Tech Questions Flashcards
What is a Critical Engine?
Engine whose failure would most adversely effect on the aircraft’s handling and performance
quality. Propeller a/c, there is a difference in the remaining yawing moments after failure of the
left or the right engine if all propellers rotate in the same direction due to the P-factor
What is a Swept wing?
A swept wing is favoured for high subsonic and supersonic speeds, and is found on almost all jet
a/c. Compared with straight wings they have a “swept” wing root to wingtip direction angled
beyond the span wise axis.
What are the advantages and disadvantages of a swept wing aircraft?
Advantages
High Mach cruise speed: Ædelays the airflow over the wing from going supersonic and
allows the a/c to maximize the jet engine potential for higher Mach cruise. The swept wing is
also designed with a minimal chamber and thickness, thereby reducing profile drag, which
further increases the wing ability for higher speed.
Stability in turbulence: Æpoor lift qualities, thereby it is more stable in turbulence compared
with a straight-winged aircraft.
Disadvantages
poor lift qualities, because the swept wing has the effect of reducing the lift capabilities of
the wing
speed instability at lower speeds and higher stall speeds because of the poor lift qualities
wing tip stalling tendency which makes the aircraft longitudinally unstable, which is a major
disadvantage.
What are high lift devices?
Intended to increase lift during certain flight conditions. They include common devices such as
leading edge and trailing edge flaps and slats. Larger wing provide more lift and reduce takeoff
and landing distance, but increase drag during cruising flight and thus increase the fuel
consumption. High-lift devices are allowing the use of an efficient cruising wing, and adding lift
for takeoff and landing.
What is a Critical Mach Number?
In aerodynamics, the critical Mach number (M CRIT) of
an aircraft is the lowest Mach number at which the
airflow over some point of the aircraft reaches the
speed of sound (LSS). At the critical Mach number,
local airflow in some areas near the airframe
reaches the speed of sound, even though the
aircraft itself has an airspeed lower than Mach 1.0.
This creates a weak shock wave. The actual critical
Mach number varies from wing to wing. In general a
thicker wing will have a lower critical Mach number.
What is a Mach Tuck?
Is an aerodynamic effect whereby the nose of an aircraft tends to downward pitch as the airflow
around the wing reaches supersonic speeds; the aircraft will first experience this effect at
significantly below Mach 1.0.
What is a coffin corner?
Is the altitude at or near which an aircraft’s stall speed is equal to the critical Mach number, at a
given gross weight and G loading. At this altitude the aircraft becomes nearly impossible to keep
in stable flight. Since the stall speed is the minimum speed required to maintain level flight, any
reduction in speed will cause the airplane to stall and lose altitude. Since the critical Mach
number is maximum speed at which air can travel over the wings without losing lift to flow
separation and shock waves, any increase in speed will cause the airplane to lose lift, or to pitch
heavily nose-down, and lose altitude.
What is a stall?
A stall is when the angle of attack, the angle at which the wings meet the onrushing air, is
exceeded and the wings lose lift causing the planes nose to drop.
The angle of attack at which this happens can vary depending upon the airspeed. Sufficient flow
of air must continue over the wings to maintain lift.
A stall can occur when one of the following happen:
x Too steep an angle of attack with insufficient flow of air over the wings causing a stall
x Insufficient airspeed at any angle, again not enough airflow over the wings.
What is a deep stall?
(or super-stall) is a dangerous type of stall that affects those aircraft which designs with a T-tail
configuration. In these designs, the turbulent wake of a stalled main wing “blankets” the
horizontal stabilizer, thus the elevators ineffective and preclude the aircraft from recovering
from the stall.
What is the Centre of Pressure?
The position of the center of pressure is not a fixed point but depends on the distribution of
pressure along the chord, which itself depends on the angle of attack. The greater the angle of
attack, the higher the suction which moves toward the leading edge. This is so because the
distribution of pressure and center of pressure point will be further forward if the angle of
attack is higher and further aft if the angle of attack is lower.
Why does an aircraft descent quicker when it is lighter?
The heavier aircraft has to maintain a lower of descent that a lighter aircraft, otherwise it would
over speed. Heavier aircraft have a greater momentum and this weight-driven momentum will
produce a greater speed in a vertical dive.
Therefore a heavier aircraft has to start its descent earlier than a lighter aircraft because it has
to maintain a shallower descent.
What is Centre of Gravity?
The point at which gravity acts on mass
What happens if CofG is outside the forward limit?
Drag increases
Fuel consumption, range, endurance decrease
Longitudinal stability increases
Increases tail down force has same effect as increased weight = higher stall speed.
Increased takeoff and landing speeds
What happens if CofG is outside aft limit?
Longitudnional stability reduced = very unstable
Spin recovery more difficult
Tendency to pitch up
What is Basic Empty Mass (BEM)?
Mass of an aircraft minus crew, fuel, pax, cargo, baggage i.e. minus Variable, traffic, and fuel load
What is Dry Operating Mass?
The Basic Empty Mass plus Variable Load
What is the Operating Mass?
Dry Operating Mass plus Fuel
What is Traffic load?
Total mass of Pax, Baggage, and Cargo
What is Variable load?
Crew and their baggage.
Catering and other removable passenger service equipment.
Food and beverages.
Potable (drinking) water.
Lavatory chemicals, and
Any other special operational equipment.
What is Zero Fuel Mass?
DOM Plus Traffic Load, excluding Fuel
What is Maximum Zero Fuel Mass? (MZFM)
The maximum permissible mass of an aeroplane with no usable fuel.
The MZFM is a structural limitation imposed by the bending moment on the main spar at
the wing root.
On the ground the bending moment is caused by the upwards force of the
main landing gear acting on the wings.
In the air the bending moment is caused by the upward force produced by lift.
What is Maximum Structural Take-off Mass (MTOM)?
The maximum permissible total aeroplane mass at the start of the take-off run.
What is Maximum Structural Landing Mass? (MLM)
The maximum permissible total aeroplane mass on landing under normal circumstances
What is Performance Limited Take off Mass? (PLTOM)
The performance limited take-off mass is the maximum take-off mass allowable to
comply with departure performance limitations such as
runway distance available and
minimum climb gradients required.
What is Performance Limited Landing Mass? (PLLM)
The performance limited landing mass is the maximum landing mass allowable to comply
with landing runway limitations, such as
runway distance available
and minimum climb gradients required in the case of a go-around
What are Regulated Masses?
Depending on the circumstances the aircraft will either be limited by structural considerations or
by performance considerations.
A short runway at a high altitude airport on a hot day
= performance limits will be more restrictive than the structural limits.
The most limiting of the two considerations determines the regulated mass.
What is Aerodrome Operating Minima? (AOM)
AOM are criteria used by pilots to determine whether they may land or take-off from any runway at night or in IMC.
AOM Consists of two parts: Cloud Ceiling and Visibility/RVR
