ppl_06_e2
.pdf
ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CH AP T ER 1 : MASS AND BALANC
GENERAL OBSERVATIONS ON MASS & BALANCE LIMITATIONS.
It must be understood that although an aircraft may be fitted with four seats and have an additional baggage area, it is not generally possible to fill all the seats, the baggage area and the fuel tanks without exceeding maximum mass limitations and CG limits.
Figure 1.8 Tandem seat aircraft may specify from which seat the aircraft must be flown solo.
Likewise, if flying an aircraft solo, although it is unlikely that the maximum mass limitations will be exceeded, the CG may well be out of limits if the pilot neglects to carry out Mass and Balance calculations. Solo flight may even necessitate ballast being carried if the crew-weight (mass) does not reach a minimum value. Some aircraft which have tandem seating may stipulate, in their Pilot’s Operating Handbook, from which seat the aircraft must be flown solo.
Always remember that an aircraft is designed to fly within certain mass and CG position limits. Consequently, an aircraft may be unsafe to fly for two principal reasons:
•The aircraft’s mass(weight) is out of limits.
•The aircraft’s CG position is out of limits.
It is the legal responsibility of the Pilot-in-Command, when preparing his aircraft for flight, to ensure that both mass and CG position are within limits.
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CH AP T ER 1 : MASS AND BALANCE Q U EST IO NS
R e p r e s e n t a t i v e P P L - t y p e q u e s t i o n s t k n o w l e d g e o f Ma s s a n d Ba l a n c e .
1.If an aircraft’s C of G is at or beyond its aft limit:
a.The aircraft will be more stable longitudinally
b.The aircraft will be difficult to rotate on take-off
c.The aircraft’s stall speed will decrease
d.The aircraft’s range will be reduced
2.An aircraft loaded in a dangerous manner, so that its C of G is beyond its forward limit, will:
a.require less effort to flare when landing
b.require less effort to rotate on take off
c.have both an increased longitudinal stability and stalling speed
d.have both an increased range and endurance
3.The flight characteristics of an aircraft which has its C of G at the forward limit will be:
a.insensitivity to Pitch Control and little Longitudinal Stability
b.sensitivity to Pitch Control and little Longitudinal Stability
c.sensitivity to Pitch Control and great Longitudinal Stability
d.insensitivity to Pitch Control and great Longitudinal Stability
4.The consequences of operating an aeroplane with the C of G beyond the aft limit will be:
I.on the ground the aircraft would be tail heavy and passenger or crew movement or fuel usage could make it tip up
II.the flying controls would be too sensitive, increasing the risk of a tail strike at rotation
III.the tendency to stall would increase and it may be impossible to achieve “hands off” balanced flight
IV. |
recovery from a spin would be much more difficult |
a.All statements are correct
b.Only statement I is correct
c.Only statements I and IV are correct
d.Only statements II and III are correct
5.When calculating the MZFM (maximum zero fuel mass), the following are included:
a.pilot, passengers & baggage, unusable fuel
b.pilot, passengers, baggage & operating fuel
c.pilot, unusable fuel, but less passengers and baggage
d.pilot, passengers, operating fuel but less baggage
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ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CH AP T ER 1 : MASS AND BALANCE Q U EST I
6.Complete the following sentence. If an aircraft is loaded such that its C of G is approaching the aft limit:
a.the stall speed increases
b.the aircraft’s longitudinal stability will decrease
c.range and endurance increase
d.stick forces increase
7.Assuming the aircraft is at rest on the ground, what term best describes image ‘A’? (See Picture 1, page 282).
a.Zero Fuel Mass
b.Take Off Mass
c.Maximum All Up Mass
d.Empty Mass
8.Assuming the aircraft is at rest on the ground, what “mass expression” best describes image ‘D’? (See Picture 1, page 282).
a.Zero Fuel Mass
b.Basic Empty Mass
c.Empty Mass
d.Maximum All Up Mass
9.What name is given to the total mass of an aeroplane, including its total load that it is carrying, at any given time?
