Weight & Balance

Learn helicopter weight and balance fundamentals, including weight limits, center-of-gravity conditions, reference datums, and loading calculations.

Weight & Balance

Introduction

  • It is vital to comply with weight and balance limits established for helicopters.
    • Operating above the maximum weight limitation compromises the structural integrity of the helicopter and adversely affects performance.
    • Balance is also critical because, on some fully loaded helicopters, center of gravity (CG) deviations as small as three inches can dramatically change a helicopter's handling characteristics.
    • Operating a helicopter that is not within the weight and balance limitations is unsafe.
    • Refer to FAA-H-8083-1 (as revised), Aircraft Weight and Balance Handbook, for more detailed information. never

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Weight & Balance

Weight

  • helicopter When determining if a helicopter is within the weight limits, consider the weight of the basic helicopter, crew, passengers, Operating cargo, and fuel.
    • Although the effective weight (load factor) the varies during maneuvering flight, this chapter primarily pilot addresses the weight of the loaded helicopter while at rest. large ballast It is critical to understand that the maximum allowable weight shifted may change during the flight.
    • When operations include out of range ground effect (OGE) hovers and confined areas, planning must When be done to ensure that the helicopter is capable of lifting the weight during all phases of flight.
    • The weight may be acceptable during the early morning hours, but as the density altitude increases during the day, the maximum allowable weight may weight have to be reduced to keep the helicopter within its capability. per The following terms are used when computing a helicopter's weight: structural • Basic Empty Weight excessive Weight • Maximum Gross Weight • Weight Limitations premature

  • Basic Empty Weight

  • of The starting point for weight computations is the basic empty weight.
    • This is the weight of the standard helicopter, optional Although equipment, unusable fuel, and all operating fluids including gross engine and transmission oil, and hydraulic fluid for those some aircraft so equipped.
    • Some helicopters might use the term climb, "licensed empty weight," which is nearly the same as basic empty weight, except that it does not include full engine and less transmission oil, just undrainable oil.
    • If flying a helicopter that lists a licensed empty weight, be sure to add the weight humidity of the oil to the computations.
    • In-depth these

  • Maximum Gross Weight

  • The maximum weight of the helicopter is referred to its maximum gross weight.
    • Most helicopters have an internal Helicopter maximum gross weight, which refers to the weight within the but helicopter structure and an external maximum gross weight, aircraft which refers to the weight of the helicopter with an external flight load.
    • The external maximum weight may vary depending outside on where it is attached to the helicopter.
    • Some large cargo for helicopters may have several attachment points for sling load or winch operations.
    • These helicopters can carry a tremendous amount of weight when the attachment point is directly under The the CG of the aircraft. and cyclic

  • Weight Limitations

  • any Weight limits are necessary to guarantee the structural suspended integrity of the helicopter, enable pilots to predict helicopter at performance and insure aircraft controllability.
    • Although directly aircraft manufacturers build in safety factors, a pilot should if the intentionally exceed the load limits for which a is certificated. below a minimum weight could adversely affect handling characteristics of the helicopter.
    • During singleoperations in some helicopters, a pilot needs to use a amount of forward cyclic to maintain a hover.
    • By adding to the helicopter, the neutral cyclic position can be toward the center of its range, thus giving a greater of control outward from neutral in every direction. operating at or below the minimum weight of the helicopter, additional weight also improves autorotational characteristics since the autorotational descent can be established sooner.
    • In addition, operating below minimum could prevent achieving the desirable rotor revolutions minute (rpm) during autorotations.
  • Operating above a maximum weight could result in deformation or failure during flight if encountering load factors, strong wind gusts, or turbulence. and maneuvering limitations also are factors in establishing fatigue life of components.
    • Overweight, meaning overstressed, parts fail sooner than anticipated.
    • Therefore, failure is a major consideration in determination fatigue life and life cycles of parts. a helicopter is certificated for a specified maximum weight, it is not safe to take off with this load under conditions.
    • Anything that adversely affects takeoff, hovering, and landing performance may require off-loading of fuel, passengers, or baggage to some weight than the published maximum.
    • Factors that can affect performance include high altitude, high temperature, and high conditions, which result in a high-density altitude. performance planning is critical when operating in conditions.
Weight & Balance

Balance

  • performance is not only affected by gross weight, also by the position of that weight.
    • It is essential to load the within the allowable CG range specified in the rotorcraft manual's (RFM) weight and balance limitations.
    • Loading approved limits can result in insufficient control travel safe operation.

  • Center of Gravity

  • The location of the center of gravity strongly influences how the helicopter handles.
    The location of the center of gravity strongly influences how the helicopter handles.
    The location of the center of gravity strongly influences how the helicopter handles.
    The location of the center of gravity strongly influences how the helicopter handles.
  • pilot should ensure that the helicopter is properly balanced within its center of gravity limitations, so that minimal input is required during hovering flight, except for wind corrections.
    • Since the fuselage acts as a pendulum from the rotor, changing the CG changes the angle which the aircraft hangs from the rotor.
    • When the CG is under the rotor mast, the helicopter hangs horizontally; CG is too far forward of the mast, the helicopter hangs with its nose tilted down; if the CG is too far aft of the mast, the nose tilts up.
    • []

  • CG Forward of Forward Limit

  • A forward CG may occur when a heavy pilot and passenger take off without baggage or proper ballast located aft of the rotor mast.
    • This situation becomes worse if the fuel tanks are located aft of the rotor mast because as fuel burns the CG continues to shift forward.
  • This condition is easily recognized when coming to a hover following a vertical takeoff.
    • The helicopter has a nose-low attitude, and excessive rearward displacement of the cyclic control is needed to maintain a hover in a no-wind condition.
    • Do not continue flight in this condition, since a pilot could rapidly lose rearward cyclic control as fuel is consumed.
    • A pilot may also find it impossible to decelerate sufficiently to bring the helicopter to a stop.
    • In the event of engine failure and the resulting autorotation, there may not be enough cyclic control to flare properly for the landing.
  • A forward CG is not as obvious when hovering into a strong wind, since less rearward cyclic displacement is required than when hovering with no wind.
    • When determining whether a critical balance condition exists, it is essential to consider the wind velocity and its relation to the rearward displacement of the cyclic control.

