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Old 12-11-2010, 09:43 PM
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MTK
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Default RE: the rational of trimming


ORIGINAL: Lnewqban
The wing is what flies, and the prop helps it; the rest of the airplane just follows.

Hence, increase your wing incidence = decrease the incidence of the rest of the airplane = same wing AOA

If the plane pulls to the belly on vertical line => decrease the incidence of the rest of the airplane = stab pushes ''down'' more and increases a nose pitch ''up'' that works against the ''pull to the belly'' tendency[/color]
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Which vertical? The full power up line or the no power downline?

If it's the full power up line, the prop dominates vectors. To push to undercarriage, thrust is set much too negative against the plane's reference line (too much downthrust)

The prop pushes back alot more air mass than the wing needs to generate 1G of lift when at full power. Modern pattern model powerplants generate at least 13-14 lbs of thrust at full power

If the plane pushes to belly on "no power" downline, it is carrying down elevator trim and/or the wing is at an extremely small AOA; possibly even negative. The CG is likely too far aft, operating at close to zero static margin. This is not typical for a pattern model. They will tend to go towards the canopy on downlines when set right for the rest of the flight envelope