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Largest problem for SST: Boom or fuel efficiency?

Posted: Sat Aug 26, 2017 1:56 pm
by mxaxai
We all know the ill-fated story of the Concorde and its sister, the Tu-144. Their market appeal was very limited because they were not only extremely expensive to fly but also couldn't really make use of their speed except on select TATL routes.
The fundamental hurdles of crossing into speeds greater than Mach 1 remain unresolved today. However, a somewhat significant amount of R&D goes to both increasing the efficiency of a potential future SST and reducing the noise and sonic boom problem. Out of those two, which needs more attention?

On the one hand, customers & passengers care more about efficiency. On the other, the general public only cares about the environmental effects. Assuming the boom problem was solved, would the current efficiency of SST designs be sufficient to make them affordable, at least as business jets? Or would the speed advantage still not be worth the added cost? Could we trade some efficiency for a significant noise reduction and still have a business case?

Re: Largest problem for SST: Boom or fuel efficiency?

Posted: Mon Aug 28, 2017 4:16 am
by cpd
I think the sonic boom trouble is almost solved.

Fuel efficiency of such a plane nowadays would also be far superior and make the plane capable of long range routes (eg, trans-Pacific).

Re: Largest problem for SST: Boom or fuel efficiency?

Posted: Mon Aug 28, 2017 8:44 am
by mxaxai
cpd wrote:
I think the sonic boom trouble is almost solved.

Fuel efficiency of such a plane nowadays would also be far superior and make the plane capable of long range routes (eg, trans-Pacific).

What I've heard of the Aerion design was that the boom is "solved" for low speeds only, i. e. Mach <1.3. This is why they have a low-noise cruise and a high-speed cruise at Mach 1.6 for legs over water. Mach 1.3 is not much faster than Mach .9.
And for the fuel efficiency you need to remember the much lower regular business cabin prices, even while offering lie-flat seats. No design I have seen so far uses anything better than premium economy or US domestic first seats.

Re: Largest problem for SST: Boom or fuel efficiency?

Posted: Mon Aug 28, 2017 9:22 am
by Starlionblue
mxaxai wrote:
cpd wrote:
I think the sonic boom trouble is almost solved.

Fuel efficiency of such a plane nowadays would also be far superior and make the plane capable of long range routes (eg, trans-Pacific).

What I've heard of the Aerion design was that the boom is "solved" for low speeds only, i. e. Mach <1.3. This is why they have a low-noise cruise and a high-speed cruise at Mach 1.6 for legs over water. Mach 1.3 is not much faster than Mach .9.
And for the fuel efficiency you need to remember the much lower regular business cabin prices, even while offering lie-flat seats. No design I have seen so far uses anything better than premium economy or US domestic first seats.


M1.3 is not much faster than Mach 0.9? I would call a 44% speed increase massive. A 10 hour cruise phase is now under 7 hours. Also typical cruise for faster airliners is 0.85, making the improvement 53% A 10 hour cruise is now around 6½ hours.

LHR-JFK is currently around 8 hours. Counting 7 hours as cruise, you're down to a bit over 4½ hours, for a total flight time of 5½ hours. Just in terms of aircraft utilisation that is pretty big..

Even using in excess of 50% more fuel per seat, the economic case seems very much there, and this is the M1.3 case, not M1.6.

Re: Largest problem for SST: Boom or fuel efficiency?

Posted: Mon Aug 28, 2017 10:02 am
by Channex757
Efficiency is the key here. A few days ago, GE announced that they had made a breakthrough in hybrid propulsion. Whilst this is going to be primarily about other modes of flight, it could be read across to supersonic propulsion and a novel engine/fan setup to power an SST.

The sonic boom issue has now been minimised to the point that it is now more of a rumble than a boom. Not much louder than a conventional jet.

Re: Largest problem for SST: Boom or fuel efficiency?

Posted: Mon Aug 28, 2017 11:15 am
by parapente
I think the Aerion solution is a good one.I believe the primary market will remain tatl but this low speed supersonic mode will allow them to reach a much wider range of cities on both sides quickly.
What I don't understand (from Aerion or Boom) is that they have both changed engine config from 2 to 3 but neither have - Ever had a power plant in mind for either config or the various thrust levels involved (i.e. 4 different engine possibilities).
The power plant is obviously - absolutely critical and yet they just play drawing board games with fantasy engines.I would love to see it happen but this approach makes me doubt either venture frankly.

Re: Largest problem for SST: Boom or fuel efficiency?

Posted: Fri Sep 01, 2017 9:00 am
by wingscrubber
The only mature supersonic engines out there are all military, and if sourcing domestically Aerion and Boom will find that the US state department won't just hand them out for free, nor will they necessarily allow civilian development of them.
My bet would be to try purchasing Russian powerplants, and have the construction line in somewhere outside US ITAR influence like the Czech republic or Norway perhaps.
Buying a pair of GE F110s or P&W F100s is just going to be a massive headache, buying Klimov RD-33s or Saturn AL-31s could be easier - but then I expect tech support in service would be terrible.
Possibly the most conducive partner might be a British supplier - enquire about EJ-200s from Rolls Royce. They'll do a very good job but will take a very very long time to do it, as is the British way these days.

Re: Largest problem for SST: Boom or fuel efficiency?

Posted: Fri Sep 01, 2017 9:06 am
by wingscrubber
Starlionblue wrote:
mxaxai wrote:
cpd wrote:
I think the sonic boom trouble is almost solved.

Fuel efficiency of such a plane nowadays would also be far superior and make the plane capable of long range routes (eg, trans-Pacific).

What I've heard of the Aerion design was that the boom is "solved" for low speeds only, i. e. Mach <1.3. This is why they have a low-noise cruise and a high-speed cruise at Mach 1.6 for legs over water. Mach 1.3 is not much faster than Mach .9.
And for the fuel efficiency you need to remember the much lower regular business cabin prices, even while offering lie-flat seats. No design I have seen so far uses anything better than premium economy or US domestic first seats.


M1.3 is not much faster than Mach 0.9? I would call a 44% speed increase massive. A 10 hour cruise phase is now under 7 hours. Also typical cruise for faster airliners is 0.85, making the improvement 53% A 10 hour cruise is now around 6½ hours.

LHR-JFK is currently around 8 hours. Counting 7 hours as cruise, you're down to a bit over 4½ hours, for a total flight time of 5½ hours. Just in terms of aircraft utilisation that is pretty big..

Even using in excess of 50% more fuel per seat, the economic case seems very much there, and this is the M1.3 case, not M1.6.


Anything less than Mach 1.8 is too close to the Mach hump to be economical, you've got to go faster.
Also, apart from FADEC systems, the technology of supersonic turbojets today is unchanged since the '70s - Aerion and Boom claiming they will make far greater fuel economy on the basis of 'improved technology' is a false premise. Mechanical systems wise there's been no quantum leap, but providing supercruise can still be attained there is still a worthwhile corner of the envelope to achieve there.

Re: Largest problem for SST: Boom or fuel efficiency?

Posted: Fri Sep 01, 2017 7:04 pm
by frmrCapCadet
Won't the competition be a more comfortable, room to work, good recline or lay flat economy-plus or business versus less travel time and a little crowded? Of course some could afford both.