Round bottom versus flat bottom aero

[jdincau]

This is an essay question;
Compare and contrast the drag reduction techneques displayed by the Goldenrod and JCB under body shape versus the Costella and Flatfire underbody shape.

[RidgeRunner]

     Both types worked for records for cars metioned.  Bottom is only a part of, and needs to work with, the total package needed for success in any given class 2, 3, or 4 wheeled. 

     When all options are considered, there are no decisions to be made.  FWIW we haven't decided for sure yet on the bottom or total body design on our Lakester, still working on the chassis and parts to be enclosed.  Product will probabley be a result of our talent/tooling/$$$ factors [all three "challenged" in today's speak].

     Reality usually prevails over theory.  Exceptions to everything is what keeps it all interesting.............

[JackD]

Flat bottoms, skirts , and stuff really suck good for a lot of things, until you get a little sideways and then they really suck up and you get to learn to fly.
All of those things working together are called an "AIR DAMN" and you are likely to get some air time.
Flying is easier than landing as most flat bottom racers willl tell you if they speak of it at all.
A correctly balanced round bottom will try to go straight if you just leave it alone.
Put enough weight in a flat bottom and you can mask some otherwise real problems.
When you are in it over your head, it is a little late to go back to fix it and you have to deal with what is left.

[Bob Drury]

Professor Dolan, I love it




























































  Professor Dolan, I love it!  With all the postings on here about c.d., drag coefficients, aero this and slipstream that, you have summed it up perfectly.  If you don't have a round belly, it better be low, heavy, and minimumly sprung, if at all........Here's to you, Professor..........................

[Bob Drury]

 How the hell did I do that?

[JackD]

"Theoretical records are set by theoretical projects."

Round, low , heavy, with very little spring ?
Are you talking about My "Dunlap"?

Dunlap: The part of your round belly that DUNLAPPED over yer belt.

[Rex Schimmer]

If you look in my favorite Aero reference books, "Race Car Aerodynamics" by Katz and "The Leading Edge" by Tamai they both have charts that show the Cd of a shape decreasing as it is ran closer to the ground and then at a height, usually given as a percentage of the total length of the body the Cd starts to go up. They also give a pretty good explanation of what happens if you take something like a tank and run it very close to the ground. But then you have Rick Yacouchi's car (Rick if I butchered your last name I'm sorry!) lower than a snakes belly and it holds more records than anyother car at B'ville or El Mirage. And when he brakes the records it is not by a couple of MPH, he destroys them. Yes flat bottom cars probably "need" to not have suspension and they certainly "need" smooth salt or dirt to go fast. I think that the really dangerous flat bottom cars are like the Mercedes sports cars that did some "test" flying at LeMans a few years ago. They had huge flat areas, located infront of the front wheels, that were ran at a very low height and as soon as they did a little lift on the "hump" on the straight they did fly! Cars like Rick's have pretty small "plan view" area and also not much over hang in the front so although they may exibit some of the problems that the Mercedes cars had I would think that it would be much less.

Rex

[russ jensen]

 :?I keep looking @ pictures of crowers T and it appears to be a flat bottom with a nose that shoves the air off to the sides, is this aproach prone to flying?? not knowing any better this looked like the front I was going to use on my oakland, good idea or bad???

[JackD]

I guess you didn't see Bruce's liner do the spin.

[PorkPie]

Flat bottoms, skirts , and stuff really suck good for a lot of things, until you get a little sideways and then they really suck up and you get to learn to fly.
All of those things working together are called an "AIR DAMN" and you are likely to get some air time.
Flying is easier than landing as most flat bottom racers willl tell you if they speak of it at all.
A correctly balanced round bottom will try to go straight if you just leave it alone.
Put enough weight in a flat bottom and you can mask some otherwise real problems.
When you are in it over your head, it is a little late to go back to fix it and you have to deal with what is left.

Flat bottom solution like the Nebelous Theorem II, the Jack Costella car which is used by Rick Yacoucci, got the advantage that they reduce the effect of the bouncing airflow along the car which is important to go really fast.

But you can do this only if you got no suspension like the NT II or extreme short spring movement - 2/10 of an inch. If you run the car like the NT II, more springload will let the car flip...

[russ jensen]

 :roll:Jack please enlighten me - no I didn;t see spin all I have is pics that crower sent, and  it appears to be in good shape, was told was one of the sweetest sounding engs on salt-- but did it fly or did it just spin and stay down??? another question that should be under rules,:: are alerons: rudder & stabilizere legal on modified roadster, would be a saftey pluss to make the landing easier & safer..

[John Nimphius]

Roadster, Coupe/Sedan and other classes where belly pans or step pans are permitted have a flat bottom by necessity.  Are some of the things we?ve heard hear, like limited or no suspension, weight carried low, also to be used for these cars as well?

To focus just on roadsters they have no flat areas ahead of the front wheels, but what about other things like:
        Should ride height be as low as possible?
        Should bottom rise at an angle front to rear to allow trapped air to exit easier?
        If so, what angle should this be?

John

[russ jensen]

I guess you didn't see Bruce's liner do the spin.

you have my curisoity way up now Jack, are the pics of bruces T pre spin as it appears to be in perfict shape< or did it flat spin with no damage??  is it one of these { if they will talk about it rides}thinking about round:a long nose like bruce used could be round bottom and blended to flat by the time the firewall is reachedwould this try to stay straight if left alone  or with a flat rear section would it agrivate things????I ain't into trying to design airplanes on wheels, I like motors, unfortunatly they need to be in something on wheels to enjoy the sound.

[JackD]

The liner did a flat spin because the weight and balance depended on the side thrust from the wheels to keep it straight.
That is not a good place to start.
He used  Gilmer Metric belts like you might use on a blower on aluminum wheels with the tooth turned in.
While they seemed like  good idea on paper they did not offer the grip required to keep it under way.
You might compare it to a dart or an arrow that needed wheels and grip on the ground to stay straight.
Would you suspect there was something wrong with the shape, and balance or would you spend more time to improve the side grip.
The motor and drive train in both cars were a master work and did very well.
The split billet 4 valve push rod heads and the quick change gear feature were totally unique.

"Flat bottoms work until they don't and then they fly up until they don't.
 Landing is where it all ends."
My kid said "They really suck until they blow." 

[russ jensen]

 :cry:Hey jack were talking about  2 different rigs here,  was interested in the 23 T withe the nash eng {the modified roadster} not the liner. please - your thoughts on what he did with the T, aero wise that is..