Author Topic: Boom Aerospace  (Read 60079 times)

Offline libra

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Re: Boom Aerospace
« Reply #40 on: 09/21/2022 12:33 pm »
Quote
. That was good enough for Concorde, back when oil was $3/barrel.

Not even close. PanAm cancelled their orders in January 1973, not 1974 - that is months BEFORE the first oil shock
. It has been calculated since that even with 74 orders and even without the first oil shock, Concorde business case would not have closed, and by a long shot.
The reason is, 130 passengers at Mach 2.0 over the Atlantic ain't enough. Not enough passengers, and not enough daily rotations between New York and Europe and back: two ain't enough, but Mach 2.05 can't do any better.

What was needed was 250 passengers at Mach 2.7 and three daily rotations between N.Y and Europe (Paris / London and back).
Wait, does that sound familiar ? Boeing 2707-300 had the economic case right, but technology couldn't fulfill it - it resulted in a bloated titanium monster (300 feet long !) with noisy and voracious GE4 turbojets, themselves scaled up XB-70 J93s.

There are many ironies in that first (and only one so far) "great SST race".

That PanAm in June 1963 was the one that started it all by buying six Concordes, forcing JFK to get another Apollo moment with the SST.
That PanAm exactly 10 years later (or close) was essentially the one that stopped it, when they canned the exact same order, six Concordes, in January 1973.
That the SST got the economic case nearly right (three daily rotations over the Atlantic takes Mach 2.7, with 250, not 140, passengers) but could not build it in the end.

A very interesting story.

Offline john smith 19

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Re: Boom Aerospace
« Reply #41 on: 09/21/2022 02:04 pm »
Quote
. That was good enough for Concorde, back when oil was $3/barrel.

Not even close. PanAm cancelled their orders in January 1973, not 1974 - that is months BEFORE the first oil shock

"Good enough" in the sense a)It got built b)It flew for the following 27 years without any major crashes.

I think I've noted on several occaisions that the general view was it was too small, and the French wanted originally to make it smaller still.

OT how would M5 with a 20 000Km range affect viability?
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 2027?. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Robotbeat

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Re: Boom Aerospace
« Reply #42 on: 09/21/2022 02:15 pm »
Option 3: Develop engine internally.

Okay, we can stop even mentioning that option right now.  It is impossible, period. 
I don’t think Boom will do that, and they’d almost certainly go bust if they tried, but that’s poppycock.

Jet engines are very complicated, but they are not magical.

This reminds me of when making pumpfed rocket engines was only considered possible for a handful of aerospace primes, now you have everyone and their mom building them. Even amateurs are building turbopumps and some of these small space companies like Ursa Major (and Launcher) are building oxygen-rich staged combustion engines, which literally no US company had done 20 years ago (and was thought practically impossible before the fall of the Iron Curtain).

An axial flow jet engine is more mechanically complicated than the typical centrifugal turbopump, but the same “impossible for the little guys” mindset that was common 20-30 years ago for pumpfed engines that people have for jet engines today is just as magical-thinking as anything else.

It’s not magic, it’s just physics and engineering.

People who talk like this demonstrate their own ignorance (on the one hand) or hubris (on the other).
« Last Edit: 09/21/2022 02:23 pm by Robotbeat »
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Offline libra

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Re: Boom Aerospace
« Reply #43 on: 09/21/2022 04:10 pm »
Nobody said it was TECHNICALLY impossible to design that engine. It is feasible, for at least the best part of the last 50 years. Near the end of SST and Concorde (mid-1970's, aproximately)  both GE4 and Olympus were still evolving (Olympus 625 and the GE4 variants described there https://www.airliners.net/forum/viewtopic.php?t=752231 ) - to a point were they would no longer need afterburner at all. Not even at takeoff or to push through the sound barrier: supercruise (Concorde already did it partially).
And the next step beyond that was "variable cycle" but it never got off the drawing boards.

Back to Boom: they could do an "ideal" engine from scratch, or one of the big players could do it. Technically - no problem.

The big impossibility is: economically. Would cost Boom or G.E or Pratt or RR or CFM an arm and a leg, and what's really annoying: the market ain't there. 500 airframes absolute best case is not enough to repay both RR and Boom billion dollars sunk into the development cost of that "ideal" engine (ideal = adapted to Boom & FAA draconian noise and fuel and pollution constraints).


