этапы отбора и ответы. Этапы отбора и ответы. REV2. Этапы отбора в Аэрофлот
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Stall (сваливание) и процедуры по выводу из сваливанияAn aircraft stall results from a rapid decrease in lift caused by the separation of airflow from the wing’s surface brought on by exceeding the critical AOA. An aircraft stalls when the streamlined/laminar airflow (or boundary layer) over the wing’s upper surface, which reduces lift, breaks away from the surface when the critical angle of attack is exceeded, irrespective of airspeed, and becomes turbulent, causing a loss in lift (i.e., the turbulent air on the upper surface creates a higher air pressure than on the lower surface). The only way to recover is to decrease the angle of attack (i.e., relax the backpressure and/or move the control column forward). When the lift developed by an airplane wing is no longer sufficient to sustain the mass of the airplane in flight, in the configuration being considered, the wing is stalled. It is caused by the total drag restricting the speed of the airplane to less than that required to produce the necessary lift. There are five types of entry to a stall; they are the low-speed stall or the high incidence angle stall, the power-on stall, the accelerated stall, the deep or superstall and the high-speed or shock stall. All of them have one common feature, that is that the boundary layer becomes detached from the upper surface of the wing. Boundary level separationAll solid objects traveling through a fluid (or alternatively a stationary object exposed to a moving fluid) acquire a boundary layer of fluid around them where viscous forces occur in the layer of fluid close to the solid surface. Boundary layers can be either laminar or turbulent. A reasonable assessment of whether the boundary layer will be laminar or turbulent can be made by calculating the Reynolds number of the local flow conditions. Flow separation occurs when the boundary layer travels far enough against an adverse pressure gradient that the speed of the boundary layer relative to the object falls almost to zero.[1][2] The fluid flow becomes detached from the surface of the object, and instead takes the forms of eddies and vortices. In aerodynamics, flow separation can often result in increased drag, particularly pressure drag which is caused by the pressure differential between the front and rear surfaces of the object as it travels through the air. For this reason much effort and research has gone into the design of aerodynamic and hydrodynamic surfaces which delay flow separation and keep the local flow attached for as long as possible. Examples of this include the fur on a tennis ball, dimples on a golf ball, turbulators on a glider, which induce an early transition to turbulent flow regime; vortex generators on light aircraft, for controlling the separation pattern; and leading edge extensions for high angles of attack on the wings of aircraft such as the F/A-18 Hornet. Boundary layer separation is the detachment of a boundary layer from the surface into a broader wake. Boundary layer separation occurs when the portion of the boundary layer closest to the wall or leading edge reverses in flow direction. The separation point is defined as the point between the forward and backward flow, where the shear stress is zero. The overall boundary layer initially thickens suddenly at the separation point and is then forced off the surface by the reversed flow at its bottom. Кривая потребных и располагаемых тяг (Thrust Required Curves for an Airplane)Thrust required is dictated by the airframe: shape (airfoil, planform, fuselage, empennage) size (surface area, frontal area, airfoil) configuration (clean, gear down, flaps down) Thrust available is dictated by the powerplant (engine type, prop) Reciprocating engine - propeller combination Turbojet Turboprop (turbine engine and propeller) Turbofan Ducted propeller Jet Engines are rated in units of force (“thrust” … lb or N) Jet Engine power: P = T x V Prop-Driven Engines are rated in units of Power (assumed: P = T x V) Accelerating the mass (of air) gives Ta (remember F = ma) PROPELLER - uses a larger mass of air & imparts a smaller ∆V∞ TURBOJET - uses a smaller mass of air & imparts a larger ∆V∞  TA & TR vs V curves provide Vmin and Vmax Assume TA = constant for all velocities TA & TR depend on altitude TA decreases as altitude increases (air is thinner) Our model TA, alt = ρ/ρο TA, sea level (inversely proportional)  PA for the Jet engine grows linearly with V PA from the Prop engine is constant with Vs  |