Fenders?

[bracketracer]

I've been reading all over this cool site and I have a question for the Pros. I see pretty much all of the fast cars are running front and rear fenders (or at least rear ones) and John's video shows that proper fenders lower the time of even a single car. I watch the video with the cardboard sail attached that demonstrated that drag does matter more than a tiny bit. I saw a (I think it was Skippy's Delayed Sword) car that has the upper back side of the wheels covered. Has anyone tried mounting fairings behind the wheels instead of or in addition to the fenders? I was playing on NASA's wind tunnel sim earlier with a cylinder shaped object and it looked like there was quite a bit of turbulence behind the cylinder, especially when it was rotating. I'm not really sure how much their sim relates to ground bound missiles like yours but I was just curious. There has to be some trade off between weight, balance, aero and speed I guess?. It could be it's not even worth messing with? Just something I was thinking about trying when I get our test track done. Stephen

 

[txchemist]

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.

 

[DerbyDad4Hire]

I have never seen a car like that do as well but I haven't done any testing with it yet. I will put that on the growing list.

 

[5KidsRacing]

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.

 

[bracketracer]

txchemist- you may have a devious streak I think! I really wondered how much the fenders help you vs how much they impair the competition. In DD4H's video, the obviously helped a car running alone and you wouldn't see so many in competition if it didn't have some benefit besides just looking fast.

DD4H- If anybody can make it work, you da man!

5Kids- I was thinking of running full fenders front to back. I thought that would cut down both the turbulence behind the front wheel and in front of the rear wheel at the same time the best. I'm still not convinced that the plusses will outweight the minuses? I'm also curious to see how well it does alone and in traffic.

Ever seen anyone make shields that go inside the wheels, something like a drum brake backing plate attached to the body? It would need to have a slight offset underneath to clear the guide I suppose. Would that keep air out of the hollow side of the wheels without adding frontal area?

 

[OPARENNEN]

FYI, I tested the same SS car with three fender shapes.
1. One over the top of the wheel, and about 1.5 inches long.
2. One 1.5 long, but the top of the fender if you sighted the fender on top, it came even with the top of the wheel.
3. One much smaller, about one inch, and shorter at the long end so you could see a bit more of the top of the wheel.

Fastest times = 3 best. 2 second (but very close). 1. was worse by far.

This was on a 42 foot single lane test track late last year. I don't remember the times any more.

I also believe that the flutter from neighboring cars would affect long fender the worst, but that is only my logic, i.e. not proven.

Also, look and pictures of some of the pro cars, i.e. F1's or Indy's.

 

[GravityX]

I'm playing with the faring behind the wheel idea. I have been putting one together, fighting the design, but it will not make it in time for the April race, work/time constraints. Who knows if it's going to be faster or not, on paper I think it would, but real world testing will be the final determining factor. I have no test track. I'll get there though.

EDIT: This thought just came to mind. Take a non-fendered cars and run it down the track backwards, I know it isn't the most effective way to do things, just after a baseline time. Then do the same thing for the fendered car, in effect placing the faring behind the wheel now. A lot of fudge factors in doing it this way though, steering, weight in the front of the car, squared backside as opposed to a sloped nose, negative camber on front wheels now, one wheel lifted in the back now, etc... MAYBE not a good idea after all. Oh well...

 

[txchemist]

A poor mans track/wind tunnel experiment. On whatever you use for a tuning board, I hope it is wide enough to "race" two cars at a time. I adjust the slope to get about a 3 second roll. Now we want to simulate the car going 10.5 MPH as it does on the typical track. Set up a fan at the finish end blowing towards the start to blow at your cars and take a good guess at the wind you are now providing (tune cars to roll with no drift).
Now start messing with fenders and have some fun as you watch the relative changes between your two cars, one with fenders and the other plain.

Obviously not as good as a real track, but surprisingly useful if you have no track.
If you only have room for one car, you can make a poor mans timing system with free sound software and a mike set on your tuning board and plugged into your laptop. I put a thin broad at the end where the cars can make a distinct sound when they hit. I use a falling object that drops when I start the run by moving another thin T-stick that the car rests against. The sound wave can be analyzed with the start and stop fairly crisp if you work at it.

 

[IAE Racing]

cool thoughts.

 

[Papa V Racing]

Posted by bracketracer

Ever seen anyone make shields that go inside the wheels, something like a drum brake backing plate attached to the body? It would need to have a slight offset underneath to clear the guide I suppose. Would that keep air out of the hollow side of the wheels without adding frontal area?

