On the Tristar, we prepared the wing on the #1 by locking the leading edge slats up, and bondo-ing all the joints where the slats fit onto the wing itself.
Used all the bondo available in the Antelope Valley.
On the first takeoff, about Vr, as the wings began to take the load off the wheels, they flexed up.... The bondo vanished in a white snowstorm..
End of test.
Removing what bondo that didn't leave ruined a lot of the wing leading edge sub-fairings.
In flight testing, we tufted, and got those things going every way, including forward at cruise Machs..
We tried fairing in the motor pylons to the wing leading edge, with a common-sense fairing everyone agreed would work...
The puddle of air 1/2 way back was a complete surprise...
We didn't use these fairings..
On the first flight with these, BTW, it was noticed the one on the right wing lifted..
"Enough to throw a small dog thru the hole", according to our Director of Flight Test, Sam Wyrick.
We found these things hadn't been screwed on to the structure.. the holes for the fasteners had been filled in with sealant, and the point of the (unique) Tri-head screwdriver pressed in the wet sealant, which was then painted.. The work had been signed off by one of our "never leave the flight shack inspectors, a continuous problem we had.