|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
MODELING
Wing propeller. Tips for a modeller
Directory / Radio control equipment In a modern seaport, you can see a picture that looks strange at first glance: a ship moving through the water ... sideways. If the water is clear and you can look under the stern, then you will be even more surprised if you do not find a rudder on the ship. However, despite this, the ship is free to maneuver. Before you is nothing but a vessel with vane propellers, replacing both the propeller and the rudder. The vane propeller is not like other propellers familiar to us - a propeller or a paddle wheel. Its blades are slightly reminiscent of oars placed vertically.
The vane propeller (Fig. 1) consists of several vertical blades located at equal distances around the circumference of the rotating disk. This disk is installed flush with the ship's plating in a round hole in the bottom of the ship. Only the propulsion blades protrude beyond the ship's hull, creating a thrust force, and all auxiliary parts that drive the disk with blades and connect it to the ship's hull are inside the hull. On what principle is the operation of a vane propeller based? The blades of the vane propeller during the rotation of the disk make two movements simultaneously: they rotate together with the disk around its axis, and each blade rotates around its vertical axis then in. one way, then the other, without making a full turn. Due to this, when the disk rotates around its axis, each propeller blade turns its leading edge outward in one half of the circle of rotation and inward - in the second half of the circle. Since the blade moves in the water all the time with the same edge forward, to create a greater thrust force and greater streamlining, it is made in the form of an aviation wing. That is why the mover is called winged. In order for the blades to move in the water all the time with the same edge forward, all the blades of the vane mover are connected by a thrust to one point, the so-called control point N. Each blade is always located perpendicular to the line connecting point N and the axis of the blade. To understand the principle of operation of the propeller blades, it is quite enough to give the following simplified diagram (Fig. 2).
When the propulsion disk rotates, the blade enters the water at some angle to the tangent to a given point of the disk circumference, and water will press on it with a force R, which, according to the rules of the parallelogram of forces, can be decomposed into two force components (Fig. 2, I): P is the blade thrust force outward from the center of the disk, and W is the blade drag force. The direction of the jet of water thrown off by the propeller is opposite to the stop force. At point III (Fig. 2), a similar position will be created, only the angle of attack of the blade will be negative, and therefore the stop force will be directed to the center of the mover O and will add up with the stop force of the first blade, creating a full stop of the mover, moving the vessel and always directed perpendicular to the segment ON. At the points (Fig. 2, II and IV) the blade planes will be parallel to the tangent to the disk circumference and will not create a stop force. With the help of a special device, the control point N can be set to any position relative to the center of the drive disk O, thereby changing the direction of the water jet thrown by the mover, and, consequently, the stop of the mover. If you put a point N above the center of the mover O (Fig. 3, 1), then the planes of all the blades will be parallel to the tangents to the circumference of the disk, drawn at the points where the axes of the blades pass. The stop force in this case is equal to zero, and, despite the fact that the drive disk will rotate, the ship will not budge. By moving the point N to the left of the center O (Fig. 3, II), we give the vessel a forward move, moving to the right (Fig. 3, IV) - reverse, and by moving the point N forward from the center of the mover, we will force the ship's stern to move to the right ( fig. 3, III), etc. Thanks to this, a vessel with a vane propeller can move forward and backward and change its direction of movement without a rudder, and if two propellers are put on the vessel, it can even move sideways.
Carefully examining Figure 3, you can see that the propeller rotates all the time in the same direction, and the ship moves in different directions. Using this property of the mover, it is possible to install simpler engines on ships - non-reversible, that is, not changing the direction of rotation. Such engines are lighter in weight compared to reversible ones, simpler in design and maintenance, and much cheaper than reversible ones. However, vane propellers also have disadvantages, the main of which is the difficulty of transferring rotation from engine to propeller, due to which high-power engines (over 5000 hp) cannot be used with vane propellers, and this limits the size of ships on which such propellers are used . Nevertheless, the main properties of ships with vane propellers - the ability to move sideways, turn on the spot, quickly change direction - make such ships indispensable when sailing in "narrows": in canals, on rivers and in ports. Vane propellers are successfully used on river passenger ships, on port cranes and tugboats; experiments are being carried out on the use of vane propellers on fishing trawlers. On ships, vane propellers are installed in places that are most convenient for a given type of vessel. On passenger ships, propellers are installed in the stern, on tugboats - in the stern or in the bow, on port cranes - in the middle of the hull. A tugboat with a propeller installed in the bow of the vessel can be taken as a sample model of a vessel with a paddle propeller. Such a tug (its theoretical drawing is shown in Fig. 4) is 24,6 m long and 7,6 m wide
had a draft of 3 m (with propeller blades of 3,8 m) and developed a speed of 10,3 knots (19,9 km / h) with an engine power of 552 kW (750 hp) from 320 rpm; the number of revolutions of the propeller was 65 per minute, and its diameter was 3,66 m.
