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keesje
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 10:02 am

I think loading doesn't change significantly if you widen the aisle. But it does if you put in an extra seat per row.

Oval I'm not sure. Pressure induced loading on the frame would cost you additional weight, the more oval the worse, probably negating any advantage in cross section.

If frontal area is unimportant, why would you want to go oval anyway ? :indifferent: ..

IMO the NMA could become oval, but probably very little oval..

On top a wider (e.g. A320 + 12-inch) fuselage could offer twin aisle where it matters/. Offering direct aisle excess in front (premium cabin) in an efficient way. Because the cargodeck height would stay as flat as required for AKH containers, the passenger cabin would be ~10 inch higher than e.g. A320, creating the walking height off center and space for serious bins above the middle seats.

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https://farm5.staticflickr.com/4125/35684933306_db156abe67_c.jpg
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flipdewaf
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 12:35 pm

and the weight...remember the weight is arguably more important then the Swet of the fuse. The weight also has the effect of increasing the required Swet of the wing dis-proportionally due to getting into the optimisation loop the wrong way and each required mm^2 of are goes both top and bottom of the wing.

Matt6461 wrote:
Just briefly re wing size: 25%smaller at constant AR means ~150ft wingspan. That's less span 763ER; just can't imagine that penciling out.

787 wing span is ~60m
25% less area at constant geometry gives ~52m
767 wing span is 48m

According to my model.
the Keesje design at 6 abreast with 168" diameter gives a fuselage weight of 11383kg
The RJMAZ design at 8 abreast has a fuselage weight of 14000kg

The assumptions I made were:
-300seats all economy
-30"pitch
Giving a cabin length

-Using a correlation of cabin length to overall length of the fuselage.

The correlation was based on previous aircraft which showed no statistical advantage/disadvantage to with single or dual aisle in terms of amount of cabin length to fuselage length and with an Rsquared adjusted of 97% (which seems pretty conclusive).

-The wing areas and geometries were left left identical so as no to affect the fuselage stiffness in either case.

The Keesje model was done at 4.26m circular cross section
The RJMAZ model was done at 5.3m circular cross section (from a weight perspective this is more optimal than the ovoid/egg scenario shown)


Any questions then please ask.

Fred
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frmrCapCadet
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 2:44 pm

Matt - since you mention automobiles I will note that nowadays a Mercedes looks like a Kia looks like a Ford etc. A 5 passenger sedan has an optimal shape, as does a 5 or 7 passenger SUV. This really jumped out at me with a Prius parked next to a Tesla S. Their side profiles were nearly identical, not that you would mistake one for the other - both were gray and at only at a glance the same. I assume that aerodynamics has dictated that profile, and it optimizes aero with the volume and interior volume for the comfort of an appropriate number of people.
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frmrCapCadet
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 6:22 pm

I did not make my point with that auto discussion very clear. The analogy is that for a plane of given passenger load, and given range (cars can just gas up enroute) it is likely there is only one or two solutions. 5, 6, 7, and 8 and etc. abreast all somewhat define a different plane. CASM, passenger comfort (it actually does figure in somewhat), safety all further limit what each plane can do.
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keesje
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 10:07 pm

The correlation was based on previous aircraft which showed no statistical advantage/disadvantage to with single or dual aisle in terms of amount of cabin length to fuselage length and with an Rsquared adjusted of 97% (which seems pretty conclusive).


The lazy, conservative interpolation method I often used on a.net :thumbsup:
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Matt6461
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 10:17 pm

Kessje wrote:
If frontal area is unimportant, why would you want to go oval anyway ?


Because an oval has a smaller perimeter and thus less wetted area than a circle of equal cabin width. :slaphappy: :silly: :yawn: :worried: :yummy: :ziplip: :whistleblower: :veryhappy: :o :bouncy: :raincloud: :puckerup: :ghost:
 
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Matt6461
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 10:19 pm

flipdewaf wrote:
787 wing span is ~60m
25% less area at constant geometry gives ~52m


Drats! Obviously you're right. I shot that reply half-cocked while I was doing something else.
 
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Matt6461
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 10:27 pm

mrmCapCadet wrote:
I assume that aerodynamics has dictated that profile


That's a bad assumption IMO. Automobile drag is far less significant than airplane drag. You're right that they size the chasis/cabin for 5-pax size, but it wouldn't be worth it to give an SUV the most aerodynamically efficient form.

Instead of looking like this:
Image

It would have to look like this:
Image

Under Keesje's conception of aerodynamics, the Ecocar would have the same drag if it had a flat square front instead of that streamlined design (same frontal area). So the folks are University of Delft's engineering program are idiots and should have called Keesje before wasting money on that protoype.

Keesje is saying that if we attached wings to this:

Image

and attached the same wing to this:

Image

The only difference would the frontal area of the log and of the Ecocar.


Now imagine attaching wings to that Range Rover and flying it to .85M. The positive pressure gradient on the grill/windshield and negative gradient at the rear would probably be 90% of your drag.

Suprise, guys: cars and airliners have different economic optima for drag.
 
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Matt6461
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 11:15 pm

flipdewaf wrote:
According to my model.
the Keesje design at 6 abreast with 168" diameter gives a fuselage weight of 11383kg
The RJMAZ design at 8 abreast has a fuselage weight of 14000kg

The assumptions I made were:
-300seats all economy
-30"pitch
Giving a cabin length

-Using a correlation of cabin length to overall length of the fuselage.

The correlation was based on previous aircraft which showed no statistical advantage/disadvantage to with single or dual aisle in terms of amount of cabin length to fuselage length and with an Rsquared adjusted of 97% (which seems pretty conclusive).


I need some clarifications to respond fully.

-can you cite/share the study?

-How does the study define cabin length? Interdoor length, bulkhead-bulkhead length, or some other measure?

-What is your calculation for cabin length? Is it rows= seats/Xab, then rows * pitch = Lcabin? How do you account for galleys/lavs? From there, is your dependent variable fuse LOA, independent variable Lcabin, and LOA calculated from your correlation curve?

-How does your model treat pressurization weight versus bending weight? Here's my intuitive sense of differentiating the two: First the fuselage is a pressure vessel sitting on the floor of a giant warehouse that can replicate FL43 conditions. Whatever's needed to keep pressuriziation is called pressure weight. Next attach wings etc. and actually fly vessel. Take whatever is added for static maneuver conditions, taxi bump, maximum yaw or sidestream moment and call that bending weight.

Just as a first take I see a serious issue with a correlation study: bigger fuses are correlated with higher range, which is correlated with higher MTOW, which is correlated with more fuselage weight for flight maneuvers/gusts and with a bigger tailplane, which means a bigger and heavier "empty" tailcone, higher LOA/Lcabin ratio, and more fuse bending weight. In addition, the data set for NMA territory (A310/767) has to contain old planes that had to lift substantially more fuel weight than NMA to achieve a given range, thus they had more maneuver gust weight penalty than would NMA.
 
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keesje
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 11:59 pm

Matt6461 wrote:
Under Keesje's conception of aerodynamics, the Ecocar would have the same drag if it had a flat square front instead of that streamlined design (same frontal area). So the folks are University of Delft's engineering program are idiots and should have called Keesje before wasting money on that protoype.

Keesje is saying that if we attached wings to this:
..
and attached the same wing to this:
..
The only difference would the frontal area of the log and of the Ecocar.



What a daft responds Matt6461.

I have never suggested / said anything like that & I wonder how get to this non-sense.

We are comparing similar shapes under similar conditions here & I have no idea what you are referencing too.

awkward..
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 12:14 am

@Keesje:

If frontal area determines drag then why wouldn't a square or a circle have equal drag if equal area?

If frontal area determines drag then why the does the A346 fuselage have more drag than A310? Same frontal area.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 12:29 am

Keesje wrote:
I have never suggested / said anything like that


Oh yeah? Who said this, then:

Keesje wrote:
If frontal area is unimportant, why would you want to go oval


This statement means the only reason to go oval is to reduce frontal area.
Which implies surface/wetted area reduction doesn't matter.
Which demonstrates - I really wish I could say this in a different way and still get my point across - substantial ignorance about aerodynamics.
Compared to some here, I am also substantially ignorant about aerodynamics. But at least I understand skin friction's importance to drag.
 
