Article on aircraft flaps.

All about Flaps

Flap is a primary flight control device that is used to increase the lift of an aircraft wing at given air speed. Flaps are installed at the trailing edge of an aircraft wings between the fuselage and ailerons. The purpose of the flap is to generate more lift at slower airspeed and more drag to slow down the airplane. Flaps usually do two things: one they increase the lift and two they increase the drag. These two features are necessary for an aircraft especially during the landing and take-off phases.

So, how flap increases the lift? The general lift equation for an aircraft is given by: L=(1/2)ρV^2 SC_L, where L, ρ,V,S and C_L stands for the lift, air density, velocity, area and coefficient of lift respectively. From the equation, the value of lift (L) increases with the increase in the value C_L. The extension of flap increases the camber of the wing and the increase in camber increases the value of C_L. This allows the aircraft to generate the required increased lift at lower speed and reducing the stalling speed. During take-off only a small amount of flap is typically deployed, usually not more than〖 5〗^°. The purpose of take-off flaps is typically to shorten the take-off roll without increasing drag.

Fig angle of attack vs coefficient of lift

How flap increases the drag? The general drag equation for an aircraft is given by: D=(1/2)ρV^2 SC_D, where D, ρ,V,S and C_D stands for the lift, air density, velocity, area and coefficient of drag respectively. The equation tells that the drag (D) is directly related to the surface area(S). Also the increased lift means increased lift-induce drag. Flaps may be fully extended for landing to give the aircraft a lower stall speed so the approach to landing can be flown more slowly, which also allows the aircraft to land in a shorter distance. For landing, full or close to full flaps is typically used (between〖 30〗^°and〖 40〗^°). This reduces the landing roll and reduces wear on wheel brakes.

Depending on the size, speed and complexity of the aircraft on which they are to be used there are different types of flap. Out of many types of flap plain flap, split flap, slotted flap and fowler flap are most used and common four types of flap and are used in many jetliners. In plain flap, the rear portion of airfoil rotates downwards on a simple hinge mounted at the front of the flap. In split flap,the rear portion of the lower surface of the airfoil hinges downwards from the leading edge of the flap, while the upper surface stays immobile. In a slotted fan there is a space for air stream while in case of fowler flap, the flap slides rearward before lowering.

                                           

Beside increasing lift and drag and helping in case of landing and take-off, flaps are also used in case of maneuvering, lowering the stall speed, decreasing the climb rates and increasing the approach angle. Therefore, flap is one of the important flight controlling devices in an aircraft and the invention of this device has been a great boost in the field of aeronautics.

You can also view it on http://aviationnepal.com/blogs/all-about-flaps/

http://aviationnepal.com/blogs/all-about-flaps/