Supersonic question.....
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From: Omokoroa, Bay of Plenty, New Zealand
Supersonic question.....
Ok… I once asked a question here about Mach speeds vs Stall speeds and got a very comprehensive reply from SNS3GUPPY . No-one growled too much (bloody simmers in our group !) and now something else is keeping me awake at night so I thought I’d try my luck again.
If I trade my (Microsoft Sim) 744 for a Concord and I’m blazing along somewhere close to FL400, at M0.85 thru M0.90 thru M0.95 thru M0.99.
Now Mmo is not going to be a problem for me so now I imagine that I’m flying up against a wall - (pushing the wall). As the afterburners push me thru M1.0 thur M1.1 I imagine that I ‘push thru’ the wall and as the wall moves (relatively slowly) along the length of the aircraft. Eventually, this pressure wave is going to get very close to some important aerodynamic controls (wings & control surfaces)
1. What happens to the aerodynamics of the wing and control surfaces whilst this is happening? (In fairly simple layman’s terms that even a simmer (with some engineering background) would understand).
2. As the afterburners continue to roar and I move to M1.2 and the ‘wall’ moves past the back of the tail of the aircraft am I now beyond the wall ? Do I now, given the same mass/power/attitude, experience increased acceleration up thru M1.5 until I start to feel the effect of the M2.0 wall approaching ?
If you HATE simmers on your forum…. Please ignore this entry.
If it just a silly question (and I should be taking sleeping tablets) – be kind explaining it to me.
Cheers
ChrisD
If I trade my (Microsoft Sim) 744 for a Concord and I’m blazing along somewhere close to FL400, at M0.85 thru M0.90 thru M0.95 thru M0.99.
Now Mmo is not going to be a problem for me so now I imagine that I’m flying up against a wall - (pushing the wall). As the afterburners push me thru M1.0 thur M1.1 I imagine that I ‘push thru’ the wall and as the wall moves (relatively slowly) along the length of the aircraft. Eventually, this pressure wave is going to get very close to some important aerodynamic controls (wings & control surfaces)
1. What happens to the aerodynamics of the wing and control surfaces whilst this is happening? (In fairly simple layman’s terms that even a simmer (with some engineering background) would understand).
2. As the afterburners continue to roar and I move to M1.2 and the ‘wall’ moves past the back of the tail of the aircraft am I now beyond the wall ? Do I now, given the same mass/power/attitude, experience increased acceleration up thru M1.5 until I start to feel the effect of the M2.0 wall approaching ?
If you HATE simmers on your forum…. Please ignore this entry.
If it just a silly question (and I should be taking sleeping tablets) – be kind explaining it to me.
Cheers
ChrisD
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From: various places .....
Chris,
No problem with flightsimmers - your questions are in the same ball park as those who play with the real birds and the answers should be of similar interest to the rest of the folk.
so now I imagine that I’m flying up against a wall
In the early days of compressible flight problems (WW2), the drag increase associated with approaching transonic speeds generated this concept of the sound "barrier". In reality, what we get is a drag hump transonically and then the drag reduces once you are reasonably well into the supersonic side (which is why we don't fly at or around M1). Not really a case of flying into a "wall" .. although it appeared that way as the thrust capabilities of the aircraft of the day were a bit modest for transonic flight .. which is why early experiments involved steep dive angles so that gravity helped out.
The other problems associated with handling tended to be associated with the movement of shockwaves and shock flow separation and were the real flight test problems until the boffins got their heads around what was going on.
the wall moves (relatively slowly) along the length of the aircraft.
Not too sure what you are thinking about here but let me have a stab at it.
At some stage (dependings on the aircraft design) you will get localised transonic flow in small regions of the airframe (typically just aft of the cockpit and somewhere near the thickest part of the wing).
As the aircraft speed increases, you end up with a shock wave as the local flow gets to the local speed of sound. This can produce significant flow problems unless the shape of the structure is designed to suit the flow requirements. There will be a small volume of supersonic flow ahead of the shock wave and the latter marks the surface where the flow transitions (quite abruptly) back to subsonic flow. An analogous situation is what you see in a sink if you turn the tap on hard - there is an outflow pattern from where the tap stream hits the sink surface and then an abrupt stationary water wave - this wave (usually referred to as an "hydraulic jump") is the equivalent of a shock wave.
