RC Hypercar Pt6 - Aeromapping

In this video, we continue the discussion around RC Hypercar's aerodynamics and we focus on aeromapping.
If you’re looking for an easy to use cloud based CFD service, checkout AirShaper:
airshaper.com/
You can also checkout the CFD results on AirShaper's website for yourself:
app.airshaper.com/projects/rc...
Here is a link to the article by Zhen W. about aero sensitivity in race car aerodynamics.
/ my-personal-aero-note-...
#3dprinting #rc #motorsport

[@GatorGlider]

Thank you, thank you, thank you for addressing right off the bat the scaling issues and Reynolds numbers! This was a huge question I had with building high performance RC sailplanes. All I can now say is, I can't wait to print my own!

[@loopie007]

Tons to do. Log everything. Monitor ride height, vs speed (aero efficiency). Rear wheel rpm vs speed. (slippage of the tires). Power usage vs speed. (Aero efficiency). Gps, Find a remote GPS location and have the car auto-steer to it. Update your acceleration rates so you don't spin the tires. So much to do.. Fun, fun, fun...

[@IndeterminateDesign]

So true. So many things to do on this car. Working on custom PCB’s for everything.

[@toolscientist]

This car really needs an indoor basketball court to see its full potential. I know top speed is currently the challenge amongst RC youtubers, but you should try to create your own challenge. Something like fastest time to do a full lap of a 6m diameter circle. Might have to do average time of clockwise and CCW to avoid someone making a crazy asymmetrical car.

[@torstonvodesil6709]

Something like “highest lateral acceleration” would be so cool

[@IndeterminateDesign]

I’ve definitely been thinking about that. I want to add a better GPS and I’ve thought about having the car drive it’s own skidpad. It’s really difficult for me driving to have repeatable results. I’ve thought about trying to take this thing to a karting track. I think that would be the perfect size for this car.

[@WolfsburgWarehouse]

You can put propellers under the car to evacuate air.

[@IndeterminateDesign]

Yes, I’ve thought about that. It would difficult to fit into this particular car but possibly in the future on another car.

[@whatev888]

You could try making the front wing unsprung. If you can attach it directly to the front wheels its ride height it would be able to keep the front wing at a standard ride height. Also this would decrease the force on the suspension and so the suspension could still be this soft because now the aero is not running through it.

[@IndeterminateDesign]

That’s definitely something I want to try at some point with an open wheeled derivative of the car. I’d love to have the rear wing tied directly to the rear suspension as well. The a softer rear would make the car a lot less twitchy at low speeds.

[@whatev888]

@@IndeterminateDesign ya that would be a super cool idea. I have always been really interested in unsprung aero so if you did anything like that I would be very curious to see how it would work.

[@wasa7]

The current body of choice on a 1/7th scale is the Delta Plastk Fc100. I managed to push one to 203mph last week end and would love it if you had any pointers for simple improvements. Thanks.

[@IndeterminateDesign]

203mph is insane. I hope someday I can get my streamliner even close to that speed. I looked at that body, I'm a bit surprised. I would have thought something more like the 8515 is going to have less frontal area. It depends really on what's limiting your top speed. Is it overall drag, stability, or the distance it takes to reach top speed? In general, the biggest source of improvement for most of these RC cars is most likely the underside of the car. You can generate much more downforce with low pressure under the car than with high pressure on the front nose or a badly designed splitter/rear wing. The control arms and everything on the bottom of the car should be as flat and smooth as possible with very small gaps, just enough room to turn the wheels maybe 5-10degrees. And then seal and tape off everything you can. For front end stability, obviously a rounded edge on your splitter helps. Sharp edges are bad. You might try venting the front wheels out the top of the body. Check out the Porsche 963 front fenders. Start small and work your way up. This can help vent high pressure out of the wheel wells and may prevent the car from flipping. Obviously in a perfect world you'd design a body and chassis from the ground up to fit the exact car, motor, and battery setup. I'd love to get into the 1/7th scale game, but those are some big dollar setups you all run.

[@wasa7]

@@IndeterminateDesign hi, Limiting factor at the moment is tyres. Nothing commercially available will with stand a combination of the rpm, load and torque. Several guys are working on ideas in the background. There is only a couple of guys to get the 8515 ( WR ) design Fast, One issue is keeping the air out to stop it parachuting, second is due to the length out front of the front wheels it’s very hard to keep rake and stop it blowing over. The shorter the front, the higher the level off attack. It’s a trade off. Part of the hobby for me is to make my own bodies over the winter, hence genuine interest in anything that could give me an edge. Cheers.

[@ryderSRliu]

This is a very cool project. I just wanted to point out that in your image at 23:00, there’s some pretty severe surface collapsing in your mesh. You may want to consider refining your surface mesh to make sure the geometry is accurate there and that you aren’t numerically impacting your CFD.

[@IndeterminateDesign]

Thanks! I ran most of the CFD for the aero map at around 1million cells which is really low, but the overall downforce numbers are within 1% or so of the finer mesh. I think the vortices around the car show up a lot better though with a finer mesh.

