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View Full Version : Why the fuss over a sonic boom? Why don't we hear them more often?



MAddis
2012-Apr-13, 05:32 PM
The media in the UK has given a lot of air time or column inches over the last couple of days to a story about a Typhoon fighter aircraft whose sonic boom was heard by a large number of people across England and which, initially, caused a lot of confusion about what it might have been.
http://www.bbc.co.uk/news/uk-england-17699357

The thing that surprised me was why a sonic boom might be so unusual and unfamiliar to people. Surely, I thought, the Royal Air Force has dozens of supersonic aircraft and they must be going supersonic all the time as part of their training regime? But apparently not. The Ministry of Defence says that they need special permission.

So, my questions are, is it really so rare for military aircraft to go supersonic? Or do they merely do it out to sea or at a high altitude where no one can hear them? Are sonic booms more commonly heard in other countries?

I grew up in the Forest of Dean and we would frequently have fighter jets (Tornados and Jaguars, plus also Harriers - although I am aware that the latter are not supersonic) screaming low and loud over our school. Was I hearing a sonic boom then, or just subsonic flight? Is a sonic boom much worse, hence the surprise and confusion across the UK on Thursday?

I'm sure that many BAUTers have the aerospace knowledge to answer me, so thanks in advance for the enlightenment. I hope I am posting these questions in the right place.

PetersCreek
2012-Apr-13, 06:14 PM
In the US, military supersonic flight is normally restricted to airspace reserved for training, so long as that area is cleared for Mach+ flight...meaning over un- or sparsely-populated areas.

Call it being a good neighbor or good public relations. Sonic booms can be annoying and even frightening to adults, children, and animals and sufficiently close by, sonic booms can cause property damage. People who are upset by these things, often complain to their elected representatives. In turn, those representatives (who may have sway over military funding) may complain to the military. When other Mach+ training areas are available, it's kind of hard to justify a necessity for doing so near a complaining populace.

IsaacKuo
2012-Apr-13, 06:17 PM
Fighter jets like the Typhoon can't sustain supersonic flight for very long, and do not regularly fly supersonic even during combat operations.

You did not hear a sonic boom, unless it was one or two loud sharp cracks.

In contrast, the Concorde was designed to sustain supersonic flight for hours.

redshifter
2012-Apr-13, 06:39 PM
I used to hear them a lot in my hometown in eastern Washington (state). They'd frequently rattle windows and would be quite loud sometimes. Over here in Seattle, I've heard them maybe twice in 20 + years. The last time we heard them here were under interesting circumstances. Apparantly an unknowing pilot flew his small craft too near the airspace around Air Force One. F-15's were scrambled from Portland and apparantly the booms were from when they decelerated out of supersonic flight. Big news item that day. IIRC the pilot was questioned and found to be no threat, he just didn't realize what was going on. Not sure if his license was revoked or not...

http://blogs.seattleweekly.com/dailyweekly/2010/08/sonic_boom_felt_in_seattle_dur.php

Gillianren
2012-Apr-13, 07:13 PM
Yeah, I was going to mention that second one. I was standing outside the grocery store at the time, and the windows shook. A bunch of us were speculating about what was going on, and when the second boom came, we all said, "Oh." But here in Olympia, it was loud.

slang
2012-Apr-13, 09:58 PM
So, my questions are, is it really so rare for military aircraft to go supersonic? Or do they merely do it out to sea [...]

Yes. For air to air combat training there are several socalled 'Temporary Reserved Airspaces' (TRA) over the North Sea.

(caveat: IIRC!) There were/are about 7 of them controlled by Dutch airforce, and I'm pretty sure the RAF has several available as well. Supersonic flight was allowed only in the northern most of those. I can't recall whether it was the northernmost 2, or more. These areas are used for live firing practices as well (using towed targets, sophisticated hit counters and flags).


