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TTailedTiger
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What made the 737 more "upgradable" than the 727?

Fri Apr 17, 2020 5:44 am

I had heard that prior to 9/11 there was interest among some airlines to convert the 727 to a two member flight deck. While it would have taken some work, it wouldn't have been too big an obstacle. The A300 and DC-10 had already undergone similar conversions.

But would it have been possible to design a twin-engine varient of the 727 with larger tail-mounted engines? I realize crews wouldn't be able to fly the theoretical twin-engine 727 alongside the original 727. Sort of like how 737-200/300/400/500 pilots wouldn't be able to fly the Max and so WN retired them quickly. But would a twin-engine 727 have provided better performance with it's rear mounted engines than the 737NG/Max? The 739 isn't the best when it comes to runway performance (although it gets greatly exaggerated by some) and of course we had the Max with it's issue of getting a bigger engine under the wing.

The 737NG got an all new wing so I assume they cpipdnhave done the same for the 727. But would it have just been too costly to redesign all of the fuel plumbing systems and reenforce the fuselage to accommodate larger engines? Or was the 727 just a heavier design compared to the 737?
 
CanadianNorth
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Re: What made the 737 more "upgradable" than the 727?

Fri Apr 17, 2020 6:04 am

All doable yes, but it a twin engine two-pilot 727 would likely do basically the same thing as an upgraded 737 would have done for the vast majority of operators. The only difference being the 737 already had a two-pilot cockpit and twin engine layout to start with, making the upgrade much easier.

I don't think such a 727 mod would have much better performance than the 737NG. Tail mounted engine designs allow a sleek look, cleaner wing and a quieter cabin, but they are harder to maintain and upgrade, they complicate weight and balance, they usually lead to a T-tail design which is harder to maintain and de-ice and usually comes with the deep-stall issue, and they increase the structural weight of the airframe. As much as I dislike modern jetliners all looking the same, there is a reason why they all look the same. Many layouts have been tried, and the 737-3+/A320/etc. style layout has consistently emerged as the best balance of efficiency and practicality for most airline applications.
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thegrew
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Re: What made the 737 more "upgradable" than the 727?

Fri Apr 17, 2020 2:05 pm

Wasn't the 757 a two engined 727 replacement with a two man flight deck?

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Dalmd88
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Re: What made the 737 more "upgradable" than the 727?

Fri Apr 17, 2020 2:33 pm

The two crew member mod would have been very expensive. That's why it was never done by any of the upgrades. You brought up the DC 10. So why could that be done and not the 727. I would guess a couple of factors came into play. First would be return on investment. Think of the payload capacity difference. The cost of the mod would likely be similar, but with the larger payload of the DC10 the cost is spread over a larger segment. I think the 10F has more than double the cargo payload as the 727F. Second is also related to ROI. The Age of the fleet. When the DC10F mod was done the fleet age was lower, yes the hours/ age in years might have been similar, but the widebody has a longer shelf life than most narrowbodies. You just could not justify the cost over the expected remaining life of the 727.

So what about using a larger tail mounted engine? The Super 27 mod did something similar. Valsan swapped out the #1 and #3 with larger JT8D-219 but kept the little 8 in the #2 slot. I think there were about a 100 done. The -219 gives a 4000 lb thrust boost. Not sure on the weight penalty but I would imagine not too much. Not enough of a gain to eliminate the #2.

That leaves us with the only other large tail mounted engine, the V2500 D5 from the MD90. Two of those actually give you a thrust rating above the old little eight package. I'm guessing here but I think the weight might have been a problem for the 727. Likely would have required a lot of structural changes to accommodate the engines. You also have to do something with the #2 duct inlet. That's a lot of cost with zero gain in cargo volume.

Guess what there are tons of cheap 737 and 757 that just need cargo door conversions. Two pilot flight decks, more efficient twin engines.
 
rfields5421
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Re: What made the 737 more "upgradable" than the 727?

