Does any manufacturer really want to design new planes? The engineers do, it's their job & mostly their passion but the shareholders won't want to if they don't have to. Every time you design a new aircraft you commit to billions of investment and lots of risk, both financial and technical.
The saying I was most often quoted in my aerospace degree "How do you make a small fortune? Start with a large fortune and invest in aerospace".
The best that you'll probably get is that once it becomes clear that a planned development needs to start that the shareholders decide to go all-out for it, and the rest of the company commit to it 100%.
And yes the engine should be able to contain a broken blade
Slight correction: the engine should be able to contain a failed fan blade. A turbine disc (or the one third disc pieces it breaks into), which is what failed on the flight here, acts like god's own laser beam and is not containable and so the aircraft will always have to be designed to tolerate that type of failure as it duly did. In fact the regulations require uncontained fan blade failures to be checked as well, even though they shouldn't happen.
Lots of natural materials exhibit really interesting properties, sometimes at odds with the way we'd expect such materials to react. For example crustacean shells are ceramic but quite tough because of the layering of the ceramic with small amounts of organic binder material which causes any fractures to be diverted before they spread though the bulk of the material.
Many natural materials exhibit high levels of hierarchy like this and it's one of the many reasons why natural structures and materials are way cooler than most of the things that we make, with the possible exception of aerogel. One of the most interesting hierarchical structures is Euplectella Aspergillum (Venus' flower basket), its structure is really complex. I can easily see this being an aerospace material in 10 years...
The Busemann biplane came up when we did supersonic aero in University back in '98 or '99 and it was always stated to be an impractical wing design because, at the supersonic zero boom/zero wave drag condition, it couldn't produce lift; this doesn't stop it being useful for other things like shells etc. where you don't mind zero supersonic lift if you can get low drag
The diagrams in the article seem to look like that condition in supersonic flow where the "inner" surfaces interfere favourably with each other to cancel wave drag and have the upper and lower surfaces with no incidence to the flow so they produce no shock waves.
Supersonically it should still produce lift quite happily if you angle it so there is incidence to the flow but I think that it should then produce wave drag and booms... For example I can't see from the article how, in a lifting condition, the shock wave from the compression of the supersonic flow on the undersurface (which produces the compression & higher pressure that helps lift the wing) could be cancelled out without having another wing underneath that; then you have the same problem with the undersurface of that wing & then you're in a "it's wings all the way down" problem.
Conventional 'low boom' solutions (like the Gulfstream/NASA "quiet spike") all tend to shape the nose of the aircraft to reduce the suddenness of the pressure increase across the shock wave but they aren't able to eliminate it...
It could be that they've found a case where they can get low wave drag/boom while still producing some lift and also getting decent subsonic lift/drag - that would be really interesting...
Take seatbelts - the oft-given example - if I don't buckle up I might die in a crash but it doesn't harm anyone else.
Incorrect. You are now a 180Lbs loose object in the car. Where your children were safely buckled, your dead body bounced to the back seat and injured them. Or you're a 450Lbs object wedged behind the steering wheel... This is slashdot after all.
Seeing as we were talking about the UK we can also talk about the fact that increased injuries of loose drivers/passengers if they don't manage to die will affect others by the increased cost and use of resources in the NHS.
I'm not sure trains are a good model either; Diesel-electric trains are effective because the torque you need for starting & driving a train doesn't easily come from a diesel motor without lots of gearing and clutches that are complex, inefficient and potentially unreliable.
Electric motors can give you all the torque you want from a standing start and so they make it easier to use diesels, avoiding the need to electrify your rail network (partly the reason Britain went with Diesel-electric trains in the '50s - they didn't have the capital to electrify).
With aircraft it's less clear where the advantage is going to come from since the kerosene motor + generator combination (and its associated losses) in an aircraft isn't solving a clear problem like lack of torque in a train and power requirements with lots of peaks and troughs as in a car.
However, a big advantage (from an environmental point of view) could be the ability to take electrical power for flight - once you have this you can gradually feed in alternative or low carbon energy into your mix. This type of aircraft could be a first step in that direction.
