1 — The Propeller Is a Rotating Wing
A propeller blade is an aerofoil, and it makes thrust exactly the way a wing makes lift — by meeting the air at an angle of attack. The air a blade meets is the resultant of the aeroplane’s forward speed and the blade’s rotational speed. Because the tip travels much faster than the root, the blade is twisted (a coarser angle at the root, finer at the tip) so that every section works at an efficient angle of attack.
2 — Fixed-Pitch vs Constant-Speed
A constant-speed (variable-pitch) propeller removes the compromise. A governor changes the blade pitch automatically to hold a selected RPM: fine pitch (low angle, high RPM) for take-off and climb, coarse pitch (high angle, low RPM) for an efficient cruise — like the gears of a car. You set RPM with the pitch lever and power with the throttle (manifold pressure), keeping the blades at an efficient angle of attack across the whole speed range.
A stopped or fine-pitch propeller that the airflow keeps turning is windmilling, and a windmilling propeller makes a lot of drag. (On a single, a fully stopped propeller actually glides a little further than a windmilling one — useful to know for a practice forced landing.)
3 — The Four Propeller Effects
A spinning propeller does more than pull — at high power and low speed (take-off, the climb) it also tries to turn the aeroplane. Switch between the four effects:
Torque reaction: the engine spins the propeller one way, so by Newton’s third law the aeroplane is rolled the other way — a roll to the left with a typical propeller, strongest at high power and low speed.
Slipstream effect: the propeller throws a spiralling slipstream back around the fuselage; it strikes one side of the fin and yaws the nose — to the left with a typical propeller.
Asymmetric blade effect (P-factor): at a high angle of attack the down-going blade meets the air at a higher angle and speed than the up-going blade, making more thrust on that side and yawing the nose left.
Gyroscopic precession: the spinning propeller acts like a gyroscope, so a pitch or yaw input is felt 90° later in the direction of rotation — noticed as a yaw as the tail rises on take-off.
- Torque reaction rolls the aeroplane opposite to the propeller’s rotation.
- Slipstream spirals back and strikes the fin, yawing the nose.
- Asymmetric blade effect (P-factor) gives the down-going blade more thrust at high angle of attack, yawing the nose.
- Gyroscopic precession makes a pitch or yaw input show up 90° later in the turn.
With a typical propeller these mostly combine to yaw and roll the aeroplane left when you apply power at low speed — which is exactly why you feed in right rudder on take-off and the climb.
4 — Flight Mechanics: Climb, Glide and Turn
The four forces from Lesson 1 never change their nature — but how they balance depends on what the aeroplane is doing. Switch between the three cases:
In a steady climb, thrust balances drag plus the rearward component of weight along the flight path — so it is excess thrust, not excess lift, that climbs. Lift is slightly less than weight (lift = weight × cos of the climb angle).
In a glide there is no thrust: a forward component of weight along the descent path replaces it. The glide angle is set by the lift-to-drag ratio, so best glide range is flown at the best L/D speed — and the still-air distance is the same at any weight (a heavier aeroplane just flies the same path faster).
In a turn the lift vector tilts: its vertical part still balances weight while its horizontal part pulls the aeroplane around. Total lift must rise, increasing the load factor (n = 1/cos of the bank) and the induced drag — so a level turn needs more power.
- Climb: thrust must beat drag plus the rearward pull of weight along the path, so it is excess thrust that climbs. Lift is slightly less than weight.
- Glide: with no thrust, a forward component of weight does the pulling. The glide angle is set by the lift-to-drag ratio, so best glide range is flown at the best-L/D speed — and the still-air distance is the same at any weight.
- Turn: lift tilts, so it must increase to keep enough pointing up; that raises the load
factor (
n = 1/cos φ, from Lesson 9) and the induced drag, so a level turn needs more power.
5 — Why This Matters, and the Subject Closes
This last lesson ties the whole subject together: the propeller makes thrust like a wing makes lift; its side-effects are why your feet are busy on take-off; and the climb, glide and turn are just the four forces re-balanced. The single most useful number here is best-glide speed — fly it after an engine failure and you cover the most ground to a field.
All propeller behaviour, glide speeds and figures are illustrative; your aircraft’s real best-glide speed, propeller controls and procedures come from its POH/AFM.
