What if

I'm inspired obviously by the LAPCAT design, at least the idea of a Mach 5 ultra-long ranged hypersonic commercial jet.  The fact that the plane can fly sub-sonically in a manner that is quite efficient too is also quite awesome.

Honestly though, as I'm thinking about it, the technology to do this has been around for such a long time.  I'm not sure how much of it was not classified and only for government use and research, and military applications, but during the 1980's so much effort was going into making a National Aerospace Plane, and McDonnell Douglas wanted to make a hypersonic airliner that a lot was probably available even then. 

The propulsion technology existed, metallurgy and heat-shield technology existed, avionics obviously existed.  The only factor that didn't exist for commercial applications was money.


KJ Lesnick
BTW:  Anybody have any knowledge on how the Scimitar works.  I have an idea, but I'm not completely certain (assuming it's not classified or anything). 

I've got to admit, I've always been a fan of hypersonic aircraft.  I was astounded by Blackbird when I was a kid & I assumed we'd just keep on going faster.  I also assumed we'd be in space regularly & I might get a chance at it.  Maybe the fledgling space tourism industry will finally kick start it, we'll just have to see, eh?  ;D

Unfortunately I don't think the technology is just there to take off the self given enough money.  The cancellation of the X-33 & therefore the VentureStar program due to the technology to build a composite hydrogen tank not being ready showed it's going to take a lot of work to get a hypersonic aircraft or spaceplane into the air.

Archibald described to me the Sabre engine that is proposed to power the Skylon spaceplane in a thread I created some years back.  The basic principal is pretty much the same as the Scimitar.  There's some more info on the Reaction Engines site as well.

http://www.whatifmodelers.com/index.php/topic,12605.0/highlight,skylon.html (http://www.whatifmodelers.com/index.php/topic,12605.0/highlight,skylon.html)
http://www.reactionengines.co.uk/sabre.html (http://www.reactionengines.co.uk/sabre.html)
http://www.reactionengines.co.uk/lapcat_scim.html (http://www.reactionengines.co.uk/lapcat_scim.html)

Kendra, I assume you have British Secret Projects: Hypersonics, Ramjets & Missiles & Secret Projects: Military Space Tecnology?  Both are well worth a read for this kind of stuff.

Mossie,

Looking at the Scimitar diagram, it looks like a turbojet with a gigantic inter-cooler in the front, I'm not sure if that's an intercooler wrapped around the outer part of the compressor and combustion chamber area or that's part of the combustion chamber.  Either way it has a rather unusual combustion chamber in at least two respects, it has a pre-burner which seems to imply multiple stage combustion as I understand it, and that that the exhaust from the combustion-chamber appears to route through a normal-turbine and through an outer-turbine which wraps around the core-nozzle and is located in the outer duct which drives an aft-fan.  There seems to be a duct-burner behind the fan according to the diagram.  

I have a number of questions to ask regarding the Scimitar engine.
- While I know the structure in front of the engine is an inter-cooler, the structure wrapped around the turbo-compressor part of the engine, is that another intercooler or heat-exchanger?
- I don't know how cold the intercooler has to cool the air down to, but since there's water vapor in the air, couldn't it ice-over?  How'd they keep it from icing and still keep it cool?
- Why do you need a pre-burner?  Why not just use one combustion chamber?
- Does the combustion chamber always route through the main-turbine and aft-fan turbine, or can it be routed through just the main core, and through the core and aft-fan turbine?

Also, I have a few questions pertaining to the SABRE engine
- In the engine, helium or liquid helium was used.  What purpose was this for?
- For achieving orbit, would you say this device was more efficient than a ramjet/scramjet duct with a strut-jet RBCC or PDWE (to get the ramjet/scramjet up to speed, and for the last push into orbit, both can be cycled into rockets)?


KJ Lesnick

I'm in the dark myself here (& fully open to holes being poked in my understanding!), but I would imagine the structure around the compressor is a heat exchanger (HX3 suggests there are two before it, one being the precooler).

