Rules of supersonic flight

[Ray Proudfoot]

I know that Concorde had to be subsonic around 55nm before landfall to avoid laying its sonic boom but could remain supersonic providing it was >20nm abeam land.

This suggests there was a cone ahead and stretching to the sides of Concorde inside which it would have to be subsonic.

But what distance would be required to keep supersonic with land at 30° off the 10 or 2 o’clock position? Is there a diagram showing the distances?

This question concerns a flight from Lisbon to Manchester up the Irish Sea and whether I could remain supersonic until 55nm before LOMVO which is roughly half-way between Anglesey and Dublin.

[Fraser Gale]

Concorde’s boom carpet was around 40nm wide, so provided you were flying straight (I’ll come back to this) and you were in cruise at M2.00, you only need 20nm either side of you.  People on the coast may still hear a rumble as often happened near the channel when the AF Concordes went past.  
 

Whenever the aircraft is in an acceleration - this includes turns in a aeronautical sense - or a deceleration, it creates a focussed boom, where several booms merge.  This accentuates the noise bearing in mind Concorde already created two booms, one at the nose and one at the top of the tail fin.  Hence it is important you are flying straight and not in a turn.  
 

The 55nm figure you quote was a safety figure really, the boom in steady flight was thrown in all directions, roughly by a similar distance but because you would be decelerating, it becomes focussed hence more distance required.  There are some diagrams in the Intro to Supersonic Flight booklet from the conversion course but they wouldn’t be much use to you really. 
 

Remember each route was looked at by planners on a case by case basis.  

[Ray Proudfoot]

Thanks Fraser. The 20nm range looks okay and for all of my flights that I can think of I accelerate and decelerate supersonically only when straight and level. Given I have no access to the document you mention and my flights aren’t affecting real people 55mm seems a reasonable target.

So as Anglesey would have been at my 2 o’clock position I’ll aim to be subsonic 45-50nm from it. I seem to recall Concorde flew test flights down the Irish Sea so it was quite feasible.

[Fraser Gale]

I think one bit of my explanation wasn’t totally clear: when I talk about the focussed boom occurring in accelerated flight I don’t mean during THE acceleration.  Any time the aircraft turns or changes speed, it is going to create a focussed, more intense boom.  This is why people on Cyprus could hear Concorde go past from miles away, as she was in a turn at the time.  
Another example was one of the first captains on Concorde, Peter Duffy, wrote about descending into England and part way through realised they would be subsonic quite early. He thought he’d slow the deceleration by opening the throttles a bit, perfectly fine and they hit the subsonic point.  A couple of days later they had complaints about the boom and it showed that the change in pitch had thrown the boom forward quite well!   Hence the fixed decel procedure. 
 

If Anglesey is that far from you and you are going straight you can remain supersonic as long as you like.  In fact at that distance even in a turn you can stay supersonic. 
Those test flights boomed a lot of people too though - they didn’t care cause they weren’t an airline trying to sell seats. 

[Fabrice Estienne]

That's absolutely correct and for your perfect information...

[Ray Proudfoot]

Fabrice, thanks for that but I’m struggling to understand it. Is there an English equivalent?

Fraser, I’ll fly this route in the next few days and post a map so you can better judge the situation.

[Fabrice Estienne]

Ray, it's technical French, but close to technical English.

If your Mach is lower than the cut-off Mach then the bang will not be heard on the ground.

Below FL360 the atmosphere is not isotropic. The temperature varies according altitude and the propagation of the sonic bang undergoes refraction.

This is why the cut-off Mach at altitude is always greater than the unit, of course provided that the ground slope is not too negative.

Regarding turns, there is a focus on the sonic bang, therefore the CPD increases.

I hope I was clear enough without using tedious derivations.

Fabrice

[Ray Proudfoot]

Fabrice, thanks for trying to explain technical things to someone who has never achieved your level of expertise. I understand the Silence and Boom sections.

Using a translation service I understand that Angle de Varage is Turn Angle and the greater the turn the greater the distance the sonic boom will extend.

Also, the DPD needs 25nm adding to any calculated distance to ensure no sonic boom is heard on the ground.

Are those assumptions correct?

[Fraser Gale]

These diagrams are different to the ones BA used but essentially the top one shows the boom area and that during the deceleration phase you need to add 25nm (AF figure) because of the focussed boom I talked about. 
 

The bottom one shows the distance the boom will propagate in a turn for the same reason, you are in an acceleration. 
 

I am glad I got something correct for a change @Fabrice Estienne

[Fabrice Estienne]

Ray, that's correct.

1) Turns:

Regarding Concorde the standard CPD is 20 NM.