a.Zero Fuel Mass
b.Gross Mass
c.Basic Empty Mass
d.Maximum Landing Mass
10.What effect will increase in the gross mass of an aeroplane have on its stall speed and take-off and landing run?
a.Increase the stall speed, but decrease the take-off and landing run
b.No effect
c.Decrease the stall speed and increase the take-off and landing run
d.Increase the stall speed and increase the take-off and landing run
11.What effect will an increase in the landing mass have on an aircraft’s landing run at any given approach speed and flap setting:
a.A decrease in landing run
b.No effect
c.Length of landing run is independent of mass
d.Increase in landing run
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Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CH AP T ER 1 : MASS AND BALANCE Q U EST IO NS
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CHAPTER 2
CENTRE OF GRAVITY CALCULATIONS
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CH AP T ER 2 : CENT R E O F G R AV IT Y CALCU LAT IO NS
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ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CH AP T ER 2 : CENT R E O F G R AV IT Y CAL
INTRODUCTION.
Figure 2.1 Weight is the force acting on the aircraft’s mass. Weight acts vertically downwards through the aircraft’s centre of gravity.
The centre of gravity (CG), is the point within a body of a given mass through which the force of gravity, acting on that mass, is considered to act. The magnitude of the force of gravity acting on the body’s mass is called the body’s weight. Weight always acts vertically downwards (See Figure 2.1) towards the centre of the Earth. If an aircraft were to be suspended by a single force, say a rope, attached to the aircraft’s CG, we could place the aircraft with its longitudinal axis horizontal, and the aircraft would remain horizontal in perfect balance, as depicted in Figure 2.2.
Figure 2.2 If an aircraft could be suspended by its CG, it would remain in any attitude in which it were placed.
In fact, if the aircraft were suspended exactly through its CG, we could put the aircraft in any attitude we wished, and it would remain in that attitude, because there could be no out-of-balance force or moment to make it move.
The
magnitude of the force of
gravity acting
on a body’s mass is called “weight”. Weight acts through a body’s centre of gravity.
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CH AP T ER 2
When manoeuvring, in flight, an aircraft rotates about its CG.
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: CENT R E O F G R AV IT Y CALCU LAT IO NS
In flight, an aircraft, when manoeuvred, rotates about its CG, but the aircraft’s weight always acts vertically downwards towards the centre of the Earth. The magnitude of the weight force of the basic aircraft and of every constituent of the aircraft’s load is of considerable importance because of the effect both on aircraft structural integrity and the position of the CG.
All aircraft have published masses, such as Basic Empty Mass, Maximum Gross Mass, Maximum Zero Fuel Mass, Maximum Take-off Mass, Useful Load (Payload and Fuel), Maximum Landing Mass, etc. Furthermore, because, during the flight, the aircraft consumes fuel, the mass (and, therefore, weight) of the aircraft constantly changes. As fuel tanks empty, the distribution of the mass throughout the aircraft will change, and, thus, the position of the aircraft’s CG will change, too.
The position of the Centre of Gravity
of an aeroplane is of crucial importance to its stability, controllability and safety.
As you have learnt, the position of the centre of gravity CG, measured horizontally along the aircraft’s longitudinal axis, is of crucial importance to the aircraft’s longitudinal stability, controllability, performance, and, ultimately, safety.
Consequently, there are forward and aft limits (see Figure 2.3) to the CG, calculated by the aircraft’s designer, within which the CG must remain throughout a flight.
Figure 2.3 The CG limits are measured with respect to a datum line.
Fore and aft Centre of
Gravity limits are measured
with respect to a defined datum.
The CG limits are measured with respect to a datum line. Figure 2.3 depicts representative forward and aft CG limits for a PA28. The datum line is an imaginary line which may be located either inside or outside the actual body of the aircraft. In the example above, the datum line is shown coincident with the tip of the propeller spinner.
