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PERSONAL TRANSPORT: GROUND, WATER, AIR
Paragliding for beginners. Personal transport
Directory / Personal transport: land, water, air At first glance, what could be simpler than a training paraglider? Low wing aspect ratio, thick profile, short lines. All this small set of characteristics, it would seem, is obliged to provide the novice pilot with a calm and comfortable flight. That's how it is, but, unfortunately, a beginner quickly gets bored with just planning, he wants to get higher and higher. And the struggle between the flight qualities of the device and flight safety begins. The clash of these conflicting requirements has given rise to many different models of paragliders used for training. In the CIS, poverty is often taught on anything. Domes, which were considered semi-sports a few years ago, migrated to the rank of training ones. Few are engaged in the creation of special paragliders. It is much more interesting for domestic designers to experiment in the sports class of devices - in the eternal race of speeds and quality. Even worse, if an unsuccessful brainchild of unfortunate designers is presented as a training dome, which did not provide the desired record-breaking flight characteristics and, therefore, was transferred to the rank of a training one (naturally, after some refinement). At the end of the winter of 1996, Paraahavis decided to take a different approach to the creation of a training apparatus, using a new series of profiles obtained in the course of work on a Competition class paraglider. The profiles of this series have an extended range of permissible angles of attack, that is, they resist folding the canopy at low angles of attack and its stall at low flight speeds. "Commander" (as the new paraglider was called) exceeded the wildest expectations of the designers. Its canopy is easy to lift and hovering over the pilot, providing him with the few seconds he needs to take off. During the takeoff run, the canopy occupies a stable position above the pilot, and its rolls are easily eliminated by running up and toggle. Flying on the "Commander" is a pleasure. Overhead - a powerful monolithic wing without any prerequisites for folding. We evaluated the "foolproofness" of this paraglider after a novice in one flight hung for a long time with fully tightened toggles, and in another he swung the canopy in pitch in a way that even test pilots do not swing. And nothing, flies! With the advent of the "Commander" it became easier to teach and learn to fly. More and more people prefer this reliable and quiet machine for amateur flights on weekends and holidays. Moreover, the quality and speed allow you to make not only soaring, but even cross-country flights.
Basic technical data of the paraglider "Commander" And now more about how the paraglider was designed. Where do they usually start? First of all, they set a task or formulate the basic requirements that a training paraglider must meet. And they are the following:
As always in aviation, these requirements are very contradictory. The first and second points are easy to provide with a low elongation and a thick profile, but this is unlikely to satisfy the rest of the requirements. So the designers had to sweat. We started by choosing a form in the plan. Here, the ellipse (minimum inductive resistance) or a figure close to it in shape (Fig. 2) is the best fit. The area of the paraglider was chosen taking into account the specific wing load q. According to statistics, there is a range of values q(3 - 3,8 kg/m2) used for training paragliders. At the same time, the limits of the range serve as a compromise between the rate of descent (more area - less speed of flight and descent) and the stability of the paraglider (less speed - less pressure in the canopy and it loses stability more easily). The take-off mass of the pilot-paraglider system is determined by the formula: Mvzl. = M0 + Msn (1), where: M0 is the mass of the pilot, Msn is the mass of the equipment (approximately 15 kg). Based on the pilot mass of 80 kg and the specific load of 3,4 kg/m2 (middle of the range), the wing area of the paraglider was obtained:
The choice of aspect ratio (the ratio of the square of the wing length to its area) significantly affects the characteristics of the paraglider: an increase in aspect ratio reduces the inductive drag and leads to an increase in the aerodynamic quality of the wing, but at the same time, flight safety is reduced due to the fact that a narrow wing is more prone to folding, and also complicates start and landing. It was decided to stop at the elongation λ= 4,8. Although it is large, we hoped to achieve good stability of the wing and resistance to its folding due to the new profile. Wing length (L) was determined by the formula:
Half an ellipse was taken as the initial shape of the wing in plan, the area of which is equal to:
where a, b are the values of the major and half of the minor axes of the ellipse. From here, assuming a = L, we found the value of the central chord b:
The number of ribs in the wing determines the quality of its surface, the speed of filling the canopy during folding and the manufacturability of the paraglider in production. After analyzing various design options with all working (power) or auxiliary ribs (Fig. 2), it was decided to stop at the first option, as more consistent with the concept of a training paraglider, that is, make 37 sections (38 power ribs) and only use two on consoles auxiliary ribs (Fig. 4).