Newbiepilot
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 3:44 am

Well, this thread has been interesting. Keesje is nothing short of consistent in advocating for wider single aisle planes while RJMAZ is opposed to 7 abreast designs. Unfortunately I’m not really seeing all that much engineering justification behind all these seat plans for wider single aisle planes or saying 7 abreast won’t work. So much appears to be measured in anecdote and opinion. It almost seems like there are two people persistently arguing against 7 abreast as devils advocates because that is what Boeing is rumored to be considering. Repeating the same opinion again and again doesn’t make it any more correct.

Thanks flipdewaf for generating some numbers although I don’t understand all the logic behind them. Sounds like a variety of cross sections can work.
 
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Qantas94Heavy
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 8:43 am

Okay, let's make things a bit more clear with aircraft cross sections, as well as discussing a bit about boarding times.

Cabin cross section and number of seats

Let's make a few assumptions so that we can do a fair comparison across different sizes:

  • Seat width: 17" (aisle/window), 17.5" (centre)
  • Armrest width: 2"
  • Aisle width: 18" (widebody), 30" (narrowbody)

Aisle width is wider for the narrowbody to allow for somewhat faster boarding (discussed later), otherwise it just ends up like another 757-300.

Here are the following armrest to armrest widths:

  • 6 abreast NB: 149" (24.83"/pax)
  • 6 abreast WB: 156" (26"/pax)
  • 7 abreast: 175.5" (25.07"/pax)
  • 8 abreast: 195" (24.38"/pax)
  • 9 abreast: 214.5" (23.83"/pax)

For comparison purposes, here are some ACAPS figures from real world aircraft:

  • A320: 143" (23.83"/pax)
  • B767: 184" (26.29"/pax)
  • A330: 204" (25.5"/pax)
  • B787: 215" (23.89"/pax)
  • A350: 220" (24.44"/pax)

As you can see, a new 7 abreast MOM would be more competitive than the A330 and are quite close relatively speaking.

The 7 and 8 abreast MOM are about 2.8% apart on this basis alone, which is easily made up with reduced weight and drag penalties elsewhere.

Aircraft with a single narrow aisle (e.g. A320) are not comparable as boarding times would be too long.
Aircraft with 9+ abreast are not comparable as that would result in a far too stubby aircraft and associated performance penalties.

Boarding time

According to this study, there are two primary causes of passengers blocking the aisle:

  • passengers loading luggage into the overhead compartments
  • passengers waiting for other passengers to get up in order to reach their seat

Now here's some homework for you to do here -- if you have a friend to help you out, even better!

Aisle width boarding experiment

First, find a carry on rollaboard or something of similar size.

Once you have done so, try standing within the door frame of your bedroom door and measure how wide it is (usually 30-36").

Then try lifting the baggage above your head, as if you were placing it in the overhead compartment. Take note of how your body fits within the dimensions.

If you have a friend with you, ask them to try passing while doing so (preferably with them lugging their own baggage as well).

If your door is not that wide (e.g. 28"-30"), try this again in the corridor, measuring how wide that is.


Would you be able to pass someone loading their carry on? How about if they were just standing there to let someone in?

These sorts of things, as well as individual passenger behaviour will dictate any boarding rate advantage for single aisle aircraft.
 
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keesje
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 10:14 am

Qantas94Heavy wrote:
Okay, let's make things a bit more clear with aircraft cross sections, as well as discussing a bit about boarding times.

Cabin cross section and number of seats

Let's make a few assumptions so that we can do a fair comparison across different sizes:

  • Seat width: 17" (aisle/window), 17.5" (centre)
  • Armrest width: 2"
  • Aisle width: 18" (widebody), 30" (narrowbody)

Aisle width is wider for the narrowbody to allow for somewhat faster boarding (discussed later), otherwise it just ends up like another 757-300.

Here are the following armrest to armrest widths:

  • 6 abreast NB: 149" (24.83"/pax)
  • 6 abreast WB: 156" (26"/pax)
  • 7 abreast: 175.5" (25.07"/pax)
  • 8 abreast: 195" (24.38"/pax)
  • 9 abreast: 214.5" (23.83"/pax)

For comparison purposes, here are some ACAPS figures from real world aircraft:

  • A320: 143" (23.83"/pax)
  • B767: 184" (26.29"/pax)
  • A330: 204" (25.5"/pax)
  • B787: 215" (23.89"/pax)
  • A350: 220" (24.44"/pax)

As you can see, a new 7 abreast MOM would be more competitive than the A330 and are quite close relatively speaking.

The 7 and 8 abreast MOM are about 2.8% apart on this basis alone, which is easily made up with reduced weight and drag penalties elsewhere.

Aircraft with a single narrow aisle (e.g. A320) are not comparable as boarding times would be too long.
Aircraft with 9+ abreast are not comparable as that would result in a far too stubby aircraft and associated performance penalties.

Boarding time

According to this study, there are two primary causes of passengers blocking the aisle:

  • passengers loading luggage into the overhead compartments
  • passengers waiting for other passengers to get up in order to reach their seat

Now here's some homework for you to do here -- if you have a friend to help you out, even better!

Aisle width boarding experiment

First, find a carry on rollaboard or something of similar size.

Once you have done so, try standing within the door frame of your bedroom door and measure how wide it is (usually 30-36").

Then try lifting the baggage above your head, as if you were placing it in the overhead compartment. Take note of how your body fits within the dimensions.

If you have a friend with you, ask them to try passing while doing so (preferably with them lugging their own baggage as well).

If your door is not that wide (e.g. 28"-30"), try this again in the corridor, measuring how wide that is.


Would you be able to pass someone loading their carry on? How about if they were just standing there to let someone in?

These sorts of things, as well as individual passenger behaviour will dictate any boarding rate advantage for single aisle aircraft.


My assumption is a 28/30 inch aisle will make passing another passenger so feasible everybody will do it. Contrary to a 18/20 inch aisle, regardless if there are 2 of them. You cannot pass over from one aisle to the other.

Apart from that, when bins / aisle can be relatively large, it is easier/faster to stow / get your luggage. Less looking for free space and more space to move around.

Agree you should do some tests in mock-ups to see how it works.
"Never mistake motion for action." Ernest Hemingway
 
flipdewaf
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 11:15 am

Matt6461 wrote:
flipdewaf wrote:
According to my model.
the Keesje design at 6 abreast with 168" diameter gives a fuselage weight of 11383kg
The RJMAZ design at 8 abreast has a fuselage weight of 14000kg

The assumptions I made were:
-300seats all economy
-30"pitch
Giving a cabin length

-Using a correlation of cabin length to overall length of the fuselage.

The correlation was based on previous aircraft which showed no statistical advantage/disadvantage to with single or dual aisle in terms of amount of cabin length to fuselage length and with an Rsquared adjusted of 97% (which seems pretty conclusive).


I need some clarifications to respond fully.

-can you cite/share the study?

Data taken from a source I have on my computer but I believe this is the same data set. https://www.scribd.com/document/303438500/DataMorichon
I would send the file but it isn't really mine to send so maybe just keep an eye out on your PMs. Its basically some historic aircraft dimension data.

The analysis was done as a simple regression of the two most significant factors of the aircraft length, the cabin length and the fuselage width. In the data there was an outlier in the Beriev Be200 which I decided was muddying the water (no pun intended) so this was removed and the analysis run.
I determined that the overall length of the aircraft could be determined by 7.74 + 0.89*(Cabin Length) + 2.04 * (Fuselage width). This number will change when I put fuselage length in rather than overall length. With the fuselage length estimated then the weight could be estimated using my method which is based on the stamford weight breakdown method.
Matt6461 wrote:
-How does the study define cabin length? Interdoor length, bulkhead-bulkhead length, or some other measure?

Not entirely sure to be honest, the length is on the database but I have no back up info on how things were measured. The data does seem to be slightly low compared to what Airbus show on their website by 0.7-1.5m.

Matt6461 wrote:
-What is your calculation for cabin length? Is it rows= seats/Xab, then rows * pitch = Lcabin?
Yep, so its basically loads of seats and not a lot else


Matt6461 wrote:
How do you account for galleys/lavs?
I don't but certainly can be added in. Not sure the standards in this area however, do we add a certain length for a galley area or a standard are per seat on the aircraft?

