Posts about: "Sonic Boom" [Posts: 24 Page: 2 of 2]¶

Some years ago I travelled to France to crew for my Dad who was bringing his small sailboat back across the channel to the UK.

About halfway across, Dad had gone below and I was sailing along in the middle of nowhere, with nothing anywhere near us.

Suddenly, I heard a very loud "ba boom" and thought, hmmm, I wonder what that was?

Dad came running up the steps from below saying "what have we hit, what have we hit" (thanks for your confidence in me Dad). Nothing I said, very offended. We both looked around seeing nothing and eventually I looked up to see the beautiful sight of a Concorde miles above us flying Westwards in a clear blue sky.

I guess the " ba boom " was the two shock waves of the nose and the leading edge sweeping past us.


Terrific sight. Terrific machine.

For those of you who never got to take a ride on Concorde, there is a start-up out of Colorado called Boom Technology that is working on a 40 passenger commercial supersonic aircraft . The company is still quite small, but it seems legit. Their technical staff has significant industry experience, and they are supported by Richard Branson and Virgin Galactic who will provide manufacturing/test capabilities.

Boom Technology says they will fly a demonstration aircraft by end of 2017.

It takes a confluence of technologies and market structure to make something viable.

Concorde could not fly as anything but a very expensive subsonic aircraft over populated land, due to sonic-boom noise pollution - ruling out a lot of the marketplace. London-Africa/South Asia, for example, or Paris-Beijing. Or even NY-LA.

Flying the Pacific non-stop requires a doubling or even tripling of range to avoid refuel stops (sitting on the ground once or twice part-way, for 90 minutes or so, plus acceleration/deceleration time, defeats a lot of the speed advantage). Technology has advanced a lot, but nowhere near doubling/tripling the efficiency/range of an Olympus-type turbojet (which, counting the thrust recovery from the brilliant nacelle designs, was already amazingly efficient).

That's why regular Concorde service (and thus aircraft sales) was, practically speaking, limited to trans-Atlantic routes only.

Work is being done on shockwave/boom attentuation, which might open up far more markets. But it is still small-scale experimental.

Airbus recently proposed - on paper - a boom-defeating flight profile: rocket-assisted vertical acceleration to supersonic (boom travels sideways rather than towards the ground) combined with Mach-4.5 cruise at 104-115,000 feet (30-35km altitude attenuates the boom effects at ground level) and near-vertical descent while passing back to subsonic. Quite a roller-coaster ride!

Using liquid H2 fuel that gets it range from London-LAX at Mach 4.5 - but carrying only a dozen or so pax (hydrogen tank fills the rest of the fuselage).

There are folks here who can correct me, but in the meantime, what I think I know is....

The DC-Dallas route, entirely over populated land, could not be flown at supersonic speeds (regulations, noise pollution, sonic booms), but Concorde could do it in high- sub sonic cruise at around Mach 0.95, somewhat faster than the norm for regular subsonic transports.

I believe the DC-MIA route was flown mostly supersonically, by climbing subsonically at Mach 0.95 straight down the Potomac to the Atlantic at Norfolk, Va., and then, 20+ miles offshore, turning SW towards Miami and making the supersonic acceleration-climb out over the water. Remained offshore (dodging the coastal bulge of the Outer Banks) until about 250nm from Miami. where the descent/deceleration phase would slow it to subsonic speed before getting too close to the shoreline.

Once at ~28,000 feet at Mach .95 - and over the water - it only took a few moments, after turning on the reheat/afterburners, to punch through Mach 1, and maybe 20 minutes (depending on weight) to reach 51000 feet* and Mach 2.02 (air termperature permitting.) And maybe 20 minutes for the deceleration/descent to Mach 0.95 at ~34000 feet.

(*I believe the afterburners were switched off at Mach 1.7 - usually about 42000 feet? - at which point the dry thrust of the engines and fancy shockwave-pressurized nacelle design could maintain the IAS and (reduced rate) climb (and increase the Mach) all by themselves.)

Across the Pond, short "experience flights" from both Paris and London were made from time to time - get out over the Atlantic, light up the afterburners, and tool around at supersonic speeds for some part of an hour before returning to base.

I'm pretty sure subsonic flight was never really efficient at any speed. Concorde was dependent on Mach 1.7 or so (and high altitudes) to maintain the efficiency of nacelle thrust modulated by supersonic intake shockwaves, without very thirsty afterburners. I think that over the Atlantic, losing just one engine (25% of thrust) was enough to make it instantly a fuel emergency situation - you were going to come down into thicker air and fuel burn would skyrocket.