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basic-T

Primary Flight Display - en:Primary flight display - teil des EFIS

Weight and balance - en:Center of gravity of an aircraft

Mean Aerodynamic Chord – mittlere aerodynamische Flügeltiefe (Tragfläche)

Luftfahrtenglisch (Aviation English) - Die Einigung auf eine weltweit einheitliche Sprache in der Luftfahrt macht Sinn, da der Luftverkehr international stattfindet. Durch die Niederlage im II. Weltkrieg verlor Deutschland völlig an Bedeutung in der Luftfahrt. Die deutsche Luftfahrtentwicklung wurde nach dem 2. WK von der amerikanischen Luftfahrtindustrie überholt.

Flugzeugabmessungen - geometrische Kennwerte von Luftfahrzeugen (Starrflügler - schwerer als Luft)

• Spannweite (wing span), Formelzeichen b,
• Flugzeuglänge (length), Formelzeichen l,
• Höhe (height), Formelzeichen h,

Tragflächen

• Flügelfläche (wing area oder wing surface), Formelzeichen deutsch: A, englisch: S (für surface),
• Profiltiefe oder Profilsehne (cord or cord line) des Fragflügelprofils (airfoil), Formelzeichen deutsch: λ, englisch c,
• Schlankheitsgrad einer Tragfläche (aspect ratio, AR), (falsche Links umbiegen - Begriffsklärung: Schlankheitsgrad, aspect ratio
• Verjüngung eines Tragflügels (Taper Ratio, λ), (korrigieren: Verjüngung ist nur eine Begriffsklärung)
• Pfeilung des Tragflügels (sweep back or sweep angle, Λ or Φ)
• positive oder negative V-Stellung des Tragflügels (dihedral -pos.V oder anhedral für neg. V),

Gewichte (weight), von Verkehrsflugzeugen, Formelzeichen deutsch: G, englisch: W,

• Leergewicht oder Basisgewicht (basic weight, BW)
• Betriebsleergewicht (dry operating weight - DOW)
• Gewicht ohne Kraftstoff (fuel) (zero fuel weight - ZFW)
• maximale Startgewicht (maximum take off weight - MTOW)
• aktuelles Startgewicht (take-off weight - TOW)
• begrenztes Startgewicht (limited take-off weight - TOW limit)
• Rollgewicht (taxi weight)

Tragflügelgeometrie - Kenngrößen eines Tragflügels

• Vorderkantenpfeilung,
• Pfeilung bei 25 % der Profiltiefe,
• Hinterkantenpfeilung,
• Theoretische Wurzeltiefe,
• Wurzeltiefe,
• Endtiefe,
• Spannweite (A-Rumpf B-Tragfläche C-Linie 25 % Profiltiefe)

Profiltiefe Die Profieltiefe (oder Flügeltiefe) ist eine geometrische Kenngröße an der Tragfläche und Profilen von Flugzeugen, Propellern, Rotorblättern von Hubschraubern und ähnlichen.

Dieses Längenmaß wird von der Vorderkante des Profils/Flügels (eng. leading edge, LE) bis zur Hinterkante des Profils/Flügels (trailing edge, TE) gemessen. Nur an rechteckigen Tragflächen ist die Profiltiefe konstant. ansonsten ändert sie sich über die Länge der Tragfläche hin. Man unterscheidet die Flügeltiefe der Tragflächenwurzel (root cord, c_r), also dem Übergang zum Flugzeugrumpfumpf, und die Flügeltiefe an der Flügelspitze (tip cord, c_t). Weiterhin gibt es die durchschnittliche Flügeltiefe (avarage cord, c_av), die im englischen Sprachraum auch als "standard mean cord" (SMC) bezeichnet wird. Nicht zu verwexhseln ist die Profiltiefe mit der Mittlere Aerodynamische Flügeltiefe (engl. mean aerodynamic cord, MAC).

Die Mittleren Aerodynamischen Flügeltiefe (engl. mean aerodynamic cord, MAC) ist eine geometrische Kenngröße an Tragflächen und Profilen bei Flugzeugen, Propellern, Rotorblättern von Hubschraubern und ähnlichen.

Die MAC ist die Flügeltiefe im Zentrum der Fläche eines Halbflügels.

