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Old 04-07-2012, 01:50 PM
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quorneng
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NFA Fabrication
It surely depends on what you want the flaps to do.
The conventional flap alters the camber of the wing section. At a low angles (up to 20 degrees) the lift is increased significantly but not the drag. At angles over 45 degrees the drag increases with little further increase in lift.
So these types of flap will reduce the stall speed but until the angle is big enough will not allow a steep approach. At low angles they can also be used to reduce the take off speed. Modern airliners have very complicated versions of these flaps.

The split flap acts more like an air brake than a lift increasing device so is used to increase the angle of approach on a 'slippery' airframe where reducing the stall speed is not required. The Spitfire used a split flap that dropped to almost 90 degrees simply to create drag to allow a reasonably steep approach. It only reduced the stall speed by a few knots.
The split flap simply added to the bottom of the wing is just a 'poor man's' version.

There is also a 'Junkers' type flap which is a small aerofoil suspended beneath the trailing edge. Very effective but of course it adds drag all the time. The JU52 used this type of flap and even its ailerons where done like this as well.
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