Calculate the negative lift of an after market inverted airfoil on car trunk?

Question

Calculating the negative lift of an after market airfoil, on a car's trunk?
I'm having trouble doing a practice problem for my exam in physics. I have to take measurements on car's inverted airfoil or find some from the internet, Which seem impossible to find.

I need the path over top of the inverted airfoil, under it, and the length of the airfoil.



I then assume the wind is going 50 mph or 100mph while on the highway. - 22.32m/s and 44.704m/s


I need to calculate the velocity under the inverted airfoil, using the same approximation that the wright brothers used ( bernoulli's equaiton?"


From that , calculate the pressure difference between the top and bottom in Pascals. From that, calculate the force in newtons on the airfoil, then to pounds.


Any help would be appreciated, tried to find measurements on an airfoil for a few hours, can't find any. This problem is driving me insane.

Answer 1

What you really need are the dimensions of said foil and the pressure readings on the top and bottom or the difference in pressures.

If the foil is a definite NACA shape then you should be able to find the coefficient of lift for the shape and then simply use the equation Lift = 1/2*density of air*velocity of the air^2*Projected downward surface area of the foil*coefficient of lift.