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A minor point on your minor point....
the NG forward section removed the drooped cuff that was placed on the Classic wing profile of the original section. The weight increase of the Classic over the 200 resulted in a need for higher Cl/aoa, gained by the cuff. The NG extended the wing span, removed the cuff, and added a re-profiling of the aft section of the mid and inboard wing providing mild aft loading. The ailerons were increased in span, and reduced in chord which permitted removal of the outboard upper surface VGs, the shockwave remains clear of the hinge line at high speed. Flap system was simplified, and track design removed the residual tracks that the Classic carried over from the JT8 aft nacelle. The thrust gate design of the Classic flap was cleaned up, giving an improvement in flap effect, while mainly avoiding impingement on the flap and associated fatigue issues.
The Classic ran out of goodness around .745 but could be pushed higher if needed at considerable fuel burn. The NG for the same weight is running .785-.795 on lower fuel burns than the classic. To run a Classic at .79 takes a lot of extra gas... and while well within the operating boundary is associated with noticeable buffet from the aileron/shock separation. The NG has relatively high approach speeds, which is a tradeoff of the simplification of the flaps. Randolph's paper on high lift devices covers the tradeoffs well.
The Classic EFIS functioned, but the PFD/ND/EIS is supportable and upgradeable on the NG, the Classic being difficult to upgrade piecemeal. The Classic handles better IMHO, but the NG is a more effective transport aircraft,
As far as the fuselage goes, the double bubble profile precludes underfloor LD3 loading, Airbus picks up freight opportunities from any 737 operators.
the NG forward section removed the drooped cuff that was placed on the Classic wing profile of the original section. The weight increase of the Classic over the 200 resulted in a need for higher Cl/aoa, gained by the cuff. The NG extended the wing span, removed the cuff, and added a re-profiling of the aft section of the mid and inboard wing providing mild aft loading. The ailerons were increased in span, and reduced in chord which permitted removal of the outboard upper surface VGs, the shockwave remains clear of the hinge line at high speed. Flap system was simplified, and track design removed the residual tracks that the Classic carried over from the JT8 aft nacelle. The thrust gate design of the Classic flap was cleaned up, giving an improvement in flap effect, while mainly avoiding impingement on the flap and associated fatigue issues.
The Classic ran out of goodness around .745 but could be pushed higher if needed at considerable fuel burn. The NG for the same weight is running .785-.795 on lower fuel burns than the classic. To run a Classic at .79 takes a lot of extra gas... and while well within the operating boundary is associated with noticeable buffet from the aileron/shock separation. The NG has relatively high approach speeds, which is a tradeoff of the simplification of the flaps. Randolph's paper on high lift devices covers the tradeoffs well.
The Classic EFIS functioned, but the PFD/ND/EIS is supportable and upgradeable on the NG, the Classic being difficult to upgrade piecemeal. The Classic handles better IMHO, but the NG is a more effective transport aircraft,
As far as the fuselage goes, the double bubble profile precludes underfloor LD3 loading, Airbus picks up freight opportunities from any 737 operators.
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Great reading! Thanks!
A quick question, what made the -700 so different? I have no comparison to the -600, but not sure if there were any...
That ac was far "slicker" and was actually a bit difficult to manage the energy if you were used to the classics.
The -800 seemed much, much better handling than the -700 and other than engines, was it a different or improved wing?
A quick question, what made the -700 so different? I have no comparison to the -600, but not sure if there were any...
That ac was far "slicker" and was actually a bit difficult to manage the energy if you were used to the classics.
The -800 seemed much, much better handling than the -700 and other than engines, was it a different or improved wing?
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The -800 has the same wing as the -700. Higher weight means that the -800 has faster approach speeds. The -700 is significantly cleaner than previous versions, and more difficult to slow down, but the -800 is still worse, in that regard. All previous versions (except the original -200, pre- "advanced") moved the slats to Full Extend when the flaps go to 10 degrees. In the -800, you have to wait until flaps 25 to get them to go to Full Extend, meaning that it is even cleaner than the -700, right when it needs to slow down. As Cleavon Little said, in Fletch Lives, "I you want to stop, you have to plan ahead."
Last edited by Takwis; 23rd Dec 2019 at 22:32.
Great reading! Thanks!
A quick question, what made the -700 so different? I have no comparison to the -600, but not sure if there were any...
That ac was far "slicker" and was actually a bit difficult to manage the energy if you were used to the classics.
The -800 seemed much, much better handling than the -700 and other than engines, was it a different or improved wing?
A quick question, what made the -700 so different? I have no comparison to the -600, but not sure if there were any...
That ac was far "slicker" and was actually a bit difficult to manage the energy if you were used to the classics.
The -800 seemed much, much better handling than the -700 and other than engines, was it a different or improved wing?
No first hand knowledge here, but educated guess is that the flap changes on the NG were probably for noise. Deployed flaps are extremely noisy - during final approach airframe noise is generally equal or greater than the engine noise - and the more complex the flaps, the more noise they end to make. That may also be why the full extend slats are delayed on the -800.
