Dumb newbie question??????

[panhead_pete]

This might be a dumb newbie question but I have been wondering why lakesters aren't built with a really pointy nose, bit like a rockets or a jet fighter. I realise most are done using old belly tanks with a "rounded" nose but am wondering why these too werent pointed as well?

[JackD]

Using that as the basis for another question, wouldn't a typical belly tank work better backwards?
If the "AERODYNAMISISTERS" get interested, you are in for quite a ride and they generally do pretty well.
We shall see.

NOTE: "AERODYNAMISISTERS" made it through spell check.
           Now I am more scared than ever !!

[hotrod]

At subsonic speeds, low drag shapes have smooth rounded noses (look at the nose on the commercial jets).

Only when you approach the speed of sound does a sharply pointed nose do you a lot of good.

A sharp nose may be used for other purposes though, for example the nose on F1 cars is very sharp so they can put more front wing on the car without exceeding max width rules.

Ideal subsonic shape is a long tear drop between 2 and 3x its maximum diameter in length as I recall.

Of course some of these "ideal shapes" may not apply in ground effect, when other considerations need to be addressed, like covering suspension pieces, skirts etc., but that is the rational behind the drop tank shape --- minimum drag for their volume and good packaging for use on a specific air frame.

Larry

[hawkwind]

good topic ,I have made a conceptual 3D model of my next project , they tell me an elongated teardrop and fish shapes are a good starting point ,it will one day be a I streamliner 


 as stated sharp /pointy shapes are for supersonic speeds
Gary

[Stainless1]

Not to mention all the aero benefit from sticking the wheels out in the wind.  Why do ya think they do that?  OK, being a smart A-- again, sometimes I just can't help myself.  I need another cup of coffee... 

Jack, I'll guessing you overwhelmed it.... 

[JackD]

Recognize that sometimes they have a little too much coffee but they mean well.
In between all this, ask yourself why a tear drop is shaped the way it is as it falls through the air ?
What forces are acting on it equally from all sides ?

[Sumner]

Here is some good reading:

Note: If you are interested in aerodynamics as applied to a race car I would strongly recommend the following three books:

1. New Directions in RACE CAR AERODYNAMICS (Designing for Speed) by Joseph Katz. I just got this book, but after looking through it briefly if you were to only buy one of these three books, I would recommend this one. It is $34.95 and the ISBN is 0-8376-0142-8.

2. AERODYNAMICS for Racing and Performance Cars by Forces Aird. It is an HP book and is a good overview of aerodynamics and presents views on aero issues without a lot of formulas and such. It was $16.95 when I bought it and the ISBN is 1-55788-267-3.

3. THE LEADING EDGE Aerodynamic Design of Ultra-streamline Land Vehicles by Goro Tamai. It summarizes the design and construction issues of solar cars and ultra light land vehicles. This book is heavy into the design of ultra streamline solar cars, but the principals can be applied to any race car. It is much more in debt and a lot heavier into math than the AERODYNAMICS book, but I feel a lot better book if you can wade through it. It covers aero issues to the smallest degree. If you really are building a streamliner, lakester or competition coupe I would strongly recommend it. Not cheap at $44.95, but that might be a small price to pay to build a body maybe just once and get it as close as you can to ideal. The ISBN is 0-8376-0860-0.

4. Vehicle Aerodynamics Recent Progress SAE-855 -- Made up of various SAE papers. The ISBN is 1-56091-119-0

Also on my "links page" (  http://purplesagetradingpost.com/sumner/bvillecar/bvillelinks.htm  ) there is a whole section on Aerodynamic Info and LSR Calculator/Spread Sheet Sites.

c ya,

Sum

[Stainless1]

  Well crap, this really is upsetting when you google raindrops.... 
here is what you get 
The artistic representation of raindrop as presented by popular culture is that of a teardrop. Actually, real raindrops bear scant resemblance to this popular fantasy (except after they have ceased to be raindrops by splattering on a window, say). It may seem too easy a target to single out the Weather Channel for criticism for their shoddy representation when virtually everyone from advertisers to illustrators of children's books do likewise. Yet, I would like to think they could be held to a higher standard as they attempt to convey the image of purveyors of accurate information.

