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Dalavia
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Blunt Noses On New Airliners

Thu Apr 28, 2005 7:40 pm

How can blunt noses be more aerodynamic than sharp noses?

I don't understand why the A380 and now the 787 have such blunt noses when a streamlined (pointy) shape should be more aerodynamic, and thus save fuel.

Can anyone help me understand why these blunt noses seem to be the shape of the future?
 
mrocktor
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RE: Blunt Noses On New Airliners

Fri Apr 29, 2005 1:31 am

A "pointy" nose is not necessarily a lower drag shape. There are several types of drag. When discussing the fuselage they are skin friction drag, form drag and wave drag.

Roughly speaking, skin friction drag is the drag related to the air "rubbing" against the aicraft surface. The nose with the smallest area will have the lowest skin friction drag. The blunt nose has less area.

Form drag is, again roughly speaking, the drag generated by displacing the air so the object can pass. It is basically related to the cross section area of the object. Both noses should have equivalent form drag (it is more related to the fuselage as a whole).

Finally there is wave drag. This is the drag generated by localized high speed airflow at near sonic speed. As the air moves around the fuselage it accelerates, if it gets close to the speed of sound in certain areas the total drag will be higher. This is where pointy noses have an advantage, since the air accelerates gradually (as the cross section increases gradually with the pointy nose) there is less chance of localized sonic airflow. At supersonic speeds a pointy nose also keeps the shock wave stable and clear of the aircraft.

This is why the B-17 could have an incredibly blunt nose, the Sonic Cruiser had a fairly pointy nose and the Concorde had a very pointy nose.

Now, for subsonic airliners there is no need for very pointy noses. Furthermore, the development of very powerful computational fluid dynamics tools has permitted the optimal design of aircraft noses - this means we now can design a fairly blunt nose (low friction drag, low weight) without having wave drag problems (becasue we find the trouble spots in the computer model and adjust the shape accordingly).

Apparently the shape of the 170/190 is pretty close to optimal (considering the nose shapes of the C-Series and 787 that came after)  Wink

mrocktor
 
rtfm
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RE: Blunt Noses On New Airliners

Fri Apr 29, 2005 1:39 am

mrocktor For all the crap and vitriol that often appears on this forum, every now and then something intelligent and educational gets posted to balance is out. I always thought that pointy shapes were more aerodynamic so thanks for a simple explanation that a fairly non-techie like me can understand!  praise 
 
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Starlionblue
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RE: Blunt Noses On New Airliners

Fri Apr 29, 2005 1:57 am

Quoting RTFM (Reply 2):
mrocktor For all the crap and vitriol that often appears on this forum, every now and then something intelligent and educational gets posted to balance is out. I always thought that pointy shapes were more aerodynamic so thanks for a simple explanation that a fairly non-techie like me can understand!

Well, you should spend more time in tech_ops, where the BS is kept to a minimum. In any case, thx mrocktor!!!
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
gearup
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RE: Blunt Noses On New Airliners

Fri Apr 29, 2005 2:40 am

Quoting RTFM (Reply 2):
mrocktor For all the crap and vitriol that often appears on this forum, every now and then something intelligent and educational gets posted to balance is out. I always thought that pointy shapes were more aerodynamic so thanks for a simple explanation that a fairly non-techie like me can understand!

Soooooooo True!
Thanks for the excellent explanation mrocktor.

GU
I have no memory of this place.
 
mrocktor
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RE: Blunt Noses On New Airliners

Fri Apr 29, 2005 4:19 am

Thanks guys, I was fully expecting to be thrashed for such an un-aerodynamics-specialist-like answer  

mrocktor

[Edited 2005-04-28 21:19:57]

[Edited 2005-04-28 21:20:31]
 
Areopagus
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RE: Blunt Noses On New Airliners

Fri Apr 29, 2005 4:31 am

Aerodynamics isn't the only explanation. A blunt nose is lighter, too. And a stubby nose and rear end can maximize the proportion of constant full width, increasing the revenue potential (particularly if the length is constrained by space at the gates).
 
goCOgo
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RE: Blunt Noses On New Airliners

Fri Apr 29, 2005 4:46 am

Quoting Mrocktor (Reply 1):
Furthermore, the development of very powerful computational fluid dynamics tools has permitted the optimal design of aircraft noses - this means we now can design a fairly blunt nose (low friction drag, low weight) without having wave drag problems (becasue we find the trouble spots in the computer model and adjust the shape accordingly).