Part of the reason that the water vapour doesn't freeze due to the airflow.  Water can supercool to very low temperatures as long as it has nothing for the ice crystals to form around.  If the water hasn't got time to form on the walls of the pre-cooler, it can't freeze.  I don't think this is the full explanation though, as the precooler takes the air down to -150^oC.  The video at the bottom mentions 'frost control', but I can't find any info so I get the feeling they don't 100% know how they're going to deel with this yet!

In the Sabre engine, the helium is there to provide cooling.  From what I gather, it's in an enclosed loop and doesn't physically come into contact with the fuel components.

Have you seen this video from the Lapcat entry?  It may help with some aspects, it describes the Sabre engine but the air breathing function is applicable to Scimitar:
Sabre engine video (http://www.space.co.uk/DataBank/VideoGallery/VideoPlayer/TabId/384/VideoId/60/Richard-Varvill-Of-Reactiion-Engines-At-IAC-2008.aspx)

Mossie,

According to that video regarding the SABRE engine, it had a pressure-ratio of 150-to-1.  How the hell did they manage that?

In the video there was one part that I didn't understand was the need for the bypass tubes, something about the efficiency of the engine breaking down at transonic speed and the need for a bypass-system.  I didn't really understand it due to the way it was explained.

While I'm definitely fascinated by the SABRE and SCIMITAR engine designs, I'm not entirely fixated on those designs.  How efficient is a hydrogen-expander engine over a traditional gas-turbine engine at sea-level and at high-mach?

It strikes me as being more efficient in that the hydrogen vaporizes readily in contact with air without the need to burn it, they don't use a traditional turbine (usually you use a small, high RPM turbine which through a gear-box drives a multi-stage fan/compressor) which isn't riding in the hot exhaust gases, probably steadily cooled to an extent with the LH2 flowing through it, and can go to higher mach numbers allowing either a higher pressure-ratio for the same mach number (unless the airflow runs the risk of ionizing or something) or a higher mach-number for the same pressure-ratio.  I would assume combustion could be more efficient as you'd be burning a completely pre-vaporized gas rather than just atomized droplets.

Also, does LH2 combustion also pose the risk of forming NoX compounds?  It rarely is mentioned, but I remember seeing a video about the LAPCAT/Scimitar in which it *was* mentioned.  So I don't know.


KJ Lesnick

I'm also wondering, how much cooling could be derived by using LH2 for active cooling by circulating it around the compressor (and any fixed guide-vanes) of a jet-engine through small passages to maximize surface-area at Mach 5?

For example, how much of a drop in temperature could you produce, and or how much higher a pressure ratio could you achieve for the same temperature? 

Any guesses, thoughts, ideas?


KJ Lesnick

I think that's how the LACE engines work that are mentioned in the Sabre article?
http://en.wikipedia.org/wiki/Liquid_air_cycle_engine (http://en.wikipedia.org/wiki/Liquid_air_cycle_engine)

Going on NO_x compounds, I don't think their should be to much to worry about.  Hydrogen burns at a much lower temperature than nitrogen.  As long as their is enough hydrogen available (double that of the available oxygen), this should tie up all the oxygen.  If the engine is starved of hydrogen for any reason (so there is unreacted oxygen) then there could be problems.

The problems of introducing nitrogen oxide in significant amounts would be two fold.  Firstly, there would be a change in the energy of the reaction, which could cause a change of fuel flow through the engine.  The second is production of nitrogen oxides that are harmful to health & the environment.

If this was a particular risk, I guess you could introduce a compound that would react with nitrogen in favour of the oxygen (unusual) that would be stable in the exhaust.  I'm sure it's doable, but I would think that it'd be more desireable to introduce an engineering soloution to restrict the amount of air coming in if their was ever any.

Any body who is more sure of there chemistry & engineering please feel free to chip in!

Mossie,

QuoteI think that's how the LACE engines work that are mentioned in the Sabre article?

I don't want to liquefy the air.  I just want to use the LH2 for active cooling.  Use the LH2 to cool off the airflow into the compressor than burn the LH2 up

QuoteGoing on NO_x compounds, I don't think their should be to much to worry about.  Hydrogen burns at a much lower temperature than nitrogen.  As long as their is enough hydrogen available (double that of the available oxygen), this should tie up all the oxygen.  If the engine is starved of hydrogen for any reason (so there is unreacted oxygen) then there could be problems.

