Helicopter, Weight-Shift, and Balance Records

6-25 360 320 280 240 200 160 120 80 40 0 −2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Load Weight (lb) Moment Index (Moment/1,000) Pilot & Front Passenger Rear Passenger Fuel Oil Baggage in Figures 6-45 and 6-46. The use of the loading graph to determine the moment for each of the useful load items is shown in Figure 6-46. The color used for each useful load item in Figure 6-45 matches the color used for the plot on the loading graph. The total loaded weight of the airplane is 2,258 lb and the total loaded moment is 99,400 in-lb. These two numbers can now be plotted on the CG envelope to see if the airplane is within CG limits. Figure 6-47 shows the CG envelope with the loaded weight and moment of the airplane plotted. The CG location shown falls within the normal category envelope, so the airplane is within CG limits for this category.

It is interesting to note that the lines that form the CG envelope are graphic plots of the forward and aft CG limits. In Figure 6-47, the red line is a graphic plot of the forward limit, and the blue and green lines are graphic plots of the aft limit for the two different categories.

Helicopter Weight & Balance

General Concepts All the terminology and concepts that apply to airplane weight and balance also apply generally to helicopter weight and balance. However, there are some specific differences that need to be identified. Most helicopters have a much more restricted CG range than airplanes. In some cases, this range is less than 3". The exact location and length of the CG range is specified for each helicopter and usually extends a short distance fore and aft of the main rotor mast or centered between the main rotors of a dual rotor system. Whereas airplanes have a CG range only along the longitudinal axis, helicopters have both longitudinal and lateral CG ranges. Because the wings extend outward from the CG, airplanes tend to have a great deal of lateral stability. A helicopter, on the other hand, acts like a pendulum, with the weight of the helicopter hanging from the main rotor shaft.

Ideally, the helicopter should have such perfect balance that the fuselage remains horizontal while in a hover. If the helicopter is too nose heavy or tail heavy while it is hovering, the cyclic pitch control is used to keep the fuselage horizontal. If the CG location is too extreme, it may not be possible to keep the fuselage horizontal or maintain control of the helicopter. Helicopter Weighing When a helicopter is being weighed, the location of both longitudinal and lateral weighing points must be known to determine its empty weight and EWCG. This is because helicopters have longitudinal and lateral CG limits. As with the airplane, the longitudinal arms are measured from the datum, with locations behind the datum being positive arms and locations in front of the datum being negative arms.

Laterally, the arms are measured from the butt line, which is a line from the nose to the tail running through the middle of the helicopter. When facing forward, arms to the right of the butt line are positive; to the left they are negative. Before a helicopter is weighed, it must be leveled longitudinally and laterally. This can be done with a spirit 6-26 Weight (lb) 1,400 180 140 210 100 228 2,258 Item Aircraft Empty Weight Pilot Front Passengers Rear Passengers Baggage Fu el Tot al Moment (in-lb) 53,900 6,000 4,500 15,000 9,200 10,800 99,400 2,400 2,300 2,200 2,100 2,000 1,900 1,800 1,700 1,600 1,500 50 55 60 65 70 75 80 85 90 95 100 105 110 115 Load Aircraft Weight (lb) Loaded Aircraft Moment/1,000 (in-lb) Normal Category Utility Category level, but often it is done with a plumb bob. For example, the Bell JetRanger has a location inside the aft cabin where a plumb can be attached and allowed to hang down to the cabin floor. On the cabin floor is a plate bearing cross hairs that correspond to the horizontal and lateral axis of the helicopter.

When the point of the plumb bob falls in the middle of the cross hairs, the helicopter is level along both axes. If the tip of the plumb bob falls forward of this point, the nose of the helicopter is too low; if it falls to the left of this point, the left side of the helicopter is too low. In other words, the tip of the plumb bob always moves toward the low point. A Bell JetRanger helicopter is shown in Figure 6-48 with the leveling plate depicted on the bottom right of the figure. The helicopter has three jack pads, two at the front and one in the back. To weigh this helicopter, three jacks would be placed on floor scales, and the helicopter would be raised off the hangar floor. To level the helicopter, the jacks would be adjusted until the plumb bob point falls exactly in the middle of the cross hairs.

