MACH TUCK / TUCK UNDER – is a high speed phenomenon.
At very high speeds, adverse pressure forms around the wings and the effectiveness of the elevator decreases significantly, because of the turbulent airflow at high speed and aircraft nose goes down, the aircraft speed increases and gets into a dive, even full pull up on the control columns has no effect on the dive. The excessive airspeed built up in the dive if not controlled can cause airframe structural failure.
To recover- Decrease the throttle to decrease the airspeed.
SHOCK STALL/SHOCK INDUCED SEPARATION – is a high speed phenomenon.
It occurs when the turbulent airflow gets separated from the wing.
When this turbulent airflow meets the tail plane of the aircraft, the whole aircraft body buffets, just as same as in normal stall buffet.
Aircraft in this state is said to be in the state of Shock Stall.
Aircraft starts losing height rapidly due to
- Buffeting of the Aircraft body.
- Aircraft nose goes down, bringing the Aircraft in the dive.
To recover- Decrease the throttle to decrease the airspeed.
Some Aircraft have automatic correction for MACH TUCK /SHOCK STALL phenomenon by the use of the sensors.
Whenever the sensors sense speed increasing beyond a specified range, they increase the angle of attack, which increases the load factor, thereby decreasing the airspeed.
Aileron Reversal – takes place at high speed and in sweep back wing a/c. The a/c rolls in the opposite direction then desired.
Example- You want to roll to the left, the left aileron moves up, and the center of lift moves forward and the wing twist downwards.
Its angle of incidence increases and therefore angle of attack increases and it produces more lift, opposite of this happens on the right wing and it produces less lift.
This cause the a/c to roll towards right, Cos. the right aileron moves down and it suddenly produces more lift, because of high speed and therefore center of lift moves towards trailing edge, wing twists upwards and it’s angle of incidence decreases and angle of attack also decreases and therefore it produces less lift.
This occurs at high speeds in a Sweep back wing A/c, because in a sweep back wing a/c the Tip Chord is less than Root Chord, as tip is weaker than root.
Therefore it can bend easily and ailerons are present at the tips on the trailing edge of the wing.
Loose Control cables cause an increase in friction in the controls and therefore temperature increases causes cable to loosen
Turnbuckles are provided in the control system to adjust the tension of control cables.
After adjustment turnbuckles are wires locked.
Any work done on control cables or flying controls requires a duplicate inspection.
Duplicate inspection is also required for work done on engines control.
Induced Drag depends upon finess Ratio Higher the Finess Ratio lower is the induced Drag
Rudder Reversal – Rudder reversal takes place at very high Mach No. At high speeds. (Above Critical Mach No.) Shock waves are formed and these shock waves reduce Coefficient of Lift.
Example- Flying at high speed if you want to yaw to left, We press the left rudder and rudder goes to the left. The velocity of air on the right side increases and it crosses the Critical Mach No., shock waves form and therefore this side Coefficient of Lift decreases and a/c tail will go to the left and nose goes to the right or a/c Yaws to the right.