Fri Apr 17, 2020 3:37 pm

The OP is talking about two separate upgrades/ changes.

Two person flight deck - doable, but the way aircraft were designed and built in the seven year gap between the B727 and DC-10 was HUGE. But it was doable. The retro-fit of the common cockpit for the DC-10 was made easier by the MD-11

Re-engine and redesign of wings/ fuselage/ engine number and placement - This would be a DC-10 to MD-11 type upgrade for the B-727. Why would Boeing want to do that? They had other aircraft in production to fit the market for that mission need.

To some extend the early jet passenger/ aircraft were developmental increments as manufacturers got better and better at designing and building aircraft. And the market, airlines got better and better at determining what their needs were.

As the usage of high speed computers because a part of the design process, many factors were determined to have been over designed. One comparison I've heard is the early jetliners like the B727 were overbuilt with higher weight / strength components. The B-727 tri-engine was built in part due to a lack of confidence in the ability of engine builders to make engines with a very low failure percentage.

Aircraft and aircraft design is still relatively NEW on the grand scale of human industrial progress. There is still at least one human alive today who is known to have been born before the Wright Brothers took to the air at Kitty Hawk.

The first commercial jet aircraft flight took off just five months before I was born.

The B727 was a wonderful bird. I enjoyed flying upon it many times. But it was a developmental STEP in the progress of learning how to built fast transport aircraft, improve reliability, improve the cost efficiency and operation of airlines.

And though it may not seem so to many, I think there is much additional progress to be made in the next century of aircraft design and usage.
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rjsampson
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Re: What made the 737 more "upgradable" than the 727?

Fri Apr 17, 2020 7:43 pm

Dalmd88 wrote:
The Super 27 mod did something similar. Valsan swapped out the #1 and #3 with larger JT8D-219 but kept the little 8 in the #2 slot.. The -219 gives a 4000 lb thrust boost.


A FedEx buddy of mine who flew the Super 27 told me that extra 4,000 lb wasn't available on takeoff (where Stage III is enforced). He said the middle engine would be brought up no higher than 60% N1 for noise abatement.
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. Unfortunately, we're grounded :(
 
BravoOne
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Re: What made the 737 more "upgradable" than the 727?

Sat Apr 18, 2020 5:25 pm

In fairness to the 727, it went through numerous upgrades over the life of the airframe. 727-100, 727-200, 727-200ADV. 727-200F along with numerous JT8D power plant, aux fuel, and gross weight iterations. Avionic upgrades could be had that were state of the art for that period in time.

Then of course there were numerous after market mods like Valson etc. Of course none of these could overcome the 3 man, 3 engine cost factors. The 737 will never be the airplane the 727 was. Just say.
 
Max Q
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Re: What made the 737 more "upgradable" than the 727?

Sun Apr 19, 2020 9:41 am

B727-200 empty weight was a little over 100k whereas a 738 is around 90k

Pretty big difference
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T18
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Re: What made the 737 more "upgradable" than the 727?

Sun Apr 19, 2020 11:27 am

Another point, by 2001, Boeing already produced a T-tail, Twin engine, 2 pilot a/c in the 717/MD80/90 series. I'm not sure given that they would have seen it profitable to redesign the 727 and start a new production line to build said type. Keep in mind as well the 727 line closed in 1984.

I'd reckon the interest in a flight deck conversion was purely to save costs as it would likely have been cheaper than buying a new airframe and training crews on the new type.
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BravoOne
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Re: What made the 737 more "upgradable" than the 727?

Sun Apr 19, 2020 4:03 pm

T18 wrote:
Another point, by 2001, Boeing already produced a T-tail, Twin engine, 2 pilot a/c in the 717/MD80/90 series. I'm not sure given that they would have seen it profitable to redesign the 727 and start a new production line to build said type. Keep in mind as well the 727 line closed in 1984.

I'd reckon the interest in a flight deck conversion was purely to save costs as it would likely have been cheaper than buying a new airframe and training crews on the new type.



