Downwash flight

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A downwash flight is called a flight maneuver with helicopters , in which the vegetation is freed from precipitation and the like by very low overflight.

Basics

Helicopter flying by the rotor a strong downdraft , English [ rotor ] downwash called produce. This downdraft, which is also directed sideways near the ground, is so intense that an adult can hardly stand upright near a landing helicopter. It also stirs up large amounts of sand, snow and even small parts like stones and branches. It can also flip up and not only lead to unstable flight, but also rob the pilot of vision ( called white-out when it is snowing ) and even damage the engines by sucking in small parts. Flying very close to the ground ( hovering ) is therefore an extremely risky flight situation.

Using the effect of the downdraft intentionally to blow off large areas can already be found in the early days of helicopter flying in the 1940s, namely in agricultural flight . However, the flight maneuver can only be used reasonably safely with modern helicopters, which have electronic devices for precise flight stabilization or blind flight and are optimized for low-level flight suitability.

application

The following maneuvers are used as an emergency measure:

  • in agricultural flight:
    • with special ground frost , when there are warm air currents slightly above; mixing can then prevent acute frost damage; the FAO recommends altitudes of 20–30 m and speeds of 8–40 km / h; the surface coverage is estimated at roughly 20–40  hectares per helicopter flight.
    • for drying cherry crops and similar sensitive fruits after rain, so that they do not get burn marks from the drops in the strong sun that follows. This is done in the USA, for example.
  • During heavy snow events : Here the trees are blown off along roads, railways or power lines if there is a particular risk of snow breakage due to large amounts of wet snow in the crowns. Because of the generally difficult winter flight conditions and especially the whiteout, this is considered highly risky and is therefore only used in the event of a crisis or disaster. This method became known, for example, during heavy snowfall in the Alps in January 2019 . The Austrian Armed Forces flew numerous downwash missions with the well-suited S-70 Blackhawk as part of the civil defense assistance mission .

Web links

Individual evidence

  1. ↑ English to wash 'wash', the reference to the downdraft but especially from the wash 'strong [washing out] current', as in river names or 'lake, wave blow', geologically '[soil] washing away , rinsing, abrasion, erosion' .
  2. ↑ For a description of the situation on the ground, see for example: Peter Mair, Josef Redolfi: Downwash - behavior during helicopter rescue operations in the mountains. In: Berg & Steigen 3/02 (2002), section Instructions for landing , p. 6 ( full article, pp. 33–38, pdf , bergundstieg.at, p. 4 there).
  3. ↑ cf. z. E.g .: E. Torenbeek, H. Wittenberg: Flight Physics: Essentials of Aeronautical Disciplines and Technology, with Historical Notes. Verlag Springer Science & Business Media, 2009, ISBN 978-1-4020-8664-9 , p. 409 ( limited preview in Google book search).
  4. ^ A b Harland Wilson: The ABC's of Crop Dusting. In: Flying Magazine , ISSN 0015-4806, Volume 44, No. 5, May 1949, Paragraph Helicopters are beeing used experimentally ... p. 40, Col. 2 ( limited preview in the Google book search).
  5. ↑ a b Richard L Snyder, J. Paulo de Melo-Abreu: Frost Protection: fundamentals, practice, and economics. Food and Agriculture Organization of the United Nations (FAO), Rome 2005, ISBN 92-5-105328-6 , Chapter 2 - Recommended Methods of Frost Protection. Active Methods: Helicopters (online document at fao.org, accessed January 14, 2018).
  6. ↑ Helicopters & Cherries - How Chelan Cherry farmers use helicopters to help maintain freshness of their Cherries. Chelanfreshcherries.com, undated (accessed January 14, 2018).
  7. ↑ Sektakuläre snow removal by Blackhawk helicopters. oe3.ORF.at, January 10, 2018.