Thursday, August 23, 2012

Winging it

(Note: Getting a bit behind on posting... will post the latest races shortly)

I'll just build a wing... it only take what a couple of hours... I'm sure you can guess how that turned out. After many more hours than I had originally planned, I bolted on my wing and closed the hatch and secured it all with hood pins. The goals for the project were these:
  1. Create some usable down force to balance out the tail-happy nature of my car. 
  2. Secure the wing without cutting holes in my Rear clam
  3. Make it possible to remove the wing for regular street driving.
  4. Don't have the wing rip off and destroy my deck lid or crush my clam.
  5. Admit that it's going to be ugly and just get on with it 
For goal 1 I figured that I didn't have money/access to things like solid-works, and my materials and workmanship were likely to be significantly sub-par, so that left only one thing... Make it BIG. I designed it to the maximum specifications allowed by the class. It is 60" wide 19" chord for just slightly less than 8 sq. ft. The width leaves about an inch of the outer swoosh of the door sticking out on either side. The height is adjustable, and with the car being 43.25 inches tall, I can raise it to the maximum height of 49.25, though I'll probably just do 49 to be safe. The front attach point is just barely less than 6" in front of the rear axle (giving it as much leverage as possible vs the pull of the wing), and the back of the wing is just forward of the out most curvature of the rear of the clam. Any bigger in any direction and it's not legal. The only thing I didn't max out was the size of the end-plates, and that's only because I misread the rules, and thought it was a total of 200 sq inches rather than 200 sq inches each.

The reason for Goal 2 is that the rear clam shell of the car is about $3000 to replace. If I screw up putting a hole in it and crack it, or the fatigue over time causes it to crack it's about five times as expensive as a deck lid. Also, the deck lid must remain functional (more rules) and if the wing lifts with it, then the wing can be bigger than the distance between the rear of the deck lid and the rear of the clam (which is a lot less than 19 inches). 

Goal 3 is strongly related to goal 5. I didn't want to spend a lifetime on this wing, or a fortune on materials, so I knew from the start it was going to be ugly. Therefore I don't want to have to wear it all the time. Besides being ugly it will also suck up gas on the highway, and possibly draw attention from the constabulary.

It might seem like goal 4 is obvious, but clearly it's also going to influence the design. Large fender washers and hood pins hold it firm. The biggest worry is that the hinges on the deck lid will give out, but after 2 races it seems to be holding ok.

Goal 5 is inevitable since I don't want to put too much time & money into this, but I've decided that this car is mostly for racing, so that comes first. The wing does get removed for regular street use anyway. Over time I may see if I can improve the looks, but don't hold your breath... How ugly? well, decide for yourself...



The result? The car has become more stable at speed. However I probably have a couple years of bad habits fighting the tail happiness to shed... I'm finding it hard to trust the car in places where it used to be difficult. As for the specific results, that's the next post...

1 comment:

Gus said...

As a follow-up I'd like to note that the wing has been a great success. I was worried that the lack of CAD and analysis, and sub par materials would prevent me from generating enough down force, or leave me with durability problems. A couple of patches have been necessary where the metal poked through the covering material, but otherwise it's held up well. It also produces more than enough downforce. In fact I have to set it at slightly less angle than the rules would allow because it causes the car to understeer in fast sweepers at full height. The conclusion - size does matter :).