In Exercise A6 Question 1 it talks about the effect of "increasing or decreasing" the stalling angle.

The answer is confusing.

It refers only to the effect of "increasing" the stalling angle with answer "d"

Surely, "decreasing" the stalling angle has the opposite effect?

So the answer is incomplete or the question is ambiguous.

In the words of a famous polly, "please explain".

Thanks.

Michael.

Hi Michael,

I'm not sure question 1 in exercise A6 is the one you are referring to since it asks "An aerofoil is said to be at its stalling angle of attack if any increase or decrease in angle attack produces...". It talks about increasing / decreasing the angle of attack not increasing / decreasing the stalling angle.

If the aerofoil is at the stalling angle of attack (or "critical angle") it has the highest lift coefficient which means at a given airspeed, that angle of attack is producing the greatest amount of lift possible.

If you increase the angle of attack you go beyond the critical angle and the aerofoil produces less lift. If you reduce the angle of attack (i.e. have less an angle of attack than the critical angle), you reduce the amount of lift being produced at that airspeed.

If you get maximum lift exactly at the critical angle, then any other angle of attack by definition is going to give you less lift.

The answer to this question is (c) produces less lift.

Cheers,

Rich

Thanks.