777222LR
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Plane Design: Would This Be Feasible?

Sat Aug 18, 2012 12:39 am

Given today's technology, and looking at the Airbus and Boeing Concept planes, I did a little design of my own. I'm looking at 300-350 pax, around the size of a 77W, around the same thrust ratings if not less because of 787 type composite technologies. A range around 9000-9500 miles, with tail mounted engines and a V-tail stabilizer. Here is a drawing of what I produced in my head:




I know the seat cost per mile would be a little higher due to a cruising speed of Mach .95, but do you think a concept like this could ever be accomplished. If you note, my engines are actually mounted on the trailing edges of the delta-esque wings and are S-ducted downward to the rear so the thrust is near the center of gravity. I believe this is a similar solution that they did on the Sonic Cruiser. (Yes, I did name it the Sonic Liner 797 for lack of a better name). What type of powerplants would you imagine would power such a beast?
 
tdscanuck
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RE: Plane Design: Would This Be Feasible?

Sat Aug 18, 2012 1:01 am

Quoting 777222LR (Thread starter):
A range around 9000-9500 miles

Why do you want to go that far? That's more than even London-Sydney direct.

Quoting 777222LR (Thread starter):
around the same thrust ratings if not less because of 787 type composite technologies.
Quoting 777222LR (Thread starter):
with tail mounted engines and a V-tail stabilizer.

The two statements above don't go together. If you go tail-moutned and V-tail you'll kill off all the weight gain that you achieved with composites. The Sonic Cruiser used exactly the same composites as the 787 and even it didn't go V-tailed (it's got canted tails but that's not aerodynamically the same thing).

Quoting 777222LR (Thread starter):
I know the seat cost per mile would be a little higher due to a cruising speed of Mach .95, but do you think a concept like this could ever be accomplished.

Technically, sure. Economically...not with current fuel costs.

Quoting 777222LR (Thread starter):
What type of powerplants would you imagine would power such a beast?

GE90s.

Maybe I'm missing something, but how is this not just a scaled up Sonic Cruiser?

Tom.
 
777222LR
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RE: Plane Design: Would This Be Feasible?

Sat Aug 18, 2012 1:12 am

Quoting tdscanuck (Reply 1):
Maybe I'm missing something, but how is this not just a scaled up Sonic Cruiser?

Exactly, sorry though, I was basing range off of the 772LR. This is a scaled up sonic cruiser, with range . capabilities of the 77L, that you are right
 
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DocLightning
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RE: Plane Design: Would This Be Feasible?

Sat Aug 18, 2012 6:43 am

Quoting tdscanuck (Reply 1):
Technically, sure. Economically...not with current fuel costs.

  

You are talking about an increase in fuel use of ~10-15%. This is in exchange for trip time reduction of less than 10%.

So on a ten-hour 777 trip will take nine hours on a 797 but raise my ticket price by a few percent. Sorry, not interested.

Now, make it 6 hours and you have my attention.
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RE: Plane Design: Would This Be Feasible?

Sat Aug 18, 2012 1:03 pm

Quoting tdscanuck (Reply 1):
That's more than even London-Sydney direct.

Yes but there is that growing demand for high yield widebody Service from London-Christchurch...NOT!
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roseflyer
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RE: Plane Design: Would This Be Feasible?

Sat Aug 18, 2012 3:39 pm

First off, you are likely going to need canards for stability at that speed.

Secondly, if we look at airplanes in service, 757s and 767s are the slowest planes used in long haul travel. DL is using 767s side by side against other airlines operating 747s. The difference between Mach .8 and Mach .85 is about 1 hour flying time on SFO-NRT. For the most part it does not make a difference because few people realize that there is a significantly different air time between the two planes since people look at price, connections, frequent flyer program, etc.
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PHX787
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RE: Plane Design: Would This Be Feasible?

Sat Aug 18, 2012 6:14 pm

Quoting tdscanuck (Reply 1):
Quoting 777222LR (Thread starter):
I know the seat cost per mile would be a little higher due to a cruising speed of Mach .95, but do you think a concept like this could ever be accomplished.

Technically, sure. Economically...not with current fuel costs.

Unless you figure out a way to use alternate fuels, this thing sounds like it could be a gas guzzler. Not economically feasible at this time.
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wingscrubber
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RE: Plane Design: Would This Be Feasible?

