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Helicopter Lesson - Maneuvers

Helicopter Lesson Guides:  Intro | Aerodynamics | Powered Flight | Load FactorControl Functions | Systems | RFM | Weight & Balance | Performance | Hazards | Precautions | Maneuvers | Glossary
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Chapter 11. HELICOPTER FLIGHT MANEUVERS (continued)

Click to open or print...NORMAL TAKEOFF FROM A HOVER

Takeoff from a hover is an orderly transition to forward flight and is executed to increase altitude safely and expeditiously.

TECHNIQUE:
  1. Bring the helicopter to a hover. Check engine and control operation. Note the cyclic stick position to determine if the aircraft is loaded properly. Check the manifold pressure required to hover to determine the amount of excess power available.
  2. Visually clear the area all around.
  3. Smoothly and slowly ease the cyclic stick forward. Apply just enough forward cyclic pressure to start the helicopter moving forward over the surface (see figure 70 above).
  4. As the helicopter starts to move forward, increase collective pitch as necessary to prevent descending, and adjust throttle to maintain RPM. The increase in power will require an increase in left pedal to maintain heading. A straight takeoff path should be maintained throughout the takeoff.
  5. As you accelerate to effective translational lift, the helicopter will begin to climb and the nose will tend to rise due to increased lift. At this point adjust collective pitch to obtain normal climb power and apply enough forward cyclic stick to overcome the tendency of the nose to rise. Hold an attitude that will allow a smooth acceleration toward climbing airspeed and a commensurate gain in altitude so that the takeoff profile will not take you through any of the crosshatched area of the height-velocity chart for the particular helicopter being flown. As airspeed is increased, the streamlining of the fuselage reduces engine torque effect, requiring a gradual reduction of left pedal.
  6. As the helicopter continues to climb and airspeed approaches normal climb speed, apply aft cyclic stick pressure to raise the nose smoothly to the normal climb attitude.
COMMON ERRORS:
  1. Failing to use sufficient collective pitch to prevent loss of altitude prior to attaining translational lift.
  2. Adding power too rapidly at the beginning of the transition from hovering to forward flight without forward cyclic compensation, causing the helicopter to gain excessive altitude before acquiring airspeed.
  3. Assuming an extreme nose-down attitude near the surface in the transition from hovering to forward flight.
  4. Failing to maintain a straight flightpath over the surface (ground track).
  5. Failing to maintain proper airspeed during the climb.
  6. Failing to adjust the throttle to maintain proper RPM.
Click to open or print...Crosswind considerations during takeoffs

If a takeoff is made during crosswind conditions, the helicopter is flown in a slip during the early stages of the maneuver. The cyclic pitch is held into the wind a sufficient amount to maintain the selected ground track for the takeoff, and the heading is kept straight along the takeoff path using the antitorque pedals (see figure 71 to the right). Thus, the ground track and fuselage are aligned with each other. In other words, the rotor is tilted into the wind so that the sideward movement of the helicopter is just enough to counteract the wind drift. To prevent the nose from turning in the direction of rotor tilt, it will be necessary to increase pedal pressure on the side opposite to rotor tilt. The stronger the crosswind component, the greater the amount of opposite pedal pressure required to maintain heading.

After approximately 50 feet of altitude is gained, a heading (crab) into the wind (see figure 71 above) should be established by a coordinated turn to maintain the desired ground track. The stronger the crosswind component, the more the helicopter will have to be turned into the wind to maintain desired ground track. Once straight-and-level flight on the desired heading is obtained, the pedals should continue to be used as necessary to compensate for torque to keep the helicopter in longitudinal trim.

NORMAL TAKEOFF FROM THE SURFACE

Normal takeoff from the surface is used to move the helicopter from a position on the surface into effective translational lift and a normal climb using a minimum amount of power.

