Looks very similar in shape to the DHP wing element.

If you were going to be putting together multi element wing, how does that change what wing elements you would choose?

Thanks,

Dave

 

Not a wing expert here, but I would assume you'd want a less cambered large element with a 2nd element about 1/3- 1/4 the size of the first. From my limited knowledge, a dual element design should allow similar or higher Cl with a lower Cd. . . or use the same highly cambered single element along with a 2nd element to gain a much higher Cl with only minimal Cd increase. . .

Email David and he can tell you what he found out in his initial wind tunnel testing back in his days of FSAE regarding overlap, AOA of 2nd element, spacing between the two, etc . . .

 

I'm no physicist but the way I see the wing's downforce is that it's not actual weight -- so it doesn't have mass. It's simply "force" in a single direction - like someone pushing downward. So this downforce will help the wheels "dig in" and "push down" for better traction but without the downsides that the extra mass would have.

In other words you don't have extra mass to accelerate (except for the drag created by the wing), decelerate, rotate, or to deal with in a lateral change of direction.

You do have a point in that it will affect the verticle tracking of the wheels over an uneven surface. But because you're not increasing mass in the verticle axis, the wing will quickly push the wheel back down to the road faster than if it was to have to rebound (up against the spring and back down again) on its own. And that's where the wheel needs to be for maximum grip right - on the road again!

Disclaimer - This is the way I have had it explained to me and the way I percieve it to work. I have no hard evidence or measurable results to support any of this. I would like to see how (and if) it really does work in practice though...

 

That's about what I would say. When you get technical you really have to be careful when you say weight or mass. This is why aero is effective. It increases normal force and increases grip, but doesn't increase inertia so it doesn't require more work to turn.

It is very effective, but hardly any sanctioning body allows it.

d

 

I assume by "optimal" you mean maximum downforce. If so, as much load as possible is carried on the first half to 2/3's (roughly) of the airfoil, then the velocity (suction) is decreased rapidly towards the trailing edge. This it not to say the airfoil won't have significant camber, but it may not look as pleasing to the eye as the airfoil in question. Finally, there are a broad range of airfoils that will perform well, the difference in max downforce between a good airfoil and the optimum airfoil for a particular car will not be great.

 

if you're only going to do a single element wing the selig 1223 profile is tough to beat.
http://www.ae.uiuc.edu/m-selig/ads/coord_database.html


RE: finding the stall angle of the wing. tuft testing will lead to false conclusions because the tape/tufts will cause the flow to separate early on the bottom side of the wing. oil dot testing is FAR more effective for stall indication. mix up some 3-in-1 oil with something to color it(chalk powder works well if you're testing a carbon colored wing). put dots of your mixed up oil in rows across the wing. cord-wise streaks tell you the flow is attached and span-wise or reversing streaks tell you the air is not attached.

also, this place is pretty cool for getting cores cut. he has tons of wing profiles already in his database. you just tell him what profile and how big and it shows up in the mail.
http://www.flyingfoam.com/CustomMain.html

 

That is a great website. The S1223 has the features I would expect for a car wing, I would order the wt data to be sure.

As for oil dots, I agree this is an excellent form of flow visualization - great suggestion. Tufts can be made to be nearly nonintrusive, but then they're hard to see. An advantage of tufts is that they don't have to be reapplied between runs, unlike oil. However, reapplying oil to a wing is no big deal.

 

Im suprised noone has talked about wicker bills (Gurney flap) yet





If you want to run a fairly high angle of attack, you should think about a gurney flap. to keep the flow attached to the wing, the gurney flap creates a low pressure twin vortex behind the wing, basically pulling the lower flow back onto the surface of the wing. less drag, more downforce is achieved.

 

I go skiing for 4 days and this thread blows up! Some good stuff in here.

In terms of the wing position on the car, it is a factor based on the cars CG. Any force applied to the rear actually creates lift in the front based on the car pivoting around the CG. That's why changes to rear down force need to be balanced with additions to front down force.

I'll read up on some of the suggested airfoil shapes tomorrow.

 

I seem to recall the Evo IX having a little rubber one on the stock wing. Anyways... back to the discussion

 

Whoa whoa whoa. How is this true? The pivot action will be around a fixed point, specifically the mount points of the rear suspension. A Seesaw doesn't pivot around the CG, it's pivot's around the fixed point. If you push really hard on the trunk (well it'll collapse) the front wheels will come up, as will the CG, but the rear wheels will remained fixed.

...right?

...and if you apply force between the front and rear axle planes, there should be none of this effect at all...

Did I miss a day of school somewhere?

d

 

 

the wing will generate a pitching moment based on it's distance from the CG. the springs will react that moment based on their distance from the CG. the exact point that it rotates around is of little consequence, but there is no guarantee that it will rotate around either front or rear tires, or the cg.

 

^^^ That's a more accurate way to put it.

 

I should have taken the Micro Air Vehicles capstone project my senior year to prep for this project