I grew up in the Forest of Dean and we would frequently have fighter jets (Tornados and Jaguars, plus also Harriers - although I am aware that the latter are not supersonic) screaming low and loud over our school. Was I hearing a sonic boom then, or just subsonic flight? Is a sonic boom much worse, hence the surprise and confusion across the UK on Thursday?

You were just hearing subsonic jet noise. The Tornado is very loud at high power settings and low altitude. Try to visit some flight demonstration days, or somewhere the Red Arrows perform. Even those can be quite loud, and they're just trainers!

PetersCreek
2012-Apr-13, 10:49 PM
You were just hearing subsonic jet noise. The Tornado is very loud at high power settings and low altitude. Try to visit some flight demonstration days, or somewhere the Red Arrows perform. Even those can be quite loud, and they're just trainers!

To that I'll add that if the Tornado is like any other fighter I worked on/around, the sound level can vary greatly depending on aspect relative to the listener. Take the F4 Phantom, for instance. They were loudest at a point approximately 45 to either side of the exhaust nozzles, while at a distance, the aircraft could seem virtually silent at certain aspects. This means a hard turning aircraft could exhibit a rapidly rising and falling rumble...kind of boomish, if you will.

Note: While deployed to Nellis AFB, Nevada one year, a squadron each of Tornadoes and Jaguars were parked down the ramp from us. I didn't get to spend any time around the jets, really but their maintenance crews were billeted in the same hotel we were. The were...um...colorful characters. We had a lot of fun off duty.

swampyankee
2012-Apr-13, 11:39 PM
Fighter jets like the Typhoon can't sustain supersonic flight for very long, and do not regularly fly supersonic even during combat operations.

You did not hear a sonic boom, unless it was one or two loud sharp cracks.

In contrast, the Concorde was designed to sustain supersonic flight for hours.

The Eurofighter Typhoon, Rafale, F-22, and possibly the Gripen can all cruise supersonically. So could, historically, the F-104, the F-14, and probably the F-15. I believe the last three could not go from M<1 to M>1 without using their afterburners; the F-22 can, and the Typhoon may be able to do so, also.

Most aircraft can't operate on afterburner very long; as a reasonable rule of thumb thrust at 35,000 ft and M=2 is the same as sea level, static thrust. Fuel consumption in afterburner is about 2 - 2.5 lbm/hr/lbf (the higher the bypass ratio, the worse the sfc with afterburner), so an aircraft with about 60,000 lbf thrust in afterburner (sea level) will burn about 120,000 to 150,000 lbm of fuel per hour. Since the internal fuel capacity of a Typhoon is about 9000 lbm, it will run its internal tanks dry in about 4 minutes of afterburner. It's dry thrust is about 25,000 lbf (it will depend on Mach number, altitude, and the intake's efficiency) and the engine's sfc (dry) is about 0.7, so it would run its tanks dry in about 30 minutes.

Tensor
2012-Apr-14, 12:00 AM
The Eurofighter Typhoon, Rafale, F-22, and possibly the Gripen can all cruise supersonically. So could, historically, the F-104, the F-14, and probably the F-15. I believe the last three could not go from M<1 to M>1 without using their afterburners;

The F-15A (B,C and D without conformal tanks) could not cruise above mach 1 and, yes, it needed AB to go above Mach 1 in level flight or in a climb. The higher weight of the F-15E models slows them down a bit, but in level flight, they can go above mach 1 in AB.

slang
2012-Apr-14, 12:29 AM
The Eurofighter Typhoon, Rafale, F-22, and possibly the Gripen can all cruise supersonically.

Ref; wiki supercruise (http://en.wikipedia.org/wiki/Supercruise)


Most aircraft can't operate on afterburner very long

So to add as much time available for training in one of the TRA's our F-16's are usually carrying external tanks. Pilots prefer a clean configuration tho, because external stores put limits to the amount of G's they can pull. So if (as planners) we had one or more clean aircraft available, they'd ask to be assigned to the local airfield TMA instead of having to travel to the TRA's first.

swampyankee
2012-Apr-14, 02:51 AM
The F-15A (B,C and D without conformal tanks) could not cruise above mach 1 and, yes, it needed AB to go above Mach 1 in level flight or in a climb. The higher weight of the F-15E models slows them down a bit, but in level flight, they can go above mach 1 in AB.