Matt6461 wrote:
From there, is your dependent variable fuse LOA, independent variable Lcabin, and LOA calculated from your correlation curve?
Yep.

Matt6461 wrote:
-How does your model treat pressurization weight versus bending weight?
It treats a shorter fuselage as being dominated by the pressure stresses, i.e. hoop stresses. as it gets longer the added bending stresses start to affect the overall weight.[/quote]

Matt6461 wrote:
Here's my intuitive sense of differentiating the two: First the fuselage is a pressure vessel sitting on the floor of a giant warehouse that can replicate FL43 conditions. Whatever's needed to keep pressuriziation is called pressure weight.
Yep, basically its pressure differential of about 0.6bar.

Matt6461 wrote:
Next attach wings etc. and actually fly vessel. Take whatever is added for static maneuver conditions, taxi bump, maximum yaw or sidestream moment and call that bending weight.
Bingo! But sometimes you don't need to add anything, particularly when the vessel is short.

Matt6461 wrote:
Just as a first take I see a serious issue with a correlation study:
The only correlative study was for determining the length of the aircraft based on the cabin lengths.

Matt6461 wrote:
bigger fuses are correlated with higher range, which is correlated with higher MTOW, which is correlated with more fuselage weight for flight maneuvers/gusts and with a bigger tailplane, which means a bigger and heavier "empty" tailcone, higher LOA/Lcabin ratio, and more fuse bending weight. In addition, the data set for NMA territory (A310/767) has to contain old planes that had to lift substantially more fuel weight than NMA to achieve a given range, thus they had more maneuver gust weight penalty than would NMA.
Point taken that this may be the case but the Stamford method does not determine the dimensions it only helps estimate the weight and if the control requirements of any aircraft are different then you have by default should design different sized control surfaces. The parts of the stamford method that deals with empennage weights takes these into account as well as the length of the moment arm of the control surfaces.

Newbiepilot wrote:
Thanks flipdewaf for generating some numbers although I don’t understand all the logic behind them. Sounds like a variety of cross sections can work.
Ultimately yes, there is a drawback to a wider fuselage in terms of weight but its difficult to understand the additional benefits from increased boarding speed. I do intend to look at the boarding time data posted on here previously and try to add that to COC/DOC models I have (I'm sure I have them somewhere).
keesje wrote:

What a daft responds Matt6461.

I have never suggested / said anything like that & I wonder how get to this non-sense.

We are comparing similar shapes under similar conditions here & I have no idea what you are referencing too.

awkward..


I think I can see the confusion here and there may be some parts lost in translation, Keesje as far I can see is not meaning that aircraft and cars have the same drivers toward their shapes but that vehicles of similar type have similar drivers to their design and so their overall shapes show the same compromises.

2 SUVs have the same combination of compromises as they have the same mission and consequently look the same
2 Track racing bikes have the same mission and so the broadly the same compromises and to consequently look the same
2 fighter jets have the same mission and so bradly have the same compromises and so consequently look the same. (Rafale vs typhoon)
Why would airliners be any different, they are not their most aerodynamic form, not by a long way but a series of compromises.

Fred
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flipdewaf
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 12:03 pm

Matt6461 wrote:
Kessje wrote:
If frontal area is unimportant, why would you want to go oval anyway ?


Because an oval has a smaller perimeter and thus less wetted area than a circle of equal cabin width. :slaphappy: :silly: :yawn: :worried: :yummy: :ziplip: :whistleblower: :veryhappy: :o :bouncy: :raincloud: :puckerup: :ghost:


Ultimately yes this has some logic but it would seem to hold true that the frontal area does to some driving overall. What happens to surface area when you go to 11 abreast? at 220 people? I would kind of agree that there is no such thing as frontal drag but then all of it is just made up to be convenient to engineers anyway. If the aim of this was to reduce surface area then you would find better ways to do it than oval. Does your reduction in area in the fuselage simply add to the wetted area of the wings due to having to carry more weight? To Keesjes point previously there are reasons why this hasn't been done before even after being studied extensively.

Fred
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Matt6461
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 12:50 pm

@flipdewaf

As I said in DM, I'll respond with my issues about the model in another post. For others - "Issues" doesn't mean I disagree with the basic approach. Correlation studies are great and it's a community service to assemble and report on or share the data. I just think the NMA will diverge from trendlines in highly significant ways.

But first I might need a fundamentals lesson: All this while I've been tacitly assuming that Swet is ~proportional to pressurization weight as defined a couple posts ago. Now that I think of it, that might be wrong: the square/cube thing. What's the relationship between pressurization stress and fuselage weight versus volume, holding Swet constant? Like if we somehow molded the A318 into a sphere of equal Swet, would its pressurization weight be equal to A318's despite the greater volume (set aside for now structural efficiency of sphere versus fuselage)?

flipdewaf wrote:
To Keesjes point previously there are reasons why [oval] hasn't been done before even after being studied extensively.


The obvious reason is weight. And to me the clearest reason Boeing likes it now is that (1) as you say, airplanes have not the most aerodynamic shape because weight/aero (among other) tradeoffs but (2) CFRP reduces the weight cost of aero optimization via the oval, so now it makes sense. CFRP reinforcement for greater oval stress harnesses CFRP's strength/weight advantage without deduction for embedded mesh grounding matrix - it's already there, just adding more pure CFRP behind the matrix as reinforcement.

While we hash out the tradeoffs here, thousands of at-least-a.net-level engineers at Boeing have concluded (apparently) that oval's time has come.
 
flipdewaf
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 2:05 pm

Matt6461 wrote:
@flipdewaf

As I said in DM, I'll respond with my issues about the model in another post. For others - "Issues" doesn't mean I disagree with the basic approach. Correlation studies are great and it's a community service to assemble and report on or share the data. I just think the NMA will diverge from trendlines in highly significant ways.
The only really correlative part of what I did was the development of the overall length based on the cabin dimensions shown in this thread. The weight estimation is based on the Stamford weight estimation method.

Matt6461 wrote:
But first I might need a fundamentals lesson: All this while I've been tacitly assuming that Swet is ~proportional to pressurization weight as defined a couple posts ago. Now that I think of it, that might be wrong: the square/cube thing. What's the relationship between pressurization stress and fuselage weight versus volume, holding Swet constant? Like if we somehow molded the A318 into a sphere of equal Swet, would its pressurization weight be equal to A318's despite the greater volume (set aside for now structural efficiency of sphere versus fuselage)?
So are you asking if a pressure vessel that has wetted area "S" would be heavier as a sphere or as a cylinder assuming that the pressure differential is maintained in both cases. I will set about calculating that for you.


Matt6461 wrote:
flipdewaf wrote:
To Keesjes point previously there are reasons why [oval] hasn't been done before even after being studied extensively.


The obvious reason is weight. And to me the clearest reason Boeing likes it now is that (1) as you say, airplanes have not the most aerodynamic shape because weight/aero (among other) tradeoffs but (2) CFRP reduces the weight cost of aero optimization via the oval, so now it makes sense. CFRP reinforcement for greater oval stress harnesses CFRP's strength/weight advantage without deduction for embedded mesh grounding matrix - it's already there, just adding more pure CFRP behind the matrix as reinforcement.
Just :wink2:

Matt6461 wrote:
While we hash out the tradeoffs here, thousands of at-least-a.net-level engineers at Boeing have concluded (apparently) that oval's time has come.
I would like something new I have to be honest.

Fred
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flipdewaf
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 2:33 pm

Matt6461 wrote:
But first I might need a fundamentals lesson: All this while I've been tacitly assuming that Swet is ~proportional to pressurization weight as defined a couple posts ago. Now that I think of it, that might be wrong: the square/cube thing. What's the relationship between pressurization stress and fuselage weight versus volume, holding Swet constant? Like if we somehow molded the A318 into a sphere of equal Swet, would its pressurization weight be equal to A318's despite the greater volume (set aside for now structural efficiency of sphere versus fuselage)?


So I did this and I accidentally used the A319 basic dims but the fundamentals are there.

