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PH-TVH
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787 Final Tail Shape

Fri Feb 03, 2006 7:46 am

I was comparing early 7e7/787 images with the latest 787 images the other day.
Now I saw, to my disappointment, that the tail has gotten a rather "classic" look after all.... It started with a really refreshing, almost organic tail. What happened to this particular design? Was it impractical? I can`t image why they would go for the classic tail after all (OK, the dorsal fin is still nicely curved). Anyone an Idea (Most intrested in Aerodynamical Reasons, if there are...)?

Greetings
 
DfwRevolution
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 8:38 am

Quoting PH-TVH (Thread starter):
It started with a really refreshing, almost organic tail.

It started with a perfectly conventional tail almost carbon copied from the 777.

The artistic impressions that followed showed varying degree of "shark tails" with the disclaimer that the external lines are by no means final. The "shark tail" lost out on basis of weight and aerodynamics, but the final tail does have a bit of sweep.
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aeropiggot
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 9:20 am

The bladed tail, has shown improved aerodynamics, as seen on the 777, and to some extent the A380. However APU placement has been a problem for the 777. The exhaust impingment on the aft fuselage/tail, has cause some maintenance problems. So we see Boeing and Airbus (787/A350) going back to the classic conical close out of the aft fuselage.
A scientist discovers that which exists, an engineer creates that which never was.
 
ikramerica
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 12:49 pm

Quoting AeroPiggot (Reply 2):
So we see Boeing and Airbus (787/A350) going back to the classic conical close out of the aft fuselage.

I was wondering why Boeing gave up on that MD style tail cone like the 777 and went back to the 767 shaped butt.

I still like the 747 as it is very unique in that regard, and one can assume it isn't and inneffecient shape or they would have changed it by the 5th iteration, no?
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DocLightning
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 1:40 pm

I'd imagine there are also some practical manufacturing issues with a shark-fin tail.

It's much easier to swivel a rudder with a straight-line seam to the rest of the stabilizer than it is to swivel a rudder with a curved-line seam.
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LTU932
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 3:03 pm

Quoting Ikramerica (Reply 3):
I was wondering why Boeing gave up on that MD style tail cone like the 777 and went back to the 767 shaped butt.

You mean the screwdriver shaped tail? Check out reply 2 for that:

Quoting AeroPiggot (Reply 2):
The bladed tail, has shown improved aerodynamics, as seen on the 777, and to some extent the A380. However APU placement has been a problem for the 777. The exhaust impingment on the aft fuselage/tail, has cause some maintenance problems. So we see Boeing and Airbus (787/A350) going back to the classic conical close out of the aft fuselage.
Sometimes the only thing more dangerous than a question is an answer. - Ferengi Rule of Acquisition 208
 
Oykie
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 6:16 pm

Quoting LTU932 (Reply 5):
Check out reply 2 for that:

Since he quoted reply two when saying that, I am pretty sure he had checked it out.

Just to show how the 787 has evolved. Here is some pictures

First draft of the 7E7 - A 767 on steroids.



Second draft - A designers dream



third draft - An engineers dream

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ikramerica
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 6:22 pm

Quoting LTU932 (Reply 5):
You mean the screwdriver shaped tail? Check out reply 2 for that:



Quoting OyKIE (Reply 6):
Since he quoted reply two when saying that, I am pretty sure he had checked it out.

Thank you. It was kind of the point of my post.
Of all the things to worry about... the Wookie has no pants.
 
whitehatter
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 8:31 pm

A lot of testing was done at Farnborough in the UK, where the wind tunnel work showed the shark tail produced substantially more drag than a clean blade type of fin. The current one is a tradeoff, as are most things in aviation design.

The airlines couldn't care less if it looked like a dog's butt as long as it is fuel efficient and lightweight.
Lead me not into temptation, I can find my own way there...
 
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distanthorizon
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 9:03 pm

Quoting WhiteHatter (Reply 8):
The airlines couldn't care less if it looked like a dog's butt as long as it is fuel efficient and lightweight.

Off course not.

But a nice design helped to fill the front pages off magazines and newspapers. The real design is very conventional and, in my opinion, rather uninteresting.

