Wormburners 101

When it comes to hot arrivals, fighter types have the run and break. But when you fly without an engine, nothing comes close to gliding’s Competition Finish.

The concept is straightforward (and slightly downward). Gliders have a known best glide angle, so there’s a reciprocal approach slope that rises out from the designated finish point. Once you intercept this slope you can forget about slow circling for height and just put the nose down on a bee-line for home.

The basics of a final glide to a finish at 'ground zero'. The red critical slope becomes steeper (and therefore closer in) if there's a headwind.
The basics of a final glide to a finish at ‘ground zero’. The red critical slope becomes steeper (and therefore closer in) if there’s a headwind.

Basically, you want to convert all your remaining altitude (potential energy) into time-saving, race-winning speed (kinetic energy). Simple, huh?

Of course the vagaries of wind and lift and sink mean it’s never quite that reliable, so ‘worm burners’ are rather frowned upon these days. Finish cylinders with a minimum altitude are much more common. Here’s why.

Glide distance (distance over the ground, not the glide ratio) changes with a head or tail wind. If only the wind would blow steadily from one direction, it would be pretty simple to make  the necessary adjustment to your final glide.

If only… And that’s not the only complication. Finding extra lift on your final glide is usually a good thing. It means you can just lower the nose and increase your forward speed. But finding sink is a different matter. If you lose too much height there’s little option but to find some lift and circle for altitude again.

So you need to build a generous safety margin into every final glide regardless of the finish line altitude, or risk paying a price in lost time later. But when your finish altitude is right down in the weeds, you could lose a lot more than time…

A Rolladen-Schneider LS4 (pilot John Roberts) dumping water ballast at about 140 knots during a competition finish. © www.whiteplanes.com
A Rolladen-Schneider LS4 (pilot John Roberts) dumping water ballast at about 140 knots during a competition finish. © http://www.whiteplanes.com
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