RH ENGINE PUMP
SYSTEM PRESSURE
ENGINE PUMP SUCTION
IDLING CIRCUIT PUMP PRESSURE
RETURN FLOW
HAND PUMP PRESSURE
HAND PUMP SUCTION hate CHECK VALVE ACCUM. AIR GAGES GEN. SYSTEM ACCUMULATOR BRAKE ACCUMULATOR •
TO BRAKE SYSTEM
RESTRICTOR
THERMAL RELIEF VALVE
FROM EMERGENCY SEL. VALVE (BRAKE)
UNLOADING AND RELIEF VALVE
SNUBBER AND VENT ENG
VL FLAPS RESERVOIR SEL. VAL.
NORMAL LAND. CEAF SEL. VALVE EMER.
SELECTOR VALVE
XXXXXXX
LH ENGINE PUMP FIGURE 2-20. Aircraft hydraulic system schematic.
for ease of reading and tracing the flow. Each component is identified by name, and its location within the system can be ascertained by noting the lines that lead into and out of the unit.
In tracing the flow of fluid through the system, it can be seen that the engine-driven pumps receive a supply of fluid from the reservoir. One-way check valves are installed in both left and right pump pressure lines so that failure of one pump will not render the pressure from the other pump ineffective. Fluid flows to the relief side of the unloading and relief valve, and through the check valve, which will hold pressure built up beyond this point. Pressure is then directed through all lines leading to each selector valve, where it is checked if no units are being operated.
Pressure builds up in the line routed to the control port of the unloading valve and begins to 48
BLOCK IN ADD DETAIL
DARKEN VIEWS ADD DIMENSIONS ¼" →T 9-13-67 WEDGE .WOK FIGURE 2-21. Steps in sketching.
charge the system accumulator. Pressure to charge the brake accumulator is routed through a check valve incorporated in the thermal relief valve; this prevents the pressure from returning to the general system.
Although the general system accumulator starts charging at the same time, it will not charge as fast, because the fluid passes through a restrictor valve. The general system pressure will bleed into the brake system whenever the brake pressure drops below system pressure.
As soon as the pressure reaches the relief valve setting, the valve will open slightly. General system pressure increases until it reaches the value established as the system operating pressure. At this point, through the line leading to the control part of the unloading valve, the pressure will force the unloading and relief valve completely open. The pressure trapped in the system by the one-way check valve holds the value open to create an idling circuit, which prevails until some unit of the hydraulic system is operated.
Schematic diagrams, like installation diagrams, are used extensively in aircraft manuals.
DRAWING SKETCHES A sketch is a simple, rough drawing that is made rapidly and without much detail. Sketches may take many forms-from a simple pictorial presentation to a multiview orthographic projection.
A sketch is frequently drawn for use in manufacturing a replacement part. Such a sketch must provide all necessary information to those persons who must manufacture the part.
A mechanic need not be an accomplished artist.
However, in many situations, he will need to prepare a drawing to present an idea for a new design, a modification, or a repair method. The medium of sketching is an excellent way of accomplishing this.
The rules and conventional practices for making mechanical drawings are followed to the extent that all views needed to portray an object accurately are shown in their proper relationship. It is also necessary to observe the rules for correct line use (figures 2-15 and 2-16) and dimensioning.
To make a sketch, first determine what views are necessary to portray the object; then block in the views, using light construction lines. Next, complete the details, darken the object outline, and sketch extension and dimension lines. Complete the drawing by adding notes, dimensions, title, date and, when necessary, the sketcher's name. The steps in making a sketch of an object are illustrated in figure 2-21.
where on the drawing. In this case, the more easily drawn symbol for cast iron is used for the sectioning, and the material specification is listed in the bill of materials or indicated in a note.
CAST IRON MAGNESIUM, ALUMINUM AND Figure 2-22 illustrates a few standard material ALUMINUM ALLOTS symbols.
Shape Symbols Symbols can be used to excellent advantage, when it is desired to show the shape of an object.
STEEL RUBBER, PLASTIC ELECTRICAL INSULATION Typical shape symbols used on aircraft drawings are shown in figure 2-23. Shape symbols are usually shown on a drawing as a revolved or removed section.
