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I came across an interesting little problem doing some work that I though I'd share. Typically, we think of three types of resistance for a wheel:

I'm modeling the wheel of an airplane for a flight simulator. When the airplane is sitting still, it has some resistive force before it starts rolling. So I just found this force using the maximum coefficient of static friction for a tire (obtained from manufacturer). Turned out I got an insanely large number. Then I realized, <duh> that would be like having the airplane on full throttle (which it nearly turned out to require) and dragging the wheels across the runway.

So the only option left was to model the friction using rolling resistance (which I am already doing when the wheels are in motion). My understanding was that rolling resistance was defined for rotation of the wheel (because my basic books on physics all just assume the wheel is turning). I looked at my vehicle dynamics book and realized the curves for rolling resistance as a function speed go all the way down to zero, and have a power relationship with speed f0+ 3.24*fs(V/100)^2.5. Anyways, the point is that "rolling resistance" is a bit of a tricky term to use. After I plugged in some values I got a frictional force of 25.5 lbs for a 2550lb aircraft. It seems like a very reasonable number.

As a side note: All tires slip in the real world when you accelerate/break and that the coefficient of friction goes down as you increase the load.

The point is, tires do a lot of non-intuitive stuff and the basic presentation of friction in most books is woeful. You have been warned.

- Static Friction
- Kinetic Friction
- Rolling Resistance

I'm modeling the wheel of an airplane for a flight simulator. When the airplane is sitting still, it has some resistive force before it starts rolling. So I just found this force using the maximum coefficient of static friction for a tire (obtained from manufacturer). Turned out I got an insanely large number. Then I realized, <duh> that would be like having the airplane on full throttle (which it nearly turned out to require) and dragging the wheels across the runway.

So the only option left was to model the friction using rolling resistance (which I am already doing when the wheels are in motion). My understanding was that rolling resistance was defined for rotation of the wheel (because my basic books on physics all just assume the wheel is turning). I looked at my vehicle dynamics book and realized the curves for rolling resistance as a function speed go all the way down to zero, and have a power relationship with speed f0+ 3.24*fs(V/100)^2.5. Anyways, the point is that "rolling resistance" is a bit of a tricky term to use. After I plugged in some values I got a frictional force of 25.5 lbs for a 2550lb aircraft. It seems like a very reasonable number.

As a side note: All tires slip in the real world when you accelerate/break and that the coefficient of friction goes down as you increase the load.

The point is, tires do a lot of non-intuitive stuff and the basic presentation of friction in most books is woeful. You have been warned.

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