jetflyer
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New Aircraft Design

Wed Feb 08, 2006 8:33 pm

I'm interested in aircraft design. I'm wondering if it would be possible to make a very efficiently designed jumbo jet by having a T-tail design and a large clean wing with a 40 degree sweep angle. Could something that weighs around 1,150,000lbs and has four rear engines be possible? It would certainly look different, and with composite materials it should be possible to implement rear engines of about 70,000lbs thrust range. I'd have thought it would be more aerodynamically efficient that something with engines on the wings, and it could also have a long, sleek fuselage with about 70 rows of seats in a ten abreast layout, say seating 600-700 passengers. With composite materials available and computerised design, something like this could be made safe and realistic, couldn't it? Not only that but it would fly faster for a lower drag level, with more swept wings and a smaller horizontal stabiliser. Are there any technical people on this board who can relate to this question with some answers? I might design a plane like this one day, but how come we don't see designs like that now? Imagine a VC-10 or something but of A380 type size. With modern technology couldn't it be done?
 
wingscrubber
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RE: New Aircraft Design

Wed Feb 08, 2006 10:56 pm

An aircraft of that size would need BIG engines, podding 4 huge turbofans at the aft fuse would be a maintenance nightmare. Also having a T-tail on an aircraft that big would incur a structural weight penalty, I don't think either of these features offer any real design advantages.
The VC-10 worked, but had low-bypass engines, nice and slim in comparison to the high-bypass engines used on the triple seven for instance; imagine 4 RR Trents bolted side-by-side at the back of an airliner, the structure required to support them would be highly stressed and as such would be heavy.
The only large jet aircraft I can think of with T-tails are transporters with hing-mounted wings where the horiz stab and elevator are mounted up high to stay out of turbulent air from the wings, so likewise it can work but its not ideal.
Anything's possible, an aircraft like which you describe could be built but, what makes it better than existing designs?
I'm sorry if it seems I'm shooting down your idea, but don't fix what aint broke.
edit: I believe T-tail aircraft as a rule of thumb generally require larger horiz stab and elevator. What would give such an aircraft lower drag?

-Peter, Final year Aero Eng Design student.

[Edited 2006-02-08 15:01:07]
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Starlionblue
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RE: New Aircraft Design

Wed Feb 08, 2006 11:34 pm

Quoting Wingscrubber (Reply 1):
The only large jet aircraft I can think of with T-tails are transporters with hing-mounted wings where the horiz stab and elevator are mounted up high to stay out of turbulent air from the wings, so likewise it can work but its not ideal.

Indeed. And those transports incur weight penalties from having to reinforce the area from the wing to the gear. When you land, the gear has to carry the wing. If the wing is sitting on top of the gear like on a 777, you're fine. If the wing is sitting way above the gear like on an An-124 it's another matter. That whole area needs to be strengthened.

Quoting Wingscrubber (Reply 1):
edit: I believe T-tail aircraft as a rule of thumb generally require larger horiz stab and elevator. What would give such an aircraft lower drag?

I think Jetflyer is pondering how a clean wing with no engines would give less drag. But with the engines far out in front of the wing like today, and judicious use of engine airflow I don't think there is much difference (I may be wrong).


Also. 70 rows of seats. Hmmmm that would probably be more than 80 metres, so you can't do it for practical reasons. And you're assuming the you will have ten abreast throughout your entire plane for 700 total. But what about first class? With 70 rows your total would probably be around 500.



But hey. It would certainly look cool Big grin
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2H4
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RE: New Aircraft Design

Wed Feb 08, 2006 11:44 pm




Quoting Wingscrubber (Reply 1):
I believe T-tail aircraft as a rule of thumb generally require larger horiz stab and elevator.

Aerodynamically, what does the horizontal stab care where it's mounted?

I always figured T-tail horizontal stabs tended to be larger not because of their vertical placement, but because of the shorter arm between the tail and the wing.

I think Piaggio's layout of the Avanti is interesting. As with any airplane, a certain amount of tail downforce is required to counteract the nose-down pitch tendency of the wing. Instead of using one large horizontal stab, however, the Avanti uses a significantly smaller horizontal stab, and a small forward wing to assist with the tail downforce duties.