Electrical Symbols BRASS, BRONZE, AND COPPER BABBITT, LEAD, ZINC AND ALLOYS Electrical syn bols (figure 2-24) represent various electrical de ices rather than an actual drawing of the units. Having learned what the various symbols indicate, it becomes relatively simple to look at an electrical diagram and determine what each unit is, what function it serves, and how it is WOOD ACROSS GRAIN WOOD WITH GRAIN connected in the system.
CARE OF DRAFTING INSTRUMENTS
CORK, FELT, FABRIC
ASBESTOS, LEATHER
AND FIBRE FIGURE 2-22. Material symbols.
The degree to which a sketch is complete will depend on its intended use. Obviously, a sketch not be dimensioned. If a part is to be manunecessary construction details.
DRAWING SYMBOLS The drawings for a component are composed largely of symbols and conventions representing its shape and material. Symbols are the shorthand of drawing. They graphically portray the characteristics of a component, with a minimum amount of drawing.
Material Symbois Section-line symbols show the kind of material from which the part is to be constructed. The material may not be indicated symbolically when Good drawing instruments are expensive precision tools. Reasonable care given to them during their use and storage will prolong their service life.
T-squares, triangles, and scales should not be used, or placed, where their surfaces or edges may be damaged. Use a drawing board only for its intended purpose, and not in a manner that will mar the working surface.
Compasses, dividers, and pens will provide better results with less annoyance, if they are correctly shaped and sharpened, and they are not damaged by careless handling.
Store drawing instruments in a place where they are not likely to be damaged by contact with other tools or equipment. Protect compass and divider points by inserting them into a piece of soft rubber or similar material. Never store ink pens without first cleaning and drying them thoroughly.
MICROFILM The practice of recording drawings, parts catalogs, and maintenance and overhaul manuals on microfilms was introduced in recent years. Microfilm is regular 16-mm. or 35-mm. film. Since 35-mm. film is larger, it provides a'better reproduction of drawings. Depending on the size of 50
SQUARE SECTION SQUARE SECTION (METAL) (WOOD)
ROUND SECTION ROUND SECTION (SOLID) (TUBULAR)
ANGLE SECTION CHANNEL SECTION (METAL) (METAL)
I BEAM SQUARE SECTION (METAL) (TABULAR) FIGURE 2-23. Shape symbols.
the drawing to be reproduced, a varying number of drawings can be photographed on one reel of 35-mm. film. To view or read drawings or manuals on a reel of film, you need either a portable 35-mm.
film projector or a microfilm reader or viewer.
The advantage of microfilm is that several reels, which represent perhaps hundreds of drawings, require only a small amount of storage space.
Too, a person working on an aircraft may need to refer to a specific dimension. He can place the reel of microfilm in a projector, locate the drawing or desired information, and read the dimension.
If he has to study a detail of the drawing, or work with the drawing for a long period of time, an enlarged photographic reproduction can be made, using the microfilm as a negative.
Microfilm of drawings has many other uses and advantages. However, microfilm is not intended to replace the need for original drawings, especially where the originals are modified and kept current over a long period of time.
When drawings are filmed on continuous reels, corrections can be made by cutting out superseded drawings and splicing in the revised ones.
When these corrections become numerous, the procedure becomes impractical and is discarded in favor of again filming all the related drawings.
A method that allows corrections to be made easily is to photograph the drawings and then cut up the film into individual slides. This has one disadvantage; it requires considerable time to convert the film into slides, insert them into transparent protective envelopes, and arrange them in sequence so that desired drawings can be located quickly.
A 70-mm. microfilm has become available very recently. With it, larger size drawings can be reproduced as individual frames or slides, and these can be inserted in regular paper envelopes and kept in an ordinary file. When held to the light, this large microfilm can be read with the naked eye.
CONDENSERS LAMPS - Red, Green, White
CONDUCTORS TOR →
SINGLE INTERSECTING CROSSING OVER TRANSFORMER SOLENOID
ELECTRICALLY EACH OTHER
MOTORS - GENERATORS 5 OR OR D.C. А.C D.C. A.C.