    Small raindrops (radius < 1 mm) are spherical; larger ones assume a shape more like that of a hamburger bun. When they get larger than a radius of about 4.5 mm they rapidly become distorted into a shape rather like a parachute with a tube of water around the base --- and then they break up into smaller drops.

    This remarkable evolution results from a tug-of-war between two forces: the surface tension of the water and the pressure of the air pushing up against the bottom of the drop as it falls. When the drop is small, surface tension wins and pulls the drop into a spherical shape. With increasing size, the fall velocity increases and the pressure on the bottom increases causing the raindrop to flatten and even develop a depression. Finally, when the radius exceeds about 4 mm or so, the depression grows almost explosively to form a bag with an annular ring of water and then it breaks up into smaller drops. See, for example Pruppacher and Klett, Microphysics of Clouds and Precipitation, (1978, Reidel, Boston), pp. 316-19, or any other book on cloud physics written by competent authors.

    The way raindrops change in shape as they grow is sketched in the cross-sections of drops below. As the drops become distorted, the meaning of a radius becomes vague, so the radius labeled is that of sphere which has the same mass.



These are cross-sections through the drop. Imagine spinning the drop through a vertical axis to see the real shape. So, what looks like some teardrops in the final illustration on the right is actually closer to being a tube of liquid just before it breaks up into small spherical droplets again.

Just ruined my day, I thought I would get a gravity and airspeed explanation of why a raindrop looks like a drip 

[JackD]

Frozen raindrops are snow flakes and don't make good shapes for LSR vehicles either.
Check out a pursuit fish and figure out how they get to eat.
Take all the complex aero stuff you can absorb from the World and apply it to something you can see move and you are able to duplicate.
If you don't like it, get a Highboy Roadster.
It seems they have not been perfected yet either.
"If you don't like any of that, try something new.

 "Remember that the Ark was built by an amateur in the back yard and the Titanic was built and operated by professionals." (Uncle Bob)

[1212FBGS]

 "Remember that the Ark was built by an amateur in the back yard and the Titanic was built and operated by professionals." (Uncle Bob)

"that's funny stuff there... i don't care who ya are, that's funny stuff" (Larry the cable guy)

[Stainless1]

 "Remember that the Ark was built by an amateur in the back yard and the Titanic was built and operated by professionals." (Uncle Bob)

"that's funny stuff there... i don't care who ya are, that's funny stuff" (Larry the cable guy)

Dang sure beats working for a livin' (the other Bob) 

[836dstr]

Noah had a much better navigator!

[desotoman]

 
 
THE SHAPE OF RAINDROPS

Most people and even many engineers would guess that the shape of a raindrop is the familiar teardrop shape:

 
However, the teardrop shape appears only in cartoons and the real shape is closer to the flattened hamburger bun shape seen in the photos at the right. In each case the water drop is falling through still air. That is, the velocity of each is downward. The scale of the pictures is roughly the same so that the lower drop is roughly half the diameter of the upper drop.
The incorrect assumption about the shape of liquid drops is so common that it has merited an entry in the Bad Science Page.

The shape of the raindrop is determined by the relative strengths of surface tension and hydrodynamic forces. Click at the highlighted text to learn a bit more about the physics .
 

[Harold Bettes]

In Momma Nature's Lab, all the critters that are fast without using too much energy to do so are rounded in the front and sharp on the exit side. Like a trout in plan view or profile seems to explain it best.  :roll:Think subsonic, minimum frontal area and great reduction of exit losses. Like a trout.

Regards to All,
HB2

[JackD]

You see ?
They are just getting warmed up and even learning from each other.

YOU MAY CONTINUE