Private Pilot Tutorial 9: Weight and Balance

tutorial nine weight and balance this tutorial will cover weight and balance compliance with the weight and balance limits of any aircraft is critical to flight safety operating above the maximum weight limitation compromises the structural integrity of an aircraft and adversely affects its performance operation with the center of gravity CG outside the approved limits results in control difficulty as discussed in tutorial for aerodynamics of flight weight is the force with which gravity attracts a body toward the center of the earth it is a product of the mass of a body and the acceleration acting on the body weight is a major factor in aircraft construction and operation and demands respect from all pilots the force of gravity continuously attempts to pull an aircraft down toward earth the force of lift is the only force that counteracts weight and sustains an aircraft in flight the amount of lift produced by an airfoil is limited by the airfoil design angle of attack AOA airspeed and air density to assure that the lift generated is sufficient to counteract weight loading and aircraft beyond the manufacturer's recommended weight must be avoided if the weight is greater than the lift generated the aircraft may be incapable of flight any item aboard the aircraft that increases the total weight is undesirable for performance manufacturers attempt to make an aircraft as light as possible without sacrificing strength or safety the pilot should always be aware of the consequences of overloading an overloaded aircraft may not be able to leave the ground or if it does become airborne it may exhibit unexpected and unusually poor flight characteristics if not properly loaded the initial indication of poor performance usually takes place during takeoff excessive weight reduces the flight performance in almost every respect for example the most important performance deficiencies of an overloaded aircraft are higher takeoff speed longer takeoff run reduced rate and an of climb lower maximum altitude shorter range reduced cruising speed reduced maneuverability higher stalling speed higher approach and landing speed longer landing roll and excessive weight on the nose wheel or tail wheel the pilot must be knowledgeable about the effect of weight on the performance of the particular aircraft being flown pre-flight planning should include a check of performance charts to determine if the aircraft's weight may contribute to hazardous flight operations excessive weight in itself reduces the safety margins available to the pilot and becomes even more hazardous when other performance reducing factors are combined with excess weight the pilot must also consider the consequences of an overweight aircraft if an emergency condition arises if an engine fails on takeoff or airframe ice forms at low altitude it is usually too late to reduce an aircraft's weight to keep it in the air weight changes the operating weight of an aircraft can be changed by simply altering the fuel load gasoline has considerable weight 6 pounds per gallon 30 gallons of fuel may weigh more than one passenger if a pilot lowers airplane weight by reducing fuel the resulting decrease in the range of the airplane must be taken into consideration during flight planning during flight fuel burn is normally the only weight that takes place as fuel is used and aircraft becomes lighter and performance is improved changes of fixed equipment have a major effect upon the weight of the aircraft the installation of extra radios or instruments as well as repairs or modifications may also affect the weight of an aircraft balance stability and center of gravity balance refers to the location of the CG of an aircraft and is important to stability and safety in flight the CG is a point at which the aircraft would balance if it were suspended at that point the primary concern in balancing an aircraft is the fore and aft location of the CG along the longitudinal the CG is not necessarily a fixed point its location depends on the distribution of weight in the aircraft the pilot should realize that if the CG is displaced too far forward on the longitudinal axis a nose heavy condition will result conversely if the CG is displaced too far aft on the longitudinal axis a tail heavy condition results it is possible that the pilot could not control the aircraft if the CG location produced an unstable condition location of the CG with reference to the lateral axis is also important for each item of weight existing to the left of the fuselage centerline there is an equal weight existing at a corresponding location on the right this may be upset by unbalanced lateral loading the position of the lateral CG is not computed in all aircraft but the pilot must be aware that adverse effects arise as a result of a laterally unbalanced condition in an airplane lateral unbalance occurs if the fuel load is mismanaged by supplying the engine unevenly from tanks on one side of the airplane the pilot can compensate for the resulting wing heavy condition by adjusting the trim or by holding a constant control pressure this action places the aircraft controls in an out of streamline condition increases drag and results in decreased operating efficiency since lateral balance is addressed when needed in the aircraft flight manual AFM and longitudinal balance is more critical further reference to balance in this handbook means longitudinal location of the CG a single pilot operating a small rotor craft may require additional weight to keep the aircraft laterally balanced flying an aircraft that is out of balance can produce increased pilot fatigue with obvious effects on the safety and efficiency of flight the pilots natural correction for longitudinal unbalance is a change of trim to remove the excess control pressure excessive trim however has the