Würde man eine Tragfläche durch ein Rechteck mit gleicher Fläche ersetzten, wobei die Spannweite (Breite des Rechtecks) gleich bleibt, dann ist die mittlere Flügeltiefe die Höhe dieses Rechtecks (FEHLER). Die Neigungsmomente für die reale Tragfläche und das idealisierte Rechteck wären gleich. Wegen der gleichen Momente trotz vereinfachter Form ist Mittleren Aerodynamischen Flügeltiefe für aerodynamsiche Berechnungen interessant. Die Schwerpunktlage (Weight and Balance) eines Flugzeugs kann in Prozent der MAC angegeben werden. Liegt der Schwerpunkt beispielsweise bei 33% MAC, und die MAC ist 150 cm lang, dann liegt er bei 50 cm von der Vorderkante der MAC aus gemessen. Wobei die MAC eine definierte Position auf der Längsachse des Flugzeuges hat.

basic-T - en:Flight instruments - Fluginstrument

Nurflügler, Pendelruder, Trimmbereich, Einmot - Gas weg reduziert Luftstrom, nickt sofot nach unten

Weight and Balance

Landung

Bild 9

Bild 10

Bild 11

Zu Landung fliegt das Flugzeug wesentlich langsamer, als während des Reisefluges. Ein modernes Verkehrsflugzeug wird vor der Landung beispielsweise von ca. 900 km/h auf ca. 180 km/h abgebremst. Dadurch verringert sich der Auftrieb an den Tragflächen erheblich.

Zur Landung werden die Landeklappen stufenweise ausgefahren, um den Auftriebsverlust infolge Geschwindigkeitsreduzierung teilweise auszugleichen (Bild 9 bis 11). Durch das Ausfahren der Landeklappen vergrößert sich die Profiltiefe und außerdem nimmt die Wölbung des Tragflächenprofils zu. Genau diese Erhöhung der Wölbung führt zu dem gewünschten Effekt, dass der Auftrieb des Flügels erhöht wird.

Bild 12

Der Auftriebspunkt des Flügels wandert bei ausgefahrenen Klappen etwas nach hinten. Wegen der ausgefahrenen Landeklappen und der daraus folgenden erhöhten Profilwölbung, erhöht sich auch der Anstellwinkel α der Tragfläche (Bild 9 bis 11 und Bild 12).

Bild 13

Bild 14

Das Flugzeug hat folglich die Tendenz den Bug zu heben ??? (Bild 13). Als Gegensteuerung muß der Pilot die Abwärtskraft am Höhenruder veringern - also die Flugzeugnase wieder nach unten drücken (Bild 14).

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Leergeicht (empty weight) Zuladung (payload = Piloten, Passagiere, Treibstoff, Gepäck) = Gesamtgewicht (gross weight)

MTOW

MAC zu ermitteln

WEIGHT AND BALANCE—The aircraft is said to be in weight and balance when the gross weight of the aircraft is under the max gross weight, and the center of gravity is within limits and will remain in limits for the duration of the flight.

FAA Weight and Balance Handbook (engl.)

1

An overloaded airplane has, to varying degrees, each of the following characteristics:

1. Increased Takeoff Speed—because more lift is necessary to counter the additional weight, higher speed is necessary to create sufficient lift to attain flight.
2. Longer Takeoff Roll—the increase in necessary speed for takeoff and slower acceleration due to increased weight translates to more runway required to accelerate the airplane to takeoff speed. It is possible to overload an airplane to a point where no amount of runway is sufficient to reach takeoff speed. Were it not for forces such as aerodynamic drag and friction of the landing gear against the runway, this would not be true, but these forces are present and limit the performance of the airplane.
3. Reduced Climb Angle—increases in weight must be countered by additional lift. Lift that is otherwise available for climb performance now must support the additional weight. The airplane's capability to out climb obstructions near the airport may be compromised.
4. Reduced Rate of Climb—for the same reason that the angle at which the airplane can climb is reduced, the rate at which it can climb is also reduced. This means more problems if an engine fails during or shortly after takeoff.
5. Lower Ceilings—because air density normally decreases as you go up in the atmosphere, there is an altitude at which an airplane climbs no more. This is known as the absolute ceiling of the airplane, and it occurs where the maximum indicated airspeed in level flight is just above stall speed. As the weight of the airplane is increased, the stall speed increases. Accordingly, an increase in weight results in a reduction in absolute ceiling and, in severe situations where there is high terrain, it may be impossible for the airplane to climb above the terrain.
6. Lower Cruising Speeds—production of additional lift to counteract greater weight results in an increase in drag. This increased drag reduces the speed at which the airplane travels, thereby exacerbating the problem of the increased stall speed.
7. Shorter Range—because cruising speeds are reduced by overloading the airplane, the range of the airplane is also reduced. On a trip that calls for most of the airplane's normal range, the destination may prove to be unreachable.
8. Less Maneuverability—the heavier the airplane is, the less maneuverable it becomes. This is so because the force necessary to change the speed or direction of an object in motion increases with the mass of the object.
9. Higher Landing Speeds—because stall speed is higher when the airplane is overloaded, higher approach and landing speeds are necessary.
10. Greater Landing Distance—increases in touchdown speed increase roll out distance exponentially. Therefore, an increase in weight that requires touchdown at a speed that is only five percent greater than normal may have a significant impact on the required runway length.
11. Aircraft Structure Overload—although the primary concern of an overloaded airplane is its effect on aerodynamic performance, a secondary concern is its effect on structural components, such as landing gears.

