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Wind Tunnel Investigation of Shielded Horn Balances and Tabs on a 0.7 Scale Model of XF6F Vertical Tail Surface

SUMMARY

An investigation was made in the LMAL 7- by
10-foot tunnel of a 0.7-scale model of the vertical
tail surface of the Grummnn XF6F airplane. The model
was also utilized for a more general investigation of
the effect on the hinge-moment characteristics of
shielded horns of different chords, spans, and nose
shapes and of trimming tabs of two nose shapes. An
unshielded horn was tested for comparison with the
shielded horn, and the results of the comparison are
given. '

Analysis of the data showed that for most tail
surfaces it will be impossible to obtain by means of
shielded horns a closely balanced surface and keep the
rate of change of hinge-moment coefficient with angle of
attack near zero without the addition of some other
balancing device. With shielded horns, the rate of
change of hinge-moment coefficient with rudder deflection
could be reduced to about 50 percent of the unbalanced
value without obtaining a positive value of the rate of
change with angle of attack large enough to give steady

. oscillations of the airplane with free rudder. Pressure-
distribution and tuft tests were made of the flow over
horns of two nose shapes. Lower peak pressures and con-
seQuently higher critical speeds were obtained for the
medium—nose horn than for the blunt-nose horn. The
tests of the two trimming tabs showed that the shape of
the tab nose made very little difference in the results.
INTRODUCTION

_ Tests were made in the LMAL 7- by 10-foot tunnel of
'_a 0.7-sca1e model of the XF6F vertical tail surface.
These tests were undertaken to obtain data for use in
the design of shielded horns in general and to obtain
data useful for the XF6F vertical tail in particular.'
Additional tests were made to determine tab character-
istics for two different tabs and flow characteristics
over several of the shielded horns.

The various shielded horn balances tested included
models of the original horn on the XF6F airplane and of
shielded horns of four chords, each of which was tested
with two different spans and nose shapes. The variation-
in horn size covers the range from no balance to over-
balance.. Flow characteristics were determined by tuft
tests of two of the smaller horns and pressure-distribution
tests of two of the larger horns. The pressure-
distribution data show the local velocity distribution of
the two nose shapes tested. For convenience, the term
"shielded horn“ will generally be referred to as "horni"
followed by a designation to indicate the horn size and
nose shape. ' c

Tests were made of an unshielded horn balance to
determine whether any correlation between shielded and
unshielded horns was possible. These tests were also
the logical extension of those of the short-span shielded
horns.

Characteristics of the tab were determined in order
to have information useful in the design of any balancing
or unbalancing device that uses tabs, as well as to have
the characteristics of the particular trimming tabs
tested. A round-nose tab of the same plan form and size
as the original tab was tested to determine the varia-
tions in characteristics, if any, from the original tab.
The round-nose tab represented the type of tab usually
used on wind—tunnel models. Both tabs were tested
sealed and unsealed.