I was referring specifically to the transition through the transonic drag rise. In general, combat aircraft are optimized for subsonic performance and manage to get supersonic through brute force. Some, between their aerodynamic design and engine properties, can cruise supersonically. I believe that, except for the F-22 it's never been a requirement.

profloater
2012-Apr-14, 12:48 PM
The Concord could fly supersonic for long periods and unfortunately for some, supersonic flying over land was banned after Boeing decided not to pursue their version. It doomed Concord to two basic routes and limited production. It used to go supersonic over the coast of Wales on the outward trip to NY and just occasionally when I lived in West Wales I caught the bang. It was very high by then and not especially frightening. I worked on that amazing aircraft and it was a pity from the technology point of view that it's routes were curtailed. Now the energy use would also be a concern.

Tensor
2012-Apr-14, 01:13 PM
I was referring specifically to the transition through the transonic drag rise. In general, combat aircraft are optimized for subsonic performance and manage to get supersonic through brute force. Some, between their aerodynamic design and engine properties, can cruise supersonically. I believe that, except for the F-22 it's never been a requirement.

Ahhhhhh, Ok. If that is the case, then in a clean configuration (no conformals, pylons, rails, tanks, missiles) then, yes, you are correct. However, the minute you start putting anything on the aircraft (either tanks, missiles or the gear needed to load them), to increase range or to make it combat capable, that ability goes away rather quickly. I think it can get away with having pylons and maybe rails.

Nicolas
2012-Apr-14, 01:45 PM
Just for clarity: an aircraft going supersonic is boomin' all the time. It doesn't go boom only when going from subsonic to supersonic or vice versa, but also as long as it is supersonic. The booms you hear are the shock waves. And a plane going supersonic has a constant shockwave, usually one at the nose and one at the tail. Hence the twin booms. You don't always hear twin booms though; sometimes it sounds more like a single boom.

As for sonic boom versus jet noise. In case of low flying aircraft, if you're not sure whether what you heard was a supersonic boom or not, then it wasn't. Don't get me wrong: jet engines can be LOUD and afterburners LOUDER. But sonic booms, they have a sudden character and the power to break things. While low flying Starfighters never shattered any of our windows, they could send a crack throughout the house's construction.

We almost never hear them anymore because of regulations.

swampyankee
2012-Apr-14, 02:38 PM
The Concord could fly supersonic for long periods and unfortunately for some, supersonic flying over land was banned after Boeing decided not to pursue their version. It doomed Concord to two basic routes and limited production. It used to go supersonic over the coast of Wales on the outward trip to NY and just occasionally when I lived in West Wales I caught the bang. It was very high by then and not especially frightening. I worked on that amazing aircraft and it was a pity from the technology point of view that it's routes were curtailed. Now the energy use would also be a concern.

Of course, part of the reason its routes were curtailed was because it was very closely tailored to the North Atlantic trade, which is still likely to be the most remunerative and most heavily used trans-oceanic route. Incidentally, I believe that the reason Boeing "decided not to pursue" their SST (the 2707) was because environmental concerns -- including sonic booms -- caused an end to government funding. In other words, Boeing decided not to pursue with their own money, especially since the likelihood was that commercial supersonic flight would not be allowed over the US.

