Post your DIY aero pics
05-05-2013, 02:18 PM
#381
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HeresJohnny - first of all, bravo, for trying some active aero.
I do see some theoretical problems with that though - usually from what I've seen air brakes are done with spoilers, not so often with actual airfoils. Coming into a braking zone and having the airfoil drastically change angles as you transition onto the brakes could do some very funky things to your grip balance - you might get a sudden increase in rear downforce as the angle increases, taking weight off your front tires momentarily, and then all rear grip will go away a moment later as the wing passes its stall angle. This would be much worse in higher speed braking zones - there are several tracks around here that have 130 mph to 50-70 mph braking areas. If this is intended for autocross, it might work better as the wing won't be creating massive downforce at those speeds, so the change in downforce as the wing moves will be less severe..
Just thinking out loud here.
-Ryan
I do see some theoretical problems with that though - usually from what I've seen air brakes are done with spoilers, not so often with actual airfoils. Coming into a braking zone and having the airfoil drastically change angles as you transition onto the brakes could do some very funky things to your grip balance - you might get a sudden increase in rear downforce as the angle increases, taking weight off your front tires momentarily, and then all rear grip will go away a moment later as the wing passes its stall angle. This would be much worse in higher speed braking zones - there are several tracks around here that have 130 mph to 50-70 mph braking areas. If this is intended for autocross, it might work better as the wing won't be creating massive downforce at those speeds, so the change in downforce as the wing moves will be less severe..
Just thinking out loud here.
-Ryan
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05-05-2013, 03:31 PM
#382
Could you revise your design to only actuate the second element of the wing? I'd expect that to make it less susceptible to the issues that Ryan voiced.
I've put some thought into active aero and have what I think would be a decent design for an active spoiler/air brake. It'd resemble any other comically large auto-x spoiler when raised and lay flat against the trunk lid with a few inches of overhang off the back when lowered. If somebody wants my CAD files, parts list, and control logic, I'd be glad to share. I mean, it's an untested design and my files aren't complete but it'd make a good starting point. It's something that I eventually would like to make however I need to get my car running first.
For example, this is the assembly that bolts to the inside of the trunk lid and forces the base of the spoiler back to raise it up. If my math is right, this will push the spoiler though it's full range of motion in under a second.
I've put some thought into active aero and have what I think would be a decent design for an active spoiler/air brake. It'd resemble any other comically large auto-x spoiler when raised and lay flat against the trunk lid with a few inches of overhang off the back when lowered. If somebody wants my CAD files, parts list, and control logic, I'd be glad to share. I mean, it's an untested design and my files aren't complete but it'd make a good starting point. It's something that I eventually would like to make however I need to get my car running first.
For example, this is the assembly that bolts to the inside of the trunk lid and forces the base of the spoiler back to raise it up. If my math is right, this will push the spoiler though it's full range of motion in under a second.
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05-05-2013, 10:12 PM
#386
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What I was thinking of awhile ago was to put a speed brake that would be like the factory trunk spoilers (or like Lightyears car with the ABS plastic around the back of the car) , then under braking it would pop up being 4"-6" taller to catch more air. That way it wouldn't disturb the air going to the rear wing as much.
Kinda like this
Kinda like this
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05-05-2013, 10:20 PM
#387
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Is the effective braking from air resistance greater or lesser than the mechanical force of the brakes and rear tires firmly planted?
If the downforce increased in the rear, would that lift weight off the front?
If the stall angle of the rear airfoil is exceeded and the downforce indeed goes away, does the rear end get light? In a very high speed corner where trail braking is occurring, a reduction in downforce could make the rear end catastrophically loose.
I think a smaller angle change might be very effective on a fast track, but as stated before, the large change would likely be effective at lower speeds such as an autocross.
But don't get it twisted, I'm very impressed with the design and the work you put into this. I would love to experiment with it.
If the downforce increased in the rear, would that lift weight off the front?
If the stall angle of the rear airfoil is exceeded and the downforce indeed goes away, does the rear end get light? In a very high speed corner where trail braking is occurring, a reduction in downforce could make the rear end catastrophically loose.
I think a smaller angle change might be very effective on a fast track, but as stated before, the large change would likely be effective at lower speeds such as an autocross.
But don't get it twisted, I'm very impressed with the design and the work you put into this. I would love to experiment with it.
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05-05-2013, 11:17 PM
#389
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My idea was to have 3 positions. Base setting would be at aoa that you require. And run low angle for straights, and high angle for brakes. Could have a switch under acc, and brake to trigger. Or buttons on steering wheel. But was only going to change a few degrees each way. Flipping up all the way will make a huge difference. Be interesting to see how you go.
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05-06-2013, 02:52 AM
#390
^^ Yes! It will take time to determine what is most effective and how much is too much in terms of stall on the wing and the potentially dangerous adjustments to the car's attitude but we all applaud you breaking new ground. Please keep us updated. It may warrant its own thread if you end up with bunch of testing and design revisions. 
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05-06-2013, 05:16 AM
#392
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HeresJohnny - first of all, bravo, for trying some active aero.
I do see some theoretical problems with that though - usually from what I've seen air brakes are done with spoilers, not so often with actual airfoils. Coming into a braking zone and having the airfoil drastically change angles as you transition onto the brakes could do some very funky things to your grip balance - you might get a sudden increase in rear downforce as the angle increases, taking weight off your front tires momentarily, and then all rear grip will go away a moment later as the wing passes its stall angle. This would be much worse in higher speed braking zones - there are several tracks around here that have 130 mph to 50-70 mph braking areas. If this is intended for autocross, it might work better as the wing won't be creating massive downforce at those speeds, so the change in downforce as the wing moves will be less severe..
Just thinking out loud here.
-Ryan
I do see some theoretical problems with that though - usually from what I've seen air brakes are done with spoilers, not so often with actual airfoils. Coming into a braking zone and having the airfoil drastically change angles as you transition onto the brakes could do some very funky things to your grip balance - you might get a sudden increase in rear downforce as the angle increases, taking weight off your front tires momentarily, and then all rear grip will go away a moment later as the wing passes its stall angle. This would be much worse in higher speed braking zones - there are several tracks around here that have 130 mph to 50-70 mph braking areas. If this is intended for autocross, it might work better as the wing won't be creating massive downforce at those speeds, so the change in downforce as the wing moves will be less severe..
Just thinking out loud here.
-Ryan
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05-06-2013, 01:04 PM
#397
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It's a great start otherwise. Use of BMW seat motor is clever too. I've tried looking at a cheap way to accomplish this and everything I found was too slow, too weak, or too expensive. I think Steve is asking all the right questions. Where do you plan on having it engage in relation to braking force? How easy would it be to do what lightyear is saying to have multiple settings using the existing wiring and components? Just considering straight line braking I would think you would benefit more from a maximum downforce configuration to keep the rear from lifting. Pics of the guts of what you got going on there would be cool too.
Thing is I'm not racing as such just doing track days but I like the challenge and testing bit nearly as much as the sideways action.
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05-06-2013, 03:54 PM
#400
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Hey, Redline Time Attack allows active aero in Modified. You have to keep your dash and glove box because they are supposed to be "street cars", but active aero/DRS/etc. is all totally acceptable. 
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