Offline john smith 19

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Re: Boom Aerospace
« Reply #44 on: 09/21/2022 04:52 pm »
This reminds me of when making pumpfed rocket engines was only considered possible for a handful of aerospace primes, now you have everyone and their mom building them. Even amateurs are building turbopumps and some of these small space companies like Ursa Major (and Launcher) are building oxygen-rich staged combustion engines, which literally no US company had done 20 years ago (and was thought practically impossible before the fall of the Iron Curtain).
Your comments reminded me of something.

Big truck turbochargers.

The sort of thing you see on 18 wheelers.

Turns out the mfgs have a similar problem. Ideally they'd like to cast them, as is done with car turbos. But the volume won't justify the non recurring engineering given the complexity of the mold needed.  :(

The solution? Machine from a solid billet. IIRC they start with a  something like a 20lb block and 19hours later it's done, with a large pile of chips to be recycled.

This would be totally impossible without 5-axis CNC fed direct from the CAD drawings and real time monitoring of key dimensions that modern machines allow. But now that hardware exists it is possible. Making what was uneconomic (given the potential market and the price they would accept) affordable. 

It might (and I'm not sure that it doesn't) not have the last 1% of efficiency because (perhaps) the blades cannot incorporate the subtlety of shape a casting could, but it's good enough to get the job done.

Just a data point to consider.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 2027?. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline butters

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Re: Boom Aerospace
« Reply #45 on: 09/21/2022 04:58 pm »
Option 3: Develop engine internally.

Okay, we can stop even mentioning that option right now.  It is impossible, period. 
I don’t think Boom will do that, and they’d almost certainly go bust if they tried, but that’s poppycock.

Jet engines are very complicated, but they are not magical.

This reminds me of when making pumpfed rocket engines was only considered possible for a handful of aerospace primes, now you have everyone and their mom building them. Even amateurs are building turbopumps and some of these small space companies like Ursa Major (and Launcher) are building oxygen-rich staged combustion engines, which literally no US company had done 20 years ago (and was thought practically impossible before the fall of the Iron Curtain).

An axial flow jet engine is more mechanically complicated than the typical centrifugal turbopump, but the same “impossible for the little guys” mindset that was common 20-30 years ago for pumpfed engines that people have for jet engines today is just as magical-thinking as anything else.

It’s not magic, it’s just physics and engineering.

People who talk like this demonstrate their own ignorance (on the one hand) or hubris (on the other).
The biggest difference between the jet and rocket engine industry is that if your jet engine is 10% less efficient than the market leader, nobody will take your calls. It's a much more mature market with much higher barriers to entry because the state of the art is much more refined. Advanced economies like Japan can't market indigenous high-bypass turbofan engines. They can only aspire to build components of jet engines as part of international alliances.

Meanwhile, the most successful rocket engine in the world at the moment is an open-cycle design than dumps lots of propellant overboard. If you've got a rocket engine in serial production that works reliably and the price is right, prospective customers will call you. The standards are much lower. Japan can make rocket engines that are good enough. At least for their own purposes if not also for customers.

In aviation even seemingly straightforward engine solutions are hard. Maybe look up how many times companies have tried and failed to market general aviation piston engines based on highly reliable Mercedes-Benz automotive diesel engines. It seems like a great idea to make light piston aircraft that don't rely on expensive and unhealthy leaded aviation gasoline, but ultimately it was easier to prove that a fancy new unleaded gasoline formulation works in everything from a Piper Cub to a B-29 Superfortress than to introduce time-tested automotive engines to the general aviation market. And that's just general aviation. Large transport category jets are subject to much more rigorous requirements.

Also, since aircraft engines are expected to be reusable, nobody just buys an aircraft engine. They also buy a service contract, and they expect a certain level of service, usually distributed around the world. This is a huge barrier to entry. Service contractors are very conservative. They know the engines they know, and they don't like engines they don't know. It's hard to predict costs. So the engine manufacturer usually has to bootstrap their own network of service providers at great expense while still offering very underwhelming service compared to the established players.

