**aerodynamics**

[perfworks]

Hello all,
I would like to hear from anyone with input to the aero dynamic issues associated with the P5 and sedan model proteges.
Why are they drag limited and what can be done to help ease the problem.
This is a thread to get some common misconceptions out into the open.
I personally love the design of my P5 and would like to improve it along with the help from fellow board members . any links and helpfull comments and suggestions will be greatly appreciated.
Thanks in advance for all your input

 

[mopiko]

No expert here, only personal opinion. Seems to me that in the recent years almost all car manufacturers roll out new compact car models with high roof line, high suspension and all to give the car a more comfortable ride for taller people and to give the suspension more room to bounce, in the Protege5 in particular, in addition to the above two points mentioned the front bumper doesn't seem too aero dynamic friendly to me as suggest to the fog light slot design as well as how the bottom of the bumper being a little bit higher in comparision to the side skirt.

The rear is of not much help either I think as the clearance height of the rear bumper, with the high bumper clearence on both front and back at extreme high speed it might very well helped the air traveling underneath the car to lift it enough to reduce aero dyanamic performance.

With my personal experience with both mod I did so far (TEIN lowered springs and a front lip) it seemed the address this issue a little bit. Being lower with a "downforcer" in the front help the car stick on the road a little bit better, I don't know much about drag, all I know is turns and Gs and with my G sensor I was able to pull better in turns after the springs, I haven't checked if my front lip make any difference, it might not, it might.....

humm.... do I make sense? Am I at least right on some points I'm trying to make? Did I actually made any point here???? Oh well, it's weekend, I can't seems to kick my brain started much.....

 

[SeminoleMan]

Being drag limited only has a bearing on top speed. It takes a certain amount of power to overcome drag. When power is equivalent to drag, there is zero acceleration. This is what happens to the P5 at top speed. It just simply doesn't have the power to overcome top speed at 111-118 MPH (Depending on the automotive source testing.)

Drag also plays a part in a cars gas mileage potential. Take 2 cars of different drag coefficents (say .32 vs .28), all things being otherwise equal, the car with the .28 drag coefficient wastes less energy pushing the car through the air, increasing mileage.

Conversely, when there is enough power to overcome drag, a car accelerates. I'm pretty sure the P5 and MSP have identical drag coefficients. But the reason the MSP can attain a higher top speed than a P5 is a result of its 40 more hp and 20lb/ft torque.

Lowering your car, putting aero parts etc can potentially lower the drag and increase top speed, but only marginally.

 

[perfworks]

these are great responces guys please keep them coming.

 

[Action Jackson]

I don't know if you've notice on old racing Mustangs [like the Parnelli Jones ones], there's that lower front "lip" that was designed to channel air up into the rad AND reduce drag.

It's not a front airdam, it's situated just behind and lower than the front airdam.

I guess you can improve airflow by smoothing out some of the body work.

Racing teams [F1, Cart and Sports Prototypes] use aircraft wax b/c it will give them a few more mph's at top speed. Remember that those are REAL racing vehicles.

 

[mopiko]

SeminoleMan, a humble question from me, an phyics idoit, how's the relationship between power and drag, meaning what is the equation with variable power, drag coefficents and top speed (?)

If the drag coefficients and top speed are inversely proportional, then lowering the drag coefficient should be more productive in terms of attaining a higher top speed?

How about combining both my idea and SeminoleMan's idea together? My idea is basically rerouting how the air should travel pass the car, and SeminoleMan's idea is increase power to the vehicle in question....

If you combine both higher power and aero, lowered component installed the aero component should further enhance the potential of any engine component that designed to give you more hp then...

Also will re-distributing the front/rear weight ratio help? a almost 50/50 weight distribution should help lower the drag in the rear section then a 60/40 car....

Humm... enough thinking for now, I'll chip in more later....

 

[SeminoleMan]

Well I am by no means a Physics god. But here is a link that can be helpful.

http://www.pumaracing.co.uk/topspeed.htm

Lowering the car, which reduces frontal area and drag, and increasing power will work to increase the top speed of the car.

As the link I provided explains, a power increase of 10-20% (typical increase for combined bolt-ons) will increase top speed 3-6%. To increase topspeed 10%, you have to realize a 33% increase in power. That alot of power increase for nominal topspeed gain in a P5 (you'd need to make approx 160hp to get the P5 to 132.)

