Why is teardrop the most sreamlined?
 

I'm really late to coming around to these streamlining discussions, and I understand a lot of work has been done by a lot of people, but why does this shape have to be accepted as being best? Airplanes go through the air well and are not that shape. Rockets are shot into space and are not that shape. Land speed vehicles are usually not that shape, nor are missiles. I think that would prove that the best shape for cutting air would be a pointy cylinder. What am I missing?

Aerodynamic drag below ~250mph is different that speeds up to ~750mpg (around the speed of sound). There are three kinds of drag (as I understand it): shape drag, surface drag, and detail drag. Shape drag is dominate for ground vehicles, and the the interaction with the ground is also important.

The wing section of an airplane is essentially a teardrop.

The physics of air is what defines the lowest drag shape. The front of the moving vehicle pushes the air outward from the stagnant point - up and down and to the sides. Then after the apex of that displacement has passed, the rate that the air can *cleanly* close back down together is fixed by two main factors: atmospheric pressure and the localized higher pressure caused by the displacement itself. The latter one changes with the speed of the vehicle (more or less) in a linear fashion up to about 250mph; and so the same shape works well for any speed up to that 250mph limit.

If the surfaces of the vehicle are at the proper angle, this keeps the air "attached" to the vehicle. Too steep an angle and the will be turbulence when the air is no longer "attached". Too shallow an angle, and there is an increase of surface drag.

I hope this helps.

the teardrop isn't the best in all situations, yet it is a good way to think about air flow management. one of the big issues for us landlubbers is ground effect, which basically makes 1/2 a teardrop much better than a whole one.

Fluid dynamics is probably the least understood science of them all. There are a few laws (mostly all related to conservation of energy) but there is not one law that can lead to the optimal solution across all scenarios. The main reason being is that fluid (including air) behaves in different states and applications.

Super-sonic jets don't utilize the tear drop because there are different applications such as how sound comes in to play, etc.

When car manufactures make cars they don't apply one law to govern the most aerodynamic shape since there isn't one. They have to use computers to run complicated models to come up with their designs. It is a iterative approach which means the next optimal output depends on the input from the first process. It just happens to be that the tear drop is the most optimal solution for the applications a vehicle will see.

In space there is not fluid so the spacecraft can be any shape it wants to be and still have the same efficiency as another. It is only when it enters the atmosphere does fluid dynamics come into affect. That is the why the space shuttle is not very efficient flyer during return flights but it was design for storage and heat displacement instead.

There are many papers/articles and people can go on and on about aerodynamics but it all boils down to that there isn't one law that encompasses all of aerodynamics.

Because it is the most efficient...
 

It has the lowest coefficient of drag and is the most efficient at cutting thru the air--that's why it's the best. Do you not understand math and science?

Yes, I do but I learned fluid mechanics in college not high school. A great book for ecomodders is "The Leading Edge" by Goro Tamai. This is mainly about the aerodynamics of solar racers but is very practical for modding passenger cars.

Yes, but is the rounded nose of a teardrop the ideal shape? Water has surface tension, which among other reasons means it won't ever develop a pointy nose. Is there something about a rounded nose that is just ideal for lowering air pressure that a pointy nose doesn't have?

I too don't quite understand why a teardrop is most optimal. it seems to me that a shape like the image I've attached would be most ideal.

Accepted science once stated that the world was flat. It was only by the acts of some pioneering souls, in the face of scorn and ridicule, that it was proven to be otherwise. Could a pointy nose be better? Does it matter if it sloped down to a point at the front(horizontally) or should it be pointed at the center vertically? Is it more efficient to cleve through the air or bend it? Wouldn't a cylinder be better at resisting a side wind than slab sides with a long trailing tail?
I not looking to reinvent the wheel, but just because a shape works, should it be accepted as THE shape?

Pointy nose helps at very fast speeds, but a blunt nose is better at speeds below 250mph. The reason as I understand it, is what I wrote in the post above.

the best way to understand is to do. find or make a wind tunnel and try all the shapes you can think of at normal vehicle windspeeds. when a vehicle is designed this is what is done.

also, most vehicle shapes are compromises. the best shape for a bike won't work for a car, and vice-versa. consideration must be made for the person/people within.

Re: pointy: keep in mind there are several TYPES of aero drag; for example a super sleek pointy shape might have lower FORM drag than a teardrop but because of the increase in surface area- if the shapes compared have equal volume- the pointy shape with the greater surface area suffers from increase SKIN drag such that the overall drag is greater.

http://ecomodder.com/forum/member-ae...e-wingless.jpg

https://d2t1xqejof9utc.cloudfront.ne...962/medium.jpg

https://forum.solidworks.com/servlet...raft+Assy2.jpg

http://www.vendian.org/envelope/Temp...-400_3view.gif

and then these as well :

http://www.geog.ucsb.edu/~jeff/115a/history/vmissle.jpg

http://images.gizmag.com/hero/6550_5120640540.jpg

http://1.bp.blogspot.com/-tTs0Jy0-Pt...gs-photo-2.jpg

http://www.explodingdinosaurs.com/sa...18_0868med.JPG

Correct me if i'm wrong, but the reason that jets and rockets don't look so much like a teardrop at the rear is also because this is where the exhaust gasses come out, and therefore there is no need to streamline for less turbulence.

