Jump Run Calculator & Drift Calculator

Jump run calculator and drift calculator

Enter a wind and a jump run heading to see how far you'll drift in freefall and how much of the wind is a headwind or crosswind. It's handy for spotting practice and for checking the numbers before a load.

Quick reference

• Drift: wind speed × freefall time. Real freefall drift uses the average wind across all the altitudes you fall through.
• Theta: the angle between where the wind is coming from and your heading.
• Headwind and crosswind: how much of the wind is on your nose (positive) or tail (negative), and how much is pushing you sideways.

Exit separation calculator

Separation is about distance on the ground, not a fixed number of seconds. Into a strong headwind the plane covers less ground each second, so groups need to wait longer to get the same spacing. Enter the plane's groundspeed and the distance you want between groups, and the calculator tells you how many seconds to wait. You can also enter a count to see the distance it gives you.

How exit separation is calculated

• Formula: separation_ft = groundspeed_kt × 1.6878 × interval_sec
• Seconds needed: interval_sec = target_ft / (groundspeed_kt × 1.6878)
• Separation in nautical miles: separation_nm = groundspeed_kt × interval_sec / 3600
• Separation in meters: separation_m = separation_ft × 0.3048
• Why groundspeed, not airspeed: what matters is how far apart you are over the ground. An Otter at 80 knots airspeed into a 30-knot headwind is only doing about 50 knots over the ground.
• How much distance: many DZs use about 1,000 ft between groups as a minimum, with more between belly and freefly groups and for tracking or wingsuit groups. Follow your DZ's numbers.

How drift and wind components are calculated

• Drift distance: drift_ft = wind_kt × 1.6878 × time_sec
• Drift in nautical miles: drift_nm = wind_kt × time_sec / 3600
• Angle to course: theta = smallest angle between wind_from and course
• Head/tail component: head_kt = wind_kt × cos(theta)
• Crosswind component: cross_kt = wind_kt × sin(theta)

Jump run calculator FAQ

What is jump run? The line the plane flies over the ground while jumpers exit. It's usually flown into the wind at altitude, so the plane slows down over the ground and groups get more time to spread out.

What is drift? How far the wind carries you sideways during freefall. 20 knots of wind over 60 seconds is about 2,000 feet.

What is exit separation? The distance over the ground between one group and the next, so you don't open on top of each other.

Spotting basics

• Look at each layer on its own (exit, freefall, canopy, surface). Then add up where each one pushes you to find the spot.
• When the upper and lower winds blow in very different directions, your drift won't be a straight line, and the spot can end up somewhere you don't expect.
• Groups that open higher (tandems, students, wingsuits) spend longer under canopy and drift further. Factor that into the exit order and the spot.
• Look out the door. Real conditions beat any forecast or calculator.

Technical references