It's not beyond current capability even in civil aviation, in fact Boeing offered a folding wing option for the 777 but (so far) no-one's bought it.
This is partly due to lack of driver (gates at airports were either wide enough or made wide enough) but also because any driver to wing folding's got to be pretty strong to overcome the weight penalty
If you were to see a _big_ increase in span for aircraft of these capacities I'd imagine that folding wings might become more popular...
You're correct that drag has a large influence, engines have a part to play also. Turbofans have a 'bucket' speed where their efficiency (specific fuel consumption or the fuel they burn per second per pound of thrust) is best* The result is that, when the aerodynamics and engine efficiency are combined, there will be a best efficiency speed (best range speed) that's not far below the theoretical 'design' speed. However many airlines fly faster than this, depending on their balance of fixed vs. hourly costs. Generally you can get higher efficiency by flying slower but you have to make changes to the aircraft, as seen here where much of the efficiency probably comes from the lower lift dependent drag that you can get from the larger spans of these aircraft. They probably get quite a lot of gain from engine improvements also, perhaps half.
*all bets are off with open-rotor or propellor engines, broadly these like to fly slower overall and you lose efficiency steadily the faster you fly.
The issue of requirements is one that I've always found interesting.
There always seems to be an assumption that customers know how to write requirements. Personally (from the position of a hobby coder who needs to use the services of professionals to get real applications written) I've always found it difficult to write intelligent requirements.
Don't get me wrong, I know that this is my fault, but I find that I need assistance from people who actually understand the ways that things _could_ be done and know the implications of the things that may be asked for. I always prefer to plan for a significant activity just to find out what I should be asking for. Motivation of the people who I ask for advice is important. If I (or the company I work for) pays the developer I know I can expect that they want to get the best results for the company as a whole.
I work in the aircraft industry and I've seen enough poorly chosen requirements for aircraft to know that this isn't a solely IT issue...
The engines-on-the-side configuration is a way to try to deal with engine weight changes. Huge trim issues arise if your engine isn't as light (or heavy) as you think it will be.
Spaceplanes with engines at the back face a real struggle with balance if _anything_ changes in the engines - they tend to be very heavy compared to anything else in the 'dry' structure of the vehicle and a small error either way can leave you with depleted uranium bulkheads to pull your CG back if it's too late in the development programme to change the configuration.
You really can't get away with stuff like that since single-stage-to-orbit is _really_ hard to do.
Couple that with the big aerodynamic centre changes that you tend to get over such a large flight regime and you may end up with a lot of mass budget being taken up by control surfaces.
I understood from a couple of lecturers at Uni and past co-workers that this would have been one of the really big problems that HOTOL would have had to deal with had it not been cancelled... (which project Alan Bond of Reaction Engines was also involved in)
Commercial jets are at lift/drag of around 18-20 now As an engineer working with fixed wings it is my firm belief that helicopters fly because they are so ugly that the ground repels them - on that basis this thing is getting to the moon.
Problem with suspending people in liquid (as summed up by Joe Haldeman in "Forever War":
'What happens if drop a wrench in a submarine?'
You overall might not be a puddle, but your guts would...
"Having worked on the Navier Stokes equation for about three years, I can say that this is a very interesting problem. Actually, the Navier Stokes equation is the equation governing an incompressible flow - that is, it is an equation that very closely approximates the flow of water. Thus to gain any understanding of this equation is to make a lot of progress in understanding turbulance. This will have great practical applications..."
Not sure where you got the incompresible bit from... The Navier-Stokes equations actually govern _any_ type of flow (unsteady, compressible, viscous and any other type you want) in their unreduced form.
If you want to assume incompressibility they will still be valid (for water and air flows up to about Mach 0.3 ish), but they won't be the full Navier-Stokes equations any more.
This problems may have a larger impact than you suggest... or less.
Computational aerdynamics can't solve the full N-S equations at all yet - and even if they could the computer power needed for the fineness of mesh needed would be beyond what's available now, for any reasonable run time at least.
Agreed, but I should point out that the problem has already been seen in jet engines where you've got _tons_ of metal spinning at tens of thousands of RPM.