Who would buy reusable rocket engines from SpaceX without a contract for SpaceX-trained maintenance teams to process the engines between flights? The same thing will gradually happen with rocket engines. Barriers to entry right now are still pretty reasonable. It won't stay that way forever. Especially because of reusability, it will become harder to market new rocket engine designs, more like it is with new aircraft engines. The standard of excellence is becoming more difficult to attain.

Offline Zed_Noir

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Re: Boom Aerospace
« Reply #46 on: 09/21/2022 05:27 pm »
Think Boom Aerospace should have settled on an engine that could be brought into service before even considering the rest of the aircraft.

Maybe a non-afterburning civilian version of of the Pratt & Whitney F119 low bypass turbofan.

Then design a supersonic airliner with maybe four PW5000 (aka F119) engines.

Note - Rolls-Royce still have nightmares with the RB211 Trent engine development.

Offline ZuluLima

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Re: Boom Aerospace
« Reply #47 on: 09/22/2022 12:07 am »
Jet engines are very complicated, but they are not magical.

An axial flow jet engine is more mechanically complicated than the typical centrifugal turbopump, but the same “impossible for the little guys” mindset that was common 20-30 years ago for pumpfed engines that people have for jet engines today is just as magical-thinking as anything else.

It’s not magic, it’s just physics and engineering.

People who talk like this demonstrate their own ignorance (on the one hand) or hubris (on the other).

People who hand-wave away knowledgeable criticisms demonstrate their own ignorance, too.  Try to grasp what is being proposed; name ONE current engine that is capable of what Boom needs.  Must be:
1. Certified as safe for commercial use and for emissions in post-2030 western world.
2. Efficient enough to support range requirements (ocean-crossing) and economics of airline industry.
3. Capable of supercruise (supersonic without afterburner) at M1.7.
4. Capable of all-day flight-cadence at over 99.8% dispatch reliability, roughly the current standard, and high Mean Time Between Overhauls.
5. Sized to fit in a smallish nacelle with all fittings.
6. MANY more technical and practical issues that suffuse the aviation industry.

I'm sure a startup with modest funding and 0 track record can easily design, manufacture, test, certify, deliver, and support such an engine with never-before-seen performance while simultaneously doing the same for the vehicle, which no one else is also even attempting.  Because, "it's not magic".
« Last Edit: 09/22/2022 12:10 am by ZuluLima »

Offline Robotbeat

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Re: Boom Aerospace
« Reply #48 on: 09/22/2022 12:31 am »
Option 3: Develop engine internally.

Okay, we can stop even mentioning that option right now.  It is impossible, period. 
I don’t think Boom will do that, and they’d almost certainly go bust if they tried, but that’s poppycock.

Jet engines are very complicated, but they are not magical.

This reminds me of when making pumpfed rocket engines was only considered possible for a handful of aerospace primes, now you have everyone and their mom building them. Even amateurs are building turbopumps and some of these small space companies like Ursa Major (and Launcher) are building oxygen-rich staged combustion engines, which literally no US company had done 20 years ago (and was thought practically impossible before the fall of the Iron Curtain).

An axial flow jet engine is more mechanically complicated than the typical centrifugal turbopump, but the same “impossible for the little guys” mindset that was common 20-30 years ago for pumpfed engines that people have for jet engines today is just as magical-thinking as anything else.

It’s not magic, it’s just physics and engineering.

People who talk like this demonstrate their own ignorance (on the one hand) or hubris (on the other).
The biggest difference between the jet and rocket engine industry is that if your jet engine is 10% less efficient than the market leader, nobody will take your calls....
Balooney. That's true for rocket engines, too. If you have a hydrolox upper stage engine with just 410s vacuum Isp (vs 450-460s), good luck getting anyone to pick up the phone.

And if just accepting 90% of their desired efficiency initially was all they'd have to do to get an engine, Boom would be happy to do it.

Really don't care for people who over-fit on the status quo of the existing, stifled ("mature") industry as the only way things can be done trying to speak authoritatively on what a new effort can and cannot "possibly" do for a new kind of aircraft (supersonic passenger jet) not represented at all in the current status quo fleet.
« Last Edit: 09/22/2022 01:00 am by Robotbeat »
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Offline Robotbeat

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Re: Boom Aerospace
« Reply #49 on: 09/22/2022 12:32 am »
Jet engines are very complicated, but they are not magical.

