Size does matter! - Why bigger gliders are better | ||
About this article 09 Dec 2015 Contents l Effect of size on performance l
I have a good friend who is a small competition pilot, He weights it at 52kg, and he always flies a Small glider or XS if he can get hold of one (it is rare for a manufacturer to make an extra small competition glider). He tells me that he has been competing on small gliders for years and is painfully aware of the difference in glide performance between sizes. He says ‘a difference of two sizes gives around the same performance difference as a whole class of paraglider’. That means that someone flying a Small competition glider would have the same glide performance as someone flying a Large Intermediate wing. If true this would be a really very large difference in performance indeed. Bigger pilots should therefore have an advantage in competitions. I have noticed some evidence to support this. If you look at the results of the World Championships for example and look at the glider sizes being flown we have: 1) Alex Hofer – Large And the PWC 2002 results give PWC 2003 is not yet finished, but it will be interesting to see. Pilot skill is obviously the main factor but if your glider goes a bit better because it is bigger, then that for sure helps. It is precisely for this reason that ballast is so popular in competitions and the FAI and PWC have had to bring in rules limiting the use of ballast. Pilots found that they perform better if they fly a bigger glider and carry ballast, rather than fly a glider that is the correct size for them. Most people do not even bother to drop ballast when the conditions are getting weaker, as the strength of the conditions is not the main reason for carry the ballast.
The fact that Alex Hofer is doing so well in all major competition also makes it look like large gliders are winning more, so I asked Alex Hofer for his view on the subject. Bruce: ‘do you feel you have a performance advantage because of your size’ Alex: ‘ Yes, though it does depend on the conditions, generally the big gliders go better, but if conditions are weak with small thermals then the tighter turning radius of small gliders can give them an advantage, this was the case with Jimmy Pacher at the Europeans when he came 3rd on a small glider.’ Bruce: ‘What weight are you and what size glider do you fly?’ Alex: ‘ 92kg naked and all up between 120 and 125kg depending on how much ballast I carry, which depends on the conditions. I always fly a Large’ Bruce: ’Why do you think Large gliders go better’ Alex: ‘When the air is moving and turbulent I think that a bigger glider is less shaken about by the air than a small one. Also I have noticed that pilots flying larger wings generally fly with a greater wing loading. On Large gliders the wing loading is around 4.3kg/sq m and on small gliders it is around 4.0kg/sq m. Gliders go better when heavily loaded.’
But it is not only glide performance that is influenced by size, the safety is also effected by size. When preparing a glider for DHV certification it is always much easier for the manufacturer to get the Large gliders to pass the tests than the Small ones. This often means that the small gliders need to be trimmed more to pass the certification which could mean for example that they are trimmed slower to get the same certification grade as their bigger brothers. Some Small or XS gliders cannot obtain certification at all, where as their bigger brother pass with no problems. So smaller gliders are less safe and have worse performance! Unfortunately this is inescapable and applies to all paragliders, even though the manufacturers try their best to produce the safest and best performing small gliders that they possibly can.
There are several factors that this can be put down to. 2) Materials. 3) Pilot drag. 4) Scaling time.
Unfortunately there is no solution to this problem, it is a fact of life we all have to live with. When writing this article I looked closely at the results of the PWC for 2003. I was surprised to see a remarkable lack of pilots doing well flying small gliders. This was even more obvious than the number of pilots doing well on big gliders. Perhaps the top of the PWC will end up looking like a team of American footballers in the future! |
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