The way that it was treated was to use a Kevlar casing to contain fragments - it's incredibly strong in tension, even under impact, and should solve the problem pretty well, although there have been cases of disc burst in aircraft (Sioux city IIRC) where a crash was caused.
BTW the flywheels would not be metal - it couldn't take the stress, you'd be much more likely to use composites - either unidirectional carbon fibre, kevlar, carbon-carbon composites, intermetallics or engineering ceramics - _much_ stronger.
Breaking a law you disagree with is attractive, hell sometimes it even works, but on the whole it's always useful to _try_ to change the law through the mechanisms that have been set up to allow that - it might not work but you are at least trying.
Some examples (UK bias):
Poll tax - ignored by many people, eventually got dumped as it was impossible to enforce and looked like an election loser (however many people just didn't pay anything and simply saw it as an excuse to avoid paying taxes, my folks paid the previous tax rate + inflation and got ignored because they'd paid _something_)
Ireland - 25 years of 'struggle' no change, everybody (including bomb-dodging Londoners) miserable. 1 ceasefire and things start happening yet people seem to forget that and talk about resuming violence, in this case it really _didn't_ do anything.. and as I said it did nothing for a quarter century
First we need a good launcher...
on
On to Mars
·
· Score: 1
The more important issue at the moment for any kind of big mission to Mars is launchers, the tonnes of mass that you need to get into orbit.
The shuttle is too expensive for doing lots of heavy lift work (and it's too unreliable partly due to the requirements for human crew safety). Every time you use most rockets these days you throw away stages to get to orbit, be they boosters or whatever. This costs big time, both in terms of all that stuff you chuck out and in terms of the cost of developing the stages. It costs about 10 billion to develop a space vehicle and that means each stage. You do a 3 stage rocket (eg Saturn V) you got about 30 billion in costs.
Then there's running costs and turnaround. The shuttle takes months to turn around after a mission, it's complex and can't carry that much to orbit (and that only to low earth orbit). What you need is a system that is really re-usable like and aircraft, preferably unmanned and easy to turn around after a mission.
The solutions? SSTO (single stage to orbit) it's the only way that we'll get the launchers that are needed for any kind of heavy launches to orbit (in terms of total tonnage over time) required for a proper manned mission to Mars.
NASA has one of these in the pipeline, the Venturestar. It's not doing too well. Call me a cynic (and a Brit one at that) but I do not have a huge amount of confidence in NASA to deliver this system. Their technology demonstrator is over weight budget by a _lot_, partly because they belived the engine maufacturer (who quoted cheapest it should be said) when they said the engines would e lighter than conventional engines... they're heavier (a lot heavier). This has resulted in them having to bolt depleted uranium to a bulkhead in the nose (high tech huh?). Its structure has had to be radically redesigned because the aerodynamic trim is wrong (you have to get this right, you haven't got any spare mass to play with) and the fancy new materials that they're using aren't working the way that they were supposed to. NASA don't seem to have learned that new stuff isn't a good idea in space, that's why satellites use 286 processors and why even in aerospace the cutting edge civil fly by wire of the bug Airbus aircraft is based on 386 chips. New things aren't predictable, and engineering analysis isn't precise enough to tell you everything that you'll need to know.
What else is there? Well not a lot. SSTO is _very_ hard. The Earth is about 10% too big for it to work easily. Still you might want to look at the (rather bad) webpages devoted to the Skylon Project [http://www.gbnet.net/orgs/skylon/skycont.htm]. It's basically all the things that were learned from the British HOTOL project in the 80's. I've seen the figures and it will work. It's clever, airbreathing rockets that use the air as oxidiser instead of having to carry all of their liquid oxygen (until the atmosphere gets too thin). It lets you get up cheaper than the shuttle or any of the rocket solutions available now.
This is the kind of vehicle that's needed and it's not even that expensive to develop, but trying to go to Mars without it will cost even more even if you assemble the Mars ship in orbit. you still have to get the parts there.
