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Why Should The Fuselage Taper At The End?  
User currently offlineGopal From United States of America, joined Jun 1999, 113 posts, RR: 0
Posted (7 years 8 months 4 weeks 8 hours ago) and read 7214 times:

Why not design commericial aircraft with a uniform cross section till the end ?The vertical and horizontal stabilizers could be attached to the end of the fuselage just the same. This will greatly increase the seating capacity without a significant increase in fuselage length. This will also allow cargo compartment to be installed in the aft of the airplane. Are there drag and lift factors involved ?

58 replies: All unread, showing first 25:
 
User currently offlineMatt72033 From United Kingdom, joined May 2005, 1617 posts, RR: 4
Reply 1, posted (7 years 8 months 4 weeks 8 hours ago) and read 7210 times:

are you suggesting a cylender shape like a can of pringles?

Quoting Gopal (Thread starter):
Are there drag and lift factors involved

yes.....huge ones


User currently offlineGopal From United States of America, joined Jun 1999, 113 posts, RR: 0
Reply 2, posted (7 years 8 months 4 weeks 8 hours ago) and read 7199 times:

I am talking about changing only the rear , not the front end of the fuselage. The front end as it exists in all airliners should remain. If the rear only is changed not to taper, will there still be a huge increase in drag ?

User currently offlineMatt72033 From United Kingdom, joined May 2005, 1617 posts, RR: 4
Reply 3, posted (7 years 8 months 4 weeks 8 hours ago) and read 7195 times:

Quoting Gopal (Reply 2):
will there still be a huge increase in drag ?

yes


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 4, posted (7 years 8 months 4 weeks 8 hours ago) and read 7186 times:

Hey man, how about some credit for the improvements the designers have made?

The legendary Connie...

View Large View Medium
Click here for bigger photo!

Photo © George Gayuski


...had no two fuselage frames the same size. It tapered from nose to waist and from waist to tail. Imagine the extra expense in jigs and dies, the extra man-hours custom fitting skin and bulb-angle to that design. No two clecos pointed in the same direction on the factory floor.

At least most jetliners after the Comet have many identical frames.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 5, posted (7 years 8 months 4 weeks 7 hours ago) and read 7161 times:

Quoting Gopal (Thread starter):
Why not design commericial aircraft with a uniform cross section till the end ?The vertical and horizontal stabilizers could be attached to the end of the fuselage just the same. This will greatly increase the seating capacity without a significant increase in fuselage length. This will also allow cargo compartment to be installed in the aft of the airplane. Are there drag and lift factors involved ?

Chopping off a shape designed to slice through the air leads to drag since turbulence will form as the air is flowing along smoothly and all of sudden there is this empty space. Vortices will form trying to fill the empty space, and those vortices cost energy to maintain.

You will sometimes find the chopped off shape, but that's because other reasons make it a better fit despite drag:
- Cars with chopped off rears. In a station wagon or van, loading and unloading are trickier if you have a teardrop.
- Bullets and shells. The back end is flat since it needs maximum surface area on the propellant and and a teardrop shape would make sealing the barrel and tumbling issues (in the barrel) tricky.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1606 posts, RR: 52
Reply 6, posted (7 years 8 months 4 weeks 7 hours ago) and read 7136 times:
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Quoting Gopal (Thread starter):
Why not design commericial aircraft with a uniform cross section till the end ?

The drag would excessive, due to the large base separation.


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 7, posted (7 years 8 months 4 weeks 7 hours ago) and read 7137 times:

Quoting Starlionblue (Reply 5):
Chopping off a shape designed to slice through the air leads to drag since turbulence will form as the air is flowing along smoothly and all of sudden there is this empty space.

Which explains why raindrops aren't square.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently onlineOldAeroGuy From United States of America, joined Dec 2004, 3423 posts, RR: 67
Reply 8, posted (7 years 8 months 4 weeks 6 hours ago) and read 7120 times:

Quoting SlamClick (Reply 7):
Which explains why raindrops aren't square.

Or spherical.



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineTod From Denmark, joined Aug 2004, 1721 posts, RR: 3
Reply 9, posted (7 years 8 months 4 weeks 5 hours ago) and read 7071 times:

Quoting SlamClick (Reply 4):
...had no two fuselage frames the same size.

A contract engineer's dream come true.

Tod  Wink


User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 10, posted (7 years 8 months 4 weeks 4 hours ago) and read 7056 times:

Quoting SlamClick (Reply 4):
clecos

Huh?
CLECO Central Louisiana Electric Co-Op



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 11, posted (7 years 8 months 4 weeks 4 hours ago) and read 7047 times:

Quoting Starlionblue (Reply 10):
Huh?
CLECO



Two clecos, one edge cleco and pair of cleco pliers.

