Theory of Flight

3. Introduction
Primary flight control
- Elevator Control System
- Aileron Control System
- Rudder Control System
Secondary flight control
- Elevator Trim Tab System
- Rudder and Aileron Trim Tab System
Auxilliary flight control
- Flap Control System
- High Lift Devices

4. Aircraft flight control systems consist of flight control
surfaces, the respective cockpit controls, connecting linkages,
and the necessary operating mechanisms to control an
aircraft's direction in flight. Aircraft engine controls are also
considered as flight controls as they change speed. They can
be divided into three main groups:
- Primary flight control
- Secondary flight control
- Auxilliary flight control

5. Primary Flight Control
Elevator Control System
An elevator is mounted on the back edge of the horizontal
stabilizer on each side of the fin in the tail. They move up and
down together. When the pilot pulls the stick backward, the
elevators go up. Pushing the stick forward causes the
elevators to go down. Raised elevators push down on the tail
and cause the nose to pitch up. This makes the wings fly at a
higher angle of attack which generates more lift and more
drag. Many aircraft use a stabilator — a moveable horizontal
stabilizer — in place of an elevator.

6. Primary Flight Control
Elevator Control System
Drive or climb
Rotate around lateral axis
Forward and aft. Action
Push / pull rod or cable

7. An Elevator Control System of a Commercial Aircraft

8. Primary Flight Control
Aileron Control System
Ailerons are mounted on the trailing edge of each wing near
the wingtips, and move in opposite directions. When the pilot
moves the stick left, or turns the wheel counter-clockwise, the
left aileron goes up and the right aileron goes down. A raised
aileron reduces lift on that wing and a lowered one increases
lift, so moving the stick left causes the left wing to drop and
the right wing to rise. This causes the plane to bank left and
begin to turn to the left. Centering the stick returns the
ailerons to neutral maintaining the bank angle. The plane will
continue to turn until opposite aileron motion returns the bank
angle to zero to fly straight.

9. Primary Flight Control
Aileron Control System
Prevent side slip, skid
Bangking / rolling
Increase and decrease wing cambers
Differential mechanism
Greater up than down

10. An Aileron Control System Linkage

11. An Aileron Control System of a Commercial Aircraft

12. Primary Flight Control
Rudder Control System
The rudder is typically mounted on the back edge of the fin in
the empennage. When the pilot pushes the left pedal, the
rudder deflects left. Pushing the right pedal causes the
rudder to deflect right. Deflecting the rudder right pushes the
tail left and causes the nose to yaw right. Centering the
rudder pedals returns the rudder to neutral and stops the
yaw.

13. Primary Flight Control
Rudder Control System

14. Secondary Flight Control
Elevator Trim Tab System
Elevator trim balances the control force necessary to
maintain the aerodynamic down force on the tail. When
aircraft is flying, a lot of trim could be required to maintain
the desired angle of attack. This mainly applies to slow flight,
where maintaining a nose-up attitude requires a lot of trim.
An important design parameter for aircraft is the stability of
the aircraft when trimmed for level flight. Any disturbances
such as gusts or turbulence will be damped over a short
period of time and the aircraft will return to its level flight
trimmed airspeed.

15. Trim Tab Up Elevator Down Trim Tab Down Elevator Up
An Elevator Trim Tab System

16. Secondary Flight Control
Types of Trim Tab System

17. Secondary Flight Control
Rudder and Aileron Trim Tab System
Trim doesn't only apply to the elevator, as there is also trim
for the rudder and ailerons. The use of this is to counter the
effects of slip stream, or to counter the effects of the centre
of gravity being to one side. This can be caused by a larger
weight on one side of the aircraft compared to the other,
such as when one fuel tank has a lot more fuel in it than the
other, or when there are heavier people on one side of the
aircraft than the other.

18. A Rudder Trim Tab System

19. Auxiliary Flight Control
Flap Control System
Flaps are hinged surfaces on the trailing edge of the wings of
a fixed-wing aircraft. As flaps are extended, the stalling speed
of the aircraft is reduced. Flaps are also used on the leading
edge of the wings of some high-speed jet aircraft, where they
may be called Krueger flaps. Flaps increase the camber of the
wing airfoil, thus raising the lift coefficient. This increase in lift
coefficient allows the aircraft to generate a given amount of lift
with a slower speed. Therefore, extending the flaps will reduce
the stalling speed of an aircraft. They also increase drag
which helps to slow the aircraft.

20. Types of flap systems:
Krueger flap: hinged flap on the leading edge.
Plain flap: rotates on a simple hinge.
Split flap: upper and lower surfaces are separate, the lower surface
operates like a plain flap, but the upper surface stays immobile or
moves only slightly.
Fowler flap: slides backwards before hinging downwards, thereby
increasing both camber and chord, creating a larger wing surface
better tuned for lower speeds.
Slotted flap: a slot (or gap) between the flap and the wing enables
high pressure air from below the wing to re-energize the boundary
layer over the flap. This helps the airflow to stay attached to the flap,
delaying the stall.
Blown flaps: systems that blow engine air over the upper surface of
the flap at certain angles to improve lift characteristics.

22. Three Staged Slotted Flap System of a commercial Aircraft

23. Spoilers
On low drag aircraft like sailplanes,
spoilers are used to disrupt airflow
over the wing and greatly increase
the amount of drag. This allows a
glider pilot to lose altitude without
gaining excessive airspeed.
Spoilers are sometimes called "lift
dumpers". Spoilers that can be
used asymmetrically are called
spoilerons and are able to affect an
aircraft's roll.
High Lift Devices

24. Rolling Effect by Spoiler

25. Slats
Slats, also known as Leading Edge Devices, are extensions to the
front of a wing for lift augmentation, and are intended to reduce the
stalling speed by altering the airflow over the wing. Slats may be
fixed or retractable - fixed slats give excellent slow speed and STOL
capabilities, but compromise higher speed performance.
Retractable slats, as seen on most airliners, provide reduced
stalling speed for take-off and landing, but are retracted for cruising.

26. Leading Edge Extension
Leading edge extensions or LEX (also referred to as leading
edge root extensions or LERX or strakes or chines) are fillets
added to the front of a modern fighter aircraft's wings in order
to provide usable airflow at high angles of attack. They are
typically roughly triangular in shape, running from the leading
edge of the wing root to a point near the cockpit along the
fuselage. They tend to be fairly small in span, extending out
less than a meter. In effect, they are small delta wings grafted
onto the front of the normal wings.

27. Leading edge cuffs are a fixed aerodynamic device employed
on fixed-wing aircraft to modify the airfoil used. They may be
either factory-installed or, more commonly, an after-market
modification. In most cases a leading edge cuff will “droop” the
leading edge of the airfoil. This has the effect of causing the
airflow to attach better to the upper surface of the wing at
higher angles of attack, thus lowering stall speed. This allows
lower approach speeds and shorter landing distances.

28. Wing vortex generators – In order to reduce the drag caused
by supersonic flow over portion of the wing, small airfoils called
vortex generators are installed perpendicular to the surface of
the wing. They are mounted in complementary pairs. This
causes the vortices being developed to add one another, thus
increasing the effect. On some aircraft, fences are installed on
the wings and elevons. This gives more stability and control of
the aircraft, reduces buffeting, and reduces high-speed stall
characteristics.

29. B777 Wing Vortex Generator

30. Wing Fence, Winglet and Wing Tip Vortex

31. This is the end of presentation.This is the end of presentation.
Thank you for your attention.Thank you for your attention.