tuft testing

Generally the tufts are placed aft of the leading edge where there is no
laminar flow. Since the tape is in the turbulent boundry layer it has no
significant effect, any more than protruding rivet heads or skin laps do aft
of the laminar region. I don't think tufts on the leading edge are a good
idea. Putting them across a wing is mainly to observe the degree and
progression of flow separation at stall. Say if you wanted to install a set
of vortex generators on your leading edge and needed to find the most
beneficial location, you would tuft the wing behind them and film the tuft
behaviour at stalling AOA with the VGS at various chordwise locations to
find the optimum spot to place the VGs.

I'm an airline support techie for a regional aircraft maker and last summer
I put tufts on the flap of a regional jet that was mysteriously rolling with
flaps fully down and with seemingly symmetrical flight spoiler deployment.
The tufts revealed that when the flight spoilers were retracted to about 8
degrees one side had attained smooth flow in the slot between the spoiler
and the flap, but the other side was still transitioning from turbulent to
smooth because it was a tiny bit higher then the other (but within service
limits). This angle happened to correspond with the first detent on the
deployment lever (it's fly by wire) so the lever could be selected to this
position and all of a sudden the aircraft would start to roll. Move the
lever a tiny bit higher or lower and the roll would stop as symmetrical
spoiled or unspoiled lift was regained. I stuck them on pretty much by
eyeball using speed tape cut into little triangles.

John



"keepitrunning" wrote in message
om...
I was reading and saw a picture of a wing being tuft tested. I was
wondering, since I do not have a clue, how much difference the tape holding
the tufts would cause. In the picture it appears that 1/2 inch blue
masking tape was used and it was torn rather than cut. The tufts were
spaced a couple of inches apart and there were seven rows and eight
columns. His results were that the wing was not showing any separation.
Just wondering if there are accepted methods of doing this type of testing?
How would you determine where to test? Any discussion and comments would
be appreciated.