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National Advisory Committee for Aeronautics, Technical Notes - Effects of Fuselage Nose Length and a Canopy on the Static Longitudinal and Lateral Stability Characteristics of 45° Sweptback Airplane Models Having Fuselages with Square Cross Sections

A wind-tunnel investigation was made at low speed in the Langley
stability tunnel to determine the effects of fuselage nose length (the
fuselage fineness ratio varied from 7.hl to 10.18) and a canopy on the
static longitudinal and lateral stability characteristics of a complete
model having a fuselage with square cross sections, a #50 sweptback wing
of aspect ratio 3 mounted low on the fuselage, and a #50 sweptback hori-
zontal tail of aspect ratio A mounted slightly above the wing chord plane.
The data were obtained through an angle—of-attack range of -10° to 52°
and an angle—of-sideslip range of —2h° to'2h0.

The results of the investigation have indicated that the static
margin at an angle of attack of 00 was decreased by about 0.09 mean aero-
dynamic chord when the ratio of the fuselage nose length to the maximum
depth was increased from 5.80 to 6.58. At small sideslip angles the
addition of the canopy to each complete model had essentially no effect
on the lift, drag, and pitching-moment coefficients for the angle-of-
attack range investigated; however, at large sideslip angles the canopy
produced some effect. With approximately the same amount of directional
stability at an angle of attack of 00 (obtained by increasing the vertical-
tail size in proportion to the fuselage size), an increase in the nose
length caused large decreases, at moderate and high angles of attack, in
the directional stability of the complete models with the canopy on or off.

The canopy reduced the directional stability of the complete models over
almost the entire angle-of—attack range for all nose lengths investigated.
For the longest fuselage, the model was directionally stable above the
stall with the canopy on but very unstable with the canopy off. It was
found, for the model having a fineness ratio of 9.26, that these changes
in directional stability due to the canopy were associated with favorable
and unfavorable sidewash caused by the canopy and that the fuselage caused
large decreases with increasing angle of attack in the tail contribution
to the directional stability as a result of adverse sidewash at the tail.
The wing caused favorable sidewash and a corresponding increase in the
contribution of the tail to the directional stability for the entire angle-
of—attack range. In comparison with the fuselage and wing effects, the
effects of the canopy were of secondary importance except for the case of
the longest fuselage above the stall.