Design and testing of an ultra-low-power persistent parachute use logger

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Abstract

After a sufficient amount of use under certain conditions, parachutes wear out and can no longer be safely employed. A simple and effective indicator of the remaining life of a parachute is the number of times it has been used, surviving opening shock, canopy inflation, transient parachute dynamics, and low velocity flight to the ground. This paper documents a small electronic device that automatically detects and logs each time a parachute has been used. Hardware and software that enables this device are described and data from bench and flight testing are detailed to highlight detection algorithm performance and long-term power consumption. Data shows that the proposed device accurately and reliably identifies individual parachute flights and that the ultra low power nature of the design permits the device to be continuously on for a period of time that is greater than the life span of the parachute. Thus, the device can be installed in the canopy during the fabrication process without the need for recharging or replacement of batteries.

Introduction

Parachute canopies are complicated systems. When used, they rapidly unfold and inflate. During this deployment process, the lines, fabric, and seams become highly loaded. Parachute components can be damaged by high or low temperature, high humidity, UV exposure, pests, chemicals, mechanical wear during use, and more. Inspection before use is critical for safety, but undetected loss of strength due to long-term degradation presents a challenge. Most parachutes are designed to be reusable and repairable. Each deployment of a parachute loads the components and degradation can occur from the stress. In addition, each jump of a parachute may expose the parachute to indirect damage. For example, after landing the parachute may be damaged by thorns or debris may accumulate in components and increase wear. Therefore, a key indicator for a parachute's remaining life is the number of jumps (for personnel parachutes) or drops (for cargo parachutes) on it. Currently, the number of times a parachute has been used is recorded in a log book, either paper or digital, with data entered by a pilot or maintenance personnel. The problem with these existing methods is that they depend on a human to enter data into the system in an accurate and reliable manner. In practice, this does not happen, leading to inaccurate data on canopy usage. This leads to canopies being used past their intended life and presents a safety problem. On the other hand, if a simple time-since-entering-service approach is used to determine lifespan, this can lead to canopies being removed from the fleet too early which increases life cycle cost.

A substantial amount of work has been reported on the wear of parachutes due to an array of effects. Weiner performed research on the useful life of nylon parachutes and parachute materials and recognized that UV radiation, storage while packed, mechanical wear, deterioration from atmospheric chemicals, and fatigue from repeated loading all limit the lifespan of nylon parachutes [1]. Templeton studied the effects of chemicals on the properties of parachute fabrics [2] while Figucia and Wells also analyzed the strength losses in nylon parachute materials with time, exposure, and use [3]. This work identified the contemporary parachute life limits of 10 years or 100 jumps on a canopy. Later, George and Browne performed non-destructive testing of nylon 6,6 to understand its degradation over time and showed estimates on strength losses from degradation due to storage and use can be determined by accelerated thermal ageing [4]. Maire and Wells studied T-10 harnesses, risers, and the T-10 troop chest reserve parachute canopies and determined sufficient strength remained at the end of their initial 10-year service life to extend for 3 more years for the harnesses and risers and 2 more years for the T-10 reserve parachute canopy [5]. Wells performed a similar study on the T-10 main parachute and determined that the 10-year lifespan for the T-10 main parachute could also safely be extended another 2 years [6]. Wells noted that there was poor data to connect jump history to the condition of parachute materials. More worrying, he noted that “many of the logbooks for parachutes in service were replacements in which ‘recorded jumps’ were based in large part by an assumed 10 jumps per year rather than the actual number.” Ericksen and Whinery studied nylon and Kevlar test samples, including a 29-year-old nylon parachute [7]. For this work, the parachute had never been used, was stored in the absence of sunlight, but had exposure to atmospheric moisture and pollutants. The parachute was occasionally exposed to high and low temperatures within the range of -50 C to +70 C. They measured no strength loss, shrinkage, or other signs of degradation on the suspension lines or ribbons. They also found no evidence of material degradation on 14-year-old nylon or Kevlar fabric samples stored in four different climatic zones which implies that disposing of parachutes simply due to age is not necessary. Egglestone and George performed accelerated aging testing of nylon parachutes by exposing samples to sustained high temperatures and to high UV exposure from sunlight in separate experiments [8].

UV exposure was particularly damaging, though short-term exposure during field operations would not be expected to lead to large strength losses. Segars studied the degradation of parachutes to attempt to extract the effects of age from the combined effects of age with multiple regression on data where parachute usage counts were known and found that age contributed only 1/10 as much as the number of jumps to strength loss [9]. The work notes that the number of jumps is by far the most significant factor in the degradation of nylon 66.

The exact process of how a parachute degrades over time is a complex phenomenon, and inspection by trained and certified specialists is the gold standard for determining flight worthiness of a parachute. A useful surrogate for determining the remaining life of a parachute that is used in practice is the number of times it has been flown. Some commercial devices exist which log the number of jumps completed by a parachutist, but they are designed to track the person's jumps, not the use of their gear. For parachutists with more than one rig, these are not the same. In addition, those commercial devices have limited battery life, and typically require the user to set them up before each jump. A summary of these devices is shown in Table 1. This paper details a parachute use counter that includes design, modeling, and testing of the device with a focus on the identification algorithm and device power consumption. Both bench and flight test results are presented to demonstrate the performance of the system.

Section snippets

Design considerations and description

The ideal parachute use logging device would be small and permanently mounted to the parachute. It could be directly sewn into the canopy or attached to a riser. The device would be sufficiently small so that it does not interfere with the operation of the parachute in any way. It would never need maintenance of any kind, including replacing or charging batteries. The intended operation would be such that it is always on and anytime a parachute is used (initial deployment with opening shock,

Ultra low power design

Ultra-low-power systems are typically designed with specific power profiles that include at least two power modes, one of them being a low-power mode. For the vast majority of the time, these systems operate in the low-power mode and power consumption in this mode is minimized. The proposed device has been designed with a low-power mode (sleep) and a high-power mode (awake). It operates in low-power mode for the vast majority of time, and the power consumption in that mode has been minimized.

Flight detection algorithm

This system uses both an accelerometer and a barometric altimeter in its flight detection algorithm. The overall logic is shown in Fig. 9. The accelerometer continually samples, and if the total measured acceleration rises above a threshold, the system wakes from its deep sleep mode and the flight detection algorithm begins to run. A configurable delay between the wake-on-acceleration event and the first barometric altitude sample is used to prevent sampling while the parachute is inflating or

Bench and flight testing

To evaluate tuning parameters of the flight detection algorithm, a software-in-the-loop testing setup was developed. A wrapper on the flight detection algorithm that is run on the embedded hardware was made. Various flight profiles, defined as barometric altitude vs. time, were created based on publicly available specifications for military personnel and cargo parachute system, recreational skydivers, and some non-flight profiles as well. The flight detection algorithm only starts running if

Conclusion

This paper presents a novel persistent parachute sensing system. It is designed for ultra-low power consumption, and is always on. In its dormant state waiting for a jump to occur, it requires less than 1 μA of current from its battery, enabling predicted battery life of greater than 15 years. This sensing system counts the total number of jumps, which is correlated with parachute wear. It also tabulates the total time spent in the air, which relates to the total UV exposure time of the

Declaration of Competing Interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: J. Wachlin, B. Leon, M. Ward, M. Costello has patent In Canopy Flight Counter pending to Earthly Dynamics Corp.

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