1. PRINCIPLES OF FLIGHT
CHAPTER 3
STABILITY AND CONTROL

2. STABILITY AND CONTROL PLANES AND AXIS AN AIRCRAFT MOVES AROUND 3 AXIS
PRINCIPLES OF FLIGHT
STABILITY AND CONTROL
PLANES AND AXIS
AN AIRCRAFT MOVES AROUND 3 AXIS
LONGITUDINAL
LATERAL
NORMAL
THESE AXIS ARE ALL AT 90° TO EACH
OTHER AND PASS THROUGH THE
CENTRE OF GRAVITY.

3. EACH AXIS HAS A PLANE OF OPERATION.
PRINCIPLES OF FLIGHT
EACH AXIS HAS A PLANE OF OPERATION.
WHEN AN AIRCRAFT MOVES IN ONE PLANE IT
ROTATES ABOUT AN AXIS.

4. AN AIRCRAFT CAN MOVE IN 1, 2 OR 3 PLANES AT ANY ONE TIME.
PRINCIPLES OF FLIGHT
PLANES
AN AIRCRAFT CAN MOVE IN 1, 2 OR 3
PLANES AT ANY ONE TIME.
MOVING IN THE PITCHING PLANE ROTATES
ABOUT THE LATERAL AXIS.
MOVING IN THE ROLL PLANE ROTATES
ABOUT THE LONGITUDINAL AXIS.
MOVING IN THE YAWING PLANE ROTATES
ABOUT THE NORMAL AXIS.

5. THIS IS THE ABILITY OF AN AIRCRAFT IN STRAIGHT AND LEVEL FLIGHT TO
PRINCIPLES OF FLIGHT
STABILITY
THIS IS THE ABILITY OF AN AIRCRAFT
IN STRAIGHT AND LEVEL FLIGHT TO
RECOVER TO IT’S PREVIOUS ATTITUDE
WHEN DISTURBED BY TURBULENCE.
LONGITUDINAL STABILITY
THIS OPERATES IN THE PITCHING PLANE
AND IS CONTROLLED BY THE TAILPLANE.
THE TAILPLANE IS A LONG WAY FROM
THE CENTRE OF GRAVITY AND THEREFORE
HAS A LARGE LEVERAGE AROUND IT.

6. PRINCIPLES OF FLIGHT
TAILPLANE
LEVERAGE
CENTRE OF GRAVITY

7. LONGITUDINAL STABILITY LIFT PRODUCED ON TAILPLANE PITCHES
PRINCIPLES OF FLIGHT
LIFT PRODUCED ON
TAILPLANE PITCHES
AIRCRAFT BACK TO
LEVEL FLIGHT.
LIFT
NOSE UP DISTURBANCE
PRESENTS TAILPLANE AT
HIGHER ANGLE OF ATTACK
TO AIRFLOW.
NEGATIVE LIFT
PRODUCED ON THE
TAILPLANE PITCHES
AIRCRAFT BACK TO
LEVEL FLIGHT.
NEGATIVE
LIFT
NOSE DOWN
DISTURBANCE PRESENTS
TAILPLANE AT A
NEGATIVE ANGLE OF
ATTACK TO AIRFLOW.

8. THE WINGS ON MOST AIRCRAFT ARE SET AT
PRINCIPLES OF FLIGHT
LATERAL STABILITY
THE WINGS ON MOST AIRCRAFT ARE SET AT
A SLIGHT UPWARD ANGLE. THIS IS KNOWN
AS DIHEDRAL ANGLE.

9. PRINCIPLES OF FLIGHT
DIHEDRAL WINGS
ANDOVER C1

10. IF A WING DROPS IN TURBULENCE, THE
PRINCIPLES OF FLIGHT
LATERAL STABILITY
IF A WING DROPS IN TURBULENCE, THE
LIFT NO LONGER ACTS VERTICALLY AND DOES
NOT EQUAL THE WEIGHT.
THIS CAUSES THE AIRCRAFT TO SLIP
SIDEWAYS PUTTING THE LOWER WING AT A
GREATER ANGLE OF ATTACK THAN THE
HIGHER WING GIVING MORE LIFT TO THE
LOWER WING WHICH ROLLS THE AIRCRAFT
LEVEL AGAIN.

11. ANOTHER EFFECT OF THIS SIDESLIP IS THE PARTIAL SHIELDING OF THE HIGHER
PRINCIPLES OF FLIGHT
LATERAL STABILITY
ANOTHER EFFECT OF THIS SIDESLIP IS
THE PARTIAL SHIELDING OF THE HIGHER
WING FROM THE AIRFLOW – SO REDUCING
THE LIFT FURTHER.
SOME AIRCRAFT DO NOT HAVE DIHEDRAL
WINGS BUT STILL HAVE STABILITY DUE TO
THIS SHIELDING EFFECT.

12. ANOTHER METHOD OF ACHIEVING STABILITY
PRINCIPLES OF FLIGHT
LATERAL STABILITY
ANOTHER METHOD OF ACHIEVING STABILITY
IS BY HAVING THE WING MOUNTED AT THE
TOP OF THE FUSELAGE.
THIS IS KNOWN AS THE PENDULUM EFFECT
THE WEIGHT OF THE AIRCRAFT ACTS BELOW
THE LIFT AXIS AND IF THE AIRCRAFT IS
DISTURBED CAUSES THE AIRCRAFT TO
SWING BACK LIKE A PENDULUM.

13. THE PENDULUM EFFECT LIFT PENDULUM EFFECT MOMMENT LIFT AXIS
PRINCIPLES OF FLIGHT
LIFT AXIS
LIFT
PENDULUM EFFECT
MOMMENT
CENTRE OF GRAVITY

14. SOMETIMES A DESIGNER WANTS TO REDUCE THE STABILITY OF AN AIRCRAFT.
PRINCIPLES OF FLIGHT
LATERAL INSTABILITY
SOMETIMES A DESIGNER WANTS TO REDUCE
THE STABILITY OF AN AIRCRAFT.
THIS IS ACHIEVED BY HAVING ANHEDRAL
ANGLED WINGS.
ANHEDRAL WORKS IN THE OPPOSITE SENSE
TO DIHEDRAL AND IS USED TO COMBAT
EXCESSIVE STABILITY IN AN AIRCRAFT DESIGN.

15. PRINCIPLES OF FLIGHT
ANHEDRAL
HARRIER GR9

16. DIRECTIONAL STABILITY
PRINCIPLES OF FLIGHT
IF AN AIRCRAFT IS DISTURBED IN YAW,
THE FIN OF THE AIRCRAFT IS PRESENTED
TO THE AIRFLOW AT A DIFFERENT ANGLE
AND WILL PRODUCE A WEATHERCOCKING
EFFECT.

17. THE AMOUNT OF STABILITY REQUIRED BY
PRINCIPLES OF FLIGHT
STABILITY
THE AMOUNT OF STABILITY REQUIRED BY
AN AIRCRAFT WILL DEPEND ON IT’S ROLE.
HIGH STABILITY REQUIRES EXTRA EFFORT
TO OVERCOME IT WHEN TRYING TO
MANOEUVRE.
LOW STABILITY REQUIRES CONSTANT
ADJUSTMENT TO MAINTAIN CONTROL.
HIGH STABILITY IS USUALLY FOUND ON
LARGE AIRCRAFT WITH A LARGE FIN AREA.
LOW STABILITY IS USUALLY FOUND ON
FIGHTER AIRCRAFT WITH A SMALL FIN
AREA.