As speed increases further, this initial shock wave surface gets bigger and moves back toward the trailing edges. At the same time the air molecules in front of the aircraft start to bunch up a bit and you get a bow wave (not unlike what you see ahead of a boat bow). Initially, this stands off a way from the front of the aircraft but moves back toward the aircraft as the speed gets into the transonic region.
As speed increases further the bow wave progresses aftwards until it intersects the sticky out bits of the front of the aircraft (nose, pitots, etc) and becomes attached to them. The "front" bump of the wave is referred to as a "normal" (ie at right angles) shock wave and is associated with significant changes in flow parameters (pressure, temperature, velocity, etc) while the slopey bits forming a cone are referred to as "oblique" shocks and have less of a flow problem. The early shocks on the aircraft move towards the trailing edges (often with quite a bit of jumping about) and attach there.
As the aircraft's speed increases supersonically through the transonic region, the flow patterns become stable and you end up with the nose shock wave and a trailing edge shock wave and the overall drag reduces to a steadier situation.
Other characteristics associated with the flow include
(a) the conical angle of the shock wave is related to the Mach number and is referred to as the Mach angle
(b) the "sonic boom" we hear about from time to time is what occurs as the leading and trailing edge shocks traverse a location. You get a rapid double pressure pulse and the characteristic "bang -bang" audio trace. The intensity of the sound depends on a bunch of parameters but, for supersonic flight at cruise level, the ground pulse signature is a fairly gentle doublet.
Eventually, this pressure wave is going to get very close to some important aerodynamic controls (wings & control surfaces)
.. and, if the design doesn't accommodate the supersonic flow and shocks appropriately, you are going to get severe flow disruptions, flow separations and all sorts of nasty pitching changes and generally deteriorating handling qualities.
What happens to the aerodynamics of the wing ..
Apart from the transition to supersonic flow, the main problem (handling related) is tied up with a general aftwards movement of the centre of pressure (net effective lift point, if you prefer). This leads to a significant increase in nosedown pitching tendency (pitching moment) and, if the aircraft is not designed for it, significant handling problems (Mach tuck). In the early days, a number of aircraft were lost as the dive was uncontrollable and led to structural failure. In addition, for subsonic designs, there is a high likelihood that the flow will separate at the shock wave and you can find your control surfaces in separation areas (ie useless). An alternative problem can see localised aftwards movement of control surface CP leading to hinge moments (tendency for the control to move one way or the other due to airloads) too high for the pilot to overcome (think of the pilot's control inputs as being intended to move the control surface and that this movement is resisted by the hinge moment - the pilot feels an increasing stick load and eventually, it all gets just to much for the pilot to push and pull as necessary to effect a movement).
until I start to feel the effect of the M2.0 wall approaching ?
I have no idea what you are considering when you refer to a "wall" around M2. Perhaps you are looking at the temperature rise associated with supersonic flow (an M^2 function so it ramps up rapidly) - generally we consider this to become a significant problem for aluminium structures due to structural weaking associated with increasing metal temperature. You will be aware that the high speed aircraft (SR-71 and similar) have all sorts of exotic materials to permit operation at these elevated skin temperatures.
No problem with flightsimmers - your questions are in the same ball park as those who play with the real birds and the answers should be of similar interest to the rest of the folk.
so now I imagine that I’m flying up against a wall
In the early days of compressible flight problems (WW2), the drag increase associated with approaching transonic speeds generated this concept of the sound "barrier". In reality, what we get is a drag hump transonically and then the drag reduces once you are reasonably well into the supersonic side (which is why we don't fly at or around M1). Not really a case of flying into a "wall" .. although it appeared that way as the thrust capabilities of the aircraft of the day were a bit modest for transonic flight .. which is why early experiments involved steep dive angles so that gravity helped out.
The other problems associated with handling tended to be associated with the movement of shockwaves and shock flow separation and were the real flight test problems until the boffins got their heads around what was going on.
the wall moves (relatively slowly) along the length of the aircraft.
Not too sure what you are thinking about here but let me have a stab at it.