I used a cylinder of 4m diameter and two domed ends to bring it to the same overall Fuselage length of the A319. The overall weight required to hold 0.6bar with no margins and perfect Manufacturing tolerances on Al at 90mpa I got a weight of 1621kg.

For a sphere of the same surface area the weight was 2632kg.

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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 4:56 pm

Automotive Aerodynamics Wikipedia

Comparison with Aircraft Aerodynamics
Automotive aerodynamics differs from aircraft aerodynamics in several ways. First, the characteristic shape of a road vehicle is much less streamlined compared to an aircraft. Second, the vehicle operates very close to the ground, rather than in free air. Third, the operating speeds are lower (and aerodynamic drag varies as the square of speed). Fourth, a ground vehicle has fewer degrees of freedom than an aircraft, and its motion is less affected by aerodynamic forces. Fifth, passenger and commercial ground vehicles have very specific design constraints such as their intended purpose, high safety standards (requiring, for example, more 'dead' structural space to act as crumple zones), and certain regulations.


and "downforce" Wikipedia

Aerodynamics of an automobile must also help keep the car glued onto road, especially at higher speeds.

Automotive engineers spend a lot of time, and manufacturers money on aerodynamics. I had a boxy Scion XB, but it had a windshield stretching way out over the hood - a lot more streamlined than it looked.
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 5:20 pm

Newbiepilot wrote:
keesje wrote:
I wonder if a lean 2-3-2 cabin has the speed and space advantages widely assumed.]


It is not just assumed, it is documented in the ACAPS.


Those are based on assumptions.

A 737-900ER with 177 passengers on the plane typically requires a minimum of 40 minutes to turn (including 10 deplaning, and 15 for boarding)

A 767-200 with 216 passengers only requires 35 minutes (including 9 for deplaning and 11 for boarding)

A 757-300 with 243passengers takes 55 minutes to turnaround (including 14 for deplaning and 27 for boarding)


And yet we see many 186/9 seat 737's turned in 25 minutes and I have personally helped to turn 275 seat condor 753's in well under 40 ...... and w/o cheating (I.e. fuelling with pax on board).

The boarding speed assumptions of 2-3-2 are documented. You can agree or disagree and specific rates vary by location, airline procedure and season, but it is hard to disagree entirely with the airport compatibility engineers when comparing different planes.


The MC-21 has wider isles for that exact reason.

All of the above being said, there is of course research and that seems to indicate two aisles is always better.

https://www.researchgate.net/publicatio ... rding_Time

Best regards
Thomas
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 5:35 pm

tommy1808 wrote:
Newbiepilot wrote:
keesje wrote:
I wonder if a lean 2-3-2 cabin has the speed and space advantages widely assumed.]


It is not just assumed, it is documented in the ACAPS.


Those are based on assumptions.

A 737-900ER with 177 passengers on the plane typically requires a minimum of 40 minutes to turn (including 10 deplaning, and 15 for boarding)

A 767-200 with 216 passengers only requires 35 minutes (including 9 for deplaning and 11 for boarding)

A 757-300 with 243passengers takes 55 minutes to turnaround (including 14 for deplaning and 27 for boarding)


And yet we see many 186/9 seat 737's turned in 25 minutes and I have personally helped to turn 275 seat condor 753's in well under 40 ...... and w/o cheating (I.e. fuelling with pax on board).

The boarding speed assumptions of 2-3-2 are documented. You can agree or disagree and specific rates vary by location, airline procedure and season, but it is hard to disagree entirely with the airport compatibility engineers when comparing different planes.


The MC-21 has wider isles for that exact reason.

All of the above being said, there is of course research and that seems to indicate two aisles is always better.

https://www.researchgate.net/publicatio ... rding_Time

Best regards
Thomas


Interesting. Scanning through the report, a modern NB design with a " wider" aisle (22 inch?) is mentioned, not quantified.
IMO a 30 inch aisle function more like 2 aisles. Passenegers can e.g. walk it in 2 opposite directions at the same time.
You get 2 aisles at the cost of 1.5. Maybe I should contact the writers and see if they still have these simulation tools.
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 6:28 pm

Keesje wrote:
IMO a 30 inch aisle function more like 2 aisles. Passenegers can e.g. walk it in 2 opposite directions at the same time.
You get 2 aisles at the cost of 1.5.


30/1.5 = 20. Few Y aisles are 20in wide.

A 2-2-2 with 17in aisles would deplane quicker than your 30in aisle. So all this effort to save 4in? Weird hill to die on.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Thu Mar 15, 2018 7:24 pm

Matt6461 wrote:
Keesje wrote:
IMO a 30 inch aisle function more like 2 aisles. Passenegers can e.g. walk it in 2 opposite directions at the same time.
You get 2 aisles at the cost of 1.5.


30/1.5 = 20. Few Y aisles are 20in wide.

A 2-2-2 with 17in aisles would deplane quicker than your 30in aisle. So all this effort to save 4in? Weird hill to die on.


I think that is totally unsubstantiated. Research would have to be done to get the dynamics.

Most aisles are 20 inch wide, or 19 or 21 inch.

https://image.slidesharecdn.com/737-161007152729/95/737-71-638.jpg

Airbus officially offers even a 25 inch aisle option. Don't ask about seat comfort.

Apparently Easyjet uses something like this. It is the airlines that decide.

https://www.flickr.com/photos/rtm67/40828507491/in/dateposted-public/
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 1:58 am

Width of aisle depends on the seat width, but a rough average of aisle width looks something like:

10 abreast 777: 17"
9 abreast 787: 18"
9 abreast A350: 18.5"
8 abreast A330: 19"
7 abreast 767: 20"
10 abreast A380: 21"

For current narrowbody aircraft the 737 is about 19-20" and the A320 is 19-25" depending on seat width.

My concern with the single aisle concept is that people won't feel comfortable enough passing someone that's lifting up heavy baggage, to avoid bumping into them or their baggage ("you're so rude, are you in such a hurry?!"). This also has to do with the dynamic movement of the body during the baggage storage motion, as well as people feeling more comfortable using all the space if it is provided.

And by the time the single aisle aircraft has an aisle width of 30"+, you end up at a very similar width/pax to a 7 abreast widebody, and slightly worse than the 8 abreast.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 3:26 am

keesje wrote:
Matt6461 wrote:
Keesje wrote:
IMO a 30 inch aisle function more like 2 aisles. Passenegers can e.g. walk it in 2 opposite directions at the same time.
You get 2 aisles at the cost of 1.5.


30/1.5 = 20. Few Y aisles are 20in wide.

A 2-2-2 with 17in aisles would deplane quicker than your 30in aisle. So all this effort to save 4in? Weird hill to die on.


I think that is totally unsubstantiated. Research would have to be done to get the dynamics.


Everything you have posted is unsubstantiated as well regarding the extra wide aisle benefits. I posted boarding times showing that twin aisles are faster at boarding and substantiated that with ACAP numbers (20 passengers per minute on a 767 vs 12 on a 737). There is no credible study stating that a 30 inch aisle functions more like 2 aisles. All I see is that you keep posting photos and repeating your opinion again and again. Repetition doesn’t substantiate an opinion.

Another interesting piece of information from the ACAPS is that a 787 using 1 door boards at 25 passengers a minute and a 777 using two doors boards at 30 passengers a minute.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 4:07 am

QantasHeavy94 wrote:
by the time the single aisle aircraft has an aisle width of 30"+, you end up at a very similar width/pax to a 7 abreast widebody, and slightly worse than the 8 abreast.


And that's assuming circular fuselage. The oval removes ~7% of fuselage perimeter.
Meant to say earlier that I appreciated your post laying out the basic math - something many posters ignore too often.

Keesje wrote:
I think that is totally unsubstantiated.

Newbiepilot wrote:
Everything you have posted is unsubstantiated as well regarding the extra wide aisle benefits.


@Newbie you're right but are you getting tired of this game as well? QantasHeavy posted a study that is at least probative of wide-aisle benefits; Keesje has posted nothing but his own speculations. He's put forward a flawed car drag index as the measuring stick for airplanes and when challenged to defend his point he just ignores it.

This isn't how this site, especially TechOps, should go. Let's stop wasting our time taking him seriously.