As an example of weighing a helicopter, consider the Bell JetRanger in Figure 6-48, and the following specifications and weighing data shown in Figure 6-49. Using six-column charts for the calculations, the empty weight and the longitudinal and lateral CG for the helicopter is shown in Figure 6-50. Based on the calculations in the helicopter is 1,985 lb, the longitudinal CG is at +108.73", and the lateral CG is at –0.31". Weight and Balance—Weight-Shift Control Aircraft and Powered Parachutes The terminology, theory, and concepts of weight and balance that applies to airplanes also applies to weight-shift control aircraft and powered parachutes. Weight is still weight, and the balance point is still the balance point. However, there are a few differences that need to be discussed. Before reading about the specifics of weight and balance on weight-shift control aircraft and powered parachutes, be sure to read about their aerodynamic characteristics in Chapter 5, Physics.

Weight-shift control aircraft and powered parachutes do not fall under the same Code of Federal Regulations that govern certified airplanes and helicopters and, therefore, do not have TCDS or the same type of FAA-mandated weight and balance reports. Weight and balance information and guidelines are left to the individual owners and the companies with which they work in acquiring this type of aircraft. Overall, the industry that is supplying these aircraft is regulating itself well, and the safety record is good for those aircraft being operated by experienced pilots. 6-27 2,400 2,300 2,200 2,100 2,000 1,900 1,800 1,700 1,600 1,500 50 55 60 65 70 75 80 85 90 95 100 105 110 115 Load Aircraft Weight (lb) Loaded Aircraft Moment/1,000 (in-lb) Normal Category CG Location Aft Limit Forward Limit Utility Category 360 320 280 240 200 160 120 80 40 0 −2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Load Weight (lb) Moment Index (Moment/1,000) Pilot & Front Passenger Rear Passenger Fuel Oil Baggage Weight-Shift Control Aircraft Weight-shift control aircraft, commonly known by the name “trikes,” have very few options for loading, because they have very few places to put useful load items. Some trikes have only one seat and a fuel tank, so the only variables for a flight are amount of fuel and weight of the pilot. Some trikes have two seats and a small storage bin in addition to the fuel tank.

The most significant factor affecting the weight and balance of a trike is the weight of the pilot; if the aircraft has two seats, the weight of the passenger must be considered. The trike acts somewhat like a single main rotor helicopter because the weight of the aircraft is hanging like a pendulum under the wing. Figure 6-51 shows a two-place trike, in which the mast and the nose strut come together slightly below the wing attach point. When the trike is in flight, the weight of the aircraft is hanging from the wing attach point. The weight of the engine and fuel is behind this point, the passenger is almost directly below this point, and the pilot is forward of this point. The balance of the aircraft is determined by how all these weights compare.

The wing attach point, with respect to the wing keel, is an adjustable location. The attach point can be loosened and 6-28 moved slightly forward or slightly aft, depending on the weight of the occupants. For example, if the aircraft is flown by a person that weighs more, the attach point can be moved a little farther aft, bringing the wing forward, to compensate for the change in CG. Figure 6-52 shows a close-up of the wing attach point, and the small amount of forward and aft movement that is available. Powered Parachutes Powered parachutes have many of the same characteristics as weight-shift aircraft when it comes to weight and balance.

They have the same limited loading, with only one or two seats and a fuel tank. They also act like a pendulum, with the weight of the aircraft hanging beneath the inflated wing (parachute). The point at which the inflated wing attaches to the structure of the aircraft is adjustable to compensate for pilots and passengers of varying weights. With a very heavy pilot, the wing attach point would be moved forward to prevent the aircraft from being too nose heavy. Figure 6-53 shows the structure of a powered parachute with the adjustable wing attach points. Weight & Balance for Large Airplanes Weight and balance for large airplanes is almost identical to what it is for small airplanes, on a much larger scale. If a technician can weigh a small airplane and calculate its empty weight and EWCG, that same technician should be able to do it for a large airplane. The jacks and scales are larger, and it may take more personnel to handle the equipment, but the concepts and processes are the same.

