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Thread: B13 aerodynamics - rear/side windows

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Posts: 1-6 of 6
2016-10-18 19:18:27
#1
B13 aerodynamics - rear/side windows
I've pondered various aerodynamic ideas since I started building my track car. Looking for some thoughts from the gallery on aerodynamic issues when removing the rear window, and any benefit from replacing the rear side windows with Lexan.

Two of the racing series I'm looking at competing in, 24 Hours of LeMons and World Racing League both allow the rear glass window to remain intact. ChumpCar, however, requires that this glass be removed, with optional replacement with Lexan or similar material. I don't see Chump in my future for 2017, but after that, who knows. Side glass in the back must come out regardless of series, so in addition to the driver and passenger door windows being absent, I've got those two largish holes in the back to consider.

One site I've been reading over and over is Car Aerodynamics Basics, How-To & Design Tips ~ FREE!, lots of good information there. But, it doesn't really cover the situation with the various windows being removed.

One thing that I've heard from a lot of places is that with the rear window gone, fumes and air in general tends to get sucked into the car from behind. I've seen more than one video of a fire from the rear of the car getting sucked into the cabin as well, not a pretty sight. So, in general, having the rear window missing seems to be a bad thing from a race perspective. I'm still trying to understand exactly what's happening with the airflow that would cause it to get sucked back in like that, lower air pressure in the cabin from the side windows being open, and higher pressure from air traveling over the top of the car is my leading theory, but I haven't found any site that shows this modeled to confirm.

Those of you that have raced B13s, any thoughts to share or any experimentation that you may have done here?

Side issue, there seems to be a lot of lift in the middle/rear of the car from air moving over the top, and I know that the B13 spoiler is more for looks than being truly helpful. Any ideas for increasing downforce in this area would also be appreciated.


And for the record, I'm definitely overthinking this whole thing and 110% have delusions of grandeur.
2016-10-19 14:43:19
#2
Both of the twins have Lexan in the rear 3. The sides are easy, just take cardboard to make a template, cut, drill holes and rivet in. The rear does require support bars, otherwise it will start flexing. The about of flex will obviously depend on the thickness of the Lexan. One thing to keep in mind is that with more sun exposure, the Lexan will fog up and require a good wet sanding to clean up.

I will try to find some pics of the rear windshield for you.
2016-10-20 14:51:00
#3
Originally Posted by LAM-PARK
Both of the twins have Lexan in the rear 3. The sides are easy, just take cardboard to make a template, cut, drill holes and rivet in. The rear does require support bars, otherwise it will start flexing. The about of flex will obviously depend on the thickness of the Lexan. One thing to keep in mind is that with more sun exposure, the Lexan will fog up and require a good wet sanding to clean up.

I will try to find some pics of the rear windshield for you.


I know this can be done, my question was really about what difference it makes to the aerodynamics of the car, the impact to performance (speed/handling/etc). I'm not in a position to be able to collect data yet with my own car.
2016-10-21 19:44:16
#4
Originally Posted by jimbo_se-r
Originally Posted by LAM-PARK
Both of the twins have Lexan in the rear 3. The sides are easy, just take cardboard to make a template, cut, drill holes and rivet in. The rear does require support bars, otherwise it will start flexing. The about of flex will obviously depend on the thickness of the Lexan. One thing to keep in mind is that with more sun exposure, the Lexan will fog up and require a good wet sanding to clean up.

I will try to find some pics of the rear windshield for you.


I know this can be done, my question was really about what difference it makes to the aerodynamics of the car, the impact to performance (speed/handling/etc). I'm not in a position to be able to collect data yet with my own car.


For a lemon's car?...lol. Dude, run the thing and have fun. When you get your first full sideswap by some pile of crap Oldsmobile 98 and and the fender is dangling half off in the breeze, you'll see how funny your "aero" concerns are. Have you ever been to a Lemons race? if not, you should go and see what you're getting yourself into....2 cents
2016-10-21 20:52:33
#5
Originally Posted by hammerin
For a lemon's car?...lol. Dude, run the thing and have fun. When you get your first full sideswap by some pile of crap Oldsmobile 98 and and the fender is dangling half off in the breeze, you'll see how funny your "aero" concerns are. Have you ever been to a Lemons race? if not, you should go and see what you're getting yourself into....2 cents


Ummm, yes, I've been to LeMons races. I've driven in 6, also driven in 3 for Chump, and 1 for WRL. Not the least bit of contact in any of those, at least while I was driving. I can't always speak as highly of my teammates...
2016-10-22 12:18:01
#6
I'm with Hank. I wouldn't worry too much about it in Lemons. Having the rear windshield gone may not be as much of a detriment as we think. Studies have been made on pickups, for example, that show that a truck is more aerodynamic with the tailgate up than it is with it down. It depends on what pockets of air are created once that window is out. Having the side windows out is definitely a negative for aerodynamics. I would cover up those if you could.

From a handling perspective usually it's beneficial that there's less weight without the glass. Although this places more weight distribution up front.

Again though, unless you are turbocharged you won't see speeds to where aerodynamics is a serious problem. A front splitter and rear spoiler is all a b13 really needs to keep buttoned down. I would focus more on driver time.
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