At some stage (dependings on the aircraft design) you will get localised transonic flow in small regions of the airframe (typically just aft of the cockpit and somewhere near the thickest part of the wing).
As the aircraft speed increases, you end up with a shock wave as the local flow gets to the local speed of sound. This can produce significant flow problems unless the shape of the structure is designed to suit the flow requirements. There will be a small volume of supersonic flow ahead of the shock wave and the latter marks the surface where the flow transitions (quite abruptly) back to subsonic flow. An analogous situation is what you see in a sink if you turn the tap on hard - there is an outflow pattern from where the tap stream hits the sink surface and then an abrupt stationary water wave - this wave (usually referred to as an "hydraulic jump") is the equivalent of a shock wave.
As speed increases further, this initial shock wave surface gets bigger and moves back toward the trailing edges. At the same time the air molecules in front of the aircraft start to bunch up a bit and you get a bow wave (not unlike what you see ahead of a boat bow). Initially, this stands off a way from the front of the aircraft but moves back toward the aircraft as the speed gets into the transonic region.
As speed increases further the bow wave progresses aftwards until it intersects the sticky out bits of the front of the aircraft (nose, pitots, etc) and becomes attached to them. The "front" bump of the wave is referred to as a "normal" (ie at right angles) shock wave and is associated with significant changes in flow parameters (pressure, temperature, velocity, etc) while the slopey bits forming a cone are referred to as "oblique" shocks and have less of a flow problem. The early shocks on the aircraft move towards the trailing edges (often with quite a bit of jumping about) and attach there.
As the aircraft's speed increases supersonically through the transonic region, the flow patterns become stable and you end up with the nose shock wave and a trailing edge shock wave and the overall drag reduces to a steadier situation.
Other characteristics associated with the flow include
(a) the conical angle of the shock wave is related to the Mach number and is referred to as the Mach angle
(b) the "sonic boom" we hear about from time to time is what occurs as the leading and trailing edge shocks traverse a location. You get a rapid double pressure pulse and the characteristic "bang -bang" audio trace. The intensity of the sound depends on a bunch of parameters but, for supersonic flight at cruise level, the ground pulse signature is a fairly gentle doublet.
Eventually, this pressure wave is going to get very close to some important aerodynamic controls (wings & control surfaces)
.. and, if the design doesn't accommodate the supersonic flow and shocks appropriately, you are going to get severe flow disruptions, flow separations and all sorts of nasty pitching changes and generally deteriorating handling qualities.
What happens to the aerodynamics of the wing ..
Apart from the transition to supersonic flow, the main problem (handling related) is tied up with a general aftwards movement of the centre of pressure (net effective lift point, if you prefer). This leads to a significant increase in nosedown pitching tendency (pitching moment) and, if the aircraft is not designed for it, significant handling problems (Mach tuck). In the early days, a number of aircraft were lost as the dive was uncontrollable and led to structural failure. In addition, for subsonic designs, there is a high likelihood that the flow will separate at the shock wave and you can find your control surfaces in separation areas (ie useless). An alternative problem can see localised aftwards movement of control surface CP leading to hinge moments (tendency for the control to move one way or the other due to airloads) too high for the pilot to overcome (think of the pilot's control inputs as being intended to move the control surface and that this movement is resisted by the hinge moment - the pilot feels an increasing stick load and eventually, it all gets just to much for the pilot to push and pull as necessary to effect a movement).
until I start to feel the effect of the M2.0 wall approaching ?
I have no idea what you are considering when you refer to a "wall" around M2. Perhaps you are looking at the temperature rise associated with supersonic flow (an M^2 function so it ramps up rapidly) - generally we consider this to become a significant problem for aluminium structures due to structural weaking associated with increasing metal temperature. You will be aware that the high speed aircraft (SR-71 and similar) have all sorts of exotic materials to permit operation at these elevated skin temperatures.
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Basically as I understand trans-Mach/Mach. Aircraft designed to do so have their wings and other horizontal airfoils designed to penetrate at the same time (many lost aircraft in this trial and error by the USAF).
