What's the best taper for the nose on a wedge design to create the most speed. Should it be angled up (angled from bottom of the wedge to top) or should it be angled down (angled from top of the wedge to bottom). Or does it matter?
Correct Angle on Nose of Wedge Design
- Thread starter DuckOfAllTrades
- Start date
Based on those cad models, it seems like the platonic idea would be to taper from the top and bottom, meeting slightly below the middle line, but that the difference will be trivial.
Yes, it definitely does matter, good question Duck.
I saw increase in drag of over 50% between different nose tapers. This translates to over 4ms time difference on a 42' besttrack.
e/o is correct, very nice job there!
The optimal front tip location is dependent on ride height. It is slightly below center line, and gets closer to the center line as the ride height increases.
Tapering all the way down is good, and the drag ever so slightly reduces (a trivial amount ~ 0.2ms difference) as you approach the optimal location below the center line, after which there is a sharp, non-linear increase in drag as the taper rises above the center line.
So down and center taper are good, upwards is bad.
No track test,
CFD simulations using validated commercial code (ANSYS CFX) to calculate body drag.
Used virtual race code I wrote to calculate race times, changing only a single variable "body drag coefficient".
Upwards taper does produce some lift (~10 mN) which would reduce some wheel/axle friction , but that race time difference is small (<1ms) and dependent on your surface friction coefficients.
IF you produce lift at the nose, you will need more drift to compensate "lighter" nose. Just to be clear, I show three nose tapers for example. A,B,C . We are most interested in reducing drag, so B is going to calculate as less drag, but in comparing A vs. C, Which one produces lift to lighten nose, and which one produces downward force on the nose according to your program.?
Yes, a tapered back end would help reduce drag. The effect is inversely proportional to the length of the body cross section, so it doesn't make a huge difference for a full 7" body length. It does not have to come to a point, even just a partial taper at a slight angle to a flat back would help reduce drag, this is called a Kamm-back in the aerodynamics world. I have not quantified how much difference, or whether the resulting change in COM would slow the car down more than the decreased drag would improve it.
From preliminary estimates either way looks plausible, with careful design, and if trailing fenders were placed behind the rear wheels as well.
What I do know is it is a heck of a lot easier to just put the wheels in back and have a better COM, and not have to worry about making short Kamm-back trailing fenders for the rear wheels. Also any difference would be pretty small, so the easy road is preferred for most.
For the lift, it was pretty linear with:
A: 11 mN
B: 1.4 mN
C: -7 mN (downforce)
for the highest ride height, and
A: 14 mN
B: 3.5 mN
C: -6 mN (downforce)
for the lowest ride height.
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If you are using scout wheel base, would there be enough room behind the rear wheel to put trailing fenders?
Talking about the drag on the end of the car. In cycling they use something called Aero Trip Strips (ATS), which are put on the lower legs or in body suits to lower drag, they work by interrupting the air flow and making the air stick longer to your body, reducing the overall drag. Could this also work on a pinewood derby car, by placing small strips on the car to break the drag on the end of the car? Or is the drag so small that the increase in air resistance would be greater than the reduced drag?
Talking about the drag on the end of the car. In cycling they use something called Aero Trip Strips (ATS), which are put on the lower legs or in body suits to lower drag, they work by interrupting the air flow and making the air stick longer to your body, reducing the overall drag. Could this also work on a pinewood derby car, by placing small strips on the car to break the drag on the end of the car? Or is the drag so small that the increase in air resistance would be greater than the reduced drag?
A trip, or "gurney" would be interesting to test. My gut says a full width trip, would increase drag, but a series of vortex generators my help.
Having an even longer taper on the back than the front, similar to an aerofoil, seems like it would be the theoretically ideal shape, and I've seen some models to that effect. But those designs seem inherently inconsistent with weight placement. I wonder if there's some tiny speed gain to be had by making a tapered version of txchemist's TxW100-12-60 piece that would be glued directly to the back of a shortened block.
What would be interring would be to quantify the rationale of horoscope to the totality of the Miz. Then you could collaborate the synthetic lobotomy of the tampon. Would that work or would it be more spectacular to ventricular the moderators so they constipate?
Confession, I’m just trying to sound smart like I know what I’m talking about.
Seriously, this is awesome information! Love it. Thank you. Makes me want to experiment more.
Confession, I’m just trying to sound smart like I know what I’m talking about.
Seriously, this is awesome information! Love it. Thank you. Makes me want to experiment more.
Turbulence off of, and behind the rear wheels probably creates more drag, than the squared off tail of the chassis itself.
Plus, how much would the wake of turbulence from the rear wheels, negate any gain from a tapered rear chassis?
Plus, how much would the wake of turbulence from the rear wheels, negate any gain from a tapered rear chassis?
I think it's time to get off the computers, put these simulations into a real car build and send them in for league racing and see how they hold up.
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