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3 Fatigue of Aircraft Structures

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Service Life Extension of Parachutes with Use of Non-Desctructive and Partially Destructive Testing Methods of Textile Materials

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Szafran K. S. , Kramarski I.

Fatigue of Aircraft Structures

2020

tom Iss. 12

113--122

The specificity of personal rescue and reserve parachutes is the fact that they are practically never used for jumping during their service life as they are intended for use only in emergency situations. Therefore, these parachutes throughout the entire period of use are only periodically aired and repacked every 6-12 months. Airing and repacking is necessary even if the parachute is only stored. Rescue and reserve parachutes’ components wear unevenly because the canopy with the suspension lines is inside the container and the cover, while the external components of the harness and the container undergo typical operational wear. Therefore, the service life of rescue parachutes can even reach 20 years (this refers to the canopy with the suspension lines alone). During normal exploitation, parachutes are subjected to non-destructive visual and tactile inspection in preparation for packing. When a parachute reaches its maximum service life, extension of its service life can be calculated based on its technical condition. The procedure for extending parachute’s service life involves non-destructive tests at a fabric air permeability test stand and partially destructive tests at the strength test stand. In the paper, both methods are described and their advantages and disadvantages are discussed. Also, observations some regarding the packers’ work and the desired new properties of raw materials that could be introduced to the parachute industry are presented.

Research on Hovercraft - Fatigue Cracks in the Engine Frame

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Szafran K. S. , Michalczyk M.

Fatigue of Aircraft Structures

2021

tom Iss. 13

106--115

Rescue patrol hovercrafts must meet the basic condition - high reliability of use in extreme conditions. The introduction to the work shows damage to the propulsion system and the fan tunnel structure resulting from a fatigue fracture of the attachment wound to the propulsion unit hull. In this paper, the author describes some ways of improving the engine frame structure. In the first phase of the exploitation crack testing of the hovercraft frame, the probable causes of damage were determined. The necessary output data for analysis of the load course were obtained from the operating documentation. The approximate number of variable load cycles acting on the frame truss rod was determined. Using the comparative testing methods, the service life of the frame was estimated. Probable resonance frequencies of the vibrating bars in the truss were determined. Vibration tests of the power transmission assemblies were carried out, which allowed to determine the amplitudes and frequencies of free vibrations. Finally, a modification of the frame shifting the resonant frequency range was proposed. In conclusions, changes to the design and a schedule of inspections were proposed. The newly designed engine frame should have an extended service life.

Fatigue Degradation of the Ram-Air Parachute Canopy Structure

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Szafran K. S. , Kramarski I.

Fatigue of Aircraft Structures

2019

tom Iss. 11

103--112

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.