As far as the weight distribution is concerned. I don't think there is much benefit. It may influence acceleration more, but the top speed should not be affected at all.

 

[trekv2]

yess!!! more knolege(hear ya) (drinks)

 

[perfworks]

great link seminole. thanks
keep up the good work guys

 

[uclap5]

take off the roof rack and rails, take off the wipers, take off the sideviews. that should help

 

[REMillers]

Drag coefficient of the MSP is around .32 the P5 is about .33

So from aero standpoint both cars are not bricks as some would point out. But least in the P5 standpoint it does not have have the power ratio to overcome the drag anymore. Gaining top end speed by lower this coefficient is not going to net huge results. About the only positive outcome would be a more stable platform for high speed runs.

Typically two things will keep a cars top speed down; rev or drag. In our case it is not drag but more engine strength to pull its body faster.

Good stuff SeminoleMan

So pretty much quick sum up; Protege line up does not have a drag issue. Its more of a engine power potentional that is limited the high speeds.

Oh and for some who "think" .33 is high. A F40 has coefficient of .32 roughly.
So don't let the shape of a car determine its coefficient, more on how it channels the air that determines a high or low coefficient.

 

[servoeyes]

Excellent answers from REmillers and SeminoleMan...RE makes the strongest point, methinks. My background is mainly fluids and aerodynamics but there is always one resounding issue...power. You make enough thrust to move something it will fly. Note also, though, that drag will increase with velocity (as will lift...actually that's what causing the drag...) That coefficient makes all things equal...just judging the shape and not the speed at which it's moving...here's the equation:

CD= Drag Force / (( .5 * freestream density * freestream Velocity ^2) * reference area)

hence...assuming the density and velocity are equal, here's the difference: Whetted Area...guessing the whetted area is less on the f40. This also means it is experiencing actual drag force less than or equal to a p5 at similar velocities. Using the assumed numbers, for the drag forces to be equivalent the whet area of a p5 must be ~3.1% more; anything larger and the p5 is experiencing a greater drag force than the f40. Everybody with me?

 

[APEXistud]

Tire width also plays a role in achieving a higher top speed. Wider tires usually means lower top speeds. I remember reading about this in Sport Compact Car. Please pardon my magazine racing, but I doubt that there is a lot of people with hands on experience with top speed testing on a Protege out there. The issue I'm refering to is the 150mph Civic SI Hatchback issue. After they put the bigger wheels on the Civic, they noticed that their top speed went back down and that's when they explained the tire width top speed relationship.

 

[zumi]

yes, i believe you will get more rolling resistance with wider tires, which would decrease top speed

 

[Strider1222]

Didn't we kinda discuss this while we were tossing up the 200+ mph P5? Well anyhoo- I was thinking back in those days and wondered... if the rear wing were made to channel air better away from the rear (forgot what it's called), but wouldn't the drag C/O be better.

I drew up an idea a while ago I'll look for it and post it then.

Strider-

 

[Pro5OnSpeed]

you also have to take into consideration the hatch. having the hatch there creates more of a vaccum in the rear thus making the car harder to accelerate at top speed. there is airflow moving across the top and along the sides of the car, but where there is that "dead" air space, it creates that vaccum. now since the P5 has that issue, a car that came up upon us would help with that smooth out the airflow.. i think i will try that. i have also been meaning to try and figure out how air moves over the roof and the spoiler. i can do that by taping strips of paper in certain places. the best way in my opinion would be to make an undercarriage spoiler like how the Mclaren F1 is designed. but since our cars arent designed to beat drag i dont think it would help much. the fastest i have ever gone in the P5 was about 132mph, and i beleive i was heading away from the wind. into the wind i can only push 120.

i doubt that a new rear wing would help, it would have to be much longer to direct airflow further from the actual body, and air underneath would either need to be maximized or decreased. since the front windshield is more forward then aft, that creates more drag. the front bumper would need to flow more air around it more smoothly. the only way i can see "beating" drag is to get more HP to the ground or fiddle with downforce, but in order for down force to work properly you have to be going pretty fast in the first place.

this weekend i am going to place strips on the car and document my findings. also i will try drafting another P5 that is if ken is up to it.

 

[servoeyes]

Anybody want me to run a CFD analysis on it?

 

[KzA]

since the front windshield is more forward then aft, that creates more drag.

Can anybody say, choptop?