effect of reducing not only aerodynamic efficiency but also primary control travel distance in the direction the trim is applied effects of adverse balance adverse balance conditions affect flight characteristics in much the same manner as those mentioned for an excess weight condition it is vital to comply with weight and balance limits established for all aircraft loading in a nose heavy condition causes problems in controlling and raising the nose especially during takeoff and landing loading in a tail-heavy condition has a serious effect upon longitudinal stability and reduces the capability to recover from stalls and spins tail heavy loading also produces very light control forces another undesirable characteristic this makes it easy for the pilot to inadvertently over stress an aircraft especially rotorcraft operating above the maximum weight limitation compromises the structural integrity of the rotor craft and adversely affects performance balance is also critical because on some fully loaded rotor craft CG deviations as small as three inches can dramatically change handling characteristics stability and control are also affected by improper balance stability loading in a nose heavy condition causes problems in controlling and raising the nose especially during takeoff and landing loading in a tail heavy condition has a serious effect upon longitudinal stability and reduces the capability to recover from stalls and spins tail heavy loading also produces very light control forces another undesirable characteristic this makes it easy for a pilot to inadvertently over stress an aircraft it is important to re-evaluate the balance in a rotor craft whenever loading changes in most aircraft offloading a passenger is unlikely to adversely affect the CG but offloading a passenger from a rotor craft can create an unsafe flight condition and out of balance loading condition also decreases maneuverability since cyclic control is less effective in the direction opposite to the CG location limits for the location of the CG are established by the manufacturer these are the fore and aft limits beyond which the CG should not be located for flight these limits are published for each aircraft in the type certificate data sheet T CDs or aircraft specification and the AFM or pilots operating handbook poh if the CG is not within the allowable limits after loading it will be necessary to relocate some items before flight is attempted the forward CG limit is often established at a location that is determined by the landing characteristics of an aircraft during landing one of the most critical phases of flight exceeding the forward CG limit may result in excessive loads on the nosewheel a tendency to nose over on tail will type airplanes decreased performance higher stalling speeds and higher control forces control in extreme cases a CG location that is beyond the forward limit may result in nose heaviness making it difficult or impossible to flare for landing manufacturers purposely place the forward CG limit as far rearward as possible to aid pilots and avoiding damage when landing in addition to decreased static and dynamic longitudinal stability other undesirable effects caused by a CG location after the allowable range may include extreme control difficulty violent stall characteristics and very light control forces which make it easy to over stress an aircraft inadvertently a restricted forward CG limit is also specified to assure that sufficient elevator control deflection is available at minimum air speed when structural limitations do not limit the forward CG position it is located at the position where full up elevator control deflection is required to obtain a high AOA for landing the aft CG limit is the most rearward position at which the CG can be located for the most critical maneuver or operation as the CG moves craft a less stable condition occurs which decreases the ability of the aircraft to write itself after maneuvering or turbulence for some aircraft both fore and aft CG limits may be specified to vary as gross weight changes they may also be changed for certain operations such as acrobatic flight retraction of the landing gear or the installation of special loads and devices that change the flight characteristics the actual location of the CG can be altered by many variable factors and is usually controlled by the pilot placement of baggage and cargo items determines the CG location the assignment of seeds to passengers can also be used as a means of obtaining a favorable balance if an aircraft is tail-heavy it is only logical to place heavy passengers in forward seats fuel burn can also affect the cg based on the location of the fuel tanks for example most small aircraft carry fuel in the wings very near the CG and burning off fuel has little effect on the loaded CG on rotorcraft the fuel tanks are often located behind the CG and fuel consumption from a tank aft of the rotor mast causes the loaded CG to move forward a rotor craft in this condition has a nose low attitude when coming to a hover following a vertical takeoff excessive rearward displacement of the cyclic control is needed to maintain a hover in a no wind condition flight should not be continued since rearward cyclic control fades as fuel is consumed deceleration to a stop may also be impossible in the event of engine failure and auto rotation there may not be enough cyclic control to flare properly for a landing weight and balance control should be a matter of concern to all pilots the pilot controls loading and fuel management the two variable factors that can change both total weight and CG location of a particular aircraft the aircraft owner or operator should make certain that up-to-date information available for pilot use and should ensure that appropriate entries are made in the records when repairs or modifications have