An excellent point, perhaps that should be brought out to those people who now hate Boeing for going back to a more traditional look. No doubt those innovative looks were tried and came out to be, well, not so innovative.
"Why you fly is your business, how you fly is ours"
 
HiFi
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RE: Blunt Noses On New Airliners

Fri Apr 29, 2005 5:58 am

A blunt nose is also cheaper to manufacture. Same goes for the 787 now-gone futuristic shapes. They may present some aerodynamic enhancement but if it costs too much to get it out of production line, it's just not worth it.

Spitfire made its fame in military missions during WWII because of its elliptical wings. Load distribution on the wings is optimized with that configuration. It never became a trend in aviation because those wings were too expensive to manufacture.


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no commercial potential
 
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Dalavia
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RE: Blunt Noses On New Airliners

Fri Apr 29, 2005 8:11 am

Thanks everyone, and especially Mrocktor.

I really appreciate your help and information.

Clear and informative.

This forum at its best!
 
aeroweanie
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RE: Blunt Noses On New Airliners

Fri Apr 29, 2005 8:58 am

Quoting RTFM (Reply 2):
mrocktor For all the crap and vitriol that often appears on this forum, every now and then something intelligent and educational gets posted to balance is out.

Amen!
 
mrcomet
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RE: Blunt Noses On New Airliners

Fri Apr 29, 2005 10:01 pm

A plane doesn't always fly level and straight. A blunt nose is better in pitch and yaw modes than a long pointy nose. If the plane does a lot of short routes, this might be considered in the design.

Design is always a compromise and no nose works for all situations.
The dude abides
 
aeroweanie
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RE: Blunt Noses On New Airliners

Sat Apr 30, 2005 2:17 am

Quoting HiFi (Reply 8):
Spitfire made its fame in military missions during WWII because of its elliptical wings. Load distribution on the wings is optimized with that configuration. It never became a trend in aviation because those wings were too expensive to manufacture.

Not quite - the Spitfire wing had twist and hence the load distribution was not optimal. The elliptical wing planform was used to enable the wing to have more chord outboard than a straight taper. This was necessary so as to keep the t/c low outboard while still allowing structural depth for the ammunition trays and outward retracting landing gear. For more information, see the article "A CFD Evaluation of Three Prominent World War II Fighter Aircraft," published in the June/July 1995 issue of the RAeS publication "Aeronautical Journal".
 
HiFi
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RE: Blunt Noses On New Airliners

Sat Apr 30, 2005 2:56 am

Aero, thanks for the details!  bigthumbsup 
All I remembered from my aerodynamics classes were "elliptical planforms -> theoretical elliptical lift distribution at any angle of attack -> less induced drag". hehehe...
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robsawatsky
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RE: Blunt Noses On New Airliners

Sat Apr 30, 2005 4:59 am

Kind of goes to show that aerodynamic performance isn't always readily apparent to the casual observer. Look back at some of the so-called "streamline" designs that were all the rage for cars, trucks, busses, trains, etc during the late 20's through to WWII. They looked slippery, but with the computerized modelling and wind-tunnel testing available today, some very blocky and sharp-edged designs are much, much better aerodynamically.
 
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RayChuang
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RE: Blunt Noses On New Airliners

Sat Apr 30, 2005 2:47 pm

It's a classsic case where the late Clarence "Kelly" Johnson's dictum of a beautiful-looking plane having good aerodynamic characteristics no longer applies nowadays.

Even though the final 787 design has a more blunt nose than originally envisaged, it's still quite different than the nose on the 767 and 777.

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