Thrust

Question 1

Thrust definition

Answer 1

power generated by the engine turns the propellers, converting rotational energy into thrust
●acts parallel to the relative wind
●opposes drag
●equal to drag in unaccelerated, straight-and-level flight

Question 2

Power

Answer 2

The time rate of doing work:
Power = Force x distance/ time

Question 3

Power/thrust in relationship to speed

Answer 3

THRUST AVAILABLE DECREASES AS SPEED INCREASES

THRUST REQUIRED INCREASES AS SPEED INCREASES

POWER AVAILABLE DECREASES AS SPEED INCREASES

POWER REQUIRED INCREASES AS SPEED INCREASES

Question 4

Propellor aerodynamics

Answer 4

A rotating airfoil driven by the engine to produce thrust to pull or push the aircraft through the air.

The amount of thrust produced by each section of the propeller is not only a function of its shape, but is also dependent upon its rotational speed and position relative to the oncoming air
Since this position varies along the propeller blade span, each small section of the propeller blade is set at a different angle to the plane of rotation.

•This gradual decrease in blade angle resulting from this gives the propeller blade its twisted appearance
•Blade twist allows the propeller to provide a more uniform thrust throughout most of the length of the blade

Question 5

Propellor blade twist

Answer 5

●The blade angle is at its highest pitch at the hub and least towards the tip
●This is done to produce uniform lift from the hub to the tip

Question 6

Effective pitch

Answer 6

the actual distance a propeller moves through the air in one revolution. The difference between the geometric pitch of the prop and the slip

Question 7

Geometric pitch

Answer 7

the theoretical distance a propeller should advance in one revolution

Question 8

Propellor slip

Answer 8

the difference between the Geometric Pitch and Effective Pitch.

Question 9

Left turning tendencies- torque

Answer 9

Newton’s 3rd law. Rotation action of a spinning prop causes torque reaction, which rotates the aircraft in the opposite direction

Question 10

Left turning tendencies- gyroscopic precession

Answer 10

the reaction to a force applied to a gyro acts in the direction of rotation and approximately 90° ahead of the point where force is applied

Question 11

Left turning tendencies- asymmetrical thrust

Answer 11

(P-factor) when the prop axis of a rotation is different from the airplane’s relative wind, the AOA of each blade changes continuously through each revolution. In a climb the AOA is at its minimum as the blade is ascending, and reaches its maximum as it descends on the other side

Question 12

Left turning tendencies- spiraling slipstream

Answer 12

backward flow of air or slipstream, which wraps around the aircraft striking the vertical stabilizer on the left side causing the tail to yaw to the right thence causing the nose to yaw to the left

Question 13

Left turning tendencies fixes

Answer 13

During cruise, the airplane has built-in factors that help counteract the left turning tendencies:
●“Canting” the engine
●Increase the angle of incidence on the left wing
●Rudder trim tab
- canting the dorsal fin of the empennage

Question 14

Jet types

Answer 14

Low bypass turbofan
High bypass turbofan

Question 15

Turbine

Answer 15

PT6A – Turboprop

Question 16

Equilibrium

Answer 16

Equilibrium exists when all force vectors are balanced. They cancel each other out

Parasitic drag curve with a constant thrust line added. The equilibrium speed will be where the drag line meets the thrust line

Question 17

Propellor thrust

Answer 17

Illustration of thrust produced by an aircraft piston engine driving a constant speed propeller

Thrust is excellent at low airspeeds but drops off quickly with increasing airspeed

Question 18

Jet thrust

Answer 18

Illustration of thrust produced by a jet engine

Thrust reduction curve is much flatter than the curve for a piston engine/propeller combination

Question 19

Prop vs. jet

Answer 19

Illustration of piston engine and jet engine thrust (shown in blue) superimposed over the aircraft total drag curve.
The equilibrium points for top speed are shown as red dots.

Assuming equal piston power vs. jet power, the piston engine gives more thrust (and acceleration) at low airspeeds while the jet engine gives more thrust at higher airspeeds.