The problems of introducing nitrogen oxide in significant amounts would be two fold.  Firstly, there would be a change in the energy of the reaction, which could cause a change of fuel flow through the engine.  The second is production of nitrogen oxides that are harmful to health & the environment.

Huh?  Nonononono...  What I'm worried about is NOx formation during combustion.  When you burn fuel and air under certain conditions you get NOx.  I'm just wondering if LH2 combustion would produce less or the same NOx levels as hydrocarbon combustion. 


KJ Lesnick

Quote from: KJ_Lesnick on October 11, 2009, 06:35:02 PM

I don't want to liquefy the air.  I just want to use the LH2 for active cooling.  Use the LH2 to cool off the airflow into the compressor than burn the LH2 up

If I've understood Archies comments in the first link, there are a number of problems with this.  The hydrogen to the point where it's no longer liquid, your using hydrogen which you need for fuel & the liquid hydrogen tends to freeze everything it's meets.

Quote from: KJ_Lesnick on October 11, 2009, 06:35:02 PM

Huh?  Nonononono...  What I'm worried about is NOx formation during combustion.  When you burn fuel and air under certain conditions you get NOx.  I'm just wondering if LH2 combustion would produce less or the same NOx levels as hydrocarbon combustion. 


KJ Lesnick

The flashpoint of hydrogen is about -253^oC, so it should start to react long before the nitrogen.  The temperature will rise quickly so you could get some NO_x forming before all the hydrogen & oxygen reacted.  If you get the amount of hydrogen right, my feeling is that it all should react before the nitrogen gets a chance.  I might be wrong though.

Ben Rich briefly mentions a hypersonic plane in his book "Skunk Works". Pretty much he saw the whole idea as infeasible, even if there is an engine capable of giving the require thrust. According to him, the main sticking points were finding a material from which to build the aircraft that would be capable of withstanding the tremendous heat on the plane's surface. He also writes "And by the way, our crews wore space suits and we still worried about boiling them alive if our air conditioning system failed. And you are proposing to fly at Mach 12 where the surface heat on the fuselage would be 2500 degrees and still have a passenger cabin filled with women, children, and businessmen sitting around in their shirtsleeves!"

Chris

Mossie,

QuoteIf I've understood Archies comments in the first link, there are a number of problems with this.  The hydrogen to the point where it's no longer liquid, your using hydrogen which you need for fuel & the liquid hydrogen tends to freeze everything it's meets.

But you can use the heat to vaporize the hydrogen which can be burned.  Gaseous H2 can be burned way easier than LH2.

I don't know about freezing everything it meets, I would think it would depend on how much LH2 was used for how much airflow, and the heat of the airflow?

QuoteThe flashpoint of hydrogen is about -253^oC, so it should start to react long before the nitrogen.  The temperature will rise quickly so you could get some NO_x forming before all the hydrogen & oxygen reacted.  If you get the amount of hydrogen right, my feeling is that it all should react before the nitrogen gets a chance.  I might be wrong though.

But the NOx would be lower than regular hydrocarbon combustion?


Coops 213,

QuoteBen Rich briefly mentions a hypersonic plane in his book "Skunk Works". Pretty much he saw the whole idea as infeasible, even if there is an engine capable of giving the require thrust.

I don't think the thrust would be that big an issue especially once up at speed.  Ram compression would seriously augment the thrust of almost any engine.  The issue is generating enough thrust to takeoff and accelerate up to hypersonic speed.  I'm not planning a hypothetical Mach 12, but a hypothetical Mach 5 or Mach 6 so it isn't as difficult to achieve.

The J-91, J-58 and J-93 while officially designed for the Mach 3 realm, were in fact, all designed for Mach 4 performance.  There is at least one book I have about the XB-70 which states the X279E which is the YJ-93 was rated for Mach 4.  The J-91, and J-58 were both designed for the same speeds.  While the XB-70 was officially designed for Mach 3 performance, the design is actually designed for Mach 4 flight.  Walt Spivak actually stated that the inlets were designed to withstand the temperatures of Mach 4 flight, and looking at a diagram of the inlet, which shows the shockwave formation, it depicts approximately 14 to 16 shockwaves, and large portions of those inlets had porous ramps as well.  For Mach 3 you do not need that many shockwaves for even a very highly efficient inlet.  From what I remember the L-2000, which was a supersonic transport, capable of protracted Mach 3 flight and had inlets that possessed a high pressure-recovery and their shock-count was only about 4 or 5 (and porous ramps).

