11
$\begingroup$

At air shows with fighter jets I would expect there would be a demonstration of supersonic flight. But in this flight of a Eurofighter Typhoon, no sonic boom was heard.

What is the reason?

Is it that there is no supersonic flight involved due to loudness or needing a bigger distance to accelerate?

Or is the sonic boom inaudible for a reason related to the short time delay of the sound between the noise source and the microphone, or some other physical reason?

$\endgroup$
  • 9
    $\begingroup$ Sonic booms over populated areas were essentially forbidden in the US sometime around 1960. Prior to that I heard several. Have not heard one since. $\endgroup$ – Hot Licks Nov 22 at 20:17
  • 1
    $\begingroup$ I think it was the late 60s because I remember hearing some as a kid. I thought it was cool... $\endgroup$ – Michael Hall Nov 23 at 0:05
  • 6
    $\begingroup$ "I would expect there would be a demonstration of supersonic flight". Why? (I, on the other hand, would hope that there would be a demonstration of supersonic flight.) $\endgroup$ – RonJohn Nov 24 at 0:14
  • 1
    $\begingroup$ I heard sonic booms on a regular basis in middle Tennessee from '05-'08. They had to flight test the F-22 Raptors over Arnold AFB and there would be 2 sonic booms. One was the F-22, the second was the chase plane. $\endgroup$ – Ryan Mortensen Nov 24 at 12:45
  • 1
    $\begingroup$ This question is being "over-answered" in very confusing ways. The only thing OP wants to be told is "There is never any supersonic flight at airshows." $\endgroup$ – Fattie Nov 24 at 19:07
40
$\begingroup$

In a lot of areas, sonic booms are illegal over land or near residential areas. Yes it's loud, yes it's potentially damaging, especially at low altitudes. I've been to a lot of airshows, I've never seen a supersonic demo.

$\endgroup$
  • $\begingroup$ this is true. In Europe, where the eurofighter is used the most super sonic flight is prohibited by the noise level limits a plane may produce. It is only alowed in acute alarm situations. I whitnessed this once in Nürnberg during an incident. You Really don´t need speakers to hear the boom. It shakes your bones from 15km away. $\endgroup$ – Nefrin Nov 22 at 11:51
  • 1
    $\begingroup$ @Nefrin Not all European countries have the luxury of the sea to train supersonic flight. In Czechia planned training supersonic flights are performed above 10 km. $\endgroup$ – Vladimir F Nov 22 at 20:28
  • 7
    $\begingroup$ While it's true that some countries (such as the U.S.) make it illegal for civilians to fly supersonic over land, this restriction is rarely, if ever, legally applicable to the military. Of course, they'll still not do this at low altitude under normal circumstances for obvious reasons. Even in the U.S. where supersonic flight over land is notoriously banned for civilians, the military does it pretty regularly, just at high altitudes. We used to hear sonic booms pretty frequently near the USAF base I used to work at. It was far enough away not to do damage, but it did shake the building. $\endgroup$ – reirab Nov 22 at 22:10
  • 2
    $\begingroup$ @MichaelHall I mean, I know they're not allowed to just whenever they want, but there are plenty of (relatively frequent in my experience) missions where they can and do fly supersonic over the CONUS. Of course, it's not like they're doing it at 1,000 ft AGL over populated areas. $\endgroup$ – reirab Nov 23 at 21:03
  • 2
    $\begingroup$ Please help us understand when and where you have seen this occur then because in all the exercises I have been involved in if there was an accidental boom the perpetrator would be shamed in the debrief. $\endgroup$ – Michael Hall Nov 23 at 21:14
53
$\begingroup$

Just for a bit of flavour, I recall an article from Air Progress from the late 70s about Darryl Greenamyer setting the low altitude absolute speed record, in his "homebuilt" F-104, of Mach 1.3 (mentioned in this article) in 1977.

For the run he had to cross very low over timing trigger devices at the start and end of the speed course at the dry lake bed at Edwards, which were set up with cars parked beside them.

I remember the description of the event by the writer who witnessed it from somewhere along the middle of the course, a safe distance away with other observers. The F-104 passed over the car at the 1st speed trap at 60 ft AGL and passed the writer in absolute silence, and it wasn't until a second or so had passed that a sound like a dynamite explosion a couple hundred feet away went off. All the glass of the cars at the speed traps blew out and their trunks popped open. The writer was warned in no uncertain terms that if he didn't protect his ears he'd get hearing damage, and not to be fooled by the initially silent passage of the jet itself into taking his fingers out of his ears.

Imagine that happening at an airshow.

