Coring thermals  

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Coring a thermal in Austria

About this article
A world record holder, Adrian Thomas, shares some thermalling tips.

Pilot profile 
Expert. Four times British National Champion, most recently 2014. World declared goal record in 2002 (287km with Bruce Goldsmith) British Declared Goal record in 2013 and 2012. 

An Oxford professor who's studies include Aviation and Evolution. Aerodynamics consultant with Airwave (paraglider and hang glider manufacturer)

17 May 2013
Original post - Paragliding Forum.com 

29 Dec 2015
Added to the Knowledge Base with Adrian's kind permission

The most common error that pilots make when they are learning to thermal is not turning tightly enough. People worry about making flat turns, and minimising sink rate when all that really matters is that you turn tightly enough to stay in the lift. A good rule of thumb is that on most wings when you are thermalling you are likely to have the inside wingtip pretty close to the horizon. Even in the sort of weak lift we get in the UK flatlands - where 2m/s is a properly good climb - I still generally have the inside wingtip close to the horizon when I'm thermalling. If you watched mixed gaggles climbing out from the hill you will see the more experienced pilots turning at steeper bank angles than the less experienced pilots.

Staying in the core of the thermal makes much more difference than any technique you can use to try to reduce sink rate or turn flatter. First priority is to get in the core and stay in the core. That means you have to concentrate really hard on what the air in the thermal is doing, which means you need to be able to distinguish between accelerations caused by your control inputs, and accelerations caused by changes in updraft.

That means it is good to practice 360s in still (or at least smooth) air so you know what it feels like when you are doing a coordinated continuous turn.

If in any doubt at all about whether your 360 is tight enough, turn tighter. Provided you don't spin the wing and continue to gain altitude what does it matter? The steeper the bank angle the higher the G-loading, so steeper bank angles make collapses less likely.

In one particularly memorable and extremely rowdy climb over Tete de l'estrop Craig Morgan and I had our wings on the point of rocking over into a spiral dive, as we spiralled up past the brickwork mountainside we chatted about the climb and both agreed it was ok locked in (because we were banked up), but the exit was going to be interesting, when it dropped to 8m/s we left and as we levelled out we both took hits. The G-loading in a well-banked up climb is your friend.

In really weak climbs it is good to thermal with relatively little brake - minimum sink rate occurs with surprisingly little brake application - but in that case you need to weightshift a lot to keep the wing banked up and turning. In those cases it also pays to keep doing smooth 360s and allow the climb to drift you to its core - you can find the core by searching, but you risk falling out, whereas if you just keep climbing the inflow of the thermal will draw you to the core (this, of course, is a large part of why we are able to thermal - there is inflow to the core - think of the passive objects that get carried up in thermals without any control inputs - dust, straw, leaves, bags).

The biggest risk from over-enthusiastic brake-useage is spin. To deal with that you need to learn the spin-point, spin-warning and spin-response of your glider. SIV is the best option. The onset of spin does feel like losing the back-end on a bike or a car, and the right response is to put the inside hand up instantly - provided you do that before the wing has turned 90 degrees the wing will recover with a gentle surge. Beyond 90 degrees things get more interesting since you've lost a lot of airspeed and the wing has to dive to recover - best avoided.

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