Abstract: A radio controlled helicopter is provided which eliminates or simplifies forward/reverse flight control for safe and easy indoor operation. Embodiments include a helicopter having a pair of counter rotating rotors which are driven at the same speed, a vertically aligned tail rotor driven by a reversible motor for controlling yaw, and a mass, such as a power supply battery, mounted for changing the center of gravity of the helicopter to adjust the tendency of the helicopter to move in a forward or reverse direction. The mass is either rigidly mounted, so that the helicopter is always moving forward during flight, or adjustably mounted so that the helicopter's forward or reverse direction can be adjusted prior to or during flight. A protective cage is provided to protect persons from injury from the rotors and to prevent damage to the rotors due to contact with objects during flight.

Abstract: A hobby aircraft arranged for vertical flight aerodynamics. A substantially-planar body is symmetrical about a central axis. An upper blade is fixed to the bottom of the body. An elastic band is aligned with the central axis for powering a lower blade that is in spaced relation to the upper blade. Rotation of the second blade is controlled by means of a locking mechanism to assure that gravity alone powers the final stage of aircraft flight.

Abstract: A method and apparatus for measuring the linear movement between first and second substantially planar surfaces and is useful, for example, in an automatic focusing system of a photographic enlarging or printing machine. The linear movement between a first plane, e.g., a lens plane and a second plane, e.g., a film or print plane, at a single point, e.g., the lens optical center, is determined by measuring the linear movement of two diametrically opposed points proximate to the lens plane equidistant from the lens optical center. The two measured distances are then averaged to yield a distance measurement at the lens optical center corrected for any deflection of the lens plane.