By the way, Keesje:
Keesje wrote:
Can you cite any serious *Airplane* aerodynamics article that uses your "Frontal Area" formula to estimate drag? I bet you can't.


You can't find even one aero source that says frontal area drag is a free-standing thing.
I've provided highly-reputable citation for Swet far outweighing anything connected to frontal area.

What is your goal here? Sometimes I think you're just trolling.
---------------------------------------------------------

Let me make an argument for a 6ab wide-aisle that's based in numerical reason:

Advantages of 6ab:
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 4:25 am

...hit submit instead of review. Continuing from my last reply:
Let me make an argument for a 6ab wide-aisle that's based in numerical reason:

Pros/cons of 6ab:

  • 1. For a given capacity, longer fuse = lower fuse Cdp and smaller empennage
  • 2. Can be ~equal to 7ab Swet/pax if 7ab remains circular
  • 3. Provided capacity stays under 2-class ~250, is likely only slightly worse than 7ab on TRT
  • 4. Longer versions of NMA will pay more fuse bending weight penalty than 7ab.

Pros/cons of 7ab
  • 1. Fuselage will have slightly more empty tailcone portion of LOA, will have slightly more Swet/pax than 6ab in constant sections thus higher overall Swet/pax if circular.
  • 2. 7ab implies bigger/heavier empennage at equal capacity vs. 6ab
  • 3. 7ab's internal volume will be greater than 6ab's, implying a pressure weight penalty - difficult to say how much
  • 4. 7ab's lower lever arms imply bending weight advantage over 6ab
  • 5. If 7ab is elliptical, it saves ~7-10% fuse Swet for some penalty to pressure weight

Given that list, 7ab makes no sense against a wider-aisle 6ab if circular. (8ab circular could make sense but set that aside for now, as Boeing seems to have done.
Ellipse, however, gives 7ab a clear advantage on fuse Swet and ambiguity about fuse weight. It all comes down to the weight penalty for ellipse and the capacity range sought (the higher it goes, the worse 6ab looks).

Boeing has studied the tradeoffs, Boeing thinks 7ab works best. Keesje disagrees but he also thinks of planes as automobiles, if he puts much thought into aerodynamics at all.

I trust Boeing's research over Keesje's prejudices. And I'm sick of this.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 5:04 am

flipdewaf wrote:
I determined that the overall length of the aircraft could be determined by 7.74 + 0.89*(Cabin Length) + 2.04 * (Fuselage width).


I might have made this point already but this formula will penalize longer-range, bigger-empennage aircraft: For A320 family, LOA=fuse LOA, 737NG/MAX's LOA looks not even a foot more than fuse LOA. Not true of longer-range aircraft.

flipdewaf wrote:
Not sure the standards in this area however, do we add a certain length for a galley area or a standard are per seat on the aircraft?


Galley carts are 12.5in X 30in: so their footprint is ~.6 of a basic Y seat. 1 cart per 10 pax is a decent rule of thumb for 6+ hour flights.
If you have enough exit-row space to fit all galleys, the galley space should be ~6% of cabin (They remove into the exit rows). But if you don't, then you need to use additional space for cart removal/stowage. Usually you don't, so ~8-10% of cabin floor ends up being galley space. This varies based on Y layout and other factors (tailcone usage, for example).

Good rule of thumb is ~45/1 for pax/lav. Assume 1 lav takes the space of 2.5-3 galleys.

Combining these, galleys/lavs should take up at least ~15% (give or take) of usable cabin area (cabin area minus regulatory minimum exit rows).

flipdewaf wrote:
It treats a shorter fuselage as being dominated by the pressure stresses, i.e. hoop stresses. as it gets longer the added bending stresses start to affect the overall weight


Per your model, would an A318 fuselage as a stationary pressure vessel weigh the same as an actual A318 fuselage?
I'm guessing these two would differ in real life: can't think of any plane that doesn't have stringers and/or increased skin thickness at fore and aft of the wing box. I recall a Leeham diagram of NB fuselage (CS100?) that clearly showed substantial skin thickness gradient nearer the wingbox and on the underside for compressive loads.

flipdewaf wrote:
For a sphere of the same surface area the weight was 2632kg.


That's what I expected when I posted my question, though somehow the effect evaded me before yesterday. It throws a wrench in some of my daydreams but opens possibilities for others. Any handy metric for a pressurization weight function of a cylinder where independent variable is volume per foot of length and dependent variable is pressurization weight per foot of length? Would Wpressure per unit of Swet escalate linearly with diameter due to D^2/D dictating pressure for a given length of cabin?

flipdewaf wrote:
I would like something new I have to be honest.


Me too but gotta admit that a horizontal oval will be less attractive than the A380's vertical oval. Maybe it's subconscious apprehension of the moment of inertia implications. Plus seeing a horizontal oval succeed while the vertical oval flounders will be a reminder of potential VLA efficiency and our failure so far to make that work.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 5:41 am

@RJMAZ re 787-3X:

RJMAZ wrote:
My answer is 100T empty, with a wing 75% of the area, similar aspect ratio and 5° less sweep accepting a slightly lower cruising speed to gain more efficiency.


I started a model of 787-3X with the current wing and got to ~240,000lbs OEW so I think your 100T estimate is ballpark valid. (lost the excel doc when my battery died overnight).

I'm not going to model the 787-3X right now, but a few more things about it:

  • I see this happening 2 ways: (1) NMA biz case doesn't close, Boeing goes with a cheaper option or (2) Boeing builds both NMA and 787-3X (plus maybe -4X as a follow-up), with -3X being a true 763ER/A332 replacement of ~6,000nm range.
  • In either (1) or (2), the project needs to be cheapish. New LG, engines, empennage, fuselage optimization should cost $4-5bn. Adding a new wing costs another ~$3bn. Does the marginal benefit of a new wing justify the development cost? Likely no, because I see a cheap revision to current wing that keeps COC competitive with the too-big wing, costs pennies to develop, and makes the plane much cheaper to produce:
  • GET RID OF THE FLAPS. Per Piano's breakdown of 788 weight, the flaps alone weigh 4,800lbs. The hydraulic/electrics to power them weigh probably 50% of that. My -3X with no flaps had a ~400k MTOW and ~50K engines (same family as NMA's engines, just uprated). Our wingloading is ~100lbs/ft2, our W/T is ~4. These are A318-ish numbers - a plane with ~3,900ft takeoff role. We're keeping the slats for high takeoff AoA; absence of flaps implies 20% Cl penalty but even with that penalty wingloading is so low that we don't need high Cl. The big wing and lower MTOW effectively remove the 2nd-segment climb constraint. My -3X should be able to get off a 10k runway at MTOW even with ~45K engines (but stick with 50k for now).
  • High-lift system typically costs almost as much as the rest of the wing. If the wing is ~25% of production cost, and flaps 70% of high-lift cost, we save ~7-9% of production cost. Given that this plane has ~36% better fuel economy than 788, fuel will be ~40% of operating cost, acquisition ~30%. Giving a discount equal to production cost savings to airlines is cost-neutral with ~10% lower fuel burn.
  • While a new wing would be more fuel-efficient, 10% is a good ballpark for its fuel delta. If that's right, then an airline sees little difference between an old-wing -3X and a new wing - they either pay Boeing or fuel man. But there's a big difference to Boeing: ~$3bn in development cost.

In short I just can't see spending the necessary ~$8bn on rewinging the 787 whether NMA launches or not. Nonetheless, I'm starting to see your broader idea increasingly favorably.
By 2025, Boeing should be nearing a 787 re-engine. The -8 will disappear, move the -9 to niche ULH staus, the -10 becomes the family centerpiece, an -11 seems feasible as well. In that world, 797 covers TATLish markets and shorthaul, 787-3X/4X covers ~11hr flights plus has payload/range for cargo on short/regional routes with cargo demand. 787-9/10/11 covers everything above but short of 777X.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 10:54 am

Matt6461 wrote:
flipdewaf wrote:
I determined that the overall length of the aircraft could be determined by 7.74 + 0.89*(Cabin Length) + 2.04 * (Fuselage width).


