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Designing a very, very large airliner…

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Designing a very, very large airliner…

Old 10th Feb 2016, 01:51
  #41 (permalink)  
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How does the AN225 undercarriage cope with the weight on touchdown? Does it land with no pitch? I can see the rear undercarriage collapsing on this mega-jumbo on landing. All the weight will be on the rear wheels.
I don't see the Antonov 225 having problems with it.




As well as many other aircraft.






Apart from that, it looks like a maintenance nightmare. You would need several cherry pickers on every transit just to check the engines and top up the oil. By comparison, the inboard engines on a 747-400 with RB211 engines can be serviced without steps.

One of the reasons the 777 is so efficient is because maintenance engineers had an input into it's design. If an aircraft is easy to work on, turnaround times are faster and it's inherently safer. Airbus didn't quite grasp this concept with the A380.

I see half the fuel supply is below the height of the engines (not so good when "gravity" feed is required).
Did it cause problems on the A380? And with the increased passengers, wouldn't the turnaround time be longer anyway. Can't engineers use that time to inspect whatever they need to inspect?
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Old 10th Feb 2016, 14:16
  #42 (permalink)  
 
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I don't see the Antonov 225 having problems with it.
´cause the Antonov has its center of lift directly above the landing gear. Thus provides smaller loads on the aft wheels whilst landing.

Can't engineers use that time to inspect whatever they need to inspect?
They do. Because it is a more adequate way to reduce the turnaround time in the design itself instead of shortening the ground crews time.

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Old 10th Feb 2016, 14:41
  #43 (permalink)  
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´cause the Antonov has its center of lift directly above the landing gear. Thus provides smaller loads on the aft wheels whilst landing.
The center of lift of the hyperjumbo IS directly above the landing gear (resultant center of lift of both wings).

Just to clarify, the projected CG and center of lift characteristics of this aircraft is similar to that of an aft-mounted engine aircraft like the MD-80 because it's 6 engines are practically mounted aft. This is why the landing gears are moved back.

Also, I've modified the landing gear a bit. It now features 2 rows of wheels in each bogie compared to just one in the previous photos.

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Old 10th Feb 2016, 15:16
  #44 (permalink)  
 
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Amusing Idea, BUT...

There are likely only 3-4 RWYs in the world that can accommodate something this large, none of the where PAX really want to go. While it would probably fly, ground infrastructure is no where close of able to accept this plane. And who would want to fly on it? Not me!
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Old 10th Feb 2016, 15:54
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From an SLF point of view, I don't think I'd like to be allocated, say, 37G on the middle deck.
But then, some people seem to get off on that sort of thing - for example, those that flock to football games and such.

A chap told us the other night that he liked travelling on the upper deck of the A380 - because the view is much better up there. (??)
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Old 10th Feb 2016, 17:33
  #46 (permalink)  
 
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The center of lift of the hyperjumbo IS directly above the landing gear (resultant center of lift of both wings).
I got that Idea. But the center of lift has to move forward on landing since your rear wing is used as elevator.

Just to clarify, the projected CG and center of lift characteristics of this aircraft is similar to that of an aft-mounted engine aircraft like the MD-80 because it's 6 engines are practically mounted aft.
Thats clear. Like i said, an forward swept wing brings in Aeroelastic problems, the bigger the wings size the bigger the problem gets. Adding 6 engines onto that structure should size that problem to another level.

Your design looks futuristic but in my opinion it is more practical to use an (Beechcraft)Staggerwing like boxwing configuration with classic elevator and rudder.
This also provides chances of turbine driven E-fans.

Greetings,
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Old 10th Feb 2016, 20:46
  #47 (permalink)  
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I got that Idea. But the center of lift has to move forward on landing since your rear wing is used as elevator.
We may never know the exact weight/balance numbers but my model and similar real-life examples demonstrate the landing gear concept to be workable. Also, pitch control is not limited to the rear wing. Yes, you can decrease lift to the rear wing to pitch up, but you can also increase lift to the front to pitch up.