MAddis
2012-Apr-14, 05:19 PM
Thanks everyone.

profloater
2012-Apr-14, 07:54 PM
I worked in the sales office during part of my apprenticeship and there were routes planned all over the world, not just the Atlantic and until supersonic flying over land was outlawed, they looked very promising. Many airstrips were already being extended or approved for extension for the much longer run Concord needed when the axe fell. Just one example was to Australia but the hops all involved overland flying. It is true the range planned was always for the New York run and all other routes used that limitation. When flying over America was assumed it was routed to avoid flying over the large cities.

publiusr
2012-Apr-15, 08:45 PM
Mystery booms/skyquakes recent...

http://news.lalate.com/2012/04/13/san-diego-earthquake-mystery-today-april-13-denied-as-sonic-boom/
http://hosted2.ap.org/ALOPE/d0066651ed0741d0a4b5a17736605923/Article_2012-03-22-Mysterious%20Booms-Wisconsin/id-f20debb5943942088c7e61ab303e3d59,

BigDon
2012-Apr-17, 04:46 PM
Also, let's not forget that ~ 45% of the regular customers of the Concord were killed in the 9/11 attacks. Can't tell me that doesn't effect your bottom line.

Delvo
2012-Apr-17, 05:59 PM
That attack happened about 8 years after the end of Concorde flights.

The book "Skunk Works" by Ben Rich, about the secret aircraft development section of Lockheed-Martin when it made the U-2, Blackbird, and F-117, tells a story about sonic booms. They had a policy of notifying the few little communities in the area where they did their tests, whenever they had supersonic test flight scheduled. But the complaints and hostility they got over the booms got so extreme that they started doing a funny little test: they'd occasionally put out a notification of upcoming supersonic flights, not actually make any such flights at those times, and sit back and watch the boom complaints roll in anyway.

cjl
2012-Apr-17, 08:37 PM
That attack happened about 8 years after the end of Concorde flights.

Concorde retired in November of 2003, more than 2 years after 9/11.


I do agree about the book Skunk Works though - it's an excellent read, and a must have for anyone interested in the history of military and high-performance aviation.

swampyankee
2012-Apr-17, 08:56 PM
Ahhhhhh, Ok. If that is the case, then in a clean configuration (no conformals, pylons, rails, tanks, missiles) then, yes, you are correct. However, the minute you start putting anything on the aircraft (either tanks, missiles or the gear needed to load them), to increase range or to make it combat capable, that ability goes away rather quickly. I think it can get away with having pylons and maybe rails.

It's not the aerodynamicist's fault that air forces want to turn their aircraft into flying airbrakes.

Tensor
2012-Apr-18, 03:42 AM
It's not the aerodynamicist's fault that air forces want to turn their aircraft into flying airbrakes.

Hehehehe, yeah, with as much stuff as they put on the E model, I'm surprised the thing got over 650 knots.

Tog
2012-Apr-18, 12:10 PM
I just want to say (somewhat tongue-in-cheek) that the F-22 doesn't really cruise at supersonic speeds as much is it desperately tries to avoid the horrendous noise it makes.

I used to live about 1 mile off the final approach for an air base. I got to the point I could identify F-16's and A-10's from the sound alone. The only thing that was really obnoxious was the KC-135 or 10's that took off to the north. They'd bank away and we'd get a tail-on shot of them for about 3 minutes as they climbed away. Any one of them made it hard to hear the TV when they went by.

Then the F-22's came to visit.

In my car, at freeway speed, with the windows up and the radio on loud enough to drown out the road noise, I can hear F-22s from miles off when they take off. When they land it's nearly as bad. It doesn't just wash out the TV, it washes out the yelling across the living room.

I've heard that the US has noise restrictions that apply to military craft, and that the Tornado is an exception since it's not a US plane. I've read where people complain about the noise Tornados make, but I can't imagine it could be much worse than an F-22.

cjl
2012-Apr-18, 08:54 PM
I just want to say (somewhat tongue-in-cheek) that the F-22 doesn't really cruise at supersonic speeds as much is it desperately tries to avoid the horrendous noise it makes.

I used to live about 1 mile off the final approach for an air base. I got to the point I could identify F-16's and A-10's from the sound alone. The only thing that was really obnoxious was the KC-135 or 10's that took off to the north. They'd bank away and we'd get a tail-on shot of them for about 3 minutes as they climbed away. Any one of them made it hard to hear the TV when they went by.

Then the F-22's came to visit.

