On Tue, 29 Aug 2006, markdrela wrote:
> In general, VP props are an aerodynamic disaster, in the sense that
> they work by blowing off the torque burst in the form of blade drag.
> To maximize duration, it would be much better to keep the blades
> unstalled, but reduce the RPM *way* down, roughly in inverse
> proportion to the torque (thrust would still be roughly the same).
Sorry to get off-topic, but this discussion is really getting intersting
to me...
Does the above apply also to outdoor rubber props, where the pitch change
is typically around 12 degrees, and high pitch is similarly used to slow
down the climb speed and slightly increase the climb duration?
The reason I ask is because the public opinion among F1B fliers is that VP
increases duration, but last winter I made rather interesting measurements
with my models and an on-board altitude logger: it seemed that models with
fixed-pitch props climbed equally high as ones with VP. DIfferent models
though, and only this winter I plan to get a model done that could be
flown with either prop to make a direct comparison.
Inreasing the pitch at the start of the climb does slow down model speed.
thus not wasting such much power to drag. But does this happen with the
cost of prop efficiency? Does reduction in efficiency overcome the wins of
reduced climb speed and longer climb? Are those expensive VP prop units
really a waste of money?
-Tapio-
Received on Tue Aug 29 2006 - 11:49:05 CEST
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