Computational and Experimental Study for Reducing Forebody Wake Effect by Proper Designing of a Slit cut Square Parachute used for Sonobuoy Drop

This paper discusses the design of a square parachute based on classical approach, computational analysis and experimentation. This parachute will be used to drop directional sonobuoy on the sea to locate and classify the submarines. Design improvements are brought out by providing slits into a solid square canopy of parachute to bring in more stability and minimum drift during descend. Specifically, the effect of upstream sonobuoy, RANS model, suspension line length, canopy size and slit size in flow structure were considered. The predicted drag coefficients obtained from CFD for square canopy with slit-cuts compared with the results of wind tunnel experiment and found that the increase in the suspension-line length and/or of the surface area of the parachute canopy helps in better stability and results in the minimum drag loss.

Експериментальне визначення стану текстильних матеріалів десантної парашутної системи Д-5 серії 2 після тривалого зберігання. Повідомлення 1. Фактичний стан міцності текстильних матеріалів основного парашуту

The subject matter of the article is a comparative analysis of indicators of strength and elasticity of textile materials of the main parachute canopy before and after long-term storage. A simplified approach proposed by N. A. Lobanov and P.O. Fomichov was used, the coefficients of degradation of the strength characteristics of the textile materials of the main parachute of the D-5 landing parachute system of series 2 after its long-term storage were experimentally determined. These coefficients are defined as the ratio of the strength characteristics of individual elements of the parachute system in the design sections after the operation or long-term storage to their initial value adopted in the design of the parachute. The goal is to obtain an array of data to assess the state of the physical and mechanical characteristics of the main parachute materials. It is known that in the process of long-term storage there is a deterioration (degradation) of the strength characteristics of the strongest elements of the frame of the parachute canopy, lines, canopy fabrics, reinforcing tapes, etc. Further operation beyond the established period while maintaining sufficient safety factors is possible only with the availability of modern data. Tasks: to develop and test a method of sampling materials, experimentally determine the characteristics of materials, choose an effective algorithm for calculating safety factors. The following methods and equipment were used. The actual value of the indicators was established by destructive strength measurements. The methodology for preparing test samples of D-5 series 2 landing parachute systems, taking point and elementary samples of textile materials of individual elements of the parachute system in design sections for laboratory research to determine mechanical characteristics (strength, elongation, and air permeability) has been improved. The tearing machine is equipped with specialized clamping devices. The batch size was 25 parachute systems. The breaking load and the relative elongation were measured for slings and braids, for fabric - along the warp and weft, a total of 1250 elementary samples. Degradation coefficients were calculated. The array of empirical data was processed by mathematical and statistical methods of the Descriptive Statistics software package from the add-in of the MS EXCEL Analysis Package. The following results were obtained. In terms of breaking load, the fabric of the main parachute canopy slightly (up to 3 percent) exceeds the standard value. The elastic characteristics of the fabric fully meet the requirements - exceeding 1 ÷ 4 percent. During storage, the slings of the main parachute lost up to 21% in strength, but at the same time retained their elastic properties - exceeding up to 3 times. The tapes have satisfactory strength characteristics (exceeding from 3 to 12 percent), in terms of elongation at break, they have lost from 15 to 25 percent. Conclusions. The novelty of the results obtained is as follows: for the first time, the strength characteristics were measured and evaluated in the design sections of the fabric, reinforcing tapes of the power frame of the canopy and lines of the main parachute of the D-5 landing parachute system of series 2 on a large sample of 25 parachutes; it is shown that the obtained data will be correct for all parachute systems produced in 1973-1974.

Evaluation of Head and Body Kinematics Experienced During Parachute Opening Shock