An axial flow jet engine is more mechanically complicated than the typical centrifugal turbopump, but the same “impossible for the little guys” mindset that was common 20-30 years ago for pumpfed engines that people have for jet engines today is just as magical-thinking as anything else.

It’s not magic, it’s just physics and engineering.

People who talk like this demonstrate their own ignorance (on the one hand) or hubris (on the other).

People who hand-wave away knowledgeable criticisms demonstrate their own ignorance, too. ...
You start throwing around words like "impossible" and you've gone beyond "knowledgeable criticisms" and have engaged in hyperbole.
« Last Edit: 09/22/2022 01:01 am by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline libra

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Re: Boom Aerospace
« Reply #50 on: 09/22/2022 03:42 am »
Jet engines are very complicated, but they are not magical.

An axial flow jet engine is more mechanically complicated than the typical centrifugal turbopump, but the same “impossible for the little guys” mindset that was common 20-30 years ago for pumpfed engines that people have for jet engines today is just as magical-thinking as anything else.

It’s not magic, it’s just physics and engineering.

People who talk like this demonstrate their own ignorance (on the one hand) or hubris (on the other).

People who hand-wave away knowledgeable criticisms demonstrate their own ignorance, too.  Try to grasp what is being proposed; name ONE current engine that is capable of what Boom needs.  Must be:
1. Certified as safe for commercial use and for emissions in post-2030 western world.
2. Efficient enough to support range requirements (ocean-crossing) and economics of airline industry.
3. Capable of supercruise (supersonic without afterburner) at M1.7.
4. Capable of all-day flight-cadence at over 99.8% dispatch reliability, roughly the current standard, and high Mean Time Between Overhauls.
5. Sized to fit in a smallish nacelle with all fittings.
6. MANY more technical and practical issues that suffuse the aviation industry.

I'm sure a startup with modest funding and 0 track record can easily design, manufacture, test, certify, deliver, and support such an engine with never-before-seen performance while simultaneously doing the same for the vehicle, which no one else is also even attempting.  Because, "it's not magic".

You have my support. Technically: certainly doable. But from a business case point of view ? it is a killer. Boom will do no better than Aerion nor any of the previous SSBJ projects (Dassault included) because of that engine issue. Could be done on technical grounds; but it would cost an arm and a leg, and the business case would not close, as the market is too small (some hundred airframes is NOT enough to repay some billion dollars of engine development cost).


Offline john smith 19

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Re: Boom Aerospace
« Reply #51 on: 09/22/2022 06:51 am »

People who hand-wave away knowledgeable criticisms demonstrate their own ignorance, too.  Try to grasp what is being proposed; name ONE current engine that is capable of what Boom needs.  Must be:
1. Certified as safe for commercial use and for emissions in post-2030 western world.
2. Efficient enough to support range requirements (ocean-crossing) and economics of airline industry.
3. Capable of supercruise (supersonic without afterburner) at M1.7.
4. Capable of all-day flight-cadence at over 99.8% dispatch reliability, roughly the current standard, and high Mean Time Between Overhauls.
5. Sized to fit in a smallish nacelle with all fittings.
6. MANY more technical and practical issues that suffuse the aviation industry.
All of which applies for a commercial product that's designed to be sold to other customers, which is probably why RR turned them down from going any further.

But if they are doing it on their own then the engine becomes a part of the package
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 2027?. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline libra

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Re: Boom Aerospace
« Reply #52 on: 09/22/2022 06:55 am »
Bottom line: whoever develop that peculiar engine has to find some billion dollars in development costs. Then - who pays for that ? That's the HUUUUGE issue with supersonic civilian, be it SSBJ or SST.

Plus the sonic boom. Flying overwater is a bit restrictive  although acceptable.

There seems to be a new, larger issue. Flying supersonic - basic physics - can only be fuel intensive. With the accelerating global warming and the growing anger at commercial aviation, it is perhaps not a good time to fly supersonic, civilian.
Aviation already has hard times trying to find a viable kerosene substitute: ammonia, hydrogen, mix of the two (my favorite solution)  SAF, batteries... none is a panacea. And this is for subsonic civilian travel.

