Supersonic flight is easy. Efficient supersonic flight is hard. Aerodynamics, aerostructure, propulsion all of them are trying to break you. Controlling all of them would definitely be an achievement.
This sounded ludicrous to me, so I tried to check it. Still not entirely convinced.
The closest source I could find was a Vice article [1]:
> A Concorde’s taxi to the end of a runway used as much fuel as a 737’s flight from London to Amsterdam.
The article links to a now-defunct 2012 story on "scotsman.com", which I found on the Wayback Machine [2]. This story interviews Jim O'Sullivan, the former general manager and chief engineer of British Airways' supersonic fleet, but does not explicitly attribute this taxi fuel consumption claim to him or anyone else.
A simulation-based fuel calculator I found says that the 737-800 would use 94,000 lb of fuel flying LHR-AMS [3]. The Concorde's fuel capacity was 211,000 lb [4].
Could any aviation nerds weigh in on how plausible it is to claim that the Concorde would somehow burn through HALF of its entire fuel load just by taxiing? Maybe "taxiing" here includes takeoff?
[1] https://www.vice.com/en_us/article/ezz8q7/concorde
[2] https://web.archive.org/web/20170626124207/http://www.scotsm...
I have seen various proposals for having some form of external taxi for aircraft, but nothing close to being adopted which I have put down to jet fuel still being cheap and the capital & operational costs being quite high for a lot of tractors with qualified drivers.
Check out the Concorde wiki[1] It states ~4.4K lbs for taxi which passes the common sense test. Taxi time is generaly planned as 15 minutes, so ~10K lbs/hr which is more than what a Boeing 767 burns at cruise - quite a lot! For comparison Concorde super sonic cruise fuel burn was 40K-55K lbs/hr.
For another reference Boeing 767s typically plan to burn 2K lbs of fuel for start-up/taxi/takeoff run.
I think it's worth adding, as is reflected by your B767 ground movement figure that all jet engines are very inefficient at low power outputs, not just the Concorde's/supersonic aircraft. This is as a large amount of energy is needed to create sufficient compression to allow them to function.
Finding ways to minimize the amount of time spent in these states has been the industry's approach to date.
I just remembered that this is a great site for Concorde facts http://www.concordesst.com.
Also this OmegaTau podcast episode is pretty fantastic, it's so detailed you could almost jump in a Concorde and fly off after you've listed to it. http://traffic.libsyn.com/omegataupodcast/omegatau-166-flyin...
Despite having zero bypass the Olympus engines in the Concorde were the most efficient heat engine of their day, achieving 43% efficiency [0]. Their propulsive efficiency was in the 50%s (compared to the 60%s for a B747-100) [1]. Despite this going at supersonic speeds does require an awful lot of energy over subsonic speeds so even with its high efficiencies it burnt a lot more fuel than an equivalent subsonic flight.
Even if Boom could produce the most efficient engines seen, it would still require a lot more energy for the total flight, and therefore would have worse total fuel consumption.
[0] https://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593
My biggest skepticism about Boom is that I don't see them even talking about this issue much. If they can't get big efficiency improvements I see this being a niche toy for the super rich rather than a mainstream transport option.
I'm not an expert, but I wonder: can you get large efficiency improvements by going to really extreme altitude where the air is thinner? Maybe that's the long term plan. But as far as I know that may require a novel engine design or the adaptation of military engines, and the latter is a minefield if classification and ITAR regulations. Extreme altitude also means you're dead if you get a major hull breach, but the increased risk there may be statistically mitigated by decreased overall flight time... and it's still going to be safer than driving a car.
Apparently re Musk's old Telas that he launched towards Mars:
>It has achieved a fuel economy of 9,886.9 miles per gallon (4,203.4 km/liter, 0.02379 liters/100 km), assuming 126,000 gallons of fuel. https://www.whereisroadster.com/
But it's not on a very popular flight route. Should be kinda near Mars Oct 7th.
There is also less drag, and both lift and drag are calculated using the same formula: Cl * A * .5 * r * V^2
- Cl (Cx for drag, Cz for lift) is a coefficient depending on the wing shape, among other factors
- A is the area (thickness for drag, wing surface for lift)
- r is the air density
- V is velocity
If you divide the air density by 4 by going higher, you get the same lift and drag by going twice as fast. Which is great, and a good reason for fast planes to fly high.
The reason it is so great is that in order to fly level, lift cancel gravity and thrust cancel drag. Because by going higher, we managed to keep the same lift and drag with higher speed, it means we got faster using the same amount of thrust.