There would have been significant training none the less had the two man 727 come to fruition.
 
LH707330
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Re: What made the 737 more "upgradable" than the 727?

Sun Apr 19, 2020 6:36 pm

There are several reasons that this would not have been a good economic idea, although possible as an engineering exercise.

Start with the wing: it's got a 35-degree sweep and triple slotted flaps so it could go both fast and slow. This means it's heavy. All of the replacements (A320, 757, 734/738) have a 25-degree sweep and lower cruise speeds. This means less wing weight and better fuel efficiency. So our redo will need a new wing.

Next, the engine and tail configuration: this was done for FOD protection, which had mostly gone away by the 1980s. At that point, it's a relic with extra structural weight. If you're going to redo it, you may as well move the engines under the wing that you needed to replace anyway.

Fuselage: this seems to work, minus the aforementioned tail. The capacity of the 727-200 seemed to be about right, in between the 737-300 and the 757-200. Incidentally, the 737 shares the same fuselage as the 727. Our friends over in Toulouse have just made the A320, which means we need a similar payload-range. So let's take our 727 fuselage with the new reduced-sweep wing and underslung engines, then put a different tail on it. It's worth noting that the existing 737-300 tail will probably do the trick, with a taller fin and lengthened stabilizers, so let's just use those.

Last step is to give our new design a name. It's now got two engines and looks more like a 737 than a 727, so let's just go ahead and call it a 737-800....
 
GalaxyFlyer
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Re: What made the 737 more "upgradable" than the 727?

Sun Apr 19, 2020 11:06 pm

LH707330 wrote:
There are several reasons that this would not have been a good economic idea, although possible as an engineering exercise.

Start with the wing: it's got a 35-degree sweep and triple slotted flaps so it could go both fast and slow. This means it's heavy. All of the replacements (A320, 757, 734/738) have a 25-degree sweep and lower cruise speeds. This means less wing weight and better fuel efficiency. So our redo will need a new wing.

Next, the engine and tail configuration: this was done for FOD protection, which had mostly gone away by the 1980s. At that point, it's a relic with extra structural weight. If you're going to redo it, you may as well move the engines under the wing that you needed to replace anyway.

Fuselage: this seems to work, minus the aforementioned tail. The capacity of the 727-200 seemed to be about right, in between the 737-300 and the 757-200. Incidentally, the 737 shares the same fuselage as the 727. Our friends over in Toulouse have just made the A320, which means we need a similar payload-range. So let's take our 727 fuselage with the new reduced-sweep wing and underslung engines, then put a different tail on it. It's worth noting that the existing 737-300 tail will probably do the trick, with a taller fin and lengthened stabilizers, so let's just use those.

Last step is to give our new design a name. It's now got two engines and looks more like a 737 than a 727, so let's just go ahead and call it a 737-800....


The tail mounted engines were NOT for FOD protection. There is no certification standard for FOD protection. They were done for 1/ field performance out of LGA; 2/ accommodate 3 engines to lower take-off weather minimums as existed in 1960 (3 engines reduced weather to 1/2 mile as opposed to twins with 1 mile); 3/ an engineering “fashion” statement. See VC-10 designed for field performance at African BOAC stations.
 
RJMAZ
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Re: What made the 737 more "upgradable" than the 727?

Mon Apr 20, 2020 5:36 am

New engines have a higher bypass ratio and are much larger in diameter.

This makes it very difficult to upgrade the 727 with new engines.

The wing was very old fashioned. A high sweep, low aspect ratio does noy give good fuel efficiency. Improvements in aerodynamics over the years allow for less sweep while maintaining speed. Less sweep reduces weight and improves fuel burn. A win win situation.

The 737NG wing was game changing.
 
LH707330
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Re: What made the 737 more "upgradable" than the 727?

Mon Apr 20, 2020 6:21 pm

GalaxyFlyer wrote:
LH707330 wrote:
There are several reasons that this would not have been a good economic idea, although possible as an engineering exercise.

