Live data from Hacker News

Boom supersonic jet readies for rollout

airlineratings.com

201–210 of 283 posts

Re: Boom supersonic jet readies for rollout

#201

> Boom’s first major airline partner in the development of the > first privately built supersonic airliner and the second ever > after Concorde, retired in 2003, is Japan Airlines with an > option for 20 aircraft. How could any reporter, especially one writing for a publication called "airlineratings", not research the topic at hand? It is widely known in the aviation community that the Soviet union flew the superson…

that faded away from memory mostly because of this: https://en.wikipedia.org/wiki/1973_Paris_Air_Show_Tu-144_cra...

"During the show, there was a "fierce competition between the Anglo-French Concorde and the Russian Tu-144".[6] The Soviet pilot, Mikhail Kozlov, had bragged that he would outperform the Concorde.[6] "Just wait until you see us fly," he was quoted as saying. "Then you'll see something."[12] On the final day of the show, the Concorde, which was not yet in production, performed its demonstration flight first.[6] Its performance was later described as being unexciting, and it has been theorized that Kozlov was determined to show how much better his aircraft was.[12]

Once in flight, the aircraft made what appeared to be a landing approach, with the landing gear out and the "moustache" canards extended, but then with all four engines full power, climbed rapidly. Possibly stalling below 2,000 ft (610 m), the aircraft pitched over and went into a steep dive.[6] Trying to pull out of the subsequent dive with the engines again at full power, the Tu-144 broke up in mid-air, possibly due to overstressing the airframe. The left wing came away first, and then the aircraft disintegrated and crashed,[6][8][10] destroying 15 houses,[13] and killing all six people on board the Tu-144 and eight more on the ground.[8] Three children were among those killed, and 60 people received severe injuries.[14]"

i mean bragging about how good it was and then crashing is a trademark of the USSR.

Re: Boom supersonic jet readies for rollout

#202

Earlier quoted context omitted.

> The reason for that is that the concorde used afterburners (basically, pump fuel into the high speed exhaust for extra thrust) which are incredibly inefficient. Concorde didn't use afterburners "at speed". The afterburners were used for takeoff, and to go through the mach wall. Concorde burned insane amounts of fuel on the ground because turbojets are very inefficient at low-speed. Not unlike the SR-71's really (th…

Didn't SR-71's also leak fuel when on the ground?

Yes but that's a separate concern. The engines were not efficient at slow speed / ground levels even ignoring the "leaks until it gets hot enough to seal the pipes" issue, the blackbird was designed to hit peak efficiency above Mach 3 (generally speaking all jets are designed to hit peak efficiency at their cruising speed, and the blackbird was designed for a cruising altitude of mach 3.2).

Re: Boom supersonic jet readies for rollout

#203
post #171

Earlier quoted context omitted.

Looking at the Concorde's fuel usage taxing is only part of the picture. All turbine engines are very inefficient at low power outputs due to the need to use energy to create sufficient compression for them to function. On top of this the Olympus engines generated a lot of thrust at idle, so much so that only two were used for taxing and it was still apparently tricky to control. While cruising at supersonic speeds t…

I'm a bit suspicious of the qualification 'thermal' in 'thermal efficiency' which sounds like it's hiding something. From the wiki article on thermal efficiency https://en.wikipedia.org/wiki/Thermal_efficiency , and I'm no wiser for reading it: "For a heat engine, thermal efficiency is the fraction of the energy added by heat (primary energy) that is converted to net work output (secondary energy)." Does thermal effi…

Yes thermal efficiency is a common rating for engines that work by burning fuel to make heat then turn that into useful power. You take the theoretical energy in a litre of fuel and work out how much of that the engine can convert into useful work.

Re: Boom supersonic jet readies for rollout

#204
post #171

Earlier quoted context omitted.

Looking at the Concorde's fuel usage taxing is only part of the picture. All turbine engines are very inefficient at low power outputs due to the need to use energy to create sufficient compression for them to function. On top of this the Olympus engines generated a lot of thrust at idle, so much so that only two were used for taxing and it was still apparently tricky to control. While cruising at supersonic speeds t…

I'm a bit suspicious of the qualification 'thermal' in 'thermal efficiency' which sounds like it's hiding something. From the wiki article on thermal efficiency https://en.wikipedia.org/wiki/Thermal_efficiency , and I'm no wiser for reading it: "For a heat engine, thermal efficiency is the fraction of the energy added by heat (primary energy) that is converted to net work output (secondary energy)." Does thermal effi…

[deleted]

Re: Boom supersonic jet readies for rollout

#205
post #171

Earlier quoted context omitted.

Looking at the Concorde's fuel usage taxing is only part of the picture. All turbine engines are very inefficient at low power outputs due to the need to use energy to create sufficient compression for them to function. On top of this the Olympus engines generated a lot of thrust at idle, so much so that only two were used for taxing and it was still apparently tricky to control. While cruising at supersonic speeds t…

I'm a bit suspicious of the qualification 'thermal' in 'thermal efficiency' which sounds like it's hiding something. From the wiki article on thermal efficiency https://en.wikipedia.org/wiki/Thermal_efficiency , and I'm no wiser for reading it: "For a heat engine, thermal efficiency is the fraction of the energy added by heat (primary energy) that is converted to net work output (secondary energy)." Does thermal effi…

A heat engine is a device that converts heat into kinetic energy. The amount of heat that is converted into movement as a proportion of the total heat is the thermal efficiency. With a jet engine it's the amount of energy in the burnt fuel that's converted to both rotation in the shaft and the speed of the expanding burnt gasses exiting the back.

