The Force of Drag equation, Fdrag= ½⋅(ρ⋅A⋅Cd⋅v²)calculates the resisting force of drag on an object flowing through a medium (e.g. air).
INSTRUCTIONS: Choose units and enter the following:
- (ρ) Density of air with a default cited below.
- (Cd) Drag Coefficient.
- (A) Surface Area.
- (V) Velocity.
Force of Drag (Fdrag) The force of drag or air-resistance is returned in newtons. However, this can be automatically converted to other force units via the pull-down menu.
The Math / Science
The formula for the force of drag is:
where:
- Fdrag is the force of drag
- ρ is the density of the medium (e.g. density of air)
- A is the cross-section area
- Cd is the drag coefficient
- v is the velocity
Measured Drag Coefficients (Cd)
The graphic shows some common drag coefficients based on the shape of the object. Note, that there are other factors besides shape that can effect drag.
Graphics courtesy of Wikipedia (Drag coefficient)
Density of Air
The density of air, ρ (Greek: rho) (air density), is the mass per unit volume of Earth's atmosphere. Air density, like air pressure, decreases with increasing altitude. It also changes with variation in temperature or humidity. At sea level and at 15 °C, air has a density of approximately 1.225 kg/m3 (0.001225 g/cm3, 0.0023769 slug/ft3, 0.0765 lbm/ft3) according to ISA (International Standard Atmosphere).
- At IUPAC standard temperature and pressure (0 °C and 100 kPa), dry air has a density of 1.2754 kg/m3 (the default above).
- At 20 °C and 101.325 kPa, dry air has a density of 1.2041 kg/m3.
- At 70 °F and 14.696 psi, dry air has a density of 0.074887lbm/ft3.
Flight and Navigation Calculators
- Correction Angle: Computes the navigation angle/azimuth correction angle using the wind speed, wind direction, flight heading and an Air Speed.
- Ground Speed: Computes the ground speed based on the wind speed, wind direction, a Flight Heading and an Air Speed.
- Haversine - Distance: Computes the distance between two points on a spherical model of the Earth along a great circle arc. This also includes the rhumb line distance and azimuth for the rhumb line.
- Travel Time between Coordinates: Computes the time to travel between to points on the globe in a great circle arc at an average velocity.
- Distance to Sea Level Horizon at Altitude: Computes the distance to the horizon from a specified height using a spherical model the mean spherical radius of the Earth
- Force of Drag: Calculates the resisting force of drag on an object flowing through a medium (e.g. air).
- Force of Lift: Computes the lifting force on the surface area of a wing based on the wing surface area, air flow velocity, density of air and a lift coefficient.
- Lift Coefficient: Compute the lift coefficient of a wing based on lift force, wing surface area, wind speed and density of air.
- Velocity Needed for Takeoff: Computes the velocity required to create more lift than the weight of an aircraft or watercraft using a wing (e.g. hydrofoil).
- Glide Ratio: Computes the glide ratio based on the change in forward distance and the change in altitude.
- Wing Surface Area: Computes the wing surface area required to achieve lift, base on a lift coefficient, lift force, wind speed and density of air.
- Velocity of Air over the Wing: Computes the velocity required to achieve a lift, based on lift coefficient, lift force, wing surface area and density of air.
- Air Speed from Pressures: It uses the Bernoulli Equation to estimate air speed based on the total Pressure measured by a pilot tube, total Static local atmospheric pressure and the Density of Air.
- Center of Mass: Computes the vehicle center of mass between two loads (masses).
References
- Wikipedia - http://en.wikipedia.org/wiki/Drag_coefficient
- Wikipedia - http://en.wikipedia.org/wiki/Density_of_air
- Light and Matter(Dr. Benjamin Crowell) Chapter 4.3 Newton's Second Law