In my car, at freeway speed, with the windows up and the radio on loud enough to drown out the road noise, I can hear F-22s from miles off when they take off. When they land it's nearly as bad. It doesn't just wash out the TV, it washes out the yelling across the living room.

I've heard that the US has noise restrictions that apply to military craft, and that the Tornado is an exception since it's not a US plane. I've read where people complain about the noise Tornados make, but I can't imagine it could be much worse than an F-22.

If you're comparing the 22 to the 16, I would imagine it would be quite a bit louder, as it is still using low bypass, afterburning turbofans, but it is twice the weight with more than twice the thrust. I doubt it's much louder than comparably sized fighters though, so an F-15 or F-14 might be a better comparison. Similarly, the A-10 shouldn't be terribly loud, as it has relatively little thrust and a higher bypass ratio. If anything, all the sources I can find on the F-22 indicate that it should generate less noise than average for a figher with its level of installed thrust and bypass ratio.

BigDon
2012-Apr-18, 10:22 PM
Mr. Tog, I can't quite disagree as I've never heard an F-22 inflight.

But I have to cast my vote for the A-6 Intruder in loiter mode.

Holy Mother of Pearl!

When one of the dirty so and so's would wander over the flightdeck about 500 feet up in said loiter mode, with a full bomb load and their exhaust nozzles pointed down, grown men wearing full flightdeck hearing protection are driven to tears from the pain. This is while wearing hearing protectection rated for a constant 128 DB enviroment.

cjl
2012-Apr-18, 10:49 PM
Here's a report on sound levels of several current fighters - interestingly enough, the 22 does seem to be one of the louder ones, especially far field. I'm having a hard time coming up with a reason why this might be, but it does seem to support your assertion.


http://www.f-16.net/f-16_forum_download-id-11481.html

BigDon
2012-Apr-18, 10:58 PM
Nice link Cjl!

swampyankee
2012-Apr-19, 12:10 AM
If you're comparing the 22 to the 16, I would imagine it would be quite a bit louder, as it is still using low bypass, afterburning turbofans, but it is twice the weight with more than twice the thrust. I doubt it's much louder than comparably sized fighters though, so an F-15 or F-14 might be a better comparison. Similarly, the A-10 shouldn't be terribly loud, as it has relatively little thrust and a higher bypass ratio. If anything, all the sources I can find on the F-22 indicate that it should generate less noise than average for a figher with its level of installed thrust and bypass ratio.

The A-10 is a fairly quiet aircraft -- those high-bypass fans, even with no special noise abatement treatments in the nacelles are quiet -- and the neighbors of the Connecticut Air National Guard were quite unhappy when it was announced that CANG was getting F-16s, which are noisy. They didn't -- the CANG's 103rd Fighter Wing became the 103rd Airlift Wing, and got Learjets (and is supposed to get G.222s) -- but I can't imagine the F-16s are as noisy as the F-100s CANG operated before the Warthogs.

Incidentally, the jet noise from an aircraft engine scales to the eighth power of the exhaust velocity. Yes, that means that doubling the jet velocity increases the radiate sound pressure level by a factor of 256.

cjl
2012-Apr-19, 02:03 AM
The A-10 is a fairly quiet aircraft -- those high-bypass fans, even with no special noise abatement treatments in the nacelles are quiet -- and the neighbors of the Connecticut Air National Guard were quite unhappy when it was announced that CANG was getting F-16s, which are noisy. They didn't -- the CANG's 103rd Fighter Wing became the 103rd Airlift Wing, and got Learjets (and is supposed to get G.222s) -- but I can't imagine the F-16s are as noisy as the F-100s CANG operated before the Warthogs.

Incidentally, the jet noise from an aircraft engine scales to the eighth power of the exhaust velocity. Yes, that means that doubling the jet velocity increases the radiate sound pressure level by a factor of 256.