Slashdot Mirror
Does any manufacturer really want to design new planes? The engineers do, it's their job & mostly their passion but the shareholders won't want to if they don't have to. Every time you design a new aircraft you commit to billions of investment and lots of risk, both financial and technical.
The saying I was most often quoted in my aerospace degree "How do you make a small fortune? Start with a large fortune and invest in aerospace".
The best that you'll probably get is that once it becomes clear that a planned development needs to start that the shareholders decide to go all-out for it, and the rest of the company commit to it 100%.
And yes the engine should be able to contain a broken blade
Slight correction: the engine should be able to contain a failed fan blade. A turbine disc (or the one third disc pieces it breaks into), which is what failed on the flight here, acts like god's own laser beam and is not containable and so the aircraft will always have to be designed to tolerate that type of failure as it duly did. In fact the regulations require uncontained fan blade failures to be checked as well, even though they shouldn't happen.
Lots of natural materials exhibit really interesting properties, sometimes at odds with the way we'd expect such materials to react. For example crustacean shells are ceramic but quite tough because of the layering of the ceramic with small amounts of organic binder material which causes any fractures to be diverted before they spread though the bulk of the material.
Many natural materials exhibit high levels of hierarchy like this and it's one of the many reasons why natural structures and materials are way cooler than most of the things that we make, with the possible exception of aerogel. One of the most interesting hierarchical structures is Euplectella Aspergillum (Venus' flower basket), its structure is really complex. I can easily see this being an aerospace material in 10 years...
The Busemann biplane came up when we did supersonic aero in University back in '98 or '99 and it was always stated to be an impractical wing design because, at the supersonic zero boom/zero wave drag condition, it couldn't produce lift; this doesn't stop it being useful for other things like shells etc. where you don't mind zero supersonic lift if you can get low drag
The diagrams in the article seem to look like that condition in supersonic flow where the "inner" surfaces interfere favourably with each other to cancel wave drag and have the upper and lower surfaces with no incidence to the flow so they produce no shock waves.
Supersonically it should still produce lift quite happily if you angle it so there is incidence to the flow but I think that it should then produce wave drag and booms... For example I can't see from the article how, in a lifting condition, the shock wave from the compression of the supersonic flow on the undersurface (which produces the compression & higher pressure that helps lift the wing) could be cancelled out without having another wing underneath that; then you have the same problem with the undersurface of that wing & then you're in a "it's wings all the way down" problem.
Conventional 'low boom' solutions (like the Gulfstream/NASA "quiet spike") all tend to shape the nose of the aircraft to reduce the suddenness of the pressure increase across the shock wave but they aren't able to eliminate it...
It could be that they've found a case where they can get low wave drag/boom while still producing some lift and also getting decent subsonic lift/drag - that would be really interesting...
Take seatbelts - the oft-given example - if I don't buckle up I might die in a crash but it doesn't harm anyone else.
Incorrect. You are now a 180Lbs loose object in the car. Where your children were safely buckled, your dead body bounced to the back seat and injured them. Or you're a 450Lbs object wedged behind the steering wheel... This is slashdot after all.
Seeing as we were talking about the UK we can also talk about the fact that increased injuries of loose drivers/passengers if they don't manage to die will affect others by the increased cost and use of resources in the NHS.
I'm not sure trains are a good model either; Diesel-electric trains are effective because the torque you need for starting & driving a train doesn't easily come from a diesel motor without lots of gearing and clutches that are complex, inefficient and potentially unreliable.
Electric motors can give you all the torque you want from a standing start and so they make it easier to use diesels, avoiding the need to electrify your rail network (partly the reason Britain went with Diesel-electric trains in the '50s - they didn't have the capital to electrify).
With aircraft it's less clear where the advantage is going to come from since the kerosene motor + generator combination (and its associated losses) in an aircraft isn't solving a clear problem like lack of torque in a train and power requirements with lots of peaks and troughs as in a car.
However, a big advantage (from an environmental point of view) could be the ability to take electrical power for flight - once you have this you can gradually feed in alternative or low carbon energy into your mix. This type of aircraft could be a first step in that direction.
It's not beyond current capability even in civil aviation, in fact Boeing offered a folding wing option for the 777 but (so far) no-one's bought it.
