# Car turning with external force help from spoiler

1. Aug 7, 2011

### mark77

Ok, so when a car turns, the tires provide the acceleration pointing toward the center of the turn. If for some reason, I put a spoiler on my car with two rectanglular pieces, one on each side that are tilted, to the left, mocking an airplane rudder, thus when the wind has contact with them, there is a force with a component backwards and to the right. If my car is turning to the right with this spoiler system, this will help with the turn and take some of the force off the tires, or even allow the car to take the turn faster as now the tires can have the same maximum component of before and then the extra from te spoiler (correct me if I am wrong). Also, with this system, how do I ensure that yaw still occurs around the proper side and the car rotates arround a corner? Thanks for the help.

2. Aug 7, 2011

### mark77

If I can get any one of the questions answered, the most helpful for me would be if I took a corner at the same speed with and without the spoiler, the lateral friction on the wheels would decrease with the spoiler than without it...?

3. Aug 7, 2011

### DaveC426913

I am not an expert but, if I understand correctly, a "rudder" is not really going to do a lot - it might be be detrimental. Anything that turns the car, that is not related to the wheels is actually going to increase likelihood of a fishtail or spin out.

The idea is to is ensure the spoiler applies a maximum downforce on the rear wheels so the car doesn't fishtail.

4. Aug 7, 2011

### mark77

Ok, thanks for the help. My way of seeing this is that to go around a turn you need x amount of cent. force. With the spoiler in place allowing for an extra component of force towards the center of the turn, the force towards the center in the rear wheels decrease by the amount of the force that is now in the spoiler a that way the cent. force remains x...I dont think the force of the rear wheels remains the same is my point. I believe it decreases by the amount of cent force acting on the spoiler. I am not sure tho, I would need some kind of evidence forme to change my mind...

Thanks again for your input though Dave

5. Aug 7, 2011

### DaveC426913

I cannot imagine any spoiler configuration that would lessen the force on the rear wheels; it would have to pull the rear of the car inward.

I guess if you were making a sharp left turn and you turned your "rudders" hard right (exactly opposite to what you'd do in an airplane), it would result in the rear of the vehicle experiencing a force to the left, which is what you're looking for.

6. Aug 7, 2011

### mark77

Yes, exactly with that configuration set up lets say

before

<---- <----

after

<-- <--

<-- <--

where bottom is force on tires and top is on spoiler

this way total cent. force is the same ( 4 "bars" as an illustration), just location of force is a bit different. So will something like this occur or no?

7. Aug 7, 2011

### DaveC426913

But to do so is to generate a strong force that wants to turn the car exactly the opposite direction you want to go. The moment you turned left, your rudders would try to turn your car right. This is not good for control.

8. Aug 7, 2011

### mark77

Hey, Dave I am a little confused on what you mean here. If the "rudder" is angled so the front is to the right, back is to the left and I turn right, there would be a force with components to the right and to the back on the rudder, thus that should help with turning as the right is were the centripetal force needs to be, not the opposite way...

9. Aug 8, 2011

### Ranger Mike

adding a rear spoiler to a " stock car" will provide minimal additional turning capability. It may in fact take away total performance.
Question- what are you trying to accomplish? Are you talking about round track racing only? road course? street racing?

I suggest you read Race car suspension Class in this forum to gain insight on what happens when you turn left

10. Aug 8, 2011

### mark77

Round track, thus the rectangular sides of the "spoiler" will be angled in a similar direction (with the left towrad the front, right toward the back for a left loop.

11. Aug 8, 2011

### DaveC426913

But that's not what you'd want.

Assume you want to make a left turn (I am imagining you are going around the track counter-clockwise).

To cause the rear of the car to experience a force to the left (taking strain off the rear tires), your rudders would have to point front-to-left, back-to-right - as if it is making a right turn.

The problem you're encountering is that a car is not an airplane. A car gets its drive and direction from its wheels, not the flow of air. A car pivots on its wheels. If you attempt to control its movement by way of air, you end up moving the wrong parts of the car. The most obvious example is that any airflow that puts torque on the car will work to make it more likely that the wheels will lose traction.

I've thought of a way you might be able to get this to work but it'll need some verification: place the rudder at the central vertical axis of the car (i.e. where a taxi has its light). In a left turn this will provide a force that pushes the car left (which is good), but does not impart a torque on the car (which would be bad).

Last edited: Aug 8, 2011
12. Aug 8, 2011

### Ranger Mike

mark77
what is the purpose of this rear spoiler?
why are you thinking of adding it?
what reason?
also thanks for the PM..slip angel and cornering G force is covered in the race car suspension class

Dave 426913
To cause the rear of the car to experience a force to the left (taking strain off the rear tires), your rudders would have to point front-to-left, back-to-right - as if it is making a right turn.

this is not correct..rear spoiler adds "strain" on rear tires

The problem you're encountering is that a car is not an airplane. A car gets its drive and direction from its wheels, not the flow of air. A car pivots on its wheels.
Dave..some what true but the suspension pivots thru its roll centers.

If you attempt to control its movement by way of air, you end up moving the wrong parts of the car. The most obvious example is that any airflow that puts torque on the car will work to make it more likely that the wheels will lose traction.
dave..depending upon the race car, and aero package..spoiler can add huge amount of down force on the rear tires, thus huge traction advantage. I think you are correct about air flow under the car with no provision for channeling air over the top side will cause the front end to float..usually about 130 mph (my experience) and the steering gets way spooky and loose

Last edited: Aug 8, 2011
13. Aug 8, 2011

### Ranger Mike

Tire Slip Coefficient
Apr2-10, 07:57 AM

Aerodynamics of sportscars
Mar9-09, 07:41 PM

Calculating G Forces or the Centripical force
Dec27-08, 01:43 AM

Race car physics
Dec29-08, 11:31 AM

does friction increases as speed increases?
Dec31-08, 07:37 AM

Tyres - why is wider better for lateral grip?
Nov5-09, 11:38 PM

14. Aug 8, 2011

### DaveC426913

Mike, please use the quote feature, or it becomes very difficult to read posts.
The OP has explained that he wants to takes strain off the tires.

