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Old 05-05-2013, 03:18 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
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Old 05-05-2013, 04:31 PM   #382
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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.
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Old 05-05-2013, 04:45 PM   #383
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Flip the end plates out?

Pulling them back in would require some force though.

Another reason for keeping the end plates huge
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Old 05-05-2013, 07:16 PM   #384
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It's a good idea. But would take a ton of force on the mounts. The boot skin may not be strong enough. I wanted to do something similar. What motor/solenoid did you use?
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Old 05-05-2013, 07:28 PM   #385
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Yeah.. needs 1/4" steel uprights for that..
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Old 05-05-2013, 11:12 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
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Old 05-05-2013, 11:20 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.
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Old 05-05-2013, 11:32 PM   #388
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Quote:
Originally Posted by sixshooter View Post
Is the effective braking from air resistance greater or lesser than the mechanical force of the brakes and rear tires firmly planted? .

Jeremy Clarkson said that the Veyron's air brake produces more braking power than a normal car
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Old 05-06-2013, 12:17 AM   #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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Old 05-06-2013, 03:52 AM   #390
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Quote:
Originally Posted by ThePass View Post
HeresJohnny - first of all, bravo, for trying some active aero.
^^ 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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Old 05-06-2013, 06:08 AM   #391
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Quote:
Originally Posted by lightyear View Post
It's a good idea. But would take a ton of force on the mounts. The boot skin may not be strong enough. I wanted to do something similar. What motor/solenoid did you use?
Used a power seat motor from a BMW, was the right speed and really strong
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Old 05-06-2013, 06:16 AM   #392
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Quote:
Originally Posted by ThePass View Post
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'm sure you're right, I started with just the top wing flipping but go carried away
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Old 05-06-2013, 06:23 AM   #393
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Originally Posted by 573 View Post
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 started out with just the top wing moving but more on the DRS lines, then went the air brake route

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Old 05-06-2013, 06:26 AM   #394
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Those mounts look a bit flimsy for that.
It's been a concern, they are stainless steel and there are 1/4" plates on the underside where it bolts through.
I'm thinking the boot skin may deform, we will soon see.
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Old 05-06-2013, 07:43 AM   #395
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Quote:
Originally Posted by sixshooter View Post
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.
Well are you trying to slow down faster or increase the downforce? For example a parachute doesnt cause downforce but will stop you a lot faster than a spoiler would.
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Old 05-06-2013, 12:00 PM   #396
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Originally Posted by HeresJohnny View Post
It's been a concern, they are stainless steel and there are 1/4" plates on the underside where it bolts through.
I'm thinking the boot skin may deform, we will soon see.
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.
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Old 05-06-2013, 02:04 PM   #397
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Originally Posted by rccote View Post
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.
The plan was to put the momentary switch under the brake pedal which would be closed off during hard braking. Although I was surprised how little the peddle arm actually moves when applying the brake so finding the right location will be tricky. Had also considered maybe taking a signal from the tachometer so it only allowed the air brake to operate above/ below a predetermined speed. But at the moment it's little steps at a time and see where it takes me TBH.
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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Old 05-06-2013, 04:02 PM   #398
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Originally Posted by Spookyfish View Post
Took most of the front tires out of the air flow:
Are your spats/canards/whatever they are called in front of the tires vertical or do they have any slant to them?
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Old 05-06-2013, 04:22 PM   #399
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Quote:
Originally Posted by HeresJohnny View Post
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.
I have only thumbed through various CCRs but my hunch is active aero would immediately put you into unlimited classes if it is allowed at all. This is probably more a project for the track day warriors many of us are.
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Old 05-06-2013, 04:54 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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