Sun Aug 19, 2012 6:54 pm

The flaw with any 'sonic cruiser' concept is that it puts you on the steepest gradiant of the Mach drag curve, why not accelerate over the hump and supercruise? You could achieve the same fuel burn with greater speed - and there are savings associated with shorter mission time. Otherwise there's no benefit in trying to outrun a Citation X this side of a sonic boom, all you'll achieve is higher fuel burn.

Quoting tdscanuck (Reply 1):
Quoting 777222LR (Thread starter):
around the same thrust ratings if not less because of 787 type composite technologies.
Quoting 777222LR (Thread starter):
with tail mounted engines and a V-tail stabilizer.

The two statements above don't go together. If you go tail-moutned and V-tail you'll kill off all the weight gain that you achieved with composites.

Tom - how does a rear engined V-tail config add weight? Doesn't seem like that would be detrimental to me - my only gripe with V-tails is the control mixing required, which results in loss of rudder authority when making simultaneous pitch and yaw inputs. I'm sure it can all be resolved with FBW flight control laws but seems needlessly complex when you can just separate those two axis.
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LH707330
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RE: Plane Design: Would This Be Feasible?

Mon Aug 20, 2012 2:38 am

Quoting wingscrubber (Reply 7):
Tom - how does a rear engined V-tail config add weight?

I bet that's a structural thing. More importantly, it adds drag. In normal cruise, the THS is trimmed slightly to even out GC/CoP discrepancies. If you do that with a V-tail, you're trimming horizontally, but you've also introduced lateral forces because of the angled stabilizers that fight one another, thus adding drag.
 
chimborazo
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RE: Plane Design: Would This Be Feasible?

Tue Aug 21, 2012 10:14 pm

Weight is added because you have to add structural strength to transfer the weight of the engines, plus the thrust stresses, through the fuselage to the lift surfaces- the wings. On wing-mounted engines the weight is borne directly by the wing so the wing root, fuselage etc doesn't have to be *as* strong. In flight on this proposal some of that will be borne by the downward canted engines, but in low thrust conditions and of course when on the Tarmac it has to be supported.
Rear-mounted all that weight has to be borne by the whole structure from the wings to the engines.
 
777222LR
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RE: Plane Design: Would This Be Feasible?

Wed Aug 22, 2012 2:50 pm

Quoting Chimborazo (Reply 9):
On wing-mounted engines the weight is borne directly by the wing so the wing root, fuselage etc doesn't have to be *as* strong

Actually, when I drew the aircraft, if you look closely, the engines are mounted on the wings, not the fuselage. If you look closely, you will see they mount on top of the wings, then S-duct downward and exhaust behind the wing at wing level.
 
Fabo
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RE: Plane Design: Would This Be Feasible?

Wed Aug 22, 2012 8:47 pm

Quoting 777222LR (Reply 10):
Actually, when I drew the aircraft, if you look closely, the engines are mounted on the wings, not the fuselage. If you look closely, you will see they mount on top of the wings, then S-duct downward and exhaust behind the wing at wing level.

I am afraid it does not look like that. In fact, by the look of it, left stabilizer is attached to the engine.
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CM
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RE: Plane Design: Would This Be Feasible?

Thu Aug 23, 2012 3:25 pm

Quoting 777222LR (Thread starter):
a cruising speed of Mach .95

You won't efficiently (or safely) cruise at 0.95 Mach with that wing planform and airfoil. If you did, you would need to provide some added pitch stabilization at the front of the airplane (canards) to address the severe Mach tuck this design would experience.
 
tdscanuck
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RE: Plane Design: Would This Be Feasible?

Sun Aug 26, 2012 4:00 am

Quoting wingscrubber (Reply 7):
You could achieve the same fuel burn with greater speed

Although the drag *coefficient* comes back down on the other side of the sound barrier, you still need to multiply by V^2 to get to actual drag. Your fuel burn still keeps going up as you go faster. The only exception I know to that is some weird very high Mach effects where ramjet engine efficiency can climb faster than drag.

Quoting wingscrubber (Reply 7):
Tom - how does a rear engined V-tail config add weight?

In addition to the stuff already posted, you can't have a nice straight-through structural member connecting the two fins like you can with a horizontal stab. In the case of a horizontal, the stab is all one piece and the mounting to the fuselage is relatively simple and reacts simple loads. For a V-tail you need to take all the load into the fuselage (including considerable bending stress you could ignore with the horizontal).

For the rear-engine I looked at the drawing and saw the engines on the fuselage with the V-tails stuck to the nacelles...that means moving big loads around the engines (like the "banjo fittings" on the DC-10). If they're actually on the wings then the engine-mounting isn't such an issue.

Tom.

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