TECHNIQUE:
  1. Place the helicopter in a stationary position on the surface, lower the collective pitch to the full down position, and reduce the RPM below operating RPM. Visually clear the area and select terrain features or other objects to aid in maintaining the desired track during the takeoff and climbout.
  2. Increase the throttle to proper RPM and raise the collective pitch slowly until the helicopter is light on the skids. Hesitate momentarily and adjust cyclic and pedals as necessary to prevent any surface movement.
  3. Continue to apply upward collective pitch and, as the helicopter breaks ground, use cyclic as necessary to assure forward movement as altitude is gained.
  4. Continue to accelerate the aircraft and, as effective translational lift is attained, the helicopter will begin to climb. Adjust attitude and power, if necessary, to climb in the same manner as a takeoff from a hover.
COMMON ERRORS:
  1. Departing the surface in an attitude that is too nose-low. This situation requires the use of excessive power to initiate a climb.
  2. Using excessive power combined with too level an attitude, which causes a vertical climb.
  3. Too abrupt application of the collective pitch when departing the surface, causing RPM and heading control errors.
STRAIGHT-AND-LEVEL FLIGHT

Straight-and-level flight is flight in which a constant altitude and heading are maintained. (The straight-and-level flight attitude is the attitude of the helicopter necessary to maintain straight-and-level flight. The level-flight attitude is the attitude of the helicopter necessary to maintain altitude. These terms are used throughout this handbook.)

The airspeed is determined by the attitude of the helicopter. The attitude of the helicopter is controlled by the movement of the cyclic control stick; altitude is primarily maintained by use of the collective pitch. To maintain forward flight, the rotor tip-path plane must be tilted forward to obtain the necessary horizontal thrust component from the main rotor. This will generally result in a nose-low attitude. The lower the nose, the greater the power required to maintain altitude (and the higher the resulting speed). Conversely, the greater the power used, the lower the nose must be to maintain altitude.

When in straight-and-level flight, an increase in collective pitch while holding airspeed constant with the cyclic control causes the helicopter to climb; a decrease in collective pitch while holding airspeed constant causes a descent. A correction on the collective pitch control requires coordinated correction on the throttle control in order to maintain a constant RPM, and on the antitorque pedals to maintain heading and to keep the helicopter in longitudinal trim. Coordinated flight should be maintained (that is, neither slipping nor skidding).

To increase airspeed in straight-and-level flight, apply forward pressure on the cyclic control stick and raise the collective pitch as necessary to maintain altitude. To decrease airspeed, apply aft pressure on the cyclic control stick and lower the collective pitch as necessary to maintain altitude.

Although cyclic pitch control is sensitive, there is a slight delay in control reaction and it will be necessary to anticipate actual movement of the helicopter. In making cyclic corrections to control the attitude or airspeed of a helicopter, care should be taken not to overcontrol. If the nose of the helicopter rises above the level-flight attitude, forward pressure is applied to the cyclic stick to bring the nose down. If this correction is held too long the nose will drop too low. Since the helicopter will continue to change attitude momentarily after the controls reach neutral, return the cyclic stick control to neutral slightly before the desired attitude is reached. This principle holds true for any cyclic pitch control correction.

The helicopter is inherently unstable. If gusts or turbulence cause the nose to drop, it will tend to continue dropping instead of returning to a straight-and-level attitude as would a fixed-wing aircraft. A pilot must remain alert and FLY the helicopter at all times.

COMMON ERRORS:
  1. Failure to trim properly, tending to hold pedal pressure and opposite cyclic.
  2. Failure to hold best airspeed. Aft cyclic pressure dissipates airspeed without significant climb.
  3. Failure to recognize proper control position for maintaining crab-type drift correction.
TURNS

A turn is a maneuver used to change the heading of the helicopter. The aerodynamics of a turn have been discussed previously - lift components, loss of vertical lift, and load factors - and should be thoroughly understood.

