uta999
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Could the 787 be scaled to create the 797?

Sat Jul 06, 2019 8:47 pm

The 787-8/9/10 appear to be the perfect aircraft. Is it possible to shrink the exact same design to create the 797, in record time to replace the MAX?

A scaled down 787 would be 40-50% smaller, with new engines and gear. All other components being scaled down to size, except doors and windows.

The cost savings of development, flight testing and final assembly would be enormous. It would also create a common Boeing family, similar to that of car manufacturers.

It would also recoup some of the billions spent on 787 development. I would estimate it would halve the time to EIS too.
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VSMUT
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Re: Could the 787 be scaled to create the 797?

Sat Jul 06, 2019 8:59 pm

No. You can't just scale things in aviation.
 
strfyr51
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Re: Could the 787 be scaled to create the 797?

Sat Jul 06, 2019 9:00 pm

I think it could be possible, But? were the fuselage made of Aluminum- Lithium? It might have more tolerance to "Road Rash" when used in Domestic Service.
The wings could be composite as well as the horizontal and vertical Stabilizers but the fuselage might be better in aluminum IMHO. ( for damage tolerance as you wouldn't need to "cook" a Patch Repair on any fuselage Ding-Dent or Puncture..to repair it.
 
Weatherwatcher1
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Re: Could the 787 be scaled to create the 797?

Sat Jul 06, 2019 9:28 pm

uta999 wrote:
The cost savings of development, flight testing and final assembly would be enormous. It would also create a common Boeing family, similar to that of car manufacturers.

It would also recoup some of the billions spent on 787 development. I would estimate it would halve the time to EIS too.


No the cost savings would not be enormous. To effectively shrink an airplane, everything has to be redesigned. As an example, with lower aero loads, the flight control surfaces can be smaller. That results in smaller hydraulic pumps, Lines and reservoirs. Nothing stays the same unless compromises are made that impact efficiency. They could keep a 45gpm pump for commonality, but that adds weight since the plane only needs 30 gpm pumps. Weight hursts efficiency

Stretches are the opposite. Only components without enough margin for the higher loads need to be redesigned. A stretch may touch 5% of the engineering drawings. An effective and efficient 40% shrink would touch 95%.
 
morrisond
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Re: Could the 787 be scaled to create the 797?

Sat Jul 06, 2019 9:41 pm

NMA is effectively a shrunk 787 (not the same barrel though) - using the technology from 787. They have been working on it for years and there are currently over 1,000 Engineers on it. That is why Boeing is saying EIS 2025 - although that seems pretty tough right now 2026/2027 is probably more likely given the probably new certification regime.

Even so - by relying on 787 tech they will be able to do it a lot faster than a complete next generation technology clean sheet program.

They may break new ground in how they manufacturer NMA though and go beyond what they did on 787.
 
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rikkus67
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Re: Could the 787 be scaled to create the 797?

Sat Jul 06, 2019 9:54 pm

Only if Section 41 (cockpit) could be grafted onto a narrower fuselage, but that's about it. The 767 Section 41 cockpit was used on the 777. IIRC the "adaptor" section to increase the cockpit diameter to meet up with the larger fuselage section was quite a design challenge, so Boeing had to use a smaller portion of the 767's Section 41. This is why the 777 has such a distinctive "forehead". Can it be done in the 787 to 797/NMA scenario? More than likely. Would it be economical? Likely not.
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LDRA
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Re: Could the 787 be scaled to create the 797?

Sat Jul 06, 2019 10:01 pm

Rather than scale 787, just make a 787-8 V2 for MoM. Redesign structure for 200T MTOW, using lessons learned from 1st gen 787 structure, new 5000lb MoM engines, center wing box tank deletion, done!

7 across is rather inefficient use of space anyways

Smaller end of MoM space can be covered by NSA
 
TTailedTiger
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Re: Could the 787 be scaled to create the 797?

Sat Jul 06, 2019 10:11 pm

morrisond wrote:
NMA is effectively a shrunk 787 (not the same barrel though) - using the technology from 787. They have been working on it for years and there are currently over 1,000 Engineers on it. That is why Boeing is saying EIS 2025 - although that seems pretty tough right now 2026/2027 is probably more likely given the probably new certification regime.

