Downwind Spotting
Introduction
The art of downwind spotting deserves special mention because of the relationship of good spot to a good style jump. Of all the parachuting disciplines, style is the most demanding of a good spot. In accuracy, spotting is made easier because of the low altitude, the slow upwind jumprun, and negligible forward throw. In relative work, spotting is somewhat more difficult, but as long as all the jumpers can land in the packing area, everybody is happy. But for the stylist, a good jumprun and a good spot become very important for several reasons:
- unless the plane is lined up perfectly on the upper windline, with the heading on the bowl, the stylist will experience lateral "drift" in freefall
- if a stylist goes over the target in freefall due to a short spot or excess forward throw, they "lose the heading" and find it very difficult to complete the set, or make an accuracy approach. In a meet, maximum score is given if a stylist goes over the judges on the bowl.
- exit airspeed variations can make it difficult for a stylist to perform a consistent exit and fallaway
Why Downwind?
Downwind jumpruns are always used in competition and should, therefore, be used for every practice style jump. The stylist always takes a heading on the bowl, or other prominent spot visible in freefall. The jumprun downwind is so that the judges can observe the jumper's exit and so that the jumper's freefall trajectory makes it easier for the judges to keep them in view. The stylist can maintain a constant heading on the bowl from exit to opening, without having to turn around after exit as on an upwind run.
Determining the Jumprun
The two variables that effect the downwind jumprun are:
- upper wind speed
- upper wind direction
Both can be considerably different from the ground wind speed and direction. Observe where others exit and open, which way and how fast cloud shadows are moving; and any sideways aircraft drift in flight. Decide on a jumprun that minimizes freefall drift and allow a good opening point for accuracy.
Lining Up the Plane
It's very important for the stylist to line up the aircraft with the upper winds to avoid drift in freefall. If drift is experienced as shown below in Figure (a), they must constantly make heading adjustments during the jump in order to turn on heading.
INSERT Figure (a) HERE
The stylist in Figure (b) is lined up correctly with the upper winds. They will experience the same amount of drift, but directly towards the target, with no changes in heading during freefall.
INSERT Figure (b) HERE
Distance
On an average day (winds 5-15 mph) the downwind exit point should be roughly 50% further upwind from the bowl than the upwind exit point. Opening points should be the same for either jumprun, of course. Be aware that the groundspeed of the plane on a downwind run is
airspeed + windspeed
If the upper winds are 30 mph, the plane will be covering ground over twice as fast downwind as it will upwind. Therefore, it is imperative to spot carefully and exit quickly. While learning, get out too far away rather than to close to allow for error.