THE EFFECTS OF RIVETS AND SURFACE ROUGHNESS ON WING DRAG

Some of the most important results of recent wind-tunnel tests conducted by the N.A.C.A. to determine the effects of common surface irregularities on wing drag are presented. The results show the increases in wing drag caused by representative arrangements of protruding and countersunk rivet heads, lapped sheet-metal joints, and surface roughness. The effects of varying rivet size, spanwise rivet pitch, and the chord position of the forward row of rivets are also given. It is shown that manufacturing irregularities may be responsible for considerable excess drag over and above that due to the rivets and lapped joints.

A method is suggested of estimating the drag due to rivets and lapped joints under conditions of dynamic scale and of rivet and lap size and arrangement outside the range of the tests. The estimated excess drag caused by rivets and lapped joints on the wing of a large airplane and the gain attained by eliminating the rivets and laps from various portions of the wing are given as an example.