5

increments of drag coefficient added by the separate addition of the
component parts were as follows:
Fillets             -0.0016
Inboard nacelles     0.0012
Tail                 0.0032
The 0.0032 increment of drag coefficient due to the tail was
measured. with the inboard nacelles removed from the model. With the
inboard nacelles in place, the increment of drag coefficient due to
the tail was 0.0051, an increase of 0.0019.
At small lift coefficient, the wing-fuelage fillets had little
or no effect on the critical speed but, at the higher lift coeffi-
cients, the critical speed was increased by the addition of the
fillets (fig. 11(c)). The addition of the inboard nacelles reduced
the critical Mach number approximately 0.02.
C CONCLUSIONS
1. The test results indicated. that the longitudinal stability
and control remained normal until speeds at least 38 percent above
the maximum predicted level-flight speeds had been reached.
2. The elevator effectiveness at lift coefficients of zero and
0.1 was maintained up to a Mach number of 0.725. This Mach n mber was
considerably higher than the critical Mach number. However, the elevator
effectiveness was less at Mach numbers above 0.6 focr lift coefficients
greater than 0.1.  The increased stability and large changes in lift
coefficient for balance at speeds above the critical rendered the
elevator less capable of controlling the attitude and lift coeffi-
cient at these speeds.
3.  The inboard nacelles caused the drag coefficient of the tail
to increase from 0.0032 to 0.0051 at a lift coefficient of 0.3, and
at a Mach number of 0.45 (a representative flight).
Ames Aeronautical Laboratory,
National Advisory Coiumittee for Aeronautics,
Moffett Field, Calif.
REFEcNCF
1. Silverstein, Abe, and White, James A.: Wind-Tunnel Interference
with Particular Reference to Off-Centr Positions of the Wing
and to the Downwash at the Tail. NACA Rep. No. 547, 1935.
L