METERS
VOLT AMMETER RESISTOR RHEOSTAT
RELAYS CONNECTORS P S
REMOVABLE FIXED B
NOT ALL ALL C
SPST MOMENTARY NORMAL OR SPDT MPDT PINS PINS D
MOMENTARY NORMAL OR SHOWN SHOW
ON MOMENTARY
CONTACTS CONTACTS P DESIGNATED PINS
S DESIGNATED SOCKETS
CIRCUIT BREAKERS
AUTOMATIC PUSH PUSH RESET SWITCH MOMENTARY RESET RESET PULL OFF TYPE SWITCH TYPE p
CURRENT BATTERY BUS
LIMITER
SWITCHES - SPST MOMENTARY SPST CENTER SPŮT SPDT MOMEN- ao SPDT CENTER OFF SPOT NORMAL OR PRES- IC THERM- SPDT A BIMETAL-
ON OFF TARY ON NORMAL OR MOMENTARY SURE AL CUT-
MOMENTARY OUT
CONTACTS 10 CONTACTS: O NORMAL POSITION - PUSH-BUTTON TYPE - A MOMENTARY POSITION ала 2,0
MPST MPDT O CENTER OFF MECHANICAL LINKAGE MOMENTARY NORMAL NORMAL OR
ON ON MOMENTARY
FUSE SPLICE GROUND CONTACTS
POLARITY BASIC DC + 10A ELECTRICAL DISCONNECT POSITIVE NEGATIVE FIGURE 2-24. Electrical symbols.
CHAPTER 3
AIRCRAFT WEIGHT AND BALANCE
PURPOSE The primary purpose of aircraft weight and balance control is safety. A secondary purpose is to achieve the utmost in efficiency during flight.
Improper loading reduces the efficiency of an aircraft from the standpoint of ceiling, maneuverability, rate of climb, speed, and fuel consumption.
It can be the cause of failure to complete a flight, or even to start it. Possible loss of life and destruction of valuable equipment may result from overstressed structures or from a sudden shift in cargo and consequent change in flight characteristics.
The empty weight and the corresponding c.g.
(center of gravity) of all civil aircraft must be determined at the time of certification. The manufacturer can weigh the aircraft, or he can compute the weight and balance report. A manufacturer is permitted to weigh one aircraft out of each 10 produced. The remaining nine aircraft are issued a computed weight and balance report based on the averaged figures of aircraft that are actually weighed. The condition of the aircraft at the time of determining empty weight must be one that is well defined and can be easily repeated.
NEED FOR REWEIGHING Aircraft have a tendency to gain weight because of the accumulation of dirt, greases, etc., in areas not readily accessible for washing and cleaning.
The weight gained in any given period of time will depend on the function of the aircraft, its hours in flight, atmospheric conditions, and the type landing field from which it is operating. For this reason, periodic aircraft weighings are desirable and, in the case of air carrier and air taxi aircraft, are required by Federal Aviation Regulations.
Privately owned and operated aircraft are not required by regulation to be weighed periodically.
They are usually weighed when originally certificated, or after making major alterations that can affect the weight and balance. Even though the aircraft need not be weighed, it must be loaded so that the maximum weight and c.g. limits are not exceeded during operation.
Airline aircraft (scheduled and nonscheduled) carrying passengers or cargo are subject to certain rules that require owners to show that the aircraft is properly loaded and will not exceed the authorized weight and balance limitations during operation.
THEORY OF WEIGHT AND BALANCE The theory of weight and balance is extremely simple. It is that of the familiar lever that is in equilibrium or balance when it rests on the fulcrum in a level position. The influence of weight is directly dependent upon its distance from the fulcrum. To balance the lever the weight must be distributed so that the turning effect is the same on one side of the fulcrum as on the other. In general, a lighter weight far out on the lever has the same effect as a heavy weight near the fulcrum. The distance of any object from the fulcrum is called the lever arm. The lever arm multiplied by the weight of the object is its turning effect about the fulcrum. This turning effect is known as the moment.
Similarly, an aircraft is balanced it it remains level when suspended from an imaginary point.
This point is the location of its ideal c.g. An aircraft in balance does not have to be perfectly level, but it must be reasonably close to it. Obtaining this balance is simply a matter of placing loads so that the average arm of the loaded aircraft falls FIGURE 3-1. An airplane suspended from its center of gravity (c.g.).
within the c.g. range. The exact location of the range is specified for each type of airplane.
MATHEMATICAL PROOF Weight and balance control consists of mathematical proof of the correct weight, balance, and loading within specified limits. These limits are set forth in the specifications for a particular aircraft. The removal or addition of equipment changes the aircraft empty weight and the c.g.
The useful load is affected accordingly. The effects these changes produce on the balance of an aircraft must be investigated to determine the effect on the flight characteristics of the aircraft.