Propulsive efficiency is how good the engine is a converting this energy into thrust. The Concorde's engines were a type where all the propulsion was from the fast gasses exiting at the back, i.e. a turbojet. Efficiency is less than 100% as energy is taken from the gasses to power the engine and not all the gasses exiting the rear usefully push the aircraft forwards.

I don't have the exact number for the Concorde to hand but looking at [1] from my previous post, we can see it was typically around 60% in 1970, but these numbers are likely for (low bypass) turbo fans. These work in a slightly different way where they have more energy in the rotation of the shaft and less in the gasses going out the back. The energy in the shaft drives the big fan at the front which pushes a large volume of air more slowly out of the back. This is to address the problem of the gasses which exit the back but don't usefully push the aircraft forward.

To get the total efficiency of the jet you have to multiply the thermal efficiency by the propulsive efficiency.

edit: changed division to multiplication

Re: Boom supersonic jet readies for rollout

#206

Please don't let COVID-19 kill this thing. They're going to need a lot of money to build the full-size plane and it's going to be hard to get it if airlines are cancelling orders and not placing any new ones for planes: https://dsm.forecastinternational.com/wordpress/2020/05/19/a...

> They're going to need a lot of money to build the full-size plane

The chance is zero of Boom succeeding, regardless of how much money they raise.

Re: Boom supersonic jet readies for rollout

#207
post #205

Earlier quoted context omitted.

I'm a bit suspicious of the qualification 'thermal' in 'thermal efficiency' which sounds like it's hiding something. From the wiki article on thermal efficiency https://en.wikipedia.org/wiki/Thermal_efficiency , and I'm no wiser for reading it: "For a heat engine, thermal efficiency is the fraction of the energy added by heat (primary energy) that is converted to net work output (secondary energy)." Does thermal effi…

A heat engine is a device that converts heat into kinetic energy. The amount of heat that is converted into movement as a proportion of the total heat is the thermal efficiency. With a jet engine it's the amount of energy in the burnt fuel that's converted to both rotation in the shaft and the speed of the expanding burnt gasses exiting the back. Propulsive efficiency is how good the engine is a converting this energ…

> To get the total efficiency of the jet you have to divide the thermal efficiency by the propulsive efficiency.

Also need to consider combustion efficiency (i.e., the percentage of fuel turned into heat as an input to the heat engine), though for gas turbines this is typically ~99.9%.

Re: Boom supersonic jet readies for rollout

#208
post #201

> Boom’s first major airline partner in the development of the > first privately built supersonic airliner and the second ever > after Concorde, retired in 2003, is Japan Airlines with an > option for 20 aircraft. How could any reporter, especially one writing for a publication called "airlineratings", not research the topic at hand? It is widely known in the aviation community that the Soviet union flew the superson…

that faded away from memory mostly because of this: https://en.wikipedia.org/wiki/1973_Paris_Air_Show_Tu-144_cra... "During the show, there was a "fierce competition between the Anglo-French Concorde and the Russian Tu-144".[6] The Soviet pilot, Mikhail Kozlov, had bragged that he would outperform the Concorde.[6] "Just wait until you see us fly," he was quoted as saying. "Then you'll see something."[12] On the final…

I thought the Cobra maneuver was a Russian trademark, just not something you should try in a Tu-144.

Re: Boom supersonic jet readies for rollout

#209

As a (pre-Covid) extreme frequent flyer, supersonic and other rapid point to point initiatives are thoroughly unenticing. Part of the reason I loved long flights was the ability to put away the laptop and zone out to a book or movie with some wine before landing, dealing with immigration, hotels, Ubers, and days of frenetic, high stress meetings afterward. The prospect of trying to optimize how fast we can jump from…

> zone out to a book or movie I can do that when I'm home. But at home I can also stand up, go for a walk, or go to the restroom without having to wait in line, or go to sleep, etc. In a long flight I can do none of these. I can instead suffer from dry air, I have a hard time sleeping in something that is a bad approximation of a bed, etc, etc. Oh, and don't ask me if my kids enjoy 10-hour flights (of which they have…

I get that some people don't travel well although I'd probably argue that a faster plane doesn't eliminate jet lag, dealing with airports, etc. And comfort, being able to walk around, etc. is mostly just a function of the market for air tickets at particular price points. After all, the upper deck on a 747 used to be a first class lounge. But it got turned into conventional seating on AFAIK all commercial flights.

Re: Boom supersonic jet readies for rollout

#210
post #102

Earlier quoted context omitted.

I think the real problem is that the Concorde wasn't fast enough to justify the cost. Whether you can fly JFK-CDG in 8 hours or 4 hours, when you factor in how irritating airports are, parking, security line ups, waiting for baggage, etc, it still takes all day to make the trip. Might as well save several thousand dollars and take a longer flight. I believe they would have to cut the flight time down to about an hour…

Flying with first class tickets will get you into an expedited security line in most airports as well as other perks like lounge access. If you're paying Concorde prices I'd expect that to also come with the same perks as a first class ticket on a slower plane. That means less waiting than the rest of us and the wait you do have is more comfortable.

You also get the expedited security line if you keep a NASA badge inside your passport.
Post reply on HN