The GDR magazine "Modelbau und Basteln" No. 10 of 1960 gives the following description of the propeller model. A round casing 5 is attached to the bottom of the vessel (Fig. 1), inside which there is a propeller rotor 2 with upper and lower disks 3. Axes 3 are passed through the rotor disks 4, to which blades 5 are attached. A tubular propeller shaft 6 is passed through the upper disk of the rotor, which is attached to the disk from below with the help of a flange. Then the shaft passes through the figured cover 7, attached to the casing 1. On top of the cover, an adjusting ring 8 is put on the shaft and pressed against the shaft, and a drive pulley 9 is put on and attached to the shaft over the adjusting ring. A drive belt 10 is put on the pulley, coming from the drive pulley 11 sitting on the shaft 12 of the engine 13 (Fig. 6). The upper end of the shaft 12 rotates in a bearing 14 attached to the deck of the model.
A steering shaft 6 is passed through the tubular propeller shaft 15, on which an adjusting ring 9a is put on top of the pulley 8. A worm wheel 16 is mounted on the upper end of the steering shaft, driven by a worm drive from a small electric motor 17. The worm gear is selected so that the worm wheel 16, and with it the shaft 15, can do 8-10 rpm. Then the model will be able to change the course from "full forward" to "full reverse" after 6-8 seconds. An eccentric 15 with a pin 18 is mounted on the lower end of the steering shaft 19. The ends of the rods 20 going to the cranks 21 turning the blades are put on the pin. On the axis 4 of the blades 5, bushings 22 are put on, on which the cranks are held. With such an arrangement of the eccentric 18 (Fig. 7), the model will move forward and turn in the specified direction. To change the speed of movement and stop the ship is possible only by changing the number of revolutions of the engine or stopping it.
This is because the value of OA (in this case, the distance from the axis 15 to the pin 19) remains constant all the time. It is impossible to change the value of the stop by moving the point N closer to the center O or to the very center O, and thereby stop the movement of the vessel (Fig. 3, I). The ON value in this model is taken within 1/6 - 1/3,5 of the radius of the drive disk. With a larger or smaller eccentricity, the angle of attack will be either too large or too small, so the blades will not create the necessary stop force. The propeller blades are made of thin metal (Fig. 8), and the front roller, on which the metal is bent, is taken twice as thick as the axis of the blade.
In the description of this model, no recommendations are given regarding the number of blades, their size and shape, so it is better to refer to the calculations of real propellers. For simplicity of the model, the number of blades is best taken equal to 4, since for real propulsors the number of blades varies from 4 to 8. The length of the blade is determined by the size of the diameter of the disk of the propulsor (about 0,7 of this diameter), and the width of the blade is taken within 0,3 ,XNUMX of its length. This width is taken in the uppermost part of the blade, since the shape of the blade is taken as half an ellipse with semi-axes equal to the length of the blade and half of its greatest width (width at the root). The value of the full stop of the propellers T is expressed by the formula: T=F*D2*n2, where: F is the total area of the blades, D is the diameter of the propeller rotor, n is the number of revolutions of the propeller From this it can be seen that it is most advantageous to take the largest possible diameter of the rotor, since with its increase the area of the blades also increases. For example, on the tug shown in Figure 4, the diameter of the propeller rotor is almost half the width of the tug. In the technical circle, you will be able to make models of the mover with full control adjustment, similar to that used in real movers.
In such a model (Fig. 9), to move the pin 19 to a position above the center of the mover (that is, so that the blades do not have a stop and the ship stops) or to move to some intermediate position between the extreme and central (to change the angle attacks of the blades and the magnitude of the stop), the steering shaft 15 is also made tubular and an adjusting shaft 23 is passed through it, at the upper end of which a worm wheel 24 is mounted, driven by a second small electric motor 25 using a worm 26 (Fig. 10). At the lower end of the adjusting shaft 23, a bracket 28 is attached, in which the eccentric pin 19 moves with the help of the slider 29. The eccentric 18 is made composite. The steering shaft 15 turns the eccentric together with the bracket 28, and when the adjusting shaft 23 is turned, the eccentric 18a begins to turn and move the slider 29 with the pin 19 along the bracket 28, setting it to the desired position (Fig. 11, 1-4). To simplify, the eccentric 18 can be made not composite, but in the form of a fork (Fig. 11, 5).
Due to the fact that the finger 19 must also move along the rods 20, these rods are made in the form of forks (Fig. 12).
The model of a vessel with a vane propeller must have either software control or radio control, since otherwise it will be impossible to identify all the qualities of a vane propeller on the go. Try to build a model of a vessel with a vane propeller in your circle and write to the editors what you got out of it. Author: N.Grigoriev
A New Way to Control and Manipulate Optical Signals
05.05.2024 Primium Seneca keyboard
05.05.2024 The world's tallest astronomical observatory opened
04.05.2024
▪ Smartphone Gionee Elife S5.5 thickness 5,6 mm ▪ Consciousness as a balance of interaction between neurons ▪ Mystery of natural mushroom factory solved
▪ section of the site Home workshop. Article selection ▪ article Man to man is a friend, comrade and brother. Popular expression ▪ Article What sports are considered Olympic? Detailed answer ▪ Bamboo article. Legends, cultivation, methods of application ▪ article Antenna matching device. Encyclopedia of radio electronics and electrical engineering ▪ article Three fountains. physical experiment
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
We recommend interesting articles Section 
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page