In addition to the aircraft’s basic mass, the mass (weight) of fuel, passengers, baggage, and other loads, must be taken into account when calculating an aircraft’s permissible mass and CG position.
Therefore, alongside such information as Maximum Gross Mass, and Maximum Take-Off Mass, the Pilot’s Operating Handbook (POH) will contain separate details of crew and passenger mass, and of the mass which may be loaded in the aircraft’s baggage compartment. The pilot must not neglect to include crew and fuel loads in
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ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CH AP T ER 2 : CENT R E O F G R AV IT Y CAL
his Mass and Balance calculations because carrying too great a load could move the CG out of limits, even if the Maximum Take-Off Mass is not exceeded.
The POH will also specify such details as minimum crew mass for solo flight.
It is one of the pilot’s major responsibilities, when preparing his aircraft for flight, to confirm that mass limitations are respected and that the centre of gravity is situated within the limits stipulated in the Pilot’s Operating Handbook.
CALCULATING THE POSITION OF AN AIRCRAFT’S CENTRE OF
GRAVITY.
Now that you have learnt how crucial the position of an aircraft’s centre of gravity (CG) is to the safety of the aircraft, let us learn how a pilot calculates the position of the CG so that he may check whether the CG lies within the prescribed forward and aft limits.
We already know that the aircraft manufacturer defines the CG limits in terms of their distance from a defined datum line. The datum line may be positioned anywhere that the aircraft designer chooses. (datum is a Latin word which means “that which is given or defined”). For the aircraft that we are going to examine, we will assume that the datum line is a vertical line which is coincident with the point of the aircraft’s propeller spinner, as depicted in Figure 2.4
Figure 2.4 The Datum Line with respect to which the CG limits are defined.
The CG limits, then, are set by the aircraft designer. The responsibility of the Pilot-in-
Command is to ensure that the CG always remains within these limits.
CG f o r t h e Ai r c r a f t ’ s Ba s i c Em p t y Ma s s .
Let us see how the position of the aircraft’s CG is calculated for the aircraft’s Basic
Empty Mass.
Consider the diagram at Figure 2.5. The diagram illustrates the aircraft being weighed with its main and nose-wheel undercarriage legs placed upon weighing devices positioned at the indicated distances behind the datum line.
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CH AP T ER 2 : CENT R E O F G R AV IT Y CALCU LAT IO NS
It is here that we see the difference between weight and mass. When we weigh an aircraft, we are measuring the force which is pulling the aircraft to the centre of the Earth. So it is the aircraft’s weight that is being recorded. However, in a constant gravitational field, weight is proportional to mass, so we can record mass if we so choose. (This is what JAA/EASA urges us to do. In many aircraft POHs, however, weight is still referred to.)
The masses recorded at each undercarriage leg are recorded in a table, such as the one shown in Figure 2.5, along with the distances behind the datum of the line of action of the weight acting on each mass.
Notice that the table at Figure 2.5 also has a column marked Moment. The Moment column, you will see, has the units “pound-inches” (lb-ins). In this column we enter the figure for the mass recorded at each undercarriage leg multiplied by the distance from the datum of the line of action of the force acting on each undercarriage leg. Many American-made aircraft still use Imperial Units so manufacturers record the mass in pounds (lb) and the distance from the datum, at which the mass is effective, in inches (ins). The moment of each mass reading, then, is given in lb-ins.
As you will learn presently:
Moment (lb-ins) = Mass (lb) X distance from datum (ins).
ITEM |
MASS |
ARM |
MOMENT |
|
(lb) |
(ins) |
(lb-ins) |
Nosewheel |
|
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|
Left Main Wheel |
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Right Main Wheel |
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TOTAL |
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|
Figure 2.5 Calculating the Position of the Centre of Gravity.
The distance of each mass reading, behind the datum, is commonly called the “moment arm”. That is why the column in Figure 2.5, in which the distances are recorded, is labelled “ARM”.
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