Even so - by relying on 787 tech they will be able to do it a lot faster than a complete next generation technology clean sheet program.

They may break new ground in how they manufacturer NMA though and go beyond what they did on 787.


Thanks for info. As soon as the Max is back in the air they need to announce the NMA. Get everyone's mind on something positive.
 
AC77X
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Re: Could the 787 be scaled to create the 797?

Sat Jul 06, 2019 10:53 pm

I don't think they can really just make a "scaled down" 787. Thats just making another plane since you have to redesign things anyway. Technology wise, aren't the 777, 787, and this proposed 797 supposed to have similar technology? If so, I guess it would be a scaled down version depending on what you define a scaled down version as.
 
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LAX772LR
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Re: Could the 787 be scaled to create the 797?

Sat Jul 06, 2019 11:09 pm

CAN it be scaled down?
...of course it can. With enough time/money, you can do anything in aviation.

But that's the wrong question. The question should be: would a scaled-down 787 be the optimal design for that market mission?
THAT is a far more pertinent thing to be asking, and the one that Boeing would be considering.
I myself, suspect a more prosaic motive... ~Thranduil
 
MEA-707
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Re: Could the 787 be scaled to create the 797?

Sat Jul 06, 2019 11:31 pm

VSMUT wrote:
No. You can't just scale things in aviation.

It has been done before. In the USSR they just made a 80% sized Tu-104 and called it the Tu-124. Almost everything was 80%, it was 4 instead of 5 abreast, smaller tail and wings, smaller engines, of course things like seats and doors were not shrunk. It seemed a reasonably efficient aircraft for that time and the more successful Tu-134 was based on it (same fuselage) and remained in production for almost 30 years, so I think it can work without getting an inefficient frankenstein aircraft.
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musman9853
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 12:09 am

strfyr51 wrote:
I think it could be possible, But? were the fuselage made of Aluminum- Lithium? It might have more tolerance to "Road Rash" when used in Domestic Service.
The wings could be composite as well as the horizontal and vertical Stabilizers but the fuselage might be better in aluminum IMHO. ( for damage tolerance as you wouldn't need to "cook" a Patch Repair on any fuselage Ding-Dent or Puncture..to repair it.


then it's not a 787 derivative. besides, one of the main reasons boeing is citing to build the 797 is to develop the ability to scale up composite production for nsa through project black diamond.
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soyuz
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 12:17 am

MEA-707 wrote:
VSMUT wrote:
No. You can't just scale things in aviation.

It has been done before. In the USSR they just made a 80% sized Tu-104 and called it the Tu-124. Almost everything was 80%, it was 4 instead of 5 abreast, smaller tail and wings, smaller engines, of course things like seats and doors were not shrunk. It seemed a reasonably efficient aircraft for that time and the more successful Tu-134 was based on it (same fuselage) and remained in production for almost 30 years, so I think it can work without getting an inefficient frankenstein aircraft.


And with only 164 units built, it wasn’t a raging success. Your point that it can be done is valid, however the subsequent 134 was a fairly drastic redesign and had little in common with the original shrink 124 apart from the fuselage diameter.

A 787 is optimised for long missions with a high percentage of its time in cruise. To simply downscale it would be to create a shorter, narrower body airframe with wings still optimised for long missions, making it quite inefficient on the shorter hops the NMA is proposed to be the master of. Furthermore, a 787 is designed to carry a lot of fuel to go those long distances. This requires certain strengthening and reinforcement which adds weight to the airframe. The NMA will need far less fuel capacity and hence less reinforcement, making the whole airframe lighter relative to its size. A scaled down 787 would retain fuel capacity and weight that is just not needed on medium haul flying.

So can it be done? Absolutely. Would it result in a capable mid-market money making machine? Absolutely not.
 
RJMAZ
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 12:36 am

LAX772LR wrote:
The question should be: would a scaled-down 787 be the optimal design for that market mission?

This is the correct question and the answer is a scaled down 787 would not be good enough.

The NMA will have significantly less range than the 787. Reducing maximum range saves weight and improves efficiency on short/medium haul.

