Yes the angle that a prop blade is set at is the blade angle, to the
best of my recollection. But the washout ("twist") on a prop blade
is set so that each part of a blade is travelling at close to the
same speed, rather than to improve its efficiency per se (although it
will be more efficient with washout than without of course). You
might be talking about a variable pitch, or constant speed,
propellor. As the aircraft's forward speed increases, the effective
angle of attack of each blade decreases so the blade's pitch is
increased. That improves the efficiency of the propellor by allowing
it to maintain similar effectiveness over a larger range of speeds.
I have not flown prop aircraft until I started teaching flying in one
(Grob 115E) in 2001 and I had to learn this stuff only so that I
could regrade as an "A2 QFI" ...
Chris
~~ >-)-
C M I Barker
Cambridgeshire, Great Britain.
+44 (0)7092 251126
www.threeshoes.co.uk
homepage.mac.com/zuiko
On 20 Jul 2005, at 02:26, Willie Wonka wrote:
> I think I got it...:)
> You are talking about the brake horsepower that the engine supplies
> and the blade converts it into thrust horsepower or lift, when
> talking about wings. The "twist" maximizes the efficiency,which
> varies anywhere between 50 and 87%, depending how much the
> propeller slips.
> What you call the angle of incidence, my fella tha Murkans know as
> simply the blade angle, not to be confused with the geometric blade
> pitch, which is the distance a propeller should advance in one
> revolution, or the effective blade pitch, which is the distance the
> propeller actually advances, simply called a slip.
> Yep, I got it....:)
> Boris
>
> From: Chris Barker <ftog@xxxxxxxxxxxxxxxx>
> Subject: [OM] Re: #225
> Date: Mon, 18 Jul 2005 17:56:28 +0100
>
> By the way, the way a wing (or prop blade) is set is called angle of
> incidence. Angle of attack is the angle between a aerofoil's chord
> line and the relative air flow; incidence is static, attack dynamic.
>
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