DIY Wing: MSHD GLTC 500

Grid Life Touring Cup (GLTC) has rules for three different size wings:

• Small – You can use a small wing or spoiler that measures under 250 square inches, and there’s no lbs/hp penalty to using one. You can buy an extruded 135cm wing on eBay for $60 or make yourself a spoiler. I tested both in the wind tunnel, and it’s definitely an advantage over using no rear aero at all.
• Medium – If your wing measures under 500 square inches, your car takes only a 1% penalty to lbs/hp ratio. The easiest solutions are a 54” 9 Lives Racing wing, or 55” Procar Innovations. I tested both wings in the wind tunnel, and they are both solid choices.
• Large – The maximum size allowed in the GLTC rules is 701 square inches, and incurs a 3% penalty to lbs/hp ratio (or 4% when used with a splitter). There are a number of quality 2D and 3D wings to choose from that are class legal.

The focus of this article is only the mid-sized 500 square inch wings. There are already a couple good aftermarket wings to choose from, but I wanted to create a custom wing that makes more downforce than anything currently available. The way I’ll do that is the following:

• By maximizing the wingspan to chord ratio, for a particular car.
• By choosing an airfoil that has the most downforce.
• By creating a 3D shape that is customized to the car’s roofline shape, at the ideal wing height and setback distance.
• By making it very stiff and light. I made this from foam and fiberglass, and the end result is half the weight of an aluminum wing, and only slightly heavier than carbon.

Dimensions

Since this wing is completely custom, I can make it any size I want. When designing a wing for a car, the general rule is to go as wide as the rules allow, which reduces relative losses from wing tip vortices. Many people have heard the concept of a high aspect ratio wing, and making the wingspan as wide as the rules allow, you get the highest aspect ratio.

This particular wing is designed for a Miata, which puts the wingspan at 64″ max. For a 500 square inch wing, this defines the chord at 7.8″. (For a 700 square inch wing, I’d use the same wingspan and make the chord 11″.)

Airfoil

The aviation airfoil with the most lift at low Reynolds numbers (low speed or small chord – same thing) is the Selig S1223 and S1223 RTL. There are several scientific papers written on the Selig S1223, and you can chase those down if you want confirmation. These scientific tests were all done on aircraft, and cars are different.

A proper motorsports wing can have even more downforce, because it doesn’t have to fly. A bunch of research was done on this by Enrico Benzing, and I refer you to my article on Car Wing Comparisons for those conclusions. There’s been additional research into car wings, and one that is particularly good is called the MSDH.

The MSHD airfoil is a lot like the Selig S1223 in shape, but has more camber. I traced the two airfoils onto a piece of paper, and the MSHD looks like someone just pushed down on a S1223 and increased the camber. The airfoil shapes are otherwise very similar.

3D shape

When you extrude a wing from aluminum, it comes out as a 2D shape. When making a custom wing from composite materials, there’s no reason to build a 2D wing.

Cars have cambered rooflines, and so air comes over the center of the roof at a different angle that at the sides. For example, on a Miata, air going over the middle of the roof comes down at a 5-degree angle. Towards the sides of the roof the angle is 7 degrees. And the area outside the wing stands is at zero degrees.

If you set a 2D wing to 10 degrees angle of attack (AOA), that means there are parts of the wing that are at 15 and 17 degrees, which on most airfoils would stall. Stall means air separates which results in more drag and less downforce. When airplane wings stall, they fall out of the sky.

If you set a 2D wing at say 3 degrees AOA, the middle of the wing is at 8 to 10 degrees, which is ideal. But you do lose a little bit of downforce at the ends of the wing, which are only at 3 degrees. So ideally the ends of the wing should be twisted downward so they are in the same 10-degree angle.

The angle that air comes down the roof different at different heights, and setback distances. I made a tool for measuring that, and so I know the exact shape of air as it hits the wing. I turn, this allows me to design a 3D shape that makes the most downforce over the entire wing.

On paper, a 3D wing calculates to about 5% more downforce than a 2D wing, which results in a 14% better lift/drag ratio in free stream air. (Free stream data is worthless, I only include that here because everyone else does.) 5% more downforce is not a huge difference, but if you’re limited by 500 square inches, you need to optimize every inch of it.

Construction

The wing is constructed of foam and fiberglass. Carbon fiber would be better, but for a prototype, the increase in cost and complexity isn’t worth it. I used biaxial fiberglass and silica microspheres to create a strong and lightweight composite.

This is a essentially surfboard construction, and weighs just 5.5 lbs. It supports my full body weight, no problem. It has some flex to it, but is way stronger than I’d anticipated, and I certainly overbuilt it.

Gurney flap

Most 3D wings have expensive Gurney flaps made out of carbon fiber. This is necessary because the rear edge of the wing is also a 3D shape, and so you can’t just slap a piece of angle aluminum on there. But I spec’d this wing to have a straight line across the rear of the wing, so that it would be easy to add a wicker (or even a second element).

The general rule in aviation is that Gurney flaps are 1-3% of the chord. Smaller is usually more efficient for airplane wings, but we are talking cars here which go slower and have terrible aerodynamics. Using a larger gurney flap makes the wing itself less efficient, but makes more downforce, which in turn makes the car as a whole more efficient.

For cars, 1/2″ Gurney flaps are the most common. This works out to 6.4% of the chord on this wing, which is a little large, and if I could find 3/8″ locally I would have used that instead, as it would result in a 5% chord wicker.

I tested the wing with and without a Gurney flap, and while the wing was 11% more efficient without the wicker, the L/D ratio of the entire vehicle was 12% better with it on. In this restricted 500 square inch size, you definitely want the wicker.

Wind tunnel testing

I tested three 500 square inch wings in the wind tunnel, and the MSHD was the clear winner. It’s difficult to say how much of the performance is from the advantages of the MSHD airfoil, the higher aspect ratio, or the 3D shape. (This was tested on a Veloster, not a Miata, but the roofline is similar enough that the 3D shape conferred some benefit.)

By fully optimizing the MSHD wing with a Gurney flap and the best performing end plate I tested, it’s possible to outperform a standard 701 square inch wing. I was surprised by this result, and it shows how important it is to customize aero to a particular car and rule set.

To recap the benefits of this wing.

• The MSHD airfoil is designed for motorsports applications and has the most downforce of any airfoil I’m aware of. This results in the greatest lift/drag ratio of the vehicle.
• The wing can be built custom to any car or rules specification. By using a 3D shape that conforms to the shape of the roofline, the wing can make the maximum amount of downforce across the entire wingspan at any height or setback distance.
• The wing is composite structure that is both strong and light, reducing weight and polar moment of inertia.

Am I selling these? No. Or at least not yet. I might sell prototypes that I’m no longer using for testing, or make a one-off for a friend. But I have zero interest in dealing with material shortages, shipping problems, irate customers, and all the other crap that goes along with being a manufacturer. Hopefully I’ve provided enough information for DIY wing builders to go on. So get on with it.