The B737NG has high approach speeds because with a long fuselage and low landing gear, pitch attitude is limited so gaining lift through a higher angle of attack isn't possible, the airspeed needs to be kept up.
There is no doubt that a clean sheet design would have been a better option to replace the B737-200, reasons why this wasn't done have been stated above. The 1950s fuselage has always been the limiting factor of the B737. Airbus got it right with the A320 which was designed with higher bypass engines in mind and is able to accommodate baggage containers in the hold, passenger comfort is better and even the amount of overhead locker space is much greater which suits low cost operators with short turn around times and pax carrying more hand luggage.
Airlines such as Southwest and Ryanair are locked into the B737 just like a bad marriage where getting divorced is too hard.
There is no doubt that a clean sheet design would have been a better option to replace the B737-200, reasons why this wasn't done have been stated above. The 1950s fuselage has always been the limiting factor of the B737. Airbus got it right with the A320 which was designed with higher bypass engines in mind and is able to accommodate baggage containers in the hold, passenger comfort is better and even the amount of overhead locker space is much greater which suits low cost operators with short turn around times and pax carrying more hand luggage.
Airlines such as Southwest and Ryanair are locked into the B737 just like a bad marriage where getting divorced is too hard.
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thank you for the replies!
Still, something different in the design between -700 and -800.
On same procedure, 2nm R to short final with the -700 were difficult, while the -800 handled no problem...any ideas?
Trust me, I didnt get any better!
Fan delta? The -700 engines were dogs.
Still, something different in the design between -700 and -800.
On same procedure, 2nm R to short final with the -700 were difficult, while the -800 handled no problem...any ideas?
Trust me, I didnt get any better!
Fan delta? The -700 engines were dogs.
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thank you for the replies!
Still, something different in the design between -700 and -800.
On same procedure, 2nm R to short final with the -700 were difficult, while the -800 handled no problem...any ideas?
Trust me, I didnt get any better!
Fan delta? The -700 engines were dogs.
Still, something different in the design between -700 and -800.
On same procedure, 2nm R to short final with the -700 were difficult, while the -800 handled no problem...any ideas?
Trust me, I didnt get any better!
Fan delta? The -700 engines were dogs.
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But seriously I could not agree more. Having a good few thousand hours on Classics in recent years, before switching back to NG's, I prefer the Classic to fly, yes its old and awkward and you have to work at it, but there is a certain charm to them. The NG is a bit easier, until you try to slow down. I always have found that the 800 is a bit more stable than the 700, similar to the 300 and 400 really, though for me the 700 is the best of the bunch, well the BBJ version anyway
And If I recall correctly re an interesting offsite conversation in the late 90's- after the time of the MDC buyout and salting the aero group with a few MDC types, there was a major push to incorporate the inboard trailing edge wedge supposedly used on the MD-11 to attempt to meet DC-11 range guarantees. About that time Aviationpartners suggested an early version of winglets and was met with bucu skeptisim- but eventually some test fights were done on a BBJ under the guise of making the BBJ at least look different than the old 737 ( executives like the deluxe hubcaps to show their importance ) provided the winglets did not cause problems. The test results compared to the 'wedge' showed a definite improvement such that ( as I recall ) a german airline ordered a few that way, and the fuel savings on relatively short flights along with takeoff performance was significant.. And the rest is history
I've flown a B737 Classic with a DTE type device, (which was pretty mild, was looking at other items) and it was interesting, the same flow structure that exists at high AOA with a Gurney Tab is what occurs in the DTE case at low angles of attack and high Mach. The same device on a Lear was effective as one would expect. The basic aero that was applied to the MD twice was not bad, but there is more that could be done, in fact Airbus went further with their work than TBC did once they cut DAC out of the herd (or were taken over depending on your point of view) some really good work was done on an A330 by the busmen. The A320, 330, 340, 380s have always utilised blunt TE's and their wings have been effective. The bus subscribes more towards the Whitcomb notion of a SC-2 style wing section than TBC has ever done, they avoid the issues of high LE suction. The wing may not look pretty at first glance but the airbus offering is remarkably efficient IMHO. Grows on you like fungus. The most interesting thing is that none of them work as advertised, a supercritical section should have any normal shock well aft on the upper surface in transonic conditions, no one operates any of them fully subsonic, there is a shock on a 767, 747, 777, 787, 320, 330 340 380 wing in cruise, and a good one on the NG... One of the most stable shocks in cruise is off of the MD80, and it is almost where it is supposed to be for the old blender (having thirsty engines doesn't help though)
A DTE analogue was flown on my helicopter, and that was probably the most remarkable flight series I ever did. The impact of that is a subject all by its own, doing it safely takes more time and money than I had to justify on it at the time, but the stall Nr went from 82% to 68%, and the simple greatest impact was that instead of running out of pedal as the rotor stalled out, (dont try that at home) a pedal turn could be done against the torque. Do the maths to work out what the difference in applied torque is, 68^2/82^2 is the comparable Cl of the TRB, and the difference is sufficient authority to enjoy turns up to the stall. The rotor Nr was optically measured and also matched the timing N1 of the engine. If I had a fenestron, I would have taken that further, but the copter had a delicate TRB root which was not confidence inspiring. My opinion is that there is more to be done on the TE than is gained at the LE, for props, rotors, fan blades, etc. (actually, those were all tried with some fun).
