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Old 09-07-2006 | 09:13 AM
  #6  
da Rock
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From: Near Pfafftown NC
Default RE: 4*40 Ailerons Trim

BTW, when you rig an aileron on a cambered airfoil up......................

You're actually creating a different airfoil. A reflex one.

But the real fun comes when you work the ailerons to roll the airplane.

One aileron is going to go up, right. And one is going down. Let's look at the one going up.

It's already been flying around trimmed up. What it's been doing all that time is reducing the lift the wing would have been able to create. And it's been creating more drag than that wing would have created had the aileron been trimmed to give the original profile of that airfoil design. And it's been causing the wing to create less lift than it would have without that aileron trim. So the wing would have been flying at a greater AOA than "necessary". Any of that sound like a benefit? So now that aileron that's about to move up starts up. It simply does all that stuff but does more of it. On the other hand..... on the other wing...... that aileron is starting down.

The down moving aileron has been killing lift and increasing drag and AOA, but now it starts down.
When it moves, all those things start to lessen. So that side of the wing gets less draggy all of a sudden. And then when the aileron gets past "neutral" it starts to get more draggy. But wait.... Everyone expects the aileron that's going down to create more lift as it moves. Does changing what amounts to a reflex profile into a positive cambered one create more lift? You'd have to check the airfoil plots. So now the aileron finally "down" and moving further. The drag ought to now increase with deflection. Good thing since it just decreased for awhile.

Reflex profiles have pitch moments. Cambered profiles do too. Cambered ones give nose down pitching moments. Symmetrical ones have none. Reflex can have down, but often have up pitching moments. What are we going to get with this cambered airfoil that is being rigged into being a reflex airfoil? Who knows, but for sure it's going to be a maze to figure out theoretically.

BTW, in theory, practice and theory are the same. In practice, they are not.