More on my modeling approach:
I plan to use the method described in my previous post to collect pairs of data (Fd, Veq),
where Fd is the total drag and Veq is the equilibrium zero-power speed for descending the given grade.
I will fit this data to the expression:
Fd = Crr + A*v + {Cd * A * 1/2 * rho * V^2}
I will use least-squares find the best fit of parameter A and Crr. I have confidence that the aerodynamic drag as computed by Sparky is accurate, so it has no parameter in this fit.
Of course it is important to control for tire pressure, Sparky's original interest. My tires are at 39 lbs/in^2.
Getting rho right for each data point is important as well. Rho is a function not just of altitude and temperature, but also humidity. The molecular weight of dry air (80% N2 + 20% O2) is:
(.8*14*2) + (.2*16*2) = 28.8.
H2O has a molecular weight of 16+2 = 18.
Humid air is lighter. Pilots correct for this fact when computing how much runway they need to take off. We should be able to drive the Leaf further at faster speeds on warm, humid days at high altitude.
Alternatively, if we have the barometric pressure, we can get rho from the ideal-gas law:
rho = p/(RT)
I plan to use the method described in my previous post to collect pairs of data (Fd, Veq),
where Fd is the total drag and Veq is the equilibrium zero-power speed for descending the given grade.
I will fit this data to the expression:
Fd = Crr + A*v + {Cd * A * 1/2 * rho * V^2}
I will use least-squares find the best fit of parameter A and Crr. I have confidence that the aerodynamic drag as computed by Sparky is accurate, so it has no parameter in this fit.
Of course it is important to control for tire pressure, Sparky's original interest. My tires are at 39 lbs/in^2.
Getting rho right for each data point is important as well. Rho is a function not just of altitude and temperature, but also humidity. The molecular weight of dry air (80% N2 + 20% O2) is:
(.8*14*2) + (.2*16*2) = 28.8.
H2O has a molecular weight of 16+2 = 18.
Humid air is lighter. Pilots correct for this fact when computing how much runway they need to take off. We should be able to drive the Leaf further at faster speeds on warm, humid days at high altitude.
Alternatively, if we have the barometric pressure, we can get rho from the ideal-gas law:
rho = p/(RT)