When entering "Trans Mach" commercial airliners have to my knowledge fallen victim to the "Mach Tuck" where ther center of lift transverses aft of the wing (loosing all lift) while the stab maintains sub mach speeds (lift) creating what had been percieved by early aviators as a stall.
Mach tuck - Wikipedia, the free encyclopedia
As I understand the leading edge of the airfoils maintain a constant pressure after the transition to mach speed is achived. "the snail crept along the razor"....
When entering "Trans Mach" commercial airliners have to my knowledge fallen victim to the "Mach Tuck" where ther center of lift transverses aft of the wing (loosing all lift) while the stab maintains sub mach speeds (lift) creating what had been percieved by early aviators as a stall.
Mach tuck - Wikipedia, the free encyclopedia
As I understand the leading edge of the airfoils maintain a constant pressure after the transition to mach speed is achived. "the snail crept along the razor"....
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A bit wide of the mark (pun intended ...)
Aircraft designed to do so have their wings and other horizontal airfoils designed to penetrate at the same time
Probably what you are thinking about here is the sweep angles being constrained to be a bit tighter than the (design) mach angle so that the forward surfaces of the aircraft are contained within the the bow wave oblique shocks. Otherwise, drag and handling problems would become a worry.
commercial airliners have to my knowledge fallen victim to the "Mach Tuck"
Applies to all the higher performance jet transports. This is one of the reasons for speed limits as too significant an excursion will put the aircraft in this region. Generally not a big deal - you just slow down a bit. However, some of the early jet upsets saw aircraft getting into a situation where stab jacks stalled and the aircraft were lost. Most aircraft with a problem will have some sort of auto trim function to act against the early stages of Mach tuck.
where their center of lift transverses aft of the wing (loosing all lift) while the stab maintains sub mach speeds (lift) creating what had been percieved by early aviators as a stall.
Not too sure where this one came from. For subsonic flow, the CP lives somewhere near the quarter chord position. For supersonic flow, the CP changes address and moves to around the half chord position. Much of the problem with the transonic region is associated with this transition of CP position. Many problems can arise if the wing profile is not designed for supersonic flow due to shock induced flow separation. The stab, like the wing, gets involved with the same sort of flow problems if it's not suitably designed.
the leading edge of the airfoils maintain a constant pressure after the transition to mach speed is achived. "the snail crept along the razor"....
Got me foxed here. The wing leading edge will be constrained to lie within the Mach cone so the flow should be similar along its length.
Regarding the Wiki link, which I have now had a chance to scan .. I wouldn't waste your time with it. Mostly a montage of gobbledegook, misunderstood airflow principles, and general nonsense. Any of the standard aero engineering texts would be a better source of description. Actually, I found it interesting to read .. this is the first Wiki reference I have followed (not many in total) which has been basically nonsense.
Aircraft designed to do so have their wings and other horizontal airfoils designed to penetrate at the same time
Probably what you are thinking about here is the sweep angles being constrained to be a bit tighter than the (design) mach angle so that the forward surfaces of the aircraft are contained within the the bow wave oblique shocks. Otherwise, drag and handling problems would become a worry.
commercial airliners have to my knowledge fallen victim to the "Mach Tuck"
Applies to all the higher performance jet transports. This is one of the reasons for speed limits as too significant an excursion will put the aircraft in this region. Generally not a big deal - you just slow down a bit. However, some of the early jet upsets saw aircraft getting into a situation where stab jacks stalled and the aircraft were lost. Most aircraft with a problem will have some sort of auto trim function to act against the early stages of Mach tuck.
where their center of lift transverses aft of the wing (loosing all lift) while the stab maintains sub mach speeds (lift) creating what had been percieved by early aviators as a stall.
Not too sure where this one came from. For subsonic flow, the CP lives somewhere near the quarter chord position. For supersonic flow, the CP changes address and moves to around the half chord position. Much of the problem with the transonic region is associated with this transition of CP position. Many problems can arise if the wing profile is not designed for supersonic flow due to shock induced flow separation. The stab, like the wing, gets involved with the same sort of flow problems if it's not suitably designed.
the leading edge of the airfoils maintain a constant pressure after the transition to mach speed is achived. "the snail crept along the razor"....
Got me foxed here. The wing leading edge will be constrained to lie within the Mach cone so the flow should be similar along its length.