Start with the wing: it's got a 35-degree sweep and triple slotted flaps so it could go both fast and slow. This means it's heavy. All of the replacements (A320, 757, 734/738) have a 25-degree sweep and lower cruise speeds. This means less wing weight and better fuel efficiency. So our redo will need a new wing.

Next, the engine and tail configuration: this was done for FOD protection, which had mostly gone away by the 1980s. At that point, it's a relic with extra structural weight. If you're going to redo it, you may as well move the engines under the wing that you needed to replace anyway.

Fuselage: this seems to work, minus the aforementioned tail. The capacity of the 727-200 seemed to be about right, in between the 737-300 and the 757-200. Incidentally, the 737 shares the same fuselage as the 727. Our friends over in Toulouse have just made the A320, which means we need a similar payload-range. So let's take our 727 fuselage with the new reduced-sweep wing and underslung engines, then put a different tail on it. It's worth noting that the existing 737-300 tail will probably do the trick, with a taller fin and lengthened stabilizers, so let's just use those.

Last step is to give our new design a name. It's now got two engines and looks more like a 737 than a 727, so let's just go ahead and call it a 737-800....


The tail mounted engines were NOT for FOD protection. There is no certification standard for FOD protection. They were done for 1/ field performance out of LGA; 2/ accommodate 3 engines to lower take-off weather minimums as existed in 1960 (3 engines reduced weather to 1/2 mile as opposed to twins with 1 mile); 3/ an engineering “fashion” statement. See VC-10 designed for field performance at African BOAC stations.

Regarding the FOD, was that not a consideration regardless of cert criteria? What other advantages does the tail-mounted config have then on the 727? Lower ground clearance at outstations while maintaining field performance?

I'd be curious to see how a VC10 compared to a 720B and how much of the difference was attributable to T/W versus layout. I know the clean wing helped, but the whole thing also weighed more as a consequence.
 
BravoOne
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Re: What made the 737 more "upgradable" than the 727?

Mon Apr 20, 2020 6:53 pm

The VC10 and B720B have little in common other than the fact they are both jet airliners. Maybe the 707-320B and Suoer VC10 would be a closer comparison? Love the VC10:)
 
GalaxyFlyer
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Re: What made the 737 more "upgradable" than the 727?

Mon Apr 20, 2020 9:42 pm

LH707330 wrote:
GalaxyFlyer wrote:
LH707330 wrote:
There are several reasons that this would not have been a good economic idea, although possible as an engineering exercise.

Start with the wing: it's got a 35-degree sweep and triple slotted flaps so it could go both fast and slow. This means it's heavy. All of the replacements (A320, 757, 734/738) have a 25-degree sweep and lower cruise speeds. This means less wing weight and better fuel efficiency. So our redo will need a new wing.

Next, the engine and tail configuration: this was done for FOD protection, which had mostly gone away by the 1980s. At that point, it's a relic with extra structural weight. If you're going to redo it, you may as well move the engines under the wing that you needed to replace anyway.

Fuselage: this seems to work, minus the aforementioned tail. The capacity of the 727-200 seemed to be about right, in between the 737-300 and the 757-200. Incidentally, the 737 shares the same fuselage as the 727. Our friends over in Toulouse have just made the A320, which means we need a similar payload-range. So let's take our 727 fuselage with the new reduced-sweep wing and underslung engines, then put a different tail on it. It's worth noting that the existing 737-300 tail will probably do the trick, with a taller fin and lengthened stabilizers, so let's just use those.

Last step is to give our new design a name. It's now got two engines and looks more like a 737 than a 727, so let's just go ahead and call it a 737-800....


The tail mounted engines were NOT for FOD protection. There is no certification standard for FOD protection. They were done for 1/ field performance out of LGA; 2/ accommodate 3 engines to lower take-off weather minimums as existed in 1960 (3 engines reduced weather to 1/2 mile as opposed to twins with 1 mile); 3/ an engineering “fashion” statement. See VC-10 designed for field performance at African BOAC stations.

