United States Parachute Association > Experienced Skydivers > SIM > Section 6-3

6-3: Freefall Rate of Descent and Time Table

A. A logging aid

  1. The following table will assist in estimating the approximate amount of freefall time to be expected from a given altitude and in logging the correct amount of freefall time for a given jump.
  2. Each skydiver should log every jump made, including the amount of freefall time experienced.
  3. The amount of freefall time logged for each jump should be actual time.

B. Computation

  1. Many factors affect the rate of fall or terminal velocity in freefall.
    1. total weight of the jumper including equipment
    2. the surface area-to-weight ratio
    3. jumpsuit
    4. altitude above sea level (air density)
    5. skydiving discipline, e.g., vertical orientations
  2. The chart lists freefall times based on three different typical terminal velocities and provides an exit altitude reference for 3,000-foot openings.
    1. 120 mph (176 feet per second) for belly-to earth orientation
    2. 160 mph (235 feet per second) for vertical head-down or standing orientation
    3. 50 mph (73.3 feet per second) for wing-suit jumps
  3. To determine the approximate amount of freefall time to expect on a jump and to log a realistic amount of freefall time for a jump, use the following procedures:
    1. Determine your approximate terminal velocity by taking actual measurements of jumps with known exit and opening altitudes (this can be done by timing video tapes, by having someone on the ground time the skydive, or using a recording altimeter).
    2. Subtract your opening altitude from your exit altitude to determine the length of your freefall.
    3. Use the chart to estimate your freefall time according to your approximate terminal velocity and the distance in freefall.