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07-A: Maneuvering during Slow Flight

Knowledge

K1: Aerodynamics associated with slow flight in various airplane configuration, including the relationship between angle of attack, airspeed, load factor, power setting, airplane weight and center of gravity, airplane altitude, and yaw effects

  • angles

    • angle of attack: angle between

      • chord line of the wing/airfoil
      • relative wind / oncoming airflow

    • angle of incidence: angle between

      • chord line of the wing
      • longitudinal axis of the aircraft

  • relationships between stalls, angle of attack, load factor,

    • increase in load factor

      • increases stall speed

    • slowing down requires

      • increase in angle of attack to maintain altitude

    • changes in the center of pressure

      • changes the aerodynamic balance and controllability

    • approaching the stall speed

      • decreases controls responsiveness
      • increases controls mushiness

  • flaps may be used in slow flight

Risk Management

R1: Inadvertent slow flight and flight with a stall warning, which could lead to loss of control

R2: Range of limitations of stall warning indicators (e.g., aircraft buffet, stall horn, etc.)

R3: Uncoordinated flight

R4: Effect of environmental elements on airplane performance (e.g., tubulence, microbursts, and high-density altitude)

R5: Collision hazards

R6: Distractions, task prioritzation, loss of situational awareness, or disorientation

  • pitch for airspeed
    • airspeed dropping, drop the nose
    • airspeed rising, raise the nose
  • power for altitude

Slow Flight

"Practive Area, Skyhawk 54U, X miles N/E/W/S/Nx/Sx of P at A feet, practicing slow flight, Practice Area"

  • lift increases nearly linearly with angle of attack up to the critical angle of attack
  • drag however increase sharply at high angles of attack
  • at high angles of attack, i.e., in slow flight, the lift to drag ratio becomes less than 1.0, i.e., we generate more lift-induced than we generate lift, - thus pitch controls airspeed
  • as we get pitch up, we get slower, and we need to add power to generate more lift again

Region of reverse command

axioms: 1) forces in equilibrium: lift = weight in level flight, thrust = drag in unaccelerated flight 2) lift = lift coefficient x density x (v^2)/2 x wing area 3) in slow flight, lift-induced drag decreases quadratically and becomes a dominant form of drag (it decreases quadratically) 4) in normal cruise, parasite drag increases quadratically and becomes the dominant form of drag

why do we need to add power to get slower in the region of reverse command: - we want to maintain altitude, but get slower - to maintain lift = weight, we need to produce the same amount of lift as before - air density and wing area are constant, so as per the lift equation, when we decrease velocity, we must increase the lift coefficient, i.e., the angle of attack - increasing the angle of attack in slow flight produces a lot of lift-induced drag - we counter the lift-induced drag by adding thrust (power) - in summary: - "In normal flight, reducing power reduces total drag (parasite drag to be specific)" - "In slow flight, reducing power increases total drag (lift-induced drag to be specific) so we need to add thrust"

Region of normal command

in normal cruise: - we are at 2100 RPM. straight, level, unaccelerated, i.e., thrust = drag, lift = weight - basics: - because of the low angle of attack, lift-induced drag is neglible - this means pitch changes don't change drag (i.e.) much, but immediately affect lift (see lift equation) and thus flight path - kinetic energy is preserved by inertia, the only reasons, we need more and more thrust is to counter quadratically increasing drag - we add power to 2300 RPM and produce more thrust. looking at the lift equation, now we have two options - Option A: keep lift constant by flattening the angle of attack (i.e, lift coeffcient) constant slightly, then velocity will increase - from the additional 200 RPM will add to the kinetic energy of the airplane - however, at higher airspeed parasite drag has now grown non-linearly and is much higher than it was at the initial velocity. - if we were to decrease the thrust to the level produced by 2100 RPM, we don’t fight the higher parasite drag anymore and we will slow down back to the original airspeed - therefore, to account for the now higher parasite drag, we need to keep the additional 200 RPM in - the pitch-reduced the lift-induced drag a tiny bit, but this is marginal for high airspeeds - to summarize, we added power and increased speed - Option B: increase lift by keeping angle of attacked fixed - the thrust will slightly increase velocity - thus producing more lift at the same drag, - and entering a veerrry slow climb - however, obviously at slower airspeed than in scenario 3 because now we put the added enegy into potential energy and we have to fight parasite drag simultaneously AND we dont lower the angle of attack, so we also have more drag from the wings - therefore, we barely notice the climb rate or velocity at small RPM increases and always climb at full power

clearance 1) clear by vision and turns

slowdown 2) reduce power to 1500 RPM 3) activate carb heat 4) keep altitude with pitch 5) below 110 knots, flaps 10 6) below 85 knots, flaps 30 7) keep altitude with pitch until reaching 55 knots 8) slow flight: pitch for airspeed (forward faster, backward slower), power for altitude; correct pitch slightly, correct throttle boldly

turns

transition to cruise