Summoner wrote:
This is more of an aviation/physics question. Can a sonic boom be mitigated if the aircraft flies higher and in thinner air? My logic is going along the lines of thinner air offering less of a "boom". Can higher flying aircraft do so supersonically?
Archibald wrote:
Nope. It doesn't work that way. Your theory make sense, and there were serious hopes (in 1960) that flying above 70 000 ft would kill the sonic boom. So they flew F-104s, B-58s and the XB-70 all over Oklahoma (in 1964) as high as they could, but it doesn't worked. At all. People just went nuts. Windows broke all over the place.
Actually the higher up the less likely the boom is to survive to reach the ground. This is highly dependent of course on the size of the aircraft since this determines the size of the 'boom' and its footprint. As the chart here shows the SR-71 flying at 80,000ft has less than half the footprint (pressure) of the Concorde flying at 50,000ft. (
https://aviation.stackexchange.com/...oom-produced-at-60-000-be-heard-on-the-ground) Above 100,000ft a sonic boom will rarely touch the ground, usually only when certain conditions and atmospheric effects are in place. And smaller airframes could avoid "sonic booms" by flying slower, (but still supersonic) and higher over populated country.
Note on the Oklahoma tests; None were above 50,000ft and most took place between 30,000ft and 40,000ft in order to cause ground pressure (booms) equivalent to those of the proposed Concorde (and its assumed American counter-part) with much smaller aircraft. (Tests ONLY used the F-101 and F-104 aircraft which were vastly smaller than the proposed SST designs) SSTs were assumed to fly no higher than 60,000ft and speeds of only Mach-2. The Oklahoma tests made no attempts to mitigate or reduce the sonic booms but specifically were designed to have the booms impact the ground in Oklahoma City eight (8) times a day for the whole test period with the assumption there would be that many (at least) over-flights per day, every day for transcontinental air routes. The aircraft did not fly "as high as possible" since the sonic booms would be barely detectable from that altitude due to the small size of the fighters used. They in fact flew BELOW nominal supersonic 'safe' altitude of the day which required supersonic flight only over 50,000ft or over 'cleared' (low or non-populated areas) BECAUSE they were trying to create ground level sonic booms.
It took me a while to figure that, but even the Space Shuttle makes sonic boom when it lands. And it comes from 200 miles high ! I mean that the shuttle confirmed the fact that, however high you fly (supersonically) in the atmosphere, there is a sonic boom heard on the ground.
Not correct as the Shuttle's sonic boom cone above Mach-3 is too narrow to impact the ground normally so you don't 'hear' it till it drops below Mach-2 and about 80,000ft to 60,000ft where the cone spreads out enough to actually impact the ground. Those how have heard the Shuttle passing over head usually hear the secondary or reflected sonic booms which sound like a low rumble rather than the sharp "boom" people are used to. Where you DO hear the Shuttle is around 10 minutes from landing as it drops to around Mach-1.5 and about 60,000ft.
And no you don't hear EVERY supersonic flight as both altitude and speed along with atmospheric conditions play a part in propagation or non-propagation of the sonic boom.
NASA has been working on lowering the sonic boom since 15 years, but progress has been very slow. They flew a modified F-5 Tiger, then a F-15. They have resumed research recently.
Actually they've been 'working' the issue since the mid-50s with the effort and support varying greatly over time

They've known for quite a while that the airframe shape had a lot to do with sonic boom propagation and combination, (most sonic booms are not one boom but the combination of multiple booms generated by the aircraft nose, body, wings and other surfaces combining as they propagate) but getting something to fly supersonic consistently has taken priority over boom mitigation till recently. They have also modified and flown an F-16XL and F-8 in attempts to modify or reduce sonic booms. There were a couple of modification proposed for their SR-71 they had for testing but not enough confidence in the outcome to risk. And that's actually the main issue in that they need a supersonic LARGE airframe to test how well the theory works. As the only models available to test with (Concord and the Russian SST) were unable to accept large changes or modifications they have been limited in what they could actually do.
Dogma my ar$$e. Or you should complain about volcanic eruptions PODs being considered ASB. sonic boom is a law of physics, or maybe the thread should be moved to ASB.
While sonic booms are the resulst of the laws of physics they are not inevitable nor are they uncontrollable. And what Riggerbob is pointing out there was a LOT of hysteria and hype over both the effects and damage generated by the SSTs, especially the Concord. (He's not kidding about the amount of media and legal hyper that would occur for ANY Concord flight whether it happened or not)
Alt history types should better read the end of my post, where I mention NASA research on sonic booms.
NACA, the military and NASA all researched at various times, means to reduce or eliminate sonic booms for various reasons. But it wasn't till after the FAA tests in Oklahoma in 1964 that the public and researchers were significantly made aware of the effects of multiple long term exposures. And this itself wasn't followed up by more in-depth studies until the early to mid-70s where the actual results were still significantly exceeded by the "claimed" consequences.
Concorde survived only because the sonic boom was tolerated... over oceans.
And yet you still had groups and individualts claiming that Concorde flights TO the US were responsible for curdling milk in Virgina and causing earthquakes in California when they landed in New York

Claims of being able to 'track' a Concord flight over the Atlantic by boats being damaged by over-flights was also never proven, or ozone depletion or fishery collapse which were also claimed to be all about the Concords sonic booms. It was in fact rare for anyone at sea to actually hear a sonic boom unless they were directly under the Concorde and even then it was more often than not a 'rumble' rather than a boom. Why? Surface and atmosphereic conditions and high humidity tended to dampen the shockwave significantly.
The Concorde was a first generation SST and showed it in performance and capability but you also needed that learning curve to transition from the over-optimism of the 50s to the reality of the 60s and move on through the 70s to an operational design.
To get a successful SST design you need to have researchers more aware of the actual problems and the public and media less hyper over the 'supposed' effects so that by the mid-70s you can start to design more economic, capable, and quieter air-frames. With time those would come as they have for smaller supersonic aircraft. Today to break into the market you have to have similar 'performance' (economics and passenger capacity) to the aircraft or significantly superior, (and Mach-1 or 2 won't cut it) performance in one or more areas.
Randy