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National Advisory Committee for Aeronautics, Research Memorandum - High Speed Wind Tunnel Tests of a Scale Model of the Lockeed YP-80A Airplane

With the primary Objective of determining the accuracy with
which full-scale airplane characteristics can.be predicted from .
high—speed windrtunnel tests of airplane models of small scale,
an inyestigation has been conducted to determine the highrspeed
performance and static longitudinal stability and control character—
istics of a l/78—scale model of the Lockheed YP—8OA airplane.

High—speed aerodynamic characteristics are presented for speeds
up to a Mach number of 0.96. Comparisons are made of the relative
aerodynamic characteristics of the l/78-scale model, a l/3—scale
model, and a full—scale YP-8OA airplane. These comparisons reveal
prematurely Occurring lift and drag force breaks for the l/78—scale
model, with the lift loss and drag rise following the force breaks
less severe than indicated by l/3-scale and flight data. Tests made
to visualize the flOW'withinEthe‘boundary layer of the l/78—scale
model revealed a very long laminar boundaryhdayer run over the wing
consistent with the scale of the tests. It is concluded that the
Reynolds number effect on l/TB—scale results at high subsonic speeds
is such as to permit its use solely as a qualitative measure of the
full—scale aerodynamic characteristics of an airplane.

Results of the stability investigation revealed a region of
static longitudinal instability to be present for the l/78—scale
YP—BOA model at moderately high lift coefficients in the Mach
number range of 0.81 to 0.90. An abrupt pitchrup motion, evident
for moderate lift coefficients in this Mach number range (0.8 to
0.9) appeared in the l/3—scale and full—scale tests only at the
limiting Mach number of the tests (approximately 0.85 Mach number).
This region of instability was effectively eliminated for the 1/78—
scale model by sweeping back the leading edges of the horizontal
and vertical tail surfaces 14-50. Beyond a Mach number of 0.9, a
severe diving tendency accompanied by a rapid increase in longi—
tudinal stability was apparent for both the conventional and. swept—
bach—tail configurations.