sive forward displacement of cyclic control to main- tain a hover in a no-wind condition. If there is a wind, you need even greater forward cyclic. If flight is continued in this condition, you may find it 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 flap- ping could cause the rotor disc to tilt aft. With full for- ward cyclic control already applied, you might not be able to lower the rotor disc, resulting in possible loss of control, or the rotor blades striking the tailboom. For most helicopters, it is usually not necessary to determine the lateral CG for normal flight instruction and passenger flights. This is because helicopter cab- ins are relatively narrow and most optional equip- ment is located near the center line. However, some helicopter manuals specify the seat from which you must conduct solo flight. In addition, if there is an unusual situation, such as a heavy pilot and a full load of fuel on one side of the helicopter, which could affect the lateral CG, 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 dramatically limited. When determining whether your helicopter is properly loaded, you must answer two questions: To answer the first question, just 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. Check that the total weight does not exceed the maximum allowable gross weight. To answer the second question, you need to use CG or moment information from loading charts, tables, or graphs in the rotorcraft flight manual. Then using one of the methods described below, calculate the loaded moment and/or loaded CG and verify that it falls within the allow- able CG range shown in the rotorcraft flight manual. It is important to note that any weight and balance com- putation is only as accurate as the information provided. Therefore, you should ask passengers what they weigh The following terms are used when computing a heli- copter’s balance. REFERENCE DATUM — 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 hori- zontal 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. [Figure 7-3] and add a few pounds to cover the additional weight of clothing, especially during the winter months. The bag- gage weight should be determined by the use of a scale, if practical. If a scale is not available, be conservative and overestimate the weight. Figure 7-2 indicates the stan- dard weights for specific operating fluids. LATERAL BALANCE Datum + – Figure 7-3. While the horizontal reference datum can be any- where the manufacturer chooses, most small training heli- copters have the horizontal reference datum 100 inches forward of the main rotor shaft centerline. This is to keep all the computed values positive.  7-3 1. Is the gross weight less than or equal to the max- imum allowable gross weight? 2. Is the center of gravity within the allowable CG range, and will it stay within the allowable range as fuel is burned off? WEIGHT AND BALANCE CALCULATIONS Figure 7-2. When making weight and balance computations, always use actual weights if they are available, especially if the helicopter is loaded near the weight and balance limits. Aviation Gasoline (AVGAS) . . . . . . . . . . . . . . . . . . .6 lbs. / gal.GLYPH<.notdef> Jet Fuel (JP-4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 lbs. / gal.GLYPH<.notdef> Jet Fuel (JP-5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8 lbs. / gal.GLYPH<.notdef> Reciprocating Engine Oil . . . . . . . . . . . . . . . . . . 7.5 lbs. / gal.*GLYPH<.notdef> Turbine Engine Oil . . Varies between 7.5 and 8.5 lbs. / gal.*GLYPH<.notdef> Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8.35 lbs. / gal.GLYPH<.notdef> GLYPH<.notdef> * Oil weight is given in pounds per gallon while oil capacityGLYPH<.notdef> is usually given in quarts; therefore, you must convert theGLYPH<.notdef> amount of oil to gallons before calculating its weight.GLYPH<.notdef>