After consulting another aviation guru and asking him to read this interesting
discussion, he emailed this reply which I'll paraphrase:
"...the point about differential thrust around the rotation of the blade being
sufficiently problematic to be worth disregarding the recommendation to have an
offset.
He is concerned about a 1.5 degree offset. But in reality, if the slip ball is
not kept well centred by the pilot there will be a yaw angle between the
fuselage
and the relative airflow and 1.5 deg seems minimal. I have never noticed any
issues with strange vibrations etc from being slightly out of balance. And
even more relevant, the effect he mentions isn't just about a lateral angle
between
prop axis and direction of airflow, the exact same situation arises when
there is a vertical angle between the prop axis and the relative airflow.
Obviously
this angle varies as the angle of attack varies, due to flying at differing
weights, speeds, and g loadings. The angle of attack can probably vary by
at least 10 degrees between low and high speed flight and this makes 1.5 degrees
pale into insignificance. Also if you consider the prop tip speed vs the forward
speed, the effect is diluted.
Of course the aircraft will be quite flyable with or without the offset, but I
think there will be less yaw with power effect with the offset. It's a bit like
having differential ailerons - not essential but it makes the aircraft easier
and more pleasant to fly (unless you like flying upside down!) and it will
require
less right rudder or right brake on a take-off roll which is surely a good
thing from a performance point of view."
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=465180#465180
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