You are not following along.

A spoiler provides downforce, true, but Mark77 is talking about a vertical spoiler to create lateral forces.

No that's not what I'm saying. When I say pivoting I mean yaw, not roll. I'm saying you can't use airflow to turn the car because it gets its traction for turning into a corner via the wheels. If you try to use airflow to turn the car, you will get slippage and lose traction.

Again, Mark77 wants to talk about lateral forces.

I've explained that the idea is really to provide downforce on the rear wheels, which will provide traction. But Mark77 is speculating about reducing stress on wheels, so we're talking about lateral forces.

15. Aug 8, 2011

### mark77

I agree with what you are saying above Dave, I am looking more into lateral forces. I also see where you are going when it comes to the yaw, which is were I stil am not 100 percent sure. First of all, do you agree with me that strain is taken off the rear tires on a turn, if not why? Also how will yaw be affected if the same size components of force will remain on the rear and front. I honestly dont really understand the concept of yaw on cars too well so any help on that if I am wrong or right would be great.

Thanks,
Mark

16. Aug 8, 2011

### DaveC426913

Well, there is certainly little strain on the tires if the car continues to go straight, instead turning left - which is exactly what the rudders are trying to do - cancel out the turn (by applying a leftward force at the rear of the car, causing the the car to want to pivot to the right).

17. Aug 8, 2011

### xxChrisxx

As tyres are the only points of contact all forces must go through them.

All an angled spoiler will do is alter (read: ruin) the balance of a car. Angled wings were used on open wheel oval racing years ago but were ditched for destroying aero balance and shredding the tyres on straights.

Last edited: Aug 8, 2011
18. Aug 8, 2011

### mark77

Ok, any ideas on how I can make the car do the "yawing" part of the turn with this system in place. More weight in the front?

19. Aug 8, 2011

### mark77

Also, Dave I am thinking about placing the spoiler directly abpve the CG that way the foprces will only go towards roll as opposed to torque because I think there are complications neither of us know about specially the yaw aspect (as I am no car expert either) having it back there. Any improvements in car handling youll see by having it at the top, or any tips in general...thanks

20. Aug 8, 2011

### xxChrisxx

What on earth are you trying to do?

21. Aug 8, 2011

### mark77

Pretty much by having the spoiler above the center of gravity, if I have the rudder at the right angle for a certain turn angle, I should be able to counteract the roll and thus the weight/load transfer and optimize friction on the wheels. Will this work?

22. Aug 8, 2011

### xxChrisxx

In a word. No.

Start at the beginning and talk about what you want to achieve. What is the car? What is the application? etc.

Also what is written above shows a lack of understanding about how a car turns. Seriously read through the suspension thread as I think it has a section on slip angles.

23. Aug 8, 2011

### mark77

I understand that cars have a centripetal force lke anything else exedrted on them by an external force in order to turn. When a car turns the patch of tire in contact with the ground is altered due partly to inertia and thus the car does not follow the direction the wheels are pointing, which is were the slip angle comes into play. The force on the tires from the ground on a turn, or the lateral force occurs (which depends on the slip angle) and contributes to both drag and the centripetal force. Anyways, I am no expert on this subject which is why I am the one asking the question as opposed to answering it, so any INPUT would be appreciated. So if there is something missing help me out.t

Now, how would the spoiler above the CG not work? There will be a small addition of force on top of the car in the opposite direction of theCG causing a roll torque in the direction opposite of that caused by the lateral force. The tires will still be in contact with the ground with just a little less grip but in proportion to each other...

24. Aug 8, 2011

### xxChrisxx

That is extremely confusing to me, as i'm not really sure what you are proposing and why you think it will be an improvement.

The lateral acceleration causes cornering through the slip. It also causes load trasfer to the outer wheels. Load transfer is not the same as weight transfer. You are proposing something that would create a force acting opposite to this (it mat or may not depending on which way the wind is blowing at the time). Any force acting opposite to this means you have a reduced lateral force for a given slip angle. So you reduce your cornering ability.

Also roll has little to do with load transfer.

It's like saying that you want to increase your acceleration in a front wheel drive car by adding a rear spoiler.

Last edited: Aug 8, 2011
25. Aug 8, 2011

### mender

First, Mark, what you are describing is a wing, not a spoiler.

Second, yes, a vertical wing can be be used to generate force in the direction of the turn and either lessen the force needing to be generated by the tires for the same cornering speed or to increase the overall cornering speed (usually the reason for using them!). Winged dirt Sprint cars have very large side panels that do exactly that, although the panels are just flat and not wing shaped. Because of the large slip angles that these cars use while cornering on dirt, the side panels have a significant angle of attack and generate enough force to justify using them.

Third, having the force from the wing acting above the roll centre of the vehicle will counteract the vehicle's typical roll reaction to the forces generated by the tires while cornering. Again, dirt Sprint cars with large side panels on their wings benefit from this, reducing the amount of roll that the car experiences while cornering. This allows the use of softer springs and anti-roll bars which generally allows the tires to work better.

http://www.world-sprintcar-guide.com/sprint-car-wings.html

Last edited: Aug 8, 2011