Open up the large version of this photo and take a look at the relatively small horizontal stab:


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I've always wondered if this layout could be successfully utilized on large-scale airliners. I suspect one of the primary reasons we haven't seen it in this application has to do with the comparative weight and lack of design flexibility inherent with predominantly aluminum airframe construction.

Perhaps upcoming carbon fiber manufacturing capabilities will change that.




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Starlionblue
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RE: New Aircraft Design

Wed Feb 08, 2006 11:50 pm

Quoting 2H4 (Reply 3):

I've always wondered if this layout could be successfully utilized on large-scale airliners. I suspect one of the primary reasons we haven't seen it in this application has to do with the comparative weight and lack of design flexibility inherent with predominantly aluminum airframe construction.

What about potentially smashing into the finger when you nose up to the gate? Looks very nice but when you have to cozy up to the terminal there's potentially a lot of stuff in the way.
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2H4
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RE: New Aircraft Design

Wed Feb 08, 2006 11:55 pm




Quoting Starlionblue (Reply 4):
Looks very nice but when you have to cozy up to the terminal there's potentially a lot of stuff in the way.

Yes....the key would be to achieve a gain in operating/fuel efficiency that would outweigh the hassle of ground ops.




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Nohag
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RE: New Aircraft Design

Thu Feb 09, 2006 12:24 am

Quoting Starlionblue (Reply 4):

Retractable "canards" ?  scratchchin 

Nah too heavy the extra hardware to do this...  Smile
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mrocktor
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RE: New Aircraft Design

Thu Feb 09, 2006 1:33 am

A few complementary considerations:

1. A T-tail is not more efficient than a regular arrangement. The T-tail means the vertical stabilizer is a load bearing structure in the "z" axis, this means more weight.

2. A T-tail, on very large aircraft especially, means a lot of your hardware is *very much* out of reach. Trim systems, elevator systems and many antennae and lights will be a major pain to access and maintain.

3. Aft mounted engines are a hassle (this has been mentioned). They are also out of reach compared to the under wing alternative.

4. Aft mounted engines do not permit a staggered arrangement, which means that a large fragment from one of them could tear through them all.

5. Aft mounted engines require a stronger fuselage, since the lift force is located at the wing and the weight being lifted at the tail.

6. Aft mounted engines require a stronger wing, since the whole lift force is transmitted to the fuselage (with wing mounted engines, the weight of the engines alleviates the upward load on the wing to an extent)

mrocktor
 
miller22
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RE: New Aircraft Design

Thu Feb 09, 2006 7:12 am

The most powerful engines in a tail mounted configuration belong to the MD-90. They had to do some rediculous strengthening of the fuselage to prevent the tail end from snapping off during hard langings with all the weight back there. The MD-90 has pushed the feasibility of the tail-mounted engine design to (past?) its limits.
 
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Starlionblue
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RE: New Aircraft Design

Thu Feb 09, 2006 12:00 pm

Quoting Nohag (Reply 6):
Quoting Starlionblue (Reply 4):

Retractable "canards" ? scratchchin

Nah too heavy the extra hardware to do this... Smile

Actually there was one airliner with retractable canards. I'll leave that as an exercise for the alert reader. Big grin
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MDorBust
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RE: New Aircraft Design

Thu Feb 09, 2006 12:44 pm

Quoting Starlionblue (Reply 9):
Actually there was one airliner with retractable canards. I'll leave that as an exercise for the alert reader.

The TU-144's were weren't they?
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HaveBlue
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RE: New Aircraft Design

Thu Feb 09, 2006 2:26 pm

Yes the Tupelov Tu-144 had retractable canards after earlier developments.
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Kukkudrill
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RE: New Aircraft Design

Thu Feb 09, 2006 5:18 pm

Quoting 2H4 (Reply 3):
Instead of using one large horizontal stab, however, the Avanti uses a significantly smaller horizontal stab, and a small forward wing to assist with the tail downforce duties

The Avanti also needs the canard wing because its main wing is set aft of the c of g to maximise cabin space. You can tell from the position of the main gear relative to the wing in this photo.