Thats clear. Like i said, an forward swept wing brings in Aeroelastic problems, the bigger the wings size the bigger the problem gets. Adding 6 engines onto that structure should size that problem to another level.
Except, it's not a simple cantilever swept-forward wing. The closed wing system should cancel out opposing forces on the two wings so as a whole, it should be as structurally sound as a very thick straight wing, without the increased drag.


Your design looks futuristic but in my opinion it is more practical to use an (Beechcraft)Staggerwing like boxwing configuration with classic elevator and rudder.
This also provides chances of turbine driven E-fans.
Thanks but why increase the weight by adding elevators when you can use the wings for pitch control? Compared to conventional design, the wings need to compensate for the negative lift the elevators are producing.
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Old 10th Feb 2016, 22:02
  #48 (permalink)  
 
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Can't engineers use that time to inspect whatever they need to inspect?
Having operated a cherry picker myself (as part of my engineering duties), I can assure you you're going to increase the inspection/top up time by a factor of 10. I can check the oils and do "front and back" inspections on a 747 in the time it takes for me to put on a safety harness and park one cherry picker at the aircraft. The presence of 2 or more cherry pickers around an aircraft would also interfere with cargo loading.

And no airline is going to wear the costs of 2 cherry pickers per aircraft (I think we only had one or two for the entire fleet at our main base).

(EDIT: Beancounters are also continually telling us that "time on the ground" is wasted. Surely the ultimate goal would be to have shorter transit times. Additional time spent on routine servicing means less time for working on non-routine problems)

I don't see the Antonov 225 having problems with it. As well as many other aircraft.
Point taken. I wonder if the main gear elements are identical on the Antonov or if there are additional reinforcements for the rear gear. The 747 wing gear does seem more robust than the wing gear. The 777 is not really a valid argument. The bogey tilt accommodates the pitch angle.

Last edited by NSEU; 11th Feb 2016 at 01:03.
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Old 10th Feb 2016, 22:31
  #49 (permalink)  
 
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I suspect your limitations will include individual tire load and speed limits. it would be fiscally untenable for an airline to have to buy a unique tire for a low-production airplane. OTOH, if you can put enough wheels on it...

Also, I think a blended wing-body concept would fare better than a conventional fuselage+wing design for something that large.

All those considerations are beyond the "need" for an airplane larger than the 747 or A380 in the first place...
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Old 11th Feb 2016, 04:47
  #50 (permalink)  
 
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From an SLF point of view, I don't think I'd like to be allocated, say, 37G on the middle deck.
But then, some people seem to get off on that sort of thing - for example, those that flock to football games and such.
Looking at the design, it would be easy to see that sitting in the vicinity of 37G is where the partying would be. First seat sold I'd say.


What's the fascination with size? Has everyone now forgotten speed? Is it for the too hard basket? Because when I fly from SYD to LAX, sitting for 13-14 hours gives me the . I want it to only be a '3 movie' flight at best.

That's what people want. Speed. The talk around the water coolers at work isn't about big aircraft. It's talk of fast aircraft. That's what us punters want. Fast sonsofbitches to get us there quick.


Impressive engineering skills though, for that aircraft. Stick another 6 engines on the sucker and THEN we'll talkin!!!
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Old 11th Feb 2016, 11:01
  #51 (permalink)  
 
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Also, pitch control is not limited to the rear wing. Yes, you can decrease lift to the rear wing to pitch up, but you can also increase lift to the front to pitch up.
It is completely anyhow how you do the pitch up in this configuration. It does result in a higher lift in the front wing, so the neutral point moves forward.

We may never know the exact weight/balance numbers but my model and similar real-life examples demonstrate the landing gear concept to be workable.
Thats true. Mainly on Transport Aircrafts.