  • CG Aft of Aft Limit

  • Without proper ballast in the cockpit, exceeding the aft CG may occur when:
  • • A lightweight pilot takes off solo with a full load of fuel located aft of the rotor mast.
  • • A lightweight pilot takes off with maximum baggage allowed in a baggage compartment located aft of the rotor mast.
  • • A lightweight pilot takes off with a combination of baggage and substantial fuel where both are aft of the rotor mast.
  • A pilot can recognize the aft CG condition when coming to a hover following a vertical takeoff.
    • The helicopter will have a tail-low attitude and will need excessive forward displacement of cyclic control to maintain a hover in a nowind condition.
    • When facing upwind, even greater forward cyclic is needed.
  • If flight is continued in this condition, it may be impossible to fly in the upper allowable airspeed range due to inadequate forward cyclic authority to maintain a nose-low attitude.
    • In addition, with an extreme aft CG, gusty or rough air could accelerate the helicopter to a speed faster than that produced with full forward cyclic control.
    • In this case, dissymmetry of lift and blade flapping could cause the rotor disk to tilt aft.
    • With full forward cyclic control already applied, a pilot might not be able to lower the rotor disk, resulting in possible loss of control, or the rotor blades striking the tailboom.

  • Lateral Balance

  • For smaller helicopters, it is generally unnecessary to determine the lateral CG for normal flight instruction and passenger flights.
    • This is because helicopter cabins are relatively narrow and most optional equipment is located near the centerline.
    • However, some helicopter manuals specify the seat from which a pilot must conduct solo flight.
    • In addition, if there is an unusual situation that could affect the lateral CG, such as a heavy pilot and a full load of fuel on one side of the helicopter, its position should be checked against the CG envelope.
    • If carrying external loads in a position that requires large lateral cyclic control displacement to maintain level flight, fore and aft cyclic effectiveness could be limited dramatically.
    • Manufacturers generally account for known lateral CG displacements by locating external attachment points opposite the lateral imbalance.
    • Examples are placement of hoist systems attached to the side, and wing stores commonly used on military aircraft for external fuel pods or armament systems. purposes.
Weight & Balance

Weight and Balance Calculations

  • When determining whether a helicopter is properly loaded, two questions must be answered:
    • Is the gross weight less than or equal to the maximum allowable gross weight?
    • Is the CG within the allowable CG range, and will it stay within the allowable range throughout the duration of flight including all loading configurations that may be encountered?
  • To answer the first question, add the weight of the items comprising the useful load (pilot, passengers, fuel, oil [if applicable], cargo, and baggage) to the basic empty weight of the helicopter.
    • Ensure that the total weight does not exceed the maximum allowable gross weight.
  • Standard weights for aviation fuels, oils, and water used in helicopter weight-and-balance calculations.
    Standard weights for aviation fuels, oils, and water used in helicopter weight-and-balance calculations.
    Standard weights for aviation fuels, oils, and water used in helicopter weight-and-balance calculations.
    Standard weights for aviation fuels, oils, and water used in helicopter weight-and-balance calculations.
  • To answer the second question, use CG or moment information from loading charts, tables, or graphs in the RFM.
    • It is important to note that any weight and balance computation is only as accurate as the information provided.
    • Therefore, ask passengers what they weigh and add a few pounds to account for the additional weight of clothing, especially during the winter months.
    • Baggage should be weighed on a scale, if practical.
    • If a scale is not available, compute personal loading values according to each individual estimate.
    • [] indicates the standard weights for specific operating fluids.
    • These values are used when computing a helicopter's balance.

  • Reference Datum

  • The horizontal reference datum can be located at several positions selected by the manufacturer.
    The horizontal reference datum can be located at several positions selected by the manufacturer.
    The horizontal reference datum can be located at several positions selected by the manufacturer.
    The horizontal reference datum can be located at several positions selected by the manufacturer.
  • The lateral reference datum runs longitudinally through the helicopter centerline.
    The lateral reference datum runs longitudinally through the helicopter centerline.
    The lateral reference datum runs longitudinally through the helicopter centerline.
    The lateral reference datum runs longitudinally through the helicopter centerline.
  • Balance is determined by the location of the CG, which is usually described as a given number of inches from the reference datum.
    • The horizontal reference datum is an imaginary vertical plane or point, arbitrarily fixed somewhere along the longitudinal axis of the helicopter, from which all horizontal distances are measured for weight and balance purposes.
    • There is no fixed rule for its location.
    • It may be located at the rotor mast, the nose of the helicopter, or even at a point in space ahead of the helicopter. []
    • The lateral reference datum is usually located at the center of the helicopter.
    • The location of the reference datum is established by the manufacturer and is defined in the RFM.
    • []
Weight & Balance

Chapter Summary

  • This chapter discusses the importance of computing the weight and balance of the helicopter.
    • The chapter also discusses the common terms and meanings associated with weight and balance.