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Recommendation:
Every pilot should plan to finance at least five hours or even ten hours of aerobatic flight instruction. This should be from a full-time aerobatics instructor. Flying upside-down will make you a better right-side-up pilot. It is here that you learn to apply forward pressure when inverted to go up.
Aerobatics can make you a better pilot. Best of all aerobatics requires that you look outside the cockpit with a far greater awareness as to what it takes to put the airplane where you want it. Just be sure you have the proper airplane and a fully qualified instructor.
You have read that an airplane can be stalled from any attitude and at any speed. Doing aerobatics gives you an opportunity to turn the theory into practice. Spin training can be taught safely if the altitudes and maneuvers are planned for safety. Those against spin training desire that stall prevention and recognition are the way to go.
Categories of Aircraft
Normal Category
Normal category aircraft are placarded against spins but they are factory/FAA tested to one turn (or three seconds) with a one-turn recovery when controls are used correctly. Speeds and load factors are not to be exceeded. Flaps may be retracted. No uncontrollable spins are possible in this category. No acrobatics or spins allowed. The weight and CG certification of the aircraft will determine its spin characteristics and recovery procedures. Beyond one turn even correct control input may not work.
Acrobatic Category
Recovery at any time in one turn Tested to six (6) turns clean and one (1) turn w/flaps Speeds and load factors not to be exceeded. Uncontrollable spins are not possible. Entry speeds listed for all maneuvers. The weight and CG certification of the aircraft will determine its spin ability and recovery ability.
Utility Category
Meets either of above requirements FAR Section 23.1567 (New types of airplanes) Pilot to assume aircraft placarded against spins may become uncontrollable in a spin. The weight and CG certification of the aircraft will determine its spin and recovery procedures.
Limited aerobatic maneuvers may be conducted in aircraft that are not certified in the aerobatic category. Some normal category aircraft when operated within the utility category of their weight and balance envelope are permitted to perform those maneuvers listed in placards or the POH.
Definitions:
SPIN An established spin is an aggravated stall that has developed auto-rotational forces. Gravity causes a helical path during the descent. The aerodynamic and inertial forces are balanced. You must upset this balance to recover. The stall, which has directional control, occurs at an angle of attack near 17 degrees. In a spin the down wing may have an angle of attack of 70-80 degrees while the up wing will be between 30 and 40 degrees. The stall prelude to the spin lacks directional control (rudder).
TAIL LENGTH This is the distance from the Center of gravity to the hinges of the tail surfaces. The longer the distance the more nose down the spin and the easier the recovery. An improperly loaded aircraft with a short tail length will spin flat and can be unrecoverable.
STALL Loss of lift and increase in drag that occurs when at angle of attack greater than angle of maximum lift.
SECONDARY STALL Stall that occurs if recovery from initial stall is inappropriately performed usually by excessive elevator.
STALL SPEED Speed at which the critical angle of the relative wind is exceeded. Stall speed decreases with aircraft weight, turbulence, bank angle, abrupt control movement, or any interference with airflow over the lifting surfaces (ice)
ANGLE OF ATTACK Angle the wing chord line has when it meets the relative wind.
CRITICAL ANGLE OF ATTACK Will always result in a stall. The flow of air cannot follow the curve of the wing. For a given flying surface the critical angle of attack never changes. The airspeed at which a flying surface will stall depends on aircraft weight, balance, and load factor.
RELATIVE WIND Speed and direction of wind causes by the aircraft movement. Velocity of relative wind is equal but opposite to speed of aircraft.
COEFFICIENT OF LIFT, (Cl) Factor giving lift created by an angle of attack at a given airspeed.
COEFFICIENT OF DRAG, (Cd) Factor giving drag created by a an angle of attack at a given airspeed.
FLAPS Flaps are lift/drag devices that lower the stall speed. The lift effect is greater than the drag. Flaps make the glide slope more steep for better aim to the landing site. Vso stall speed in the landing configuration.
Vsi Stall speed in a specific configuration.
Va Maneuvering speed at which the airplane will not fold, crumble or mutilate if stalled. No guarantee if stalled above Va.
LOAD FACTOR Is ratio of available lift to total weight. Load factors can be increased by steep turns, abrupt control movement, and turbulence. In level flight the load factor is one. In a 30° bank the factor becomes 1.15, at 45° bank it becomes 1.40, at 60° bank it becomes 2.00, at 70° bank it becomes 3.00, and at 80° bank it becomes 6.00.
CENTER OF GRAVITY CG has indirect effect on angle of attack and the control forces required on the elevators. The CG does affect the aircraft stability and spin recovery. With an aft CG very light control forces could cause a stall from which the available elevator power could not lower the nose for recovery.
WEIGHT The greater the weight the higher the stall speed. The AFM/POH give approach speeds based on allowable gross. At less than gross weights lower approach speeds are allowable. For intentional spins the actual weights must be computed. A rule of thumb is that a 2% increase in weight will cause a 1% change in stall speed.
DENSITY ALTITUDE High altitude and temperature give higher true airspeeds. Since stalls occur at indicated speeds as per the AFM/POH density altitude is not a factor.
TURBULENCE At approach speeds turbulence may cause stalls by changing angle of attack. At cruise fly above stall but less than maneuvering speed.
TRIM Trim is the pilot's pitch management tool which decreases the effect of distractions.
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