

Hypersonic Flight ‘Breakthrough’ Could Have Us in Tokyo by Lunch - jordhy
http://www.wired.com/autopia/2012/11/reaction-engines-hypersonic/

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omegant
I wonder if it would have any effect adding a statoreactor tube to the end of
a rocket engine ( as a kind of postcombustion chamber) to take advantage of
all that heat. Maybe adding some fuel to that part to make use of atmosferic
oxigen to increase power. Above 30km you may drop it. I don't think it would
be too heavy as it doesn't have moving parts. The question is if it would
generate power enough to be worth all the trouble.

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jasonwatkinspdx
I'm not sure I understand what you're suggesting, but it sounds like some form
of ram afterburner?

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omegant
Yes exactly. Has it been done or studied?.

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jasonwatkinspdx
I do not understand how the physics of a ram afterburner would work. A ram
duct generates compression via aerodynamic drag. It slows and compresses the
air forced into it by controlling shocks.

The expansion stage of a brayton cycle engine maximizes exhaust velocity
rearward and hence by Newton's third law creates thrust. Constricting the
exhaust will only reduce efficiency.

If you're talking about an expansion duct with secondary combustion, that has
nothing to do with ram effect and is just an afterburner.

By and large afterburners are hideously inefficient, but many military craft
still include them because it is easier to manufacture an afterburner tolerant
of secondary combustion temperatures than a turbine. SABRE erodes this
motivation as the incident temperature into the flame holders (or rocket
nozzles) is dramatically lower than common in a turbine engine, so you can get
more of the energy possible from the oxygen density of the engine's intake
flow without secondary combustion.

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raverbashing
And of course, if you leave NYC after breakfast and head to Tokio you won't
get there by lunch

More likely you'll get there for dinner and a night out

At Mach 5 this will take 2h (not considering acceleration/deceleration times)

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stygianguest
Then standing in line for two hours at security will be even more ironic.

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da3da
Does this happen anymore? I flew out of Boston the day before Thanksgiving
(when I would imagine tons of people are traveling) and it took <5 minutes to
get through security. Same thing on the way back.

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sylvinus
One data point doesn't mean anything... It's the uncertainty that you _might_
spend 1h in line that makes you waste time in the end.

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imperio59
I thought another big issue with flying at such fast speeds was that you end
up tearing pieces off your fuselage every time... This looks like one piece of
a bigger puzzle to achieve what the headline of the article is suggesting.

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loeg
That and cost. No one is willing to pay for supersonic flight, and the sonic
boom makes it obnoxious over land.

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NickPollard
People are willing to pay for supersonic flight. Concorde made a profit on
most of it's flights, and it was only after the World Trade Center attacks and
subsequent downturn in international commercial flight that it became a
problem. Also, because not many Concordes were made, the R&D costs were never
properly amortized.

The sonic boom however is an issue - Concorde was limited to a small selection
of routes that passed mainly over water (e.g. London -> New York) because it
was not allowed to go supersonic over a lot of countries. If you could fly
supersonic all the way from London to Tokyo, or San Fransisco, or Sydney, then
I'm sure it would be worth even more.

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frozenport
I think 9/11 was coincidental and unrelated. The important trend in 2001+ was
the growth of telecommunications phenomena that reduced travel demand. I am
not sure if the sonic boom was nearly as big a problem as it was made out to
be. I think we can do some cursory math.

If 30% was at 50% of the speed, the total distance covered would be 85% less,
adding about 20% flight time increase. Something that normally takes 8+ hours
now take 3 or 4 hours. Did this kill the concord?

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geori
Airline stocks went down almost 40% the next day. Yes, the economy went down
because of other factors, but the immediate hit to airlines was definitely
caused by 9/11.

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wkearney99
Which still doesn't change the times involved getting to and from the airport.
These are often worse than the flights themselves. Better to engage remotely
rather than travel at all.

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michaelochurch
Meh... you know what I want? I want to be able to go to Tokyo and not have the
ticket cost multiple fucking days of work. In 2012, four-digit airfares for
coach are fucking inexcusable. We were supposed to be better than that, 20
years ago. And don't get me started on business class: those tickets are more
than some people in the world make in a fucking year. I want travel that
doesn't belch a bunch of CO2 into the air, leaving our grandchildren with a
world where there are palm trees in Winnipeg and a year-round hurricane
season. That's what I care about. If this Mach-5 travel costs the same as
airfare currently does, and burns a bunch of fucking hydrocarbons to get
there, then I'm not impressed.

I'm sure the technology is cool, but would someone please solve the real
problem? The real problem is that transportation hasn't improved since the
1960s. In the US, we call exorbitantly-priced, 130-mph trains "high speed", we
use airplanes for mid-distance travel and it's ass-expensive as it should be
because it makes no economic sense, and most of our transportation relies on
burning fossil fuels in tin cans that can't be safely operated above about 90
miles per hour. Solve that one, please.

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c1u
Transportation CO2 emissions make up a tiny fraction of total greenhouse
gases. Water vapour is by FAR the biggest greenhouse gas. I wonder if a 787
burns more hydrocarbons flying 250 people from NY to LA than 250 cars driving
that distance? Roughly ~9000gal (2500mi 787 @ cruise) is 36gal per car.
Assuming everyone gets perfect highway mileage even if they're Prius it wont
get them the whole way (50MPG*36gal=1800mi). And that's not considering the
energy required to build and maintain 250 Prius cars vs. the cost of one 787.
The retail cost alone for 250 Prius is nearly $90M. A 787 is more like $250M,
but lasts a least 3x longer than a car.

Transportation has improved since the 1960 by a HUGE amount. Modern cars,
trains, and airplanes are significantly better (safer, cheaper, more
efficient) than those in the 1960s. I'm curious how much travelling you did in
the 1960s compared to today?

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lauraura
_Transportation CO2 emissions make up a tiny fraction of total greenhouse
gases. Water vapour is by FAR the biggest greenhouse gas._

Water vapor is the largest greenhouse gas, but it's a relatively constant
contribution; it's _not_ part of anthropogenic contributions to greenhouse
gases (which is usually what people are referring to in this sort of context).

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c1u
Good point. I'm not trying to start an off-topic climate change debate, just
trying to step back and look at the problem a little more broadly, but there's
at least one big error in my calcs as has been pointed out.

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ColinWright
Also discussed extensively here:

<http://news.ycombinator.com/item?id=4842867>

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michael_miller
Does anyone know how practical this is? Is it economically feasible to do this
on a jetliner, at Concorde prices? A business jet?

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djisjke
"could have us", who is us?

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mvkel
The engine has never been the problem. Heat dissipation is the problem.

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ForwardShadow
They'll probably never let humans travel by air at hypersonic speeds, its far
to dangerous.

They'll simply use Evacuated tube maglev(Elon Musk's HYPERLOOP) for long
distances, same hypersonic speed.

Looking forward to breakfast in San Fransisco, Lunch in LA, and Dinner in
Washinton DC.

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sliverstorm
Haven't they let humans travel by air at hypersonic speeds already?

<http://en.wikipedia.org/wiki/Concorde>

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dalke
Concorde has a max speed of just over Mach 2.0. Hypersonic means Mach 5.0 or
higher. The rocket-powered X-15 max speed was 6.7, and of course the Space
Shuttle also went faster than Mach 5.0, so yes, humans have already flown at
hypersonic speeds.

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sliverstorm
_HYPERsonic means Mach 5.0 or higher_

Whoops.

