RC Hypercar Pt5 - Topside Aerodynamics
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- เผยแพร่เมื่อ 1 มิ.ย. 2023
- In this video, I walk through the topside aerodynamics of the RC Hypercar
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...
#3dprinting #rc #motorsport - ยานยนต์และพาหนะ
I think what I'd really appreciate is seeing direct comparisons between this car and another one with similar (or the same) electrics and motors. Maybe you could 3d print a different chassis that's just a box to illustrate points. Or maybe how different versions of front / rear wings perform. I get how all this aerodynamics work is good on a conceptual level but it'd be cool to see it in practice. RC Testflight just did something kinda similar with airplane shapes and it was actually really interesting to see how all the theory worked out in practice.
That's an interesting idea. I'll see what I can come up with. I need to get the car to a point where the suspension is fully developed and all of the data logging is up and running so we can have a consistent platform for comparison.
I'll go into it more after the aero videos, but this car is in uncharted territory for an RC car.
@@IndeterminateDesign Ohhhh yeah, it probably wouldn't be very cool / interesting without data logging, didn't think of that. I totally understand that there's a difference between you doing interesting work for yourself and putting out HOT CONTENT that I ENGAGE WITH tho.
From what i understand, the backed off center rear wing is basically working off of the angle of attack of the oncoming air that's influenced by the bodywork ahead of it. Because of the monocoque bulge that drops off right ahead of the rear wing, the flow there is attached to the bodywork and at a slight downward angle compared to the flow to the side, where its relatively flat. The backed off center is just tuning the approach angle of the wing to work best with the oncoming air. This is apparent in the flowlines in your cfd too. Great work these videos are fascinating, and i hope the car exceeds expectations! Cheers
Thanks! Now that I see it, that makes perfect sense. I’m surprised at how much of an affect this has.
I'd love to see some pseudo wind tunnel tests. Maybe a leaf blower and some different coloured smoke sticks
I'd love to do some of that kind of testing. I've been looking at pressure probes and ride height sensors to maybe make the car more of a rolling wind tunnel.
@IndeterminateDesign I'd just be interested in a basic flow visualisation comparison between the CFD and reality. At this scale, I imagine print inaccuracy and layer artefacts could change the flow quite a bit.
Great video, thanks! How much does the relative viscosity at model scale affect the aero elements?
Thanks. It's very hard to compare to a full size car since I was always designing within the paradigm of this being a small car. With the low Reynolds number, the aero devices are far less efficient and effective than on a full size car.
I've had to oversize the aero devices considerably. The front wing would be 3.5m or 11.5ft wide on a full size car. The aero devices seem to be more sensitive as well. Airfoils that should handle 12+ degrees AoA, tend to separate at around 10 degrees. So if this was made into a full size car it would look very different. This car has a lift of drag of around 3.8:1 and a full size car like this is probably be well over 6:1.
Also definitely not an expert in this by any means.
Question on your aero modeling. I am involved with RC sailplanes. A saying that we toss around when talking about designs is "air molecules don't scale". What we jokingly are referring to is that a design that works at one scale, say on a full sized aircraft, won't give similar performance on a model. Vice versa, going from a design that works great at model scale exhibits poor performance at full scale. Are your simulations taking this into account? After watching these last two videos I've been wondering if the performance that you're expecting is actually feasible at the size if the car relative to the air passing over it. Kudos for another great viseo!
I've had a few people bring this up and I can cover it a bit in the next video. The CFD software does take into account the physical size of the car. This car was always designed to function at this scale, so it has relatively massive aero devices. The RC car is really inefficient compared to what it would be if was a full size car. Maybe only half as efficient.
I think that's where the "air molecules don't scale thing" comes into play. If you scale down a full size plane to an RC model, it's going to have very different lift and drag numbers than what would be expected if it had scaled perfectly.
Hats off to the things you do on this channel, the f1 gearboxes as well! I'm playing around putting an RC car in a race simulator and it is going well. I've also found the side forces to be actually noticeable. I would like to put something like an aero map and also aero side forces and moments you may have found, in the sim to actually feel how the car drives. We could import a 3D model (not a million polies) into the game as well.. I'm sure some things can't be modelled and the tires will remain a question, but I would love to play around with it for fun if you're up for it. Video of current state of my work: watch?v=v2oZENGrPZs
That's really cool. I would have loved to learned how to do that. Your link didn't come through on the comment. I know a lot of FSAE race teams use Adams car for simulation, and I thought about trying to use a chassis simulator like this. It's hard because there's no data out there for RC car tires, and my testing shows they're very different than a pneumatic tire. You can download the STL for the body from AirShaper app.airshaper.com/projects/rc-hypercar-final-589b61
Great stuff.