Built-In Electronic Weighing One difference that may be found with large airplanes is the incorporation of electronic load cells in the aircraft’s landing gear. With this type of system, the airplane can weigh itself as it sits on the tarmac. The load cells are built into the axles of the landing gear, or the landing gear strut, and they work in the same manner as load cells used with jacks. This system is currently in use on the Boeing 747-400, Boeing 777, Boeing 787, McDonnell Douglas MD-11, and the wide body Airbus airplanes like the A-330, A-340, and A-380. The Boeing 777 utilizes two independent systems that provide information to the airplane’s flight management system (FMS). If the two systems agree on the weight and CG of the airplane, the data being provided are considered accurate and the airplane can be dispatched based on that information. The flight crew has access to the information on the flight deck by accessing the FMS and bringing up the weight and balance page.

Mean Aerodynamic Chord On small airplanes and on all helicopters, the CG location is identified as being a specific number of inches from the datum. The CG range is identified the same way. On larger airplanes, from private business jets to large jumbo jets, the CG and its range are typically identified in relation to the width of the wing. The width of the wing on an airplane is known as the chord. If the leading edge and trailing edge of a wing are parallel to each other, the chord of the wing is the same along the wing’s length. Business jets and commercial transport airplanes have wings that are tapered and that are swept back, so the width of their wings is different along their entire length.

The width is greatest where the wing meets the fuselage and progressively decreases toward the tip. In relation to the aerodynamics of the wing, the average length of the chord on these tapered swept-back wings is known as the mean aerodynamic chord (MAC). On these larger airplanes, the CG is identified as being at a location that is a specific percent of the mean aerodynamic chord (% MAC). For example, imagine that the MAC on an airplane is 100", and the CG falls 20" behind the leading edge of the MAC. That means it falls one-fifth of the way back, or at 20 percent of the MAC. airplane. The datum is forward of the nose of the airplane, and all the arms are being measured from that point. The CG for the airplane is shown as an arm measured in inches. In the lower left corner of the figure, a cross section of the wing is shown, with the same CG information being presented.

To convert the CG location from inches to a percent of MAC, for the airplane shown in Figure 6-54, the steps are as follows: 1. Identify the CG location, in inches from the datum. 2. Identify the leading edge of the MAC (LEMAC), in inches from the datum. 3. Subtract LEMAC from the CG location. 4. Divide the difference by the length of the MAC. 5. Convert the result in decimals to a percentage by multiplying by 100. As a formula, the solution to solve for the percent of MAC would be: CG – LEMAC Percent of MAC = × 100 MAC The result using the numbers shown in Figure 6-52 would be: CG – LEMAC Percent of MAC = × 100 MAC 6-29 55.16" forward of the front jack point centerline Plumb line from ceiling left rear cabin to index plate on floor +106" to +111.4" at 3,200 lb +106" to +112.1" at 3,000 lb +106" to +112.4" at 2,900 lb +106" to +113.4" at 2,600 lb +106" to +114.2" at 2,350 lb +106" to +114.2" at 2,100 lb Straight line variation between points 2.3" left to 3.0" right at longitudinal CG + 106.0" 3.0" left to 4.0" right at longitudinal CG +108" to +114.2" Straight line variation between points Empty weight includes unusable fuel and unusable oil Datum: Leveling Means: Longitudinal CG Limits: Lateral CG Limits: Fuel and Oil: Left Front Scale Reading: Left Front Jack Point: Right Front Scale Reading: Right Front Jack Point: After Scales Reading: Aft Jack Point: Notes: 650 lb Longitudinal arm of +55.16" Lateral arm of –25" 625 lb Longitudinal arm of +55.16" Lateral arm of +25" 710 lb Longitudinal arm of +204.92" Lateral arm of 0.0" The helicopter was weighed with unusable fuel and oil. Electronic scales were used and zeroed with the jacks in place, so no tare weight needs to be accounted for.

