Principles of Flight

EUGC Training TalkWednesday 28th September 2005

It's all about wings● How they work● What else we need to use them

– Stabilisers, control surfaces... and a cockpit● How we control them

– Primary and secondary effects of controls.● When they won't work

– Stalls, spins and stresses● How to make the best of them

– Speed, sink and polar curves

What is a wing?● Ask a five year old...

– What does it look like?● “it's big and flat”

– large surface area– What does it do?

● “it keeps the plane up”– must produce some anti-gravity force

– When does it work?● “when it goes forward”

– requires horizontal speed

A first guess● A wing is big and flat, and converts horizontal

speed to an anti-gravity force.

Aha!

● “No, that doesn't look right!”– Why?

Lift

Drag

Force

A better wing● It works better if it's a bit more streamlined

– Smoother airflow; generates less drag.● The shape can also give us some extra lift.

– Called the Bernoulli Effect.

Varying the angle● Lift and drag increase as the angle between

the wing and the airflow increases.– This is called the angle of attack.

● At a critical angle of around 17°, the airflow stops being smooth. The drag increases and the lift collapses. The wing has stalled.

What else do we need?● Can we go flying with just a wing?

– Yes, but it's a bit of an awkward design...

● A wing on its own is not particularly stable.

How can we stabilise a wing?● Use a small wing, and some leverage.

– Feedback mechanism opposes tilting.

● Could be either in front or behind!

● Also gives us pitch control with an elevator.

How can we stabilise a wing?● Use two wings, tilted upwards.

– This is called dihedral.

● Another feedback mechanism.

● Add ailerons for roll control.

How can we stabilise a wing?● We can still swing from side to side.

– Add a fin – just like a boat's keel.– Feedback again!

● Add a rudder to give yaw control.

The finished result● We have invented the aeroplane!

● Now, how do we fly it?

Using the controls● We can use the elevator to control pitch.

● This also sets our speed. Why?

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Using the controls● We can use the rudder to control yaw.

● At low speeds this can also induce roll. Why?

Using the controls● We can use the ailerons to control roll.

● This causes adverse (opposite) yaw. Why?

Co-ordinated turns● Turning efficiently requires all three controls.

● Where should the string be?

When it stops working● We can pitch the nose up temporarily.

– We can even go all the way around (a loop).● If the nose stays high, we lose speed.● At low speeds our wings have a greater angle

of attack. Too slow and the wings will stall.– Put the nose down to regain safe flying speed.

● What happens if we're yawing when we stall?– Spinning!– How do we recover from this?

Discussion

(and beer)