Cable cap system
A cable cap system , also wire protection system or (uncommon) protection system in the event of wire collision ( English cable cutter , wire cutter , wire strike kit or Wire Strike Protection System (WSPS) ) is a safety device (passive safety system) in helicopters .
General
A cable cap system is used to protect against accidents caused by collisions with ropes, wires and cables (e.g. overhead lines , cable cars , guy ropes). If the pilot sees a steel rope too late and the rope hits the helicopter, depending on the height of impact, it may become entangled with runners or undercarriage, and the cabin, the rotor control or the rotor head may be destroyed. With the cutting system, the rope, if it does not hit too close to the rotor, can be caught and cut, which makes the worst consequences of accidents avoidable. The system was developed by Bristol Aerospace in 1979 for a Bell OH-58 , and various companies now offer the appropriate equipment for various helicopter models.
technology
The system consists of five parts: The most clearly visible are the sword-shaped guide rails protruding diagonally upwards at characteristic angles of 45 ° from the horizontal at the top of the cabin roof or diagonally downwards under the cabin. In between there is a vertical strut a deflector (windshield deflector) in front of the often two-part windshield. In the two inner angles that these three rails form with each other, massive scissors (lower wire cutter, upper wire cutter) made of hardened steel with a fixed, very small opening angle are mounted. Ropes arriving in flight from the front (and not too high) are caught by the rails and guided to one of the shears. The inertial force of the rope and the horizontal resultant of the tensile stress of the two rope ends, which is built up by deflection, push and pull the rope into the scissors, where it is severed by the two blades, finally it breaks and snaps away in two halves.
Force impulses are transmitted to the helicopter through impact, deflection and cutting, which twist the helicopter and require control corrections.
In some systems (e.g. the Bell OH-58 Kiowa), the deflection rail on the windshield is designed to be abrasive , so that the wire is partially chafed when sliding over the deflection rail and is thus weakened before it reaches the upper or lower cutting knife .
This safety equipment is not prescribed by the manufacturer or legislator for most helicopter operations, but increases the safety especially for helicopters with special tasks at low altitudes. The system with the specially hardened wire cutters has its price and burdens the helicopter with a contribution to the weight. A cable cap system cannot be installed on all types of helicopters. Each type requires an adapted set, possibly additional deflectors in front of antennas and the windshield wiper axes and correspondingly stable attachment points.
In most accidents with wire ropes, the rope slips onto the top of the helicopter, as the foremost point of the helicopter nose is usually relatively low. There the wire rope tears off the rotor. With the cable cap system, the pilot survives contact with a (single) wire with a high probability, with multiple wires the probability of survival decreases.
These figures do not take into account the more or less large inclined position of the rotor, depending on the flight position, and thus the different probability that the rotor or rotor head itself will collide with the rope.
Identification of obstacles
Regardless of whether the helicopter is equipped with a cable cap system, overhead lines on flight routes and destinations of rescue flights, such as along motorways, but also on rivers, are marked with red balls ( English wire marker , German rope marker ) to make them recognizable for helicopter pilots when visibility is reduced to improve. Rescue helicopters in particular navigate along the motorway during their missions, on which they may also have to land. In Germany this regulation is regulated in the general administrative regulation for the marking of aviation obstacles section 2 "day marking " in point 5.4 and in Austria by the civil airfield regulation (ZFV 1972) 6th section "marking of obstacles" in § 68.
literature
- Niels Klußmann, Arnim Malik: Aviation Lexicon . 4th edition. Springer-Verlag, Berlin 2018, ISBN 978-3-662-54040-4 , pp. 99–100 , Cable Cutter , doi : 10.1007 / 978-3-662-54040-4 ( google.de [accessed on August 18, 2019]).
Web links
- Glenn S. Bloom: Helicopter Education Site: How Helicopters Work. In: The Helicopter Page. 2018, accessed August 18, 2019 (American English, Controversial Information on the Effectiveness of Cable Ending Systems).
Individual evidence
- ^ Magellan Aerospace Corporation: Wire Strike Protection System (WSPS ™). Retrieved on August 18, 2019 (American English): "The WSPS ™ [is ...] uniquely suited to each helicopter model [...] Available for more than 70 models of [...] helicopters."