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While some may debate the finer points, in general this is sage advice proven through the years. Thought it was worth sharing here for those who have never seen or those wanting another pass through...
DAVE THORNBURG'S RULES
Drift with the lift. Thermals tend to blow along with the wind, so follow them.
Stay with what you've got. Low thermals have down air nearby. There ain't no zero lift.
A weak, low thermal will almost always grow.
If you're not sinking, there's some lift.
If you're sinking, move someplace else — fast!
Don't leave a thermal and come straight back upwind.
Sink holes follow thermals.
Strong lift will usually have strong downs nearby — and vice versa. If some air is going up, some other air must be coming down to replace it, and vice versa. Sometimes the patch of down air (sink) is so large that you can't get out of it.
Fuselage angle indicates rising or sinking air.
Thermals will tend to push the plane outward, so turn back against lift-induced turn to get into the core.
Establish where the core is by making a couple of passes through the lift.
Once circling in lift, notice which side of the circle is better, and drift in that direction.
The implicit rule is: Slow down in lift, and speed up in sink. Once you find a thermal, don't lose contact with it! Sometimes you find a nice thermal and think you've got your 10 minutes made. You relax. The next thing you know, you're sinking, and you're wondering where the heck the lift went!
Develop a minute sensitivity to air quality.
Lift comes through in cycles.
Hot spots for thermals and ridge-type lift tend to stay put for a long time
A thermal passing through as you launch can often be overtaken downwind.
A sudden wind shift usually indicates a thermal nearby — the wind on the ground blows toward the thermal. You need to feel small air-temperature changes — warmer means lift, colder means sink. You need to know which way the wind is blowing without looking at your ribbon.
Learn to use ballast.
Wing loading translates into flying speed (the heavier the plane, the faster it must fly).
The trick is to add enough ballast to achieve good glide speed without handicapping the ship in weak lift or making it too hard to land.
If the wind is strong enough to require ballast, flying downwind is usually bad.
The fast, more efficient ships benefit most from ballast. There's no point putting a pound of lead in a Windrifter for 20 mph conditions, because it won't fly faster than 20 mph anyway.
Ways of finding lift. There are several visible signs of lift that you should watch for: shifts in the wind or temperature, swifts chasing bugs, other sailplanes, etc. Soaring birds may be around to key off of, but they may be up too high for accurate thermal telltale. Piggybacking off another flier also works!
From Model Builder, Sept. '87 / NSS journal, Nov. - Dec. '88
DAVE THORNBURG'S RULES
Drift with the lift. Thermals tend to blow along with the wind, so follow them.
Stay with what you've got. Low thermals have down air nearby. There ain't no zero lift.
A weak, low thermal will almost always grow.
If you're not sinking, there's some lift.
If you're sinking, move someplace else — fast!
Don't leave a thermal and come straight back upwind.
Sink holes follow thermals.
Strong lift will usually have strong downs nearby — and vice versa. If some air is going up, some other air must be coming down to replace it, and vice versa. Sometimes the patch of down air (sink) is so large that you can't get out of it.
Fuselage angle indicates rising or sinking air.
Thermals will tend to push the plane outward, so turn back against lift-induced turn to get into the core.
Establish where the core is by making a couple of passes through the lift.
Once circling in lift, notice which side of the circle is better, and drift in that direction.
The implicit rule is: Slow down in lift, and speed up in sink. Once you find a thermal, don't lose contact with it! Sometimes you find a nice thermal and think you've got your 10 minutes made. You relax. The next thing you know, you're sinking, and you're wondering where the heck the lift went!
Develop a minute sensitivity to air quality.
Lift comes through in cycles.
Hot spots for thermals and ridge-type lift tend to stay put for a long time
A thermal passing through as you launch can often be overtaken downwind.
A sudden wind shift usually indicates a thermal nearby — the wind on the ground blows toward the thermal. You need to feel small air-temperature changes — warmer means lift, colder means sink. You need to know which way the wind is blowing without looking at your ribbon.
Learn to use ballast.
Wing loading translates into flying speed (the heavier the plane, the faster it must fly).
The trick is to add enough ballast to achieve good glide speed without handicapping the ship in weak lift or making it too hard to land.
If the wind is strong enough to require ballast, flying downwind is usually bad.
The fast, more efficient ships benefit most from ballast. There's no point putting a pound of lead in a Windrifter for 20 mph conditions, because it won't fly faster than 20 mph anyway.
Ways of finding lift. There are several visible signs of lift that you should watch for: shifts in the wind or temperature, swifts chasing bugs, other sailplanes, etc. Soaring birds may be around to key off of, but they may be up too high for accurate thermal telltale. Piggybacking off another flier also works!
From Model Builder, Sept. '87 / NSS journal, Nov. - Dec. '88