Regarding the FOD, was that not a consideration regardless of cert criteria? What other advantages does the tail-mounted config have then on the 727? Lower ground clearance at outstations while maintaining field performance?

I'd be curious to see how a VC10 compared to a 720B and how much of the difference was attributable to T/W versus layout. I know the clean wing helped, but the whole thing also weighed more as a consequence.


I flew it and have dozens who flew, FOD is not design criteria. If it were, even then, how’d the 707 and 737 get built?

The field performance with tail mounted engines is better for number of reasons—“clean” wing meaning unobstructed high lift devices; closer thrust lines dan mean lower Vmcg and Vmca for starters. At the time minimums for take-off were higher for twins.

GF
 
BravoOne
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Re: What made the 737 more "upgradable" than the 727?

Mon Apr 20, 2020 9:48 pm

Max Q wrote:
B727-200 empty weight was a little over 100k whereas a 738 is around 90k

Pretty big difference



Perhaps, but recall that over the life of the 727, went from somewhere around 172,000 up to 208,000 TOGW which is pretty significant. Not sure what those numbes would like for the 737. Regardless, the 737 evolved to surpass the the 727 for all the previous reasons mentioned.
 
MatthewDB
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Re: What made the 737 more "upgradable" than the 727?

Tue Apr 21, 2020 6:35 am

CanadianNorth wrote:
As much as I dislike modern jetliners all looking the same, there is a reason why they all look the same. Many layouts have been tried, and the 737-3+/A320/etc. style layout has consistently emerged as the best balance of efficiency and practicality for most airline applications.


Just to add to your point, consider:

- Bombardier already had the rear engine, T tail CRJ. What did they replace it with? The C series that looks like the 737/A320.

- Embraer already had the rear engine, T tail ERJ. What did they replace it with? The E series and then the E2 series that looks like the 737/A320.

Seems to be a pretty strong pattern...
 
Max Q
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Re: What made the 737 more "upgradable" than the 727?

Tue Apr 21, 2020 9:38 am

BravoOne wrote:
Max Q wrote:
B727-200 empty weight was a little over 100k whereas a 738 is around 90k

Pretty big difference



Perhaps, but recall that over the life of the 727, went from somewhere around 172,000 up to 208,000 TOGW which is pretty significant. Not sure what those numbes would like for the 737. Regardless, the 737 evolved to surpass the the 727 for all the previous reasons mentioned.



I think there was one option for a 210K MGTOW
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Faro
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Re: What made the 737 more "upgradable" than the 727?

Wed Apr 22, 2020 2:56 pm

Max Q wrote:
B727-200 empty weight was a little over 100k whereas a 738 is around 90k

Pretty big difference



That’s it right there...there’s a reason why no-one builds T-tailed airliners anymore...that’s all the reason you need...the rest is secondary...


Faro
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LH707330
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Re: What made the 737 more "upgradable" than the 727?

Fri Apr 24, 2020 6:00 pm

GalaxyFlyer wrote:
LH707330 wrote:
GalaxyFlyer wrote:

The tail mounted engines were NOT for FOD protection. There is no certification standard for FOD protection. They were done for 1/ field performance out of LGA; 2/ accommodate 3 engines to lower take-off weather minimums as existed in 1960 (3 engines reduced weather to 1/2 mile as opposed to twins with 1 mile); 3/ an engineering “fashion” statement. See VC-10 designed for field performance at African BOAC stations.

Regarding the FOD, was that not a consideration regardless of cert criteria? What other advantages does the tail-mounted config have then on the 727? Lower ground clearance at outstations while maintaining field performance?

I'd be curious to see how a VC10 compared to a 720B and how much of the difference was attributable to T/W versus layout. I know the clean wing helped, but the whole thing also weighed more as a consequence.


I flew it and have dozens who flew, FOD is not design criteria. If it were, even then, how’d the 707 and 737 get built?

