If this was a movie, that would be a Really Cheesy Effect

[major_clanger]

A video of an incredible aerodynamic phenomenon at a recent rocket launch. The real fun starts at about 1:50 in:

Watch on YouTube

(alt = http://www.youtube.com/watch?v=SsDEfu8s1Lw)

There's some discussion of it on this Metafilter thread. It gets a bit confused, including the usual tedious pseudo-geek response of "if I don't understand it it must be fake" so I've added a comment explaining what is going on, and why the 'ripples' seem to be travelling outwards far faster than sound. (It's an illusion; what we are seeing is a very shallow conical shock wave from a barely-supersonic rocket intersecting the flat layer of ice crystals that is responsible for the sundog.)

Comments

[ffutures.livejournal.com]

That's gorgeous. Suppose it's only possible under exactly the right conditions (very thin ice crystal layer) or we'd see things like that more often.

[sharikkamur.livejournal.com]

Yes, like the conditions for normal sundogs they're not that common. We get them up here 'relatively' frequently thanks to the lower temperatures.

[quercus.livejournal.com]

Aren't those still-air conditions also likely to be the best sort of conditions for launches from Florida in February? They scrubbed the first on account of winds.

[bellinghwoman.livejournal.com]

Cool!

[owlfish]

That's so lovely!

[hairyears.livejournal.com]

Your point about shallow shock cones at low Mach numbers, and 'more pointed' ones at higher speeds, reminds me of a question I asked as a schoolboy...

An aircraft accelerating hard from subsonic speed to Mach 2 produces a shallow Mach cone at the sound barrier and, further forward, a much sharper one. Modelling this as two separate cones, it seems that there is an intersection of the two (picture a wizard's hat sitting on the broad cone of a coolie's hat). It occurs to me that this region of air would be subject to severe buffeting and shocks, and that the airspace around an accelerating aircraft (or an ICBM or orbital launch vehicle) would be quite dangerous.

Is this correct? And did interceptor pilots in the Cold War ever use this when 'buzzing' particularly persistent intruders who refused to be shepherded out of our airspace?

[major-clanger.livejournal.com]

Yes, you probably would get that effect.

As for using shock waves as a weapon, I think it's been used not so much as a weapon against other fixed-wing aircraft but rather against helicopters. I spoke to a Tornado pilot once about this; a slow-moving, low-flying helicopter can be quite a difficult target with guns or missiles, but you can apparently swat it out the sky with a fast close flyby.

Certainly, low supersonic passes have been used as a sort of gigantic stun grenade against opposition on the ground. I've been under a Tornado doing a merely subsonic (about 500mph) pass at roughly 250' altitude, and it's just a massive sudden explosion of sound. Make it Mach 1.2 at 50' - which a Tornado is quite capable of - and your eardrums would probably meet somewhere in the middle of your skull.

[sbisson.livejournal.com]

Back in the day when the RAF displayed Vulcans regularly I was under one when it did a low pass over St Aubin's Bay as part of the Jersey Air Display.

All I can say is. Wow.

[j-lj.livejournal.com]

From my parents home in Cardiff I used to watch Concorde flying up The Bristol Channel where it would break the sound barrier, fun to watch and hear.

[quercus.livejournal.com]

I believe that Jaguars were (in practice) faster at RAF Standard Altitude than Tornados and better at this sort of "bounce", on account of their higher wing loading. If a Tornado tried to do it, the problem was the shock wave reflecting back up at them and making the aircraft uncontrollable. There was a similar issue between the F16 and the F15, although the US obviously weren't flying quite so low.

A hypothetical British F104 would probably have been even better at it, except that Welsh weather would have killed them first.

[hairyears.livejournal.com]

Oh, I'd know about the stun grenade effect. Ask an old-timer Tornado pilot if he remembers the 'Brave Defender' full-scale NATO exercises. Maybe he'll know how there was great disappointment among a small party of schoolboys who'd cycled up to Cottesmore, all the way from Leicester, and by careful map-reading and a guess at the wind direction, placed themseves directly under the flight path.

Imagine our dismay when they all took off the 'wrong' way, making tactical take-offs directly over the dismal huddle of peace protesters holding some kind of 'peace mass' at the perimeter fence... Who were thrown to the ground, hard, by a physical shock and shaking that we felt from about two miles away. Thrown repeatedly... we started giving them marks for style, and I recall wishing we'd brought scoring-cards to hold up like the Figure-Skating judges at the Olympics.

I'd known that the Tornado was noisy, and had borrowed my dad's ear-cans from the factory... Sod-all use, the noise was a physical assault that went through you: 'awesome' doesn't come close.

[woolymonkey.livejournal.com]

Cool! Thanks :)