Regarding the Wiki link, which I have now had a chance to scan .. I wouldn't waste your time with it. Mostly a montage of gobbledegook, misunderstood airflow principles, and general nonsense. Any of the standard aero engineering texts would be a better source of description. Actually, I found it interesting to read .. this is the first Wiki reference I have followed (not many in total) which has been basically nonsense.
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From: If this is Tuesday, it must be?
"for supersonic flight at cruise level, the ground pulse signature is a fairly gentle doublet."
Hmm, you obviously never had the joy of being in a boat underneath Concorde's path. It used to be a bit like two rounds from a rifle right beside your ear. After I heard that a couple of times I realised why they couldn't let it fly supersonic over land.
Hmm, you obviously never had the joy of being in a boat underneath Concorde's path. It used to be a bit like two rounds from a rifle right beside your ear. After I heard that a couple of times I realised why they couldn't let it fly supersonic over land.
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From: various places .....
Indeed, the signature can be damaging (significant or minor)/distressing/benign/non-existent (at ground level) depending on a bunch of parameters relating to atmospherics, height, and manoeuvring.
As a friendly balance to your Concorde observation, when the initial proving flight to Australia was conducted (as I recall around 1971 ?), the doublet (which was recorded by a DCA team enjoying the Central Australian sunshine at the time) as the bird came over at cruise was a benign pop-pop sort of audio thing.
However, I have a variety of mates who are ex-MIL FJ and they have tales by the legion relating to broken windows etc., etc. Hence the regulatory problems which beset Concorde's general commercial success with limitations restricting supersonic flight to overwater and some overland areas.
We all have experienced similar and higher overpressure levels when we hear the crack of the shock wave associated with thunderstorm lightning strikes ... well do I recall one in Jo'burg when I was working there some years ago .. and the bolt strike blew off a goodly section of the roof on the adjoining motel room ... while I was idly lazing about at the door looking at the rain outside ... now, that got my attention ... not to mention causing a degree of tinnitus for the next day or so.
I guess that, when I relax a bit and ease out of the politically correct, I am a lover of Speys, early JT8Ds, F111s, F16s and the like .... if it's not noisy ... what use is it ?
As a friendly balance to your Concorde observation, when the initial proving flight to Australia was conducted (as I recall around 1971 ?), the doublet (which was recorded by a DCA team enjoying the Central Australian sunshine at the time) as the bird came over at cruise was a benign pop-pop sort of audio thing.
However, I have a variety of mates who are ex-MIL FJ and they have tales by the legion relating to broken windows etc., etc. Hence the regulatory problems which beset Concorde's general commercial success with limitations restricting supersonic flight to overwater and some overland areas.
We all have experienced similar and higher overpressure levels when we hear the crack of the shock wave associated with thunderstorm lightning strikes ... well do I recall one in Jo'burg when I was working there some years ago .. and the bolt strike blew off a goodly section of the roof on the adjoining motel room ... while I was idly lazing about at the door looking at the rain outside ... now, that got my attention ... not to mention causing a degree of tinnitus for the next day or so.
I guess that, when I relax a bit and ease out of the politically correct, I am a lover of Speys, early JT8Ds, F111s, F16s and the like .... if it's not noisy ... what use is it ?
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From: Hampshire
Just to add a few elaborations to John T's excellent replies:
As the wing approaches M1 the local mach no over the top of the wing will reach M1 before the rest of the aircraft does (faster local airflow over the wing). The shockwave normally starts to form at about the half chord position and then moves aft as speed increases. At about the same time the leading edge shock also forms. Eventually the shock that started to form at the half chord position moves right back to the trailing edge of the wing and once the aircraft is fully supersonic, there will be a very clear shock wave attached to the wing leading edge, and another attached to the trailing edge.
The problems come during the transonic phase, as the aircraft transitions from subsonic to supersonic speed. For example, mach tuck (as already mentioned) due to the pressure distribution on the wing moving aft. Not only does this cause a nose-down pitching moment, but it also changes the directional stability and pitch stability. Also, as the wing shockwave moves aft it can cause control problems such as control reversal, excessively large control forces, or control surface failure.