2

The onboard weight and balance system is designed to provide measurements of the B777 Freighter's weight and center of gravity. Operators benefit from having accurate and reliable weight and balance measurements provided in real time. In addition, the system can quickly validate manual weight calculations.

Momentengleichgewicht: Gesamtmoment = Summe aller Einzelmomente

MALTOW = MIN [ MTOW; MLW TF; MZFW TOF]

The distribution of weight is also of vital importance since the position of the centre of gravity affects the stability of the airplane. In loading an airplane, the C.G. must be within the permissible range and remain so during the flight to ensure the stability and manoeuvrability of the airplane during flight.

Airplane manufacturers publish weight and balance limits for their airplanes. This information can be found in two sources:

1. The Aircraft Weight and Balance Report.

2. The Airplane Flight Manual.

The information in the Airplane Flight Manual is general for the particular model of airplane.

The information in the Aircraft Weight and Balance Report is particular to a specific airplane. The airplane with all equipment installed is weighed and the C.G. limits calculated and this information is tabulated on the report that accompanies the airplane logbooks. If alterations or modifications are made or additional equipment added to the airplane, the weight and balance must be recalculated and a new report prepared.

Standard Weight Empty: The weight of the airframe and engine with all standard equipment installed. It also includes the unusable fuel and oil.

3

Optional or Extra Equipment: Any and ail additional instruments, radio equipment, etc., installed but not included as standard equipment, the weight of which is added to the standard weight empty to get the basic empty weight. It also includes fixed ballast, full engine coolant, hydraulic and de-icing fluid.

Basic Weight Empty: The weight of the airplane with all optional equipment included. In most modern airplanes, the manufacturer includes full oil in the basic empty weight.

Useful load (or Disposable load): The difference between gross take-off weight and basic weight empty. It is, in other words, all the load which is removable, which is not permanently part of the airplane. It includes the usable fuel, the pilot, crew, passengers, baggage, freight, etc.

Payload: The load available as passengers, baggage, freight, etc., after the weight of pilot, crew, usable fuel have been deducted from the useful load.

Operational Weight Empty: The basic empty weight of the airplane plus the weight of the pilot. It excludes payload and usable fuel.

Usable Fuel: Fuel available for flight planning.

Unusable Fuel: Fuel remaining in the tanks after a runout test has been completed in accordance with government regulations.

Operational Gross Weight: The weight of the airplane loaded for take-off. It includes the basic weight empty plus the useful load.

Maximum Gross Weight: The maximum permissible weight of the airplane.

Maximum Take-Off Weight: The maximum weight approved for the start of the take-off run.

Maximum Ramp Weight: The maximum weight approved for ground manoeuvring. It includes the weight of fuel used for start, taxi and run up.

Zero Fuel Weight: The weight of the airplane exclusive of usable fuel.

Passenger Weights: Actual passenger weights must be used in computing the weight of an airplane with limited seating capacity. Allowance must be made for heavy winter clothing when such is worn. Winter clothing may add as much as 14 lbs to a person's basic weight; summer clothing would add about 8 lbs. On larger airplanes with quite a number of passenger seats and for which actual passenger weights would not be available, the following average passenger weights may be used. The specified weights for males and females include an allowance for 8 lbs of carry-on baggage.

4

	 Summer  	

Winter Males (12yrs&up) 182 lbs 188 lbs Females (12yrs&up) 135 lbs 141 lbs Children (2-11 yrs) 75 lbs 75 lbs Infants (0-up to 2 yrs) 30 lbs

30 lbs

Maximum Landing Weight: The maximum weight approved for landing touchdown. Most multi-engine airplanes which operate over long stage lengths consume considerable weights of fuel. As a result, their weight is appreciably less on landing than at takeoff. Designers take advantage of this condition to stress the airplane for the lighter landing loads, thus saving structural weight. If the flight has been of short duration, fuel or payload may have to be jettisoned reduce the gross weight maximum or maximum landing weight.

Maximum Weight - Zero Fuel: Some transport planes carry fuel in their wings, the weight of which relieves; the bending moments imposed on the wings by the lift. The maximum weight - zero fuel limits the load which may be carried in the fuselage. Any increase in weight in the form of load carried fuselage must be counterbalanced by adding weight in the form of fuel in the wings.

