GRAUPNER GmbH & Co. KG D-73230 KIRCHHEIM/TECK GERMANY
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12/2010
0062196
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approximately correct. It is bound to fail if the model is a long way out of balance and / or
there is a strong wind. In breezy conditions it is difficult to set up the model for normal cruise
speed, as it is hard to judge its speed relative to the surrounding air.
Trim the model carefully for normal cruising speed, which should be comfortably above
stalling speed. The model should show no tendency to “hunt” up and down, or mush along
close to the stall. It should respond normally to all controls. Keep the flaps at the “neutral”
position.
Now - assuming that you have plenty of height in hand - apply full down-elevator briefly to
place the model in a vertical dive. Immediately centre the stick and watch the aeroplane
carefully. If it recovers to normal flight in a broad, gentle curving arc (100 m) by itself, without
ballooning up above the horizontal, then the CG is correct.
If the model bounces up again immediately and climbs strongly, the CG is too far forward.
Remedy:
remove lead ballast from the fuselage nose; apply slight down-elevator trim.
If the model shows no tendency to recover by itself - the dive may even become steeper - the
CG is too far aft.
Remedy:
immediately recover the model with gentle up-elevator. Add a little lead ballast to
the fuselage nose, fix it securely, and apply a little up-trim.
Flat-field flying
Flat-field flying is relatively non-hazardous since there is no risk of the model “landing out” at
the foot of the hill, as with slope soaring.
Nevertheless, making the best use of flat field thermals is not particularly easy, and calls for
considerable skill and experience. Areas of rising air are harder to detect and recognise at a
flat field, because they tend to occur at higher altitude than at the hillside, where it is often
possible to find lift while the model is cruising along the edge of the slope and then circle
away in it. A thermal at a flat field which occurs directly overhead is very hard to recognise,
and exploiting it to the full requires a highly skilled pilot. For this reason it is always best to go
thermal seeking off to one side of where you are standing.
You will recognise thermal contact by the model’s behaviour. Good thermals are obvious
because the model will climb strongly, but it takes a practised eye to detect weak thermals,
and you will need a lot of skill to make use of them. With a little practice you will be able to
recognise likely trigger points for thermals in the local landscape. The ground warms up in
the sun’s heat, but heat absorption varies according to the type of terrain and the angle of the
sun’s rays. The air over the warmer ground becomes warmer in turn, and the mass of warm
air flows along close to the ground, driven by any breeze. Strong winds usually prevent
thermal build-up. Any obstruction - a shrub or tree, a fence, the edge of a wood, a hill, a
passing car, even your own model on the landing approach - may cause this warm air to
leave the ground and rise. Imagine a drop of water on the ceiling, wandering around aim-
lessly, and initially remaining stuck to the ceiling. If it strikes an obstruction it will fall on your
head. A triggered thermal can be imagined as the opposite of the drop of water.
The most obvious thermal triggers include sharply defined snow fields on mountain slopes.
The air above the snow field is cooled, and flows downhill; at the edge of the snow field, part-