Last edited by fdr; 24th Dec 2019 at 11:56.
Just a note that, as we were discussing why the NG came to be yesterday, the last one was being delivered.
Only half a speed-brake
And long may she fly! The last ever produced Classic is still running strong: https://www.flightradar24.com/UTA325/234c20b8., 20 years since the first flight. For 3 years the production ran in parallel.
Two admirable facts, below the skin-deep level:
- fuel capacity 21000 kgs (direct competitor 18730)
- max seating capacity 189 (direct competitor 180 until about 2 years ago), massive 5%.
Boeing 737 Detailed Technical Data, Mr. Brady's site also a legend of its own.
Two admirable facts, below the skin-deep level:
- fuel capacity 21000 kgs (direct competitor 18730)
- max seating capacity 189 (direct competitor 180 until about 2 years ago), massive 5%.
Boeing 737 Detailed Technical Data, Mr. Brady's site also a legend of its own.
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The -800 has the same wing as the -700. Higher weight means that the -800 has faster approach speeds. The -700 is significantly cleaner than previous versions, and more difficult to slow down, but the -800 is still worse, in that regard. All previous versions (except the original -200, pre- "advanced") moved the slats to Full Extend when the flaps go to 10 degrees. In the -800, you have to wait until flaps 25 to get them to go to Full Extend, meaning that it is even cleaner than the -700, right when it needs to slow down. As Cleavon Little said, in Fletch Lives, "I you want to stop, you have to plan ahead."
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Last edited by Takwis; 24th Dec 2019 at 16:08.
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The -800 is relatively fast on approach, the -700 pretty sedate. I have used approach speeds as low as 108kts on that one, and Vr below 100 on departure (good thing we used an 80 call, the airbus 100 would not have worked...). However, in thermals the -700 behaves with those slow speeds kinda like a glider plane and yaws around a lot, making it kinda uncomfortable especially in the rear of the cabin or even the aft galley. That said, i simply loved the climb performance. My record with a full pax load was 16 minutes to FL410, albeit on a short sector, therefore low fuel load.
I kinda liked the fact that the EFIS was able to grow over the production run of the plane, from the compatibility view to the classic, over the classic 777 style system to the more advanced version with navigation performance scales, vertical situation display and IAN capability, as well as GLS capability out of the box. And of course the fact that it can do CAT IIIb to no DH and 75m RVR, but with an alert height of 200ft instead of the airbus 100ft, with a 25kt crosswind capability as well during autoland, not to mention flap 30 OEI autoland which is quite convenient.
I kinda liked the fact that the EFIS was able to grow over the production run of the plane, from the compatibility view to the classic, over the classic 777 style system to the more advanced version with navigation performance scales, vertical situation display and IAN capability, as well as GLS capability out of the box. And of course the fact that it can do CAT IIIb to no DH and 75m RVR, but with an alert height of 200ft instead of the airbus 100ft, with a 25kt crosswind capability as well during autoland, not to mention flap 30 OEI autoland which is quite convenient.
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Great reading! Thanks!
A quick question, what made the -700 so different? I have no comparison to the -600, but not sure if there were any...
That ac was far "slicker" and was actually a bit difficult to manage the energy if you were used to the classics.
The -800 seemed much, much better handling than the -700 and other than engines, was it a different or improved wing?
A quick question, what made the -700 so different? I have no comparison to the -600, but not sure if there were any...
That ac was far "slicker" and was actually a bit difficult to manage the energy if you were used to the classics.
The -800 seemed much, much better handling than the -700 and other than engines, was it a different or improved wing?
The -800: high approach speeds, increased tailstrike risk, excessive floating tendency in the flare, and quite a handful to properly manage speed in descents.
The -800 may be more appreciable from the pax side due to less of a yaw tendency in the approach speed regime, but that's about it.
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Better handling of the -800? I personally don't think so. The -700 was a joy to fly, powerful, reasonable approach speeds, and, albeit "slippery", still well manageable in descents.
The -800: high approach speeds, increased tailstrike risk, excessive floating tendency in the flare, and quite a handful to properly manage speed in descents.
The -800 may be more appreciable from the pax side due to less of a yaw tendency in the approach speed regime, but that's about it.
The -800: high approach speeds, increased tailstrike risk, excessive floating tendency in the flare, and quite a handful to properly manage speed in descents.
The -800 may be more appreciable from the pax side due to less of a yaw tendency in the approach speed regime, but that's about it.