I might have made this point already but this formula will penalize longer-range, bigger-empennage aircraft: For A320 family, LOA=fuse LOA, 737NG/MAX's LOA looks not even a foot more than fuse LOA. Not true of longer-range aircraft.


Point noted, I have rerun the analysis based on fuselage length rather than overall aircraft length. The new estimate equation is 5.37+0.89*(cabin length) + 2.2*Fuselage width. The R^2 value was 0.99 on this analysis.
Matt6461 wrote:
flipdewaf wrote:
Not sure the standards in this area however, do we add a certain length for a galley area or a standard are per seat on the aircraft?


Galley carts are 12.5in X 30in: so their footprint is ~.6 of a basic Y seat. 1 cart per 10 pax is a decent rule of thumb for 6+ hour flights.
If you have enough exit-row space to fit all galleys, the galley space should be ~6% of cabin (They remove into the exit rows). But if you don't, then you need to use additional space for cart removal/stowage. Usually you don't, so ~8-10% of cabin floor ends up being galley space. This varies based on Y layout and other factors (tailcone usage, for example).

Good rule of thumb is ~45/1 for pax/lav. Assume 1 lav takes the space of 2.5-3 galleys.

Combining these, galleys/lavs should take up at least ~15% (give or take) of usable cabin area (cabin area minus regulatory minimum exit rows).


Matt6461 wrote:

flipdewaf wrote:
It treats a shorter fuselage as being dominated by the pressure stresses, i.e. hoop stresses. as it gets longer the added bending stresses start to affect the overall weight


Per your model, would an A318 fuselage as a stationary pressure vessel weigh the same as an actual A318 fuselage?
Nope

Matt6461 wrote:
I'm guessing these two would differ in real life: can't think of any plane that doesn't have stringers and/or increased skin thickness at fore and aft of the wing box. I recall a Leeham diagram of NB fuselage (CS100?) that clearly showed substantial skin thickness gradient nearer the wingbox and on the underside for compressive loads.


Matt6461 wrote:
Yes, probably by quite a large factor. A hollow tube doesn't have windows or floors or wings attached and doors and has fatigue issues and people driving trucks into them.

flipdewaf wrote:
For a sphere of the same surface area the weight was 2632kg.


That's what I expected when I posted my question, though somehow the effect evaded me before yesterday. It throws a wrench in some of my daydreams but opens possibilities for others. Any handy metric for a pressurization weight function of a cylinder where independent variable is volume per foot of length and dependent variable is pressurization weight per foot of length? Would Wpressure per unit of Swet escalate linearly with diameter due to D^2/D dictating pressure for a given length of cabin?


Matt6461 wrote:
eeeerrrrr.... I'll read that a few times and make sense of it in my head then maybe do some fiddling on excel and JMP and then read again and then respond.... :P


flipdewaf wrote:
I would like something new I have to be honest.


Me too but gotta admit that a horizontal oval will be less attractive than the A380's vertical oval. Maybe it's subconscious apprehension of the moment of inertia implications. Plus seeing a horizontal oval succeed while the vertical oval flounders will be a reminder of potential VLA efficiency and our failure so far to make that work.


I want to see a double deck 3-3/3-3 or 2-2 top and 3-3 bottom. I used to have autocad on my work laptop which was great for layout config stuff but I didn't use it enough so I had to hand my license to my colleague and so I have lost my design stuff.

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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 11:04 am

Matt6461 wrote:
GET RID OF THE FLAPS. Per Piano's breakdown of 788 weight, the flaps alone weigh 4,800lbs. The hydraulic/electrics to power them weigh probably 50% of that. My -3X with no flaps had a ~400k MTOW and ~50K engines (same family as NMA's engines, just uprated). Our wingloading is ~100lbs/ft2, our W/T is ~4. These are A318-ish numbers - a plane with ~3,900ft takeoff role. We're keeping the slats for high takeoff AoA; absence of flaps implies 20% Cl penalty but even with that penalty wingloading is so low that we don't need high Cl. The big wing and lower MTOW effectively remove the 2nd-segment climb constraint. My -3X should be able to get off a 10k runway at MTOW even with ~45K engines (but stick with 50k for now).


Landing? With this shorthaul version you are landing closer to MTOW than you were previously. Every approach a flapless one? :crazy:

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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 11:21 am

Qantas94Heavy wrote:
Width of aisle depends on the seat width, but a rough average of aisle width looks something like:

10 abreast 777: 17"
9 abreast 787: 18"
9 abreast A350: 18.5"
8 abreast A330: 19"
7 abreast 767: 20"
10 abreast A380: 21"

For current narrowbody aircraft the 737 is about 19-20" and the A320 is 19-25" depending on seat width.

My concern with the single aisle concept is that people won't feel comfortable enough passing someone that's lifting up heavy baggage, to avoid bumping into them or their baggage ("you're so rude, are you in such a hurry?!"). This also has to do with the dynamic movement of the body during the baggage storage motion, as well as people feeling more comfortable using all the space if it is provided.

And by the time the single aisle aircraft has an aisle width of 30"+, you end up at a very similar width/pax to a 7 abreast widebody, and slightly worse than the 8 abreast.


I think in the current ~ 19-20 inch aisles most people won't feel comfortable passing someone lifting luggage. And they probably won't do so. But it is usually takes 2-3 seconds. Many people are doing something with their luggage, waiting for another passenger to get in/out the non aisle seats etc.

For 200+ seat aircraft, a 7 abreast cabin takes 40 inch extra cross section. A wide 6 abreast (longer) cabin 10 inch extra. That 40 inch is a very large impact, cascading into all thinkable economics. The economics must be challenging, evidenced by Boeing who have been contemplating for 5 years. I terms of new materials, weight savings, I don't expect breakthroughs / miracles.

The current benchmark, A321 NEO weighs around 50t empty. A stretched, beefed up, carbon re-winged version maybe 60-65t? The lightest 767-200 2-3-2 weighted 80t, 40 years ago. Since then requirements made it heavier, a 763ER weighs 90t. Weight has proven to be unforgiving on fuel consumption and operating costs. I hope Boeing can make a 2-3-2 cabin competitive.

In terms of cross section, the 3-3 has proved to be the superior option for up to 220-240 seats over the last decades. My assumptions is we might stretch that 220-240 up a bit, by fighting the typical disadvantages of longer NB's (753 access, fuselage weight, comfort) before you have to move over the something significantly larger.

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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 12:02 pm

Matt6461 wrote:
[*]GET RID OF THE FLAPS. Per Piano's breakdown of 788 weight, the flaps alone weigh 4,800lbs. The hydraulic/electrics to power them weigh probably 50% of that. My -3X with no flaps had a ~400k MTOW and ~50K engines (same family as NMA's engines, just uprated). Our wingloading is ~100lbs/ft2, our W/T is ~4. These are A318-ish numbers - a plane with ~3,900ft takeoff role. We're keeping the slats for high takeoff AoA; absence of flaps implies 20% Cl penalty but even with that penalty wingloading is so low that we don't need high Cl. The big wing and lower MTOW effectively remove the 2nd-segment climb constraint. My -3X should be able to get off a 10k runway at MTOW even with ~45K engines (but stick with 50k for now).

Very interesting idea. It would actually work extremely well. The flaps are very important on the longer model as it keeps the fuselage more level avoiding tail strikes.

The 787-8 is already quite short and a 6m shrink would have no issues with tail strikes without flaps. It would be a very simple solution to make a lightweight and cheaper 787.

There is no chance they will make a 797 and a lightweight 787. There will make one or the other.

The NMA apparently will be called the 6X and 7X. This is breaking the normal trend for Boeings number system. This definitely point us to it being below the 787-8.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 12:23 pm

RJMAZ wrote:
Matt6461 wrote:
[*]GET RID OF THE FLAPS. Per Piano's breakdown of 788 weight, the flaps alone weigh 4,800lbs. The hydraulic/electrics to power them weigh probably 50% of that. My -3X with no flaps had a ~400k MTOW and ~50K engines (same family as NMA's engines, just uprated). Our wingloading is ~100lbs/ft2, our W/T is ~4. These are A318-ish numbers - a plane with ~3,900ft takeoff role. We're keeping the slats for high takeoff AoA; absence of flaps implies 20% Cl penalty but even with that penalty wingloading is so low that we don't need high Cl. The big wing and lower MTOW effectively remove the 2nd-segment climb constraint. My -3X should be able to get off a 10k runway at MTOW even with ~45K engines (but stick with 50k for now).

