Aerodynamics ?

General discussions for car and semi-truck racers.
Pacfanweb
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Re: Aerodynamics ?

Post by Pacfanweb » Thu Feb 08, 2018 9:09 pm

IMO, aero isn't the first, or even the second prime factor in a fast car.

Friction is. And the 2 things that affect friction the most are alignment and axle/wheel bore prep. Without these, no car will be fast. But a car without a great aero shape or weight placement can still be fast if the friction is minimalized.

Now, the point of the post is "before you cut that block". So I guess aero is a major consideration before you do that, no doubt.



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Re: Aerodynamics ?

Post by Speedster » Fri Feb 09, 2018 5:55 am

Pacfanweb, Thank you for your last line.
Thanks to all who have contributed to this topic.



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Darin McGrew
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Re: Aerodynamics ?

Post by Darin McGrew » Sat Feb 10, 2018 1:58 pm

Pacfanweb wrote:
Thu Feb 08, 2018 9:09 pm
Now, the point of the post is "before you cut that block".
Our "before you cut that block" emphasis is related to alignment (friction), not aerodynamics. We make sure that the kids press their axle holes before they cut the block, so all the sides of the block are still square.

We saw a huge improvement in the overall performance of the cars in our derby when we started having the kids press their axle holes with a drill press at our workshops. But aerodynamics doesn't make that much of a difference.

Sure, the cars that add a lot of (low-density) material to make the car significantly bigger (e.g., my Calvin & Hobbes car, my sub sandwich car, my friend's banana split car) are slow. But the race winners might be low-profile "Hershey bar" designs, or they might be typical "cut the original block into a car shape" designs.



Pacfanweb
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Re: Aerodynamics ?

Post by Pacfanweb » Sat Feb 10, 2018 3:03 pm

Darin McGrew wrote:
Sat Feb 10, 2018 1:58 pm
Pacfanweb wrote:
Thu Feb 08, 2018 9:09 pm
Now, the point of the post is "before you cut that block".
Our "before you cut that block" emphasis is related to alignment (friction), not aerodynamics. We make sure that the kids press their axle holes before they cut the block, so all the sides of the block are still square.

We saw a huge improvement in the overall performance of the cars in our derby when we started having the kids press their axle holes with a drill press at our workshops. But aerodynamics doesn't make that much of a difference.

Sure, the cars that add a lot of (low-density) material to make the car significantly bigger (e.g., my Calvin & Hobbes car, my sub sandwich car, my friend's banana split car) are slow. But the race winners might be low-profile "Hershey bar" designs, or they might be typical "cut the original block into a car shape" designs.
We don't to the drill/press holes until after the block is cut and weight pockets routed, etc. Basically until all the wood working is done, in case the work warps it. And they WILL warp. So we drill the axle holes (whether using the slots or not) last.



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Re: Aerodynamics ?

Post by chromegsx » Sat Feb 10, 2018 3:28 pm

Pacfanweb wrote:
Sat Feb 10, 2018 3:03 pm
Darin McGrew wrote:
Sat Feb 10, 2018 1:58 pm
Our "before you cut that block" emphasis is related to alignment (friction), not aerodynamics. We make sure that the kids press their axle holes before they cut the block, so all the sides of the block are still square.

We saw a huge improvement in the overall performance of the cars in our derby when we started having the kids press their axle holes with a drill press at our workshops. But aerodynamics doesn't make that much of a difference.

Sure, the cars that add a lot of (low-density) material to make the car significantly bigger (e.g., my Calvin & Hobbes car, my sub sandwich car, my friend's banana split car) are slow. But the race winners might be low-profile "Hershey bar" designs, or they might be typical "cut the original block into a car shape" designs.
We don't to the drill/press holes until after the block is cut and weight pockets routed, etc. Basically until all the wood working is done, in case the work warps it. And they WILL warp. So we drill the axle holes (whether using the slots or not) last.
:agree: Same here. one of the last things I do. It can be tricky making sure you don't temporarily warp the car in drill setup and then it will look like you can't drill straight when you check the drill job. i think this is going off topic, but being that the intent of the thread was mislead by the title... it may of already been off topic.