This is partly due to lack of driver (gates at airports were either wide enough or made wide enough) but also because any driver to wing folding's got to be pretty strong to overcome the weight penalty
If you were to see a _big_ increase in span for aircraft of these capacities I'd imagine that folding wings might become more popular...
You're correct that drag has a large influence, engines have a part to play also.
Turbofans have a 'bucket' speed where their efficiency (specific fuel consumption or the fuel they burn per second per pound of thrust) is best*
The result is that, when the aerodynamics and engine efficiency are combined, there will be a best efficiency speed (best range speed) that's not far below the theoretical 'design' speed. However many airlines fly faster than this, depending on their balance of fixed vs. hourly costs.
Generally you can get higher efficiency by flying slower but you have to make changes to the aircraft, as seen here where much of the efficiency probably comes from the lower lift dependent drag that you can get from the larger spans of these aircraft. They probably get quite a lot of gain from engine improvements also, perhaps half.
*all bets are off with open-rotor or propellor engines, broadly these like to fly slower overall and you lose efficiency steadily the faster you fly.
The issue of requirements is one that I've always found interesting.
There always seems to be an assumption that customers know how to write requirements. Personally (from the position of a hobby coder who needs to use the services of professionals to get real applications written) I've always found it difficult to write intelligent requirements.
Don't get me wrong, I know that this is my fault, but I find that I need assistance from people who actually understand the ways that things _could_ be done and know the implications of the things that may be asked for. I always prefer to plan for a significant activity just to find out what I should be asking for. Motivation of the people who I ask for advice is important. If I (or the company I work for) pays the developer I know I can expect that they want to get the best results for the company as a whole.
I work in the aircraft industry and I've seen enough poorly chosen requirements for aircraft to know that this isn't a solely IT issue...
The engines-on-the-side configuration is a way to try to deal with engine weight changes. Huge trim issues arise if your engine isn't as light (or heavy) as you think it will be.
Spaceplanes with engines at the back face a real struggle with balance if _anything_ changes in the engines - they tend to be very heavy compared to anything else in the 'dry' structure of the vehicle and a small error either way can leave you with depleted uranium bulkheads to pull your CG back if it's too late in the development programme to change the configuration.
You really can't get away with stuff like that since single-stage-to-orbit is _really_ hard to do.
Couple that with the big aerodynamic centre changes that you tend to get over such a large flight regime and you may end up with a lot of mass budget being taken up by control surfaces.
I understood from a couple of lecturers at Uni and past co-workers that this would have been one of the really big problems that HOTOL would have had to deal with had it not been cancelled... (which project Alan Bond of Reaction Engines was also involved in)
Commercial jets are at lift/drag of around 18-20 now
As an engineer working with fixed wings it is my firm belief that helicopters fly because they are so ugly that the ground repels them - on that basis this thing is getting to the moon.
Problem with suspending people in liquid (as summed up by Joe Haldeman in "Forever War": 'What happens if drop a wrench in a submarine?' You overall might not be a puddle, but your guts would...
"Having worked on the Navier Stokes equation for about three years, I can say that this is a very interesting problem. Actually, the Navier Stokes equation is the equation governing an incompressible flow - that is, it is an equation that very closely approximates the flow of water. Thus to gain any understanding of this equation is to make a lot of progress in understanding turbulance. This will have great practical applications..."
Not sure where you got the incompresible bit from... The Navier-Stokes equations actually govern _any_ type of flow (unsteady, compressible, viscous and any other type you want) in their unreduced form.
If you want to assume incompressibility they will still be valid (for water and air flows up to about Mach 0.3 ish), but they won't be the full Navier-Stokes equations any more.
This problems may have a larger impact than you suggest... or less.
Computational aerdynamics can't solve the full N-S equations at all yet - and even if they could the computer power needed for the fineness of mesh needed would be beyond what's available now, for any reasonable run time at least.
Agreed, but I should point out that the problem has already been seen in jet engines where you've got _tons_ of metal spinning at tens of thousands of RPM.