$\endgroup$
  • 1
    $\begingroup$ Sound travels at ~1100ft/s. If it was 60ft away, it wouldn't take a couple of seconds. It should basically be instant. $\endgroup$ – vidarlo Nov 24 at 10:40
  • 1
    $\begingroup$ The boom occurs at the point at which the plane goes supersonic tho, so unless the plane went supersonic as it passed the reporter, they would see a delay. I think they're saying the plane was 60ft away, not that it went supersonic 60ft away. As long as the plane is accelerating, the distance between the plane passing, and the boom passing would be increasing. $\endgroup$ – djsmiley2k - CoW Nov 24 at 17:03
  • 15
    $\begingroup$ @djsmiley2k-CoW “the boom occurs at the point at which the plane goes supersonic”. This is not correct at all. The “boom” is the wave front of the sound generated by the jet. It is actually a constant roar. The only difference is that the wave front is compressed so that by the time it passes over you that roar happens at a single instance. It travels behind the jet and dissipates outwards at the speed of sound. It is not a single event. It is a continuous sound that you only get to hear a short snippet of. $\endgroup$ – Fogmeister Nov 24 at 17:51
  • 2
    $\begingroup$ This answer is just an anecdote. It's completely confusing. The OP is asking a very basic question "Is There Supersonic Flight At Airshows?" The four paras here completely fail to simply answer the question! JK, perhaps add one introductory sentence stating the answer, then your anecdote. There's a common problem on these sites where leading experts in a field simply fail to answer very very simple questions, because to the experts it's totally obvious. $\endgroup$ – Fattie Nov 24 at 19:09
  • 1
    $\begingroup$ @Fattie That is true, but the anecdote is so interesting that it's worth an answer anyway. I was aware that if it's loud, it is really loud. But that's more than just loud by an order of magnitude or two. I did not expect that, I did not do the math, and if I had, it would not give me an intuition. The answer is implicit, but the implication gives information that other answers can not convey. $\endgroup$ – Volker Siegel Nov 24 at 20:49
23
$\begingroup$

Sonic booms have a lot of, lot of, lot of throw. There would be no way to confine a sonic boom to just the airfield. People two towns over would have have car alarms set off and houses shaken. It would upset animals, it would upset people! It would trigger PTSD for some and panics for others. It would generate hundreds of phone calls to 911.

Keep in mind the airplane has to accelerate to and through supersonic well before the airfield, and then has to slow down again. It's covering a mile every 5 seconds, so this, combined with the throw, sweeps a whole lot of area.

$\endgroup$
  • $\begingroup$ Does that mean that it's illegal to have an aircraft with a higher landing speed than 250KIAS? I know some extreme aircraft (e.g. the Shuttle) land at very high speeds. $\endgroup$ – Skyler Nov 22 at 18:42
  • 2
    $\begingroup$ @Skyler Military does not need to foloow civilian rules. One is GAT, one is OAT. $\endgroup$ – Vladimir F Nov 22 at 20:20
  • $\begingroup$ @Skyler Even civilians can get the 250 below 10,000 speed restriction waived by ATC. It's mostly just there to make traffic deconfliction easier. If ATC has other ways to guarantee no traffic conflicts (and, for the Space Shuttle, they definitely did,) then there's no problem with waiving the speed restriction. $\endgroup$ – reirab Nov 22 at 22:29
  • 4
    $\begingroup$ They don't need to follow civilian system, they just do as a matter of policy, because of Hughes 706. $\endgroup$ – Harper - Reinstate Monica Nov 23 at 0:30
  • 1
    $\begingroup$ When I say "policy" I mean the policies set as a result of the agreement between the armed serviceS and FAA that they would follow ATC (mostly). news.google.com/… As a result of the agreement, Congress did not mandate it with legislation. in actual implementation, it is at the services' discretion, but they have to make a good showing of it if they don't want Congress to intervene. $\endgroup$ – Harper - Reinstate Monica Nov 25 at 0:18
5
$\begingroup$

John K has already provided an example of what a sonic boom feels like from very close, and Harper - Reinstate Monica describes it in general terms. Let me give you a practical example of what a sonic boom did in a radius of 100 km.

On 22 March 2018, Air France flight AF671A from Réunion to Paris Orly was flying over northern Italy when it lost radio contact with Air Traffic Control. Two Eurofighter Typhoons were sent to investigate, and as they rushed there they broke the sound barrier.

The sonic booms were heard from Aosta to Bergamo, which are 180 km apart. And at first they were mistaken for bombs. The result? Among other things, there were hundreds of calls to the police, people ran out of buildings in panic, some schools and offices were evacuated, and some windows got broken.

And at an airshow they'd fly much lower, so it would be louder!

To be fair, it was explained that the wind and weather conditions were unfortunate, as they favoured the propagation of sound, but in any case a sonic boom is way too loud to be done for fun: it's only allowed in case of emergencies.

By the way, in the end it turned out it was a false alarm, so at least there was a happy ending.

[Sources: in English, in Italian]

$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.