Air is being accelerated in a more downward angle, epically towards the rear of the rotor system.
Angle of attack decreases in rear (reaction is 90 degrees to the right) causes helicopter to pull to the right.</li></ul>Auto-rotations: Emergency capability in case of engine failure<br /><ul><li>In normal flight, air is pulled down through rotors
Slows airspeed, and increases volume of air blowing through rotors eg: more energy available.
Add full right peddle (to keep fuselage from spinning)
Around 10 ft. pull up on the collective to slow as much as possible before touchdown. (uses up built up airspeed in rotor system)</li></ul>Altitude is important in autorotation<br />” Dead mans curve”<br />Retreating Blade Stall: Extreme dissymmetry of lift, at very high forward air speeds.<br /><ul><li>Excessive angle of attack on retreating blade side.
Either slow down or lower the collective</li></ul>Vortex Ring State (Settling with power): During steep approaches. Slow your decent. Coming down fast, you get into your downwash. Increase in power will increase the effect eg: speed your decent more.<br /><ul><li>If descending at 300 fpm or more
Longitudinal Axis = Roll</li></ul>Three basic controls: Cyclic (stick between your legs), Collective, Pedals<br />To go forward, you need rotor to drop in front and raise rotors in rear. To raise rotors in rear, you need force on left.<br />Cyclic<br /><ul><li>Pitch
Roll</li></ul>The cyclic controls the swash plate.<br />This swash plate is setup for a two blade helicopter (note there is only 2 pitch links)<br />Collective: Changes amount of pitch to main rotor system (all blades affected the same)<br />Pull up on collective, more lift. As you pull up on collective, more throttle is requred.<br />The end of the collective is the engine throttle.<br />Starter button is commonly on the end of the collective.<br />Pedals: Yaw left and right.<br />On takeoff when adding more collective, need to add left peddle to fight drift.<br />Tail Rotors: Most of the noise you hear from a helicoptor is the tail rotor.<br />Types:<br /><ul><li>Semi-Rigid
Air flowing over the curved surface “sticks” to that surface and creates lift sideways
“A variable pitch fan is enclosed in the aft fuselage section immediately forward of the tail boom and driven by the main rotor transmission. This fan forces low pressure air through two slots on the right side of the tail boom, causing the downwash from the main rotor to hug the tail boom, producing lift, and thus a measure of directional control. This is augmented by a direct jet thruster and vertical stabilizers.” –Wikipedia</li></ul>Stabilizer Surfaces <br />Fixed Horizontal<br />Creates download on tail to keep fuselage more level during high speed flight<br />Synchronized Elevator<br />Connected to Cyclic<br />Changes pitch to change tail down load for various flight speeds<br />Fixed Vertical<br /><ul><li>For directional stability</li></ul>Hydraulics<br />For larger or heavier M/R systems<br />Mostly use Irreversible type systems to overcome flight loads and dampen vibrations in sticks<br />Stabilizer Controls<br />Are inherently unstable<br />As rotor lift/thrust vector tilts away from vertical = creates vector to pull away from center<br />= negative stability<br />Compensations<br />Bell Stabilizer Bar<br />Bar below M/R @ 90o to blade span<br />Acts like gyroscope and uses Rigidity in Space characteristic to try and keep rotor and aircraft in one attitude<br />Worked too well so needs hydraulic damper to limit it’s effectiveness and allow reasonable maneuverability <br />Offset Flapping Hinge<br />On fully-articulated rotor heads and on some tail rotors<br />Hinge moved a distance from rotor’s rotation axis = acts like lever to provide restoring force<br />Stabilization Augmentation System (SAS)<br />Like simple autopilot<br />One- or two-axis<br />Only to aid stability, not true autopilot<br />