I was thinking about looking into drag reduction on the neon by doing some simple detailing and adding a front splitter and rear spoiler. I dont have access to a full scale wind tunnel but I do have access to a small one so I was thinking about doing some scale model tests to see where there is room for improvement. Would make the car alot more responsive at freeway speeds or gain a little bit more trap speed at the strip.

 

I'm not sure I'd mess with it too much, drag reduction doesn't really come into play until speeds of around Mach 1. Some spoilers for downforce would probably be an improvement, but even then, not up until say 160 mph. If the wind tunnel is free, go for it.

 

Dude what are you talking about? Mach 1? and spoilers dont give you downforce - wings (lifting airfoils) do and all wings add drag - spoilers are for reduction of trailing vorticies (tumbling of air) when it frees itself from sticking to your car (have u ever driven with snow on your car and seen it go swirling off the back, thats what happens all the time - you just cant see it) and a splitter which goes on the front (an air dam) keeps air from getting under the vehicle and sticking to the bottom surface creating friction drag. I don't think you have any idea what you are talking about with drag - there are two forms: pressure and friction and on cars pressure drag is the most significant. And with gas prices being so high why do you think they post drag coefficients in vehicle specifications now? Just to give you an idea of how much force opposes you at 70 mph on the freeway i'll run thru some calcs:

On a 70°F day the density of air is 0.00233 slug/ft^3

70 mph = 102.7 ft/s

The drag coefficient of a 2g neon is about 0.34 and the frontal area is about 23.6 sq. ft.

Drag Force = 0.5 * (air density) * (frontal area) * (drag coeff) * (speed)^2

Do the math and your get a drag force of 98.6 lb at 70 mph

Power is force times velocity so if you do this and note that there are 550 ft-lb/s in a horsepower you get:

18 Hp getting sapped away by the air!!! - not good when most standard neons are lucky to have 110 hp max at the wheels,
thats over 16% of max!!

Now at 100 mph this jumps to 201 lb and almost 54 Hp!!! and when you consider wheel hp is what drives you, this is huge, almost 50%!!

Lowering drag is essentially like adding wheel hp at higher speeds

A 15% reduction in the drag coeff, which is entirely possible could drop these numbers to:

15.7 hp (~13% increase in effective wheel power) at 70 mph and

45.7 hp (~15 % increase in effective wheel power) at 100 mph

Aerodynamic drag is evil and limits your top speed (unless the computer does first), your fuel consumption per mile, quarter mile times, etc....certainly not only applicable at supersonic speeds.

 

Relax, killer, what I meant by spoiler was a splitter, I've just never heard it called that.
All I'm saying is that maybe there are better areas to spend your money to add horsepower/mpg, than by looking at drag. And as for not knowing anything about drag, I have a bachelors in Aerospace Engineering and I have worked for the Air Force Research Labs for two years as a civilian before entering the military and getting my private pilot license. When you're worried about drag, you're usually dealing with stuff that it REALLY matters, like fighters and formula 1 racers, not neons. I'm not looking to be a jerk, just giving you my advice on your post. Your decision to listen to me or not, but don't cop an attitude.

Here are a few questions for you to consider if you continue to look at this, just as help:

How are you getting the surface area? Drag force is different on a slanted surface as opposed to a flat surface so be careful what you assume. Plus, as surface angles change, the angle of incident changes as well.

What method are you using to calculate? Panel method might be the best.

Are you going to add weight by modifying the body? Will this affect the outcome significantly?

You sound like you have an interesting project on your hands and you're on the right track. If you have access to a wind tunnel then you probably have some experience in this area. Good luck and have fun.

 

Sheesh if you have your bachelors degree in aerospace you must have been sleeping during fluid mechanics and aerodynamics or you would know that the drag coeffiecient for pressure drag is defined using the projected frontal area, except in wings where the plan form area (product of the span and the chord) is used. Drag coefficients were "invented" using dimesional analysis - buckingham's pi theorm ring a bell? Obviously those numbers I was throwing out were rough estimates and as you should know the drag coeff is a function of reynolds number, another famous dimensionless parameter. I would really like to look into this for racing purposes, in particular touring car road course racing and I dont see it costing too much money, wind tunnel time is free to me and the fabrication would be fairly simple....I was just throwing it out there to see what ppl would say and get some feedback - I wasn't actually expecting anyone to be interested in aero - just think its interesting how no one really understands how important it is, Boeing 747 or Neon....

