Mon, 30 Jun 2008

Low flying aircraft

Late this morning people in Sydney were treated to the sound and then sight of a largish four engine aircraft flying a somewhat unusual and fairly low flightpath on its way across the Northern Beaches on approach into Sydney. What made it a bit more interesting was:

1. the thing was painted gray
2. it had a fighter flying in close formation off its tail

Huh. Certainly a bit unusual to see on its way into SYD, but the fact that it was obviously a military aircraft, with a fighter escort, was more than reassuring. Mostly we figured it was a head of state or senior officer from some allied nation on the way in, getting a nice escort. I will admit that Katrina and I are both a little jumpy when it comes to very loud engines close overhead; the scream from the fighter’s jet engine mixed in did give it an unusual timbre. (Which most people aren’t used to; if you haven’t experienced fighters up close and personal, it’s not a roar but more a thin penetrating shriek. Hollywood never gets these things even remotely close). So, {shrug}. Residual jumpiness aside, what I learned from the last time a large jet flew down my street is that if you are hearing the engines firewalled, at least it is already past you.

Anyway, it all turns out to be quite innocent. The Royal Australian Air Force is retiring it’s last Boeing 707, and they did a photo shoot over Sydney. How nice.

Even though I only got a brief glance, I should have recognized the airframe. Bah. The US military still fly a number of C135 derivatives; that it might have been one did flash through my mind, but I they’re kinda getting on in years and I didn’t expect to see one hereabouts. A 707 isn’t that large, but sometimes scale is hard to tell from afar. Alas

I wouldn’t have ever given it a moment’s thought again except that a glance this evening at a local paper’s website showed it headlining an article about it, much to my surprise. Somewhat less of a surprise was them using the occasion to be all alarmist about low flying planes over cities.

After we get past the quotes of office workers who were terrified and who ran screaming from their buildings, we get to the mention that the plane was “trailing smoke”. That’s awesome. Uh, in case you didn’t know, that’s what turbofan engines do at low speed. Airplanes are made to be efficient at high altitude cruise. Pouring out power to keep a plane going at low speed is, unfortunately, somewhat inefficient. Kinda like your car starting after a red light. Jet engine manufacturers work hard on this sort of thing, but older planes are (surprise) less efficient. Which is why aircraft manufactured in the 1960s are somewhat less than ideal from an operations cost standpoint. Not to mention noise, and, yes, the black gunk pouring out the back.

The principal complaint is that people seem to feel they should have been told about this. While I’m sure the press will be full of scary headlines in the morning, and no doubt the politicians will hang the Air Force out to dry, the air navigation regulations for the Sydney terminal airspace clearly allow for aircraft doing photo op orbits over Sydney harbour and explicitly detail the procedures to be used. Gotta get that bridge and concert hall in or it just doesn’t count, right? So, quite sensibly, ATC around Sydney allows for pilots requesting permission to do so.

Now, admittedly, the average photo op by a circling Cessna doesn’t attract much attention; a largish jet is a bit more ostentatious. Neglecting for a moment that most of the approach paths bring low flying aircraft right over Sydney and its suburbs anyway, should the populace be given advanced notice of plans to orbit planes a bit lower? Hm.

Apparently at least one local radio station did know about this ahead of time, so I’d say the RAAF did its part¹ (and that’s assuming that it had an obligation to do so, which frankly, I’m not convinced of). If the journos didn’t think it newsworthy to mention in their broadcasts, that’s not the Air Force’s fault. And there in lies the problem. So long as the media is busy reporting on the latest antics of Britney Spears and how the 6 year long US presidential election campaign is getting on, I doubt there will ever be much time for public service announcements, even if we did decide that such things were topical.

AfC

¹ Update: Here’s the Department of Defence press release, released last week.

low-flying-aircraft, posted by Andrew Cowie in /andrew/comment at 10:13, 30 Jun 2008.

Wed, 11 Jun 2008

Voyager and the speed limit

As often happens, an IRC channel veered off-topic and onto an interesting one instead. We got to talking about clocks and frames of reference and while we were chatting back and forth someone claimed that we hadn’t made anything that had reached relativistic speed yet (or, at least nothing on the scale of the questions you get on your average physics exam about the spacecraft doing 0.9c). That may be true, but that had me wondering just how fast the fastest thing was.

That would be Voyager 1, launched 5 September 1977. It’s now about 15.9 billion km out, and is booking along at about 17 km/s which is 0.000056c. That’s pretty fast! Still going to take a while to get to the next stop, though.

Image Credit: NASA/Walt Feimer.

Finding the speed number led me to a JPL page on the NASA site about the Voyager missions. Quite interesting reading, especially about the choice of trajectories they had which allowed them to have Voyager 2 reach not just Jupiter and Saturn but also Uranus and Neptune in “12 years rather than 30”.

http://voyager.jpl.nasa.gov/news/factsheet.html

AfC

voyager-speed, posted by Andrew Cowie in /andrew/science/space at 13:20, 11 Jun 2008.

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