Spin Tests of Two Models of a Low-Wing Monoplane to Investigate Scale Effect in the Model Test Range Page: 2 of 23

                                
NATIONAL ADVISORY COMMITTEE FOR -AERONAUTICS

TECHNICAL NOTE NO. 807
SPIN TESTS OF TWO MODELS OF A -LOW-WING MONOPLANE
TO INVESTIGATE SCALE EFFECT IN THE MODEL TEST RANGE
By Charles J. Donlan..
SUMMARY
Concurrent tests were performed on a 1/16- and a
1/20-scale model (wing spans of 2.64 and 2.11 ft, respec-
tively) of a modern low-wing monoplane in the NACA 15-
foot free-spinning wind tunnel. Results are presented in
the form of charts that afford a direct comparison be-
tween the spins of the two models for a number of differ-
ent conditions.
qualitatively, the same characteristic effects of
control disposition, mass distribution, and dimensional
modifications were indicated by both models. Quantita-
tively, the number of turns for recover and the steady-
spin parameters, with the exception of the inclination of
the wing to the horizontal, were usually in good agree-
ment.
The results presented indicate that, within the
range of Reynolds numbers used in the present investiga-
tion, such factors as difficulty. of ballasting and test-
ing are more important in determining proper model size
than the changes in scale effect likely to result from
the use of different sizes of models.
INTRODUCTION
The size of models used for testing in the NACA free-
spinning wind tunnel is usually dictated by considera-
tions of tunnel operating technique and ease of ballast-
ing. With large models 'the actual testing is often dif-
ficult; with small models the proper mass or inertial
balance.is difficult to obtain. In general, the partic-
ular choice of model size is somewhat arbitrary because
usually more than one size can be tested.  It was there-
fore considered expedient to determine to what extent the
experimental results vary with the actual size of the mod-
el tested.