This invention was not produced under federally sponsored research or development.
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Ornithopters, or flapping-wing aircraft, are becoming popular among radio-control hobby enthusiasts. Their appeal lies in the fact that they fly like a bird. Many hobbyists regard this as an exciting form of recreation. Some of the barriers to further development include poor efficiency, difficulty of customizing the models or developing new designs, and poor resemblance to real birds. Additionally, typical ornithopter steering mechanisms are fragile compared with airplane steering mechanisms.
U.S. Pat. No. 6,550,716, assigned to Neuros Co., Ltd., describes a typical radio controlled ornithopter. Three aspects of the ornithopter design are of particular interest here: 1) the wing structure, 2) the steering mechanism, and 3) the appearance and construction of the body or fuselage.
1) Wing Structure. The wing structure of U.S. Pat. No. 6,550,716 assigned to Neuros Co., Ltd., consists of a fabric sail with battens. The wing must be able to change shape aeroelastically, taking on a cambered shape as it passes through the air, but it must not be overly flexible. Therefore, the wing is braced by a semi-flexible rod, introduced in U.S. Pat. No. 2,859,553 (P. H. Spencer). The stiffness or diameter of this bracing rod must be correctly chosen in order to achieve the correct degree of flexibility. The bracing rod is heavy, and it interferes with the profile of the wing, causing air resistance.
2) Steering Mechanism. U.S. Pat. No. 6,550,716 (Neuros Co., Ltd.) includes a steering mechanism that is typical of radio-controlled ornithopters. U.S. Patent Application #2002/0173217 by Andrew Sean Kinkade describes a similar system. The aircraft has a tail controlled by two hobby servos. One servo moves the tail up and down. The other servo moves the tail left and right, for steering. Maneuverability of the aircraft is similar to that of an airplane with rudder and elevator controls. However, the tail has to be mounted directly onto the servo output arm, causing the servo to break easily.
3) Appearance of the Fuselage. Most radio-controlled ornithopters have used a body frame that has been milled from a flat sheet of composite material, such as fiberglass. This technique simplifies the construction, but it results in a thin, flat, body, which does not resemble the three-dimensional body of a real bird. Moreover, all of the radio system components are mounted externally on the flat plate fuselage. A realistic appearance would require a three-dimensional, hollow body, with components mounted inside. Although the ornithopter of U.S. Pat. No. 6,550,716 (Neuros Co., Ltd.) provides a flexible plastic covering over the flat plate fuselage, this must conform to the shape of the underlying frame, and there is little opportunity for hobbyists to customize the appearance.
The claimed invention is an ornithopter that has an improved, more efficient wing, a steering mechanism that reduces the likelihood of damage to the servos, and a modular design allowing more control over the external appearance of the model. The modular design permits the individual hobbyist to customize the model, and it also creates the opportunity for hobby kit manufacturers to produce additional body designs without having to take on the complex task of designing a new flapping mechanism.
In the preferred embodiment, the present invention consists of an ornithopter, having: 1) a modular design, 2) cable-tensioned wings, 3) and a steering mechanism that reduces the likelihood of damage to the servos by separating them from the tail. These three features may be used in their six other combinations as well, such as an ornithopter that lacks the modular design, but has the cable-tensioned wings and improved steering mechanism. Another alternative embodiment is a free-flight (not radio-controlled) ornithopter, which uses the cable tension system but has no steering mechanism. Certainly as well, the modular design could be used in the absence of the other two improvements. Indeed, the modular approach favors experimentation with various other steering mechanisms, since it becomes possible to try new ones without having to build a whole new ornithopter.
Typical ornithopter wings consist of a thin membrane on a frame of some strong, lightweight material. The leading edge of the wing surface is attached to a strong spar, which drives the flapping of the wings. Often, a bracing rod, arranged diagonally across the wing, prevents the wing from being too flexible in torsion. The diagonal brace increases the torsional stiffness of the wing by limiting the bending of the leading edge wing spar and by directly supporting the wing surface. However, the diagonal brace creates a ridge across the wing surface, which interferes with the ideal, cambered cross section of the wing, and increases air resistance.
In the prior art, the tail is typically mounted directly onto one of the servos, and that servo provides for the rotation of the tail about its longitudinal axis. The other servo tilts the rotation servo up and down, the tail along with it. In the event of a crash, the rotation servo can break easily, because the shock load on the tail is transferred directly to this one servo. In the present, improved mechanism, the shock load on the tail is shared by both servos, and conveyed through a linkage, allowing some of the energy to be absorbed before reaching the servo. This reduces the risk of damage to the servos. Since the servos are not subjected to as much stress, lighter servos can be used, which benefits flight performance. Also, the use of more durable and more expensive metal-gear servos might be avoided, and that would lower the cost.
The output of each bellcrank contains a ball and socket joint (19). A ball with a hole through it and typically made of steel or other hard material is free to rotate within a spherical cavity of the bellcrank arm. The ball is fastened to the tail base piece (20) by a machine screw or other fastener (21), allowing the ball to slide along the shaft of the fastener. Alternatively, the ball may be fixed, taking advantage of the flexibility of the parts to provide the required range of motion, or the ball could be eliminated, in favor of a simpler coupling (e.g., screw fitting loosely in hole). The latter will increase play.
The tail base piece has a hole through its longitudinal axis and pivots about the rod (22), which is secured to the body by a fork (23). The fork allows the rod to swing up and down. The fork arrangement could be replaced by some other method of hinging the rod onto the body. When both bellcrank outputs are raised, together, the fork and the tail base piece swing upward. When both bellcrank outputs are lowered, together, the fork and the tail base piece swing down. This provides an up-and-down motion of the tail (7). Moving the bellcranks in opposite directions causes the tail base piece to rotate about the rod. This provides the steering motion of the tail.
Additional variations are possible, such as using ball-link connecting rods to link the servo to the bellcrank, or using ball bearings in the mechanism to reduce friction. In the preferred embodiment, these variations are not depicted, because they would add additional complexity, weight, and cost.
In the preferred embodiment, the wing membrane is entirely supported by a structure attached to the drive unit. Alternatively, the body may include a hard point for attaching the rear edge of the wing membrane (8). This may consist of a reinforced hole into which a screw can be inserted, to secure the wing. Alternatively, the wing membrane may be hooked onto a post projecting from the body, or secured with any other appropriate type of fastener.
This application claims the benefit of Provisional Patent Application Ser. No. 61/278,126, filed Oct. 5, 2009 by the present inventor.
Number | Date | Country | |
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61278126 | Oct 2009 | US |