Boundary layer flap ( Blown flap ) - a flap equipped with a boundary layer control system. The flap boundary blowing system is designed to improve aircraft landing characteristics. The essence of controlling the boundary layer is to provide continuous flow around the wing in a sufficiently large range of angles of attack due to an increase in the energy of the boundary layer. The boundary layer arises as a result of viscous friction of the air flow on the streamlined surfaces of the aircraft, and the flow velocity at the skin drops sharply to zero. The impact on the boundary layer is designed to weaken or prevent the stall of the flow on the streamlined surface, to preserve the laminar flow .
Content
- 1 Device and history
- 2 Jet flap
- 3 See also
- 4 notes
- 5 Links
Device and History
Air for blowing off the boundary layer is taken after the last stage of the engine compressor and is supplied to special compartments in the wing and then through the slots to the upper surface of the flaps over their entire range . The control elements of the blowing system are an electromechanism and two signaling devices. The electromechanism with two electric motors working on a common differential gearbox is connected by a rigid rod system with dampers regulating the air supply to the right and left flaps. The pressure behind the dampers is measured by two-stage sensors-alarms. The boundary layer blowing system is switched on automatically when flaps are released at an angle greater than 30 °.
For the first time, a flap with blowing of the boundary layer was designed in the UK and was popular in the aircraft industry of the 1960s. However, over time, its use came to naught due to the complexity of the blowing system in service.
In Soviet aircraft construction, the boundary layer blowing system on the MiG-21 was first developed to increase the wing lift during landing and take-off [1] . Pressure was drawn from the engine compressor and blown through a slot in the leading edge of the flaps.
Jet Flap
A similar method of increasing the coefficient of lift is a jet flap ( eng. Jet flap ). It is a flat stream of air flowing at high speed through the trailing edge at an angle to the bottom surface of the wing. Due to the jet flap, the effective area of the wing increases, the nature of the flow around the profile changes, due to the impulse of the leaky jet, a vertical component of the force that unloads the wing is created.
The use of a jet flap makes it possible to obtain a large value of the coefficient of lift, however, this requires a significantly larger pulse coefficient of the blown jet than for controlling the boundary layer. The efficiency of the jet flap drops significantly with decreasing wing elongation. Near the ground, the jet flap does not provide the calculated values of the increment of the coefficient of lift. This explains the fact that the jet flap has not yet received wide distribution and is at the stage of experimental and theoretical developments [2] .
See also
- Boundary layer
- Coanda effect
- Plate cutter
Notes
- ↑ Central Museum of the Air Force of the Russian Federation //monino.ru
- ↑ Jet flap Archival copy of August 8, 2014 on Wayback Machine //stroimsamolet.ru