Size Matters

December 2001
 
 


Photo: James Stevenson

Developments over the years have given us main parachutes that perform like nothing before. We have found that by loading the wing, performance improves. More speed equals more lift and combined with the hook turn or, more correctly, the front riser turn, the landings possible have added a whole new dimension to the sport.

At 15 stone with all my gear I have personally experimented with main canopies as small as 97 square feet. In one day I jumped myself through the complete range from one manufacturer, starting with a 150 then dropping each time to the next one down, 135, 120, 105 and finally the 97. With my experience the experiment was without incident and I learned a lot about the way performance changes as the wing loading increases. Just because it is possible to fly and land safely under an extremely small parachute, does not mean that it will be safe under all circumstances.
 

There is an optimum size for your weight so performance does not improve the smaller you go. For an example, for me, the 97 was too small so to get the lift necessary for a safe landing I had to increase the flap and generate more lift. This put the canopy into a configuration that made a high speed stall extremely likely.

A 135 will level off, then maintain altitude as the brakes are progressively increased, decelerating to a point where a soft and acceptably slow landing can be made. Compare this to the 97, which will stall when the brakes are increased. The size of wing is no longer enough to keep you airborne unless you are travelling very fast. The natural tendency is to increase the brakes as normal, causing a stall. When a small wing, at high speed with a lot of weight under it, finally gives up, it happens very quickly indeed. The stall will usually happen on one side first and the result is an extreme one.

 

The photo to the right shows an intermediate pilot with a lot of talent who has learned to land correctly. He has been under observation over the years and has always had more experienced pilots to give advice and sometimes give minor punishment for doing something stupid. He generally looks very cool when he lands. On this occasion this 12 and a half stone skydiver was jumping an Icarus FX 82. The photo shows that the canopy is just at the point of giving up. Under less perfect conditions this landing could easily have caused an injury.

It is possible for a heavy person to jump a tiny main and, let's face it, there are many reasons that make it attractive to do so. But jumping a tiny main on a regular basis is definitely not what is required for a long and incident-free swooping career.

The optimum size for my weight is a 135. I know that the performance will not improve if I go smaller. In fact it is quite the opposite, the reduction in performance would put me into a danger area that is not really apparent until the s**t hits the fan!
 


Photo: Gary Wainwright

Unfortunately, some designers today may be guilty of being too good at their job and the inflatable wings they produce are incredibly efficient. To gain a pilot's licence you have to fly an aircraft in a manner that satisfies an examiner, as well as pass a number of exams. The theories of flight are taught to quite a high level on the course, unlike the basic theories that are covered on a skydiving course. High performance mains today perform more like their bigger brothers [aircraft] and require greater skill to land correctly. A greater understanding of the theory of flight and a correct choice of wing loading can only benefit those who aspire to swoop into the landing area looking as cool as you like.

Size really does matter!

Words by: Dave Morris

dave@daleside2.demon.co.uk

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