Edited by Mr. Dennis Zurawski
We live on the bottom of an ocean of air that covers our world. Some people venture up into that ocean as aviators. Some even get out of their aircraft and allow their density to pull them back down to the bottom. Currently this can only be survived through the use of a parachute.
Although, skydiving seems like an extreme activity to many people, in good weather conditions the risks are very low. When weather conditions change, risks are compounded. That is why these daredevils must be very aware of the currents and conditions of this ocean of air.
Wind Conditions and SkydiversThe factor that is most important to skydivers is wind conditions. Modern square parachutes have approximately a twenty mile per hour forward speed. This forward speed affords the skydiver great maneuverability.
On a day with no wind, a parachutist can go twenty miles per hour in whatever direction they prefer. When the wind is blowing, the wind speed and direction must be taken into consideration in order to land in the designated landing area. Just like a boat on a river, the currents of air will push a parachute in the direction that it is flowing.
Using Winds for SpottingSkydivers learn a skill called spotting, which is to pick out the location above the ground that will allow the wind to best assist the skydiver with getting back to the landing zone.
There are three ways to figure out the best spot for the jump:
- Skydivers may use the winds aloft forecast provided by the National Weather Service.
- The skydiver may simply look at the movement of the clouds aloft for the upper winds.
- Looking at the wind socks and flags on the drop zone for surface wind speed and direction also works.
The effects of Winds on the Drop ZOneA 10 mile per hour wind will drift a skydiver a half a mile in a normal 3000 foot descent under canopy. Because a skydiver in freefall is going at speeds ranging from 120 mph and 180 mph on average, they only stay in freefall for between 45 seconds to a minute.
With less surface area to cause drift, freefall drift is much less than the wind drift under canopy. So skydivers look at an aerial view of the area and find an easily visible landmark that is as far upwind of the landing area as their estimated drift. Once in the air the real trick is to able to look straight down and direct the plane over that spot. One degree of angle becomes quite a large distance off the spot, when looking from a height of two miles up.
Modern GPS technology has made the job in the aircraft much easier, because all the pilot has to do is head into the wind and look at the GPS for the distance from the center of the landing zone, but a good skydiver still knows how to look for the spot.
The Dangers of Wind Turbulence and SkydivingAs air flows over objects close to the ground, it will roll, just like water flowing over a rock. This rolling air is known as turbulence. Turbulence is very dangerous to skydivers because if a jumper gets caught in a downward flow of air, it will accelerate the parachutist toward the ground, which can result in injury or death.
Unlike water on a river, this flow is invisible, so skydivers must be aware of the objects that cause turbulence such as buildings, trees, or mountains. Depending on wind speed, turbulence can be created downwind of that obstacle at a distance of ten to twenty times the height of the obstacle. That is one of the reasons why skydivers don't typically jump when the winds are more than 20 to 30 mph.
Clouds and the ParachutistClouds are also a factor when skydiving. In the United States skydiving falls under visual flight rules, which basically means a skydiver needs a clear view of the ground from the height that they wish to jump. Although clouds are droplets of condensed water and would not hurt the skydiver if they fell through them, it is what is on the other side of them that the skydiver can't see, such as an airplane, that could hurt them.
The FAA has specifications as to how far away from clouds you must be depending upon what altitude you are at, and they are listed in FAR 105.17.
Beware of ThunderstormsEspecially dangerous to skydivers are thunderstorms. They are generally accompanied by very strong and erratic winds and have even been known to have updrafts that are strong enough to lift a skydiver into dangerous levels of the atmosphere where there is very little oxygen.
Now that you know what kind of weather you need to skydive safely, pick a beautiful day and head out to your local skydiving center. The United States Parachute Association is the only national organization that is recognized by the International Federation of Aeronautics. The USPA offers a list of member skydiving centers (dropzones) that promise to follow the basic safety requirements for skydiving.
Other Skydiving Information
- United States Parachute Association
- International Federation of Aeronautics
- USPA member skydiving centers
If parachuting sounds like a great summer hobby, or just an adventure you want to try out, Darlene Kellner can be reached at paskydive.com