Originally Posted by rharris19 (Post 1186590)

The first reason is that I didn't want to have the natural state of the wing in a high drag position in case something failed and it stayed there.

Second, for us to take advantage of the wing at a higher angle in the turns, we would need a much better front aero setup than what we have or the car would have pushed.

Most importantly, I wanted to make it a passive system that didn't require the driver to think about one more thing during his 2 hour stint.

I suspected that, at the speeds we were at, we wouldn't get a whole lot out of a low drag system anyway. The air brake was our main curiosity to test functionality and reliability. It met and exceeded our expectations on both. We are still looking at a low drag setup that can be integrated fairly easily into our current if for nothing other than to play around with for grins.

In the video above, it seems as thought there is an initial delay in response from the wing, but that is because I had to switch it on to show the guys it could be turned on and off.

Originally Posted by rharris19 (Post 1186593)

Even if we wanted to set it up this way, we couldn't as the system to actively control it would cost enough to be prohibitive to ChumpCar's rules.

Originally Posted by cyotani (Post 1186595)

Wouldn't the natural state of the wing be at the normal angle of attack you set up if it were an static wing?

Originally Posted by cyotani (Post 1186595)

An arduino is $15 and can control the system. But if I'm understand that correctly, in the rules the added cost for an additional control module is excessive vs no added cost for activating it off a brake switch?

Originally Posted by Jack Olsen (Post 1186550)

100 mph is about the slowest speed I'd be using it at. Does the news get any better at 130?

Originally Posted by rharris19 (Post 1186629)

Using a stock head light motor you only have two positions out of the four :higher drag, braking, low drag, and the position you would use for a static. We chose to use it for where we would have it for a static wing and braking for the sake of simplicity for this first test.

I could easily adjust the rod down some to where it would be going between a low drag angle and higher drag for turns. The switch could be moved to the steering wheel on a button to actuate it, but this would now make it an active system that my drivers would need to pay attention to. I'm hesitant to add yet another thing to pay attention to in an endurance race.




You are understanding that correctly. To be fair though, to make the Arduino Board work, you will also need a GPS antenna and steering angle sensor, so the whole setup is more than just the cost of the board itself.

Originally Posted by Failure (Post 1186665)

According to tonight's napkin math, your wing creates 18 lbf of drag at 0* AoA and somewhere between 55 and 73 lbf of drag at 15* AoA and 120 MPH.

Originally Posted by cyotani (Post 1186667)

Does your equation take into account the gurney flap?

Originally Posted by Failure (Post 1186665)

According to tonight's napkin math, your wing creates 18 lbf of drag at 0* AoA and somewhere between 55 and 73 lbf of drag at 15* AoA and 120 MPH.

Originally Posted by Jack Olsen (Post 1186670)

So... worth it, or wasted effort?

And while I've got a smart guy's ear, what's the correct way to measure wing angle with an airfoil that's been modified for increased camber. Is it still a line from foremost to aftmost points, even if that seems at odds with the bulk of the airfoil?

Originally Posted by cyotani (Post 1186708)

Originally Posted by Failure (Post 1186722)

Well damn, now I wish I hadn't corrected myself earlier. I could have claimed to be able to do CFD calculations with nothing but a pen, paper, and an XFOIL analysis. On topic, can you do this again at 0* AoA and post results for comparison?

Originally Posted by Leafy (Post 1186709)

For something like this I just do a 2d solve for an area thats is a convenient multiple of with wing length and multiply but the length of the wing and assume its going to be a little big higher lift and lower drag than if I spent hours waiting for a 3d solve. For my wing to get accuracy in the slot I've got to be damn fine mesh, which means 10 minutes to 2d solve or go to bed for a 3d solution.

Originally Posted by cyotani (Post 1186724)

Your math method might be closer to the actual solution. However if it leaves out the gurney flap I would question it since that's a major part of the airfoil design.

Originally Posted by Failure (Post 1186728)

Even without the issue of the gurney flap, my method doesn't consider the effects of what's going on at the wing tips. It doesn't seem like too bad of an issue for DIY aircraft hobbyists, but it is for us since we're so limited on span and have to make up that surface area with more chord. Lower aspect ratios mean that wingtip vortices affect a greater percentage of the wing, so endplate design has a huge effect here and that's an area I've found almost no reading material on. I don't even know if the effect of endplates varies with AOA or not.

For the time being, I'm just going to consider the whole matter of endplates black magic and leave it to you and your CFD wizardry.

Originally Posted by rharris19 (Post 1186590)

In the video above, it seems as thought there is an initial delay in response from the wing, but that is because I had to switch it on to show the guys it could be turned on and off.