The J-91 had a pressure-ratio of 7 to 1, the J-58 had a pressure-ratio a little under 9 to 1, but used a variable guide-vane to lower pressures at higher mach to keep the turbine temps in check, the J-93 had a pressure ratio of 8.8 to 1.  None of these engines were turbo-ramjets (I'm talking about the original J-58 prior to it being re-designed for the A-12 program).

You could probably get hypersonic performance out of a bleed-bypass J-58/J-93, and I wouldn't be surprised if the SR-71 could achieve such performance.  

QuoteAccording to him, the main sticking points were finding a material from which to build the aircraft that would be capable of withstanding the tremendous heat on the plane's surface.

Not really.  According to Paul Csysz, I believe, and I've heard other sources state similarly that the A-12 was made out of an unusual titanium called Beta-Titanium.  From what was said, it had useable temperatures up to 1,200 C.  That seems more than suitable for Mach 5 or Mach 6 flight.  

Additionally, also according to Paul Csysz, McDonnell did a lot of work in the 1960's with the Flight-Dynamics Laboratory at Wright-Patterson, and developed a variety of light-weight, high-strength thermal protection systems, or heat-shields which could maintain room-temperature even at speeds of at least Mach 12, if not up to orbital velocity without the need for using the fuel as a heat-sink.  They were said to be sturdier, lighter, and had a much longer service life than the Space-Shuttle's tiles.  I wouldn't be surprised if they were heavier than a typical aircraft skin, but if you were going for Mach 5 or Mach 6, you probably wouldn't need as much insulation as you would for Mach 12, Mach 22, or Mach 25.

QuoteHe also writes "And by the way, our crews wore space suits and we still worried about boiling them alive if our air conditioning system failed.

Technically, they had two air-conditioning systems, one for the suit (which I gather was quite insulated) and one for the cockpit itself.  Both were capable of keeping the pilot cool.  There was at least one case where one of the air conditioning systems in the RSO's cockpit of the SR-71 failed, the air-conditioning in the pressure-suit remained operational and the pilot lived.

QuoteAnd you are proposing to fly at Mach 12 where the surface heat on the fuselage would be 2500 degrees and still have a passenger cabin filled with women, children, and businessmen sitting around in their shirtsleeves!"

Well, for the purposes of an airliner I think the heat-shield approach would be a more practical solution.  It would work by simply reflecting almost all the heat away from the plane rather than relying on a complex cooling system.  Cooling systems could fail.  I suppose structures can fail too, but structures are tested so that doesn't happen and a plane wouldn't be allowed to enter service that was sufficiently reliable.


KJ Lesnick

Quote from: KJ_Lesnick on October 08, 2009, 11:25:06 AM
I have a number of questions to ask regarding the Scimitar engine.
- While I know the structure in front of the engine is an inter-cooler, the structure wrapped around the turbo-compressor part of the engine, is that another intercooler or heat-exchanger?
- I don't know how cold the intercooler has to cool the air down to, but since there's water vapor in the air, couldn't it ice-over?  How'd they keep it from icing and still keep it cool?
- Why do you need a pre-burner?  Why not just use one combustion chamber?

Kendra, do a search using 'turborocket' this is what the Brits originally called these types of engines.  A turborocket is part turbine and part rocket as we traditionally know them.  The pre-burner is used to power the turbine part until it reaches an altitude (and speed) where the rocket works full time.  BSP-Hypersonics, Ramjets & Missiles goes into a lot of discussion about these engines which can be powered two ways, liquid oxygen and air breathing. The book says that the intake temperature at Mach 5 can be as much as 1000C (1832F) just from ram air compression alone and the exchanger cools this air down, from what I understand from the book this is how the pressure is made be 150 psi, at least that's how I understand a ram jet works.

