Helicopter Dynamics is a study within aerospace engineering that researches the theoretical and mechanical aspects of a helicopter flight. A normal helicopter aerodynamic fundamentals range from thermodynamics to electromagnetism where everything works in perfect order to thrust the helicopter up. It is a complex research on air currents, forces and blade torques which affects the helicopter during its flight.
Forces Acting on The Aircraft edit
Once a helicopter leaves the ground it is affected by 4 main forces: lift, weight, thrust, and drag.
- Lift is the force that gets or keeps the aircraft high. It affects the aircraft on a perpendicular axis.
- Weight is the combined weight of the whole aircraft that pushes the aircraft down on a perpendicular axis. This force works against the "lift" force.
- Thrust is the force produced by the power plant/ propeller or rotor. It opposes or overcomes the force of drag. As a general rule, it acts mostly parallel to the longitudinal axis.
Lift edit
When an object changes the direction of a fluid's flow or when the fluid is forced to move by the object passing through it, lift is created. The force required to complete this work causes an equal and opposing force, which is lift, when the object and fluid move relative to one another and the object turns the fluid flow in a direction perpendicular to that flow.
The object may be moving through a stationary fluid or the fluid may be flowing past a stationary object—either way, both of them are practically identical because the only difference is the viewer's frame of reference. An airfoil's lift is determined by a variety of factors, like:
- Speed of airflow
- Density of the air
- Total are of the segment or airfoil
- Angle of attack (AOA) between air and airfoil.[1]
The Angle of attack is the angle at which the object meets the air flow(or the other way around).The lift contains 2 laws of physics, one being the Bernoulli's Principle, where the fluid or air flow's static pressure will decrease if the fluid's velocity increases. Another law of physics applied when generating lift is Newton's 3rd Law of Motion which states that every action there is an equal and opposite reaction. These laws combined will contribute to generating lift. For example a flat object is set parallel to the air flow, when we give it an angle of attack(moving one tip of the object in a certain angle against the air flow) the air flow will change accordingly. The bottom flow of the object will have a lower velocity than the upper flow of the object. This will create a difference between their static pressure and the air will flow downwards. The object will have to react the opposite way according to Newton's 3rd law of motion resulting in the object moving upwards. In simplicity the air flow goes down and the helicopter reacts by going the other way which is up.[2]
Weight edit
The weight of the aircraft will force the aircraft down using gravitational pull. The weight factor changes how much angle of attack the helicopter needs to stay in the air. Also the weight changes mid-flight when the petrol of the helicopter depletes causing the angle of attack to be lower to stay in the air.[1]
Thrust edit
Thrust is generated by the main rotor disk(the propeller). The main rotor can use the thrust force to go forwards, backwards and sideways. Its opposition force is drag.
Drag edit
Drag is the force that resists kinetic energy. Drag can be generated by air resistance or Newton's 1st law(an object wants to stay at a certain momentum).There are 3 types of drag: profile, induced and parasite.
Profile Drag edit
The profile drag is simply air friction caused by the parts that contribute to the lift force of the aircraft. This kind of drag is created from the air friction the rising helicopter generates while using the main rotor engine, it increases when the velocity of the main rotor increases(when the propeller starts spinning faster). There is a slight increase in profile drag when the angle of attack is increased.
Induced Drag edit
Induced Drag is generated when the pressured air beneath the spinning main rotor flows upward towards the less pressured air causing a vortex or spiral of air on the tip of the main rotor. This kind of drag is more visible on airplanes on the tip of their wings, where we can see a vortex of air.[3]
Parasite Drag edit
Parasite Drag is practically any air friction caused from any part of the aircraft that is not related to generating the lift force of the aircraft. Parasite drag changes with the square of the velocity therefore when the forward velocity of the aircraft increases the parasite drag will increase at a much larger scale.
D = Cd x ρ x V^2 x A x 0.5 (coefficient x density x velocity^2 x reference area x 0.5)[4]
Use of the Tail Rotor edit
When the main rotor spins while the aircraft is in the air the body starts moving on the opposite torque(rotational force) of the main rotor. This happens because of Newton's 3rd law of motion where every action has an equal and opposite reaction. In a helicopter's point of view the main rotor starts spinning(the action) in the air the helicopter's body will move the opposite direction(the reaction). To keep this from happening, helicopters are installed with a tail rotor that spins vertically and affects the helicopter horizontally. With the tail rotor, the reaction force created by the spinning of the main rotor is equaled out by the force created by the tail rotor. The tail rotor also helps turn the helicopter’s tail left and right.[5][1]
Forward Flight edit
The main rotor helps the aircraft rise up in the air. It also helps the aircraft go sideways or any direction it needs to go. For the aircraft to go forward it needs to go through certain steps. The main objective is to shift the main rotor in a way that the angle of attack is small at the front of the helicopter and big in the rear of the main rotor disc, so that the helicopter's main rotor tips a little bit forward and the main rotor can be used as a force to go forward as well as keeping the aircraft in the air. To accomplish this objective, helicopters have a complex mechanism called a "swashplate". The swashplate helps the main rotor to tip forward, which then can exert force to go forward. The swashplate changes the main rotor’s angle so that the helicopter can go any direction it wants to.[6][5]
References edit
- ^ a b c d Department of Transportation, U.S (2012). Helicopter Flying Handbook. Oklahoma City: United States Department of Transportation.
- ^ a b A.R.S, Bramwell (2000). Bramwell's Helicopter Dynamics. Heinemann: Elsvier Ltd.
- ^ "Induced Drag - SKYbrary Aviation Safety". www.skybrary.aero. Retrieved 2021-11-03.
- ^ "The Drag Equation".
{{cite web}}: CS1 maint: url-status (link) - ^ a b "Helicopter Aerodynamics - Hubschrauberflug". www.helicopterflights.com. Retrieved 2021-11-02.
- ^ "Helicopter Aerodynamics of Flight". Aircraft Systems. Retrieved 2021-11-02.