Offline john smith 19

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Re: Boom Aerospace
« Reply #53 on: 09/22/2022 06:57 am »
Balooney. That's true for rocket engines, too. If you have a hydrolox upper stage engine with just 410s vacuum Isp (vs 450-460s), good luck getting anyone to pick up the phone.

And if just accepting 90% of their desired efficiency initially was all they'd have to do to get an engine, Boom would be happy to do it.
True.
Quote from: Robotbeat
Really don't care for people who over-fit on the status quo of the existing, stifled ("mature") industry as the only way things can be done trying to speak authoritatively on what a new effort can and cannot "possibly" do for a new kind of aircraft (supersonic passenger jet) not represented at all in the current status quo fleet.
But if Boom want to go this way they will have to offer support for their product, and in the aircraft world that means on a global basis (SX will have to do this if they go ahead with their ballistic transport ideas as well).
That sort of logistics support simply does not exist in the rocket launch market.

MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 2027?. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline john smith 19

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Re: Boom Aerospace
« Reply #54 on: 09/22/2022 07:10 am »
Bottom line: whoever develop that peculiar engine has to find some billion dollars in development costs. Then - who pays for that ? That's the HUUUUGE issue with supersonic civilian, be it SSBJ or SST.
That's the circle you have to square. The market is tiny and the engine is key. Concorde designers had an adequate engine on hand with the Olympus before they started.

Quote from: libra
Plus the sonic boom. Flying overwater is a bit restrictive  although acceptable.
Depends on how much range you have. With 20 000Km going M5 is not impossible even with subsonic segments.

Quote from: libra
There seems to be a new, larger issue. Flying supersonic - basic physics - can only be fuel intensive. With the accelerating global warming and the growing anger at commercial aviation, it is perhaps not a good time to fly supersonic, civilian.
Aviation already has hard times trying to find a viable kerosene substitute: ammonia, hydrogen, mix of the two (my favorite solution)  SAF, batteries... none is a panacea. And this is for subsonic civilian travel.
With CO2 having an atmospheric lifetime of 300-1000 years even if all CO2 production stopped tomorrow it would take a minimum of 3 centuries to drop back to pre-industrial levels (except they wouldn't be pre-industrial levels as there are seveal billion more people on the planet). Given some GHG's have lifetimes in milenia and global warming potentials in the 1000s it will take active GHG reduction measures to save the human race.

Supersonic flight is a red herring that will change nothing about global warming, although O3 depletion is more of an issue. Mitigation methods exist for H2 combustion and NH3 is an option with work Reaction Engines have done.

One idea I don't think anyone has considered is to power the compressor with batteries.

Someone has acutally built such a jet engine (for a bench test) using an electric motor to drive the compressor. I've literally no idea if the mass numbers work out, but it would ditch all the heavy high temperature turbine section and greatly simplify the hardware.

Otherwise water spray injection as they proposed for Peace Jack. Knocking 1.5M off the top speed will certainly lower the temperatures (of some parts) quite considerably.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 2027?. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline libra

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Re: Boom Aerospace
« Reply #55 on: 09/22/2022 08:24 am »
Quote
With 20 000Km going M5

I would rather go suborbital with a rocket in the tail, rather than hypersonic inside the atmosphere with any scramjet. Use kerosene as fuel, and whatever few begning oxidizer on hand (that's the real PITA: bar N2O and H2O2, there are preciously little alternatives to classic LOX, a deep cryogen a bit annoying for airports ground crews, or a military base mechanics).

A specific impulse of 345 and a prop mass fraction of 0.80 could get 6500 m/s of delta-v, and with that ballistic range could be  7000 km to 12 000 km - depends whether or not the trajectory is flattened to not hit the lower van Allen belts. Ballistics are certainly a b**tch, as are the rocket equation and the heat barrier, the latter for hypersonics. Also sonic booms. Together they are kind of four horsemen of non-subsonic aerial passenger transportation.

But we are disgressing away from Boom... (or bust, which I don't wish them: I love their design).

