Remote-Controlled Hypercar Slices Through Air

Almost all entry-level physics courses, and even some well into a degree program, will have the student make some assumptions in order to avoid some complex topics later on. Most commonly this is something to the effect of “ignore the effects of wind resistance” which can make an otherwise simple question in math several orders of magnitude more difficult. At some point, though, wind resistance can’t be ignored any more like when building this remote-controlled car designed for extremely high speeds.

[Indeterminate Design] has been working on this project for a while now, and it’s quite a bit beyond the design of most other RC cars we’ve seen before. The design took into account extreme aerodynamics to help the car generate not only the downforce needed to keep the tires in contact with the ground, but to keep the car stable in high-speed turns thanks to its custom 3D printed body. There is a suite of high-speed sensors on board as well which help control the vehicle including four-wheel independent torque vectoring, allowing for precise control of each wheel. During initial tests the car has demonstrated its ability to  corner at 2.6 lateral G, a 250% increase in corning speed over the same car without the aid of aerodynamics.

We’ve linked the playlist to the entire build log above, but be sure to take a look at the video linked after the break which goes into detail about the car’s aerodynamic design specifically. [Indeterminate Design] notes that it’s still very early in the car’s development, but has already exceeded the original expectations for the build. There are also some scaled-up vehicles capable of transporting people which have gone to extremes in aerodynamic design to take a look at as well.

17 thoughts on “Remote-Controlled Hypercar Slices Through Air

  1. Kinda surprised it’s “only” 2.6 lateral G, spitballin but I think F1 pulls like 4 lateral G and considering how, relatively, this car has no mass and essentially an epic power:weight ratio. Didn’t watch video but I’ll guess it’s a top end speed compromise. Cool Stuff.

    1. This was the first test. It honestly is suspension and tire limited, and at 5,500 ft it makes about 20% less downforce. It will probably be a few more iterations of the car, but I do expect 3-4G is possible.

      1. Downforce is kind of the opposite of aerodynamically slick. You are not slicing through the air if you are trying to achieve downforce. You are trying to change a drag vector to point downward. You are trading energy of propulsion for the friction required to corner and transfer power to the ground. In racing you are trying to achieve the minimum downforce required for traction in order to not drop your top speed and fuel economy. Every pound of downforce consumes energy that could be used for endurance or speed. Thats why F1 has the adaptive spoilers that allow them increased speed for a pass. The physics are so well known that if they allowed all cars to use adaptive aero all the time the racing would be pretty boring with a pass nearly impossible.

      1. Its a balance between tire life, speed, and handling. Sticky tires corner well and accelerate well but wear quickly and are slower. Too sticky and you will lead until tire wear kills your handling. Sticky also adds drag. F1 racing is most difficult with tight corners and long straights because there is no downforce/tire combo that is great for both.

    2. Im not so sure the RC car has a superior power/weigh ratio. Batteries are relatively heavy and dense compared to F1 racing engines and fuels. It would be interesting to know the actual weight power ratio of both.

      1. I’m thinking material differences make more of the difference here.

        Even fancy carbon infused filaments are nowhere near the strength to weight ratio of the exotic composites used by multimillion dollar race cars.

        The powertrain is likely less a bottleneck since there’s no requirement to run pump gas, limit displacement, or have the endurance for an hour long race.

  2. I did a 5 year dual-degree program in physics and aerospace engineering. First three years was exclusively physics, and the constant statement was “neglect air resistance.” Bothered me to no end…

    Then I got to the aero program and found out why… 600+ page textbook devoted to nothing but the Navier-Stokes equation….

    1. Just wondering does aerodynamics of fluids scale well? You can scale down the car and force but does air or water linearly follow that scale? Some things in physic do not scale well since the molecular of materials do not change in size and while you scale dimensions linearly other things are changing exponentially.

      1. Yes, you can scale aerodynamics by the Reynold’s number, which is a dimensionless ratio of dynamic forces (relating to the speed and mass of the object) to viscous forces (the drag of whatever the object is moving in). This is highly used in concept testing as it allows tests to be performed on smaller models.

        To make the test valid, the Reynold’s number of the scale model needs to match the Reynold’s number of the actual object. Since the model is much smaller size, the things that can be changed to make the numbers match are the speed and the viscosity of the fluid. Changing the speed can be tricky, because increasing the speed can cause extra effects due to the speed of sound (compressibility of the fluid). So often the fluid has to be changed (gas composition, or even using liquids). Pretty neat that it can be done though.

        Just as an example, a bee flying through the air will have a very low Reynold’s number: Small mass and low speed, divided by the viscosity of air (in short). But a fighter jet will have a very high Reynold’s number: faster and heavier, divided by the same viscosity. So if you scale the fighter jet down to bee size, using the same air won’t give you the right picture, unless you also scale down the viscosity by using a thinner fluid. On the flip side, if you want to scale the bee up to the size of the fighter jet, you may have to test the giant bee in molasses to match the viscosity effects.

        I’m sure there are better reads, but here’s the customary…

  3. Interesting but there would seem to be a point of diminishing returns. All that downforce would translate into an effectively heavier vehicle. Just like aircraft and boats you reach a point where it takes incredible amounts of power to go faster. High downforce is great for cornering but a penalty for straightline speed.

    1. The car does have a lot of drag but compared to the power it’s insignificant. The car weighs 1.7kg right now (1st prototype so quite heavy) and 1kw or so per motor. Lift to drag ratio of 3.8:1

      The tires are difficult because they aren’t pneumatic and can’t handle the loads. I’m testing custom tire inserts to stiffen their sidewalls.

      The suspension also has some issues both kinematically and because suspension isn’t stiff enough to transfer all the downforce to the wheels.

  4. There’s a relatively huge “scale” velocity range here. Like you are trying to optimize ThrustSSC to drive around town. This has effects like needing suspension damping that works from a few hertz to 20 or so kilohertz. I was thinking that maybe skateboards built for high speed might offer clues, but the ratios of sprung mass to unsprung mass might be in their favor due to rider weight. I think they mostly use the wide range self damping properties of rubber though. So you may want to go that route, rubber block suspension, or you will be into active suspension tuning, higher pressure in the shocks at high speed or something.

    Might also need to use active aero, to get enough downforce, couple of high speed fans in the rear body, sucking it to the road and thrusting down.

    As mentioned in previous comments, if there is an intention to model behavior of full scale vehicle, this isn’t it, the viscosity of air is not to scale, so things have to be done differently than they would be on a human scale vehicle. So it’s gonna look “off”, and lessons learned will not necessarily be applicable to a human scale vehicle (Even though deep down under it all the math is the same) So if one wanted to build a model to test a hypercar for potential full scale concept, you’d be closer with something dinky car sized that you could race round your bathtub when it was full of water.

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