The field performance with tail mounted engines is better for number of reasons—“clean” wing meaning unobstructed high lift devices; closer thrust lines dan mean lower Vmcg and Vmca for starters. At the time minimums for take-off were higher for twins.

GF

Thanks for the elaboration, and good point on Vmca and Vmcg, those definitely alter the picture.
 
LH707330
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Re: What made the 737 more "upgradable" than the 727?

Fri Apr 24, 2020 6:03 pm

BravoOne wrote:
The VC10 and B720B have little in common other than the fact they are both jet airliners. Maybe the 707-320B and Suoer VC10 would be a closer comparison? Love the VC10:)

Both were designed to have good performance at the expense of seat mile cost, especially relative to their larger siblings you mentioned. It's worth noting that the Super and the 320B were significantly heavier, but had the same engines, effectively swapping runway performance for payload.
 
BravoOne
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Re: What made the 737 more "upgradable" than the 727?

Fri Apr 24, 2020 7:03 pm

Actually the 720B had 17,00 pound thrust JT3D-??, while the 320B/C had 18,000 lbs. Those numers look so small by todays engine thrust numbers.
 
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Re: What made the 737 more "upgradable" than the 727?

Sat Apr 25, 2020 5:24 am

CanadianNorth wrote:
I don't think such a 727 mod would have much better performance than the 737NG.


Everywhere I've read, the '727 - while being a lot more fuel thirsty, would get from A to B a little (or a lot) faster then the NG. Thats what we want. Speed. Flight times have gone backwards over the decades. Something not right there.
 
Max Q
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Re: What made the 737 more "upgradable" than the 727?

Sat Apr 25, 2020 10:52 am

Ruddman wrote:
CanadianNorth wrote:
I don't think such a 727 mod would have much better performance than the 737NG.


Everywhere I've read, the '727 - while being a lot more fuel thirsty, would get from A to B a little (or a lot) faster then the NG. Thats what we want. Speed. Flight times have gone backwards over the decades. Something not right there.



It was a lot faster, MMO was .91 and I’ve cruised at that speed, insane fuel flows though


.83 to .86 was quite practical though when flying into a headwind and/ or running late
The best contribution to safety is a competent Pilot.


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GalaxyFlyer
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Re: What made the 737 more "upgradable" than the 727?

Sat Apr 25, 2020 3:42 pm

The noise level would be insane, too.
 
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Ruddman
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Re: What made the 737 more "upgradable" than the 727?

Sat Apr 25, 2020 8:41 pm

Max Q wrote:
Ruddman wrote:
CanadianNorth wrote:
I don't think such a 727 mod would have much better performance than the 737NG.


Everywhere I've read, the '727 - while being a lot more fuel thirsty, would get from A to B a little (or a lot) faster then the NG. Thats what we want. Speed. Flight times have gone backwards over the decades. Something not right there.



It was a lot faster, MMO was .91 and I’ve cruised at that speed, insane fuel flows though


.83 to .86 was quite practical though when flying into a headwind and/ or running late



Yeah one sweet machine. Yep, and that's fast! Boeing's best looking aircraft too I think. :)
 
Calledonian
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Re: What made the 737 more "upgradable" than the 727?

Tue Apr 28, 2020 7:21 pm

Faro wrote:
Max Q wrote:
B727-200 empty weight was a little over 100k whereas a 738 is around 90k

Pretty big difference



That’s it right there...there’s a reason why no-one builds T-tailed airliners anymore...that’s all the reason you need...the rest is secondary...


Faro

Comac would disagree with that statement...
 
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Faro
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Re: What made the 737 more "upgradable" than the 727?

Wed Apr 29, 2020 6:52 am

Calledonian wrote:
Faro wrote:
Max Q wrote:
B727-200 empty weight was a little over 100k whereas a 738 is around 90k

Pretty big difference



That’s it right there...there’s a reason why no-one builds T-tailed airliners anymore...that’s all the reason you need...the rest is secondary...


