NASA has unveiled details of an electrically-powered, tail-sitting vertical take-off and landing (VTOL) single-pilot concept called the Puffin.
NASA, which released first details of the unusual vehicle this week at the American Helicopter Society (AHS) aeromechanics conference in San Francisco, Calif, stresses the aim is to develop a technology integration demonstrator that can show the potential of an electrically-powered vehicle rather than develop a prototype for any specific product.
The tail-sitter, more details of which will feature in a forthcoming edition of Aviation Week, was originally inspired by a 2007 AHS graduate student contest to design a stealthy Special Operations vehicle. The concept was aimed at a virtually silent VTOL craft that could be deployed from a Ohio Class U.S. submarine. The VTOL was designed to fit into a buoy that could be launched from the submarine while submerged. The buoy, with VTOL and sole crew member on board, would then deploy to the surface following a delay to enable the vessel to clear the area.
Three years on and the Puffin is being evaluated under a research project between NASA, National Institute of Aerospace (NIA), Massachusetts Institute of Technology, Georgia Institute of Technology, and Phoenix, Ariz-based M-dot Aerospace. Unlike much larger, earlier tail-sitters including the Lockheed XFV-1, Convair XFY-1 Pogo, and the Vought V-173 Flying Flapjack, the lightweight Puffin is powered by electric motors rather than gas turbine or reciprocating engines.
Several views of the tail-sitting Puffin. (NASA)
Configured for a 6,000-ft, 95 deg F hover, the Puffin is equipped with two sets of 7.5-ft diameter, four blade ‘Zimmerman’ prop-rotors. The four rotors on each nacelle are divided into two pairs and move together rather than counter-rotate. However they also move in the opposite direction to the rotors on the other nacelle to counter torque.
Named after the NASA researcher who developed the V-173 and XF-5U, the Zimmerman prop-rotors were flown on the ‘Flying Flapjack’ but suffered high levels of fatigue due to the bending cyclic loading on the prop during transition, says NASA Langley Aeronautical Systems Analysis Branch engineer and Puffin project lead Mark Moore. However, in the Puffin configuration the Zimmerman prop-rotor “permits the two sets of blades to teeter and flap to relieve the bending moments caused at the approach transition high angle of attack,” says Moore.
The pilot will fly the Puffin from a prone position (NASA)
So far the battery technology available today means the 6,000-lb vehicle will likely have a range of only around 50 miles, but researchers are confident that improvements in battery density will provide greater range in future. One of the team members, M-dot Aerospace, is also building a one-third scale demonstrator to prove the concept is viable.