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oly720man
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RE: New Aircraft Design

Thu Feb 09, 2006 10:22 pm

The problem of having high bypass engines in close proximity is that they'll try to suck in each other's air, reducing the efficiency so there will need to be a fair amount of separation to reduce this effect. They're better hanging off wings.
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Starlionblue
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RE: New Aircraft Design

Thu Feb 09, 2006 10:56 pm

Quoting HaveBlue (Reply 11):
Tupelov

The Crazy Nitpicker Strikes: Tupolev. I would guess it's pronounced Too-po`-leff.
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wingscrubber
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RE: New Aircraft Design

Fri Feb 10, 2006 5:03 am

The canards, wing and rear horiz stab/elevator on the avanti all produce lift, the aircraft is in fact a triplane. 2H4 read up on it...
Incidentally, the position where a horizontal stabiliser is mounted does affect the aerodynamics of the aircraft, forward or aft positioning affects stability, higher or low mounting affects susceptibility to ground effect or deep stall, again, maybe read up on it?
Starlionblue, the information about high-winged aircraft structure is interesting, but my point was in fact that commonly the large transport aircraft that utilise a T-tail only do so because they have a high wing...
I wasn't insinuating that Jetflyer believed a T-tail gave lower drag either, it was a general query on his aircraft concept.
Podded engines will give the same amount of parasite drag where ever you put them, unless of course they're embedded in the wings like the De-Havilland comet/Nimrod.
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Starlionblue
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RE: New Aircraft Design

Fri Feb 10, 2006 5:11 am

Quoting Wingscrubber (Reply 15):
Starlionblue, the information about high-winged aircraft structure is interesting, but my point was in fact that commonly the large transport aircraft that utilise a T-tail only do so because they have a high wing...

Yeah no prob. My thought on T-tails is that they're either there (as you say) to get them out of wing wash, or to get them out of the way of tail mounted engines.

Otherwise (and I'm just guessing) you would have to make the fin strong enough to keep the stabilizer with the plane, instead of just strong enough to stay on the plane. With a fuse mounted stab, it's less of a problem since the fuse has fewer shape restrictions compared to a fin, and thus the whole structure can be made of perhaps lighter materials in a better shape. If you want to see the lengths you sometimes have to go to in order to make a fin strong, check out the bajo fitting on an MD-11!

Quoting Wingscrubber (Reply 15):
Podded engines will give the same amount of parasite drag where ever you put them, unless of course they're embedded in the wings like the De-Havilland comet/Nimrod.

Indeed. But we all know how maintenance would love embedded engines in a modern jet, not to mention the complications in airflow and the fact that you can hardly embed a GE-90 in a modern wing.
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Devilfish
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RE: New Aircraft Design

Fri Feb 10, 2006 8:51 am

Quoting 2H4 (Reply 3):
Instead of using one large horizontal stab, however, the Avanti uses a significantly smaller horizontal stab,

The Beech STARSHIP had a neater solution.

Quoting 2H4 (Reply 3):
the comparative weight and lack of design flexibility inherent with predominantly aluminum airframe construction.

Perhaps upcoming carbon fiber manufacturing capabilities will change that.

Alas, the materials technology then available doomed that futuristic design.
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Tornado82
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RE: New Aircraft Design

Fri Feb 10, 2006 9:06 am

With the props that far behind the cabin, what are the acoustics like inside of those things? I'm guessing quieter, or is there some kind of weird harmonic wave thing going on? I've seen one in and out of ABE a few times, but have obviously never been in it.

For the original poster's question, wouldn't this thing be a CG nightmare with all that weight in the back from those huge engines? I've heard that there can be some issues with the DC10/MD11, so I'd imagine this hypothetical design would be worse with 4 engines.

Also, with how that Piaggio looks kind of funky to begin with being such a unconventional design... you have to love the registration of that picture 2H4 had.
 
Bobster2
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RE: New Aircraft Design

Fri Feb 10, 2006 9:19 am

Clean wing? Four rear engines?