Quicktime - Have you tried doing this to all your wheels by chance? Maybe this is something to look into doing.. I had a post and SK had did one about covering the top open area where the wheel was opened...

Bracketracer now brings up an interesting idea and I knew your car had it done on one of the wheels and was thinking if it had ever been done for all 4 wheels... I am not sure how long it takes to do a set of wheels like your front left wheel....

txchemist you keep us all thinking on this board I know I read your threads and I continue to research....

Got to go power is getting shut off to to fix power failure earlier.... Hope to read more about this idea.....

V

 

[bracketracer]

FYI, I tested the same SS car with three fender shapes.
1. One over the top of the wheel, and about 1.5 inches long.
2. One 1.5 long, but the top of the fender if you sighted the fender on top, it came even with the top of the wheel.
3. One much smaller, about one inch, and shorter at the long end so you could see a bit more of the top of the wheel.

Fastest times = 3 best. 2 second (but very close). 1. was worse by far.

I could see that being true. Maybe I should try a fender made like #3 in front and behind the wheel and then try a long pod the length of the car. I'll put that on the list!

Maybe I could use a fog machine to see the effect of cars racing side by side? I don't know if time alone would tell the whole story.

Papa V, I saw that covered wheel. I thought that was just on his NDFW? That's the one he used packing tape on or something else? Same idea, keep the air from swirling in the cavity of the wheel. I noticed his car has the shorter height fenders too, not over the tops of the wheels.

 

[Kinser Racing]

When I first started racing Pro, I used covers like that on all the wheels and it made no difference. The car was slow. /images/boards/smilies/smile.gif

 

[5KidsRacing]

I filled the wheels with very light Styrofoam, I think I copied it off of DD4H... it was not faster for me/images/boards/smilies/frown.gif

 

[bracketracer]

When I first started racing Pro, I used covers like that on all the wheels and it made no difference. The car was slow.

Given my level of experience at this, I bet my first entries will be slow too! I'm just trying to build a faster slow car!

 

[bracketracer]

I filled the wheels with very light Styrofoam, I think I copied it off of DD4H... it was not faster for me

Wouldn't that make the wheels heavier though? I want to attach it to the car body instead.

 

[Quicktimederby]

I have made the same covers for the rear wheels of my SP once, for me there was no gain to be found. I never went any further with it. .

 

[5KidsRacing]

I filled the wheels with very light Styrofoam, I think I copied it off of DD4H... it was not faster for me/images/boards/smilies/frown.gif

Wouldn't that make the wheels heavier though? I want to attach it to the car body instead.

Yes, but I believe at the time I just copied everything John did.... quite the follower I was/images/boards/smilies/smile.gif

I think a racer back in the PDDR days built a slick looking car that had something like that on it? I could be wrong here, but was it Advanced Technologies? He never raced that car and I know he is a member here... maybe he will speak up.

 

[txchemist]

A way to run some tests. As suggested, a barge board ( or faring) is a way to divert the turbulent air from a spinning wheel away from the car so the back of the car does not have to deal with it. The diverted air might also effect the car next to it.
Thin aluminum from a soda can.
Punched hole with a paper punch where axle goes.
Glue with Gorilla Glue.
Easy to put curve or straight fin behind DFW. Easy to change distance from wheel effect. I will say that fin straight was very close to speed without fin but slower, so I would say the additional surface drag was more than dropping turbulence inside the wheel well, but this fin is a bit big to study potential mess up the car next to you.



and with the wheel in place. Ran tests with different amounts of curve. Kept frontal area of car no wider than existing wheel. Ran another car in the next lane and studied effects.

out of focus shot close up.
Have fun. All I will say is I can get some violent changes in time.

 

[bracketracer]

I will say that fin straight was very close to speed without fin but slower, so I would say the additional surface drag was more than dropping turbulence inside the wheel well, but this fin is a bit big to study potential mess up the car next to you.

Wow, even though the fin was flat, just having that extra surface area to drag through the air slowed the car. I think that just might reinforce the need to try just a shield inside the wheel? I know it wouldn't increase the frontal area and the increase in profile surface area should be minimal. I just want to study a reduction in turbulence in the wheels to see if there's a measurable gain. From what QT wrote it doesn't sound like it's going to help, but I think I should try it anyway.

 

[resullivan]

Does anyone have a template they use for fenders?