Float Buoyancy: The maximum permissible gross weight of a seaplane is governed by the buoyancy of the floats. The buoyancy of a seaplane float is equal to the weight of water displaced by the immersed part of the float. This is equal to the weight the float will support without sinking beyond a predetermined level (draught line).

The buoyancy of a seaplane float is designated by its model number. A 4580 float has a buoyancy of 4580 lb. A seaplane fitted with a pair of 4580 floats has a buoyancy of 9160 lbs.

Regulations require an 80% reserve float buoyancy. The floats must, therefore, have a buoyancy equal to 180% of the weight of the airplane.

To find the maximum gross weight of a seaplane fitted with, say 7170 model floats, multiply the float buoyancy by 2 and divide by 1.8 (7170 x 2)/1.8 = 7966 lb.

5

C. computing the load

A typical light airplane has a basic weight of 1008 lb. and an authorized maximum gross weight of 1600 lb. An acceptable loading of this airplane would be as follows:

Basic Empty Weight . . . . . . . . . . . . . .1008 lb.

Consisting of Weight Empty . . . . . . . . . . 973 lb.

Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 lb.

Extra Equipment . . . . . . . . . . . . . . . . . . . .20 lb

Useful Load . . . . . . . . . . . . . . .. . . . . . . . 592 lb.

Consisting of Pilot . . . . . . . . . . . . . . . . . . .150 lb.

Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 lb.

Payload: Passenger . . . . . . . . . . . . . . . . . .175 lb.

Baggage . . . .. . . . . . . . . . . . . . . . . . . . . . . 121 lb.

D. balance limits

The position of the centre of gravity along its longitudinal axis affects the stability of the airplane. There are forward and aft limits established by the aircraft design engineers beyond which the C.G. should not be located for flight. These limits are set to assure that sufficient elevator deflection is available for all phases of flight. If the C.G. is too far forward, the airplane will be nose heavy, if too far aft, tail heavy. An airplane whose centre of gravity is too far aft may be dangerously unstable and will possess abnormal stall and spin characteristics. Recovery may be difficult if not impossible because the pilot is running out of elevator control. It is, therefore, the pilot's responsibility when loading an airplane to see that the C.G. lies within the recommended limits.

If the C.G. is too far forward, the airplane will be nose heavy, if too far aft, tail heavy. An airplane whose centre of gravity is too far aft may be dangerously unstable and will possess abnormal stall and spin characteristics. Recovery may be difficult if not impossible because the pilot is running out of elevator control. It is, therefore, the pilot’s responsibility when loading an airplane to see that the C.G. lies within the recommended limits.

Usually the Airplane Owner's Manual lists a separate weight limitation for the baggage compartment in addition to the gross weight limitation of the whole airplane. This is a factor to which the pilot must pay close attention, for overloading the baggage compartment (even if the plane itself is not overloaded) may move the C.G. too far aft and affect longitudinal control.

The Airplane Owner's Manual may also specify such things as the seat to be occupied in solo flight (in a tandem seating arrangement) or which fuel tank is to be emptied first. Such instructions should be carefully complied with.

As the flight of the airplane progresses and fuel is consumed, the weight of the airplane decreases. Its distribution of weight also changes and hence the C.G. changes. The pilot must take into account this situation and calculate the weight and balance not only for the beginning of the flight but also for the end of it.

6

E. definitions

The centre of gravity (C.G.) is the point through which the weights of all the various parts of an airplane pass. It is, in effect, the imaginary point from which the airplane could be suspended and remain balanced. The C.G. can move within certain limits without upsetting the balance of the airplane. The distance between the forward and aft C.G. limits is called the centre of gravity range.

The balance datum line is a suitable line selected arbitrarily by the manufacturer from which horizontal distances are measured for balance purposes. It may be the nose of the airplane, the firewall or any other convenient point .

The moment arm is the horizontal distance in inches from the balance datum line to the C.G. The distance from the balance datum line to any item, such as a passenger, cargo, fuel tank, etc. is the arm of that item.

The balance moment of the airplane is determined by multiplying the weight of the airplane by the moment arm of the airplane. It is expressed in inch pounds. The balance moment of any item is the weight of that item multiplied by its distance from the balance datum line. It is, therefore, obvious that a heavy object loaded in a rearward position will have a much greater balance moment than the same object loaded in a position nearer to the balance datum line.

The moment index is the balance moment of any item or of the total airplane divided by a constant such as 100, 1000, or 10,000. It is used to simplify computations of weight and balance especially on large airplanes where heavy items and long arms result in large unmanageable numbers.