When a turn is necessary to avoid an area to be protected, the turning point must be chosen in such a way that the ground path of the aircraft remains at least at a distance from the CPD increased according the angle of the turn.

The angle of turn is defined by the paths of the aircraft that bypass the area to be protected.

For CPD = 20 NM, the (CDD + d) value is given in the following table:

 

2) Protection against sonic bang on arrival:

The DPD (Deceleration Projection Distance) is the ground distance between the point where the aircraft begins to decelerate and the point where the last bang is perceived on the ground. It varies according the weight of the aircraft, the altitude at the end of supersonic cruise, the rate of descent, temperature, and wind. The DPD includes a margin of 25 nautical. In other words, this margin is added to the ground deceleration distance from supersonic cruise to Mach 1.

The NBFDA (Normal Boom Free Distance at Arrival) is the ground distance where the last bang is perceived on the ground and the destination airport. It varies according the rate of descent and wind.

The RPDA (Required Protection Distance at Arrival) is the ground distance between a ground point where the area to be protected begins and the destination airport.

If NBFDA ≥ RPDA : no subsonic cruise to add;  the deceleration point is at a distance equal to NBFDA + DPD from the destination airport.

If NBFDA < RPDA :  subsonic cruise to add;  the deceleration point is at a distance equal to RPDA + DPD from the destination airport.

Fabrice

 

[Ray Proudfoot]

Hi Fabrice,

Thanks for your latest post. I think rather than trying to describe my situation I'd post a screenshot of the routing and see if what I am doing breaks any rules.

My plan is to be at FL360 / Mach 0.95 at LOMVO indicated by a red X. Thereafter there is a big right turn but because I'm now subsonic I can forget all the rules about supersonic turns. As you can see from the latter stages of the flight the decel started whilst in straight flight between Ireland and Wales. I'm sure being >20nm off both coasts I don't break any regs.

There is a distance scale bottom left and LOMVO is >20nm off Anglesey. Thoughts?

[Andrew Wilson]

Hi Ray,

In real life I think they’d have gone up the English Channel, via TAKAS and ORTAC (decel 60 to ORTAC) and then up to EGCC subsonic. That’s how they flew the bay charters back into MAN.

[Ray Proudfoot]

1 minute ago, Andrew Wilson said:

Hi Ray,

In real life I think they’d have gone up the English Channel, via TAKAS and ORTAC (decel 60 to ORTAC) and then up to EGCC subsonic. That’s how they flew the bay charters back into MAN.

Thank god for simulators then Andrew. No way would I fly that routing. It’s 1h 25m from Lisbon to Manchester the route I fly. I suspect that flying the ORTAC one there would be hardly any gain over subsonic.

I’m happy to stick to noise regs but enjoy creating my own routes. In reality there would never have been a LPPT-EGCC service so I feel my fictitious routing is legit. 

[Andrew Wilson]

If it’s of any interest: G-BOAC flew MAN - LIS 29 Aug 94 - flight time was 1h 23mins.

Return was subsonic to LHR.

[Ray Proudfoot]

6 minutes ago, Andrew Wilson said:

If it’s of any interest: G-BOAC flew MAN - LIS 29 Aug 94 - flight time was 1h 23mins.

Definitely of interest Andrew. With that flight time it must have flown something very close to my routing. Very similar to that shown above. Subsonic until west of Anglesey at which point the transonic phase started. Decel starts abeam Porto and FL120 at BUSEN for a 02 landing.

Have you got the plan please?

[Andrew Wilson]

25 minutes ago, Ray Proudfoot said:

Have you got the plan please?

Sadly not - as with most of the paperwork, especially during the 90's - I'd imagine it was binned 

[Ray Proudfoot]

Ho hum. Thanks all the same. I’ll use mine as the official one given the flight times are so similar.

[Fraser Gale]

Well can I make one Concorde-like suggestion?  If she were to fly that route I would think they’d have flown further north before doing the right turn, so that they could stay supersonic as long as possible. 
 

So continue on heading at LOMVO to a ghost waypoint if necessary (one in the flight plan that isn’t an official turning point) then turn right 

[Ray Proudfoot]

Fraser,

I chose that arrival as I could fly the MALU1M STAR picking up the L975 airway at LYNAS. The descent was more or less continuous from LOMVO to be at FL100 at WAL and FL60 at MIRSI.

The problem by flying further north is the Isle Of Man and laying a sonic boom there. The IOM VOR is only 50nm from LOMVO so unless I am subsonic at LOMVO that would cause an issue. The other problem of flying further NE is the turn would be >90 degrees inbound to WAL.

[Fabrice Estienne]

20 hours ago, Ray Proudfoot said:

There is a distance scale bottom left and LOMVO is >20nm off Anglesey. Thoughts?

