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Extreme Aerodynamics RC Car (X3)

I modified an RC car to use some interesting aero devices. Here’s how that went.

I’m interested in the engineering of Formula 1 and how cars went from looking like ‘this’ to ‘this’, with the advent of aerodynamics being used in motorsport to stick cars into the track. I was inspired by watching Driver 61’s video on Pikes Peaks cars which have zero rules which result in crazy designs with huge aero devices to take on the fierce course.

Bare Chassis Testing

So how fast could the car go without any aerodynamic devices? I decided to base this project around my seriously quick Arrma Limitless RC Car. With a stock setup it can accelerate 0-60 in just 3.4 seconds. Safe to say it’s way, way quicker than my ‘real’ car. Some people have even got these same RC models to travel at over 160mph! It’s not really a car for corners, it’s one for straight lines which might actually make it more interesting to see how fast we can get it to corner despite its focus on straight line speed.

First off, I wanted to set a benchmark to see how fast the car could corner without its bodywork. This meant I removed absolutely all of the the stock bodywork, including the wings, splitter and defuser. I removed all of this stuff so I just had a bare chassis. Now the car was set up like the earliest Formula 1 cars that relied entirely on mechanical grip to go around a corner.

Mechanical grip the between tires and track pavement provided entirely by suspension and tires. These big fat tires are pretty grippy but are quite worn which should make testing a little more interesting. So how much would it slide around? Would the car be really unstable without aerodynamics or would it grip the road with ease? Time to fine out.

Aerobody Testing

Back in my workshop, I set to work building the new body of the car from lightweight and strong materials. Foam board, although not all that strong, is a good lightweight material that I usually use to make RC aircraft. It’s easy to work with and can be hot glued together. I made the wings from sheet aluminium, mainly to make sure they were super strong and could take a knock or two. Let’s face it, it was only a matter of time before testing the car to the limit resulted in a huge crash.

Now, I saw little point in doing this in a half measure, so I went ahead and made the hugest wings with the biggest surface area so I could get as much downforce as possible. Lift increases to the square of the wing area which means that doubling the size of the wings quadruples the amount of lift. It’s exponential. F1 car wings were quickly limited in size because they were ruled to be dangerous. We can go all out though, because who cares about making this thing safe!

The car was a little faster with the wings, but improvements could be made. I took this opportunity to have another look at the aerodynamics.

Firstly, with the front wing, as mentioned earlier, I had suspected the huge shovel like surface is probably creating a deadzone of low pressure which lessens the effectiveness of the rear wing. You can see here the way the air deflects and completely misses the rear wing. This means that the front of the car is being pushed into the ground, increasing front end grip, but the rear isn’t being pushed down as much, offsetting the balance. Ive read that the front wing is the most important part of a car as it’s what determines how the air flows around the rest of the car – so yes my wing is doing a pretty awful job at allowing the rear wing to do it’s job.

Secondly, drag! Look at all that drag! What’s happening here is boundary layer seperation caused by the extreme angle of this wing and the speed of the air traveling over it. The air should flow nicely around and under it, following the contour of the surface. Boundary layer separation occurs due to an adverse pressure gradient encountered as the flow expands, causing an extended region of separated flow. This results in a huge amount of drag behind the wing. Drag will cause the car to slow down in a straight line and reduce downforce.

I had a lot of comments about ignoring boundary layer separation being a key error in my experiments, but from my experience of flying model aircraft, huge wings at high angles of attack are still more effective at producing loads of lift at this small scale than smaller ones with less drag. I’m going to have to look into this more, and maybe this could have been something to investigate in this video. Maybe a future video could look to find the optimum wing for an RC car.

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