Except, it's not a simple cantilever swept-forward wing. The closed wing system should cancel out opposing forces on the two wings so as a whole, it should be as structurally sound as a very thick straight wing, without the increased drag.
As you may read in the paper: The wingtips are heavily loaded parts of the structure only after an Aerodynamic evaluation. Aeroelastic evaluation wasn´t done until that point.
Concluding: The Wingtips may get heavier than planned which means a loss in capacy (and an increase in maintenance costs).

Compared to conventional design, the wings need to compensate for the negative lift the elevators are producing.
Not on the conventional design. The Wings have to compensate the angle of attack induced by the elevators, the center of lift (nearly) stays fixed in this configuration.

Thanks but why increase the weight by adding elevators when you can use the wings for pitch control?
As seen from above.

P.S.: If you want an futuristic and stable design with elevators at this size:
Try an P.180 layout with both wings swept forward, engines between the wings (fixed on upper and lower) providing extra stiffness.

That's what people want. Speed. The talk around the water coolers at work isn't about big aircraft. It's talk of fast aircraft. That's what us punters want. Fast sonsofbitches to get us there quick.
Thats true. Just adding engines wouldn´t do that thing. Have you already read about SABRE engines?

Greetings,

Last edited by Sokol; 11th Feb 2016 at 13:04.
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Old 11th Feb 2016, 11:48
  #52 (permalink)  
 
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Originally Posted by Jonno_aus View Post
.
That's what people want. Speed. The talk around the water coolers at work isn't about big aircraft. It's talk of fast aircraft. That's what us punters want. Fast sonsofbitches to get us there quick.
The evidence suggests that the opposite is true.
Since the 70s airliners have got a lot slower.
Airlines noticed that passengers are upset by being late, not slow. They then increased all the scheduled times so that if delayed the aircraft could speed up from the usual economical cruise to catch up. VC10 was a rocket ship compared to current airliners.

Incidentally, who among you even knows which airliners are the fastest? Surely if it actually mattered people would chose to fly on the fast ones?
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Old 11th Feb 2016, 13:17
  #53 (permalink)  
 
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Can a closed wing design such as this achieve positive longitudinal static stability?

I recall a certain ultralight with a similar wing, which crashed a lot.
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Old 11th Feb 2016, 13:27
  #54 (permalink)  
 
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Ligeti's Stratos?
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Old 11th Feb 2016, 17:28
  #55 (permalink)  
 
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I have been a fully paid up member of the RAeS for over sixty years, but as I don't want to be accused of nit-picking (post#8) I will refrain from any direct comment on the HyperJumbo as presented and confine myself to remarks on the general concept.
The box-wing has been around for a long time and although the details differ the HyperJumbo under discussion has noticeable similarities to the 1995 Lockheed Boxwing.







This latter was put together by a professional design team so we can assume it to have been properly thought through. It was assessed by a NASA/Boeing/Stanford group as having achieved the minimum theoretical vortex drag in a configuration with "reasonable" high speed performance (it had favourable transonic area ruling) and some structural advantages.
The problem areas identified, but not resolved, included landing gear integration, maximum lift penalties, fuel volume and low sectional Reynolds Numbers.

The general concept of drag reduction by use of non-planar wings has been studied in detail by Prof. Ilan Kroo of Stanford University. There are a couple of papers worth reading if you want more detail.
Highly Nonplanar Lifting Systems: Ilan Kroo, Stanford University; John McMasters, Boeing Commercial Airplane Group, and Stephen C. Smith, NASA Ames Research Center: Transportation Beyond 2000: Technologies Needed for Engineering Design: September 26-28, 1995
Nonplanar wing concepts for increased aircraft efficiency. I Kroo Stanford University USA; VKI lecture series on Innovative Configurations and Advanced Concepts for Future Civil Aircraft. June 6-10, 2005
The more important conclusions are summarised on the following chart, extracted from one of those papers.