Ray, that's correct assuming this track would be authorized as you indicate.

Fabrice

[Ray Proudfoot]

2 hours ago, Fabrice Estienne said:

Ray, that's correct assuming this track would be authorized as you indicate.

Fabrice

Well I authorised it so it's perfectly legitimate. As Andrew said earlier this route was never flown in real life but I've designed the route trying to stick to all of Concorde's rules and regs.

[Fraser Gale]

It was just a suggestion though I think it would have been the way they’d have done it if it had been done.  
 

You don’t need to go very far north. 

[Ray Proudfoot]

1 hour ago, Fraser Gale said:

It was just a suggestion though I think it would have been the way they’d have done it if it had been done.  
 

You don’t need to go very far north. 

I thought I made it clear why I didn't amend my plan. The southern tip of the IOM is 50nm from LOMVO so they would probably hear a mild boom already had I been supersonic. Any further north and it just gets louder.

[Ray Proudfoot]

@Fraser Gale, you’ve got PFPX haven’t you? Knock me up a plan if you don’t mind from LPPT to EGCC. Let’s see how different yours is compared to mine.

[Fraser Gale]

4 hours ago, Ray Proudfoot said:

I thought I made it clear why I didn't amend my plan. The southern tip of the IOM is 50nm from LOMVO so they would probably hear a mild boom already had I been supersonic. Any further north and it just gets louder.

No need to become confrontational, you asked for our thoughts after all.  
I cannot see anything on your map that would interfere with the version in my head plus as has just been explained, travelling in non-accelerated flight 50nm is plenty clearance, no boom.  Now admittedly when you start the turn you would cut it fine but with waypoints placed strategically to get a gentle INS guided turn, you could do it.  Distant rumbles were accepted if not always ideal.

4 hours ago, Ray Proudfoot said:

@Fraser Gale, you’ve got PFPX haven’t you? Knock me up a plan if you don’t mind from LPPT to EGCC. Let’s see how different yours is compared to mine.

Indeed. I believe I wrote the Concorde profile for it…. 
 

I really don’t have time right now as I am extremely busy with other things, hence late night/early morning replies on here.   It’s also not an exciting enough route for me so I’d be wasting my time.  If I do get time I’ll try. 

[Ray Proudfoot]

8 hours ago, Fraser Gale said:

No need to become confrontational, you asked for our thoughts after all.  
I cannot see anything on your map that would interfere with the version in my head plus as has just been explained, travelling in non-accelerated flight 50nm is plenty clearance, no boom.  Now admittedly when you start the turn you would cut it fine but with waypoints placed strategically to get a gentle INS guided turn, you could do it.

I’m not sure why you thought my reply was confrontational. I can’t see what’s in your head hence why I asked you to provide a plan. If you don’t have time that’s fine.

[Andrew Marshall]

No speed limits on the Isle of Man right? I figure you could go supersonic right over the top no problems

[Rado Sutto]

Very intetesting reading about sonic boom is on Wiki https://en.m.wikipedia.org/wiki/Sonic_boom

On that page is basic formula for cone angle.

[Ray Proudfoot]

Thanks Rado. I understood a reasonable amount but the formulas defeated me.

It would have been an experience to hear the boom from an F4 breaking the sound barrier at 100ft. 

[Rob Ainscough]

Say thank you Lockheed Martin ... fuel efficient and low noise (hopefully low enough for land crossing).  This version capped at 940 mph with "community" sound checks to commence in 2024.  Full size passenger version (100 passengers) aimed for 3 or 4 times speed of sound to hopefully be picked up by the big aircraft companies.

https://www.dallasnews.com/business/airlines/2022/02/11/the-quiet-supersonic-jet-from-nasa-and-lockheed-martin-is-nearing-its-first-flight/

Don't see any Microsoft involvement here ... hehe 

Cheers, Rob.

[Ray Proudfoot]

After 5 seconds it went behind a paywall. 

[Rado Sutto]

Dear developers team, did You test Concorde on the route from Caracas to Paris ?

Some info about that is here - https://www.airliners.net/forum/viewtopic.php?t=190337

[Ray Proudfoot]

Posted in wrong topic.

[Andrew Wilson]

1 hour ago, Rado Sutto said:

Dear developers team, did You test Concorde on the route from Caracas to Paris ?

Some info about that is here - https://www.airliners.net/forum/viewtopic.php?t=190337

We have the route, yes - it's one that is waiting to be built and tested. They'd normally have gone via SMA - I think on a few occasions they calculated it was possible to get into CDG without a fuel-stop if they had the winds and temps in their favour.