DH
Regards
Nelson SE
 
Oykie
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 9:16 pm

Quoting DistantHorizon (Reply 9):
But a nice design helped to fill the front pages off magazines and newspapers. The real design is very conventional and, in my opinion, rather uninteresting.

DH

There is allot of things that is new in the Boeing 787 design. The new nose, nice wings and the tail also looks good in my opinion. It is not as cool as the artistic impression. But they usually don't turn out that way. It is like the car insustry when they show concept cars. What you see in an autoshow is not what you end up bying. But it shows in what direction we are moving to.
Dream no small dream; it lacks magic. Dream large, then go make that dream real - Donald Douglas
 
CHRISBA777ER
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 9:31 pm

Could it be that the concept drawings were deliberately made to look more different and innovative than was actually the case, to give the impression that the 787 was more innovative, different, and new than say, a more conventional-looking competitor? Adding credibility to some bold-performance claims?

Product differentiation = setting your product apart from competitors thorugh clever use of marketing techniques.
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Oykie
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 10:06 pm

Quoting CHRISBA777ER (Reply 11):
Could it be that the concept drawings were deliberately made to look more different and innovative than was actually the case, to give the impression that the 787 was more innovative, different, and new than say, a more conventional-looking competitor? Adding credibility to some bold-performance claims?

Product differentiation = setting your product apart from competitors through clever use of marketing techniques.

That may very well be the case. Also don't forget the positive side of designers showing a different approach to how things looks. They often look at things in nature and comes up with ideas in our man-made products. Then the engineers look at it, tests it and comes up with the best result
Dream no small dream; it lacks magic. Dream large, then go make that dream real - Donald Douglas
 
DAYflyer
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 10:54 pm

Quoting WhiteHatter (Reply 8):
A lot of testing was done at Farnborough in the UK, where the wind tunnel work showed the shark tail produced substantially more drag than a clean blade type of fin. The current one is a tradeoff, as are most things in aviation design.

Thank you for the clarification on this issue. I still like the tail they eventually came up with. And yes, drag and fuel consumption are critical factors in design of this bird. It will be very cool to see the announcements regarding production and assembly of the first aircraft.
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Crosswind
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RE: 787 Final Tail Shape

Fri Feb 03, 2006 11:29 pm

The original 787 "look" was devised by industrial designers for a distinctive feel, the final design is the result of serious aerodynamic engineering work - I believe this is the first time Boeing have deliberately tried to make an aircraft look different for no reason other than marketing. Another area where the original design was changed due to economic reality were the flightdeck windows which were changed to a much more conventional design.

Personally I like the final look of the aircraft...

Here's a closup of the final tailfin design from some Boeing drawings - there's still a very slight curve to the trailing edge of the fin;



Regards
CROSSWIND
 
Sinlock
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RE: 787 Final Tail Shape

Sat Feb 04, 2006 12:33 am

Quoting Crosswind (Reply 14):
Another area where the original design was changed due to economic reality were the flightdeck windows which were changed to a much more conventional design.

Thats not Boeings stand on the change, Mike Blair during the 787 Town Meeting early last year said the window layout was being changed due to pilot feedback of an early mockup. The contour of the nose area was changed for drag and wing noise issues but not the window layout itself.
 
aeroweanie
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RE: 787 Final Tail Shape

Sat Feb 04, 2006 2:58 am

Quoting AeroPiggot (Reply 2):
The bladed tail, has shown improved aerodynamics, as seen on the 777, and to some extent the A380. However APU placement has been a problem for the 777. The exhaust impingment on the aft fuselage/tail, has cause some maintenance problems.

I was told by the 787 Chief Engineer that the 777 screwdriver tail caused a lot of ramp noise when the APU was operating. The flat surface around the exhaust acts as a good reverb board. The 787 went back to a 757/767 type tail cone, despite a 1% drag penalty.

Quoting Sinlock (Reply 15):
he contour of the nose area was changed for drag and wing noise issues but not the window layout itself.