The 787 family has three unique family members. The 787-10 is the aircraft that has the shortest range and best medium haul efficiency. The member gives us a hint on what the 797 must do to achieve excellent medium haul efficiency. The 787-10 has the biggest cabin area relative to empty weight. It is also heavier with the same size wing giving it a lower wing size relative to weight.

The 797 will need to be more like a scaled down 787-11 (a further stretch of the 787-10). The 797 will need a huge cabin area relative to its empty weight and a big fuselage relative to the wing size. The 797 can achieve this easily as a cleansheet with either a longer 7ab or shorter 8ab fuselage.

The cosmetic appearance of the 797 it will most likely look like a 767 fuselage stuck on top of a 757 sized wing and landing gear. Engines will be similar thrust to the 757 but a higher bypass ratio. Obviously made out carbon.

A few extra inchs of width over the 767 will allow for tight 8ab for most airlines. The 767 already has 8ab cabins for charter airlines so an extra 4-6inchs should make 8ab fine for the majority of airlines.
 
RJMAZ
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 1:02 am

LDRA wrote:
Rather than scale 787, just make a 787-8 V2 for MoM. Redesign structure for 200T MTOW, using lessons learned from 1st gen 787 structure, new 5000lb MoM engines, center wing box tank deletion, done!

7 across is rather inefficient use of space anyways

Smaller end of MoM space can be covered by NSA

This is why I think it will definitely be 8ab and slightly shorter. Any disadvantage to a stubbier fuselage is more than made up by the superior aisle efficiency of 8ab versus 7ab.

I always thought the 787-8 lightweight was a good option. It is worth noting that 200T MTOW on the 787-8 is still way too high for the NMA mission. It does reduce the MOM gap significantly though by providing a big efficiency boost to the 787-8 on shorter missions.

Boeing has different takeoff weights on their ACAP's and a standard 787-8 can fly 250 passengers nearly 5500nm with a 200T MTOW. Removing say 10,000kg of empty weight would increase range even further with that 200T MTOW. Removing that weight would actually be easy as the 787-8 has so many parts shared from the heavier 787-9/10. These parts are simply derated like the engines or overbuilt for the 787-8.

The centre fuel tank on the 787 is pretty large so unless the empty weight could come closer to 100T deleting the centre tank might not allow it to fly over 5000nm.

The more changed that get made to improve the 787-8 the closer you get to a cleansheet.
 
rgustafson
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 2:23 am

morrisond wrote:
NMA is effectively a shrunk 787 (not the same barrel though) - using the technology from 787. They have been working on it for years and there are currently over 1,000 Engineers on it. That is why Boeing is saying EIS 2025 - although that seems pretty tough right now 2026/2027 is probably more likely given the probably new certification regime.

Even so - by relying on 787 tech they will be able to do it a lot faster than a complete next generation technology clean sheet program.

They may break new ground in how they manufacturer NMA though and go beyond what they did on 787.


Wow. A 1,000 engineers already on it. I have to admit I am really looking forward to seeing what the Boeing NMA ultimately becomes. I've got a feeling it may be a surprise. Hope so.
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ctrabs0114
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 2:24 am

I know it's probably not the same thing as you're suggesting re:787/797, but wasn't the 737 essentially a scaled down version of the 707 or based off the 727 design?
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LDRA
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 3:27 am

RJMAZ wrote:
LDRA wrote:
Rather than scale 787, just make a 787-8 V2 for MoM. Redesign structure for 200T MTOW, using lessons learned from 1st gen 787 structure, new 5000lb MoM engines, center wing box tank deletion, done!

7 across is rather inefficient use of space anyways

Smaller end of MoM space can be covered by NSA

This is why I think it will definitely be 8ab and slightly shorter. Any disadvantage to a stubbier fuselage is more than made up by the superior aisle efficiency of 8ab versus 7ab.

I always thought the 787-8 lightweight was a good option. It is worth noting that 200T MTOW on the 787-8 is still way too high for the NMA mission. It does reduce the MOM gap significantly though by providing a big efficiency boost to the 787-8 on shorter missions.

Boeing has different takeoff weights on their ACAP's and a standard 787-8 can fly 250 passengers nearly 5500nm with a 200T MTOW. Removing say 10,000kg of empty weight would increase range even further with that 200T MTOW. Removing that weight would actually be easy as the 787-8 has so many parts shared from the heavier 787-9/10. These parts are simply derated like the engines or overbuilt for the 787-8.

