Induced flow and Angle of attack

[Cron]

It's probably all very simple but me being same can't see how induced flow alters the angle of attack.

Any explanation gratefully received.

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London Tower this is Skyflash...

[StevieTerrier]

Cron it you want a technical simple(-ish) description :the angle of attack is the angle between the blade chord line and the relative air flow. If there is no induced flow, then the relative air flow is coincident with the plane of rotation. Introduce induced flow, and this results in the RAF being a resultant of the two airflows over the blade(from the plane of rotation and the induced flow). The induced flow causes the RAF to move away from the POR vector and towards the Chord Line, thus reducing the angle of attack.

Hope that helps???

[ShyTorque]

Cron,

A vector diagram is needed to explain it properly and my explanation is simplifying things slightly; but for a starter,

Imagine a fixed wing moving forward through still air. The angle of attack in this case is simple to visualise, it's the angle between the relative airflow (from straight ahead) and the chord line / rigging angle of the wing.

I think you will agree that this wing will deflect air downwards during its passage through the air (downwash).

Now imagine a second wing immediately behind and below the first. This wing will experience a different relative airflow because the air through which it passes has been deflected downwards. The angle of attack will be less.

Helicopter rotor blades suffer from the same thing as they all follow each other round the mast. The induced flow is the cause of the reduced A of A.

ShyT

[Multp]

I can almost visualise Ray Lawrence giving that explanation, Shy-Torque. Takes yer back! Can't think of a better explanation.