ABSTRACT Introduction The U.S. Army conducts airborne operations in order to insert soldiers into combat. Military airborne operations are physically demanding activities with a unique loading environment compared with normal duties. A significant amount of research surrounding airborne operations has focused on assessing the incidence and type of associated injuries as well as the potential risk factors for injuries. During parachute opening shock and other high-acceleration events (e.g., fixed wing flight or vehicle crashes), the neck may be vulnerable to injury if inertial loads overcome the voluntary muscular control of the cervical spine and soft tissue structures. A recent epidemiological survey of sport skydivers showed that the neck, shoulders, and back were the most frequently reported sites of musculoskeletal pain. In addition, the survey indicated that wing loading (a measure of the jumper’s weight divided by the size of the parachute canopy) was a potential contributing factor for developing musculoskeletal pain. Recently, there have been efforts to measure the severity of parachute opening shock as an additional potential risk factor for injury; however, no studies have measured both head and body accelerations and no studies have measured head or body angular rate during parachute opening shock. The purpose of this study was to measure and characterize the accelerations and angular rates of both the head and body during parachute opening shock as well as investigate potential factors contributing to higher severity opening shock, which may link to the development of musculoskeletal pain or injury. Materials and Methods Data were collected from the U.S. Army Parachute Team, The Golden Knights, under an approved Medical Research and Material Command Institutional Review Board protocol. Subjects were instrumented with a helmet- and body-mounted sensor package, which included three angular rate sensors and three single-axis accelerometers each. Data were collected at 2,500 samples per second. Kruskal-Wallis tests were used to determine if helmet-mounted equipment (e.g., cameras), neck length, neck circumference, or wing loading (the ratio of jump weight to the size of the main parachute canopy) affected the accelerations or angular rates of the head or body. Results A total of 54 jumps conducted by 19 experienced free-fall jumpers were analyzed. For the head, the mean (± SD) resultant accelerations and angular rates were 5.8 (± 1.6) g and 255.9 (± 74.2) degrees per second (deg/s), respectively. For the body, the resultant accelerations and angular rates were 4.3 (± 1.5) g and 181.3 (± 61.2) deg/s, respectively. A wing loading above 1.4 pounds per square foot (lb/ft2) was found to have a significant effect on head (P = .001) and body (P = .001) resultant acceleration as well as body angular rate about the Y-axis (P = .001). Conclusions There is evidence to suggest that wing loading has an influence on individual head and body resultant accelerations. However, no significant effects were found for the other variables (e.g., neck length and circumference, helmet-mounted equipment, etc.). Future research should focus on identifying additional factors that result in changes in accelerations and angular rates of the head and body during parachute opening shock events.

A modern approach to the design of foreign landing parachute systems

Landing parachute systems are among the most demanded samples of parachute equipment. The purpose of the study was to find new principles for developing parachutes with increased stability according to the analysis of the results of numerical and experimental studies of canopies of various shapes. The paper proposes to supplement a traditional definition of the stability of a parachute system with the obligatory consideration of the system’s ability to maintain a given trajectory of movement with a neutral canopy, regardless of the change in the payload mass. It is the expanded concept of stability that is taken as the basis of the modern approach to the design of foreign landing parachute systems. The study substantiates the main criteria for choosing the optimal cutting shape for parachute systems of increased stability of various types at the stage of preliminary design. The results of numerical modeling of canopies are presented: quarter-spherical, hemispherical, polyconic canopies and a T-11 type parachute canopy. Based on the analysis of these results, the study was first to propose a hypothesis that a decrease in the intensity of vortex formation in the wake leads to an increase in the stability of the parachute descent. The results of numerical modeling of canopies of various shapes, as well as experimental studies of a model polyconic parachute, which prove the correctness of the proposed hypothesis, are presented.

Forebody Wake Effects on Parachute Performance for Re entry Space Application

Forebody generates its own wake that influences the performance of aerodynamic decelerators during the flights. Many parachute Jumpers have experienced the failure of an ejected pilot chute as the parachute canopy collapsed and fell back on the Jumper because of wake developed behind the Jumper. In the available literature, limited data is available to predict the exact loss of parachute drag in presence of the forebody (FB). The purpose of this paper is to generate a comprehensive aerodynamic data to study the behaviour of FB-parachute dynamics by conducting the wind tunnel experiments. Wind tunnel test has been carried out to establish the initial design parameters of aerodynamic parachute. The experiment was carried out on a scale down model of 20 degree conical ribbon drogue parachute and FB with and without each of them at a subsonic speed for studying dynamic stability characteristic for different orientation of FB. The test results indicate that to ensure adequate stability for the capsule to descend vertically at a low subsonic speed, a cluster of two drogue parachutes be used. Under such condition, the overall drag coefficient found to be above 0.50 providing not only a safe descends velocity but increasing reliability of mission as well.

