Aeronautics and astronautics – Safety lowering devices – Parachutes
Reexamination Certificate
2000-08-03
2001-10-09
Eldred, J. Woodrow (Department: 3644)
Aeronautics and astronautics
Safety lowering devices
Parachutes
C244S137300, C073S838000, C073S794000, C073S812000, C340S946000, C340S665000
Reexamination Certificate
active
06299104
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and apparatus for evaluating strain and stress in textiles and flexible materials under strain. More particularly, the invention relates to the use of fiber optics technology with high speed data transmission and acquisition devices to provide a novel remote sensory evaluation system, such as for parachutes during deployment and Inflation.
BACKGROUND OF THE INVENTION
For any parachute system, it is important to predict the opening forces it will experience in order to make a safe and economic choice of materials to be used. Only limited data for these decisions is available and any numerical model sought to be used is also limited by the lack of data to use and to verify the model. Novel techniques are therefore needed to determine the structural behavior of a parachute during inflation. A different method for experimental measurement of parachute behavior during opening is also needed. There are other fabrics and textiles that are subjected to stress, such as, for example, balloons and the like.
The schematic of the standard quasi-static circular canopy parachute is shown in FIG.
1
. This parachute comprises two main parts: the canopy and the suspension lines. A parachute drop generally consists of three principal stages: deployment, inflation, and descent. The deployment phase begins with the ejection of the payload from the aircraft, rocket or the like, and ends when the suspension lines and folded canopy have been fully extracted from the deployment bag. The full extension of the parachute system is marked by the “snatch” force impulse, an acquisition event that occurs when the falling payload accelerates the parachute mass up to its own velocity.
In most military airdrops, the deployment bag is attached to the aircraft by a static tether; hence, the time lag between payload ejection and the snatch point is usually small. In free-fall personnel drops and sport parachute jumps, the time delay is usually longer. In either case, the parachute shape at the end of the deployment phase is essentially that of an elongated but deflated tube. During the subsequent inflation phase, the elongated parachute transforms from a closed tube to an open canopy, ultimately increasing the aerodynamic drag and decelerating the payload. Eventually, a steady-state condition or descent is reached where the aerodynamic drag balances gravity and the payload drifts to earth at a relatively constant velocity.
A typical plot of the force on the payload versus time during parachute opening is shown in FIG.
2
. As this figure indicates, the force on the payload, with the exception of the snatch impulse is small during the initial stages of inflation. As the inflation continues, the opening force exerted by the continually filling canopy increases to a peak, then decreases over time.
In the design of parachute systems, therefore, it is very important to use structural properties that have been developed under the representative force rates expected in flights. Without such data, the designer is potentially forced to incorporate unrealistic safety margins, resulting in a parachute that is heavier and costlier than necessary. Laboratory test data has generally been limited to that which can be acquired at quasi-steady strain rates. Past work has suggested that the properties of textile materials obtained through the typical quai-static testing process are inapplicable to dynamic strain conditions.
Past reported work presents the use of electronic strain gauge equipment for measuring stresses under various loading conditions. Testing materials at representative high strain rates of dynamic forces requires much more sophisticated equipment than found in a typical material testing laboratory.
It would be a great advantage in the art to have an improved methodology and apparatus, which takes advantage improved data acquistion techniques, such as that of advances in fiber optic sensors for fabrics, textiles and other flexible structures.
Still another advantage would be to use fiber optics technology to determine the stress/strain relation of flexible devices such as parachutes during deployment and inflation.
It is therefore an object of this invention to provide a method and apparatus for high speed data acquisition devices as well as electronic RF (radio frequency) transmitter receivers are used for signal processing and transmission of the information to a ground station.
Another object is to provide a method and apparatus using fiber optics technology to evaluate parachutes under load.
Yet another object is to obtain a means of determining the dynamic properties of structural materials in-situ and in real-time.
Other objects will appear hereinafter.
SUMMARY OF THE INVENTION
It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. The unique aspect of this invention is the use of advances in fiber optic sensors. This fiber optic sensory system provides a means of determining the dynamic properties of structural materials in-situ and in real-time. The developed invented testing methodology uses fiber optics technology to determine the stress/strain relation of parachutes during deployment and inflation as one example of in-situ real-time material evaluation. In addition, high speed data acquisition devices as well as electronic RF (radio frequency) transmitter receivers are used for signal processing and transmission of the information to a ground station.
This methodology and the apparatus therefore provide the novel remote sensory system of the present invention for use with a parachute. Parachutes include a canopy, a plurality of suspension lines attached thereto at one end and, of course, a load attached to the suspension lines at the other end therof. The term load is intended to cover parachutists and inanimate payloads such as packages of supplies and the like. The present invention is intended for use with all types and varieties of parachutes used for any purpose.
A plurality of first sensors are attached to the canopy and/or the suspension lines for measuring localized axial strain and stress measurements. Preferred are fiber Bragg gratings (FBG) type sensors. In addition, a plurality of second sensors are attached to the canopy and/or the suspension lines and are, preferably, modal power distribution (MPD) type sensors. Both sensor types are provided with a light source, such as a light emitting diode, to transmit light along the axis of the Bragg fiber for the FBG type sensors or the multimode optical fiber for the MPD type sensors. At the other end of the sensor is a light receiving device, such as one or an array of photodetectors, forming a fiber optic network interconnecting the sensors to provide sensor outputs. Of course, deployment of the sensor system and processing elements is intended for use with any flexible structure under strain, using the concepts of this invention as disclosed herein.
The sensor outputs are received by a transmitter, converted to electronic signals, modulated and transmitted to a receiving station for receiving and processing the data. The data then allows the user to evaluate the forces on the parachute (or other fabric) with respect to the particular load used, the conditions of deployment, and the like.
REFERENCES:
patent: 3698667 (1972-10-01), Studenick et al.
patent: 4420755 (1983-12-01), Primbs, Jr.
patent: 4429580 (1984-02-01), Testa et al.
patent: 6070832 (2000-06-01), Redd
El-Sherif Dina M.
El-Sherif Mahmoud A.
Lee Calvin K.
Eldred J. Woodrow
Munday John S.
Photonics Laboratories, Inc.
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