Very interesting idea. It would actually work extremely well. The flaps are very important on the longer model as it keeps the fuselage more level avoiding tail strikes.

The 787-8 is already quite short and a 6m shrink would have no issues with tail strikes without flaps. It would be a very simple solution to make a lightweight and cheaper 787.

There is no chance they will make a 797 and a lightweight 787. There will make one or the other.

The NMA apparently will be called the 6X and 7X. This is breaking the normal trend for Boeings number system. This definitely point us to it being below the 787-8.



While technical possible I think a 787 NMA would be oversized / overpriced for most of the market.

All kinds of smart things could be done on the wing to e.g. control AOA during critical flights phases.
A wing good for cruise efficiency needs high lift (devices) for take-off landing. Specially if it does 4-6 flights a day.

Image

Getting operating costs / weight down significantly seems impossible without redoing everything and a bit more..

http://www.airliners.net/forum/viewtopic.php?f=3&t=1358167
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 12:50 pm

keesje wrote:
While technical possible I think a 787 NMA would be oversized / overpriced for most of the market.

All kinds of smart things could be done on the wing to e.g. control AOA during critical flights phases.
A wing good for cruise efficiency needs high lift (devices) for take-off landing. Specially if it does 4-6 flights a day.

Flaps simply increase lift and lower the nose slightly at low speeds. With the flaps down the average wing angle of attack increases relative to the fuselage. This lowers the nose (raises the tail) which isnt needed on the shorter fuselage length.

This is why the A321 has expensive double slot flaps, it helps avoid tail strikes.

Lots of flights including 767's takeoff without flaps on a regular basis if the takeoff weight is low. The 767 has a very big wing. Slats are however always required. Flaps 1 setting puts down the front slats but does not lower the flaps.

A 787 sized wing with a 170T maximum takeoff weight would not need any flaps at all even on a relatively short runway. Matt's idea is actually a perfect way to get weight and complexity down on a lightweight 787.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 5:41 pm

flipdewaf wrote:
Landing? With this shorthaul version you are landing closer to MTOW than you were previously. Every approach a flapless one? :crazy:


In the world of our -3X projection, MEW decreases by ~44,000lbs. OEW and/or payload would see a further decrease to account for weight/seat improvements 2005-2025 (e.g. 11lb titanium oxide Y seats ). Call that ~5,000lbs. MLW's component of fuel (MLW-MZF) for reserves and 30min holding declines in proportion to max-range MZFW trip fuel: -.4 * 25,000 = ~10,000lbs.

Total delta is ~59,000lbs, MLW drops from 380k to 321k, wing loading @MLW is ~15% lower than 788.
If no flaps causes ~20% loss of lift at equal speed, we need only 3% higher landing speed than 788. That should be fine as 788 already has very-low wingloading and likely an approach speed far below a maximum of 170kn.

RJMAZ wrote:
get weight and complexity down on a lightweight 787.


And with 787's absence of heavy checks, routine maintenance of flight controls is probably the bulk of its frame maintenance cost. Flaps maintenance is probably ~half of frame maintenance.

RJMAZ wrote:
There is no chance they will make a 797 and a lightweight 787. There will make one or the other.


Ok just smash my dreams why dontcha? Let's imagine the possibilities a little before ruling things out.

Say Boeing launches NMA's -6/-7 with 5,000/4,500 range and little cargo capacity. It's a big hit but Asian carriers still want a trunk-route hauler with cargo capacity and every carrier would still like an option for ~12hr long/thin routes. This is the 763ER and A332 market: not worth huge investment but $4bn? Maybe. Look at the difference between 4,500nm and 5,500 (assuming real-world range is still ~10% lower than spec range):

Image
Image
Image

-3X's higher range opens up most of Europe-Asia, western N.A.-Europe. It would allow some cargo on 8hr routes where NMA won't carry any.

With $4bn price tag we'd want to see annual profit stream of at least $1bn. Assuming $20mn/plane profit, that means 50 annual sales. Seems pretty doable, especially once simple stretch, regional/transcon -4X follow up is added at a cheap development cost (perfect 1-1 replacement for A333's on regional routes).
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Fri Mar 16, 2018 7:05 pm

Cl max for the 787 in Lansing config I would guess is somewhere around 2.7. Clmax for takeoff config is probably around 1.8 and Cl max clean is ~1.4, all based on static reference area.

The reason that you put high lift devices on isn't to make more lift but to reduce the sacred Swet when you are cruising. That's why they put so much effort to getting them stored away nicely.

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Matt6461
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sat Mar 17, 2018 1:22 am

flipdewaf wrote:
Cl max for the 787 in Lansing config I would guess is somewhere around 2.7. Clmax for takeoff config is probably around 1.8


I'm saying divide these Cl's by ~1.2 for flaps removal and increase landing speed by ~3%. My guess is that 788's MLW minimum approach speed is around the A380's 140kn. We could increase that to 160kn if we had to (isn't 170kn the typical approach limit?). With quieter engines and no flaps, total vehicle noise would still be lower most likely.

EDIT: Ok you're saying we need to account for Fowler flap area that retracts in cruise. Good point. But that's like 5% of Sref? Even if it's 10% then just increase landing speed an additional 5% and we should still be fine (plus allows a smaller tailplane as speed increases while lift/nose-down-moment stays the same).
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sat Mar 17, 2018 7:11 am

Matt6461 wrote:
flipdewaf wrote:
Cl max for the 787 in Lansing config I would guess is somewhere around 2.7. Clmax for takeoff config is probably around 1.8


I'm saying divide these Cl's by ~1.2 for flaps removal and increase landing speed by ~3%. My guess is that 788's MLW minimum approach speed is around the A380's 140kn. We could increase that to 160kn if we had to (isn't 170kn the typical approach limit?). With quieter engines and no flaps, total vehicle noise would still be lower most likely.

EDIT: Ok you're saying we need to account for Fowler flap area that retracts in cruise. Good point. But that's like 5% of Sref? Even if it's 10% then just increase landing speed an additional 5% and we should still be fine (plus allows a smaller tailplane as speed increases while lift/nose-down-moment stays the same).


What I'm saying is that the Clmax for for various stages of flight is a good estimate for what would happen if you removed the flaps rather than an arbitrary 20%.

In landing config you have slats and big flap delploynent. In takeoff config you have slaps and small flaps deployment and for cruise you have no flaps and no slats so the Cl max for no flaps and some slats probably lies somewhere lower than the takeoff config but not that much say ~1.7 this isn't 20%, this is knocking on for a 40% reduction.

With regards to the reference area this is just a note that even though a Cl might be given for a particular configuration the reference area stays the same for the aircraft and doesn't change to the new wing area for that configuration, same is you would for referencing Swetfuse back to Wing reference area.

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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sat Mar 17, 2018 7:24 am

flipdewaf wrote:
Clmax for for various stages of flight is a good estimate for what would happen if you removed the flaps rather than an arbitrary 20%


Not arbitrary. I got it from a NASA study. Not at my computer now but you can find it by googling NASA high high lift devices. I'll post it later though and should have before.

Rather than take an average of landing/takeoff, I'd prefer to disaggregate the contributions of slats/flaps. Slats' primary function is to enable higher AoA - though some leading edge devices add Fowler area too.

By my lights, Max Cl is a product of max AoA (slats' primary job) plus a flaps factor.

Per NASA, the flaps delta to Clmax is ~20% IIRC.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sat Mar 17, 2018 6:49 pm

Matt6461 wrote:
flipdewaf wrote:
Clmax for for various stages of flight is a good estimate for what would happen if you removed the flaps rather than an arbitrary 20%


Not arbitrary. I got it from a NASA study. Not at my computer now but you can find it by googling NASA high high lift devices. I'll post it later though and should have before.

Rather than take an average of landing/takeoff, I'd prefer to disaggregate the contributions of slats/flaps. Slats' primary function is to enable higher AoA - though some leading edge devices add Fowler area too.

