FAA CFI slide presentation created by Thomas Bergen and David Hogg in 2015. No guarantee as to accuracy of content in any way.

1. Principles of Flight

2. Introduction
Ever wondered how this can get airborne?

3. The Four Forces
● Lift
● Weight
● Thrust
● Drag

4. Weight
Result of Gravity
acting on a Mass

5. Thrust
Force pulling aircraft
forward
Created by engine

6. Drag
Resistance to forward
motion

7. Lift
Opposes gravity
How is it created?

8. Lift: Bernoulli’s principle

9. Static Air Pressure untouched
Lift is created
Reduced Static Air Pressure

10. Lift - advanced
Lift depends on several factors:
● Lift characteristics of the wing
● Air Density
● Airspeed
● Surface area of the wing
Formula: CL½ρ V2 S

11. Airfoil Design Characteristics
5
3
4
6

12. Airplane Stability

13. Airplane Stability
Tendency to return to its original flight path
Two types:
Static Stability Dynamic Stability

14. Static Stability
Refers to the initial response to disturbance
● Positive
● Neutral
● Negative

15. Dynamic Stability
Refers to the response over time
● Positive
● Neutral
● Negative

16. Airplane Axes

17. Dynamic Stability
The stability applies to all three axes:

18. Longitudinal Stability
Depends primarily on CG / CL arrangement
What happens in case of :
AOA disturbance
Airspeed change

19. If aircraft suddenly nose up…
...we want forces to bring nose back down
Longitudinal Stability

20. Longitudinal Stability

21. Lateral Stability
Four main design factors:
● dihedral
● sweepback
● keel effect
● weight distribution

22. Dihedral
The most common design feature.

23. Dihedral

24. Sweepback
The low wing presents its leading edge at an angle that is
perpendicular to the relative airflow.

25. “Weather vane” effect.
Similar to the keel of a ship.
Greater portion of the keel area
has to be above and behind CoG.
Keel Effect and Weight Distribution

26. Vertical Stability or Directional Stability
We want to achieve the weather vane
effect.
Area aft of the CG contribute to
directional stability
Greater surface aft of the pivot point

27. Turning Tendencies
Torque Effect
Spiraling Slipstream
P-Factor (Asymmetric Loading)
Gyroscopic Precession

28. Torque Reaction From Engine and Propeller
Newton’s Third Law of Physics — for every action, there is an
equal and opposite reaction.
An equal force opposes direction of propeller

29. Torque Reaction From Engine and Propeller
Way to counteract this phenomenon:
● Rigging the airplane
● Engine offset to counteract this effect of torque.

30. Torque Reaction From Engine and Propeller
On the Ground:
During takeoff roll more weight is placed on left main landing gear.
More ground friction, or drag, on that side.
Right rudder during takeoff.

31. Spiraling Slipstream
Propeller gives a corkscrew or spiraling rotation to the
slipstream.
At high propeller speeds, it is very compact, increasing effect.

32. P-Factor (Asymmetrical Loading)
At high AOA, the “bite” of the downward moving blade is greater than
the “bite” of the upward moving blade.

33. Gyroscopic Precession
The rotating propeller of an airplane makes a very good gyroscope
and thus has similar properties:
● rigidity in space
● precession

34. Torque Reaction, Spiraling Slipstream, P-Factor and left turning
tendencies
Gyroscopic Precession is a right or left turning tendency depending
on where the force is applied.

35. Load Factors in Airplane
Design

36. Load Factor
● Ratio of lift over the aircraft weight (lift / weight)
● Force applied to deflect its flight path from a
straight line (Newton’s first law)
● Unit = G (acceleration of gravity)

37. Load Factor
It is the result of two forces:
● Centrifugal force
● Gravity

38. Load Factor in a Turn
Load Factor increases very sharply at AOB
above 60° ... and stalling speed too!

39. What is the approximate stall speed of an
airplane in a 60° bank turn if VS is 40kias?
Load Factor in a Turn
and stalling speed too!
Load Factor increases very sharply at AOB
above 60° ...

40. An aircraft must be designed to withstand certain load factors
without any structural damage:
Normal (up to 4000lbs gross weight) _______ 3.8 to –1.52
Utility (mild acrobatics, including spins) ___ 4.4 to –1.76
Acrobatic _____________________________ 6.0 to –3.00
A 50% safety factor is added to those load factors. (Parts of the
aircraft may still bend or twist and some structural damage occur).
Load Factor in Aircraft Design

41. Wingtip Vortices
Risks and Precautions
AIM 7-3-1
AC 90-23

42. Every aircraft in flight generates wake vortices.
Result of of pressure differential
The strength of the vortex is
governed by the weight, speed
and wing shape.

43. Wake is only generated when the aircraft is airborne

44. The most likely encountered hazard is an induced rolling moment that
can exceed the roll control capability of the encountering aircraft.
This is particularly dangerous close to the ground.

45. Vortices from Large Aircraft

46. Precautions to be taken
En Route:
● Maintain a good lookout as always
● Avoid crossing the flight path of a preceding Large
aircraft. You should have at least 5 miles of
separation.
● Remember helicopters also generate vortices

47. Takeoff
Thrust Stream Turbulence
or “Jet Blast”
Precautions to be taken

48. Takeoff
When departing behind a larger aircraft on the same runway, pilots
should:
1. Note the larger aircraft’s rotation point and rotate prior to the
larger aircraft’s rotation point.
2. Continue climb above the larger aircraft’s climb path until turning
clear of the wake
3. Avoid subsequent headings which will cross below and behind the
larger aircraft
4. Be alert for any critical takeoff situation which could lead to a
vortex encounter.
Precautions to be taken

49. Landing
Landing behind a larger aircraft on the same runway:
● Stay at or above the larger aircraft’s final approach
flightpath
● Note the touchdown point and land beyond it.
Precautions to be taken

50. Request update about separation.
Do not hesitate to request downwind
extension or orbit in circuit
You are the ONLY ONE responsible for the
safety of your aircraft!

51. End!

54. Different Designs for Different Purposes

55. Longitudinal Stability
What happens in case of :
● AOA disturbance
● Airspeed change
Longitudinal Stability depends primarily on the CG / CL
arrangement.

56. When the aircraft is disturbed and one wing dips, the fuselage
weight acts like a pendulum returning the airplane to its
original attitude.
This is true as long as a greater surface of the fuselage is
located above and behind the CG.

57. Lift
Bernoulli’s principle