This document sums up all the important information concerning Principles of Flight. Principles of Flight (PoF), is one of the fourteen subjects that a student pilot needs to pass in order to continue the ATPL-training program. It is written by myself and can therefore contain faults. I tried to co...
ATPL THEORY
Principles of Flight - Complete Summary
,Table of Contents
General rules 4
Units 4
Newton 4
Kinetic energy 4
Gas laws 4
Definitions 5
Aircraft components 6
The equation of continuity 6
Dynamic pressure 7
Lift 7
Angle of attack 7
Ground effect 8
Coefficient of lift (CL) 8
Cambered airfoils 8
Centre of pressure position 9
Aerodynamic centre (AC) 9
Negative pitching (0 lift) 9
Negative camber airfoils 9
Load factor 9
Calculating a new CL-value with changing speed 10
Attitude, Angle of Attack and Angle of Incidence 10
Parasite and induced drag 10
Airflow separation 11
High speed flight 11
Shock waves 11
Subsonic vs. supersonic airflow 12
Lift in supersonic flight 14
Situation at MFS = 0.89 14
Situation at MFS = 0.98 15
Situation above MDET 15
Drag 15
Stability 15
Climbing and descending 17
Forces in climb 17
Lift in the climb 17
Factors affecting flight path angle 18
High altitude climb 18
Straight, steady descent 19
Glide descent 19
Turning 19
Radius of turn 20
Turn rates 20
Unbalanced turns 20
Ailerons 21
Stall 21
Stall development 22
Stall identification 22
Recovering from a stall 23
2
, Stall warning 23
Stalling speed 23
Swept wings stalling 24
Swept wing stall warning and prevention 24
High lift devices 25
Flaps 25
Controls of an aircraft 27
Control balancing systems 28
Trim tabs 28
Balance tabs 28
Artificial feel 29
Ailerons 30
Adverse yaw 30
Spoilers 30
Elevators 31
Rudder 31
Powered controls 32
Stability 33
CM-alpha graph 34
Factors affecting stability 35
Stick force and stability 36
Weight, power and configuration 37
Directional, lateral and speed stability 37
CN-diagram 37
Lateral static stability 37
Wing contribution 38
Dutch roll 39
Propellers 39
Propeller secondary effects 42
Power absorption 43
Asymmetric flight (due to engine failure) 44
Sideslip 45
Minimum control speeds 46
Icing conditions 47
Emergency descent 48
Speed limitations 48
Load factor limitations 48
Design speeds 49
Gust envelope 50
Turbulence speeds 50
Calculating the gust load factor 51
Aerodynamic ceiling (AC) 51
3
,General rules
Units
The units used in principles of flight, are called SI-Units. These are the Systeme International Units.
Always convert given information to SI-units before
using formulas. Otherwise, the answers will not be
in the correct units and will provide you with wrong
information. A ratio can be used whenever the
both elements are in the same units.
Weight: force felt by an object in normal
gravity (1G).
Mass: the number of kilograms an object
has.
So, an object with a mass of 10.000kg will have a
weight of 98.100N (x 9,81).
Newton
- First law.
A body will continue in a state of rest or uniform motion unless acted by an external force.
- Second law.
Rate of change of momentum of a body is proportional to the applied force
(F = m * a)
- Third law.
For every action, there is an equal and opposite reaction.
!"#$ &"'( = * ∗ , (&.,/0'1()
Power is a rate of work done.
Kinetic energy
Kinetic energy: the amount of energy a moving object has:
4
3$ = ∗ 675 or, when an airflow is involved instead of a mass:
5
4
3$ = ∗ 875
5
Gas laws
The atmosphere obeys the gas laws (Boyle, Charles & Pressure law). Combining these laws, results
in:
;
9(',./: = where p is the pressure, R is a constant and T is the temperature.
<∗=
The atmosphere is assumed to be a mix of ideal gasses. The temperature decreases while altitude
increases. The air density also decreases.
A summary:
4
, - Low altitudes: high pressure and air density.
- High altitudes: low pressure and air density.
o At 20.000 ft à ½ of sea level air density.
o At 40.000 ft à ¼ of sea level air density.
Definitions
5
, Aircraft components
The equation of continuity
Gives the relation between area, speed and density for an airflow flowing through a pipe:
>0,, ?@"A = B#(0 ∗ C;((& ∗ 9(',./:
When air enters a tube, you’d expect the same amount of air
coming out at the end again. So, mass flow is constant. The
picture aside shows that speed is increasing as the diameter of
a pipe decreases. This applies to situations up to 0.4M, since air
will start to compress with higher speeds.
6
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