Really? The eighth power? Is that for a comparable mass flow rate, a comparable thrust, or a comparable jet diameter, because if it's for the same jet diameter or mass flow rate, the two engines won't really be comparable to each other (as the higher jet velocity engine will also have substantially more thrust). That would explain why rockets are so loud though, as they have jet velocities approximately an order of magnitude higher than commercial jets, and perhaps 4 times higher than afterburning military jets.

Ara Pacis
2012-Apr-19, 06:21 PM
So, why do they allow home construction so close to airbases? Prohibiting that would seem like common sense.

Don, do they wear active noise-cancelling headphones on deck? Although those always make my head hurt, like it's under pressure under water or something.

Delvo
2012-Apr-19, 08:41 PM
Concorde retired in November of 2003, more than 2 years after 9/11.Akhck, I doubled the wrong digit in the number of the year "2001", and got "2011"! :eek:


In general, combat aircraft are optimized for subsonic performance and manage to get supersonic through brute force. Some, between their aerodynamic design and engine properties, can cruise supersonically. I believe that, except for the F-22 it's never been a requirement.
Ahhhhhh, Ok. If that is the case, then in a clean configuration (no conformals, pylons, rails, tanks, missiles) then, yes, you are correct. However, the minute you start putting anything on the aircraft (either tanks, missiles or the gear needed to load them), to increase range or to make it combat capable, that ability goes away rather quickly.That, along with radar signature reduction, is why modern fighters try to keep as many weapons as possible either semi-recessed (Typhoon) or totally enclosed (F-22, F-35). Anything that a plane needs to be "clean" to do, an F-22 can do while carrying 8 missiles.

Also, when talking about supercruising, at least among fighters, one should keep in mind that there are a couple of different definitions: according to one, anything over Mach 1 counts, but according to the other, it really needs to be at least 1.5 or so. The reason is that the low supersonic range isn't enough faster than high subsonic to make a significant difference, either tactically or economically. (The investors in the Concord, for example, paid for a plane that could fly twice as fast as the competition, but might not have thought it was worth it to pay for one that only went 50% faster.) Most fighters that are said to be able to supercruise right now, such as Typhoons, can only do so by the former, lower standard. The latter, higher standard is the one Lockheed-Martin is held to with F-22, which has about the same cruise speed as Concorde. As a result, it's not public knowledge yet whether or not their other new fighter, F-35, could be counted as a supercruiser according to the easier definition.


So, why do they allow home construction so close to airbases? Prohibiting that would seem like common sense.There's not really much of a choice. Where people live now is mostly where they already lived before airplanes existed, especially supersonic ones, so it's more a matter of building bases near the homes. And the base staff need to live somewhere and that usually means having a general population around them too, and these planes fly so far on each flight that there's practically no place a base could be put that isn't relatively "near" something. And for the remotest of remote sites, secret projects have priority over open, routine stuff. And the original post here was from a country that doesn't have anything like Siberia or the USA's desert Southwest (and even those regions are still populated anyway, even if not densely).

slang
2012-Apr-19, 08:57 PM
So, why do they allow home construction so close to airbases?

At the airbase where I served the vast majority of noise complaints came from people who had recently moved there, not the long term residents. There is a much bigger noise problem near the big commercial airfields. Military traffic (at least at 'my' airbase) tends to be a bunch of take-offs in the morning, and a bunch of landings. Repeat in the afternoon. At the bigger commercial airfields traffic is almost continously.

swampyankee
2012-Apr-19, 09:24 PM
Really? The eighth power? Is that for a comparable mass flow rate, a comparable thrust, or a comparable jet diameter, because if it's for the same jet diameter or mass flow rate, the two engines won't really be comparable to each other (as the higher jet velocity engine will also have substantially more thrust). That would explain why rockets are so loud though, as they have jet velocities approximately an order of magnitude higher than commercial jets, and perhaps 4 times higher than afterburning military jets.

Same diameter. It may actually be a lower mass flow rate (hotter gas, less dense). There is a noise benefit to smaller diameter; if I remember (no guarantee ;)) noise level falls by r-0.5, which is why aircraft like the straight-jet (J-57) engined 707s and DC-8s had these elaborate nozzles.