Kitnut,

So the Pre-burner is the combustion chamber for the gas-turbine?

Quote from: KJ_Lesnick on October 12, 2009, 07:59:00 PM
Kitnut,

So the Pre-burner is the combustion chamber for the gas-turbine?

Yes, that's how I understand it.  The idea for these engines was to get around the huge size that 'combination' engines were progressing too, see Andy's (General Melchet) E.E. P.42 build to see what I mean.

How does Liquid Methane fare in terms of NoX production over LH2?  Also how does LCH4 fare in NOx production over heavier hydrocarbons like regular Jet-A?

That's out of my realm Kendra, but the BSP book goes into a lot of designs for Mack 5-10 projects.  Some had the liquid gas to cool the airframe then the engine parts but there's an interesting diagram comparison in the book.  A design using LH would be almost twice as big as a design using kerosene for something that did the same job.

Okay as for aerodynamic shapes... 

I was wondering if a shape like this could be suitable for a hypersonic-airliner type design

(https://www.whatifmodellers.com/proxy.php?request=http%3A%2F%2Fimg527.imageshack.us%2Fimg527%2F6395%2Fairbreathingwaveriders.jpg&hash=999cd21c6c896acdc407a63a98e0d00a5cd7da6a)

The design in the middle is more like the designs in the book.  One thing though, the book says things like keeping the electronics and payload (people that is) cool, wasn't really taken into account as all the designs were only in the 'paper' design stage.  I guess that would have been looked after if any of the projects came to being.

Most of the designs took into account that air could be pre-compressed before it went into the air intake, this was done by careful design of the underside of the nose and forward fuselage.  This had a byproduct --- called heat,  one of two sources of heat that had to be accounted for, the other being frictional heat.

Kitnut617,

QuoteThe design in the middle is more like the designs in the book.

Sort of.  However, I have seen a Northrop-Grumman design which kind of looks like a shield, like this...

(https://www.whatifmodellers.com/proxy.php?request=http%3A%2F%2Fimg41.imageshack.us%2Fimg41%2F5590%2Fnorthropgrummanb30001.jpg&hash=f64c9d65f04a98ff86e273823166cb6f695569c9)

Which doesn't look too much different (from an overhead view) as the designs I showed.

QuoteOne thing though, the book says things like keeping the electronics and payload (people that is) cool

If you have a sufficiently effective light-weight heat-shield most of the heat will be reflected away rather than absorbed.  The electronics and passengers should remain reasonably cool (room temp)

QuoteMost of the designs took into account that air could be pre-compressed before it went into the air intake, this was done by careful design of the underside of the nose and forward fuselage.

I'm aware of that, the idea was to avoid using an excessively long or complex inlet system and instead using the underbelly for that purpose instead.  Also the pressure increase from that could be used to prop the plane up in flight (i.e. compression lift)


KJ Lesnick

There are several more blended projects in the SP Space book.

I found this on the Concorde page on aerospaceweb which is along similar lines to the two blended designs you've posted Kendra.  I don't know where the design originates.

(https://www.whatifmodellers.com/proxy.php?request=http%3A%2F%2Fi72.photobucket.com%2Falbums%2Fi176%2FMossie105%2FAircraft%2FHypersonicAirlinerDesign.jpg&hash=2a2a0593ac58a1c5aa1e3fe0e39ae4531795bbaf)

Mossie,

QuoteThere are several more blended projects in the SP Space book.

I didn't know there was a Secret Project's book simply on space designs.

QuoteI found this on the Concorde page on aerospaceweb which is along similar lines to the two blended designs you've posted Kendra.  I don't know where the design originates.

I believe that design comes from a Popular Science or a Popular Mechanics book.


KJ Lesnick

Yeah, Secret Projects: Military Space Technology.  Like the others, it's a good read & there are some paralells with the BSP Hypersonics book.  It focus on military projects as per the title, so there's not much on hypersonic airliners or civilian space planes, but you can make some comparisons.  The HOTOL/Skylon/Lapcat story gets a good few pages.