The centre fuel tank on the 787 is pretty large so unless the empty weight could come closer to 100T deleting the centre tank might not allow it to fly over 5000nm.

The more changed that get made to improve the 787-8 the closer you get to a cleansheet.


New MoM engine should be more efficient than GenX or T1000. No need for center tank
 
strfyr51
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 3:42 am

musman9853 wrote:
strfyr51 wrote:
I think it could be possible, But? were the fuselage made of Aluminum- Lithium? It might have more tolerance to "Road Rash" when used in Domestic Service.
The wings could be composite as well as the horizontal and vertical Stabilizers but the fuselage might be better in aluminum IMHO. ( for damage tolerance as you wouldn't need to "cook" a Patch Repair on any fuselage Ding-Dent or Puncture..to repair it.


then it's not a 787 derivative. besides, one of the main reasons boeing is citing to build the 797 is to develop the ability to scale up composite production for nsa through project black diamond.

So? Who said that it HAD to be a clone copy of the B787? The 797 as I understood it was to be a short and medium range airplane to replace the B767-300 series Twin Aisle. Not be the B787-3!! That ship never set sail.
 
travelhound
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 3:46 am

The value equation would relate to using the 787's technologies, manufacturing processes and supply chain rather than a scaled down 787.

I suspect the cost to create a NMA sub system using 787 technology would be far less than original cost of development associated with the 787.
 
RJMAZ
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 4:07 am

LDRA wrote:
New MoM engine should be more efficient than GenX or T1000. No need for center tank

Both wing tanks total only 48,000kg of fuel. The centre tank is 63,000kg. That is a big reduction if the centre tank is disabled

That is the same fuel capacity as the A300 and A310. I guess for most airlines with higher density cabins 48,000kg of fuel in the 787-8 would be fine. It probably wouldn't be able to do those longer point to point routes with a lower density premium cabin.

If we assume the 787-8's empty weight can come down from 120,000kg to 110,000kg, we can add 48,000kg of fuel in the wing tanks and 30,000kg of payload that gives us a takeoff weight of 188,000kg.

It would probably not be worth having a MTOW much higher than that weight.

The 787-10 received a lot of strengthening in the wingbox with extra carbon layers etc. This exact same technique can work in reverse to reduce weight due to the much lower loads. The fuselage pushing down and the wings lifting up is the main force on the centre wing box which is called wing root bending moment. Having fuel in the wings causes less wingroot bending than having fuel in the centre fuselage. So disabling the centre fuel tank would allow the centre wing box to be significantly lighter due to the lower loads.

Likewise reducing max payload weight of the 787-8 from 43,000kg to say 35,000kg would reduce loads on the wingbox even further but most important would be a lighter maximum landing weight. The 787-8 already has lighter landing gear trucks and smaller tyres, they could fit the brakes and tyres off the 767 onto the 787-8 very easily. Scoot and Jetstar have 335 passengers in the 787-8 so 35,000kg would still cover the max passenger load it just means no extra cargo in the belly.
 
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Nomadd
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 4:19 am

Composites don't scale down that well because certain properties, mostly impact resistance, keep them from getting much thinner than the 787's are. If the narrowbody is composite, it will be mostly for reasons other than weight savings.
 
Yonderlust
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 5:23 am

LAX772LR wrote:
CAN it be scaled down?
...of course it can. With enough time/money, you can do anything in aviation.

But that's the wrong question. The question should be: would a scaled-down 787 be the optimal design for that market mission?
THAT is a far more pertinent thing to be asking, and the one that Boeing would be considering.


...And what, in your opinion, is the answer to that question?
 
JayinKitsap
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 5:23 am

travelhound wrote:
The value equation would relate to using the 787's technologies, manufacturing processes and supply chain rather than a scaled down 787.

I suspect the cost to create a NMA sub system using 787 technology would be far less than original cost of development associated with the 787.


