Fenders?

[Guest]

This is an area that could be interesting. What if it made your car a little faster, but it mostly disrupted the cars on either side of you and slowed them down. Would it push a car with mild drift off course?.
Then we would have teams with some cars built to help each other and some cars that disrupt on purpose all interacting and making life interesting.

Oh man! That is such a cool idea!

Like roller derby. Each car will have a purpose.

 

[LightninBoy]

Yes, I was referring to the leading edge being a parabolic shape. I'm going to make the trailing edge come to a point. Kinser's right, though. By the time you get them (leading and trailing fenders) to an optimal shape, they are too heavy to retain a benefit.

Make them out of balsa and they won't be too heavy.

The trick to minimizing frustration with the balsa is this. After cutting the rough shape and radius, coat the inner radius with thin CA glue. After that dries, go to town shaping the fender. The glue prevents large chunks of balsa from coming off while you shape. Once the shape is final, coat the entire fender in CA and sand smooth.

Example:

http://www.pinewoodderbyonline.com/post/show_single_post?pid=1282437440&postcount=13

 

[GravityX]

This is an area that could be interesting. What if it made your car a little faster, but it mostly disrupted the cars on either side of you and slowed them down. Would it push a car with mild drift off course?.
Then we would have teams with some cars built to help each other and some cars that disrupt on purpose all interacting and making life interesting.

Oh man! That is such a cool idea!

Like roller derby. Each car will have a purpose.

I was thinking NASCAR myself. /images/boards/smilies/smile.gif

 

[Guest]

Oh Paul!

You and your fanciful analogies.

Ok fine. NASCAR

You certainly do have a flair for the dramatic don't you?

Good tip LB.

I like that car more every time I see it.

 

[Guest]

I have seen a couple cars with fenders in front and behind the wheels. I know Carolina's Operation Mindcrime has one behind the DFW. I don't have any idea if it is faster, but in my opinion as long as you don't make the footprint (when looking from the front) of the car any larger then there are no negatives when running alone. I have also seen people run fenders full height between the front and rear wheels. I think this is probably fine alone, but IMO any turbulence from cars on either side and then those big fenders act like sails.

5 Kids first law-

I don't have any idea if it is faster, but in my opinion as long as you don't make the footprint (when looking from the front) of the car any larger then there are no negatives when running alone.

*See also the "Lightning Boy Oath".

*Well the main similarity is "first, do no harm". Which in this case translates to avoiding the addition of any frontal area. The second similarity is starting at the center of the wheel tread (approximately) and displacing air to both sides as well as to the top/bottom. You've taken that a bit further, even, than I have.

 

[down4derby]

This parallel thinking just might LEAD to something. A lot of what you guys are talking about has been built into my current car with my own TWIST. Laser has seen a pic. It's amazing how we all think alike sometimes.

 

[ChrisF]

Yes, I was referring to the leading edge being a parabolic shape. I'm going to make the trailing edge come to a point. Kinser's right, though. By the time you get them (leading and trailing fenders) to an optimal shape, they are too heavy to retain a benefit.

Were you thinking along these lines?




I made the four fenders out of CA sealed Balsa (ala Lightnin Boy's post). Four fenders weighed a total of 0.1 oz. About 30 minutes of work with 5 minutes dedicated to separating my CA glued fingers (first time that's ever happened...I promise!)

 

[Guest]

Picard to Enterprise

I got some CA glue on my upper lip the other day.

Only the second time that has ever happened.

 

[bracketracer]

Yes, I was referring to the leading edge being a parabolic shape. I'm going to make the trailing edge come to a point. Kinser's right, though. By the time you get them (leading and trailing fenders) to an optimal shape, they are too heavy to retain a benefit.

Were you thinking along these lines?




I made the four fenders out of CA sealed Balsa (ala Lightnin Boy's post). Four fenders weighed a total of 0.1 oz. About 30 minutes of work with 5 minutes dedicated to separating my CA glued fingers (first time that's ever happened...I promise!)

That's what I was talking about. That shape was slower for me when I got around to trying it. How's it working for you?

 

[bracketracer]

Picard to Enterprise

I got some CA glue on my upper lip the other day.

Only the second time that has ever happened.

Hey, it's better than that time you got it on your tongue!

 

[ChrisF]

That shape was slower for me when I got around to trying it. How's it working for you?

Hard to say. In testing it beat two conventionally fendered cars (but that doesn't mean much as they were different cars). I attached the fenders incrementally...first the fronts, then with the rears too. The car was incrementally faster as the fenders were attached. But in this case as well it would be hard for me to draw any conclusions from that because I would worry about the car naturally getting faster over time as the graphite broke in.

When it mattered, it didn't get a chance to do it's best. It was received back after the races with one of the rear axles pulled out a quarter inch. One of several problems I was made aware of that some of the faster racers experienced during this particular race.

 

[B_Regal Racing]

I do not know if this helps, but my fenders are not an afterthought. By this I mean, the car is designed and sanded with the fenders in place, and not glued on afterwards. Most of the time, they are molded into the body and rounded in all directions (see the front fenders). I usually do the same for the rear, but I was time constrained. I did however, ensure the front of the rear fenders come to a point (somewhat like the GEE fenders). In a sense, I never have the very front of the fender increase the frontal surface area nor do I have any hard edges (if I have the time). I'm far from a master builder, but it does seem to give me the best results.

 

[Obsessedderbydad]

2 lane track... so jealous...

 

[ChrisF]

Heh Heh..not mine...belongs to a friend. Funny story behind that shot that I should share one day.

Question for aksnowfun; The Re number you had mentioned was higher than anticipated (but not real high in the scale of Re Numbers). In my mind, that means that fender shape matters little?

One more shot of fenders in process;

 

[Bullet]

Hey Chris,

The Re number is high because the viscosity is so low for air, its the bottom number in the equation (divided by this number) at around the 60K range even for these slower speeds. I updated the drag numbers posted in the other thread just recently. One wheel cross-section will give about 0.23 oz of drag at 12 mph with a drag coefficient of .55 (its prob higher). Since drag coeffs are different for each shape, it will make some difference...I would think it would be small unless there is a visually drastic difference between them...just my quick thoughts on it. /images/boards/smilies/smile.gif

You can look up coeffs for common shapes like triangles and spheres and kind of draw your own conclusions...google images shows some charts.

 

[Guest]

mmmm kay.
https://www.youtube.com/watch?v=zVE9VRQQFGk

 

[Bullet]

/images/boards/smilies/rofl.gif...love that show!

BTW, those fenders look cool, and will probably work well...much better than a wheel! I would run them any day...with a fox or in a box, on a train or in the rain! lol

 

[The Iceman]

From what I've read the Tear drop is the best and if you can't trail it off you cut it off square. I've showed this video before and I think tells alot! [video]http://www.youtube.com/watch?v=2ArW-sA8NsQ[/video]

 

[Crash Enburn]

Dang. Every time I think I've got something figured out, something else comes along to disprove or at least challenge it.