If loads are forward of the balance datum line their moment arms are usually considered negative (-). Loads behind the balance datum line are considered positive ( )*. The total balance moment is the algebraic sum of the balance moments of the airplane and each item composing the disposable load.

• In many cases the positive ( ) sign is omitted, but the negative (-) sign is always shown. To simplify matters, both are included in our example

The C.G. is found by dividing the total balance moment (in inch-pounds) by the total weight (in lb.) and is expressed in inches forward (-) or aft ( ) of the balance datum line.

The centre of gravity range is usually expressed in inches from the balance datum line (i.e. 39.5" to 45.8"). In some airplanes, it may be expressed as a percentage of the mean aerodynamic chord (25% to 35%). The MAC is the mean aerodynamic chord of the wing.

To calculate the position of the C.G. in percent of MAC. Let us assume that the weight and balance calculations have found the C.G. to be 66 inches aft of the balance datum line and the leading edge of the MAC to be 55 inches aft of the same reference (Fig. 3). The C.G. will, therefore, lie 11 inches aft of the leading edge of the MAC. If the MAC is 40 inches in length, the position of the C.G. will be at a position (11 ~ 40) 27% of the MAC. If the calculated C.G. position is within the recommended range (for example, 25% to 35%), the airplane is properly loaded.

There are several methods by which weight and balance calculations may be made for any loading situation.

7

C. weight and balance and flight performance

The flight characteristics of an airplane at gross weight with the C.G. very near its most aft limits are very different from those of the same airplane lightly loaded.

For lift and weight to be in equilibrium in order to maintain any desired attitude of flight, more lift must be produced to balance the heavy weight. To achieve this, the airplane must be flown at an increased angle of attack. As a result, the wing will stall sooner (i.e. at a higher airspeed) when the airplane is fully loaded than when it is light. Stalling speed in turns (that is, at increased load factors) will also be higher. In fact, everything connected with lift will be affected. Take-off runs will be longer, angle of climb and rate of climb will be reduced and, because of the increased drag generated by the higher angle of attack, fuel consumption will be higher than normal for any given airspeed. Severe g-forces are more likely to cause stress to the airframe supporting a heavy payload.

An aft C.G. makes the airplane less stable, making recovery from manoeuvres more difficult. The airplane is more easily upset gusts. However, with an aft C.G., the airplane stalls at a slightly lower airspeed. To counteract the tail heaviness of the aft C.G., the elevator must be trimmed for an up load. The horizontal stabilizer, as a result, produces extra lift and the wings, correspondingly, hold a slightly lower angle of attack.

An airplane with a forward centre of gravity, being nose heavy, is more stable but more pressure on the elevator controls will be necessary to raise the nose - a fact to remember on the landing flare. The forward C.G. means a somewhat higher stalling speed another fact to remember during take-offs and landings.

Every pilot should be aware of these general characteristics, shared by most airplanes, when they are loaded to their weight and balance limits. The important thing to remember is that these characteristics are more pronounced as the limits are approached and may become dangerous if they are exceeded. Overloading, as well as the immediate degradation of performance, subjects the airplane to unseen stresses and precipitates component fatigue.

8

design maximum safe operating weight which is the maximum gross weight permitted by the aircraft designer for structural safety reasons.

In the type approval process an aircraft is tested by national regulatory authorities to see that the design MTOW is considered safe; subsequently the third category, a certificated MTOW, is issued which will not be greater than – but may be less than – the regulatory standard MTOW; and, additionally, may be less than the design maximum safe operating weight.

Eventuell wird aus Gründen der Typzulassung des zertifizierte Gewicht reduziert (E-flugzeuge)

However as aircraft age they also suffer from service weight pickup; they tend to put on weight through modifications, additional instruments or avionics, larger fuel tanks, heavier tyres and accumulation of paint and dirt; all of which reduce payload capability and make it rather easy to unwittingly exceed MTOW.

In the general aviation field most of the privately owned recreational tourers are single engine, fixed undercarriage, four seat aircraft like the Piper Warrior or the Cessna 172. Generally these aircraft have a MTOW around 1150 kg, an empty mass which is about 55% of MTOW, a fuel capacity about 15% MTOW and consequently 30% MTOW , or 345 kg, is available for carriage of the pilot, passengers and various types of baggage.

If MTOW is exceeded AND the cg is outside its aft limit then very serious longitudinal stability problems are introduced.

Balance refers to the location of the cg along the longitudinal axis. Location of the cg across the lateral axis is important but the design of practically all aircraft is such that the empty weight is always symmetrical about the longitudinal centreline. However the location of the cg along the longitudinal axis is both variable and critical.