I agree. The whole architecture will be 787 pipped a bunch, with digital design the whole structure is modeled, with the freedom to optimize closely. There would be little difference in certification between new parts and resized parts. Existing 787 parts, say fasteners that have a specific capacity will be selected. Windshields might be a part brought over from the 767, etc. New design APU, new landing gear, new actuators for flaps, etc.

A big part of this is the crews, and mechanic already certified for the 787 will be able to get certified relatively quickly.

The 787 technologies and data is probably cutting the NMA design cost to 40%. The NMA is a clean sheet, the 787 had to make the paper from scratch too.
 
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LAX772LR
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 7:47 am

Yonderlust wrote:
LAX772LR wrote:
But that's the wrong question. The question should be: would a scaled-down 787 be the optimal design for that market mission?
THAT is a far more pertinent thing to be asking, and the one that Boeing would be considering.

...And what, in your opinion, is the answer to that question?

In my completely amateur assessment: no, it wouldn't be optimal.

Because were it that simple, Boeing and the engine OEMs would've long since done it.
I myself, suspect a more prosaic motive... ~Thranduil
 
iberiadc852
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 12:46 pm

The thing is, (also from a completely amateur standpoint)

You could start with the 767 skeleton to aim the lets say 767-300ER model in range and capacity, AND:
- Make use of existing production lines. (if possible)
- Apply 787 technologies, production techniques, materials, etc
- Apply newer engines
- Apply 777X fuselage thinning to put 8 abreast instead of 7 with the same cell (or similar, if not possible the same)
- Apply thinner seats
- Apply tanks reduction
- Apply newer lighter wings because of all ot the above.

So you could have huge synergies there to make, let's say a 767-200 size aircraft with the capacity and range of a 767-300ER while having a quite lower weight and operating costs than the 762. (which is currently a not so catastrophic aircraft).

If what I said doesn't have huge flaws, (otherwise of course, forget it).........how much more efficient could be that aircraft than a A321XLR, for example?
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mwhcvt
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Re: Could the 787 be scaled to create the 797?

Sun Jul 07, 2019 2:40 pm

You specify to save money on development and testing, given then current situation at Boeing there will be absolutely no chance any airline or regulator will accept any attempt to reduce development and or testing, hell I’d not be surprised if the next programme the 797/MOM/NMA what ever you want to call it or what ever it eventually turns out to be is required to go through extra hours of flight testing just to be shown to be making that extra effort above and beyond the normally required 2500hrs of flight testing
Must think up a new one soon, slow moving brain trying to get into gear ;)
 
gtargui
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Re: Could the 787 be scaled to create the 797?

Mon Jul 08, 2019 12:51 pm

rikkus67 wrote:
The 767 Section 41 cockpit was used on the 777. IIRC the "adaptor" section to increase the cockpit diameter to meet up with the larger fuselage section was quite a design challenge, so Boeing had to use a smaller portion of the 767's Section 41. This is why the 777 has such a distinctive "forehead".


I had always wondered why the 777 looked the way it does. This explains it all now!
 
Delta777Jet
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Re: Could the 787 be scaled to create the 797?

Mon Jul 08, 2019 1:24 pm

A 757-250 ( right in between a -200 and a -300) with all the features and design of a 787 would be the ultimate !
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keesje
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Re: Could the 787 be scaled to create the 797?

Mon Jul 08, 2019 1:44 pm

uta999 wrote:
The 787-8/9/10 appear to be the perfect aircraft. Is it possible to shrink the exact same design to create the 797, in record time to replace the MAX?

A scaled down 787 would be 40-50% smaller, with new engines and gear. All other components being scaled down to size, except doors and windows.

The cost savings of development, flight testing and final assembly would be enormous. It would also create a common Boeing family, similar to that of car manufacturers.

It would also recoup some of the billions spent on 787 development. I would estimate it would halve the time to EIS too.


It is possible but unlikely IMO

Image

As someone said, you still end up with all the costs & in efficiencies of a long haul, cargo capable aircraft.

Image
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slcdeltarumd11
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Re: Could the 787 be scaled to create the 797?

Mon Jul 08, 2019 2:08 pm

With the disaster the 737 MAX has become, i doubt Boeing will consider anything but a full from scratch redesign. Just scaling things and not spending money on engineering seems like a bad shortcut.
 
Dave05
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Re: Could the 787 be scaled to create the 797?