[@alex07guerrero]

Great review man, but have you considered increasing the size of the mesh? It looks too coarse at some points.

[@IndeterminateDesign]

Thanks. It’s definitely coarse but I found the overall force numbers are very close to the finer meshed simulations. Once I have version 2 designed I’ll definitely be running everything at a much higher level of refinement.

[@NicksStuff]

How did you choose the direction of the wheel turbofans?

[@IndeterminateDesign]

The turbofans I’m using have straight blades, so they can be used either side. From what I’ve read, the straight blade generally has the highest air flow. A curved blade will give you more pressure at higher speeds.

[@NicksStuff]

What's the µ of tires suitable for your car? Do you know how much it decreases with the load?

[@IndeterminateDesign]

Tests in the car without the aero shows the mu is around 1.1. They’re not a very grippy tires. I may have to build a tire test rig to measure the actual decrease with load. The tires aren’t pneumatic so the inner foam used on the tires affects how they deform greatly. I’ve been playing with different densities of foam.

[@NicksStuff]

9:06 You didn't map pitch and squat? (With the rear goes higher while the front goes lower and vice-versa)

[@IndeterminateDesign]

Are you referring to the N/A cells in the table? Those were limitations due to the front wing or diffuser hitting the ground plane.

[@shawnington]

Is it actually suspension limited? In other high downforce racing applications its understood, especially with ground effect, that suspension stiffness limits are based on the needed to not shake the driver to death, where as an ideal platform would be essentially rigid once you have enough downforce to overcome chassis perturbation from bumps. You actually highlighted the reason in one of your first aero videos, as you pointed out the difference in expansion ratio for the diffuser based on suspension movement. For this reason running on hard stops where the expansion ratio can remain well controlled is preferred. The inability to do this with a driver in the car in f1 is the primary mode that caused the famous porpoising issues with the reintroduction ground effect. The lotus 79 cars were designed to run double chassis so that the ground effect generating portion was essentially running on hard stops at speed for this reason. Have you done the math based on the road surfaces you are optimizing for to see at what speeds downforce is sufficient as to where essentially running on hard stops is the preferred mode? Where the downforce is sufficient to prevent road imperfections from changing the ride height and thus the expansion ratio?

[@IndeterminateDesign]

That's an interesting point. I do have a urethane heave springs that are more or less a hard stop. This version of the suspension make the heave spring stiff enough because of bad kinematics. My hope with the revised suspension is that the car will only have 3-4mm total suspension/tire compression under full downforce. I'm making custom coil springs and new heave springs for the next version, and I plan on actually measuring the spring rates with a load cell to get the exact right values. I'm going to design the suspension around 8kg of downforce based on the CFD, but of course I expect the downforce in real life to be lower than the CFD figures.

[@piotrhelios1518]

Are you going to share the files when its done? Really looking forward to build it. Also what motors did you use?

[@IndeterminateDesign]

I'm planning on sharing the files when it's done. I'm not sure the best way, the car is going to be a very complicated build. The motors I'm using are BrotherHobby Avenger 2812's. I'm planning on using smaller motors for the front wheels.

[@piotrhelios1518]

@@IndeterminateDesign ok, thank you

[@NicksStuff]

Can you explain why the downforce doesn't increase when the car is pitching? A layman would assume you increase the wings incidence

[@IndeterminateDesign]

I didn’t break out all of the forces on the individual components, but it’s the interplay between the wings and the floor. The rear wing’s downforce may increase by pitching forward but the underfloor’s may decrease. Sometimes decreasing the effectiveness of the front wing increases the downforce created by the floor because it gets more airflow. Unfortunately, downforce and aero balance aren’t linear between various attitudes of the car. That’s part of what makes aerodynamics for race cars so difficult.

[@toolscientist]

10:38 do you judge pitch sensitivity by looking across the zero row/column? Rear zero column looks stable as the front dives (good in breaking), but poor when the front rises (bad when accelerating in corners and rebounding from a bump). Front zero row looks the worst. Loss of front downforce with any movement at the rear

[@IndeterminateDesign]

Now that I look at it, the rear moves the front downforce a lot as well. I’m not sure why, other than the angle of attack on the front wing. I’m definitely going to run some more simulations after I make changes to the underfloor due to the suspension changes. I’m wondering now if I’m loosing downforce more from the vortex generators at the front of the floor.

[@ryderSRliu]

@@IndeterminateDesign It's pretty common in cars to have shifts in front and rear when changing the rear ride height. Your diffuser performance is influencing the front of the floor as well, which based on how far forward your floor leading edge is will affect your front balance.

[@IndeterminateDesign]

@@ryderSRliu Yeah, I was torn on how far forward to start the floor. The downforce from the vortex generators is really sensitive.

[@namhorhelohs6913]

what scale did you use in this rc project?

[@IndeterminateDesign]

It started out 1/10, but it’s probably closer to 1/9 scale.