CP vs CG

[Sumner]

.... So the added weight to the car which is then transferred to the tires doesn't increase the mass [or weight]?

No, because it is a force not a weight, you did not add weight to the car you are subjecting it to a downward force.  Does your weight go up when walking or biking into a strong wind?

Sumner

  So down force is not measured in lbs?

           JL222

 Well devils don't have wings, but if they had inverted wings standing on a scale, into a head wind, wouldn't their weight register more?

You would be measuring the force of the wind.  Not weight.  Torque from your engine is a force, does it add weight to the car?

Once the car becomes unstable you can quickly loose the down-force from the wing or body itself, as mentioned above, so now what you have left to keep the car from swapping ends or spinning is the car's actual weight and where it is located in relation to the center of pressure,

Sumner

[tortoise]

As a purely pedantic aside, not directly related to the discussion, the center of mass and the center of gravity are not exactly the same point. Mass further from the center of earth is subjected to a lesser gravitational force. Thus, for a tall building, (or to a much lesser extent, a car), the center of gravity will be a bit lower than the center of mass. Sorry, I couldn't help myself.

[tortoise]

   Its you that doesn't understand the question or doesn't want to answer it.

  You remind me of the engineers in the 50ths that said a dragster could never go more than 150mph in the 1/4 mile.

 You need to understand that wings and spoilers increase down force from aero loads changing CP VS CG.

          JL222

"‘When I use a word,' Humpty Dumpty said, in rather a scornful tone, ‘it means just what I choose it to mean—neither more nor less.'

‘The question is,' said Alice, ‘whether you can make words mean so many different things."

‘The question is,' said Humpty Dumpty, ‘which is to be master—that's all.'"

[jl222]

.... So the added weight to the car which is then transferred to the tires doesn't increase the mass [or weight]?

No, because it is a force not a weight, you did not add weight to the car you are subjecting it to a downward force.  Does your weight go up when walking or biking into a strong wind?

Sumner

  

  
 Well devils don't have wings, but if they had inverted wings standing on a scale, into a head wind, wouldn't their weight register more?

You would be measuring the force of the wind.  Not weight.  Torque from your engine is a force, does it add weight to the car?

Once the car becomes unstable you can quickly loose the down-force from the wing or body itself, as mentioned above, so now what you have left to keep the car from swapping ends or spinning is the car's actual weight and where it is located in relation to the center of pressure,

Sumner

  Sumner..are you saying wings don't add lbs?

  I know the dynamics of loosing down force. we're tilting the spoiler up adding a flap and more and bigger side plates.

  This to increase aero lbs. of weight on rear tires for more traction with out adding lbs of static weight.

  Bigger side plates should help for better CP, but mainly more wind resistance to stop a spin.

  I think this added aero weight will change the CP VS CG ratio at speed, others don't.

        jl222

  P.S. If spoilers keep a car from getting lite and unloading the suspension, why wouldn't wings make them heavier and load the suspension?

  

        

  

[tortoise]

  Sumner..are you saying wings don't add lbs?

If I stand on my bathroom scale under the doorway and push up on the door frame, do I gain weight? The scale reading goes up, so I must be heavier, right?

[jl222]

  Sumner..are you saying wings don't add lbs?

If I stand on my bathroom scale under the doorway and push up on the door frame, do I gain weight? The scale reading goes up, so I must be heavier, right?

  The scale thinks so.

                JL222

[tortoise]

  The scale thinks so.

Not an answer.

[joea]

I want to COMMEND everyone who has participated in this discussion..!!!!!!!

Seriously, most of us care deeply about this type of discourse, and many of us have levels
of understanding and or ignorance related to this type of subject matter similar to many who have posted....

this is priceless, and I and many are better for seeing it

thank you

Joe

[debgeo]

AMEN Joe

[desotoman]

Here is an old thread that will help on this subject.

CoG vs down force

http://www.landracing.com/forum/index.php/topic,9301.0.html

Tom G.

[jl222]

 The scale thinks so.

Not an answer.

 The scale shows more weight, it doesn't know our care where it came from. Same as aero lbs of force or added weight on tire patch.

 OK I'm standing on the scale holding  a beer it goes up 1 lb. Now I drink it-scale goes up 1 lb. Scale doesn't know what happened.

                       JL222

[Sumner]

 The scale thinks so.

Not an answer.

 The scale shows more weight, it doesn't know our care where it came from. Same as aero lbs of force or added weight on tire patch.

 OK I'm standing on the scale holding  a beer it goes up 1 lb. Now I drink it-scale goes up 1 lb. Scale doesn't know what happened.

                       JL222

John a couple pages back you asked....

.....What changes does the CP-CG have when the spoilers and wings add downforce? .....

You've gotten the answer over and over from a number of different people but just don't want to think they are right for some reason that I can't figure out so I guess it comes down to you will have your view of the effects of spoiler/wings on CP-CG and we will have ours.

Good luck with the car I'm sure it will go fast,

Sumner

[7800ebs]

Ok... My turn..

"OK I'm standing on the scale holding  a beer it goes up 1 lb. Now I drink it-scale goes up 1 lb. Scale doesn't know what happened."

200 lb guy + 1 lb beer (in hand) = 201   Now,  move beer from hand to stomach, still holding bottle, very big bottle, lol    200 lb guy + 1 lb beer (in stomach) = 201 


  What we are really doing with a wing / spoiler is increasing the friction / load on the tire, so as to keep it from allowing tire spin and or loss of directional control. This friction is separate from the CP of the car. The wing / spoiler can add a component of drag to the whole package, that can affect the center of pressure though.(think top fuel wing on front of a roadster, bad things will happen, although front end has got hell of a load ) The matter of size / design of side plates on the wing / spoiler, is another factor in the CP story. Bigger Side plates will almost always help... if they're in the back of the car.

Now ...

Why do wings and spoilers work ?    Newton or Bernoulli or Coandă ?     

[kustombrad]

I so love this "techy" stuff and having to twist what little brain function I have around it! When referring to CG though, my question would be are we looking at it while "static" or while at speed? I'm building my streamliner to go fast and yes, chase records at "speed". If I have it on scales with me in it and CG is is in one point while sitting " static", but at 300mph (using my magic "speed" scales) it's now in a different location because of airflow, isn't that what we're actually looking for? In this sport/hobby it's actually ALL about airflow. Sitting on scales in the shop looking for CG is pretty much irrelevant from my perspective. Am I wrong?

[7800ebs]

It would seem to be..... until your airflow (downforce) didn't stop the tires from spinning... then you are subject to the CG/CP theory for airplanes, we have been enjoying.