Mon Jul 08, 2019 11:59 pm

slcdeltarumd11 wrote:
With the disaster the 737 MAX has become, i doubt Boeing will consider anything but a full from scratch redesign. Just scaling things and not spending money on engineering seems like a bad shortcut.


The 787 with all the various models has its niche firmly in the market it seems. Its just that the 737 market share is being over taken by the a320/a321 and only a new from scratch replacement would help Boeing retake the lead in the market share. If Boeing is to design the 737 from scratch they would deliver a aircraft capable of matching Airbus A32x in all variations. The stumbling block of the current 737 is just that it sits too low to the ground, minimizing any efforts in stretching the aircraft longer.....
 
Sokes
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 9:10 am

uta999 wrote:
The 787-8/9/10 appear to be the perfect aircraft. Is it possible to shrink the exact same design to create the 797, in record time to replace the MAX?

A scaled down 787 would be 40-50% smaller, with new engines and gear. All other components being scaled down to size, except doors and windows.
...

The question was if it's possible to shrink the exact same design.

VSMUT wrote:
No. You can't just scale things in aviation.


Nomadd wrote:
Composites don't scale down that well because certain properties, mostly impact resistance, keep them from getting much thinner than the 787's are. If the narrowbody is composite, it will be mostly for reasons other than weight savings.


I suppose a lot of things "don't scale".
AFAIK double the wing length is four times the lift, but eight times the volume. That has to be a simplification or wrong, otherwise B787 wouldn't sell against A330Neo. (B777-X will have 71,8 m wingspan and 352 t MTOW. That's a bit more than double the wing length and roughly five times the MTOW of A220.)
AFAIK a wing which has 80% of length, width and height of B787 wing would have 51,2% of the volume, but 64% of lift.
80% wingspan of B787 is 48,1 m. That fits in 52 m/ group IV category. But it's something to consider.
Can one scale engines?
What about the distance of engines to floor?
The topic excluded landing gears. I wonder how landing gear and tires scale?
What about the location of the cabin floor in the fuselage? Floor thickness?

How does one design a plane from scratch? Take the cabin floor layout, payload and range requirements and design the plane around the cabin floor?
Why can't the world be a little bit more autistic?
 
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Aesma
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 9:41 am

It's not even certain that using a CFRP barrel makes sense at the size of an A320.
New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
 
asdf
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 9:48 am

VSMUT wrote:
No. You can't just scale things in aviation.


i think you can use the FBW logic , hardware and system more or less 1:1
you will of course have to change the parameters

and that is the thing what is missing @the 737 most of all
 
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keesje
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 9:54 am

It would have to involve a new wingbox, new wings, new engines, new landing gear. Those diemensioned for the current 250 MTOW.
Theoretically it could cut OEW by around ~30t. Still heavier than a 763, but in the same ballpark.

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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 10:26 am

keesje wrote:
It would have to involve a new wingbox, new wings, new engines, new landing gear. Those diemensioned for the current 250 MTOW.
Theoretically it could cut OEW by around ~30t. Still heavier than a 763, but in the same ballpark.

Image


And with all this new, there remains very little old parts to use. And those would be easy to do new as well.Load bearing structures do not scale down very well.
 
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keesje
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 10:38 am

seahawk wrote:
keesje wrote:
It would have to involve a new wingbox, new wings, new engines, new landing gear. Those diemensioned for the current 250 MTOW.
Theoretically it could cut OEW by around ~30t. Still heavier than a 763, but in the same ballpark.

Image


And with all this new, there remains very little old parts to use. And those would be easy to do new as well.Load bearing structures do not scale down very well.


I would not be downscaling, but entirely new designed, optimized parts. Optimized for a 171t MTOW. The fusealge, cockpit, systems, cabin, tail would be largely the same. Still a significant investment, maybe $6-8B, 5-6 yrs. Still you would fly a round athe 250t ready 787 fusealge, making an entirely new aircraft probably becomes a better idea.

