After the fabric is glued, a calibrated iron is used to shrink and tighten the fabric in stages.
The first shrink is done with the iron set to 250 degrees f., then 300, and the final shrink is done to 350 degrees.
This makes the fabric very tight.
Its important to not just start at one ind of the wing and start ironing. I use a specific pattern.
The black things laying on the wing are removed as I move around the wing. Doing this ensures I don't miss a spot.