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Old 07-06-2007, 11:59 PM
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dhk79 dhk79 is offline
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Join Date: May 2006
Location: Alexandria, VA
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That pretty much finishes the trim topics that can effect the simulator's physics. There are, however, some other problems that can have an affect on real RC aircraft. Most of these problems have their root in the construction of the airplane.

The first problem occurs mostly at low-speed and high angles of attack, and has probably contributed to more RC landing mishaps that all other causes combined. The problem is uneven aileron hinge gaps (this is not a problem in the simulator). It occurs very unpredictably, but when it occurs you often do not have time to recover (i.e. landing). It is better to fix this problem before it ever bites you and the fix is easy. Just seal the gaps between the ailerons and the wing, so that the higher pressure air from under the wing cannot pass through the gap. It only takes a couple of minutes to use tape or monocote to create the seal, before you take a bird out for its first flight. It's cheap insurance...

The second problem is lateral (side-to-side) balance. The instructions for most ARFs (and kits too) only tell you to balance the plane from end-to-end to set the CG, but the lateral balance is important too (especially if you want to do more than fly around in a level pattern). The lateral balance is only effected by gravity and so it does not change with airspeed, but it will cause the plane to roll towards the heavy side in “High-G” maneuvers (i.e. loops). The solution to keeping the plane balanced at all speeds is to have the aircraft weight balanced from side-to-side. The easiest way to do this is to take the prop off and suspend the plane from the prop shaft and a cord passed under a rudder hinge (use the hinge closest to, but above the aircraft center of mass). Add weight to the high side until you get the plane to balance.

The third problem is imperfect airfoils. These are tiny differences in airfoil shape (especially the rounding of the LE) that can require that the ailerons be trimmed to counteract. The aileron deflection and resulting airfoil shape will have different airspeed characteristics, so the required trim will change with airspeed. There is not much that can be done about this after the fact, so use care if you are building a kit.

The last problem is wing warps, even subtle ones. These also require aileron trim to counter and vary with airspeed. A warp will usually maintain its influence at very low speeds, however, while any aileron trim loses effectiveness. Some minor wing warps can be fixed, if the wing is covered in heat shrink covering. Have someone twist the wing in the opposite direction of the warp and small creases will appear in the covering. While the wing is being held, use a heat gun to shrink out the creases. As the covering cools, it will hold against the warp and hopefully flatten out the wing.
- Knowing why ten things will not work is more important than not knowing why one does.
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Last edited by dhk79; 07-10-2007 at 01:55 PM.
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