Faro

Comac would disagree with that statement...



I think I'll refrain from commenting on that one...


Faro
The chalice not my son
 
744SPX
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Re: What made the 737 more "upgradable" than the 727?

Wed Apr 29, 2020 8:54 pm

Calledonian wrote:
Faro wrote:
Max Q wrote:
B727-200 empty weight was a little over 100k whereas a 738 is around 90k

Pretty big difference



That’s it right there...there’s a reason why no-one builds T-tailed airliners anymore...that’s all the reason you need...the rest is secondary...


Faro

Comac would disagree with that statement...


So would Gulfstream and Bombardier (Global series) They are technically not commercial but are the same size as commercial aircraft and in some cases larger.
 
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scbriml
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Re: What made the 737 more "upgradable" than the 727?

Wed Apr 29, 2020 9:39 pm

Ruddman wrote:
CanadianNorth wrote:
I don't think such a 727 mod would have much better performance than the 737NG.


Everywhere I've read, the '727 - while being a lot more fuel thirsty, would get from A to B a little (or a lot) faster then the NG. Thats what we want. Speed. Flight times have gone backwards over the decades. Something not right there.


I suspect the vast majority would prefer the lower fares derived from more efficient cruise speeds than saving a few minutes.
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CanadianNorth
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Re: What made the 737 more "upgradable" than the 727?

Thu Apr 30, 2020 2:15 am

Ruddman wrote:
CanadianNorth wrote:
I don't think such a 727 mod would have much better performance than the 737NG.


Everywhere I've read, the '727 - while being a lot more fuel thirsty, would get from A to B a little (or a lot) faster then the NG. Thats what we want. Speed. Flight times have gone backwards over the decades. Something not right there.


Seems to be a popular quote, so I'll elaborate a little.

By performance I was meaning overall bang for your buck more so than speed specifically. In most cases a 737NG vs a 727NG would be able to carry more payload over longer distances for less operating costs. Sure it would be slightly slower cruise speed (though probably 20 minutes if not less in most cases) and need a better runway (also I'm betting most places they actually fly have a good enough runway already anyway), but probably perform better in almost every other department (payload, range, fuel burn, maintenance costs, etc.)

The industry has stagnated on the speed thing for sure, but I believe that is mostly because as speed goes up so does cost, and people seem to have reached a consensus for now on approximately how much speed they're willing to pay for. The 172 is slower than a 182, but people still buy them because they're cheaper. The ATR 72 is slower than the Q400, but airlines still line up to buy them because they burn less fuel The Convair 880 and 990 were faster than the DC-8s and 707s, but yet they were a swing and a miss in the sales department because for basically the same price Boeing and Douglas jets could move more payload across longer routes. Seems to be fairly consistent for a few decades now that across the industry speed is great but price does matter.

At the end of the day, the airplane that ticks the most boxes for the airline's bottom line wins. The 727 is one of the nicest looking airliners going for sure, even parked it looks fast, I love the speed and the look of it and if the airline I worked for ever bought a 727 I would probably need a minute, but the reality is for the airline bean counters the upgraded 737 simply ticked more boxes for less price, and so the vast majority of customers went that way.
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Vctony
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Re: What made the 737 more "upgradable" than the 727?

Thu Apr 30, 2020 3:46 am

LH707330 wrote:
There are several reasons that this would not have been a good economic idea, although possible as an engineering exercise.

Start with the wing: it's got a 35-degree sweep and triple slotted flaps so it could go both fast and slow. This means it's heavy. All of the replacements (A320, 757, 734/738) have a 25-degree sweep and lower cruise speeds. This means less wing weight and better fuel efficiency. So our redo will need a new wing.

Next, the engine and tail configuration: this was done for FOD protection, which had mostly gone away by the 1980s. At that point, it's a relic with extra structural weight. If you're going to redo it, you may as well move the engines under the wing that you needed to replace anyway.

