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National Advisory Committee for Aeronautics, Technical Notes - Full Scale Tunnel Research on Tail Buffeting and Wing Fuselage Interference of a Low Wing Monoplane

This report is a presentation of some preliminary re-'
sults of an investigation conducted in the N.A.G.A. full—
scale wind tunnel to determine the best means“tr reducing
the tail'buffeting and wing-fuselage interference of a
low-wing monoplane. Data indicating the effects 3?_an h‘
N. A. G. A. engine cOWling, fillets, auxiliary airfoilo of
short span, reflezed trailing edge, propeller slipstream,
and various combinations of these features are included.

The results of the tests showéd that the N. A. C. A.
cowling reduced the interference and buffeting to magni-
tudes small enough to be considgred ugobjectionable at __
angles of attack up to within 3 or 4 of the stall. The
fillets, either alone or in cofibination with the N.ALQ.A.
cowling or a reflexed trailing edge; reduced the buffeting
and interference to unobjectionable magnitudes at angles
of attack up to the stall. A large fillet, when used
alone, reduced the buffeting oscillatiOns to one eevenFfi
their original amplitudes thus giving the _greatest reduc—
tion obtained. The best all— round results were obtained
by the use of fillets together with the N. A. O. A. -cowling.
This combination reduced the tail buffeting 0801lla tions
to one fourth their original amplitudes, increased the
maximum lift 11 percent, decreased the minimum drag g per—
cent, and increased the maximum ratio offllift to drag 19_
percent.

The increasing use of low— wing monoplanes_ has em a—
sized the susceptibility of this type of airplane_ to get—'
rimentel winghfuselage interference. This interference
was first indicated by inferior aerodynamic characteristics
of the low—wing as compared to the high—wing monoplane.

In addition to reducing the aerodynamic efficiency.
this interference produces other highly objectionable con—
ditions resulting from the eddying wake from the region
of the wing—fuselage intersection floWing over the empen—
nage. The position of the tail surfaces in this eddying
Wake sometimes makes difficult the attainment of satisfac-
tory longitudinal control and stability. The buffeting
action of the eddying wake often causes an irregular oscil-
lation, or shaking, of the tail surfaces.