They are temporary 'rivets' used in laying up a sheet metal job for riveting.

edit: It is amazing what you can learn to do when you can't find a flying job.
 Smile

[Edited 2006-07-27 23:41:31]


Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 12, posted (7 years 8 months 4 weeks 4 hours ago) and read 7041 times:

Quoting SlamClick (Reply 7):
Which explains why raindrops aren't square.

Does a raindrop get shaped by the air like it does because it is the perfect shape, from an aerodynamic point of view?

Quoting Starlionblue (Reply 10):
CLECO Central Louisiana Electric Co-Op

A google search doesn't always net the right results.  Smile I'm guessing making the stretched version of the Constellation was a pain without any constant section.

Chris



Don't blame me, I don't work here...
User currently offlineKELPkid From United States of America, joined Nov 2005, 6264 posts, RR: 3
Reply 13, posted (7 years 8 months 4 weeks 4 hours ago) and read 7031 times:

Quoting SlamClick (Reply 11):
edit: It is amazing what you can learn to do when you can't find a flying job.
Smile

Is Capt. Slam Click secretly building a Van's RV-series homebuilt these days?  Wink



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineKlaus From Germany, joined Jul 2001, 21353 posts, RR: 54
Reply 14, posted (7 years 8 months 4 weeks 3 hours ago) and read 7017 times:

Quoting OldAeroGuy (Reply 8):
Quoting SlamClick (Reply 7):Which explains why raindrops aren't square.
Or spherical.

True - but as far as I know they're actually elliptical (flattened spheres), not at all "drop-shaped" as usually imagined.

Quoting N8076U (Reply 12):
Does a raindrop get shaped by the air like it does because it is the perfect shape, from an aerodynamic point of view?

The shape is a result of multiple forces interacting: Surface tension, drag and air friction. The form is not ideal for minimal drag at all - it's closer to the opposite, in fact:

Are raindrops tear-shaped?

[Edited 2006-07-28 00:43:21]

User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 15, posted (7 years 8 months 4 weeks 3 hours ago) and read 7013 times:

Quoting Klaus (Reply 14):
- it's closer to the opposite, in fact.

That didn't stop Sunbeam (Alpine and Tiger) from using it as an example in a ads selling their car's aerodynamics.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineKlaus From Germany, joined Jul 2001, 21353 posts, RR: 54
Reply 16, posted (7 years 8 months 4 weeks 3 hours ago) and read 7012 times:

Quoting SlamClick (Reply 15):
That didn't stop Sunbeam (Alpine and Tiger) from using it as an example in a ads selling their car's aerodynamics.

That just reinforces what we always knew about advertising, doesn't it? Big grin


User currently offlinePtrjong From Netherlands, joined Mar 2005, 3884 posts, RR: 19
Reply 17, posted (7 years 8 months 4 weeks 3 hours ago) and read 7003 times:


Why doesn't a bullet taper at the end, though? Design compromise?

Peter



The only difference between me and a madman is that I am not mad (Salvador Dali)
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 18, posted (7 years 8 months 4 weeks 3 hours ago) and read 6985 times:

Quoting Ptrjong (Reply 17):
Why doesn't a bullet taper at the end, though? Design compromise?

First of all, the picture shows both bullet and casing. This conglomerate is often called a bullet but strictly speaking that is incorrect. It may be more correctly referred to as a round or a shell. The casing contains the propellant and the bullet is seated in the top. The bottom of the casing contains an explosive cap, which when struck by the hammer ignites the propellant. Due to this ignition, pressure increases in the casing, ejecting the bullet to travel down the barrel. The casing stays with the gun until it is ejected. So the only part that needs to be aerodynamic is the bullet. The casing just needs to be a good shape to hold the propellant and also to be handled by the firing mechanism.

Also, the picture shows low velocity ammunition. Rifle bullets are much more pointy and indeed often somewhat tapered at the back. See this pic of rifle ammunition.


However, you are correct in that the bullet itself has a flat butt and that this is the result of design compromises. This is for three reasons:
- Flat contact area means that it can be pushed uniformly by the propellant.
- Wide sides ensure gases do not escape past the bullet in the barrel.
- A teardrop shaped bullet would not travel cleanly through the barrel. It might well start tumbling before exit. Bad.

Here's nice image of shockwaves created by a bullet


If we move into the realm of very fast shells, there is one type that is tapered. It is the sabot round, typically used as tank ammunition. It is composed of a dart sitting in a holder (sabot) that falls of when it exits the barrel. The dart, typically made of tungsten, depleted uranium and other hard stuff, is much thinner than the caliber of the barrel, enabling it to travel faster and be equipped with stabilizing fins. This dart is tapered at both ends. It has no charge, depending on kinetic energy alone to kill armored vehicles.