Fuselage: this seems to work, minus the aforementioned tail. The capacity of the 727-200 seemed to be about right, in between the 737-300 and the 757-200. Incidentally, the 737 shares the same fuselage as the 727. Our friends over in Toulouse have just made the A320, which means we need a similar payload-range. So let's take our 727 fuselage with the new reduced-sweep wing and underslung engines, then put a different tail on it. It's worth noting that the existing 737-300 tail will probably do the trick, with a taller fin and lengthened stabilizers, so let's just use those.

Last step is to give our new design a name. It's now got two engines and looks more like a 737 than a 727, so let's just go ahead and call it a 737-800....


I agree. The 737-800 was the 727NG. Airlines seemed to think so too with AA, DL, and CO replacing their large 727 fleets with 737-800s.
 
ELBOB
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Re: What made the 737 more "upgradable" than the 727?

Fri May 01, 2020 6:40 am

RJMAZ wrote:
The wing was very old fashioned. A high sweep, low aspect ratio does noy give good fuel efficiency. Improvements in aerodynamics over the years allow for less sweep while maintaining speed. Less sweep reduces weight and improves fuel burn. A win win situation.

The 737NG wing was game changing.


You've defeated your own argument there. The 737 needed a new wing, and therefore the NG wing was designed and was indeed remarkable.

The 727NG would have needed a new wing. But that was nothing unexpected; the 727-300 project of 1974-76 incorporated a new wing as well as a fuselage stretch and new bogie undercarriage. And the -300 wing was designed for retrofit to the 727-200 as the 200B to give a long-range thin-route variant.

So re-winging the 727 was neither novel nor infeasible.
 
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dennypayne
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Re: What made the 737 more "upgradable" than the 727?

Fri May 01, 2020 5:02 pm

ELBOB wrote:
RJMAZ wrote:
The wing was very old fashioned. A high sweep, low aspect ratio does noy give good fuel efficiency. Improvements in aerodynamics over the years allow for less sweep while maintaining speed. Less sweep reduces weight and improves fuel burn. A win win situation.

The 737NG wing was game changing.


You've defeated your own argument there. The 737 needed a new wing, and therefore the NG wing was designed and was indeed remarkable.

The 727NG would have needed a new wing. But that was nothing unexpected; the 727-300 project of 1974-76 incorporated a new wing as well as a fuselage stretch and new bogie undercarriage. And the -300 wing was designed for retrofit to the 727-200 as the 200B to give a long-range thin-route variant.

So re-winging the 727 was neither novel nor infeasible.


Anything's feasible if you throw enough money at it. But you cropped out the other part of his 'argument' regarding engine upgrades, and I'm sure other cost calculations entered the picture as well. Clearly the more cost-effective decision was to shelve that project and take a different path.

I too think the 727 is a much better looking airliner than the 737, but economic realities drive aircraft development.
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GalaxyFlyer
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Re: What made the 737 more "upgradable" than the 727?

Fri May 01, 2020 5:33 pm

Boeing would have needed a high bypass engine to upgrade the 727, then fit in the tail. That’s a new airplane, although UPS tried with RR Tays which didn’t work out.
 
BravoOne
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Re: What made the 737 more "upgradable" than the 727?

Fri May 01, 2020 6:54 pm

I have seen models at Boeing of a two engined 727, so obviously it was a consideration that never came to pass.
 
ELBOB
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Re: What made the 737 more

Sat May 02, 2020 7:07 am

dennypayne wrote:

Anything's feasible if you throw enough money at it. But you cropped out the other part of his 'argument' regarding engine upgrades


OK, in 1982 Boeing completed studies into re-engineing the 727-200 with two derated RB211-525 or PW2037 as a modification package. American Airlines was particularly interested.

There is no technical reason why the 737 'won' within Boeing. In fact the 727-300 and 737-300 were intended to be complementary sales models into the mid-80s. The reason the 737 continued into NG and Max models was purely due to politics within the organisation; technically it was probably less adaptable to new technology.

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