WEIGHT AND BALANCE DATA Weight and balance data can be obtained from the following sources:
a. The aircraft specifications.
b. The aircraft operating limitations.
c. The aircraft flight manual.
d. The aircraft weight and balance report.
When weight and balance records have been lost and cannot be duplicated from any source, the aircraft must be re-weighed. A new set of weight and balance records must be computed and compiled.
TERMINOLOGY In the study of weight and balance principles, computation, and control, it is necessary to know the meaning of the terms used. The following terminology is used in the practical application of weight and balance control, and should be thoroughly studied.
The Datum The datum is an imaginary vertical plane from which all horizontal measurements are taken for balance purposes, with the aircraft in level flight attitude. It is a plane at right angles to the longitudinal axis of the aircraft. For each aircraft make and model, all locations of equipment, tanks, baggage compartments, seats, engines, propellers, etc., are listed in the Aircraft Specification or Type Certificate Data Sheets as being so many inches from the datum. There is no fixed rule for the location of the datum. In most cases it is located on the nose of the aircraft or some point on the aircraft structure itself. In a few cases, it is located a certain distance forward of the nose section of the aircraft. The manufacturer has the choice of locating the datum where it is most convenient for measurement, locating equipment, and weight-and-balance computation.
The datum location is indicated on most aircraft specifications. On some of the older aircraft, where the datum is not indicated, any convenient datum may be selected. However, once the datum is selected, it must be properly identified so that anyone who reads the figures will have no doubt about the exact datum location. Figure 3-2 shows some datum locations used by manufacturers.
The Arm The arm is the horizontal distance that an item of equipment is located from the datum. The arm's distance is always given or measured in inches, and, except for a location which might.
be exactly on the datum (0), it is preceded by the algebraic sign for plus (+) or minus (-). The plus (+) sign indicates a distance aft of the datum and the minus (-) sign indicates a distance forward of the datum. If the manufacturer chooses a datum that is at the most forward location on an aircraft (or some distance forward of the aircraft), all the arms will be plus (+) arms. Location of the datum at any other point on the aircraft will result in some arms being plus (+), or aft of the datum, and some arms minus (-), or forward of The arm of each item is usually included in parentheses immediately after the item's name or weight in the specifications for the aircraft,
e.g., seat (+23). When such information is not given, it must be obtained by actual measurement.
Datum, arm, c.g., and the forward and aft c.g.
limits are illustrated in figure 3-3.
The Moment A moment is the product of a weight multiplied by its arm. The moment of an item about the datum is obtained by multiplying the weight of the item by its horizontal distance from the datum. Likewise, the moment of an item about the c.g. can be computed by multiplying its weight by the horizontal distance from the c.g.
A 20-pound weight located 30 inches from the datum would have a moment of 20 X 30 or 600 Ib.-in. Whether the value of 600 Ib.-in. is preceded by a plus (+) or minus (-) sign depends on 54
Datum
(a) Firewall location
(b) Nose location
(c) Nose location
(d) Center line of rotation location FIGURE 3-2. Various datum locations.
whether the moment is the result of a weight Any weight item removed is a minus weight.
being removed or added and its location in relation When multiplying a weight by an arm, the reto the datum. Any item of weight added to the sulting moment is plus if the signs are alike and aircraft either side of the datum is plus weight. minus if the signs are unlike.
Datum Arm Limits Arm Fwd. A Aft
c.g.
(Average Arm) FIGURE 3-3. Datum, arm, c.g., and c.g. mits.
Center of Gravity The c.g. of an aircraft is a point about which the nose-heavy and tail-heavy moments are exactly equal in magnitude. An aircraft suspended from this point would have no tendency to rotate in either a noseup or nosedown attitude. It is the point about which the weight of an airplane or any object is concentrated.
Maximum Weight The maximum weight is the maximum authorized weight of the aircraft and its contents, and is indicated in the specifications. For many aircraft there are variations to the maximum allowable weight, depending on the purpose and conditions under which the aircraft is to be flown.
For example. a certain aircraft may be allowed a maximum gross weight of 2,750 pounds when flown in the normal category, but when flown in the utility category, the same aircraft's maximum allowable gross weight would be 2,175 pounds.
Empty Weight The empty weight of an aircraft includes all operating equipment that has a fixed location and is actually installed in the aircraft. It includes the weight of the airframe, powerplant, required equipment, optional or special equipment, fixed ballast, hydraulic fluid, and residual fuel and oil.
