General Aviation Modifications Inc. (GAMI) says the gunk that smeared the underside of the left wing of the AOPA Beech Baron fuel test bed aircraft at AirVenture originated with a leaky patch in the 50-year-old bladder in the tank. In a report prepared by GAMI, the company said the mechanics who removed all four bladders from the Baron found the leak in an old patch on the ancient bladder that has been used to hold G100UL for the past nine months. Fuel then settled between the leaking bladder and "chafe tape" that is applied to the inside metal of the wing to protect the bladder from wearing against the metal. The fuel dissolved the glue on the tape and it became the sticky residue that dramatically appeared on the underside of the wing while the plane was on display at the show. There is 100LL in the right tank and AOPA is gathering comparison data on the use of the fuels in real-world conditions.
This is a companion discussion topic for the original entry at https://www.avweb.com/aviation-news/aopa-baron-wing-stain-traced-to-leaking-bladder-patch