Lately, The Flying Bulls have been busy replacing the tanks of their Mitchell B-25, as it was installed back in 1997 in the USA as part of a general overhaul. New tanks should prevent leakage, which was caused by the deterioration of the old tanks. While they were busy, the mechanics also installedsome extra tanks with an added capacity of around 1,150 liters, increasing the B-25’s flying time by approximately 2.5 hours.
3D scans were used to retrofit the new tanks. This technique is used increasingly for the reproduction of parts for warbirds, especially when those parts are scarce, or notproduced anymore. A 3D scan captures the original to the last inch, which allows for an exact reproduction of the respective piece. In the B-25’s case, the cavities that house the tanks were scanned and used as a basis for the production and installation of the new tanks.
The replacement of fueltanks in a relatively large aircraft like the B-25 requires a lengthy process of preparation: the outer wings need to be removed, which in itself is abig job. In order to remove the ailerons and outer flaps, all cable pushrods used to control them, need to be disconnected. There are also around 150 bolts, which hold each outer wing together. They need to be loosened and removed in a specific order to prevent twisting or damaging the structure.
The new tanks were custom-made by a British company that also manufactures fuel tanks for Formula 1 cars. The tanks are made from ballistic nylon and coated with a synthetic elastomer. This makes them thinner and lighter than older generation tanks.
The tanks are rigorously leak tested both at the factory after manufacturing and prior to installation. The complexity of the installation makes it a lengthy process that can take several days. This process requires great care, as scraping or scratching may cause leaks. Once installed, the tanks are frequently checked, including a pre-flight checkprior to takeoff. Aviation fluid (AVGAS) is very viscous, making leaks easy to spot on the exterior of the aircraft.
Experienced mechanics and preciselabor ensures that the tanks are replaced quickly and efficiently, enabling the B-25 to take off once more and wow spectators with its spectacular maneuvers.