It's been done already. Big grin


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Starlionblue
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RE: New Aircraft Design

Fri Feb 10, 2006 10:46 am

Quoting Tornado82 (Reply 18):

For the original poster's question, wouldn't this thing be a CG nightmare with all that weight in the back from those huge engines? I've heard that there can be some issues with the DC10/MD11, so I'd imagine this hypothetical design would be worse with 4 engines.

Well the normal solution is to move the wing back.
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PurdueAv2003
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RE: New Aircraft Design

Fri Feb 10, 2006 6:52 pm

Quoting Bobster2 (Reply 19):
Clean wing? Four rear engines?

It's been done already.

Even before that! Remember the XB-35, YB-35, and YB-49? However, no one will be using that design for an airliner anytime soon. Try finding the window seats!
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wingscrubber
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RE: New Aircraft Design

Fri Feb 10, 2006 7:26 pm

I heard this new design is quite good...

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Nohag
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RE: New Aircraft Design

Fri Feb 10, 2006 10:15 pm

Not really an answer on Jetflyer's initial question but also another look at airrliner design.

I'm really a rookie on aerodynamical design and formulas etc. so don't shoot me please  Smile

Imagine..... in a few decades or so there would be a need for a larger airliner than the A380-900. We all know that the A380-900 almost touches the edges of the virtual box (80m x 80m) used as the max dimension for airport-planning/handling/architecture. Say it's obligatory (for commercial succes) to remain within these dimensions (So no Antonov-225's). I assume you would need a lot more wing to generate lift to get something

What would be the options.

A bi-plane?

http://www.dewilde-claeys.be/DIV/A380biplane.jpg

(This photo is copyrighted by Eric Fortin!!! Really great picture!! I just changed it to explain what I mean).

Or a configuration like the Piagio 180 but on a much much larger scale? (with the canards) ?

Or a fuselage higher and wider than an A380 hanging under a "forward" wing and a rear "wing" ? (Like A C-130 but much larger and with 2 wings: a forward one and a rear one)

Maybe some unconventional solutions to remain within the 80m x 80m box...

Your remarks or ideas would be welcome. (not declaring me insane of course...  Smile )
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Starlionblue
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RE: New Aircraft Design

Fri Feb 10, 2006 10:24 pm

Quoting Nohag (Reply 23):
Imagine..... in a few decades or so there would be a need for a larger airliner than the A380-900. We all know that the A380-900 almost touches the edges of the virtual box (80m x 80m) used as the max dimension for airport-planning/handling/architecture. Say it's obligatory (for commercial succes) to remain within these dimensions (So no Antonov-225's). I assume you would need a lot more wing to generate lift to get something

What would be the options.

A bi-plane?

Maybe, but it would look probably more like this:


BTW this is yet another creature from the murky depths of Mr Rutan's quirky brain.
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Nohag
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RE: New Aircraft Design

Fri Feb 10, 2006 10:41 pm

Quoting Starlionblue (Reply 24):
BTW this is yet another creature from the murky depths of Mr Rutan's quirky brain.

His quirky brains produces stunning results, breaks records, lay the foundations of the future. I quite admire him for his vision.

As Airbus, Boeing, Embraer.... are just commercial companies producing planes requested by the airline companies they lack this visionary aspect. Okay they try to improve the performances of their existing models but imagine Boeing or Airbus offering a 1.000 seat plane modeled like this Proteus....... do you think one airline company (okay except Virgin of course  Smile ) would buy it? Such an unconventional shape...

The Proteus is more or less what I meant with "the fuselage hanging under 2 wings".
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Starlionblue
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RE: New Aircraft Design

Sat Feb 11, 2006 2:25 am

Proteus is optimized for loiter time, so it's extremely efficient at cruising slowly at high altitude.

But I agree with all you say about vision. Some outside the box thinking would be good.
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Devilfish
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RE: New Aircraft Design

Sat Feb 11, 2006 8:06 am

Quoting Starlionblue (Reply 26):
But I agree with all you say about vision. Some outside the box thinking would be good.

 boxedin  This was definitely outside the box! Ain't she a beauty?



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