The lateral and longitudinal position of the cg on any flight will vary according to the weight in the pilot and passenger seats, the amount of fuel in the tank/s, the placement of any baggage and also the weight and location of modifications and additional equipment.

For safe aircraft operation there must be calculated limits to the forward (nose heavy) and the aft (tail heavy) cg movement, measured from a datum point and specified by the manufacturer or by the amateur designer. The datum point is an imaginary vertical plane through the fuselage possibly located at the engine firewall, the wing leading edge or just the most forward point of the fuselage — the tip of the spinner for example. If the cg is situated between the fore and aft limits the aircraft will have positive static longitudinal stability.

There is a point on the wing's mean aerodynamic chord [see below] called the aerodynamic centre [AC] where the pitching moment coefficient [ Cm ] about that point is very small [for the NACA 2412 aerofoil the coefficient is minus 0.1, the negative value indicating the moment forces a nose-down rotation] and the coefficient remains more or less constant with changes in the angle of attack but increases sharply at the stall. For the cambered aerofoils used in most light aircraft wings that aerodynamic centre will be located in a position between 23%—27% of the chord length aft of the leading edge but for standardisation aerodynamicists generally establish the lift, drag and pitching moment coefficients at the 25% [quarter] chord position. The pitching moment at quarter chord is termed Mc/4.

The pitching moment is consistently nose down, changing in magnitude as airspeed increases. If plotted on a graph the moment coefficient CMc/4 will generally be a horizontal line for most of the angle of attack range but the straight line may have a slight slope if the actual aerodynamic centre varies a little from the 25% chord location.

The pitching moment equation is much the same as the lift and drag equations with the addition of the mean aerodynamic chord [c] for the moment arm so you can see that as the coefficient is constant [up to the stall] then V² is the significant contributor to the nose down pitching force, which must be offset by tailplane forces to keep the aircraft in balanced flight. However high torsion loads may still exist within the wing structure,

The concept of the aerodynamic centre is useful to designer/builders because it means the centre of application of lift can be assumed fixed at quarter chord and only the lift force changes. For non-rectangular wings a mean aerodynamic chord [MAC] for the wing has to be calculated

Consequently the aerodynamic centre for the aircraft as a whole, known as the neutral point, will not be in the same location as the wing aerodynamic centre but — for a tailplane aircraft — behind it and on the fuselage centreline. This is the fixed point from which net lift, drag and aircraft pitching moment are assumed to act.

Forward cg limit — nose heavy The forward cg limit is determined by the elevator's ability to flare the aeroplane at low speed when landing in ground effect i.e. the least forward cg position where full up elevator will obtain sufficient moment [arm] to rotate to the stall angle of attack without requiring the pilot to exert an excessive pull on the control column. The forward position is constrained because the further forward it is the more download the horizontal stabiliser/elevator is required to produce to balance it, consequently the tailplane must fly at a greater negative aoa, thus decreasing total aircraft lift and the wing must then fly at a greater aoa to counter the loss so more drag from wing and tailplane and reduced performance. The pitching moment characteristics of the wing must also be considered.

If a nose wheel undercarriage aircraft is landed in a nose heavy condition the possibility of touching down nose wheel first – wheelbarrowing – is greatly exacerbated and a slowing aircraft, pivoting on the nose wheel, is in a grossly unstable condition. The possibility of an extreme ground loop, with consequent aircraft damage, is high.

Aft cg limit — tail heavy The aft limit is determined by the amount of reduction in the length of the horizontal stabiliser moment arm (which decreases the effectiveness of the moment) and the increase in the nose-up pitching moment of the cg/ac couple because of the cg distance behind the ac. It is the elevator authority available at low speed which determines the aft cg limit. A cg outside the aft limit will decrease longitudinal stability and the ability to recover from stalls and spins and may, in itself, lead to a departure stall i.e. a stall shortly after starting to climb out from the airfield with the engine at maximum power because there is insufficient elevator authority to lower the nose. A go-around with the cg near the aft limit, with flaps extended, full power and nose-up trim applied can be particularly dangerous for the unwary pilot.

An aircraft does not have to be near MTOW for the cg fore or aft limits to be breached, as can be seen in the weight/cg position limitations section below.

Cg position will change as fuel is consumed. Actually the pilot of a light aircraft can vary the cg position just by leaning forward or backward in the seat! The following is an extract from an RA-Aus incident report:

"The aircraft, with instructor and student on board, was returning to the airfield when a pitch down occurred. [The elevator control horn assembly had failed.] Control stick and trim inputs failed to correct the situation, but a reduction in power did have a correcting influence, although not enough to regain level flight. A satisfactory flight condition was achieved by the pilots pushing their bodies back as far as possible and hanging their arms rearward. A successful landing at the airfield was accomplished."

