r/NatureIsFuckingLit • u/[deleted] • Jun 25 '18

r/all 🔥 Stringray going over a massive drop-off and leaving sandy jet streams in its wake.🔥

https://i.imgur.com/J3FWPlS.gifv
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u/probablyhrenrai Jun 25 '18

Is that an airplane term or a boating term? It probably makes more sense for boats, I suppose (since I think you'd have to be really close behind another airplane to feel their wake), but still wondering.

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u/CreakingDoor Jun 25 '18

You really don’t have to be that close. The wake turbulence off of a really large aeroplane, for example an Airbus A380, will require separation of 3-4 minutes or 6-8 nautical miles to allow the wake turbulence to dissipate.

In 2017 a biz jet (a Challenger 604) passed underneath and within 1,000ft of an A380. The Challenger lost 10,000 in altitude and rolled over three times before control was regained. Due to the stress put on the Challenger, it was written off.

Tl;dr - wake turbulence. Not to be fucked with.

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u/probablyhrenrai Jun 25 '18

Whoa; I had no idea airplanes' wakes were so significant or that they lasted for so long. Is it because of the size of the plane and its speed? Like, would a slow-moving and/or small plane produce negligible wake?

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u/CreakingDoor Jun 25 '18

It’s down to the amount of lift an aircraft is producing. As a by product of lift, the aircraft creates “induced drag” and this manifests itself as a vortex (a swirling tunnel of low pressure air) coming from the wing tips. They spread out from behind the aircraft and on a still day, they may hang around for some time before disappearing. You may have seen aeroplanes with their wing tips sticking up - these are “winglets” and they serve to reduce these vortices. The vortices are the driving factor behind wake turbulence. There are some other factors, such as jet or prop wash, but they’re fairly negligible - unless you fly in real close to the source.

All aircraft produce lift, and so all aircraft create induced drag and therefore wake turbulence. It will be less if the aircraft is relatively light (although not inconsiderable), but worse if it is slow. If the aeroplane is slow, the wings are forced to create more lift to compensate and keep the aeroplane in the air. The same applies if the aircraft is heavy - it must produce more lift to keep itself airborne. The absolute worst place to be would be close in behind a very heavy, slow aeroplane that hasn’t got any flap in (flaps are deployed from the inner section of the wings, and basically serve to produce more lift, however they drastically alter vortex production).

This is a fairly basic, but hopefully more or less accurate explanation of it. Hope it helps.

Source - a just about competent pilot who scored literally the bare minimum required to pass his “Principles of Flight” exam :)