There are certainly complications somewhere. For example at supersonic speeds you get shock drag but suffice to say, high altitude is good for speed.
Still there is a good reason why planes don't just get higher to get speed for free. And that's because planes are not rocket powered. Air breathing engines lose efficiency the faster you get, they are also designed to operate at specific speed ranges.
Yep. In fact, this is one of many things that makes the Concorde so special: being able to cruise for a long time at Mach 2+. Supercruise has only come to fighter jets fairly recently, and there it is usually in the Mach 1.4-1.6 range. This means that if the Concorde has even a small head-start, it can outrun most fighter jets that might want to intercept it. The SR-71 could keep it company but is unarmed. Maybe the Mig-31, although its range also diminishes rapidly with increased velocity.
> efficiency is what has kept civilian supersonic flight from being a thing
This was an issue, but less than you might suspect, for example it didn't actually burn that much more than its contemporaries. The planned Concorde B [1] was to have more efficient engines that would have allowed the same performance without afterburners. Along with having larger fuel tanks, this would have led to a dramatic increase in range and therefore in the possible routes.
Alas, the US effectively killed Concorde before that could happen by not allowing overflight, due to noise, particularly the sonic boom, and one suspects also the fact the the US SSTs weren't making much progress. And of course the oil price shock.
Concorde tickets were actually quite a bit cheaper than the public expected, BA (and AF, presumably) later raised prices to match public perception, with a nice boost to profitability.
> extreme altitude where the air is thinner
Jets in general (~35K feet) and Concorde in particular (~60K feet) already do this. IIRC, jet engines are actually not very efficient, but they continue to operate well at high altitudes where the air is so much thinner that the plane becomes more efficient overall, whereas both piston engines and the propellers they drive become significantly less efficient at altitude.
I also can't quite avoid that suspicion. The Concorde was noisy, but not that noisy and Concorde B should be quieter from the aerodynamic improvements.
Perhaps putting the pilots in pressure suits would be sufficient. I think it's a matter of how quickly pilots could descend with the plane, which is probably a complicated question for aviation engineers to solve. This all said, only pilots getting pressure suits probably wouldn't inspire passenger confidence.
You can't just mindlessly descend because that would overstress/overspeed the airframe.
In any event, I think the Concorde proves that operating at that altitude is feasible. It's not like 60,000 feet at supersonic speeds is survivable. The pilots would have minutes to get down before passengers were brain damaged. The chemical oxygen generators giving oxygen to the passengers don't last long, not nearly as long as the oxygen bottles for the pilot/crew, and that's assuming the passengers can get the masks on.
If all the meat sacks pass out, drop out of mach and drop down in altitude, send SOS, find somewhere to land. At this point ground control could start commanding the plane remotely too.
We are not quite ready for pilotless passenger planes, but pilotless as a fallback is viable.
He said it's impossible to commercialize supersonic flight without breaking some laws of physics. I confess to not understanding the reasoning that got him there. It's not a controversial opinion in physics, though.
I suspect Boom may end up being the uBeam of aviation.
Then those "laws" have been duly broken.
https://en.wikipedia.org/wiki/Concorde
"Laws" that can be broken hardly seem to qualify as "laws of physics".
An increase in maintenance costs due to the planes being very old and out of production also doesn't qualify:
British Airways and Air France were able to operate Concorde at a profit, in spite of very high maintenance costs, because the aircraft was able to sustain a high ticket price.
Its estimated operating costs were $3,800 per block hour in 1972, compared to actual 1971 operating costs of $1,835 for a 707 and $3,500 for a 747; for a 3,050 nmi London–New York sector, a 707 cost $13,750 or 3.04c per seat/nmi, a 747 $26,200 or 2.4c per seat/nmi and the Concorde $14,250 or 4.5c per seat/nmi.
So 50% more expensive per seat/mile than a 707 and twice as expensive as a 747.
Part of the calculation is that supersonic flight is so energy-intensive that we'd need a major breakthrough in fuel extraction/storage/efficiency. More fuel weighs more, whether stored as a liquid hydrocarbon or as a battery.
I wouldn't. Some people would, but considering that Spirit is the fastest-growing airline in the US (or was), I think low prices are more important than any other feature of a plane ride.
I think Boom and its competitors are targeting people who would otherwise use a private jet and can afford $30k tickets. If they're targeting typical consumers, I think they're already doomed.
Sure, some people paid for tickets, but it's a stretch to call that 'commercialization' in the context of the impossibility of ever recovering the programme's losses.
There's other factors, but this dominates.