Aerodynamic Forces:
Drag:  (FD)= CDqA = (CD(1/2) r V2)A

Lift:  (FL) = CLqA = (CL(1/2) r V2)A

Side Force:  (FS ) = CSqA = (CS(1/2) r V2)A

CD = Coefficient of Drag is a reflection of the aerodynamic efficiency of the shape
CL = Coefficient of Lift
CS = Coefficient of Side Force
q = Dynamic Pressure in the Test Section
r = Mass Density of Air
A = Frontal Area of Vehicle
V = Velocity

This is the same drag you feel when you place your hand outside the window of your automobile.  There is a noticeable difference in drag force felt on your hand when you palm is facing the oncoming air opposed to you palm facing down.

Aero Horse Power:  Horsepower required to move the shape through the air at a specified velocity.  Neglects any rolling resistance and losses through drive train.
HP = (DV)/550 = (CDqAV)/550 = (CDA 1/2 r V2)V / 550 = (CDA 1/2 rV3)/ 550

D = Drag Force
CD = Coefficient of Drag is a reflection of the aerodynamic efficiency of the shape
V = Velocity
q = Dynamic Pressure in the Test Section
A = Frontal Area of Vehicle
r = Mass Density of Air

Aerodynamic Drag:
CD: Coefficient of Drag
Invariant with velocity unless there is Reynolds Number sensitivity.  The lower the CD the more efficient the shape is to the air.  With a reference frontal area of 21 ft2, a production car will have a CD around the 0.340 range

CDA: Coefficient of Drag Area
Coefficient of Drag x Area: CD x A

Reynolds Number: the ratio of inertial forces (vsρ) to viscous forces (μ/L) and consequently it quantifies the relative importance of these two types of forces for given flow conditions.

Dynamic Pressure: (PSF)  A2 measures the test section speed in q which is the dynamic pressure.>>>
q = ½ r V2

Flow Rate: (ft3/minute)
CFM = Area (ft2) x Speed (ft/min)
Calculating Frontal Area:
There are several good ways to calculate the frontal area of your vehicle. One is to simply measure the height multiplied by the width and take 85% of it to acuminate the smaller green house.
F.A. = (height x width) x 0.85  
Another good way to calculate frontal area is to overlay the picture with transparent graph paper.  Determine the area of one square by counting the number of squares in a given measurement (height or width).  Once you determine the area of one square you just need to count all the squares touching the model and keep track of whole and half squares to get the total frontal area.
Tufting: Don't be greedy when it comes to tufting a vehicle.

BL - Boundary Layer - The slow moving air near any stationary surface (wind tunnel or test car)

Ground Plane - The portion of the wind tunnel floor built to allow for the mounting of a vehicle model directly above it.

Ht - Height

L/D - Lift to drag ratio - the same, whether calculated in the form of coefficients or forces

LE - Leading Edge - The front of a surface, often the edge exposed to maximum airflow energy

Lift - (-) Lift is down force.

Mod. - Modifications

N. A. C. A. - The National Advisory Committee for Aeronautics. This agency operated from 1917 until 1958, and compiled a huge library of studies conducted in aeronautics and aerodynamics. Wing shapes are identified using a N.A.C.A. based naming system.

Rake Angle - The tilt or pitch of a vehicle's body from front to rear, expressed in degrees, relative to the surface to which it is attached.

Rad - Radiator

Roll Moment - Force acting side to side.  A (-) negative roll moment would roll the car to the left side.

Side Force - Lateral force pushing from the side.  A (-) negative side force would be pushing the model to the left.

TE - Trailing Edge - The rear of a surface, the edge at which air must separate from the surface

Tuft - A short (1-2 inch) piece of contrasting yarn or string that is taped to the surface to act as surface flow tracer - even large numbers of them have virtually no effect on a car’s aero (very rare exceptions are possible)

TS - Test Section -  The high speed test chamber of a wind tunnel

VG - Vortex generator - Device which generates vortices near a surface and helps energize the BL

VR - Velocity ratio (rad., ducts, scoops) = Speed of air thru area divided by speed of main airflow
Wing/Spoiler Stall Angle - The angle, expressed in degrees, at which the lift generated by a wing/spoiler reaches its maximum...this is the point at which maximum downforce is applied to the rear wheels

Yaw - The difference between the direction a vehicle's body is pointing and the direction it is traveling (or in the case of a wind tunnel, the direction from which the air stream is originating).
Phone Number
117 Godspeed Lane,
Mooresville NC 28115
Office Hours
Monday-Friday 8AM-5PM

2013 A2 Wind Tunnel