Down on the bottom right Configuration "A" is the closed wing arrangement proposed for the HyperJumbo. It offers the maximum reduction in theoretical vortex drag.
However, Kroo established that you do not need to close the wing to get this drag reduction. Configuration "C" has pretty well the same drag reduction but without the problems associated with the complete boxwing. Kroo developed this thinking into a "C wing" design as shown.




You may, or may not be a convert of the blended wing philosophy, but it does look plausible.

Before getting too excited it might be worthwhile reflecting that the drag reductions being claimed relate to the theoretical vortex drag; that is to the inviscid drag produced by the particular distribution of vorticity over the wing. This theoretical vortex drag is a large part of the total drag due to lift, but is by no means the whole of it.
Staying with the American practice of using Oswald efficiency to describe induced drag, the Oswald efficiency of a modern wing in cruise is of the order 0.8. The theoretical vortex drag contribution would be around 0.9 to 0.93, the rest comes from lift (or aoa) sensitive viscous flow effects giving rise to minor flow separations which in turn produce drag.
Until we know how these viscous effects will operate on unconventional configurations such as the Hyperjumbo we cannot be sure how much of the theoretical drag gains will actually be achieved.
Note also that modern wings are NOT designed to cruise with the theoretically optimum vortex drag. The objective is to produce the best wing not simply the most aerodynamically efficient. It generally pays to back off the theoretical optimum, have a span loading with a more inboard centre of pressure than an elliptic loading and cash the weight saving. That is without winglets of course.
This general thought must be carried over to any new proposals - the object is the best overall design not necessarily the most aerodynamically efficient.
Go back to the second chart and consider Configuration "B". This has less potential gain than A or C but it is a much simpler arrangement. In fact the reduction in theoretical vortex drag is 90% of the theoretical maximum reduction, but the only change to a planar wing is the addition of Longhorn style vertical winglets.
Now if, and it is a very big IF, a viable market emerges for an aircraft with more capacity than be squeezed out of an A380, would you tear up everything and go for an untried unconventional layout or would you chicken out and adopt a simple vertical winglet modification to the A380 for slightly lower potential gains but much less commercial risk?


PS I have just discovered that the illustrations may not appear. They were OK on my PC but not on the ipad. I seem to have a problem with Dropbox which I will attempt to sort out. Meantime, if anyone is desperate to see the pictures they are lifted directly from the two papers I cited. For the first illustration see the Kroo/McMasters/Smith paper p338, for the second see the same paper p346 or p 353, or a slightly different presentation in the Kroo paper Fig 18 (p.18) and for the third illustration see the Kroo paper Fig 13 (p. 15)

Last edited by Owain Glyndwr; 12th Feb 2016 at 13:02. Reason: Retry at inserting illustrations
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Old 14th Feb 2016, 16:53
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But I wasn't too familiar with airport pavement design. I thought if I added more wheels the distribution of weight will be spread out similar to an A380 or 747. Could you share some numbers?
You will find tons of information regarding the A380 in this document:

A380 AIRCRAFT CHARACTERISTICS AIRPORT AND MAINTENANCE PLANNING:
http://www.airbus.com/fileadmin/medi...80-Dec2014.pdf

Since you want to design you aircraft to the same restrictions as an A380 has the document might apply to your design as well.
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Old 14th Feb 2016, 17:29
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I agree on earlier posts that the limit is the airport designs.

I have always marvelled at the inefficiency of nose in parking. Once during apron works we had to park side on, and de-boarding/boarding all happened quicker with two sets of steps equidistant from the gate entrance. Bags were kept away from the passengers too.

A properly designed pier system with underground passages for service vehicles and provision to connect airbridges front AND rear would allow aircraft like the B777, A380 and B747 turn quicker. Smaller aircraft would benefit even more as they are not limited to the constraints of the larger long haul ships, slots and spacing to enable two flight daily cycles, etc.