Amazon link here, clicky. (http://www.amazon.com/Secret-Projects-Military-Space-Technology/dp/1857802969/ref=sr_1_1?ie=UTF8&s=books&qid=1255988603&sr=8-1)

Thanks for identifying the hyperliner pic. :thumbsup:

Mossie,

QuoteThanks for identifying the hyperliner pic. :thumbsup:

No problem.  I have a photographic memory and I have a great many Popular Science and Popular Mechanics magazines


BTW:  I just ordered the book on Amazon.


KJ Lesnick

Enjoy the book Kendra! :thumbsup:

Okay, now the next question. 

I know a spatular shape works better than a wedge-shape.  How does a "shield" shape like that Northrop-Gruman proposal (just the basic shape) compare over a spatular nose (i.e. a spatular nose with the spatular section having a sweep angle of 0-degrees) or a wedge-shape?

If you don't have exact figures, guesstimates would do fine. 


KJ Lesnick

Erm!  well !  ;D  although there's a lot of clever people here that can help with a lot of subjects Kendra, I don't think hypersonic engineering is one of them -----  :lol:

The books I have just by their nature, only gloss over most of the subject.  The in-&-outs of why something was decided over another isn't explained.

Kitnut617,

QuoteErm!  well !  ;D  although there's a lot of clever people here that can help with a lot of subjects Kendra, I don't think hypersonic engineering is one of them -----  :lol:

Yeah, I know it is an esoteric subject.  Still I figure an aviation related forum would probably be a place to ask.  I would have asked on Secret Projects, or A.net, but I'm not allowed to post on Secret Projects, and I'm no longer a member of A.net anymore.  So, I figure this would be a good place to start.

I have a few people on my Yahoo IM list who are pilots (at least one of which has an aerospace engineering degree) but none of them are online much obviously. 

QuoteThe books I have just by their nature, only gloss over most of the subject.  The in-&-outs of why something was decided over another isn't explained.

I do know some basics which are covered in two Aerospace Engineering books which I actually own.  However basics are still basics.  I suppose I can guesstimate...


KJ Lesnick

I'm looking at some drawings of the X-30.  Ones that have been declassified in the past 5 years or so that actually show a sharp nose.  Even though the nose is somewhat spatular, it was rounded a bit at the leading-edge.  Considering the X-30 was a design conceived with 1980's technology, it sounds like it would be adequate enough.

I'm drawing up a basic shape incorporating a spatular nose with a somewhat highly swept wing shape.  It is a very rough drawing and incorporates no area ruling.  Just very basic geometries.

(https://www.whatifmodellers.com/proxy.php?request=http%3A%2F%2Fimg194.imageshack.us%2Fimg194%2F2818%2Fhypersonictransport0002.jpg&hash=4aa7e78408d4a3f1b6f2d055950b7c3c98f33406)

I haven't figured out where to put the vertical stabs, but the two lines I drew on the rear wing section on the top view were locations I was thinking of 


KJ Lesnick
You know, this sounds so retarded, but I haven't used a pencil for drawing in years.  It's amazing how big an improvement it makes when you can actually erase your mistakes  :o

I'm no rocket scientist, but I suspect that a spatular or rounded nose shape probably prevents the accumulation of too much heat in too small an area. Perhaps the aerodynamic advantages of a pointy front end are outweighed by thermodynamic issues as speed increases?

SSgt Baloo

QuoteI'm no rocket scientist, but I suspect that a spatular or rounded nose shape probably prevents the accumulation of too much heat in too small an area. Perhaps the aerodynamic advantages of a pointy front end are outweighed by thermodynamic issues as speed increases?

No the surface would be sharp.  The spatular term pertains to it's overhead look

Quote from: KJ_Lesnick on October 23, 2009, 04:40:41 PM
SSgt Baloo

QuoteI'm no rocket scientist, but I suspect that a spatular or rounded nose shape probably prevents the accumulation of too much heat in too small an area. Perhaps the aerodynamic advantages of a pointy front end are outweighed by thermodynamic issues as speed increases?

No the surface would be sharp.  The spatular term pertains to it's overhead look

:unsure: I'm confused. That's what I was talking about (the "overhead look"). Even though the surface may look "pointy" in side view, the bluff overhead view affords more mass per unit of surface area than a conical point would afford. As I said, I'm no rocket scientist, so the reason I gave could quite easily be an incorrect one.