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The cut off the wingtips, paper derate quick & dirty 787-3 didn't work out.
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 10:50 am

Just taking an existing aircraft design and scaling it does not really save any money. All the parts still have to be detailed, all the calculations and tests still done, and all the tooling designed and built. And since many characteristics affecting airliners are not linear, you would end up with a less than optimal design. Some things will be too weak (like fuselage skin thickness) and will have to be strengthened, some (like wing spars) will be stronger than necessary and hence heavier than necessary. With the intense focus on efficiency that characterizes the airliner manufacturing industry today that just won’t cut it. Everything MUST be optimized, and short cuts just don’t get you there.
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 11:00 am

seahawk wrote:
And with all this new, there remains very little old parts to use. And those would be easy to do new as well.Load bearing structures do not scale down very well.

Agreed.

If every part is scaled and optimised then it may as well be a cleansheet design. It wouldn't take much more effort to then change to a better cross section suitable for the size range.

There would be some parts that would be better bang for buck when it comes to making a lightweight 787. Drawing a line limiting how many parts get lightened would be the way to go. For example 767 wheels and tyres and a centre fuel tank delete would be the best bang for buck starting point to make a lower MTOW 787. These would drop the weight by only 1% but would be extremely cheap. Reduced carbon layers in the wing and narrower bulkheads in the centre wingbox would also be good bang for buck with big weight savings. They would have much bigger weight savings but would also be much more costly. New engines should get done instead of derating the existing. I would draw the line at trying to lighten the tail, actuators, nose landing gear leg etc.

It would be extremely easy to drop the 787-8 weight by 10% if the MTOW is significantly reduced. It would still be able to have very good commonality with the 787-9.
 
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 11:17 am

I agree simple scaling doesn't work and this explains why stretch is easier.

You have a part that needs to take a stress path but is also required to have an element of torsional stability.

You design the part for scale factor 100 (default) and find that given the stress elements you are taking there is plenty of torsional rigidity so that comes almost as a given.

You now need to scale up. You add additional stress so you need to add metal to cope with that additional stress. Again on validation the torsional rigidity comes for free.

Now however you want to scale down. You do the calcs and reduce the metal. Now however due to the reduced metal you no longer have the torsional performance - so you need to add metal back. So it becomes relatively heavier.
 
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 12:00 pm

VSMUT wrote:
No. You can't just scale things in aviation.

Isn’t the 737 a scaled down 707?
 
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 12:24 pm

797 Thread 9000+

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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 1:25 pm

The 797 should be built with the technology developed for the 787. To me without a question is what Boeing should do.
 
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 1:36 pm

If they wanted a 767 with the domestic range, they could probably bring back the 787-3 with the smaller wingspan. It was a 788 with a different wing. That thing was a burner with its short field takeoff performance. It was something like 6,400’ with full load and I think 3500 mile range. Good enough for transcon, Hawaii and the Atlantic. This would satisfy the small gate gauge used by the 767 vs. the sub 200’ span. The rest wouldn’t be “scalable” per se, but it will definitely look “a lot like” a 787 inside and out. I’m thinking composite panels like the A350 or aluminum lithium like the A220.
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 1:45 pm

Bobloblaw wrote:
VSMUT wrote:
No. You can't just scale things in aviation.

Isn’t the 737 a scaled down 707?


Scale means taking an object and making it smaller (or bigger) without changing any dimensions/proportions. The 737 used the upper fuselage lobe and nose section of the 707, nothing else. Everything else is "new".
 
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 9:05 pm

asdf wrote:
VSMUT wrote:
No. You can't just scale things in aviation.


i think you can use the FBW logic , hardware and system more or less 1:1
you will of course have to change the parameters

and that is the thing what is missing @the 737 most of all


No, you couldn't:

Aerodynamics will be different. The airframe changes in size, but the air molecules don't. That affects how air flows around the aircraft.

The materials don't scale. The skin or stringers of a small plane will be pretty much the same as the 787. If you scale the gauge of the components, they will end up paper thin and with no strength. If you don't scale the gauge, parts won't fit without a costly redesign.

The 787 is designed for very long flights. It is over winged and over built for short missions. Simply scaling down the design would result in the same. Remember how the 1980s A330 handily beat the 1990s 777 on medium range missions? Or the A321 beat the 757? That's because they had a smaller, therefore lighter wings. Big wings are good for cruising a long time, a costly burden for climbing multiple times a day.

