Abstract: Double propeller for propelling aircraft, with two coaxially and axially offset propellers that can be driven separately by associated drive mechanisms through a central shaft and a hollow shaft. To reduce noise and maintain safe operation even when one propeller drive breaks down, the propellers rotate in the same direction and can at at least one prescribed angle of rotation to each other be coupled together in such a way that they cannot rotate in relation to each other by means of a clutch that can be disengaged.

Abstract: A cartesian toy including at least one partly transparent liquid container in which there is at least one freely floating body movable by buoyancy changes. This is variable in that an air bladder located in a cavity of the floating body casing is compressible to a greater or lesser extent by the liquid pressure in the liquid container being varied by a pressurizing device. When this device causes expansion of the air bladder or the air zone located in the floating body, liquid flowing out of the floating body casing additionally imparts to the floating body or parts thereof by recoil or reaction force an in particular horizontally directed acceleration or movement. Also, particularly sized and arranged casing parts on the floating body cause this body to move in one rotary direction or the other when the casing parts contact the container or objects in the container.

Abstract: A toy helicopter rotor comprises a hub with rotor blades radiating therefrom. The hub comprises upper and lower hub parts having formations which releasably lock the parts together upon relative turning therebetween. Each blade has a root which is received in a complementary recess in the lower hub part and is trapped by the upper part, whereby the blades are secured to the hub. Projections on the blade roots retain the blades against radial, lateral and torsional movement and prevent them flying out of the hub in use.