If you look at modern supersonic aircraft, most have all-moving tailplanes (or canards and/or elevons if they have a delta wing) driven by powerful hydraulic (irreversible) flight control actuators to ensure control is retained throughout the transonic phase.
As the wing approaches M1 the local mach no over the top of the wing will reach M1 before the rest of the aircraft does (faster local airflow over the wing). The shockwave normally starts to form at about the half chord position and then moves aft as speed increases. At about the same time the leading edge shock also forms. Eventually the shock that started to form at the half chord position moves right back to the trailing edge of the wing and once the aircraft is fully supersonic, there will be a very clear shock wave attached to the wing leading edge, and another attached to the trailing edge.
The problems come during the transonic phase, as the aircraft transitions from subsonic to supersonic speed. For example, mach tuck (as already mentioned) due to the pressure distribution on the wing moving aft. Not only does this cause a nose-down pitching moment, but it also changes the directional stability and pitch stability. Also, as the wing shockwave moves aft it can cause control problems such as control reversal, excessively large control forces, or control surface failure.
If you look at modern supersonic aircraft, most have all-moving tailplanes (or canards and/or elevons if they have a delta wing) driven by powerful hydraulic (irreversible) flight control actuators to ensure control is retained throughout the transonic phase.
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From: Bracknell, Berks, UK
"for supersonic flight at cruise level, the ground pulse signature is a fairly gentle doublet."
Hmm, you obviously never had the joy of being in a boat underneath Concorde's path. It used to be a bit like two rounds from a rifle right beside your ear. After I heard that a couple of times I realised why they couldn't let it fly supersonic over land.
Hmm, you obviously never had the joy of being in a boat underneath Concorde's path. It used to be a bit like two rounds from a rifle right beside your ear. After I heard that a couple of times I realised why they couldn't let it fly supersonic over land.
YouTube - concorde sonic boom
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From: east of 10° west
for all interested..
if you want to learn about Concorde and supersonic flight the definite book I would like to recommend is:
Flying Concorde
by Brian Calvert..
Brian Calvert used to be fleet chief Concorde at BA when the bird was spec'ed and introduced..
Superb writing from one who knew that bird intimately..
http://http://www.amazon.com/Flying-.../dp/1840373520
Flying Concorde
by Brian Calvert..
Brian Calvert used to be fleet chief Concorde at BA when the bird was spec'ed and introduced..
Superb writing from one who knew that bird intimately..
http://http://www.amazon.com/Flying-.../dp/1840373520
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From: Oil Capital of Central Scotland
For what it's worth, way back in my college days, some of the guys on my course tied their brains in knots when the fluid dynamics lectures moved from wind tunnel mach applications (fixed, static wing) to flying applications (moving, cranked wing).
The way that my lecturer (sharp cookie) talked them round was to tell them that for a straight wing, as per the classic WW2 fighter lost in the dive scenario, the shockwave would form at the top of the wing chord and as speed build up would creep back to form a nice line just at the ailerons on the wing and likewise a smaller but deadlier one could form on the tailplane and creep back to mask the elevator, depending on the vertical arrangement of the wing and tailplane. However, he told them that the modern delta or cranked wing arrangement encouraged the shockwave to form in a line across the control surface, rather than along the entire control surface.
I can't quite recall just how accurate the explanantion is at present as it's been nigh on 20 years since I graduated, but it seemed to do the trick when I saw it used in anger.....
The way that my lecturer (sharp cookie) talked them round was to tell them that for a straight wing, as per the classic WW2 fighter lost in the dive scenario, the shockwave would form at the top of the wing chord and as speed build up would creep back to form a nice line just at the ailerons on the wing and likewise a smaller but deadlier one could form on the tailplane and creep back to mask the elevator, depending on the vertical arrangement of the wing and tailplane. However, he told them that the modern delta or cranked wing arrangement encouraged the shockwave to form in a line across the control surface, rather than along the entire control surface.
I can't quite recall just how accurate the explanantion is at present as it's been nigh on 20 years since I graduated, but it seemed to do the trick when I saw it used in anger.....