Did you ever consider enclosing the wheels to lower drag? Advantages / Disadvantages?
I thought enclosing the rear like the Jaguar XJR-9, but it definitely complicates things. Enclosing the rear would make it very difficult to remove heat from the motors (They're pulling over 500watts each at full throttle). The entire front end could be changed to reduce a lot of drag, but to enclose the front wheels the car would need to be really wide.
The hardest part of designing this car is I wanted to generate huge amounts of downforce at 60mph or less, and efficiency is really hard to achieve at this size and low speed. Honestly, almost all of the drag on the car comes from the giant wings and downforce generating stuff. The drag from anything else is trivial, probably
@@IndeterminateDesign you should try copying the "enviate hypercar 2021" should be one of the first search results, it has concave cutouts on the rear wheel covers to induce a vortex and to make downforce while cooling the rear brakes which i believe could work on that car as they are very similar (my speculation), in fact i think it would be even better due to the turbo fans keeping the air from hitting the rim
What do you use for the CAD design? I'd have nightmares trying to create such a complicated design, let alone a design that needs to be tweaked. Did you ever need to start from scratch?
I'm using Fusion 360 as it's free for hobbyists. This car definitely pushes the boundaries in terms of complexity and performance for Fusion 360. In the beginning, I redid the car 3-4 times. I learned a lot from that experience about how to best setup the model so that it's easier to change and doesn't crash Fusion as often. The model can still be quite fragile, but I've gotten good at fixing it.
@@IndeterminateDesign yeah, I'm on F360 as well after Solidworks got rid of the EAA licence. I think it'd take me a year and a dozen starts from scratch to make something this complicated.
Well at this point I've done quite a bit in Fusion 360, with my F1 gearbox and streamliner models. You really need to plan your model ahead of time to ensure you have all of your geometry laid out.
@@toolscientist Solidworks has a $99 maker's license now. I just don't have the energy to convert my models.
@IndeterminateDesign it's diff software, though. I can't remember the details, but I looked into it when it happened and people were scathing of it. Lots of bugs and issues with models not being transferable between maker and full version. So if you ever wanted to upgrade, all your old models and parts libraries would be useless.
why doesnt the front fender have a gurney flap on the side just behind the front canards just like the rear wing? is there a reason for that?
That's a great idea. The front wing should definitely have a gurney. As an added bonus it would make the front wing easier to 3d print as well.
@@IndeterminateDesign so it was an oversight?
@@IndeterminateDesign oh and i just want to clear up i meant the front fender wheel well openings, its good for sucking air out of the wheel well
@@gp8666 That would be a good idea as well. I'll have to see what it does in CFD. I've been finding more and more that's the only way to tell if these smaller bits work on this particular car with all of the other airflows.
I'm tempted at some point to make the entire front fender narrower at the bottom so I can jet that air out lower down. Kind of like what the Aston Martin Valkyrie does right in front of the fender. I think having the outwash down lower maybe more beneficial.
@IndeterminateDesign I've been planning on making a similar car to yours for a year or so but I have mostly just been collecting ideas and trying to see how my work has turned out to be so I can get a good rule of thumb.
By the way I've been really hesitant about underbody aero due to the studies on how the ground boundary layer affects full size diffuser efficiency at low heights, do you know how much it affects a small scale car?
Maybe you can find inspiration from some older race cars like the Toyota eagle mk3 or Toyota gt one, they both are sort of predecessors to the underbody aero you see on modern lmp cars or rather hypercars as they are now called, the mk3 is probably the most out of the ordinary in terms of front diffusers and I'm most likely going to copy it on my next track car project due to how much potential it has, I recommend looking up "mulsannes corner" website, it looks a little sketchy at first glance but it has lots of small information you can't find anywhere else which is why I recommend it
I can offer some guidance regarding aero over discord call if you want, I am an aerodynamicist
i also suggest making your own discord server, although it may be a pain to manage, i would love sharing ideas and pictures of my rc car project
Thank you for the offer! I'm in the midst of a major redesign of the monocoque/suspension, but once I get that sorted out I may have some questions. I guess I'm old now, I need to go look at what discord is.