Here's a picture of a dart at sabot separation. The illusion of a rocket exhaust is created by gases being ejected from the barrel following the sabot


[Edited 2006-07-28 01:11:51]

[Edited 2006-07-28 01:14:21]

[Edited 2006-07-28 01:15:29]

[Edited 2006-07-28 01:19:23]

[Edited 2006-07-28 01:34:08]

[Edited 2006-07-28 01:35:31]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 19, posted (7 years 8 months 4 weeks 3 hours ago) and read 6983 times:

Quoting Gopal (Thread starter):
Why Should The Fuselage Taper At The End?

Aerodynamically speaking, the fuselage it is all pure drag and does not support lifting the airplane, i.e. useless. From a business sense, the fuselage is all purpose and the wings are useless because it takes (fuel) instead of giving back (revenue from payload).  Wink

The back end of things is where the drag comes from, that is why fuselages are tapered as you say. Drag like lift is speed dependent, slow objects with square ends don't suffer much due to drag, i.e. like automobiles, like those Scion vans.

Aerodynamics is everything on a plane. It figures the overall performance such as range, cruise speed and altitude. Whether you can make money out of an airplane is based on making the airplane work first. We can make your suggested airplane with a squared off tail, but it would suffer in range and speed due to the drag, so what is the point of carrying that extra stuff?



The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlinePtrjong From Netherlands, joined Mar 2005, 3884 posts, RR: 19
Reply 20, posted (7 years 8 months 4 weeks 3 hours ago) and read 6970 times:

Quoting Starlionblue (Reply 18):

Very informative. Thanks.



The only difference between me and a madman is that I am not mad (Salvador Dali)
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 21, posted (7 years 8 months 4 weeks 2 hours ago) and read 6942 times:

Quoting Ptrjong (Reply 20):
Quoting Starlionblue (Reply 18):

Very informative. Thanks.

I've always been almost as fascinated by guns and other miltech as by aircraft. I even used to have a subscription to "Military Technology" magazine ( http://www.amazon.com/gp/product/B00...-1130384-4554500?v=glance&n=599858 ). The problem is that gun boards are populated by a certain, how to put it, crowd, that tends to become rather, how to put it, political. I just want to discuss how the damned thing works in a technical way, not the rest of it. The cool thing about military technology is that it is just as extremely optimized as aviation technology.

BTW when you're ready, we can discuss caseless ammo. It's a: fascinating development. I wrote a paper on it once.


EDIT: Added some more pics and text to my earlier post. http://www.airliners.net/discussions...h_ops/read.main/161998/6/#ID161998

[Edited 2006-07-28 02:14:13]

[Edited 2006-07-28 02:15:04]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineMikkel777 From Norway, joined Oct 2002, 370 posts, RR: 1
Reply 22, posted (7 years 8 months 4 weeks 1 hour ago) and read 6921 times:

Area Rule

A google search will explain what that actually is, but Citation X and 747 are the best examples of how effective it is to control the area...


User currently offlineKlaus From Germany, joined Jul 2001, 21353 posts, RR: 54
Reply 23, posted (7 years 8 months 4 weeks 1 hour ago) and read 6912 times:

Quoting Mikkel777 (Reply 22):
Area Rule

Area rule won't help you on either end of the aircraft.

As long as it has a non-zero volume (which is kind of desirable) you'll have to live with the violation of the area rule both nose and tail represent (area going from or to zero relative to the area of the wing/fuselage combination).

Area rule can only help you once you've already established the desired area to (hopefully) keep it somewhat constant between nose and tail cone.

How well that violation goes and how much drag you're "paying" for it is the question. And a completely blunt nose or tail doesn't seem to be the best solution in most cases, especially at higher speeds.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 24, posted (7 years 8 months 4 weeks 1 hour ago) and read 6907 times:

Quoting Klaus (Reply 23):

How well that violation goes and how much drag you're "paying" for it is the question. And a completely blunt nose or tail doesn't seem to be the best solution in most cases, especially at higher speeds.

It would also seem that a beavertail may have advantages over a strict cone. Examine for example the 777 and MD-80 new variant tail. Is this a function of the effects of the empennage or would this be the case even without the empennage?

