High speed aerodynamics advice

[Bicycle Bob]

Why not go scale? Do a Chaparral 2J and get the record too. The other nice thing about a sucker car is the constant effective weight and ride height.

[LibertyMKiii]

Originally Posted by Bicycle Bob

Why not go scale? Do a Chaparral 2J and get the record too. The other nice thing about a sucker car is the constant effective weight and ride height.

That is a valid point, I'll have to do some research into some ducted fans.

-Liberty

[LibertyMKiii]

Here is a quick sketch in MS Paint that I came up with. I'm open to any thoughts/suggestions.



The battery behind the front wheel would be level with the chassis like the front lower battery is. That was drawn in incorrectly.
-Liberty

[freebeard]

Do you follow the other threads in Aerodynamics? This is kach22i's latest post in the smoke and wind tunnels thread:


http://ecomodder.com/forum/showthrea...tml#post564458

It appears there is an underbody tunnel to the height of the axle line. What is it's width? Could you group the batteries in between the wheels on each side, in a catamaran body for less frontal area.

The fan could pull 10-15% of it's flow off the top or sides of the tail to eat any attached turbulence at the last moment before it's added to the wake.

[LibertyMKiii]

Originally Posted by freebeard

Do you follow the other threads in Aerodynamics? This is kach22i's latest post in the smoke and wind tunnels thread:

It appears there is an underbody tunnel to the height of the axle line. What is it's width? Could you group the batteries in between the wheels on each side, in a catamaran body for less frontal area.

The fan could pull 10-15% of it's flow off the top or sides of the tail to eat any attached turbulence at the last moment before it's added to the wake.

I had poked around in that thread but had not made it to page 70 yet. I love wind tunnel tests, I hope to have my own scaled tunnel at some point in the future with load cells, pitot tubes, rotation for crosswind etc...

The Catamaran design is more inline with what I had hoped to build. I want to utilize the air flow under the car to my advantage and should have a much lower drag on the car with that design.
There is a large space between the front and rear wheels for the battery packs.
The width of this area is not 100% defined at this point. I have not determined how narrow I want to make the wheel/tire combo. It would range any where from 1" up to 2.5"

-Liberty

-Liberty

[freebeard]

http://oldconceptcars.com/wp-content...lver_Fox_6.jpg

[LibertyMKiii]

Originally Posted by freebeard

http://oldconceptcars.com/wp-content...lver_Fox_6.jpg

I was thinking while out to lunch how someone might accomplish this shape with a standard road car. Thanks for sharing the photo.

My design for this RC would be much more like how the EV solar teams do theirs. The only significant difference would be that they design for neutral lift at speed where I would be adding around 5 degrees AOA of the airfoil for some downforce.

-Liberty

[wdb]

Sucker cars were designed to hold the car to the road, including around corners. They had virtually unlimited HP to work with because their racing class allowed it. That suction costs power. You need to consider the tradeoff. My money is on it being a non-starter, else other LSR cars would have already done it.

[LibertyMKiii]

Originally Posted by wdb

Sucker cars were designed to hold the car to the road, including around corners. They had virtually unlimited HP to work with because their racing class allowed it. That suction costs power. You need to consider the tradeoff. My money is on it being a non-starter, else other LSR cars would have already done it.

It certainly adds some complexity, cost, and risk to the car that I'd rather avoid.

A small pebble in the road is like a 5" tall rock to a real car. Breaking suction is too high of a risk given the scale and scenarios possible.

I will have way more HP than necessary to reach my speed goal so I believe the downforce / drag penalties will be just fine.

After doing some quick sketches with the catamaran type designs I am liking what I see. I can do some things here that LSR guys probably cannot given there is no occupants in the vehicle.

-Liberty

[Bicycle Bob]

That sucker skirt should sweep off any pebbles the suspension can't absorb. Given the non-lethal nature of accidents, the excess power, and the course length, I'd go for a pure sucker for downforce, and anything like a widened half-bullet on top.
I'd still argue for a stable glider, except any launch is likely to cause a roll as well, and roll stability is a slow response.