 

I don't know what you said, but it touched me. Actually i understand, jus messin. Carbon fiber adjustable spoiler ot the kaminari carbon fiber wing spoiler, would be good bets for testing, look goo too. As for spitters, not sure at what angle would be good, but mess around with it and let me know if you see inporvements or changes that way i can consider doing it too.

 

Well I have to do this with a scale model so I was pretty much planning on coming up with new stuff - not really testing whats already there but I'm also not planning on reinventing the wheel per sae - I have some friends who are fairly insane about composites so I might be able to coax them into making some molds if anything pans out but I know they are fairly jammed up with some variable pitch prop designs - If i do anything it will be with aluminum becuase its fairly cheap and easy to work with - I'm thinking that if I actually go thru with this I'll make it fairly universal i. e. applicable to most any car. If you want I can look at any wings or spoilers you may be interested in and let you know if they will actually work although dimensions would be handy.

 

In Aero we look at more advanced and higher resolution methods of calculating drag coefficient than using projected frontal area because for aircraft, you just can't assume, even using planform area, which we only used in classes at the end of our freshman year before moving on to more advanced methods. The panel method takes into account that the angles of the surfaces change with respect to the angle of incident of the airflow, so as the object surface curves, the airflow is seeing different frontal areas. If you want a rough estimate, then what you are doing is perfectly fine and is a great way to do it. But look at it this way, with your example, a stop sign would have the same airflow characteristics over it as a drop tank off of an aircraft. Doesn't quite sound right does it? If you're going for more accurate results, then you can't assume the area the airflow is seeing is the same as the cross-sectional area of the car. The Drag Coefficient equation hinges on the selection of a reference area. If the time is free and the fabrication cheap, then go for it. I'm especially curious about the effects of the car's undercarraige on the airflow going underneath. How big is the test section of your wind tunnel? I'm just curious how big your model would be. And what speeds is the windtunnel capable of? Do you work with the wind tunnel or just at the facilities and have access to them?
Also, are you trying to increase or decrease downforce? If you start to develop a lifting force over these splitters and wings, then you're going to start creating more induced drag. And you probably already know with your experience at the tunnel that you need to find the point where the total drag is lowest.

 

Do you really need more advanced methods if you have a wind tunnel to test with? not really as long as you are consistent and auto manufacturers ALWAYS use the frontal area for determining drag coefficients, while this may not be the best method it gives some consistency for comparison - in the tunnel measure force with a balance - what it is, is what it is with the accompanying uncertainties and experimental errors - there are obvious challenges in scaling and simulating air flow over a vehicle in a small wind tunnel - all of which i understand and accept, the biggest of which is simulating the moving ground... and do I think I really understand aero - NO - nobody does! If you can solve the navier - stokes equations for REAL viscid flows or come up with a new, better way to describe fluid behavior I will believe you are above and beyond everyone else - if not your in the same boat as everyone else...point of the matter is my approach to this would be highly emperical which as I see as neither a bad, nor a spectacular, but it works if you understand its limitations.... I am not an aeronautical engineer, I am a mechanical engineer although my degree says automotive - its funny that I have never heard of any schools teaching FM and Aero freshman year - u think you would have at least had take differental equations and even paritial differetial equations with boundary value problems before you could even understand the simplest of theory for ideal flows but hey what do I know -

 

All I'm saying is that while the drag coefficient gives you a comparison between models, its not going to help with you trying to improve your drag reduction. I'm not an aero god or anything like that, I'm still in the learning phases, too. It sounds like a nice lil project to have fun with, knock yourself out. I only meant to give you advice on your theories and how to go about increasing your accuracy. Just giving you some constructive criticism. And I was only interested in the tunnel size so I could get an idea of how big your model would be, not to rip you on loss of accuracy. Everyone has to deal with loss of accuracy when they scale stuff down, you take it into account in the errors.
Enjoy your project, it will be a learning experience for you.