Return to Answer

Leading edge flaps are less efficient than trailing edge flaps. Efficiency here means the ratio of change of lift to change in flap angle.

With every flap deflection, both camber and angle of attack of a surface change. While, for example, a nose-down deflection decreases angle of attack while increasing camber such that both effects work against each other, the changes in angle of attack and camber of a trailing edge flap work in the same direction.

Also, a leading edge flap needs to be connected to the wing at its rear end which is a poor choice for a hinge line: The added forces due to deflection will drive the flap to larger deflections. This means it is unstable, always attempting to run into the stops at maximum deflection. To keep the flap under control will require heavy actuators. At the trailing edge the hinge line is ahead of the added lift forces and this will drive the flap to a neutral position regarding tail surfaces while the interconnection of ailerons will keep both sides equally loaded. Trailing edge flaps are inherently stable.

Leading edge devices are only helpful to increase the maximum angle of attack: While the whole airplane will adjust angle of attack to compensate, the flap will reduce the suction peak at the leading edge so flow separation is delayed.

Leading edge flaps are less efficient than trailing edge flaps. Efficiency here means the ratio of change of lift to change in flap angle.

With every flap deflection, both camber and angle of attack of a surface change. While, for example, a nose-down deflection decreases angle of attack while increasing camber such that both effects work against each other, the changes in angle of attack and camber of a trailing edge flap work in the same direction.

Also, a leading edge flap needs to be connected to the wing at its rear end which is a poor choice for a hinge line: The added forces due to deflection will drive the flap to larger deflections. This means it is unstable, always attempting to run into the stops at maximum deflection. To keep the flap under control will require heavy actuators. At the trailing edge the hinge line is ahead of the added lift forces and this will drive the flap to a neutral position regarding tail surfaces while the interconnection of ailerons will keep both sides equally loaded. Trailing edge flaps are inherently stable.

Leading edge devices are only helpful to increase the maximum angle of attack: While the whole airplane will adjust angle of attack to compensate, the flap will reduce the suction peak at the leading edge so flow separation is delayed. This is particularly helpful when you combine slotted flaps inboard with regular ailerons outboard. Without a suitable leading edge flap ahead of the ailerons, the circulation added by the inboard flaps will make the outer wing stall before the inboard wing reaches its full potential. This leads to rather unpleasant stalling characteristics, something to avoid especially during approach and landing.

Leading edge flaps are less efficient than trailing edge flaps.

With every flap deflection, both camber and angle of attack of a surface change. While, for example, a nose-down deflection decreases angle of attack while increasing camber such that both effects work against each other, the changes in angle of attack and camber of a trailing edge flap work in the same direction.

Also, a leading edge flap needs to be connected to the wing at its rear end which is a poor choice for a hinge line: The added forces due to deflection will drive the flap to larger deflections. To keep the flap under control will require heavy actuators. At the trailing edge the hinge line is ahead of the added lift forces and this will drive the flap to a neutral position regarding tail surfaces while the interconnection of ailerons will keep both sides equally loaded.

Leading edge devices are only helpful to increase the maximum angle of attack: While the whole airplane will adjust angle of attack to compensate, the flap will reduce the suction peak at the leading edge so flow separation is delayed.

Leading edge flaps are less efficient than trailing edge flaps. Efficiency here means the ratio of change of lift to change in flap angle.

With every flap deflection, both camber and angle of attack of a surface change. While, for example, a nose-down deflection decreases angle of attack while increasing camber such that both effects work against each other, the changes in angle of attack and camber of a trailing edge flap work in the same direction.

Also, a leading edge flap needs to be connected to the wing at its rear end which is a poor choice for a hinge line: The added forces due to deflection will drive the flap to larger deflections. This means it is unstable, always attempting to run into the stops at maximum deflection. To keep the flap under control will require heavy actuators. At the trailing edge the hinge line is ahead of the added lift forces and this will drive the flap to a neutral position regarding tail surfaces while the interconnection of ailerons will keep both sides equally loaded. Trailing edge flaps are inherently stable.

Leading edge devices are only helpful to increase the maximum angle of attack: While the whole airplane will adjust angle of attack to compensate, the flap will reduce the suction peak at the leading edge so flow separation is delayed.

Leading edge flaps are less efficient than trailing edge flaps.

With every flap deflection, both camber and angle of attack of a surface change. While, for example, a nose-down deflection decreases angle of attack while increasing camber such that both effects work against each other, the changes in angle of attack and camber of a trailing edge flap work in the same direction.

Also, a leading edge flap needs to be connected to the wing at its rear end which is a poor choice for a hinge line: The added forces due to deflection will drive the flap to larger deflections. To keep the flap under control will require heavy actuators. At the trailing edge the hinge line is ahead of the added lift forces and this will drive the flap to a neutral position regarding tail surfaces while the interconnection of ailerons will keep both sides equally loaded.

Leading edge flaps are less efficient than trailing edge flaps.

With every flap deflection, both camber and angle of attack of a surface change. While, for example, a nose-down deflection decreases angle of attack while increasing camber such that both effects work against each other, the changes in angle of attack and camber of a trailing edge flap work in the same direction.

Also, a leading edge flap needs to be connected to the wing at its rear end which is a poor choice for a hinge line: The added forces due to deflection will drive the flap to larger deflections. To keep the flap under control will require heavy actuators. At the trailing edge the hinge line is ahead of the added lift forces and this will drive the flap to a neutral position regarding tail surfaces while the interconnection of ailerons will keep both sides equally loaded.

Leading edge devices are only helpful to increase the maximum angle of attack: While the whole airplane will adjust angle of attack to compensate, the flap will reduce the suction peak at the leading edge so flow separation is delayed.