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Jet Boundary Corrections for Reflection Plane Models in Rectangular Wind Tunnels

A detailed method for determining the Jet—boundary
corrections for reflection—plane models in rectangular
wind tunnels is presented. The method includes the deter—
mination of the tunnel span load distribution and the
derivation of equatiOns for the corrections to the angle
of attack, the lift and drag coefficients, and the
pitching—, rolling—, yawing—, and hinge—moment coeffi—
cients. The principal effects of aerodynamic induction
and of the boundary—induced curvature of the streamlines
have been considered. An example is included to illustrate
the method. Numerical values of the more important correc—
-tions for reflection—plane models in 7— by 10—foot closed
wind tunnels are presented.

INTRODUCTION

-The influence of the Jet boundaries upon the air flow
at and behind two-dimensional—flow models and complete
models has been rather extensively investigated from theo—
retical considerations. The results of several of these
investigations are given in references 1 to 4. A few ex—
perimental checks of the theory have Been successfully
_made. The theoretical methods may be extended to determine
the influence of the Jet boundaries upon the characteris-
tics of semispan models mounted on reflection planes in
rectangular wind tunnels.’ One of-the walls of a c1Ogad
wind tunnel may serve as the reflection plane, as shown
in figure 1. The Jet—boundary corrections are usually
larger and the changes in the span load distribution are
somewhat greater for reflection—plane models than for
complete models, especially with regard to the character—
istice of the lateral—control devices. Greater care is
therefore required in the computations and more factors
2

must be considered'for'reflectienvplane-model corrections
than for the usual completeamcdel corrections.

The present investigation was undertaken to develop
general methods of calculating the various corrections
and methods of determining the changes in the span load
distribution caused by the Jet boundaries. Numerical vale
ues of the more important corrections were calculated for
a series of representative models mounted in 7— by 10—
foot closed rectangular wind tunnels. The numerical val—
ues are presented in the form of graphs and empirical
equations in a separate section of the report, in order
that the values may be obtained without referring to the
detailed calculation procedure, Tables-of the numerical
values of the Jet—boundary—induced upwash velocity for 7-
by lowfoot closed wind tunnels are included and should be
used if it is desired to compute the corrections for mod-
els having unusual proportions, The complete calculation
procedure is illustrated in detail by an example.“

The basic method used to determine the Jetnboundary
corrections is to determine the increments of aerodynamic
forces and moments acting on a model which is twisted by
the amount of the boundary—induced upwash angle. Methods
of calculating the boundaryninduced upwash angle along the
model span and chord and methods of calculating the vari—
ous Jetqboundary corrections. accounting for the princi-
pal effects of aerodynamic induction. are presented in
separate sections in the present report. -

The formulas and corrections presented apply to com—
plete models for which the spans are twice the spans of
the reflectionwplane models. If a model of only the outer
wing panel is tested, the measured characteristics will be
for a model of the aspect ratio. taper ratio. and lateral—
control—device span ratio actually tested. Additional
plaanorm corrections n that is. the usual aspectnratio
and taper—ratio corrections plus corrections for the ratio
of the lateralrcontrolrdevico span to the wing span. ref—
erence 5 - must therefore be made to determine freepair
data for the actual airplane from the corrected data for
the model,