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From: Moses Lake, WA
Concorde sonic booms
When I was at test pilot school in France we had a very interesting sonic boom lecture. In North America, to avoid complaints from the public, military jets were prohibited from supersonic flight, except in some very specific areas. The French had a very adult approach to sonic booms from military jets - they spent hours teaching you about sonic boom propogation, so you had a chance of predicting which spots on the ground would get hit by a sonic boom if you did certain things, and then they told you "you can fly as fast as you want, where ever you want, but don't bang any populated areas".
The lecturer was a very experienced sonic boom expert, who had participated in the sonic boom studies that were done when Concorde was in development. He explained that as the sonic booms from Concorde were coming down towards the ground, they would be refracted as the speed of sound changed due to the increasing air temperature. If the atmosphere was close to standard conditions, and the ground level was close to sea level, the sonic boom from Concorde in cruise would be refracted such that the angle of descent of the boom decreased at it approached the ground. The angle of descent of the boom would reach zero several thousand feet above the ground, then it would start going upwards, without touching the ground. It would be refracted as it increased in altitude, and its angle of ascent would increase until it hit the tropopause, where the air temperature became constant, and thus the speed of sound was constant. The boom would continue to very high altitude, when the air temperature would start increasing as the altitude increased, which would cause the boom to be refracted again. It's angle of ascent would decrease with altitude, and it would eventually start coming down again. It would be coming down quite steeply on this pass, and it would hit the ground. But it would have travelled such a long distance by the time it hit the ground that it would be quite weak, and at a very acceptable level.
Of course, the atmospheric temperature profile is often quite far from standard, and it was possible for the Concorde sonic boom to hit the ground on the first pass. In this case it would be very strong, and probably not acceptable to the public. The sonic boom would also be very strong when the aircraft was accelerating, or if it was turning in supersonic flight, as these manoeuvres would focus parts of the boom, such that the sonic energy created at different locations along the flight path would be concentrated in a small area.
I was home visiting my parents in south western Nova Scotia many, many years ago. I was helping my father work outside, and I noticed that he kept looking at his watch. I asked him why, and he said that he had noted a very faint boom about the same time each day, which he assumed came from Concorde. Sure enough, at the appointed hour I heard a very, very faint boom - I would not have noticed it unless I had been looking for it. Later, I tracked down the Concorde schedules, and it was plausible that he was hearing the boom as it went by Nova Scotia.
The lecturer was a very experienced sonic boom expert, who had participated in the sonic boom studies that were done when Concorde was in development. He explained that as the sonic booms from Concorde were coming down towards the ground, they would be refracted as the speed of sound changed due to the increasing air temperature. If the atmosphere was close to standard conditions, and the ground level was close to sea level, the sonic boom from Concorde in cruise would be refracted such that the angle of descent of the boom decreased at it approached the ground. The angle of descent of the boom would reach zero several thousand feet above the ground, then it would start going upwards, without touching the ground. It would be refracted as it increased in altitude, and its angle of ascent would increase until it hit the tropopause, where the air temperature became constant, and thus the speed of sound was constant. The boom would continue to very high altitude, when the air temperature would start increasing as the altitude increased, which would cause the boom to be refracted again. It's angle of ascent would decrease with altitude, and it would eventually start coming down again. It would be coming down quite steeply on this pass, and it would hit the ground. But it would have travelled such a long distance by the time it hit the ground that it would be quite weak, and at a very acceptable level.
Of course, the atmospheric temperature profile is often quite far from standard, and it was possible for the Concorde sonic boom to hit the ground on the first pass. In this case it would be very strong, and probably not acceptable to the public. The sonic boom would also be very strong when the aircraft was accelerating, or if it was turning in supersonic flight, as these manoeuvres would focus parts of the boom, such that the sonic energy created at different locations along the flight path would be concentrated in a small area.
I was home visiting my parents in south western Nova Scotia many, many years ago. I was helping my father work outside, and I noticed that he kept looking at his watch. I asked him why, and he said that he had noted a very faint boom about the same time each day, which he assumed came from Concorde. Sure enough, at the appointed hour I heard a very, very faint boom - I would not have noticed it unless I had been looking for it. Later, I tracked down the Concorde schedules, and it was plausible that he was hearing the boom as it went by Nova Scotia.