Forward ballast station +13" Forward jack point +55.16" +25" and −25" laterally Datum Leveling plate +117.7" Plumb bob Leveling plate with crosshairs Aft jack point +204.92" Aft ballast station +377" Left side Right side Nose Tail 6-30 Longitudinal CG Calculation Item Scale (lb) Tare Wt. (lb) Nt. Wt. (lb) Arm (inches) Moment (in-lb) Left Front 650 0 650 +55.16 35,854.0 Right Front 625 0 625 +55.16 34,475.0 Aft 710 0 710 +204.92 145,493.2 Total 1,985 1,985 +108.73 215,822.2 Lateral CG Calculation Item Scale (lb) Tare Wt. (lb) Nt. Wt. (lb) Arm (inches) Moment (in-lb) Left Front 650 0 650 −25 −16,250 Right Front 625 0 625 +25 +15,625 Aft 710 0 710 0 0 Total 1,985 1,985 +.31 −625 Nosewheel steering Throttle Pivot bar to control turning Wing attachment point adjustable for CG Wing attachment point adjustable for CG 945 – 900 = × 100 180 = 25 percent If the CG is known in percent of MAC, and there is a need to know the CG location in inches from the datum, the conversion would be done as follows: 1. Convert the percent of MAC to a decimal by dividing by 100.

2. Multiply the decimal by the length of the MAC. 6-31 Center of gravity 945" CG at 945" Leading edge of MAC 900" Datum Trailing edge of MAC 1,080" LEMAC 900" Chord line MAC = 180" 45" MAC=180" 3. Add this number to LEMAC. As a formula, the solution to convert a percent of MAC to an inch value would be: CG in inches = % MAC ÷ 100 × MAC + LEMAC For the airplane in Figure 6-54, if the CG was at 32.5 percent of the MAC, the solution would be: CG in inches = % MAC ÷ 100 × MAC + LEMAC = 32.5 ÷ 100 × 180 + 900 = 958.5

Weight & Balance Records

When a technician gets involved with the weight and balance of an aircraft, it almost always involves a calculation of the aircraft’s empty weight and EWCG. Only on rare occasions are technicians involved in calculating adverse-loading CG checks, how much ballast is needed, or the loaded weight and balance of the aircraft. Calculating the empty weight and EWCG might involve putting the aircraft on scales and weighing it, or a pencil and paper exercise after installing a new piece of equipment. The FAA requires that a current and accurate empty weight and EWCG be known for an aircraft. This information must be included in the weight and balance report, which is a part of the aircraft permanent records. The weight and balance report must be in the aircraft when it is being flown.

There is no required format for this report, but Figure 6-55 is a good example of recording the data obtained from weighing an aircraft. As it is currently laid out, the form would accommodate either a tricycle gear or tail dragger airplane. Depending on the gear type, either the nose or the tail row would be used. If an airplane is being weighed using jacks and load cells, or if a helicopter is being weighed, the 6-32 Aircraft Weight and Balance Report Results of Aircraft Weighing Make Model Serial # N# Datum Location Leveling Means Scale Arms: Nose Tail Left Main Right Main Scale Weights: Nose Tail Left Main Right Main Tare Weights: Nose Tail Left Main Right Main Weight and Balance Calculation Aircraft Current Empty Weight: Aircraft Current Empty Weight CG: Aircraft Maximum Weight: Aircraft Useful Load: Computed By: Certificate #: (print name) (signature) (A&P, Repair Station, etc.) Date: Item Nose Tail Left Main Right Main Subtotal Fuel Oil Misc.

Total Scale (lb) Tare Wt. (lb) Net Wt. (lb) Arm (inches) Moment (in-lb) 6-33 item names must be changed to reflect the weight locations. If an equipment change is being done on an aircraft, and the new weight and balance is calculated mathematically instead of weighing the aircraft, the same type of form shown in of a four-column solution, instead of six columns, and there would be no tare weight or involvement with fuel and oil.