The length of the lines affects the strength of the paraglider and the tension of its surfaces. The branching scheme of the lines determines their total length. An analysis of possible branching options, subject to the minimum total length of the lines, showed that the optimal option is when the lines of the first two lines ("a" and "b") of each half-wing are reduced to the corresponding separate free ends (Fig. 1), and the lines "c" and "d" - to the general one (Fig. 3).
The most important work in the design of the dome is the aerodynamic calculation. The new profile (Fig. 5) with the characteristics of Xc max = 28% and Cmax = 17%, created on the basis of a well-proven profile from the Grand paraglider, has a characteristic "belly". It is stable at low angles of attack, which is very important for the safety of the paraglider. The stall characteristics of the profile also turned out to be successful.
Painstaking work was carried out on the distribution of geometric and aerodynamic twist, as a result of which a compromise was found between stability, controllability and quality. Computer programs were used to obtain patterns for the details of the dome. So what happened?
Characteristics of the seams used when stitching tapes LTK-44-1600
The paraglider wing is made of a special airtight fabric and is sewn together from two panels (Fig. 4). Each section of the dome has an upper, lower panels and ribs. On the front edge, the panels are not connected, forming air intakes. To redistribute air along the length of the wing in case of uneven filling, the ribs have holes, and in the attachment areas of the lines and along the leading edge they are reinforced with dacron stripes. Slings (Fig. 9) are made of SVM cord in a nylon braid. Their ends are loops 55-70 mm long. Slings were mounted with a "noose" from the upper tier to the lower one (Fig. 1). Moreover, their diameter increases from 0,8 mm to 1,6 mm in the same direction. The slings of the lower tier are attached to the rings of free ends made of LTKP-25-1000 tape and having three rows. The control lines are fixed on one line tied to the toggle. The risers are equipped with "trim tabs" and an accelerator, allowing you to change the flight speed in a wide range. However, they are recommended only for experienced pilots. At a certain stage in the development of paragliding, it became clear that the desire to fly faster, higher and farther than anyone else can not be provided only by the design of the paraglider wing. The question arose of creating a new suspension system that would meet the requirements of pilots, primarily in terms of ergonomics and flight safety. This entailed the inclusion of a number of new elements in the suspension system and the modernization of traditional units. Depending on the class, a modern harness system consists of a harness, a seat, pockets for equipment and equipment, a protection and rescue system (Fig. 6). The harness (Fig. 7) connects the pilot to the paraglider or rescue parachute, if used. Its main element is the "frame", sewn from durable nylon ribbons, which includes: the main circular strap, back-shoulder, leg and waist girths, chest jumpers. A circular strap through two carabiners (like climbing) is connected to the free ends of the paraglider. What matters here is the distance between the riser attachment point and the pilot's center of gravity. Usually, they strive to maximize it, thereby reducing the moment that overturns the pilot back when working with the accelerator or when flying in a turbulent atmosphere. The seat is designed to evenly distribute the load on the pilot's body, provide comfort and protect him in a collision with the ground. It can accommodate pockets, as well as protection and rescue systems. The position of the pilot that is convenient for work, in which he experiences the least muscle tension and more easily tolerates the effects of overloads (accelerations), is when the body is tilted back at an angle of 16-18 °. The width of the seat is calculated according to the maximum width of the human pelvis, taking into account some margin for clothing. On average, it is 390 - 450 mm. The shape of the seat back, its height and width ensure the correct and comfortable position of the pilot. The seat together with the backrest are covered with soft shock-absorbing embossed material to eliminate the pressure of the harness system on the pilot's body and improve ventilation in the back area. A paraglider is an aircraft. Therefore, he, like most of his "big brothers", is supplied with protection and rescue systems. They are divided into active and passive. The former include rescue parachutes, pneumatic shock absorbers filled with compressed air after the pilot puts the parachute into operation. And to the second - a board and a rigid seat back, pneumatic shock absorbers filled before the flight. The "Commander" uses suspension systems of the "Classic" or "Profi" type, which meet the highest requirements to the maximum. That, in fact, is all. At first glance it seems that this device is not very complicated. But to anyone who decides to make a paraglider on their own, I strongly recommend showing it to specialists before testing. And it would be nice to make the first flights under the supervision of an instructor. Author: I.Volkov
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