Aerodynamics and drag coefficient

[element180]

I like the idea of backup cameras instead of mirrors not to mentio being able to place the monitor/monitors where the driver does'nt have to turn his/her head as much taking they're eyes off the road.I think it would be cool to have the monitor mounted in the headliner and flip down (motorized) when the car is started and back up when it's turned off.Makes for a cleaner look when the power is off

[djslik]

One thing I remember from my fluid dynamics class is that there have been instances of lowering the drag force on a car to the point of hindering performance. I forget the complete explanation right now and I don't really feel like doing all the math but one of the car manufacturers designed a car with good aerodynamics which resulted in a low drag force. When the car went up hill and down hills they noticed that the car was being less efficient and actually required more fuel consumption and power to overcome the hills because of the low drag force. Frontal area directly affects the drag force and also does the material you are flowing through essentially air. You also have to take into consideration the profile of the front plate because this creates different laminar and turbulent flow profiles. Having a flat frontal area obviously will have more drag force than a rounded front but you also have to think about the turbulance behind the car created from these profiles. With a better aerodynamic shape you have less turbulence behind the car.

[Fuelie Fan]

I'd like to hear more about that. The only thing i could think of is that you're lowering the load on the engine, resulting in a more efficient operating point on the bsfc map. The cure would probably be to re-gear it. otherwise, P=F*v. if you've lowered F, you've lowered P, and if you've lowered P, you've lowered the amount of fuel that needs to be burned.

[element180]

P=F*v. if you've lowered F, you've lowered P, and if you've lowered P, you've lowered the amount of fuel that needs to be burned.

My brain hurts

[djslik]

I have to do some research if you are really interested I can call up my buddies from college because I know someone knows the exact reasoning behind it, but as far as I can remember, but my memory can be bad sometimes so don't be mad if I'm wrong here, it had some relationship to the pressure behind the car. But I agree my head hurts and I remember why I was happy to finish that class.

[Norm Peterson]

A couple of related items:

Center of Pressure - as it may move relative to the CG and (I think) resultant tire force, this has directional stability impact. IIRC, aerodynamic refinements to reduce drag move this point rearward.

Induced drag - lift, either upward or downward, is a force that's not purely perpendicular to the road surface. It has a longitudinal drag component.


Norm

[hotroddr]

It took me long enough but here are the pictures I promised. Really There is nothing that special about what I have done here so far. A lot of it seems to be fairly good design from the factory and I have built on it.

Here is a front shot of the tire air deflectors. I know that these could have been done a lot better but I was in a hurry and the mounting location was convenient. More experimentation is necessary. For reference they are 2" off the ground


This is the view from the front. It looks like the tire sticks out but it really doesnt. Im not sure if it was turned slightly or what.
It appears that there is some room for improvement here. As colvindesign suggested to me, wickers or air deflectors could be implemented here to improve this area. A good example I think of the idea in use is a second generation camaro/firebirds moulding on the front of the wheelwell. It deflects air outward. As I understand it these work like a side spoiler. The area in front of a spoiler whether its on a top surface or a side surface is a high pressure zone due to the air bunching up from trying to get around the spoiler. The area right behind a spoiler is a low pressure zone. On the wheelwell this it desireable because the low pressure zone created in the wheelwell will help to evacuate the air that went through the radiator and into the engine compartment.

here is sami Z01's camaro for an example of air deflectors/wickers/side spoilers in front of the wheel wells


Next we have a picture of the gravel peppered front of the car as it sits now. I need to block off more panels on the front. You can see the extended air dam which sits 3" off the ground. The bumper is 5.5" off the ground. The ex fog light hole on the drivers side is now the air intake. This grill cover is simple but effective. I hope more people try this out(hopefully with more effort put into the paint matching).


I tried to capture the streamlined stalks of the side mirrors here but Its kind of hard to see unless you see it in person. Unfortunately I also got my shoddy thrown together block off panels in the picture as well complete with black primer, D'OH.


This picture doesnt show much since there is not before picture. You couldnt see the transmission from the wheelwell as it was originally because there was a plastic panel there. I removed it to allow the air to exit the wheelwell if it so desires to do so. It was important to not allow any openings in the front part of the inner wheelwell though because that allowed air to bypass the radiator and bunch up in the wheelwell. I made this mistake at first and noticed a difference in steering feel on the freeway.


Here is the rear of the car with the rear lip as it came from the factory

I removed it mainly because I hit something on the freeway and broke some mounting clips but also because it allows air to exit the underside of the car easier. Here it is now without the lip.


Underbody trays or a belly pan as you may with to call it would help a whole bunch Im sure but Im saturated in school, work, ebay, and too many other car projects. The aerodynamics only get attention when Im about to go on a road trip. I know there is a ton of stuff that would make a big difference but I just wanted to share a few ideas I had. Anyone else try anything out or have any ideas they want to throw out there? Next year I will be taking some aerodynamics courses and will gain access to the wind tunnel at school so I will try to test out some ideas on scale models. I hope to come up with results that the average joe can apply to any car to increase gas mileage, and/or performance.

[boodlefoof]

hotroddr, it looks great!

You wouldn't happen to be going to school at Old Dominion U would you? I think the Langley wind tunnel is about the closest wind-tunnel to me... also the largest in the country from what I understand... but my car isn't that big. ;) I'm hoping to get my Z project in there at some point to try out a few things.

I've recently been looking at under-car air management and throwing around some ideas. I'm still a real novice in the area, but here is a sketch of my most current iteration of the belly pan. I've also tried to start an basic intro-level writeup about the theory behind what I will be doing on the car. Again, I'm a novice. If there are mistakes, let me know!

http://www.geocities.com/boodlefoof/...odynamics.html

[hotroddr]

You wouldn't happen to be going to school at Old Dominion U would you

No actually Im at ASU in Phoenix. It may be a party school for most but us engineers didnt get that memo. Im planning on taking a bunch of aerospace classes to further my knowledge in aerodynamics and airplane technology.
I looked at the drawing on that link. Explain to me what some of the strakes are there for. What is your reasoning behind the ones in front of the tires? I would think it would be better to either deflect the air to the side of the tires of down towards the ground to minimize drag from wind hitting the front of the tire.
It looks like you have the right idea for the rear of the car and the strakes to straighten and channel the air under the car. I still have a lot of testing to do with underbody airflow so I dont know for sure. What is the area that is right under where the radiator will be? The vents on the side to help air exit the engine compartment look good. Are you going to put any vents in the hood to allow air from the radiator to exit?

[CamaroAJ]

so lets say you build a belly pan for your car, with that pan you now have more heat traped in between the pan and floor from the transmission and depending on your design the exhaust. is there a way to vent that heat out without taking away from the pan like adding vents that will act like a vacuum and pull the heat out? maybe Louvred vents? like this only on the bottom of the car

[boodlefoof]

The area under the radiator is a front diffuser that will put air through the radiator. It will then vent through the hood ala an old GT-40 type of hood nostril. The strakes supposedly help airflow follow a sloping underpan.

As for the design in front of the tires. I can't really take credit. I copied the designs for the most part from race cars shown over at Mulsanne's corner. This type of item seems to be somewhat common, althought my instincts tell me that one would be better off just trying to divert airflow around the tires rather than over them. They obviously know much more than I do on the subject though.

CamaroAJ - I had the same idea. I plan to incorporate some louvres into the undertray.