The way that it was treated was to use a Kevlar casing to contain fragments - it's incredibly strong in tension, even under impact, and should solve the problem pretty well, although there have been cases of disc burst in aircraft (Sioux city IIRC) where a crash was caused.
BTW the flywheels would not be metal - it couldn't take the stress, you'd be much more likely to use composites - either unidirectional carbon fibre, kevlar, carbon-carbon composites, intermetallics or engineering ceramics - _much_ stronger.
Breaking a law you disagree with is attractive, hell sometimes it even works, but on the whole it's always useful to _try_ to change the law through the mechanisms that have been set up to allow that - it might not work but you are at least trying.
Some examples (UK bias):
Poll tax - ignored by many people, eventually got dumped as it was impossible to enforce and looked like an election loser (however many people just didn't pay anything and simply saw it as an excuse to avoid paying taxes, my folks paid the previous tax rate + inflation and got ignored because they'd paid _something_)
Ireland - 25 years of 'struggle' no change, everybody (including bomb-dodging Londoners) miserable. 1 ceasefire and things start happening yet people seem to forget that and talk about resuming violence, in this case it really _didn't_ do anything.. and as I said it did nothing for a quarter century
The more important issue at the moment for any kind of big mission to Mars is launchers, the tonnes of mass that you need to get into orbit.
The shuttle is too expensive for doing lots of heavy lift work (and it's too unreliable partly due to the requirements for human crew safety). Every time you use most rockets these days you throw away stages to get to orbit, be they boosters or whatever. This costs big time, both in terms of all that stuff you chuck out and in terms of the cost of developing the stages. It costs about 10 billion to develop a space vehicle and that means each stage. You do a 3 stage rocket (eg Saturn V) you got about 30 billion in costs.
Then there's running costs and turnaround. The shuttle takes months to turn around after a mission, it's complex and can't carry that much to orbit (and that only to low earth orbit). What you need is a system that is really re-usable like and aircraft, preferably unmanned and easy to turn around after a mission.
The solutions?
SSTO (single stage to orbit) it's the only way that we'll get the launchers that are needed for any kind of heavy launches to orbit (in terms of total tonnage over time) required for a proper manned mission to Mars.
NASA has one of these in the pipeline, the Venturestar. It's not doing too well. Call me a cynic (and a Brit one at that) but I do not have a huge amount of confidence in NASA to deliver this system. Their technology demonstrator is over weight budget by a _lot_, partly because they belived the engine maufacturer (who quoted cheapest it should be said) when they said the engines would e lighter than conventional engines... they're heavier (a lot heavier). This has resulted in them having to bolt depleted uranium to a bulkhead in the nose (high tech huh?). Its structure has had to be radically redesigned because the aerodynamic trim is wrong (you have to get this right, you haven't got any spare mass to play with) and the fancy new materials that they're using aren't working the way that they were supposed to. NASA don't seem to have learned that new stuff isn't a good idea in space, that's why satellites use 286 processors and why even in aerospace the cutting edge civil fly by wire of the bug Airbus aircraft is based on 386 chips. New things aren't predictable, and engineering analysis isn't precise enough to tell you everything that you'll need to know.
What else is there? Well not a lot. SSTO is _very_ hard. The Earth is about 10% too big for it to work easily. Still you might want to look at the (rather bad) webpages devoted to the Skylon Project [http://www.gbnet.net/orgs/skylon/skycont.htm]. It's basically all the things that were learned from the British HOTOL project in the 80's. I've seen the figures and it will work. It's clever, airbreathing rockets that use the air as oxidiser instead of having to carry all of their liquid oxygen (until the atmosphere gets too thin). It lets you get up cheaper than the shuttle or any of the rocket solutions available now.
This is the kind of vehicle that's needed and it's not even that expensive to develop, but trying to go to Mars without it will cost even more even if you assemble the Mars ship in orbit. you still have to get the parts there.
We are quite capable of getting beyon LEO, how do you think that Communications atellites get up there?
Even if you don't want to ressurect Saturn v rockets (which is very possible) an extra stage on an Ariane 5 could get you to a Mars transfer orbit.
I thought they were Von Neumann machines?