The Development of Satisfactory Flying Qualities on the Douglas Dive Bomber, Model SBD-1 Through Flight Testing Successive Modifications in Control-Surface Area, Hinge-Line Location, and Aerodynamic-Balance Nose Shape Page: 25 of 73
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24
4. The aileron control forces are considered satisfactory
throughout the required flight range. It is possible
that the forces may be considered somewhat light below
airspeeds of 65 knots.
5. With the reduction in chord and travel, the ailerons pro-
duce adequate rolling moments within 5 knots of the
stall. Although it is possible to overbalance the
ailerons in a steady sideslip with angle of bank 150
at indicated airspeeds below 68 knots, this charac-
teristic is considered not extremely objectionable.
In the configuration described above, the XBT-2 airplane was
taken to the Naval Air Station at Anacostia for acceptance. Upon
the basis of Navy tests the lateral stability was considered sat-
isfactory; however, directional stability was considered marginal
in the carrier-landing condition with flaps and gear extended and
with cruising power. It was observed that in this condition the
increased dihedral angle caused more roll than is desired for a
given amount of yaw, and that the rudder-control force had an
undesirable tendency to reverse near full-surface throw. It was
desired that positive directional stability and trim be provided
in the carrier-landing condition down to 65 knots, with rudder
free. The flight tests of phase V were concerned with satisfying
this requirement by a successive series of modifications in
vertical-surface plan form and rudder trim tab, without jeopard-
izing the progress already made in obtaining satisfactory lateral
stability.
The test used to compare the directional stability in the
carrier-landing condition obtained by the various modifications
was to find the minimum indicated airspeed for recovery from a
directional oscillation started by a 100 displacement of the rud-
der immediately followed by pedal release, with lateral and
longitudinal trim maintained by use of the stick. For the con-
figuration at the beginning of phase V this speed was 85 knots;
whereas the desired value was 65 knots. Progressive increase in
fin area gave the expected reductions in minimum speed for direc-
tional stability in the carrier-landing condition: an increase
of 0.8 square foot added by the small fin extension of figure 4p
reduced the speed to 72 knots indicated; whereas a further increase
of 0.9 square foot added by the large fin extension of figure 4q
brought the speed to 68 knots indicated. Although the directional-
stability requirements could be met easily by increasing the size
of the fin, the additional requirement that the rudder overbalance_ _
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Root, L. E. The Development of Satisfactory Flying Qualities on the Douglas Dive Bomber, Model SBD-1 Through Flight Testing Successive Modifications in Control-Surface Area, Hinge-Line Location, and Aerodynamic-Balance Nose Shape, report, May 1942; (https://digital.library.unt.edu/ark:/67531/metadc61066/m1/25/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.