By my lights, Max Cl is a product of max AoA (slats' primary job) plus a flaps factor.

Per NASA, the flaps delta to Clmax is ~20% IIRC.

You'll see from the piano x data for the 787 that the Cl max for different flight configurations fall right within the bounds I described. I would be very surprised if any transport category aircraft today was only adding 20% to the Cl max with flaps, does the NASA source describe the same type of flaps used in modern transport category aircraft?

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william
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 26, 2018 6:48 pm

Matt6461 wrote:
flipdewaf wrote:
Landing? With this shorthaul version you are landing closer to MTOW than you were previously. Every approach a flapless one? :crazy:


In the world of our -3X projection, MEW decreases by ~44,000lbs. OEW and/or payload would see a further decrease to account for weight/seat improvements 2005-2025 (e.g. 11lb titanium oxide Y seats ). Call that ~5,000lbs. MLW's component of fuel (MLW-MZF) for reserves and 30min holding declines in proportion to max-range MZFW trip fuel: -.4 * 25,000 = ~10,000lbs.

Total delta is ~59,000lbs, MLW drops from 380k to 321k, wing loading @MLW is ~15% lower than 788.
If no flaps causes ~20% loss of lift at equal speed, we need only 3% higher landing speed than 788. That should be fine as 788 already has very-low wingloading and likely an approach speed far below a maximum of 170kn.

RJMAZ wrote:
get weight and complexity down on a lightweight 787.


And with 787's absence of heavy checks, routine maintenance of flight controls is probably the bulk of its frame maintenance cost. Flaps maintenance is probably ~half of frame maintenance.

RJMAZ wrote:
There is no chance they will make a 797 and a lightweight 787. There will make one or the other.


Ok just smash my dreams why dontcha? Let's imagine the possibilities a little before ruling things out.

Say Boeing launches NMA's -6/-7 with 5,000/4,500 range and little cargo capacity. It's a big hit but Asian carriers still want a trunk-route hauler with cargo capacity and every carrier would still like an option for ~12hr long/thin routes. This is the 763ER and A332 market: not worth huge investment but $4bn? Maybe. Look at the difference between 4,500nm and 5,500 (assuming real-world range is still ~10% lower than spec range):

Image
Image
Image

-3X's higher range opens up most of Europe-Asia, western N.A.-Europe. It would allow some cargo on 8hr routes where NMA won't carry any.

With $4bn price tag we'd want to see annual profit stream of at least $1bn. Assuming $20mn/plane profit, that means 50 annual sales. Seems pretty doable, especially once simple stretch, regional/transcon -4X follow up is added at a cheap development cost (perfect 1-1 replacement for A333's on regional routes).


I think a 797 and 787-3X is doable, but the 787 project would be a on a tight budget leash, real tight. The real question would how much efficient would such an aircraft be to the A330NEO that it would be competing against? And are there engines on the horizon for such a 787-3X?

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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 26, 2018 8:15 pm

William wrote:
The real question would how much efficient would such an aircraft be to the A330NEO that it would be competing against?


Huh? Even if we assume 787 and A330NEO are equally efficient, this is a massive improvement (on shorter missions) over 787 and therefore over A330NEO.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 26, 2018 8:52 pm

william wrote:
And are there engines on the horizon for such a 787-3X?


The point of my proposal is to keep the too-large 788 wing so we can take off with NMA's engines despite higher-than-NMA MTOW. No reasonable OEM would make a clean-sheet engine for a -3X.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 26, 2018 9:14 pm

Matt6461 wrote:
william wrote:
And are there engines on the horizon for such a 787-3X?


The point of my proposal is to keep the too-large 788 wing so we can take off with NMA's engines despite higher-than-NMA MTOW. No reasonable OEM would make a clean-sheet engine for a -3X.


Using the NMA engines (an upsize of the narrow body engines) is interesting. I did not know if you were proposing that or de rating larger engines.
 
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Matt6461
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 26, 2018 9:46 pm

Flipdewaf wrote:
You'll see from the piano x data for the 787 that the Cl max for different flight configurations fall right within the bounds I described. I would be very surprised if any transport category aircraft today was only adding 20% to the Cl max with flaps, does the NASA source describe the same type of flaps used in modern transport category aircraft?


Sorry for the delay in getting back to you. The NASA study I was thinking of is here: https://ntrs.nasa.gov/archive/nasa/casi ... 052267.pdf

It's a 166-page document and I'm having trouble finding the exact graph I thought I remembered. I'll come back with the page if/when I find it.

Page 78 shows a graph of different planes' implied landing Cl versus their wingloading at MLW and approach speed. The paper is from 1996 so doesn't include many contemporary planes.

Look at the 747SP: Its landing Cl is ~1.24, MLW wingloading is ~82lbs/ft2, MLW approach speed is ~138kn.

On our 787-3X, MLW wingloading is ~80lbs/ft2; our approach speed is up to 160kn (a la 77W) or even 170kn (regulatory limit, IIRC).

By ratio of wingloadings and approach speeds (squared) to 747SP, our -3X needs an approach Cl of only ~0.90.

Doesn't 0.9 Cl seem easily doable with full slats and a high (~15%) AoA? A plane doesn't land at approach AoA; it levels out after landing flare for touchdown (most are limited to ~8degree AoA/rotation angle on the ground by fuselage length).

Beyond full slat removal, other similar options are possible, though more expensive to develop and slightly heavier (still far cheaper than a new wing). On the 747SP, Boeing moved from a triple-slotted flap to a single-slotted and left the wing otherwise unchanged. The 787 already has single-slotted flaps; an unslotted, simply-hinged flap would be lighter and case less cruise drag than the current system. Boeing could also remove the flaps and extend the slats slightly: page 93 discusses how leading edge devices can be used to increase lift by themselves, instead of merely extending the AoA-Cl curve. If necessary, Boeing could probably revise the slats sufficiently to generate needed lift while omitting the flaps.

But if ~.9 approach Cl is ballpark, we probably don't need flaps at all - just slats.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 26, 2018 9:55 pm

I neglected to mention another advantage of no flaps in prior -3X posts: large decreases in interference and control-surface-gap drag, a small delta to skin friction drag from losing flap track fairings. I'd have trouble quantifying this impact... IIRC control-surface-gap drag is significant - at least 1% of total drag? Flaps must constitute the majority of control surface gaps and therefore of CSG drag.

IDK how much interference drag happens around the flap-track fairings, but there must be some. Otherwise it wouldn't be worth the extra weight/Swet of fairings to smooth the wing/track junctions at all.

Flap fairing delta to Swet is ~20-25m2?: 6 fairings, ~10ft long, ~2ft wide, ~2ft tall, minus covered wing area.
That would mean ~1-1.2% of Swet saved and ~.6% of total drag saved.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 26, 2018 11:26 pm

@flipdewaf I looked at the Piano 787 data again. A few points:

  • Piano lists 2.66 as 788's maximum landing Cl. It doesn't specify that this value is actually used in the approach speed analysis. The need for landing flare just prior to leveling off for touchdown implies that approach cannot be at maximum landing Cl - else flare would cause stall. Given the NASA study (page 78) places many airliners at 1.3-1.7 Cl on approach, with none above ~2.1 (Bae-146-200 and it's an outlier), and given the time-trend up to 1996 was towards lower approach Cl and less-intricate flaps, it would be odd if 788 reversed these trends and used the highest approach Cl ever, while having one of the lowest wing-loadings. So I'm pretty sure 2.66 is not 788's approach Cl.
  • Piano has 133kn for 788 approach at 365k-lbs. That implies 135.7kn at MLW of 380k-lbs, which is lower than the 140kn I estimated upthread. Using a 160kn approach speed implies 28% lower approach Cl; -3X MLW of 321k-lbs gets us to 40% lower approach Cl. So unless flaps increase lift by ~67%, we should be fine without them.
  • Higher approach speed should be fine because (1) 788 landing distance is only 4,986ft and (2) total vehicle noise will be fine given no flaps and super-high BPR engines. Assuming quadratic escalation of landing distance with approach speed, we're still below 7,000ft landing distance. That's far less than ~9,300ft takeoff run so won't be a constraint except on the very last flight to the bone yard.

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