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Boom supersonic jet readies for rollout

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Re: Boom supersonic jet readies for rollout

#171

Post by agurk »

DomenicoMazza wrote: post #18

If I recall correctly the Concorde used about 2 tonnes of fuel rolling on the ground alone.. I wonder how this new aircraft fares for fuel consumption? I believe the Concorde is a marvel. You could travel faster than the rotation of the earth in it! However I don’t think we need more environmentally unsustainable travel.

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 the engines were actually the most efficient machines of their time achieving 43% thermal efficiency [0]. Despite being very efficient they still had high fuel consumption rates as the total amount of energy required to sustain those speeds is a lot higher than subsonic.

Modern jet are in the 50%s thermally efficient [1] but despite airframe improvements there has been no way to improve fundamental aerodynamics so that supersonic energy costs aren't high.

The Concorde did use reheat to take off and break the supersonic barrier which is very fuel inefficient.

Using a modern airframes and engines that also don't need reheat will reduce fuel consumption but not to a level anywhere similar to a modern jetliner.

[0] https://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593

[1] https://www.nap.edu/read/23490/chapter/6#38

Re: Boom supersonic jet readies for rollout

#172

Post by Someone »

gardenfelder wrote: post #31
catalogia wrote: post #21

Earlier quoted context omitted.

It's hard to say how efficient this plane will be before it's built (or more details made public) but from what I've read sofar the big version, 'Boom Overture', is meant to use turbofan engines. That alone should provide significant fuel savings over the Concorde, which used turbojet engines with afterburners on takeoff. Even so, supersonic flight is less efficient than getting there a bit slower. Unfortunately, air…

Seems to me that everything is nonlinear in the domain of aircraft, particularly when concerned with "efficiency". There is an equation [1] which makes it clear that the power required to maintain flight is a function of air density, drag coefficient, lift coefficient, wing area, and -- velocity cubed. All things being equal (which they never are), double the speed and you need 8 times the power. So in the most simpl…

“if you double the speed to fly from say London to NY, would you cut the time to fly to less than 1/8th what it would otherwise be?”

It’s bad, but not that bad. If you double the speed, you need 8 times the power, but only half as long for a given distance, so energy use is ‘only’ 4 times what you had.

(Of course, were talking about a very rough approximation that likely is so inexact that 8 might even be a better estimate)

Re: Boom supersonic jet readies for rollout

#173

Post by jyounker »

callamdelaney wrote: post #75
chemeng wrote: post #55

Earlier quoted context omitted.

You would leave a long trail of broken windows and reports from the moment you went supersonic in their territory, charting your trajectory. Threat detection is a network, not a single point. However, if you're moving fast enough and the target is close enough, your premise is valid. They would not have time to react. Cruise missiles tend to be used for those mission profiles.

Has it perhaps occured to any of you that flying at below radar altitude at supersonic or above speeds, would be dangerous and would have no benefit? If the enemy doesn't know you're there, you don't need to go fast.

if the enemy knows you’re there but doesn’t know exactly where then it’s a huge benefit to get in and out as quickly as possible. it’s also a huge advantage if the enemy is moving fast and you know where he is, but you don’t want them to know that you’re coming at them.

Re: Boom supersonic jet readies for rollout

#174

Post by masklinn »

dwd wrote: post #148
rob74 wrote: post #133

Earlier quoted context omitted.

True, but it was a supersonic airliner, 16 pieces were built and it did have 55 passenger-carrying flights (according to Wikipedia), so if you make a list without further qualifiers as in the article ("second ever"), it's a bit strange to gloss over it completely...

It also flew before the Concorde, but we can't have inconvenient facts like that in the middle of a cold war. From my childhood I was under the impression that it was a rip-off copy like the Buran.

> From my childhood I was under the impression that it was a rip-off copy like the Buran.

That's never been proven-proven, but there still are lots of suspicions: it looked strangely like earlier concorde design, at least one person (Sergei Pavlov) was caught smuggling concorde design documents, and there are many declassified reports (e.g. from the CIA) of a large industrial espionage ring targeting Concorde in both France and the UK.

Also regardless of the previous, the TU-144 had flagrantly been rushed to arrive before Concorde, the inside design was complete garbage, it needed braking parachutes to stop, and it was very unstable at low-speed. This necessitated serious improvements and refinements which led to its first passenger flight taking place almost 2 years after Concorde's (November 1977 versus January 1976).

Re: Boom supersonic jet readies for rollout

#175

Post by beambot »

chrisco255 wrote: post #157
phunctional wrote: post #141

Earlier quoted context omitted.

They are also working on a deal to use carbon neutral fuel from a company called Prometheus https://www.prometheusfuels.com/

Tried to read their FAQ but it is sort of handwavy. Do you have any links on the research behind this tech? I understand it uses CO2 from the atmosphere and solar + wind to build hydrocarbons? But what are the technical details there? How is this being done and why wasn't this done sooner?

Article about Prometheus in Science:

https://www.sciencemag.org/news/2019/07/former-playwright-ai...

Re: Boom supersonic jet readies for rollout

#176

Post by iso947 »

catalogia wrote: post #123
dreamcompiler wrote: post #111

Earlier quoted context omitted.

> You could travel faster than the rotation of the earth in it! You can do that in a conventional jet at latitudes far from the equator. You can walk faster than the earth rotates if you're very close to a pole (very very close).

> (very very close). Eh, within 15 miles or so. 4MPH * 24h = 96 mile circumference circle, 96 miles / 2pi ~= 15 miles.

You are going to struggle to walk at 4mph in Antarctica

Re: Boom supersonic jet readies for rollout

#178

Post by gorgoiler »

Is there an intuitive everyday explanation as to why the sound barrier is so hard to break?

I know that the forces in an airframe change a lot as you go faster, and that the controls invert for some reason, but I’ve never really had a good feel as to why.

Perhaps something related to swimming?

Re: Boom supersonic jet readies for rollout

#179

Post by Jabbles »

gorgoiler wrote: post #178

Is there an intuitive everyday explanation as to why the sound barrier is so hard to break? I know that the forces in an airframe change a lot as you go faster, and that the controls invert for some reason, but I’ve never really had a good feel as to why. Perhaps something related to swimming?

The speed of sound is vaguely the speed at which air can get out of the way. If you try travelling faster than that the air bunches up into a shockwave, which causes all kinds of problems and is generally different to travelling through air slowly.

Re: Boom supersonic jet readies for rollout

#180

Post by jasin »

gorgoiler wrote: post #178

Is there an intuitive everyday explanation as to why the sound barrier is so hard to break? I know that the forces in an airframe change a lot as you go faster, and that the controls invert for some reason, but I’ve never really had a good feel as to why. Perhaps something related to swimming?

In simplistic terms, at supersonic speeds the air particles do not have sufficient time to "get out of the way" of the body moving in the air. This causes the air particles to be compressed into a dense "shock wave", which can cause separation of the air flow from the surface of the airfoil, leading to a stall. The properties of a wing that handles supersonic airflow well are often at odds with a subsonic wing.
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