There was an AIAA paper published by someone at Boeing last year showing that the nose was contoured to reduce noise in the cockpit and in the crew rest area, which is above and behind the cockpit.
 
aeropiggot
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RE: 787 Final Tail Shape

Sat Feb 04, 2006 3:19 am

Quote:
AeroWeanie: I was told by the 787 Chief Engineer that the 777 screwdriver tail caused a lot of ramp noise when the APU was operating. The flat surface around the exhaust acts as a good reverb board. The 787 went back to a 757/767 type tail cone, despite a 1% drag penalty.

Good point, and I did remember hearing something of the sort, the noise issue no doubt may have been a bigger driver than the maintenance issues.
A scientist discovers that which exists, an engineer creates that which never was.
 
flyinghippo
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RE: 787 Final Tail Shape

Sat Feb 04, 2006 3:25 am

Quoting AeroWeanie (Reply 16):
I was told by the 787 Chief Engineer that the 777 screwdriver tail caused a lot of ramp noise when the APU was operating. The flat surface around the exhaust acts as a good reverb board. The 787 went back to a 757/767 type tail cone, despite a 1% drag penalty.

If I am an airline, would I want to give up the 1% on drag penalty for a quiet APU exhaust?? hm..
 
747400sp
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RE: 787 Final Tail Shape

Sat Feb 04, 2006 3:26 am

The current tail design on the 787 was shown some time back.
 
ACYWG
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RE: 787 Final Tail Shape

Sat Feb 04, 2006 3:37 am

Quoting FlyingHippo (Reply 18):
If I am an airline, would I want to give up the 1% on drag penalty for a quiet APU exhaust?? hm..

to Bad Bombardier didn't do the same thing! it drove me nuts working around those RJ's! How is it that the APU on an RJ is louder than its own engines!
 
A319XFW
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RE: 787 Final Tail Shape

Sat Feb 04, 2006 4:43 am

Quoting Crosswind (Reply 14):
The original 787 "look" was devised by industrial designers for a distinctive feel, the final design is the result of serious aerodynamic engineering work - I believe this is the first time Boeing have deliberately tried to make an aircraft look different for no reason other than marketing.

I would agree on that. I saw two versions for the vertical stabilizer. The original shark-fin was still in the press but then in engineering-orientated documents the current one was apparent.
So to me it seems as if it was a marketing tool to capture the imagination of people and later on it was even said by Boeing that the current form is more aerodynamic.

[Edited 2006-02-03 20:44:48]
 
Sinlock
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RE: 787 Final Tail Shape

Sat Feb 04, 2006 4:46 am

Quoting AeroWeanie (Reply 16):
There was an AIAA paper published by someone at Boeing last year showing that the nose was contoured to reduce noise in the cockpit and in the crew rest area, which is above and behind the cockpit.

Oops, That should say wind noise not wing noise.....  white 
 
lehpron
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RE: 787 Final Tail Shape

Sat Feb 04, 2006 5:25 am

Aerodynamically speaking, any shape of any object experiences 3 types of drag: 1) parasite (skin friction also known as shear) and 2) pressure (dynamic, induced, etc) 3)wave drag which is a result of shockwaves. (Since we are talking about a subsonic airplane, I will skip this part)

Pressure drag is based on motion, i.e. it is dynamic. Skin friction is static, also refered to as zero velocity drag, it is the resultant drag after subtracting the effects of motion. Every object has a constant no matter how it is scaled.

For example, a sharp object will produce little pressure drag but more skin friction. On a graph, based on velocity, the drag starts out high and slowly goes up. If an object were blunt, it may have a low skin friction (due to lack of surface area) but a higher pressure drag. This object will start out with low drag but increase dramtically with speed. Parachutes are an extreme example.

In engineering any machine, there are balances between the benefits and disadvantages to produce the *perfect* product for whatever technology is available at that time period that a company can afford.

My guesses are that Boeing may have discovered a slight decrease in drag with the classic profile and doing so has another benefit: cost. The 'shark fin', as it was called here, I'd say had 10-15% more surface area than the classical fin shape. This results in more material to buy and cut and deal with. Of course less area on the vertical fin means less yaw force to turn. I'd suppose to maintain the moment (and thus stability), the fin had to have been moved forward somewhat, which will slightly vary the center of gravity. As you can see, to engineer something is a big deal.