SSgt Baloo,

I'm not sure how it's heat-distribution would fare over a pointed nose design honestly

The hypersonic side of the equation is complicated, but does anybody have any idea how a design like this would behave subsonically, particularly at takeoff speed?

(https://www.whatifmodellers.com/proxy.php?request=http%3A%2F%2Fimg41.imageshack.us%2Fimg41%2F5590%2Fnorthropgrummanb30001.jpg&hash=f64c9d65f04a98ff86e273823166cb6f695569c9)

I would imagine fairly well.  It looks to me like a lifting body style design.

Mossie,

QuoteI would imagine fairly well.  It looks to me like a lifting body style design.

Would you say you think it's takeoff and landing speeds would be good?

It's an ogival delta, I can't think of another aircraft that has had quite the same shape wing.  Concordes is similar being an ogee, if not quite the same.  Concorde tends to have a fairly high angle of attack when taking off & landing like many big deltas, but it's fairly forgiving IIRC as long as you're not maneuvering hard.  If that is a glazed nose, it shouldn't cause any problems visibility wise.

Mossie,

QuoteIt's an ogival delta, I can't think of another aircraft that has had quite the same shape wing.  Concordes is similar being an ogee, if not quite the same.  Concorde tends to have a fairly high angle of attack when taking off & landing like many big deltas, but it's fairly forgiving IIRC as long as you're not maneuvering hard.  If that is a glazed nose, it shouldn't cause any problems visibility wise.

So you'd speculate that it's takeoff speeds and landing speeds would be similar to the Concorde?

Quote from: KJ_Lesnick on October 31, 2009, 06:47:54 PM
Mossie,

QuoteIt's an ogival delta, I can't think of another aircraft that has had quite the same shape wing.  Concordes is similar being an ogee, if not quite the same.  Concorde tends to have a fairly high angle of attack when taking off & landing like many big deltas, but it's fairly forgiving IIRC as long as you're not maneuvering hard.  If that is a glazed nose, it shouldn't cause any problems visibility wise.

So you'd speculate that it's takeoff speeds and landing speeds would be similar to the Concorde?

The landing speed would be largely dependent upon the overall size and weight of the platform, not simply the shape of the wing.

Regards,

Greg

GTX,

QuoteThe landing speed would be largely dependent upon the overall size and weight of the platform, not simply the shape of the wing.

Good point!

Okay, since I was thinking 300 passengers sounds good, I'm basically using the cabin widths of the McDonnell-Douglas Orient-Express as a start-off point.

(https://www.whatifmodellers.com/proxy.php?request=http%3A%2F%2Fimg202.imageshack.us%2Fimg202%2F9881%2Fmd2001cabindrawing.jpg&hash=afd2f2ec0c69337e92d068f7059b7f90ddf56b02)

Does anyone here know how wide a typical coach airline-seat is, how big the aisles are, or how tall the ceilings are typically?  I need to establish a baseline figure for the width of the cabin.


KJ Lesnick

Standard width is about 17in/43cm.

Mossie,

QuoteStandard width is about 17in/43cm.

Is that modern day or back in say 1980 to 1989?  Because this design is essentially based on the presumption that with technology of that era such a plane could be built.  So I was planning to build around those specifications.

Regardless does that width include just the seat or the arm-rests and everything?  

Modern day, I have absolutley no idea how it was back in the 80's, although having a sit in 70's airliner at museum I found it wasn't much different.  You're only going to get a rough idea of size anyway, so I'd take it on the basis of 17 inches.  If you increase the seat size to a slightly more comfortable 18.5 inches, it shouldn't make much of a difference to the overall size of the aircraft.

Mossie,

QuoteModern day, I have absolutley no idea how it was back in the 80's, although having a sit in 70's airliner at museum I found it wasn't much different.  You're only going to get a rough idea of size anyway, so I'd take it on the basis of 17 inches.  If you increase the seat size to a slightly more comfortable 18.5 inches, it shouldn't make much of a difference to the overall size of the aircraft.

I'll go with 18.5 for the time being.  Regardless, does that 18.5 inches include the arm-rests or not?

I don't think so, I think it's the seat back only.