For the beginner it might be better to drill the block first under the assumption the block is square to start with. which i haven't found one that has been in my last 8 years of doing it.



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Re: Aerodynamics ?

Post by Speedster » Sat Feb 10, 2018 6:13 pm

Yep, the Hershey Bar car won. He also won the OUTLAW race and his young sister came in Second in the OUTLAW race.



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Re: Aerodynamics ?

Post by Pacfanweb » Mon Feb 12, 2018 10:01 am

chromegsx wrote:
Sat Feb 10, 2018 3:28 pm
Pacfanweb wrote:
Sat Feb 10, 2018 3:03 pm


We don't to the drill/press holes until after the block is cut and weight pockets routed, etc. Basically until all the wood working is done, in case the work warps it. And they WILL warp. So we drill the axle holes (whether using the slots or not) last.
:agree: Same here. one of the last things I do. It can be tricky making sure you don't temporarily warp the car in drill setup and then it will look like you can't drill straight when you check the drill job. i think this is going off topic, but being that the intent of the thread was mislead by the title... it may of already been off topic.

For the beginner it might be better to drill the block first under the assumption the block is square to start with. which i haven't found one that has been in my last 8 years of doing it.
I don't worry about whether the block is square or not. Doesn't matter, because the drill fixture is going to drill perfectly parallel holes regardless. And since the fronts are going to be steering, doesn't matter if they're straight that much, either. Even for a 4 wheel touching car (the single most idiotic rule in PWD), still going to make it a rail runner. Just make one wheel *barely* touch, then lube the tread up with graphite so if it does touch it doesn't "grip". And then steer it with the other.



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Re: Aerodynamics ?

Post by Vitamin K » Mon Feb 12, 2018 10:11 am

Pacfanweb wrote:
Mon Feb 12, 2018 10:01 am
chromegsx wrote:
Sat Feb 10, 2018 3:28 pm


:agree: Same here. one of the last things I do. It can be tricky making sure you don't temporarily warp the car in drill setup and then it will look like you can't drill straight when you check the drill job. i think this is going off topic, but being that the intent of the thread was mislead by the title... it may of already been off topic.

For the beginner it might be better to drill the block first under the assumption the block is square to start with. which i haven't found one that has been in my last 8 years of doing it.
I don't worry about whether the block is square or not. Doesn't matter, because the drill fixture is going to drill perfectly parallel holes regardless. And since the fronts are going to be steering, doesn't matter if they're straight that much, either. Even for a 4 wheel touching car (the single most idiotic rule in PWD), still going to make it a rail runner. Just make one wheel *barely* touch, then lube the tread up with graphite so if it does touch it doesn't "grip". And then steer it with the other.
Ah, clever, I like the idea of making the barely-touching wheel more slippery! Finally a reason for graphite on the tread! ;)



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Re: Aerodynamics ?

Post by Pacfanweb » Tue Feb 13, 2018 8:16 pm

Vitamin K wrote:
Mon Feb 12, 2018 10:11 am
Pacfanweb wrote:
Mon Feb 12, 2018 10:01 am

I don't worry about whether the block is square or not. Doesn't matter, because the drill fixture is going to drill perfectly parallel holes regardless. And since the fronts are going to be steering, doesn't matter if they're straight that much, either. Even for a 4 wheel touching car (the single most idiotic rule in PWD), still going to make it a rail runner. Just make one wheel *barely* touch, then lube the tread up with graphite so if it does touch it doesn't "grip". And then steer it with the other.
Ah, clever, I like the idea of making the barely-touching wheel more slippery! Finally a reason for graphite on the tread! ;)
Yep, we make 'em look like those graphite-coated wheels you can buy, lol



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