GeorgeLeRoyTirebiter
2012-Apr-19, 10:57 PM
Where people live now is mostly where they already lived before airplanes existed, especially supersonic ones, so it's more a matter of building bases near the homes.

That depends on what you mean by 'near.' Much of the central and western US was undeveloped enough that civilian and military airports could be built on farm/ranch lands well outside of the cities they served. In the years since, many of those cities have greatly expanded to abut or even surround those bases.

Trebuchet
2012-Apr-19, 11:47 PM
Mr. Tog, I can't quite disagree as I've never heard an F-22 inflight.

But I have to cast my vote for the A-6 Intruder in loiter mode.

Holy Mother of Pearl!

When one of the dirty so and so's would wander over the flightdeck about 500 feet up in said loiter mode, with a full bomb load and their exhaust nozzles pointed down, grown men wearing full flightdeck hearing protection are driven to tears from the pain. This is while wearing hearing protectection rated for a constant 128 DB enviroment.

I'll agree on the A-6, based just on one experience. I was out on the flight line at Paine Field in Everett, WA, with another engineer and there was an EA-6B from NAS Whidbey was doing touch and goes. The "go" part was almost painfully loud. I commented on it to the other guy and he said "Yeah, the F-14's are quieter." I'd forgotten he previously worked for Grumman on Long Island where they built both.

swampyankee
2012-Apr-20, 01:34 AM
Akhck, I doubled the wrong digit in the number of the year "2001", and got "2011"! :eek:

That, along with radar signature reduction, is why modern fighters try to keep as many weapons as possible either semi-recessed (Typhoon) or totally enclosed (F-22, F-35). Anything that a plane needs to be "clean" to do, an F-22 can do while carrying 8 missiles.

Also, when talking about supercruising, at least among fighters, one should keep in mind that there are a couple of different definitions: according to one, anything over Mach 1 counts, but according to the other, it really needs to be at least 1.5 or so. The reason is that the low supersonic range isn't enough faster than high subsonic to make a significant difference, either tactically or economically. (The investors in the Concord, for example, paid for a plane that could fly twice as fast as the competition, but might not have thought it was worth it to pay for one that only went 50% faster.) Most fighters that are said to be able to supercruise right now, such as Typhoons, can only do so by the former, lower standard. The latter, higher standard is the one Lockheed-Martin is held to with F-22, which has about the same cruise speed as Concorde. As a result, it's not public knowledge yet whether or not their other new fighter, F-35, could be counted as a supercruiser according to the easier definition.

There's not really much of a choice. Where people live now is mostly where they already lived before airplanes existed, especially supersonic ones, so it's more a matter of building bases near the homes. And the base staff need to live somewhere and that usually means having a general population around them too, and these planes fly so far on each flight that there's practically no place a base could be put that isn't relatively "near" something. And for the remotest of remote sites, secret projects have priority over open, routine stuff. And the original post here was from a country that doesn't have anything like Siberia or the USA's desert Southwest (and even those regions are still populated anyway, even if not densely).

Supersonic is supersonic. Saying a plane isn't supercruising because it's going M=1.2 instead of M=1.5 is sophistry. It might not make tactical sense. Military aircraft never have to make economic sense -- air forces are money sinks.

Kuchemann argued that, for a transatlantic flight, 1 < M < 2 wasn't worthwhile because the aircraft needed to make twice as many round trips per day to be economically viable. This may argue that something like M=5 would be the next logical step, because it takes a little time to get passengers and their luggage off of and on to an airplane, clean out the potties, restock the galley, etc.

