High speed aerodynamics advice

[freebeard]

If we're back to The Template, I'm in favor of a autofellater with a squircular cross-section:

[ChazInMT]

Here's my take on it, stretched version of the Aero Template, bottom does angle up slightly from front to back, have not been able to get my head around how to create some down force during max acceleration then have it go back to neutral nearing top speed to allow maximum speed. But it's a start. The Catamaran thing looks like problems to me. What I have drawn is more a test sled than a mini "Car" since we aren't going to be putting anyone in it, why bother making it look like you could. A starting point perhaps in the direction of a clean small aero shape.

[freebeard]

A free weight on a slide with a return spring. It's connected by a bellcrank to your active aero.

Modern practice seems to be a trimaran approach.

http://images.thecarconnection.com/med/2011-nissan-lmp2-race-car_100351544_m.jpg

[gumby79]

Mount the , for lack of better term wing /downforce device to the suspension to apply downforce directly . This allows for a softer springs -> better handling.
Im thinking somekind of sail on the bottom of the car that when you getting excess of airflow underneath of your air dam indicating lift, the airflow would push on the cell pushing and turn pushing a lever that would add pitch/AOA to the front wing. Kind of like a self deploying countermeasure. kind of like the roof Flaps in NASCAR but in a whole different context.
Mechanical force under the car versus the force on the wing above the car maybe too far away from each other. this can be solved with two servos. the first Servo can be the smallest one you can find you're only interested in the potentiometer and the ability to add a linkage. the second Servo would control the wing receiving its commands from the first servo having its potentiometer wired in place of the second servo. Considered an electro mechanical leverage.
another potential means of controlling this undesired vertical movement is with another pair of gyros to control the front wing and rear wing independently

[freebeard]

Sounds complicated. I agree with applying downforce directly to the unsprung weight.

I just think it should be a mass free to slide fore-and-aft. Stupid simple. In fact I was thinking about pointing to the Deltawing config as a trimaran.


http://i.wheelsage.org/image/format/picture/picture-medium/nissan/deltawing_experimental_race_car/autowp.ru_nissan_deltawing_experimental_race_car_2 5.jpeg

60s gassers used to ride nose high to get weight transfer off the line. You could have a Delta wing configuration where the front nacelle shortens to put weight on the drive wheels and then lengthens for longitudinal stability as the acceleration slackens.

[Bicycle Bob]

If your course spoils many runs by breaking the vacuum of a sucker car, you could fire small rockets upward from a contact on the droop stops.

[freebeard]

Reactive aerodynamics!

[aerohead]

Just now caught your thread.
*With 1:1 scale racing,you'd want as much weight as the chassis and tires could survive,and use 8-12-miles of run-up to achieve your terminal velocity.
*Liquid fuel would have thousands of kW-hr capacity.
*You don't have either luxury.
*1:1-scale race cars don't have any suspension at all.They don't want any induced drag to alter the inclination of the body at any time.
* The scale of your racer may necessitate some wheel travel,as at 30" overall length,and small diameter wheels/tires,the smallest track deformity could cause the car to be thrown out of control.
*Really spongy-gummy tires might deform enough to absorb some surface irregularities.Don't know.
*If so,then you'd want a body shape incapable of generating lift,most likely would want to intentionally generate downforce,of which the motor /battery will have to overcome this additional drag.
*At 30-inches,instead of 30-feet length,you'd have to test your model at 2,400 mph,to properly simulate 200-mph full-scale effects.
*That's impossible,due to compressibility effects.
You have some really unique challenges. Quite a project! I'll do some thinking.

[LibertyMKiii]

Originally Posted by aerohead

Just now caught your thread.
* The scale of your racer may necessitate some wheel travel,as at 30" overall length,and small diameter wheels/tires,the smallest track deformity could cause the car to be thrown out of control.
*Really spongy-gummy tires might deform enough to absorb some surface irregularities.Don't know.
*If so,then you'd want a body shape incapable of generating lift,most likely would want to intentionally generate downforce,of which the motor /battery will have to overcome this additional drag.
*At 30-inches,instead of 30-feet length,you'd have to test your model at 2,400 mph,to properly simulate 200-mph full-scale effects.
*That's impossible,due to compressibility effects.
You have some really unique challenges. Quite a project! I'll do some thinking.

The 2,400 mph comment is that in relation to wind tunnel testing? I was hoping multiple 150mph related leaf blowers might do the job.

I have had some issues with suspension, which I will not get into. The world record holder did not have suspension.
My current setup which I believe is great uses aftermarket A-Arms which are high in nylon content and solid links in replacement of the shock/spring combo. The Nylon A-Arm acts lick a spring itself yet is very stiff also. There is also some give in the BSR foam tire. I previously had some very stiff springs rated around 25lbs each and with the down force of my front splitter the front chassis was scraping.

Here is an image of the current setup. I need to get over to my friends house with a TIG welder and adapt the "shock tower" to have the shock mount be lower and more directly over that location. This should help reduce the frontal area.



I had a great image showing c/d ratings related to the bottom of the car's height off the ground but at 3.5 cm I do not believe there is much room there to take advantage of significant air flow?

-Liberty

[freebeard]

We're back to Idea #1 and Idea #2.