The position of the fore and aft cg limits is measured as per cent of MAC from the MAC leading edge. Usually for a one or two seat aircraft the most forward position would be aft of 15% MAC and the most aft position forward of 30% or 35% MAC. Thus the cg range in a light aircraft shouldn't exceed 20% MAC. The linear distance between the fore and aft limits is maybe 15 to 20 cm.

Helicopters Weight and balance of a helicopter is far more critical than for an airplane. A helicopter may be properly loaded for takeoff, but near the end of a long flight when the fuel tanks are almost empty, the CG may have shifted enough for the helicopter to be out of balance laterally or longitudinally. For helicopters with a single main rotor, the CG is usually close to the main rotor mast. Improper balance of a helicopter’s load can result in serious control problems. In addition to making a helicopter difficult to control, an out-of-balance loading condition also decreases maneuverability since cyclic control is less effective in the direction opposite to the CG location.

Ideally, the pilot tries to perfectly balance a helicopter so that the fuselage remains horizontal in hovering flight, with no cyclic pitch control needed except for wind correction. Since the fuselage acts as a pendulum suspended from the rotor, changing the center of gravity changes the angle at which the aircraft hangs from the rotor. When the center of gravity is directly under the rotor mast, the helicopter hangs horizontal; if the 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 weight located aft of the rotor mast becomes less.

This condition is recognizable when coming to a hover following a vertical takeoff. The helicopter will have a nose-low attitude, and the pilot will need excessive rearward displacement of the cyclic control to maintain a hover in a no-wind condition. In this condition, the pilot could rapidly run out of rearward cyclic control as the helicopter consumes fuel. The 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, the pilot may not have enough cyclic control to flare properly for the landing.

A forward CG will not be 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. 

An aft CG condition can be recognized by the pilot when coming to a hover following a vertical takeoff. The helicopter will have a tail-low attitude, and the pilot will need excessive forward displacement of cyclic control to maintain a hover in a no-wind condition. If there is a wind, the pilot needs even greater forward cyclic. If flight is continued in this condition, the pilot 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 flapping could cause the rotor disc to tilt aft. With full forward 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. Lateral balance For most helicopters, it is usually not necessary 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 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. Weight and Balance Calculations When determining whether an aircraft is properly loaded, the pilot must answer two questions:

  1. Is the gross weight less than or equal to the maximum 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? 

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 aircraft. Check that the total weight does not exceed the maximum allowable gross weight.

To answer the second question, the pilot needs to use CG or moment information from loading charts, tables, or graphs in the manual. Then calculate the loaded moment and/or loaded CG and verify that it falls within the allowable CG range, also shown in the manual.

The location of the reference datums is established by the manufacturer and is defined in the aircraft flight manual. The horizontal reference datum is an imaginary vertical plane or point, arbitrarily fixed somewhere along the longitudinal axis of the aircraft, from which all horizontal distances are measured for weight and balance purposes. There is no fixed rule for its location. For helicopters, it may be located at the rotor mast, the nose of the helicopter, or even at a point in space ahead of the helicopter. While the horizontal reference datum can be anywhere the manufacturer chooses, most small training helicopters have the horizontal reference datum 100 inches forward of the main rotor shaft centerline. This is to keep all the computed values positive. The lateral reference datum, is usually located at the center of the helicopter.[3]

Lemma Nickstabilität (Flugzeug) -

Die Nickstabilität eines Flugzeuges ist die Stabilität um die Querachse des Flugzeuges. Die Nickstabilität wird im Flug durch die aerodynamische Balance zwischen dem Gewicht des Flugzeuges und dem Auftrieb durch das Höhenruder aufrechterhalten.

Die Nickstabilität (um die Querachse) zusammen mit der Richtungsstabilität (um die Hochachse) macht die Längsstabilität eines Flugzeuges aus.

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engl. wiki

Der 'Schwerpunkt des Flugzeuges (engl. center fo gravity, CG) ist der gedachte Punkt, an dem man das Flugzeug aufhängen könnte, so dass das Flugzeug ausbalanciert ist, ohne dass es aus seiner waagerechten Position kippt. Es ist das Massezentrum des Flugzeuges, der theroretische Punkt, an dem das gesamte Gewicht des Flugzeuges konzentriert ist. Er stellt eine mathematische und physikalische Vereinfachung bei der Betrachtung der Gewichte der verschiedenen Flugzeugteile dar. So muss für mathematische und physikalische Modelle des Flugzeuges nur noch ein Punkt betrachtet werden. Its distance from the reference datum is determined by dividing the total moment by the total weight of the aircraft. The center-of-gravity is an important point on an aircraft, which significantly affects the stability of the aircraft. To ensure the aircraft is safe to fly, it is critical that the center-of-gravity fall within specified limits.

