Doug Riley
Platinum Member
- Joined
- Jan 11, 2004
- Messages
- 6,968
What J-John said. Watch that gear geometry.
Bensen's original landing gear configuration (the "tail sitter") is very right, IMHO. The aircraft sits on its nosewheel and mains with the pilot in the seat, with about 30-40 lb. weight on the nosewheel. As the rotor spools up early in the takeoff roll, the aircraft soon rocks back, increasing the disk AOA and assisting with rotor spinup. The rock-back, IIR, is about 5-6 degrees, or around 6" at the tailwheel.
Some people find that the fact that a Bensen gyro sits on its tailwheel when parked to be undignified (much as they find the plywood scrub brake, overhead stick, or "lawnchair" seat undignified).
Those who have varied the Bensen design have sometimes altered its landing-gear formula in a way that discards its advantages. For example, the stock Gyrobee has very limited rock-back -- only some 3"-- perhaps because of the "stacked' 2x2 keel/tail tubes. This reduces the available disk AOA during the early part of the takeoff roll, when you could use more to bring up RRPM.
Others have placed the main axle back so far that rock-back is delayed or eliminated. If you happen to have a full- RPM prerotator (as the McCulloch J-2 and Air & Space 18A do) then it doesn't matter. With the typical partial-RPM (or zero!) prerotator found on homebuilt gyros, however, eliminating rock-back is not helpful.
Bensen's original landing gear configuration (the "tail sitter") is very right, IMHO. The aircraft sits on its nosewheel and mains with the pilot in the seat, with about 30-40 lb. weight on the nosewheel. As the rotor spools up early in the takeoff roll, the aircraft soon rocks back, increasing the disk AOA and assisting with rotor spinup. The rock-back, IIR, is about 5-6 degrees, or around 6" at the tailwheel.
Some people find that the fact that a Bensen gyro sits on its tailwheel when parked to be undignified (much as they find the plywood scrub brake, overhead stick, or "lawnchair" seat undignified).
Those who have varied the Bensen design have sometimes altered its landing-gear formula in a way that discards its advantages. For example, the stock Gyrobee has very limited rock-back -- only some 3"-- perhaps because of the "stacked' 2x2 keel/tail tubes. This reduces the available disk AOA during the early part of the takeoff roll, when you could use more to bring up RRPM.
Others have placed the main axle back so far that rock-back is delayed or eliminated. If you happen to have a full- RPM prerotator (as the McCulloch J-2 and Air & Space 18A do) then it doesn't matter. With the typical partial-RPM (or zero!) prerotator found on homebuilt gyros, however, eliminating rock-back is not helpful.