I Want to Build a Go Fast RC !

[zeropointbug]

I say that because there are racing wings for the rear of the car, but underneath the bumper, that points down towards the front of the car, creates a low pressure and thus downforce on the car.

I would at least put a full lexan under body as to create a consistent air flow over the car, top and bottom. IMO.

[PBO]

Originally Posted by zeropointbug

I say that because there are racing wings for the rear of the car, but underneath the bumper, that points down towards the front of the car, creates a low pressure and thus downforce on the car.

I'm not sure what you're explaining?

As for the enclosed underside, it has been done & Nic Case makes the best example with one of his streamliners



If you look at the large image you can see channels that train the underbody airflow out of the vehicle which does create low pressure

Sunny mentioned leaving openings for airflow to enter the inside of the vehicle - this also works and both Nic & Sunny are using the venturi effect. If you don't create a venturi (somewhere for the air to escape) you are typically creating an aerofoil (the top of the body resembles the top of a wing, the flat, solid bottom - the bottom of the wing) which in itself creates lift because the airflow over the top is at a lower pressure than the airflow under the body...then you suffer blow overs at a certain speed depending on length/width/weight/speed

So it can be done but without the veturi effect the airflow underneath compresses to become higher pressure than the airflow over the top...you can of course change the airflow over the top by changing the body shape to create lower pressure than underneath but it's much harder than creating venturi's

I hope that makes sense? I've glossed over a few things

[DCastaneda]

ZeroPointBug is talking about a rear diffuser as with on F1 cars

[SunnyHouTX]

Rear diffusers in an RC car are only mildly effective IMHO.

The way that Nic has his car set up in the photo that PBO posted, and the way we set up our RC drag car bodies, makes the whole body act the same way as a diffuser, but at higher effectiveness, and the down force is distributed over much of the length of the car rather than just behind the rear wheels (which will cause the front end to pick up).

[DCastaneda]

Diffusers in the traditional sense may have negligible effect on our little cars but some slightly unorthodox diffuser designs will create a significant difference. You're basically trying to make a relatively flat front end and streamlined rear. A teardrop shape or airfoil of sorts but for ground effect. That combined with some vertical stabs and you're set. This is all very unnecessary to only hit 100mph but to go beyond this point they may be needed or atleast aid in maximizing speed with the power available.

[zeropointbug]

PBO, that's exactly what I'm talking about in the picture, nice streamlined, with channels to hold the low pressure and reduce eddy's. The openings are also something I had in mind, was looking for the term Venturi's, which makes alot of sense.

[SunnyHouTX]

Originally Posted by zeropointbug

... hold the low pressure...

^^^ Very key. Holding the sides of the body steady and not flapping around plays a big part here as well. Actually, something to keep the sides from being sucked in is all that's needed sometimes.

[SunnyHouTX]

Here's the back of my RC funny car showing an "aid" to evacuate air out the back of the car:



And same from my True 10.5/Pro Stock



Mind you, the funny car goes 90+mph and weighs at 48oz (3lbs) and hasn't been airborne at those speeds. That gives you an idea how effective low pressure under the body is. Also note that the angle of the wickerbill is not that extreme: just enough to be effective and not create a lot of resistance.

[PBO]

Originally Posted by SunnyHouTX

Here's the back of my RC funny car showing an "aid" to evacuate air out the back of the car:

That is in essence a diffuser...just a very large & efficient one, sucking the car down harder, the faster you go

[SunnyHouTX]

I don't consider it a diffuser in the strictest sense simply because the area of influence of the low pressure created is much larger here, but that's just me

But the important thing is that this all helps keep the car stuck to the ground

[PBO]

Hahaha...fair enough. Giant venturi is probably more acurate

[nitrostarter]

As far as aerodynamics, what do you guys think of the dirt oval body Ofna has?

Or any suggestions for the most aerodynamic body? My LHS guy did 112mph at ISC with a Ferrari body. I would get one but I want to be different than his.

[SunnyHouTX]

That dirt oval body should work fine, but will still benefit from rear stabilizers, splitters, diffusers, et cetera ad nauseum.

[Bondonutz]

When making these nessasary add on pieces can I make them of .040 or the .060 all the better ??

[PBO]

I'd use .040, plenty strong enough

I've used the same with 1/8 aluminium rivets before to great effect