Helicopters: How They Work
Rotary Wing Terminology
Lets talk a moment about terminology. There are many terms associated with rotary wing flight. One must become familiar with the terminology of rotorcraft before they can expect to understand the mechanics of rotary wing flight. Let's look at a few definitions.
Main Rotor System
- Root: The inner end of the blade where the rotors connect to the blade grips.
- Blade Grips: Large attaching points where the rotor blade connects to the hub.
- Hub: Sits atop the mast, and connects the rotor blades to the control tubes.
- Mast: Rotating shaft from the transmission, which connects the rotor blades to the helicopter.
- Control Tubes: Push \ Pull tubes that change the pitch of the rotor blades.
- Pitch Change Horn: The armature that converts control tube movement to blade pitch.
- Pitch: Increased or decreased angle of the rotor blades to raise, lower, or change the direction of the rotors thrust force.
- Jesus Nut: Is the singular nut that holds the hub onto the mast. (If it fails, the next person you see will be Jesus).
Main Rotor Blade
- Leading Edge: The forward facing edge of the rotor blade.
- Trailing Edge: The back facing edge of the rotor blade.
- Chord: The distance from the Leading Edge to the Trailing Edge of the rotor blade.
- Swash Plate: Turns non-rotating control movements into rotating control movements.
- Collective: The up and down control. It puts a collective control input into the rotor system, meaning that it puts either "all up", or "all down" control inputs in at one time through the swash plate. It is operated by the stick on the left side of the seat, called the collective pitch control. It is operated by the pilots left hand.
- Cyclic: The left and right, forward and aft control. It puts in one control input into the rotor system at a time through the swash plate. It is also known as the "Stick". It comes out of the center of the floor of the cockpit, and sits between the pilots legs. It is operated by the pilots right hand.
- Pedals: These are not rudder pedals, although they are in the same place as rudder pedals on an airplane. A single rotor helicopter has no real rudder. It has instead, an anti-torque rotor (Also known as a tail rotor), which is responsible for directional control at a hover, and aircraft trim in forward flight. The pedals are operated by the pilots feet, just like airplane rudder pedals are. Tandem rotor helicopters also have these pedals, but they operate both main rotor systems for directional control at a hover.
Here are some of the component parts that make up a helicopter. While this is an example of one specific helicopter (UH-1C), not all helicopters will have all of the parts listed here. Some of this may be a bit more of the same old stuff we have just discussed, but it will show everything as it relates to everything else on the aircraft and the location of each component.
Anatomy of a Helicopter
- Rotor Blade: The rotary wing that provides lift for the helicopter.
- Stabilizer Bar: Dampens control inputs to make smoother changes to the rotor system.
- Swashplate: Transfers non-moving control inputs into the spinning rotor system.
- Cowling: The aerodynamic covering for the engine.
- Mast: Connects the transmission to the rotor system.
- Engine: Provides power to the rotor systems.
- Transmission: Takes power from the engine and drives both rotor systems.
- Greenhouse Window: A tinted window above each of the pilot seats.
- Fuselage: The body of the helicopter.
- Cabin Door: Allows access to the cabin and cockpit.
- Skids: Landing gear that usually have no wheels or brakes.
- Crosstube: The mounting tubes and connection for the skids.
- Motor Mount: A flexible way to attach the engine to the fuselage.
- Tailboom: Also known as an "empenage" is the tail of the helicopter.
- Synchronized Elevator: A movable wing that helps stabilize the helicopter in flight.
- Tailrotor: Provides anti-torque and in-flight trim for the helicopter.
- Tail Rotor Driveshaft: Provides power to the tailrotor from the transmission.
- 45 Degree Gearbox: Transfers power up the vertical fin to the 90 degree gearbox.
- 90 Degree Gearbox: Transfers power from the 45 degree gearbox to the tailrotor.
- Vertical Fin: Holds the tailrotor and provides lateral stabilization.
- Tail Skid: Protects the tailboom when landing.
This picture illustrates how the helicopter moves when using the appropriate controls. Up and Down movements are controlled by the "Collective". Side to Side and Forward and Back motions are controlled by the "Cyclic". Lateral control (Also called directional control or "Yaw") is achieved by using the "Foot Pedals".
While you are looking at the picture of the controls (Left side of this paragraph), I will explain how to do a normal takeoff. First, you must make sure the throttle is all the way open (For a turbine powered helicopter, advanced properly for a reciprocating engine powered helicopter). Once you have established the proper operating RPM, then you can pull up slowly on the collective. As you increase collective pitch, you need to push the left pedal (In American helicopters...right pedal for non-American models) to counteract the torque you generate by increasing pitch. (In reciprocating engined models, you will advance the throttle as you increase collective pitch). Keep pulling in pitch and depressing the pedal until the aircraft gets light on the skids. You may sense a turning motion to the left or right, if so, you may need more or less pedal to maintain heading. The cyclic will become sensitive and (depending on how the aircraft leaves the ground heels or toes of the skids last) as you continue to pull in pitch and depress the pedal, you will put in the appropriate cyclic input to level the aircraft as it leaves the ground. As the aircraft eases into the air, forward cyclic will be required to start the aircraft in a forward motion. As the aircraft advances forward, it will gain speed until about 15 knots and then the aircraft will shudder a little as you transition through ETL (Effective Translational Lift...See the unique forces page for a more in depth explanation of ETL). As you transition through ETL, the collective will need to be reduced, the pedal will need less pressure, and the cyclic will need to be forced forward to counteract the force against the front of the rotor system. Failure to push forward will result in an abrupt nose high attitude and a reduction in forward speed. After the shudder of ELT is experienced, you will see a marked gain in forward airspeed, a reduced need for pedal input and a reduced need for collective pitch as the rotor system becomes more efficient. The airspeed indicator will most likely jump from zero to 40 knots indicated airspeed and will smoothly advance as the aircraft goes faster. Now you have taken off and with a little release of foward cyclic pressure, the aircraft will establish a climb and continue to gain airspeed. At this point, the pedals are only used to trim the aircraft, and most maneuvers are accomplished by using a combination of the cyclic and collective controls. (That wasn't so hard...was it?)
We don't need no stinking runways!