Before beginning any turn, the area in the direction of the turn should be carefully cleared above, below, and at the flight level. To enter a turn from straight-and-level flight, apply sideward pressure on the cyclic stick in the direction the turn is to be made. This is the only control movement necessary to start the turn. Do not use the pedals to assist the turn. The pedals should be used to compensate for torque to keep the helicopter in longitudinal trim. The more the cyclic stick is displaced, the steeper the angle of bank; therefore, adjust the cyclic stick to obtain and maintain the desired bank throughout the turn. Increase collective pitch and throttle as necessary to maintain altitude and RPM, and increase left pedal pressure to counteract the added torque effect and to maintain longitudinal trim. Depending on the degree of bank, additional forward cyclic pressure may be required to maintain airspeed.

Recovery from the turn is the same as the entry except that pressure on the cyclic stick is applied in the opposite direction. Since the helicopter will continue to turn as long as there is any bank, start the rollout before reaching the desired heading.

The discussion on level turns is equally applicable to making turns while climbing or descending, the only difference being that the helicopter will be in a climbing or descending attitude rather than the level flight attitude. If a simultaneous entry is desired, merely combine the techniques of both maneuvers - climb or descent entry and turn entry.

Skids

A skid occurs when the helicopter slides sideways away from the center of the turn. It is caused by too much pedal pressure in the direction of turn, or by too little in the direction opposite the turn in relation to the amount of collective stick (power) used. If the helicopter is forced to turn faster with increased pedal pressure instead of by increasing the degree of bank, it will skid sideways away from the center of turn. Instead of flying in its normal curved pattern, it will fly a straighter course.

In a right climbing turn, if insufficient left pedal is applied to compensate for increased torque effect, a skid will occur. In a left climbing turn, if excessive left pedal is applied to compensate for increased torque effect, a skid will occur.

In a right descending turn, if excessive right pedal is applied to compensate for decreased torque, a skid will occur. In a left descending turn, if insufficient right pedal is applied to compensate for the decreased torque effect, a skid will occur.

A skid may also occur when flying straight-and-level if the nose of the helicopter is allowed to move sideways along the horizon. This condition occurs when improper pedal pressure is held to counteract torque and the helicopter is held level with cyclic control.

Slips

A slip occurs when the helicopter slides sideways toward the center of the turn. It is caused by an insufficient amount of pedal in the direction of turn (or too much in the direction opposite the turn) in relation to the amount of collective stick (power) used. In other words, if improper pedal pressure is held, keeping the nose from following the turn, the helicopter will slip sideways toward the center of turn.

In a right climbing turn, if excessive left pedal is applied to compensate for the increased torque effect, a slip will occur. In a left climbing turn, if insufficient left pedal is applied to compensate for the increased torque effect, a slip will occur.

In a right descending turn, if insufficient right pedal is applied to compensate for the decreased torque effect, a slip will occur. In a left descending turn, if excessive right pedal is applied to compensate for the decreased torque effect, a slip will occur.

A slip may also occur in straight-and-level flight if one side of the helicopter is low and the nose is held straight by pedal pressure. This is the technique used in correcting for a crosswind during an approach and during a takeoff when at a low altitude.

Summarizing then, a skid occurs when the rate of turn is too fast for the amount of bank being used; a slip occurs when the rate of turn is too slow for the amount of bank being used.

COMMON ERRORS:

1. Using pedal pressures for turns. This is usually not necessary for small helicopters.

NORMAL CLIMB

The entry into a climb from a hover has already been discussed under "Normal Takeoff From a Hover." This discussion will be limited to a climb entry from cruising flight.

TECHNIQUE:
  1. To enter a climb from cruising flight, apply aft cyclic stick to obtain the approximate climb attitude; simultaneously increase collective pitch to obtain climb manifold pressure, adjust throttle to maintain or obtain climb RPM, and increase left pedal pressure to compensate for the increased torque.
  2. As the airspeed approaches normal climb airspeed, make further adjustments of the cyclic control to obtain and hold this airspeed.
  3. Throughout the maneuver, maintain climb attitude, heading, and airspeed with cyclic control, climb manifold pressure and RPM with collective pitch and throttle, and longitudinal trim with antitorque pedals.
  4. To level off from a climb, start adjusting attitude to the level flight attitude a few feet prior to reaching the desired altitude. The amount of lead will depend upon the rate of climb at the time of level-off - the higher the rate of climb, the more the lead. Apply forward cyclic to adjust to and maintain the level flight attitude, which will be slightly nose low; maintain climb power until airspeed approaches desired cruising airspeed, at which time the collective should be lowered to obtain cruising manifold pressure and throttle adjusted to obtain and maintain cruising RPM. Throughout the level-off, maintain longitudinal trim and constant heading with pedals.
COMMON ERRORS:
  1. Failure to hold proper manifold pressure and airspeed.
  2. Holding too much or too little left pedal.
  3. In level-off, decreasing power before lowering the nose to cruising attitude.
NORMAL DESCENT