Fatigue Degradation of the Ram-Air Parachute Canopy Structure

In this work, the authors continue researching issues related to fatigue of aircraft structures made of fabrics. Parachute systems are widely used in military, sport and recreational aviation. Braking parachutes as well as skydiving and troop parachutes are characterized by the repeated use of parachute canopies, which are exposed to wear and fatigue. Until now, parachutes were difficult to design aviation systems due to their complex and unsteady opening characteristics, large changes in the geometry of canopies, suspension lines and tape risers as well as exposure to stochastic atmospheric turbulence. The fatigue of the canopy fabric, suspension lines and tape risers is a problem that must be addressed by textile designers and designers of reusable parachute systems. The authors of this work demonstrate the complexity of operating a parachute in hard multiple use conditions and propose ways to extend the parachute’s service life without compromising safety.

УСТАНОВЛЕНИЕ ОГРАНИЧЕНИЙ ПО МАКСИМАЛЬНЫМ СКОРОСТЯМ ДЕСАНТИРОВАНИЯ С УЧЁТОМ ДЕГРАДАЦИИ ПРОЧНОСТНЫХ ХАРАКТЕРИСТИК МАТЕРИАЛОВ КУПОЛА ПАРАШЮТА. СООБЩЕНИЕ 1. ЗАВИСИМОСТЬ ПРОЧНОСТИ ПАРАШЮТОВ ОТ ДЕГРАДАЦИИ ПРОЧНОСТНЫХ ХАРАКТЕРИСТИК КОНСТРУКЦИОННЫХ МАТЕРИАЛОВ

It is introduced the concept of the degradation coefficients of the parachute canopy power structure materials strength characteristics. These coefficients are defined as the ratio of destructive loads after long-term operation or storage to the original, taken at the design stage. It is noted revealed the dependence of safety factors on degradation factors. It was determined the condition of safety factors equality after the long-term operation and during the design stage. It was shown that the ratio of maximum permissible loads is equal to the degradation coefficient. It was defined as the method for calculating the load on the parachute during deployment. It was applied to the simplified approach proposed by N. A. Lobanov. The following statement was determined according to this approach: a dynamic coefficient equal to two, a method for determining the dangerous section of the dome when assessing the fabric strength, the dependence of the speed at the moment of full filling of the parachute canopy from the generalized empirical coefficient. Characteristics of the standard atmosphere, depending on the height of throwing the aircraft are given by approximating functions. The movement of the body until the parachute opens is given in the form of differential equations with known initial conditions. The equation allows you to find the falling speed at the initial moment of the parachute opening, depending on the delay time. It is given the speed of steady free fall without the introduction of a parachute into the work and with a stabilizing parachute, the landing speed with the main parachute. The dependences of the maximum permissible loads on the dome at the opening moment on the strength degradation factors for the fabric of the dome, lines, and free ends of the suspension system are established. It was proposed the correlations for the maximum allowable speed at the time of the beginning of the parachute opening on the requirements of strength. This speed determines the maximum allowed landing speed for a particular type of parachute after long-term operation or storage.

Numerical and experimental investigation of damage effect on a hemispherical parachute performance

The effect of the canopy fabric damage on parachute performance has been investigated numerically and experimentally in the present paper. For this aim, first, flow structure around the parachute canopy has been studied for both damaged and undamaged parachutes. Then, the drag coefficient as the main characteristic of a parachute performance has been examined and compared experimentally and numerically in four Reynolds numbers. Experimental tests for undamaged and damaged canopies have been carried out in an open-circuit wind tunnel laboratory at the velocities 15, 20, 25, and 30 m/s. In order to measure the drag force, a valid tensile load-cell has been used. Also, the smoke flow visualization has been utilized to find the flow behavior at different regions of the parachute. For the numerical simulation, an incompressible pressure-based CFD code using the finite volume method has been applied to solve the complex turbulent flow field around the inflated parachute canopy. To increase accuracy of the numerical simulation, the permeability boundary condition on the parachute canopy has been implemented and its effects have been considered on the flow field. The numerical results indicate that the permeability assumption on the canopy makes desirable results compatible with the experimental ones. Moreover, comparison of the results between damaged and undamaged canopies demonstrates significant differences in the streamlines, pressure distributions, and drag coefficients. As the reliability is the main criterion for the parachute system, investigation on the damage effects would be useful and it has been considered in the present work.