Shaula
2012-Apr-20, 05:25 AM
I've heard that the US has noise restrictions that apply to military craft, and that the Tornado is an exception since it's not a US plane. I've read where people complain about the noise Tornados make, but I can't imagine it could be much worse than an F-22.
The GR4s and the ADVs have a fairly low thrust to weight, at least compared to something like an F-14 or F-22. Fully loaded they like to turn on the afterburners to get airborne without getting catcalls from the fighter pilots. Might be why they are so noisy. And for some reason even with afterburners they are loader than the F-14s - I've had the 'pleasure' of being right next to a runway without protective gear when both craft did full afterburn takeoffs and, as far as I could tell in my stunned state the Tornado hurt slightly more.

Ara Pacis
2012-Apr-20, 05:31 PM
That depends on what you mean by 'near.' Much of the central and western US was undeveloped enough that civilian and military airports could be built on farm/ranch lands well outside of the cities they served. In the years since, many of those cities have greatly expanded to abut or even surround those bases.

That's what I was thinking. At least commercial airports often have lots of parking lots and hotels and warehouses and manufacturing plants near them instead of homes on the other side of the fence. I'm thinking it might help for crashes too.

swampyankee
2012-Apr-21, 01:42 AM
That's what I was thinking. At least commercial airports often have lots of parking lots and hotels and warehouses and manufacturing plants near them instead of homes on the other side of the fence. I'm thinking it might help for crashes too.

Occasionally, local zoning authorities (for the BAUTers outside the US, or at least my part of the US, these are municipal organizations that decide what can be built where in towns and cities.) don't bother to talk to the FAA. The result can be rather grim.

That is what happened in this case (http://www.airdisaster.com/cgi-bin/view_details.cgi?date=06071971&reg=N5832&airline=Allegheny+Airlines). Many of the houses were condemned, as they were built too close to the airport's approach paths. Incidentally, at the normal 3 degree glide slope, an aircraft is about 275 ft (85 m) above the ground a mile from the runway.

Aircraft are not noisy on approach and landing -- the engines are roughly at idle -- but they are when taking off. Most combat aircraft are, by civilian standards, insanely overpowered, (air forces don't exist to make money) and, so, have much higher angles of climb than do commercial aircraft (the overpowered bit, probably because combat pilots really dislike being targets for any longer than absolutely necessary; commercial pilots try to stay away from people who are shooting at them), so they may have smaller noise footprints. This is almost certainly the case with modern fighter aircraft; it wasn't with F-100s, which made roughly as much noise as a 707 and probably had about the same angle of climb.

Incidentally, one of the reason modern commercial aircraft tend to have two engines, vs four (or three) is that certification requirements specify climb rates with one engine inoperative. This means that an aircraft with two out of two engines operating has twice the thrust needed to maintain its mandated one-engine-inoperative climb rate (minus the couple of percent extra thrust allowed by "one engine inoperative ratings", so the excess thrust may only be 1.95 times the thrust with one engine out) while a four engined aircraft has only 1.33 times the thrust it needs for the OEI climb rate: twins climb faster and, more importantly, more steeply, with one engine out than with four-engined aircraft.

headrush
2012-May-06, 08:04 AM
I live in Devon, south west England and we were used to hearing Concorde every night at around 19.30 (IIRC) as it went supersonic. It was only really loud when you considered how far away it was when you heard it. Close up it would have been devastating, but the altitude deadened the noise quite a bit.

It can't have been too intrusive, because after Concorde was grounded, I don't ever remember an occassion when I missed hearing the bangs.

On a different note, I was riding my motorbike on a road on Dartmoor one day and heard a terrifying screeching noise that was just like a car skidding towards me from behind. I panicked and pulled over in a hurry just as 2 Tornadoes screamed past at about 400 ft ! They do that quite a bit around here :-)

swampyankee
2012-May-06, 03:08 PM
On a different note, I was riding my motorbike on a road on Dartmoor one day and heard a terrifying screeching noise that was just like a car skidding towards me from behind. I panicked and pulled over in a hurry just as 2 Tornadoes screamed past at about 400 ft ! They do that quite a bit around here :-)

A friend had something similar happening: he was riding a horse in Wisconsin and heard a very loud noise. He dismounted, and a few seconds later got to see a B-52 roaring overhead.