helicopter dynamics
- 1. HELICOPTER AND ROTOR BLADES NAME: USN: PRASHANT THAPA 1NT21AE058 SANSKRUTI S CHINCHEWADI 1NT21AE068 TRISHANK M 1NT21AE085
- 2. Helicopter • A helicopter is a type of aircraft that uses rotating, or spinning, wings called blades to fly. Unlike an airplane or glider, a helicopter has wings that move. Unlike a balloon, a helicopter is heavier than air and uses an engine to fly.
- 3. Basics of Helicopter ◦ There are four fundamentals of flight upon which all maneuvers are based: Straight-and-level flight Turns Climbs Descents ◦ All controlled flight maneuvers consist of one or more of these four fundamentals of flight.
- 4. Forces acting on a helicopter in flight ◦ Lift - The upward force created by the effect of airflow as it passes around an airfoil. ◦ Weight - Opposes lift and is caused by the downward pull of gravity. ◦ Thrust – The force that propels the helicopter through the air. ◦ Drag – Directly opposes lift and thrust and is the retarding force created by development of lift and the movement of an object through the air
- 5. ◦ Additionally, there are certain additional physical characteristics and effects that are unique to a helicopter and its rotor system while in flight: ◦ Pendular Action – Helicopter fuselages tendency to oscillate as a pendulum and/or laterally. ◦ Coning – Main rotor blades rise to form a “cone” owing to production of lift. Coning is balanced by centrifugal force produced by spinning blades. Coning Pendular Action
- 6. Coriolis Effect – Rotor blade tendency to accelerate and decelerate as its center of mass moves due to flapping. Ground Effect – Affects rotor efficiency by reducing induced rotor flow Ground Effect Coriolis Effect
- 7. Gyroscopic Precession – Main rotor act as a gyroscope, and is has precession properties. ◦ The spinning main rotor of a helicopter acts like a gyroscope. As such, it has the properties of gyroscopic action, one of which is precession. ◦ Gyroscopic precession is the resultant action or deflection of a spinning object when a force is applied to this object. This action occurs approximately 90° later in the direction of rotation from the point where the force is applied.
- 8. Take off in helicopter ◦ Helicopter uses the vertical take-off and landing (VTOL) method for take-off as well as for landing. ◦ A normal takeoff from a hover is an orderly transition to forward flight and is executed to increase altitude safely and expeditiously. ◦ During the takeoff, fly a profile that avoids the cross-hatched or shaded areas of the height-velocity diagram.
- 9. 1.Rotary take off(direct take off/slant take off): ◦ To accelerate, a helicopter needs to tilt its main rotor system forwards to create horizontal thrust. ◦ The main rotor system is attached to the fuselage so the whole helicopter also points nose down as it accelerates during take-off. 5°-15° nose down are typical pitch down attitudes on take-off. .
- 10. 2.Powerlift take off: ◦ A powered lift aircraft takes off and lands vertically under engine power but uses a fixed wing for horizontal flight. ◦ Like helicopters, these aircraft do not need a long runway to take off and land, but they have a speed and performance similar to standard fixed wing aircraft in combat or other situations.
- 11. Types of flights 1.Translational Flight and Forward Flight ◦ While in forward flight, the tip-path plane is tilted forward, thus tilting the total lift-thrust force forward from the vertical. This resultant lift-thrust force can be resolved into two components—lift acting vertically upward and thrust acting horizontally in the direction of flight. ◦ In addition to lift and thrust, there is weight as the downward acting force, and drag as the rearward acting or retarding force.
- 12. 2.Turning Flight ◦ In forward flight, the rotor disc is tilted forward, which also tilts the total lift-thrust force of the rotor disc forward. ◦ When the helicopter is banked during forward flight, the rotor disc has a sideward tilt, and a component of the resultant lift now acts horizontally towards the direction of turn (centripetal force) to oppose inertia (centrifugal force). ◦ As the angle of bank increases, the total lift force is tilted more toward the horizontal, thus causing the rate of turn to increase because more lift is acting horizontally. Since the resultant lifting force acts more horizontally, the effect of lift acting vertically is deceased.
- 13. • To compensate for this decreased vertical lift, the angle of attack of the rotor blades must be increased in order to maintain altitude. • The steeper the angle of bank, the greater the angle of attack of the rotor blades required to maintain altitude. • Thus, with an increase in bank and a greater angle of attack, the resultant lifting force increases and the rate of turn is faster.
- 14. Sideward and Rearward Flight ◦ In sideward flight, the tip-path plane is tilted in the direction that flight is desired. This tilts the total lift-thrust vector sideward. In this case, the thrust component now acts sideward with drag acting to the opposite side. ◦ For rearward flight, the tip-path plane is tilted rearward, which in turn tilts the resultant lift/thrust vector rearward. Drag now acts forward.
- 15. Hovering ◦ The phenomenon in which a helicopter maintains a constant position over a selected point, usually a few feet above the ground is called hovering.
- 16. ◦ To maintain a hover at a constant altitude, enough lift and thrust must be generated to equal the weight of the helicopter and the drag produced by the rotor blades. ◦ While hovering, the amount of main rotor thrust can be changed to maintain the desired hovering altitude. This is done by changing the angle of incidence (by moving the collective) of the rotor blades and hence the AOA of the main rotor blades. Changing the AOA changes the drag on the rotor blades, and the power delivered by the engine must change as well to keep the rotor speed constant.
- 17. ◦ The weight that must be supported is the total weight of the helicopter and its occupants. If the amount of lift is greater than the actual weight, the helicopter accelerates upwards until the lift force equals the weight gain altitude; if thrust is less than weight, the helicopter accelerates downward. ◦ When operating near the ground, the effect of the closeness to the ground changes this response. ◦ The drag of a hovering helicopter is mainly induced drag incurred while the blades are producing lift. There is, however, some profile drag on the blades as they rotate through the air. The term drag includes both induced and profile drag.
- 18. ◦ To counteract this torque-induced turning tendency, an antitorque rotor or tail rotor is incorporated into most helicopter designs. ◦ A pilot can vary the amount of thrust produced by the tail rotor in relation to the amount of torque produced by the engine. As the engine supplies more power to the main rotor, the tail rotor must produce more thrust to overcome the increased torque effect. ◦ This is done through the use of antitorque pedals.