Hiller Ten99The Hiller Ten99 was an American 1961 experimental helicopter, created by Hiller Aircraft.Design and developmentThe helicopter seated six and was similar to other helicopters by Hiller, but featured a larger, box-shaped cabin. It has four doors, and a set of clamshell doors on its aft side. The aircraft was powered by a Pratt & Whitney Canada PT6, and in July 1961, was the first aircraft to have been powered solely by a PT6 engine. The Ten99 was developed for a United States Navy Assault Support Helicopter program. However, the Navy eventually selected the Bell HU-1 instead. A civilian model was proposed, but not produced, and the project was eventually abandoned.