29 replies to this topic

[Mark H]

I was just thinking last night that a teardrop tether car style thingie body with the rear wheels exposed would look cool. Seems like something that could have been done back in the day.

I'll draw a picture and post it.

[TSR]

[Don Weaver]

Wouldn't areodynamics say that the direction of the car should be reversed?

Don Weaver

[TSR]

Heck, no! Separation is much more important than penetration. As an example, a piece of square tubing vs a piece or round tubing of the same section produce the same aerodynamic wake. Add a streamlined form behind either, and the wake is greatly reduced. This is why land-speed record machines are so long, to create a streamlined object behind the basically blunt frontal area.

[One27ray]

Hummm....

Yes! That design would work. I would add a rear wing spoiler/fin to enhance the aerodynamic flow of air, directionally stabilizing the rear wheels??

We'll have to wait and see your design.

[MSwiss]

I've wanted to a belly tank style body but have been discouraged by the engineering dilemma/limitation of the width
of two bearings to support the axle with a crown gear in between them.

Also the diameter of the crown gear is an issue.

IOW, how "tear-droppy" can the body get in the back and still house the required running gear?

But that's with a car that I would want to look like an existing 1/1 car. With a thingie, the axle and related parts could be moved as far forward as required to fit underneath the tapered back.

[ravajack]

I assume then that front of the car in Philippe's picture above then is in the top left, and the rear is the pointy part to the right, right?

Ergo this is a front wheel drive vehicle.

But what about the copper tubing up front? Isn't that an exhaust pipe?

[MSwiss]

Bertil,

I don't think the vehicle pictured is a slot car.

Probably some sort of rocket/jet/air powered, run it on any flat surface, vehicle.

[ravajack]

Mike,

I know it's not a slot car.

It's an old school tether car meant to be run around a pole in a circle, a Duro-Matic Teardrop Streamliner, powered by a McCoy Hornet 60 combustion engine. And the copper pipe really is an exhaust for the engine. So how can the "blunt" end of the car be the front as per Philippes definition? Wouldn't the pipe and the exhaust fumes disturb the aerodynamics?

[MSwiss]

I even missed "tether car" in the first post.

Yes, it seems weird the exhaust would go out the front of the car.

It appears like the gas tank could be moved to the other side and the exhaust could be flipped 180 degrees and exit out somewhere along the side.

[Don Weaver]

This is why land-speed record machines are so long, to create a streamlined object behind the basically blunt frontal area.

Correct. I pictured the car as being a rear wheel drive given the location of the exhaust... assuming it would be in the rear, not front, of the car.

[TSR]

The shell on the car shown is one thing. That the builder chose to orient the exhaust forward is a bit bizarre but not really hampering the aero at the 150 MPH speeds this car would be able to reach when the engine reaches its "sweet spot" as it leans down after a dozen laps. The restriction caused by airflow may in fact act as some form of using it instead of a resonance chamber in a more evolved two-stroke engine.

Either way, if you want to go fast, make sure that the blunt area is on front, not on back!

[miko]

Gentlemen, I believe what you are referring to as the exhaust is actually a ram type intake pipe as the exhaust port is facing straight up.
You will also notice the carburetor needle valve at the base of the copper pipe.

[MSwiss]

Duh.

Thanks for pointing that out.

[TSR]

This is what happen when one is blind as a mole and not very observant.

[chaparrAL]

I once asked a guy where he got that thingie body on one of his cars.
He explained it was the bubble pack from a diecast car from walmart that he bought for his kid..

[Mark H]

when i thought of this i was concerned about motor bracket, crown gear ect... but my drawing is like a classic asp in the back. with a little wing. ill scan my drawing now its just a scetch i did last night.

[Mark H]

okay cant see the scetch very good got to outline it in ms paint

[Mark H]

[TSR]

Bedbug?

[Phil Smith]

I thought this was pretty interesting.

[TSR]

Phil, there is one picture missing here, that of a piece of square tubing with the same section as that of the round tubing. It would have excactly the same wake. The "resistance" values are also very approximate and should only be taken with a grain of salt... but it shows that an object with identical frontal area, but fitted with a streamlined shape behind it, greatly reduces its CD (penetration coefficient). In road automobiles, it is impossible to make the shape long enough to be efficient, so a few tricks are used:
1/ the "Kamm" effect of simply interrupting the shape (see prewar Adler Le Mans and postwar Citroen DS19).
2/ Using the Kamm effect plus a small spoiler (the "Gurney flap" effect). The small spoiler reattaches the airflow closer behind the vehicle, greatly reducing drag.

Most people believe that an object will be aerodynamic if its front end looks rounded or pointed. Nothing could be further from the truth, it is the BACK of the shape that counts, many times more. A barn door can be efficient if a streamlined shape is stuck behind it!

[ravajack]

Gentlemen, I believe what you are referring to as the exhaust is actually a ram type intake pipe as the exhaust port is facing straight up.

Surprise!
So this is indeed a front wheel drive vehicle.

But what about the front drive wheels? Very narrow, and only one of them seems to be in charge...



...and the "fat one" also seems to have a somewhat slanted profile. Why is that?

[TSR]

These vehicles are tethered and race on a specialized track around a pole. So traction to only one wheel is required, just enough to make sure that the car does not... spin its wheel! Some have a solid front axle, some have only the inner wheel used for drive on a "split axle". The way they work is that once the engine has been started, they are placed on the track and gently pushed. The first laps are quite slow as the engine is run rich, but as it leans out from the centrifugal force, the speed increases. The last laps before the fuel tank runs empty are the fastest, then the car coasts to a halt.
I used to watch those things in the 1950s, very impressive to see one running as fast as they do. The current record is held by an Italian in the 10cc class at 214 MPH...

[miko]

Found this info here,

http://www.jalopyjou...80837&showall=1

Here is one in action. The cable is atached to the bridle so that the center of gravity lifts all but the inside drive tire off of the ground to reduce the rolling resistance.

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