THERMALS - AND HOW TO CATCH THEM
SUMMARY -What are Thermals - Trimming - Launching - Timing - Let your glider talk to you
WHAT ARE THERMALS?
Thermals are rising bubbles or columns of air. As they rise they suck up the air around.
Area of ground that is heated by the sun.
The colder air above is displaced by the warm air and falls towards earth as sink.
If the prevailing breeze drops it may be because there is a thermal in front of you sucking up the breeze that you were expecting to hit your face.
If the breeze increases it may mean the thermal is now behind you. What is now hitting your face is the prevailing breeze AND the extra air that is about to be sucked up into the thermal behind you. You may also note that the breeze is slightly cooler.
A change in wind directionmay mean a thermal off to the side swinging the breeze around.
The days and times of the greatest probability of thermals: - puffy clouds, light/variable winds, generally before mid afternoon - the warming earth heats the cool air. Watch for the signs. Look at the birds. If they’re not flapping their wings a thermal is giving them lift. If a bungee parachute is coming down slower than usual, it may be because of a thermal. Watch other gliders and rubbish (plastic bags) going up. Join them!
TRIMMING YOUR GLIDER
To maximise your thermal catching you need to tune your glider to best advantage. Your trims should be set and the glider balanced so that (with throttle off) you centre the control sticks (even let them go) and it will and gently fly flat and straight, neither diving nor porpoising. Spend a bit of time on the important task of balancing and trimming your glider and get an experienced pilot to help you if necessary. (Also, see article on this sitetrimming your plane.)
WHEN TO LAUNCH
If you launch into the breeze when it is at its strongest you are launching straight into "sink" caused by the thermal that has just gone! Better to launch when the wind is starting to die to catch the up-draft of the next thermal rather than the down draft of the one that’s just passed. The strongest thermals are generally higher up.
For bungee launched gliders, work on maximising your launch height. This will require a good throw to get the glider to flying speed, an appropriate "rotation" (ie lifting of the nose) to climb angle and having the tow hook in the best place (generally about 30 degrees ahead of centre of gravity) so your glider goes up like a kite, without being pulled too far forwarded and wasting all the stretch in the bungee or lifting its nose so it pops off the line. If you’ve been clever enough to have pre-drilled a small line of holes for your bungee tow hook before covering, or you have an adjustable hook, you may be able to experiment with different tow hook positions on the field.
For a few extra feet of climb, learn to dip the nose at the top of the climb up the bungee, gain a little speed, then nose up again to drop the bungee. By doing this you gain more height that you would have without the "dip", just like the lads with the winches but on a lesser scale. Seek assistance from experienced pilots to help you with all this.
For you electric glider pilots, take off and up at what you have found to be your best climb angle, throttle back to nil when you’ve got to around 250 feet and settle your craft down to a gentle cruising speed. Then go sniff out some lift.
LET YOUR GLIDER TALK TO YOU!!!
Here is the big secret - let go of your controls. Now, (apart from radio glitches) any movement in your glider must be caused by thermal activity! If you are pushed up to the right it was probably an up-draft pushing up your left wing. Steer left to get into the area of lift! Even if you can’t see the glider going up you will find this simple action will increase your flight times considerably.
Flying straight into a thermal should cause your glider to buck a little. If your glider never bucks, try a little up trim or bring the centre of gravity back a little, but only a millimetre or two at a time or it will fly like a pig. Move the battery back slightly, take a little weight out of the nose or add a small amount of blu-tack on the tail.
Elsewhere in the sky, put your glider into a gentle banked turn. Let go of the controls again and observe. Is it flying steady in a gentle circuit? If it isn’t, you may be around lift so keep sniffing around. If it is flying steady (and you cannot see it rising) point it in some other direction and let go of the sticks.
If your electric glider seems to be climbing faster than normal under power, you’re probably in a thermal. Throttle off, settle your glider and try to keep with it.
If you find yourself descending in "sink" (the opposite of lift!) get out of it - fly somewhere else. Use power if you need to.
DON’T fly in a gale, leave that for the experts.
DON’T let go of the sticks if you are close to the ground(!!).
Turn slowly down wind, not quickly or your glider could fall out of the sky as its speed drops relative to the wind. This is more pronounced with a heavier electric model than a lighter un-powered glider. (SeeLearn to fly)
Avoid mid air collisions by flying the same direction as the other glider(s) in the thermal.
if you’re too high come down a little. Big thermals can eat gliders! Spin (full rudder, full up) or fly away from the lift. A fast dive can destroy a glider. If you see your wings flutter, slow down! Was that your favourite glider? Did you have your phone number on it……..?
As mentioned, it may be possible to determine that a thermal has just past you by the increase in the wind strength and a slight decrease in air temperature. An experienced pilot with a glider that has good penetration to get back may be capable of following the thermal downwind. However I would recommend against the beginner venturing downwind because of the very high risk of not being able to get the glider back. (SeeLearn to fly)
Balance your glider, watch the birds and other gliders doing well. Launch high and go forward. Let go of the controls as often as you can and watch what your glider is trying to tell you. Find your thermals - embrace them. Fly often and fly safe - Ian Pullar
(PS – Some trainers may shoot me for suggesting you let go of the controls – so simply centre them instead.)
Fly safe - and fly often
YOU'RE PROBABLY READY