Example here being the SR-71 - Look at the rear appendage which tapers off like a teardrop, versus the tips of the engines ( and yes the SR-71 is pointy because it goes Mach 3 . Commercial jets have rounded 'blunt ' fronts because they do not break the sound barrier. )

http://www.google.com/imgres?imgurl=...QEwAw&dur=3043

But then, note how the Space Shuttle has a blunt front.
Makes it all confusing doesn't it ?

You know you are into streamlining when you read the thread title and you think
"There is only one streamlined shape and this is it. Round at the front, pointy at the rear."

The boxfish shape is also very streamlined. However I cannot for the life of me find a 3d model of one.

I did read a little bit about the work Mercedes did( Bionic) and the boxfish. That would seem to be close to the optimum shape for a car.
The Bionic Car project - Image 12 of 12
This would make it seem that it is better to 'bend' the air(image #2) than to cut through it for a passenger vehicle. Formula One or Indy car designers feel it's better to cut through the air, evidenced by the pointy fronts and rounded sides. I was thinking that, for a motorcycle( being relatively tall, short, and narrow) a modified wedge-low pointy front, wide@ the beltline and tapering top and bottom(all sharp angles)- would be best. Now I have no clue!!!

Biomimicry is something we should look at a lot more. This is the starting point for my CarBEN EV5 - the first Boxfish/Bionic models with 4 wheels:

The Bionic Car project - Image 3 of 12

Also, note that the Bionic car does not have a pointed front end, but rather rounded and has a good amount of slope like a teardrop.

Here is the top view:

http://2.bp.blogspot.com/_4n0AsDJuAJ..._bionic_05.jpg

The original more streamlined design ( which is Neils inspiration above ) was even more
teardrop like in appearance :

http://www.mercedesclass.net/wp-cont...05c2545_85.jpg

Also note that it is a CAR! I'm thinking a motorcycle here.....:p

1. Optimum aero is not the only (or primary) design criterion in transportation, even air transport. The fuselage of a commercial airliner looks like a rounded barrell because that is one of the easiest shapes to pressurize without fatigue stresses downing the airliner after a few thousand "cycles."

(Also notice that "new" designs often have extended fuselages based on previous designs, due to the fact that the previous design has already gone through certification, and a modified design can be put into production more cheaply and quickly. Example: DC-9 and MD-80.)

2. Pointy noses are best when supersonic, as the air ahead of the vehicle "doesn't know what's coming" and slams into the leading edge. Subsonic, the air starts getting out of the way before the object ever gets there.

(A pointy leading edge isn't all that bad, subsonic, provided you never, ever, have a crosswind. Pointed leading edges are very intolerant of wind hitting it sideways.)

3. A teardrop, of defined "fineness ratio," is the optimum shape to enclose a given volume. Usually, that isn't the primary concern: the P-51 was designed to have a frontal area just large enough to encapsulate the pilot. This made for a plane that was "too skinny," in terms of fineness area, for optimal aero, but it wouldn't make sense to make the plane "fatter" just to meet the teardrop ideal--humans aren't fluids, and you can't "make up" for a deficiency in one dimension by making a surplus in another!

(Now, a auxillary fuel tank encloses a fluid, and thus makes an excellent candidate for a teardrop shape.)

So, as I now understand it, a blunted rounded front pushes a "cushion" of air in front of it, which bends the air around the following shape reducing frictional or surface drag. A pointy nose cuts through the air easier, but results in an increase in this surface/frictional drag-while being more unstable encountering cross winds.
Thanks

your pretty much right,just cut the cylinder in half,we don't need all that extra surface area.Generally speaking in the front, it can be narrowed for a good low cd, coefficient of drag[keep the front to a reasonably small amount of surface area] and that long tail lets the air run clean and doesn't create any any bad air to swirl around and come back,creating drag].The idea is to keep the air running clean,undisturbed by mirrors,sharp edges,short corner's etc.The worlds fastest bicycle goes 82 mph,on a non air-streamed bike,90 percent of your pedal power,goes to overcoming air resistance.So you see how important it is,done right you can double the mileage of a motorcycle,but it's not easy to do.Banning it on early motogp bikes,because of crashes and the high speeds they saw,didn't help the learning curve.The manufactures weren't to concerned about aerodynamics,more about packaging and keeping up with all the other square boxes with rounded corner's,though it seems to be changing a little.I'm really surprised BMW hasn't put into a limited production,their concept the Simple,which is a showcase of good technology,that can be built right now.Hope this helps a little,putting all the comments together should answer your question pretty good.

One of the things that I remember reading about the leading edge of wings is that they could be angled with a hard edge if they would only be flown at a particular angle against the wind. The blunt/rounded (teardrop) shape lets them move through the wind at a wide range of angles without generating turbulence.

In a car, we drive forward, but we encounter x-winds; a hard/pointy edge on the front might work for head on, but it would generate an eddy in a x-wind.