Just a thought.
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Old 14th Feb 2016, 21:15
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Imaginative design. It shows a lot of work and thought. But my concern is as a passenger. The five- and six-across middle rows look like a nightmare. I don't see how it is going to work with just two aisles -- unless they are double-wide so that at least two people can pass simultaneously. Think of the extra time to load the plane as people already seated need to get up and enter the aisle to let later-arriving middle seat passengers get in. Also, I think evacuation would present a problem.
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Old 15th Feb 2016, 09:34
  #59 (permalink)  
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You will find tons of information regarding the A380 in this document:

A380 AIRCRAFT CHARACTERISTICS AIRPORT AND MAINTENANCE PLANNING:
http://www.airbus.com/fileadmin/medi...80-Dec2014.pdf

Since you want to design you aircraft to the same restrictions as an A380 has the document might apply to your design as well.
Thanks! That's quite a useful document there!


I agree on earlier posts that the limit is the airport designs.

I have always marvelled at the inefficiency of nose in parking. Once during apron works we had to park side on, and de-boarding/boarding all happened quicker with two sets of steps equidistant from the gate entrance. Bags were kept away from the passengers too.

A properly designed pier system with underground passages for service vehicles and provision to connect airbridges front AND rear would allow aircraft like the B777, A380 and B747 turn quicker. Smaller aircraft would benefit even more as they are not limited to the constraints of the larger long haul ships, slots and spacing to enable two flight daily cycles, etc.

Just a thought.
I agree too. Personally I think the future would be about both size and efficiency. And with that comes along gradual airport innovations as well.


Imaginative design. It shows a lot of work and thought. But my concern is as a passenger. The five- and six-across middle rows look like a nightmare. I don't see how it is going to work with just two aisles -- unless they are double-wide so that at least two people can pass simultaneously. Think of the extra time to load the plane as people already seated need to get up and enter the aisle to let later-arriving middle seat passengers get in. Also, I think evacuation would present a problem.
Thanks. 5 middle row seats already exist (see DC-10/MD-11, B777, and soon the A380). 6 middle row seats though are new territories for airlines. I don't see why not when it's practically two A320/737s side by side. But I would expect most airlines would choose 5 middle row seats though over 6 for a total of 11 abreast. I just showed that 12 abreast is possible with 17.5in seats and 15in aisles.

I'm confident evacuation wouldn't be a problem since I configured my aircraft with sufficient exits per deck. The aircraft would have 4 pairs of type A doors on the upper deck, 5 on the main deck and 6 on the lower deck. Each pair of type A door is allowed 110 passengers and I have 15 pairs for a total of 1650 allowable pax capacity. Each exit is within the 60ft separation limit and spaced almost evenly throughout the fuselage.

This is why I chose box wing design over blended wing body. A blended wing body would force you to have exits spaced more than 60ft. And if you put exit openings at the belly, it would be difficult if you have a landing gear collapse. This would need a lot of convincing to the FAA to certify.


Anyway, I have been playing around cabin configurations. Some standard features unique to this aircraft is the forward atrium and mezzanine on the main and upper deck. Since the fuselage curves downward at the nose, the "forehead" would be impractical to fill with galleys and seats, so I decided to leave it empty. Premium airlines can use that space for an ultra-luxurious first/business class lounge or potential for two loft-type suites (a-la Etihad Residence but on steroids). There will also be a lift (option for two) that can carry people and trolleys across the three decks. There will also be two staircases. One in the front, one at the back. Here are some preliminary studies I've came up with:

Ultra dense: Maximum possible configuration. Lavs and galleys of the lower deck are transferred to the main deck so this configuration might only be seen on military or special ops versions.



Dense: We might see this configuration for long-haul LCCs or holiday charter airlines.



Standard single class: This would probably serve as the basis of most configurations for major airline customers out there. This shows the second lift at the back.



I'll post 2-class and 3-class and more soon!
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Old 15th Feb 2016, 13:52
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have you seen the Cranfield study of 2010?

https://www.youtube.com/watch?v=8ojMUAEj-ho
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