The systems are overbuilt for a narrowbody. Hardly needs to be explained why cabin pressurization and ventilation systems for a 400+ seat 787 would be a burden on a 200 seater. Same with fuel pumps, generators and so on.
 
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Re: Could the 787 be scaled to create the 797?

Tue Jul 09, 2019 9:12 pm

rikkus67 wrote:
Only if Section 41 (cockpit) could be grafted onto a narrower fuselage, but that's about it. The 767 Section 41 cockpit was used on the 777. IIRC the "adaptor" section to increase the cockpit diameter to meet up with the larger fuselage section was quite a design challenge, so Boeing had to use a smaller portion of the 767's Section 41. This is why the 777 has such a distinctive "forehead". Can it be done in the 787 to 797/NMA scenario? More than likely. Would it be economical? Likely not.


Some years ago a Boeing engineer said that the only parts that were retained from the 767 were the cockpit windows and the area immediately forward of them. It turned out that trying to graft a 767 Section 41 onto the 777 resulted in too many small-radius turns that ruined the aerodynamics.
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Re: Could the 787 be scaled to create the 797?

Wed Jul 10, 2019 9:51 pm

DocLightning wrote:
Some years ago a Boeing engineer said that the only parts that were retained from the 767 were the cockpit windows and the area immediately forward of them. It turned out that trying to graft a 767 Section 41 onto the 777 resulted in too many small-radius turns that ruined the aerodynamics.


Exactly. So when we apply the same methodology from the 787 to the NMA, the scenario would likely repeat.
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brindabella
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Re: Could the 787 be scaled to create the 797?

Thu Jul 11, 2019 12:57 pm

RJMAZ wrote:
LDRA wrote:
Rather than scale 787, just make a 787-8 V2 for MoM. Redesign structure for 200T MTOW, using lessons learned from 1st gen 787 structure, new 5000lb MoM engines, center wing box tank deletion, done!

7 across is rather inefficient use of space anyways

Smaller end of MoM space can be covered by NSA

This is why I think it will definitely be 8ab and slightly shorter. Any disadvantage to a stubbier fuselage is more than made up by the superior aisle efficiency of 8ab versus 7ab.

I always thought the 787-8 lightweight was a good option. It is worth noting that 200T MTOW on the 787-8 is still way too high for the NMA mission. It does reduce the MOM gap significantly though by providing a big efficiency boost to the 787-8 on shorter missions.

Boeing has different takeoff weights on their ACAP's and a standard 787-8 can fly 250 passengers nearly 5500nm with a 200T MTOW. Removing say 10,000kg of empty weight would increase range even further with that 200T MTOW. Removing that weight would actually be easy as the 787-8 has so many parts shared from the heavier 787-9/10. These parts are simply derated like the engines or overbuilt for the 787-8.

The centre fuel tank on the 787 is pretty large so unless the empty weight could come closer to 100T deleting the centre tank might not allow it to fly over 5000nm.

The more changed that get made to improve the 787-8 the closer you get to a cleansheet.


Yes, I've always seen the most prudent strategy as an NMA at "generous" 7ab also allowing a :crowded: 8ab.

This allowing better volumetric efficiency as well as preventing a future AB 8ab "overunning" a "strict" 7ab BA bird - that is, avoiding the 767 vs A330 redux.

However an alternative strategy might go like this:
1) the NMA is indeed set at a "strict" 7ab, thus minimising cross-section/weight/drag/cost and maximising competitiveness with A321X/A322X in the specific MOM space; (**)
2) meanwhile in the event of AB subsequently launching a clean-sheet 8ab, then the 787 fuse is in turn given a whole new wing/wing box/gear/powerplant/empennage(?)


That is, in a direct competition, a good 8ab will defeat a good 7ab ... ("apples vs apples")
however in similar direct competition, a good 9ab will in turn defeat a good 8ab ... ("apples vs apples")
and BA already have the basis of the "good 9ab" ...

What think you?

cheers Bill

(**) not to stress that the NMA offer-for-sale IMO marks the start of the big wheels turning which will eventually produce the NSA ... and the closer the NMA is to the NSA, the more-accurately the evolved NMA production-system will scale-down to the 6ab NSA

just sayin' ... :D
Billy

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