Residual fuel and oil are the fluids that will not normally drain out because they are trapped in the fuel lines, oil lines, and tanks. They must be included in the aircraft's empty weight. Information regarding residual fluids in aircraft systems which must be included in the empty weight will be indicated in the Aircraft Specification.
Useful Load The useful load of an aircraft is determined by subtracting the empty weight from the maximum allowable gross weight. For aircraft certificated in both the normal and utility categories, there may be two useful loads listed in the aircraft weight and balance records. An aircraft with an empty weight of 900 pounds will have a useful load of 850 pounds, if the normal category maximum weight is listed as 1,750 pounds. When the aircraft is operated in the utility category, the maximum gross weight may be reduced to 1,500 pounds, with a corresponding decrease in the useful load to 600 pounds. Some aircraft have the same useful load regardless of the category in which they are certificated.
The useful load consists of maximum oil, fuel, passengers, baggage, pilot, copilot, and crewmembers. A reduction in the weight of an item, where possible, may be necessary to remain within the maximum weight allowed for the category in which an aircraft is operating. Determining the distribution of these weights is called a weight check.
Empty Weight Center of Gravity The empty weight c.g., abbreviated EWCG, is the c.g. of an aircraft in its empty weight condition. It is an essential part of the weight and 56
balance record of the aircraft. It has no usefulness in itself, but serves as a basis for other computations and not as an indication of what the loaded c.g. will be. The EWCG is computed at the time of weighing, using formulas established for tailwheel- and nosewheel-type aircraft.
Empty Weight Center of Gravity Range The EWCG range is an allowable variation of travel within the c.g. limits. When the EWCG of the aircraft falls within this range, it is impossible to exceed the EWCG limits using standard specification loading arrangements. Not all aircraft have this range indicated on the Aircraft Specifications or Type Certificate Data Sheets.
Where it is indicated, the range is valid only as long as the aircraft is loaded according to the standard specification. The installation of items not listed in the specification will not permit use of this range.
Operating Center of Gravity Range The operating c.g. range is the distance between the forward and rearward c.g. limits indicated in the pertinent Aircraft Specification or Type Certificate Data Sheets. These limits, deternined at the time of design and manufacture, are the extreme loaded c.g. positions allowable within the applicable regulations controlling the design of the aircraft. These limits are shown in either percent of MAC (mean aerodynamic chord) or inches from the datum of the aircraft.
The loaded aircraft c.g. location must remain within these limits at all times. Accordingly, detailed instructions for determining load distribution are provided on placards, loading charts, and load adjusters.
Mean Aerodynamic Chord The MAC is the mean average chord of the wing. An airfoil section is a cross section of a wing from leading edge to trailing edge. A chord is usually defined as an imaginary straight line drawn parallel to the airfoil through the leading and trailing edges of the section. The MAC of a constant chord wing would be the same as the actual chord of the wing. Any departure from a rectangular wing plan form will affect the length of the MAC and the resulting distance from the MAC leading edge to the aircraft wing leading edge. Figure 3-4 shows the MAC for a sweptwing The aircraft c.g. is usually placed at the maximum forward position of the center of pressure on the MAC to obtain the desired stability. Because of the relationship between the c.g. location and the moments produced by aerodynamic forces, the greatest of which is lift, the c.g. location is generally expressed with respect to the wing. This is done by specifying c.g. in percent of the wing's The location of the MAC, in relation to the datum, is given in the Aircraft Specifications or Type Certificate Data Sheets, the weight and balance report, or the aircraft flight manual.
Compute the c.g. location in percent of MAC
(1) Find the difference between the distance to the empty weight c.g. location from the datum and the distance to the leading edge of MAC from the datum.
(2) Divide the difference by the length of the MAC.
(3) Multiply the answer by 100.
(4). The final answer is then expressed in percent.
An example problem that utilizes the equation for computing percent of MAC is shown in figure
3-5.
Aircraft Leveling Means Reference points are provided for leveling the aircraft on the ground. They are designated by the manufacturer and are indicated in the pertinent Aircraft Specifications. The most common leveling procedure is to place a spirit level at designated points on the aircraft structure. Some aircraft have special leveling scales built into the airframe structure. The scale is used with a plumb bob to level the aircraft longitudinally Weighing Points In weighing an aircraft, the point on the scale at which the weight is concentrated is called the weighing point. When weighing light- to mediumweight land planes, the wheels are usually placed on the scales. This means that the weighing point is, in effect, the same location obtained by extending a vertical line through the center line of the axle and onto the scale.
