PRINCIPLES OF FLIGHT CHAPTER 3 STABILITY AND CONTROL

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.

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.

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.

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.

PRINCIPLES OF FLIGHT TAILPLANE LEVERAGE CENTRE OF GRAVITY

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.

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.

PRINCIPLES OF FLIGHT DIHEDRAL WINGS ANDOVER C1

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.

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.

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.

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

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.

PRINCIPLES OF FLIGHT ANHEDRAL HARRIER GR9

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.

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.