A normal descent is a maneuver in which the helicopter loses altitude at a controlled rate while in a controlled attitude.

TECHNIQUE:
  1. To establish a normal descent from straight-and-level flight at cruising airspeed, lower collective pitch to obtain proper manifold pressure, adjust throttle to maintain RPM, and increase right pedal to maintain heading. If cruising airspeed is the same as, or slightly above descending airspeed, simultaneously apply the necessary cyclic stick pressure to obtain the approximate descending attitude. If cruising airspeed is well above descending airspeed, the level flight attitude may be maintained until airspeed approaches descending airspeed, at which time the nose should be lowered to the descending attitude.
  2. Throughout the maneuver, maintain descending attitude and airspeed with the cyclic control, descending manifold pressure and RPM with collective pitch and throttle, and heading with pedals.
  3. To level off from the descent, lead the desired altitude by an amount that will depend upon the rate of descent at the time of level-off, for example, the higher the descent, the greater the lead. At this point, increase collective pitch to obtain cruising manifold pressure, adjust throttle to maintain RPM, increase left pedal pressure to maintain heading, and adjust cyclic stick to obtain cruising airspeed and the level flight attitude as the desired altitude is reached.
COMMON ERRORS:
  1. Failure to hold constant angle of descent (training purposes only).
  2. Failure to adjust pedal pressures for changes in power.
APPROACHES

An approach is a transition maneuver in which the helicopter is flown from traffic pattern altitude to a hover at normal hovering altitude and with zero groundspeed. It is basically a power glide made at an angle of descent corresponding to the type of approach that is made. A helicopter pilot should be proficient in performing three basic types of approaches - normal, steep, and shallow - and should know how to analyze influential outside factors, and know how to plan an approach to fit any particular situation. Choice of approach is governed by the size of the landing area, barriers in the approach path, type of surface, temperature, altitude, density altitude, wind direction, windspeed and gross weight.

All approaches should be regarded as precision approaches and should be made to a predetermined point. Rate of descent and airspeed are independently controlled by the pilot. Therefore, little tolerance should be given to overshooting a chosen landing spot. To maintain a maximum margin of safety in each type of approach, effective translational lift should be retained as long as practicable.

Factors to consider when making approaches

Evaluation of existing wind conditions must be made before starting an approach. Although the approach is generally made into the wind, conditions may indicate that entry will have to be made from a downwind or crosswind position. The traffic pattern is generally flown at normal or nearly normal cruise airspeed. The velocity of the wind determines the airspeed that will be maintained after the approach is initiated. Airspeed should be increased in proportion to any increased wind velocity. Angle of descent should remain constant, regardless of wind velocity.

Before attempting normal and steep approaches to a hover, the pilot should know that sufficient hovering power is available. For a shallow approach terminating in a running landing, a surface area of sufficient length and smoothness must be available.

Crosswind approaches are made by crabbing or slipping, or by a combination of both. To make running landings in strong crosswinds, it may be necessary to touch down initially with the windward (upwind) skid to avoid drifting.

RPM should remain constant during all approaches. If RPM is allowed to fluctuate or change abruptly, variations of torque forces will cause the fuselage to yaw around the vertical axis and control will be difficult. To maintain proper directional control, changes in RPM and/or collective pitch settings must be made smoothly and must be accompanied by appropriate changes in antitorque pedals.

<< Previous | Next (continued) >>

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