Performance I Flashcards
What is the key element for determining an aircraft’s performance?
The drag polar.
CD stands for (note the capital D)?
The drag coefficient for the entire aircraft.
C_D_0 stands for?
The parasite drag coefficient for the aircraft.
The Oswald efficiency factor is represented using the symbol ___.
e
For basic performance, lift is considered to be _______.
Perpendicular to the flight path direction and equal and opposite to the weight.
For basic performance, drag is considered to be _____ to the flight path direction.
Parallel
True or False
For an aircraft in flight, the thrust is often inclined with respect to the flight path although the angle is usually small.
True
The angle between the horizontal plane and the flight path is given the symbol ____.
theta
True or False
The flight path is drawn in a straight line, however, the AC is generally traveling in a curved path (especially when viewed from a distance).
True
In the most basic sense, all flight is ______ as opposed to straight.
Curvilinear
The case where the acceleration of the aircraft is equal to zero is referred to as _________.
Static performance.
For completely level flight, the angle between the horizontal and the flight path is _______.
Zero
True or False
In steady level flight with no acceleration or disturbances, T = D and L = W.
True
Thrust required varies proportionally with _______ and inversely with ______.
The drag coefficient times the weight
The lift coefficient
T = (CD*W)/CL = W/(CL/CD)
Thrust required varies inversely with the _____ ratio.
Lift to Drag
The thrust required is directly proportional to the ____ ratio.
Drag to lift (D/L)
Note: T = 1/(L/D) = D/L
Since Thrust required varies ____ with the lift to drag ratio, the minimum thrust required will occur when ______.
Inversely
The aircraft is flying at a velocity where the L/D ratio is at a maximum
True or False
The L/D ratio is a measure of the structural efficiency of the AC.
False, its a measure of the aerodynamic efficiency.
On the velocity vs thrust required curve, a low speed corresponds to what five aerodynamic characteristics?
- High angle of attack
- High CL
- High CD_i (induced drag)
- Low q_infinity
- Low CD_0
On the velocity vs thrust required curve, a high-speed corresponds to what five general aerodynamic characteristics?
- Low angle of attack
- Low C_L
- High q_infinity
- High C_D_0
- Low C_D_i
Induced thrust decreases with ________.
Increasing velocity and vice versa.
Note: Induced thrust required is proportional to inverse velocity squared.
Parasite thrust increases with ________.
Increasing velocity and vice versa.
Minimum thrust required occurs where ____.
The airspeed at which the lift to drag ratio is at a maximum.
At (L/D) max, the airframe’s induced drag is equal to ______.
The parasite drag.
CD_0 = CD_i
Thrust required is an ______ associated phnomenon.
Airframe
Thrust available is an ______ associated phenomenon.
Engine
For a propeller driven aircraft, thrust at a zero velocity is at a ____________.
Maximum
For a propeller-driven aircraft, thrust varies as forward speed changes in accordance with ______.
The efficiency of the propeller (\Nu_prop)
For a reaction jet engine, the thrust _____ slightly with forward speed due to _______.
Increases
Inlet pressure recovery
If the thrust increases to the maximum amount available, the aircraft’s speed is ______.
Fixed
The intersection of what two curves defines the maximum aircraft speed?
The Tr (thrust required) and the Ta (thrust available) curve.
For gliding flight, the descent angle is strictly a function of ______.
The lift to drag ratio.
At low speeds, C_D_0 includes _____ and _____.
Skin friction
pressure drag
Pamadi, Pg. 72
What is power required?
The power required is the power necessary to overcome the aerodynamic drag of the airplane.
Pamadi, Pg. 72
What is thrust required?
The thrust necessary to balance the aerodynamic drag of the aircraft.
Pamadi, Pg. 72
For a given altitude, the power developed by a piston engine is virtually constant with _______.
Flight Velocity
Pamadi, Pg. 73
Power developed by a piston engine decreases with an increase in altitude because of _______.
The decrease in density.
Pamadi, Pg. 73
What is required for a piston aircraft’s propulsive efficiency to be assumed constant over the operating range?
The aircraft must be equipped with a variable pitch, constant speed prop.
Pamadi, Pg. 73
For gliding flight, the flattest glide occurs when ____.
The glider flies at (CL/CD) max or the minimum drag per unit weight.
Pamadi, Pg. 80
What CL/CD condition is required for max range in a glider.
Max CL/CD
Pamadi, Pg. 80
For a glider, the rate of sink is at a minimum when _____.
CL^(3/2) / CD is maximum.
Pamadi, Pg. 81
For a glider, the maximum endurance occurs when ______.
CL^(3/2) / CD is maximum.
Pamadi, Pg. 84
For a glider, endurance is _______ when sink rate is minimum.
Maximum
Pamadi, Pg. 84
