Science Buddies: "Ask an Expert"

Hello,
I have been doing lots of research on aerodynamics, and especially with wings and winglets for my science fair project. This area is of an interest to me mainly because I fly real airplanes and already know about the forces of flight and such. However, I recently changed my topic because of the difficulty in measuring forces on a wing such as drag in a wind tunnel. Now, I have decided to measure the drag of model cars in a wind tunnel that I am building myself. I am not sure what my variables could be - I have thought about comparing the drag of a model car, truck, van, and SUV. I don't think I will be very satisfied in picking a variable such as this. My question is - what other possibilities do I have for variables in measuring the drag on a model car? Thanks

P.S. I found this for a guide for my wind tunnel. I am designing it to be similar to this, but able to use larger cars for more reliable data. http://www.techdirections.com/BuildAWindTunnel.pdf

Most of the typical areodynamic studies of buildings and cars and trucks involve questions like "How can I alter this thing to reduce some unwanted propert?" because these are the kinds of questions that have an associated economic factor. If you can reduce the wind load on some stationary structure you can design for lower forces. If you can reduce the wind resistance of a vehicle, the you get a better fuel efficiency. Not sure that this helps you figure out what you want to investigate; however, as an engineer, I would start with some scientific question that has some economic cost factor and us that as a basis for my scientific hypothesis. But that is just an engineer's perspective on doing physical science.

Drag is only one of the forces placed on a vehicle when its in motion. Gravity and lift will also be acting on you models while they are in the wind tunnel. In other words, you can check if how increases in wind speed cause the vehicle to hug the ground more, or does a vehicle tend to lift and become lighter. Both of these factors will affect the vehicles' traction. These factors can cause safety problems on highways where lots of cars and trucks travel at high speeds.

Another interesting area you can investigate in wind tunnels is the slipstream created by certain vehicle designs. Slipstreams are the areas behind moving objects where pressure is lower because the object pushes the air out of the way. When one object follows another in its slipstream the reduced drag can improve the second vehicle's fuel efficiency. Migrating geese flying in a V-shpe formation use the slipstream. Their leader cuts through the air and the others following in the arms of the V get to fly along with a svings of energy to themselves because they are flying in the slipstream of the ones ahead of them. Following another motor vehicle closely on the highway (not reccommended for safety reasons) and staying in its slipstream allows the vehicle that is behind to save fuel due to reduced drag. Professional race car drivers use the slipstream to their advantage during races to follow and even slingshot past cars in their lead.

Its a great project idea! Have fun and good luck.