been accomplished the removal or addition of equipment results in changes to the cg weight changes must be accounted for and the proper notations made in weight and balance records the equipment list must be updated if appropriate without such information the pilot has no foundation upon which to base the necessary calculations and decisions before any flight the pilot should determine the weight and balance condition of the aircraft simple and orderly procedures based on sound principles have been devised by the manufacturer for determination of loading conditions the pilot uses these procedures and exercises good judgment when determining weight and balance in many modern aircraft it is not possible to fill all seats baggage compartments and fuel tanks and still remain within the approved weight and balance limits if the maximum passenger load is carried the pilot must often reduce the fuel load or reduce the amount of baggage the pilot should be familiar with terms used in working problems related to weight and balance the following list of terms and their definitions is standardized and knowledge of these terms aids the pilot to better understand weight and balance calculations of any aircraft arm moment arm the horizontal distance in inches from the reference datum line to the CG of an item the algebraic sign is plus if measured after the datum and - if measured forward of the data m-- basic empty weight the standard empty weight plus the weight of optional and special equipment that have been installed centre of gravity CG the point about which an aircraft would balance if it were possible to suspend it at that point it is the mass center of the aircraft or the theoretical point at which the entire weight of the aircraft is assumed to be concentrated it may be expressed in inches from the reference datum see limits the specified forward and aft points within which the cg must be located during flight these limits are indicated on pertinent aircraft specifications CG range the distance between the forward and aft CG limits indicated on pertinent aircraft specifications Dada 'm referenced adam an imaginary vertical plane or line from which all measurements of arm are taken the datum is established by the manufacturer once the datum has been selected all moment arms and the location of CG range are measured from this point mean aerodynamic chord Mac the average distance from the leading edge to the trailing edge of the wing moment the product of the weight of an item multiplied by its arm moments are expressed in inch pounds total moment is the weight of the airplane multiplied by the distance between the data and the CG station a location in the aircraft that is identified by a number designating its distance in inches from the datum the datum is therefore identified as station 0 an item located at station plus 50 would have an arm of 50 inches useful load the weight of the pilot copilot passengers baggage usable fuel and drainable oil it is the basic empty weight subtracted from the maximum allowable gross weight this term applies to general aviation GA aircraft only principles of weight and balance computations it might be advantageous at this point to review and discuss some of the basic principles of weight and balance determination the following method of computation can be applied to any object or vehicle for which weight and balance information is essential by determining the weight of the empty aircraft and adding the weight of everything loaded on the aircraft a total weight can be determined a simple concept a greater problem particularly if the basic principles of weight and balance are not understood is distributing this weight in such a manner that the entire mass of the loaded aircraft is balanced around a point CG that must be located within specified limits the point at which an aircraft balances can be determined by locating the CG which is as stated in the definition of terms the imaginary point at which all the weight is concentrated to provide the necessary balance between longitudinal stability and elevator control the CG is usually located slightly forward of the center of lift this loading condition causes a nose-down tendency in flight which is desirable during flight at a high AOA and slow speeds as mentioned earlier a safe zone within which the balance point CG must fall is called the CG range the extremities of this range are called the forward CG limits and aft CG limits these limits are usually specified in inches along the longitudinal axis of the airplane measured from a reference point called the datum reference the data is an arbitrary point established by aircraft designers which may vary in location between different aircraft the distance from the datum to any component part or any object loaded on the aircraft is called the arm when the object or component is loaded aft of the datum it is measured in positive inches if it is located forward of the datum it is measured in negative inches or minus inches the location of the object or part is often referred to as the station if the weight of any object or component is multiplied by the distance from the datum arm the product is the moment the moment is the measurement of a gravitational force that causes a tendency of the weight to rotate about a point or axis and as expressed in inch pounds to illustrate assume a weight of 50 pounds is placed on the board at a station or point 100 inches from the datum the downward force of the weight can be determined by applying fifty pounds by 100 inches which produces a moment of 5,000 inch pounds to establish a balance a total of five thousand inch pounds must be applied to the other end of the board any combination of weight and distance which when multiplied produces a five thousand inch pound moment will balance the board and the example shown here if a 100 pound weight