I came across this reply in a dead Supersonic Travel thread.
If TL;DR, the statement says that fears about sonic booms were too hyped, as at high altitudes, the sonic boom's intensity would be very low. The user basically says that had knowledge about sonic booms been discovered earlier, people would have been more well-informed and not be too scared of SSTs and that efforts to lessen the sonic boom to tolerable levels would have been made, and thus they would have been widely used*. IMO, this also is a good case to make that had knowledge about sonic booms been discovered earlier, the SSTs would also have been widely used between inner cities as well.
*That is, if there were many SSTs before the 1973 Oil Crisis, or there were no 1970s Oil Crises at all, which would make SST travelling much cheaper
With that, what innovative technologies could have been available in the 1960s to mitigate sonic boom levels to extremely tolerable ones*2, so much that SSTs are the dominant form of travel not just in Continental and Transatlantic flights, but also, for intercity flights, e.g. between cities in the continental US like LAX-JFK?
*2 Even then, as the reply below said, the sonic boom, without much regulation, would even just be a low rumble if the SST flies at high altitudes.
If TL;DR, the statement says that fears about sonic booms were too hyped, as at high altitudes, the sonic boom's intensity would be very low. The user basically says that had knowledge about sonic booms been discovered earlier, people would have been more well-informed and not be too scared of SSTs and that efforts to lessen the sonic boom to tolerable levels would have been made, and thus they would have been widely used*. IMO, this also is a good case to make that had knowledge about sonic booms been discovered earlier, the SSTs would also have been widely used between inner cities as well.
*That is, if there were many SSTs before the 1973 Oil Crisis, or there were no 1970s Oil Crises at all, which would make SST travelling much cheaper
With that, what innovative technologies could have been available in the 1960s to mitigate sonic boom levels to extremely tolerable ones*2, so much that SSTs are the dominant form of travel not just in Continental and Transatlantic flights, but also, for intercity flights, e.g. between cities in the continental US like LAX-JFK?
*2 Even then, as the reply below said, the sonic boom, without much regulation, would even just be a low rumble if the SST flies at high altitudes.
Summoner wrote:
Archibald wrote:
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.
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.
Actually they've been 'working' the issue since the mid-50s with the effort and support varying greatly over timeThey'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.
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)
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.
And yet you still had groups and individuals claiming that Concorde flights TO the US were responsible for curdling milk in Virgina and causing earthquakes in California when they landed in New YorkClaims 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