Visiting the Yuri I in Japan


Todd and museum director, Mr. Nagaura Atsuhiro, standing in front of the Yuri I.

Todd and museum director, Mr. Nagaura Atsuhiro, standing in front of the Yuri I.

At the same time that Cameron was visiting the team at the University of Maryland, I was on the other side of the world standing in awe of the Yuri I at the Kakamigahara Aerospace Museum in Japan. I happened to be in Asia for a friend’s wedding and couldn’t pass up the opportunity to see this historical human-powered helicopter. The Yuri I was built by Prof. Akira Naito and the Nihon Aero Student Group, as the 5th helicopter in their quest for human-powered flight. In 1988, using mostly bamboo construction, the Yuri set a 19.46 second endurance record that stood untouched until the University of Marylands flights with Gamera II in 2012. The Yuri’s highly innovative quad-copter design was a breakthrough that made clear the possibility of stable and efficient flight.

The Yuri I camouflaged amongst the truss-work of the ceiling.

The Yuri I camouflaged amongst the truss-work of the ceiling.

Before describing the details of the Yuri I, I have to say a huge thank you to the staff at the Kakamigahara Aerospace Museum and their director Mr. Nagaura Atsuhiro. Everyone was incredibly welcoming, kind and helpful, going so far as to drive us 25 minutes back to the nearest train station! The museum is a great place to visit, with helicopters and airplanes from the dawn of aviation to the present!

Helicopters on display in front of the Kakamigahara Aerospace Museum.

Helicopters on display in front of the Kakamigahara Aerospace Museum.

The Yuri I is similar to the Gamera, with a recumbent pilot hanging beneath the large truss. The longitudinal members of the truss appear to be made from carbon fibre, with the shear members made from aluminum, a further refinement of the all-bamboo truss that is seen in most pictures and video of the Yuri I. It was also interesting to see the battle scars, the patches and the tape, that seem to appear on any well used human-powered aircraft. This was an aircraft that was flown, and pushed to its limits.

The pictures below give a sense of some of the intricate design details of this incredible machine. 

Pilot's seat hung from the truss with carbon tubes and bracing wire on the sides.

Pilot's seat hung from the truss with carbon tubes and bracing wire on the sides.

The right hand side of the drive system using a modified chainring for a tensioner.

The right hand side of the drive system using a modified chainring for a tensioner.

The drive spool (somewhat smaller than Atlas) at the end of each truss arm.

The drive spool (somewhat smaller than Atlas) at the end of each truss arm.

The rotors attach below the truss with very minimal ground clearance.

The rotors attach below the truss with very minimal ground clearance.

The rotor has a slightly tapered planform with a reduced tip chord.

The rotor has a slightly tapered planform with a reduced tip chord.

The ribs appear to have a wood cap strip with a delicate foam truss.

The ribs appear to have a wood cap strip with a delicate foam truss.

Cross-bracing lines connect truss arms to increase torsional stiffness. This design featured was missed when we did our background research, and it wasn't until we had implemented it ourselves that we found out Gamera and Yuri had done the same. An interesting example of convergent designs even though much of the structure is quite different.

Cross-bracing lines connect truss arms to increase torsional stiffness. This design featured was missed when we did our background research, and it wasn't until we had implemented it ourselves that we found out Gamera and Yuri had done the same. An interesting example of convergent designs even though much of the structure is quite different.

Comment