Offline Asteroza

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Re: Boom Aerospace
« Reply #56 on: 09/22/2022 08:27 am »

One idea I don't think anyone has considered is to power the compressor with batteries.

Someone has acutally built such a jet engine (for a bench test) using an electric motor to drive the compressor. I've literally no idea if the mass numbers work out, but it would ditch all the heavy high temperature turbine section and greatly simplify the hardware.

Battery boost was sorta proposed with some SUGARVOLT concepts I think, but that was turbofan takeoff power mostly. If you're burning fuel though, and not running a turbine, then you're basically running an electrically pumped rocket right? That's gonna be LOUD, meaning getting tier 3/4 noise pollution clearance will be an issue.


I think the last time there was talk of electrically driven compressors was the S-MAGJET/H-MAGJET Hypermach guys with their Sonicstar bizjet, who essentially proposed a shaftless engine using electric rim drive motor compressor counterrotating blisks and rim drive generators driven by counterrotating  turbine blisks, turbine power also powering a MHD accelerator aft of the turbine as the exhaust was seeded. The aim was to allow dissimilar rotation rates for the turbines and compressors beyond what geared turbofan style planetary gear systems could provide, so the compressors and turbines could be better tailored to their individual environments (and allow compressor boost from batteries).

S-MAGJET as a design alone doesn't really solve the hot turbine blade problem though if they are using mostly conventional axial turbine blades. They were also fooling around with plasma combustion so they could somehow achieve laminar flow over the turbine blades.


Offline john smith 19

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Re: Boom Aerospace
« Reply #57 on: 09/22/2022 09:55 am »
I would rather go suborbital with a rocket in the tail, rather than hypersonic inside the atmosphere with any scramjet.
I wasn't thinking of a SCramjet. That's what Reaction Engines were looking at for the baseline design for LAPCAT II. The Germans wanted to go with kero for their SCramjet design but couldn't get the range to go Brussels/Sydney  :( There was a follow up EU programme that looked at structures for such a design.
Quote from: libra
A specific impulse of 345 and a prop mass fraction of 0.80 could get 6500 m/s of delta-v,transportation.

But we are disgressing away from Boom... (or bust, which I don't wish them: I love their design).
As I mentioned on the Radian thread the Virgin Atlantic Global Flyer built by Scaled was the best fuel fraction plane I could find and that was 84% fuel, so everything else (including the pilot) was what was left.

A vehicle that's 20% structure is not far off and with TPS as well. OTOH air breathing gets you Isp of several 1000s, allowing wings, landing gear that can handl full GTOW etc.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 2027?. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Proponent

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Re: Boom Aerospace
« Reply #58 on: 09/22/2022 03:03 pm »
A specific impulse of 345 and a prop mass fraction of 0.80 could get 6500 m/s of delta-v, and with that ballistic range could be  7000 km to 12 000 km - depends whether or not the trajectory is flattened to not hit the lower van Allen belts.

Even if the exposure to the van Allen Belts is regarded as acceptable, I think the trajectory would have to be flattened to avoid punishing G-loads.  People tend to be rather more finicky about that than are ICBM warheads.
« Last Edit: 09/22/2022 03:04 pm by Proponent »

Offline libra

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Re: Boom Aerospace
« Reply #59 on: 09/22/2022 03:23 pm »
Yes. And that's the moment when ballistics become such a PITA... such an annoyance. Ballistic trajectories are pointy: altitude grows faster than range. And if you try flattening, range takes a big hit.
A good resource with some numbers here.
https://www.alternatewars.com/BBOW/ABM/BM_Classes.htm
https://www.alternatewars.com/BBOW/ABM/DeltaV_BMs.htm

Ballistics are unforgiving, really. But Boom isn't going ballistic, and I don't want to hijack the thread...

Quote
OTOH air breathing gets you Isp of several 1000s, allowing wings, landing gear that can handl full GTOW etc.

Hydrogen turbofans are close from 8000 seconds (blew my mind when I realized this recently), alas only at subsonic speed... go supersonic then hypersonic and that awesome number (in your face, Gas Core Nuclear Rocket) instantly collapses. Still around 2000 seconds at Mach 2 or Mach 3, a very respectable number. Well, then there is SABRE.

 

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