Phineas and Ferb: Season 2, Episode 11
Thaddeus and Thor/De Plane! De Plane! (15 Jun. 2009)
In "Thaddeus and Thor", Phineas and Ferb compete with two visiting brothers to build the best treehouse. In "De Plane! De Plane!", the stepbrothers set out to build a plane like what Howard Hughes had built, using papier-mâché.