is placed at a point station 25 inches from the datum and another 50 pound weight is placed at a point station 50 inches from the datum the sum of the product of the two weights and their distances will total a moment of 5,000 inch pounds which will balance the board an aircraft's weight and balance restrictions should be closely followed the loading conditions and empty weight of a particular aircraft may differ from that found in the AFM Poh because modifications or equipment changes may have been made sample loading problems in the AFM Poh are intended for guidance only therefore each aircraft must be treated separately although an aircraft is certified for a specified maximum gross takeoff weight it will not safely take off with this load under all conditions conditions that affect takeoff and climb performance such as high elevations high temperatures and high humidity high-density altitudes may require a reduction in weight before flight is attempted other factors to consider prior to takeoff our runway length runway surface runway slope service wind and the presence of obstacles these factors may require a reduction in weight prior to flight some aircraft are designed so that it is difficult to load them in a manner that will place the CG out of limits these are usually small aircraft with the seats fuel and baggage areas located near the CG limit pilots must be aware that while within CG limits these aircraft can be overloaded and wait other aircraft can be loaded in such a manner that they will be out of CG limits even though the useful load has not been exceeded because of the effects of an out-of-balance or overweight condition a pilot should always be sure that an aircraft is properly loaded there are various methods for determining the loaded weight and CG of an aircraft there's the computational method as well as methods that utilize graphs and tables provided by the aircraft manufacturer the following is an example of the computational method involving the application of basic math functions one lists the weight of the aircraft occupants fuel and baggage remember that aviation gas of gas weighs six pounds per gallon and is used in this example to enter the moment for each item listed remember weight x arm equals moment three find the total weight and total moment four to determine the CG divide the total moment by the total weight another method for determining the loaded weight and CG is the use of graphs provided by the manufacturers the same steps should be followed as in the computational method except the graphs provided will calculate the moments and allow the pilot to determine if the aircraft is loaded within limits to determine the moment using the loading graph find the weight and draw a line across until it intersects the item for which the moment is to be calculated then draw a line straight down to determine the moment the redline on the loading graph represents the moment for the pilot and front-passenger all other moments were determined in the same way once this has been done for each item total the weight and moments and draw a line for both weight and moment on the CG envelope graph if the lines intersect within the envelope the aircraft is loaded within limits in this sample loading problem the aircraft is loaded within limits when weight is shifted from one location to another the total weight of the aircraft is unchanged the total moments however do change in relation and proportion to the direction and distance the weight is moved when weight is moved for the total moments decrease when weight is moved aft total moments increase the moment change is proportional to the amount of weight moved since many aircraft have forward and aft baggage compartments weight may be shifted from one to the other to change the CG if starting with a known aircraft weight CG and total moments calculate the new CG after the weight shift by dividing the new total moments by the total aircraft weight table method the table method applies the same principles as the computational and graph methods the information and limitations are contained in tables provided by the manufacturer this figure is an example of a table and a weight and balance calculation based on that table in this problem the total weight of 2799 pounds and moment of 2278 over 100 are within the limits of the table computations with a negative arm this table is a sample of weight and balance computation using an airplane with a negative arm it is important to remember that a positive times a negative equals a negative and a negative would be subtracted from the total moments computations with zero fuel weight this table is a sample of weight and balanced computation using an aircraft with a zero fuel weight in this example the total weight of the aircraft less fuel is 40 240 pounds which is under the zero fuel weight of 4,400 pounds if the total weight of the aircraft without fuel had exceeded 4,400 pounds passengers or cargo would have needed to be reduced to bring the weight at or below the max 0 fuel weight operating an aircraft within the weight and balance limits is critical to flight safety pilots must ensure that the cg is and remains within approved limits for all phases of a flight additional information on weight balance CG and aircraft stability can be found in F aah 8:08 3-1 aircraft weight and balance handbook those pilots flying helicopters or gyroplanes should consult the rotor craft flying handbook FAA h8 0 8 3 - 21 for specific information relating to aircraft type this concludes your introduction to weight and balance we hope you learned a lot please help us spread the word about pilot training system and we look forward to further servicing your flight training needs

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Id: k8BEhtVeWWg

Length: 27min 32sec (1652 seconds)

Published: Thu Jul 14 2016