Other structural locations capable of supporting the aircraft, such as jack pads on the main spar, 57
MAC
241.9"
848.2" 786.2" = Datum• FIGURE 3-4. The c.g. shown in relation to MAC.
may also be used if the aircraft weight is resting on the jack pads. The weighing points should be clearly indicated in the weight and balance report.
Zero Fuel Weight The zero fuel weight is the maximum allowable weight of a loaded aircraft without fuel. Included in the zero fuel weight is the weight of cargo, passengers, and crew. All weights in excess of the zero fuel weight must consist of usable fuel.
Minimum Fuel The term "minimum fuel" should not be interpreted to mean the minimum amount of fuel required to fly an aircraft. Minimum fuel, as it applies to weight and balance, is the amount of fuel that must be shown on the weight and balance report when the airplane is loaded for an extremecondition check.
The minimum fuel load for a small aircraft with a reciprocating engine for balance purposes is based on engine horsepower. It is calculated in the METO (maximum except take-off) horsepower and 58
Datum X MAC H = Distance from the datum to the EWCG - 170 inches.
X = Distance from the datum to the MAC leading edge = 150 inches.
C = Length of MAC = 80 inches.
H - X
c.g. in % of MAC= × 100 170 - 150 % of MAC = × 100 = 80 20 × 100 = 25% 80 FIGURE 3-5. Finding percent of MAC.
is the figure used when the fuel load must be reduced to obtain the most critical loading on the
c.g. limit being investigated. Either of 2 formulas may be used.
Formula 1:
Minimum fuel =12 gallons per horsepower.
hpX1½X6 lb.
1200X1½X6=1200X1½X6=600 lb. fuel.
Formula 2:
Minimum fuel =½ lb. per engine horsepower.
hp×½=minimum fuel.
1200 × ½=600 1b. fuel.
This will be the minimum pounds of fuel required for the forward or rearward weight check.
For turbine-engine powered aircraft, the minimum fuel load is specified by the aircraft manufacturer.
The fuel tank location in relation to the c.g. limit affected by the computation determines the use of minimum fuel. For example, when a forward weight check is performed, if the fuel tanks are located forward of the forward c.g. limit, they are assumed to be full. If they are located aft of the forward c.g. limit, they are assumed to be empty.
If the minimum fuel required for a particular aircraft exceeds the capacity of the tanks located forward of the forward c.g. limit, the excess fuel must be loaded in the tanks that are aft of the forward c.g. limit. When a rearward weight check is conducted, the fuel loading conditions are opposite to those used for the forward check.
Full Oil Full oil is the quantity of oil shown as oil capacity in the Aircraft Specifications. When weighing an aircraft, the oil tank may either contain the number of gallons of oil specified or be drained. When an aircraft with full oil tanks is weighed, the weight of the oil must be subtracted from the recorded readings to arrive at the actual empty weight. The weight and balance report must show whether weights include full oil or if the oil tanks were drained.
Tare Weight Tare includes the weight of all extra items, such as jacks, blocks, and chocks on the weighing scale platform, except that of the item being weighed.
The weight of these items, when included in the scale reading, is deducted to obtain the actual weight of the aircraft.
AIRCRAFT WEIGHING PROCEDURE Before beginning a study of aircraft weighing procedure or attempting the actual weighing of an aircraft, it is necessary to become familiar with the weight and balance information in the applicable Aircraft Specification or Type Certificate Data Sheet.
The specification for Taylorcraft, model BC and BCS airplanes, illustrated in figure 3-6 has been reproduced in its entirety. A few of the items need explaining; the rest are sell-explanatory.
The designation 2 PCLM is read "2-place, closed land monoplane" and indicates that the airplane seats two persons, has an enclosed cockpit, can be operated from the solid part of the earth's surface, and has only one wing. Two PCSM indicates that the airplane is a "2-place, closed sea monoplane." It should be noted that the c.g. range, EWCG range, and the maximum weight are different for the landplane and the seaplane. The location of the seats indicates a side-by-side arrangement. The datum and the leveling means are shown in the portion of the specification that is pertinent to all models. Since the datum and the leveling means are directly connected to weight and balance, they would be among the first items referred to in planning the weighing operation.
Although the location or arrangement of the 59