Spring is coming... Chest Straps, Stirrups and Pods
The turbulent days of spring will be with us imminently; we have already had a few good thermalling days and February has barely started.
The rougher air may encourage less well informed pilots to change their chest/waist strap setting. Before doing so, you must be aware of the effects of the riser separation:
Too wide and although you will have good feedback and weightshift authority, this may become wearing. You will also experience increased spiral stability (the tendency to stay spiralling - not a good thing) and within a range of deflations you will get tilted more aggresively. This tilting can result in line twists.
Too narrow and you will not get enough feedback to tell you when to land, you are also more likely to suffer deflations and more likely to suffer line twists.
Every glider has a designed chest/waist strap setting which will optimise perofrmance and safety. Use it! If in doubt of the setting for your wing, RTFM.
The pilot's moment of inertia will also affect the likelihood of line twists. If you fly very upright, with your feet down, 'the old man position' you will exhibit pretty much your lowest possible moment of inertia and would be unlikely to get line twists. If you fly very supine &/or with your feet out as if in a stirrup or pod, then you exhibit a high moment of inertia. This is not all bad, but it can complicate the handling of big deflations. It is far simpler, whenever you feel a deflation is likely, to lower your feet and maybe also sit up. This has the added benefit of making most harnesses less rigidly cross braced and so more likely to ride out the rough air.
If it's rough and you are near the ground, say 100', you should go into the PLF position. You may not think it looks cool, but walking away from a 60% deflation and subsequent crash looks a whole lot cooler than the alternative. In which regard, the next time you are on the hill waiting for conditions, why not have a PLF practice session. It'll definitely be a good laugh, because most pilots are hopeless at them!
If you find you have a big deflation when fully supine, initially roll with it and bring your legs down slowly. What you don't want to do is find yourself rotating and then quickly lower you're legs as that will cause the rotation to accelerate.
In my experience, line twists are usually caused not on any initial deflation, but occur when the initial deflation recovers fast and the canopy violently rotates in the opposite direction. This is when you want your moment of inertia to be as low as possible.
Don't forget your sunscreen, I managed to get sunburnt on Tuesday!
TTFN
Steve Purdie