<DOC>
<DOCNO>
210
</DOCNO>
<TITLE>
propeller in yaw .
</TITLE>
<AUTHOR>
ribner,h.s.
</AUTHOR>
<BIBLIO>
naca r820, 1945.
</BIBLIO>
<TEXT>
  it was realized as early as 1909 that a propeller in yaw
develops a side force like that of a fin .  in 1917, r. g. harris
expressed this force in terms of the torque coefficient for the
unyawed propeller .  of several attempts to express the side
force directly in terms of the shape of the blades, however, none
has been completely satisfactory .  an analysis that incorporates
induction effects not adequately covered in previous work
and that gives good agreement with experiment over a wide
range of operating conditions is presented herein .  the present
analysis shows that the fin analogy may be extended to the form
of the side-force expression and that the effective fin area may
be taken as the projected side area of the propeller .  the effective
aspect ratio is of the order of 8 and the appropriate dynamic
pressure is roughly that at the propeller disk as augmented by
the inflow .  the variation of the inflow velocity, for a fixedpitch
propeller, accounts for most of the variation of side force
with advance-diameter ratio v nd .
  the propeller forces due to an angular velocity of pitch are
also analyzed and are shown to be very small for the pitching
velocities that may actually be realized in maneuvers, with the
exception of the spin .
  further conclusions are ..  a dual-rotating propeller in yaw
develops up to one-third more side force than a single-rotating
propeller .  a yawed single-rotating propeller experiences a
pitching moment in addition to the side force .  the pitching
moment is of the order of the moment produced by a force equal
to the side force, acting at the end of a lever arm equal to the
propeller radius .  this cross-coupling between pitch and yaw
is small but possibly not negligible .
  the formulas for propellers in yaw derived herein (with the
exception of the compressibility correction) and a series of
charts of the side-force derivative calculated therefrom have been
presented without derivation in an earlier report .
</TEXT>
</DOC>
