The United States Navy's aerobatic flight demonstration team, the Blue Angels, performs the Diamond 360 at the Andrews Airforce Base Joint Services Open House. In this formation, the wing tips are 18" from the canopies.
Air show photography tip: Because of the distance air show craft are typically performing at, even the widest apertures on most handholdable telephoto lenses will provide enough DOF to deliver an all-in-focus subject. More important may be to stop down the aperture enough to eliminate any vignetting that will be noticeable on an evenly-colored sky.