[Edited 2006-07-28 03:13:56]


"There are no stupid questions, but there are a lot of inquisitive idiots."
25 Klaus : I guess structural manufacturing technologies and new aerodynamic findings will always lead to changes in the exact shapes... I don't know how those s
26 Post contains images AeroWeanie : The fuselage of an aircraft typically carries some lift. This is in part because the wing pressure distribution carries over onto the fuselage. This
27 RichPhitzwell : Would this not also be bad upon rotation? More prone to tail strikes?
28 L-188 : Yup. Have you even seen a floatplane with a skiff tied to the floats? You will never see one flying for one with the bow pointed forward. this is bec
29 Post contains images Ptrjong : The butt of the Space Shuttle looks untapered with those massive engines, to the extent that it gets faired over when transported by the 747. I guess
30 Post contains images Starlionblue : True. Also it's much easier to design the ass of the shuttle without a cone. Indeed. But even they tend to have a flat surface at the end. Also a cas
31 Vzlet : Wunibald Kamm's work shows that a truncated taper (like the boattail bullets) produces less drag than one than continues to a fine point. (Although I
32 Post contains images Bobster2 : Airplane fuselages look a lot like submarines. And they both stole the design from whales.
33 Starlionblue : At some level, fluids are fluids.
34 Post contains images Mikkel777 : The area rule seeks a non-constant area between the nose and the tail, from constantly increasing to constantly decreasing. [Edited 2006-07-29 14:57:
35 Lehpron : I know what you mean, I guessed for traditional subsonic aircraft designs it was somewhat neglible, but whenever I mention that and associate it's ow
36 Post contains links and images L-188 : Apparently nobody told the late Vincent J Burnelli. http://www.historynet.com/ahi/bl-vincent-burnelli/ More photos http://www.aircrash.org/burnelli/c
37 OldAeroGuy : Engine TSFC and empty weight are also big players. Yes, and that's why lifting body fuselages have had such a significant impact on airplane design.
38 474218 : A bullet is also spinning, which provides stability. I don't thing a spinning aircraft fuselage would be very confertable.
39 AC320tech : Since were talking abou the aerodynamic effency, we might as well mention McDD's move from the pointy cone to the flat cone on the MD-80.
40 Post contains links Klaus : Okay; I was thinking of it from a different angle. Of yourse in reality the total change of frontal area has to be optimized. (Aerospaceweb.org | Ask
41 L-188 : Ever wonder why the F-14 fuselauge was shaped the way it is....cut it in half and you can clearly see the airfoil section.
42 OldAeroGuy : Fine, but it is unpressurized and has a seating capacity of zero. Burnelli kept pushing lifting body fuselages for passenger airplanes.
43 Windowseater : Interesting point ! What would be the implications of going in for a flying wing concept aircraft then, which considers both the aerodynamic as well
44 Starlionblue : Most rifle bullets spin. But many bullets/sheels do not. For example most mortar shells and all sabot shells do not spin. And the spin has little bea
45 777236ER : This is a bit garbled. The boundary layer will be turbulent, regardless of whether the fuselage is tapered or not. What happens is that the flow sepa
46 Starlionblue : Thanks for the clarification.
47 Meister808 : So does this suggest that the Connie is one of the more 'perfect' airliner designs? -Meister
48 Post contains images Starlionblue : In more ways that one! Seriously, I think it illustrates how airliners are a compromise between practicality and design perfection. The Connie may ha
49 474218 : The Connie was designed back in the days of real aircraft designers. Some how Lockheed managed to build 846 of them.
50 Starlionblue : Sure. But I wonder if they could have managed to stay competitive nowadays with that sort of shape. Labor was way cheaper back in the day and automat
51 Post contains images AeroWeanie : No - the area rule simply states that two configurations with the same cross-sectional area distribution will have the same wave drag, as wave drag i
52 Mikkel777 : Thank you, english is not my native language, so writing what I think is not always easy, but you did it for me! The Citation X is also a plane that
53 Post contains links and images 2H4 : I remember reading that the Shorts 330, 360, and Skyvan fuselages produce 30% of the total lift generated by the aircraft: Look how tiny the wing is
54 AeroWeanie : 30% sounds very high. I'd guess more like 10-15%.
55 Post contains images KELPkid : I could've sworn that they produced lift by creating their own moving vacuum: the air molecules are so repulsed by the aircraft's appearance that the
56 2H4 : I have my own theory. I'm not yet able to produce proof, but I theorize that the atmosphere recognizes the similarity between the Shorts' fuselage sh
57 Post contains links Mikkel777 : Want to see how much lift the aircraft body can produce? http://www.youtube.com/watch?v=e1aKxAN7bAs&search=f15%20wing One of the most impressive video
58 Viv : Yes! The ideal shape for subsonic speeds is a teardrop. The objective is to delay flow separation for as long as possible.[Edited 2006-08-07 15:15:05
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