I hope I helped you and anyone else out.
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
787engineer
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RE: 787 Final Tail Shape

Sat Feb 04, 2006 5:55 am

Quoting Lehpron (Reply 23):
Aerodynamically speaking, any shape of any object experiences 3 types of drag: 1) parasite (skin friction also known as shear) and 2) pressure (dynamic, induced, etc) 3)wave drag which is a result of shockwaves. (Since we are talking about a subsonic airplane, I will skip this part)

Pressure drag is based on motion, i.e. it is dynamic. Skin friction is static, also refered to as zero velocity drag, it is the resultant drag after subtracting the effects of motion. Every object has a constant no matter how it is scaled.

For example, a sharp object will produce little pressure drag but more skin friction. On a graph, based on velocity, the drag starts out high and slowly goes up. If an object were blunt, it may have a low skin friction (due to lack of surface area) but a higher pressure drag. This object will start out with low drag but increase dramtically with speed. Parachutes are an extreme example.

In engineering any machine, there are balances between the benefits and disadvantages to produce the *perfect* product for whatever technology is available at that time period that a company can afford.

My guesses are that Boeing may have discovered a slight decrease in drag with the classic profile and doing so has another benefit: cost. The 'shark fin', as it was called here, I'd say had 10-15% more surface area than the classical fin shape. This results in more material to buy and cut and deal with. Of course less area on the vertical fin means less yaw force to turn. I'd suppose to maintain the moment (and thus stability), the fin had to have been moved forward somewhat, which will slightly vary the center of gravity. As you can see, to engineer something is a big deal.

I hope I helped you and anyone else out.

For the most part your points were valid. However I have to disagree with you on a few points. Less area on the fin doesn't means less yaw force to turn. Yaw force to turn is dependent mostly on the size of the rudder. Also, unless I'm missing something really obvious, how does a sharp leading edge vertical fin have more skin friction than a blunt one? AFAIK, skin friction is dependent on the surface area, and the atmospheric conditions. As far as the fin is concerned there's also interference drag; drag as a result of the fin-fuselage intersection.

The 787 fin has been worked over quite a bit, and it is the best balance between performance and cost that Boeing could come up with. A shark fin would undoubtedly be more difficult (i.e. cost more) to build and maintain just because of its unique design. Not to mention more research to determine exactly the right curvature to optimize fin size vs. performance. I think the concept car vs. production is a good analogy. Many of the features and gadgets in the concept car just aren't feasible for mass production.
 
fuffla
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RE: 787 Final Tail Shape

Sat Feb 04, 2006 7:20 am

What is not to like about this!
Perfect design in my opinion.
 
lehpron
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RE: 787 Final Tail Shape

Sat Feb 04, 2006 10:28 am

Quoting 787engineer (Reply 24):
how does a sharp leading edge vertical fin have more skin friction than a blunt one? AFAIK, skin friction is dependent on the surface area

As I was defining, I was thinking of steep surface like a wedge as opposed to a cylinder. Say a 30-degree internal wedge has more area, such that like you said, more friction drag than a cynindrical volume like a 'classical' airfoil's leading edge with the same frontal area.

Quoting 787engineer (Reply 24):
As far as the fin is concerned there's also interference drag; drag as a result of the fin-fuselage intersection.

You mean turbulent boundry layers? I do not know exactly how thick they are by the time the flow gets back to the fins. In addition, I would rather not think the drag related to is as negligible as the change from sharp fin to classical trapezoid.

Quoting 787engineer (Reply 24):
Many of the features and gadgets in the concept car just aren't feasible for mass production.

Is feasibility determined by how much work was done prior to applying it? Something new would add the development costs. Since the PBS specials on 777 from a long time ago and the NASP from even longer, I've got it in my head that 'less R&D = greater op cost'. While I know examples that go in both ways, I believe in the opposite.
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
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zippyjet
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RE: 787 Final Tail Shape

Sun Feb 05, 2006 4:20 am

Quoting Fuffla (Reply 25):
What is not to like about this!
Perfect design in my opinion.

I agree! Call me conservative on this one but, the "shark" tail never did anything for me. In fact, I felt it distorted the overall shape of the now 787.
The current design is the classic updated slightly. Why change a good thing?
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