Terms

• Ballast

Removable or permanently installed weight in an aircraft used to bring the center of gravity into the allowable range.

• CG Limits

The specified longitudinal (forward and aft) or lateral (left and right) points within which the CG must be located during flight. These limits are indicated in the aircraft operator manuals.

• CG Range

The distance between the forward and aft (or left and right) CG limits indicated in the aircraft operator manuals.

• Weight and Balance

The aircraft is said to be in weight and balance when the gross weight of the aircraft is under the max gross weight, and the center of gravity is within limits and will remain in limits for the duration of the flight.

• Reference Datum

A reference plane that allows accurate, and uniform, measurements to any point on the aircraft.

• Arm

The horizontal distance from the datum to any component of the helicopter or to any object located within the helicopter is called the arm. Another term that can be used interchangeably with arm is station.

• Moment

If the weight of an object is multiplied by its arm, the result is known as its moment. You may think of moment as a force that results from an object’s weight acting at a distance. Moment is also referred to as the tendency of an object to rotate or pivot about a point. The farther an object is from a pivotal point, the greater its force.

• Center-of-gravity Computation

By totaling the weights and moments of all components and objects carried, you can determine the point where a loaded aircraft would balance. This point is known as the center-of-gravity.

Helicopters

Weight and balance of a helicopter is far more critical than for an airplane. A helicopter may be properly loaded for takeoff, but near the end of a long flight when the fuel tanks are almost empty, the CG may have shifted enough for the helicopter to be out of balance laterally or longitudinally. For helicopters with a single main rotor, the CG is usually close to the main rotor mast. Improper balance of a helicopter’s load can result in serious control problems. In addition to making a helicopter difficult to control, an out-of-balance loading condition also decreases maneuverability since cyclic control is less effective in the direction opposite to the CG location.

Ideally, the pilot tries to perfectly balance a helicopter so that the fuselage remains horizontal in hovering flight, with no cyclic pitch control needed except for wind correction. Since the fuselage acts as a pendulum suspended from the rotor, changing the center of gravity changes the angle at which the aircraft hangs from the rotor. When the center of gravity is directly under the rotor mast, the helicopter hangs horizontal; if the 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 weight located aft of the rotor mast becomes less.

This condition is recognizable when coming to a hover following a vertical takeoff. The helicopter will have a nose-low attitude, and the pilot will need excessive rearward displacement of the cyclic control to maintain a hover in a no-wind condition. In this condition, the pilot could rapidly run out of rearward cyclic control as the helicopter consumes fuel. The 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, the pilot may not have enough cyclic control to flare properly for the landing.

A forward CG will not be 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.

An aft CG condition can be recognized by the pilot when coming to a hover following a vertical takeoff. The helicopter will have a tail-low attitude, and the pilot will need excessive forward displacement of cyclic control to maintain a hover in a no-wind condition. If there is a wind, the pilot needs even greater forward cyclic. If flight is continued in this condition, the pilot 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 flapping could cause the rotor disc to tilt aft. With full forward 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.

Lateral balance

For most helicopters, it is usually not necessary 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 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.

Weight and Balance Calculations

When determining whether an aircraft is properly loaded, the pilot must answer two questions:

1. Is the gross weight less than or equal to the maximum 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?

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 aircraft. Check that the total weight does not exceed the maximum allowable gross weight.

To answer the second question, the pilot needs to use CG or moment information from loading charts, tables, or graphs in the manual. Then calculate the loaded moment and/or loaded CG and verify that it falls within the allowable CG range, also shown in the manual.

The location of the reference datums is established by the manufacturer and is defined in the aircraft flight manual. The horizontal reference datum is an imaginary vertical plane or point, arbitrarily fixed somewhere along the longitudinal axis of the aircraft, from which all horizontal distances are measured for weight and balance purposes. There is no fixed rule for its location. For helicopters, it may be located at the rotor mast, the nose of the helicopter, or even at a point in space ahead of the helicopter. While the horizontal reference datum can be anywhere the manufacturer chooses, most small training helicopters have the horizontal reference datum 100 inches forward of the main rotor shaft centerline. This is to keep all the computed values positive. The lateral reference datum, is usually located at the center of the helicopter.

External links

• Generic Weight and Balance Calculation Spreadsheet