I'm making some guesstimates here, but I'm figuring since the MD-2001, the McDonnell Douglas Orient-Express was 14-abreast internally which essentially consists of 2 x 5 abreast cabins, and 1 x 4-abreast cabin.  So based on that I've made some guesstimates based on the following.  The DC-9/MD-80 and Convair-880/Convair 990 which both have five abreast fuselages have cabin widths of 132 to 134.5 inches, the Concorde which has a fuselage of 4 abreast has a fuselage width of 8'8" or 104-inches.  

So 132 x 2 + 104 = 368 inches, and 134.5 x 2 + 104 = 373".  Granted each cabin has a divider on the inside so there could be a couple extra inches between.  Assuming each seat is 18.5 inches, the divider is about 1/3 to 1/4 that of the seat-width so that would add between 4.625" to 6.167" with a median of 5.286"

Which yields an a cabin width anywhere between 372.625" to 379.167"


KJ Lesnick

Do my numbers sound right?

Maybe this will help, scroll down a bit and you'll find a table which has fuselage inside diameters of various airliners. It also gives seat widths in various configurations:

http://en.wikipedia.org/wiki/Wide-body_aircraft

Okay so a DC-9 is 124 inches on the interior, Concorde's interior is 104 inches, with that said the plane essentially has three cabins side-by-side of which 2 are 5 abreast with the center at 4 abreast.

This roughly computes out to 364" with two 6" dividers between the cabin.  Since I think the MD-2001 was to use fuel as a heat-sink and not employ a heat-shield, and I'm thinking of using a heat-shielded structure are those six-inch dividers needed?  The plane could be made a foot thinner otherwise...


KJ Lesnick

Okay, let's go back to the issue of propulsion

Could one develop a hydrogen expander that would incorporate strut-jet like features?  Rather than having a turbo-compressor over the duct, instead the air would go through the compressor, the fuel would vaporize as a function of external heat and the heat of combustion and would drive the turbines.  Rather than having a traditional shaped combustion chamber, you'd have a combustion chamber with geometry more like the strut-jet (not square shaped, it would be annular but with a convergent divergent geometry) that would produce high power rocket-like performance which would be similar to the strut-jet.

You would not need to shut the turbo-compressor off because even as fast as you're going the turbine would not be subject to similar temperature restrictions as it would not be driven by hot gas blasting through the turbines, instead the heat would be absorbed by the LH2 and would then expand and drive the turbine which is very small and located inside the engine (like the P&W 304 engine that powered Suntan), driving the fans/compressor via a reduction gearbox.  I should also note that if it could produce similar performance to the RBCC they had very high power to weight ratios and reasonable subsonic performance (similar to a 1960's era military turbofan)

I don't know if anybody would have thought of it back then truthfully, but considering you had guys coming up with unorthodox engines like those used on HOTOL, and the later SABRE engine design.  Granted those guys were from the UK and this Hypersonic Transport would likely be an American design (Since I'm basing it on American technology that existed already, and the fact that there was an Orient Express proposal devised in the United States in the mid-1980s.)


KJ Lesnick

Here are some diagrams depicting my ideas


This picture depicts the basic concept behind the hydrogen expander engine

(https://www.whatifmodellers.com/proxy.php?request=http%3A%2F%2Fimg691.imageshack.us%2Fimg691%2F9862%2Fp155.jpg&hash=31e698a3f5dd6fb8a5b0d93cb019913c3d1e4e72)


This picture depicts the operation of the P&W 304 hydrogen expander engine in particular

(https://www.whatifmodellers.com/proxy.php?request=http%3A%2F%2Fimg691.imageshack.us%2Fimg691%2F8351%2Fpw304001.jpg&hash=6b0cc4b8ee525229bb10fd88db492766d528bfc5)


This picture depicts a strut-jet RBCC type design

(https://www.whatifmodellers.com/proxy.php?request=http%3A%2F%2Fimg407.imageshack.us%2Fimg407%2F1207%2Frbccstrutjet001.jpg&hash=1537b0bf1da4dfb6811b50b19a3770979295a664)



The method of deriving power from hydrogen expansion would be pretty much as depicted in the first and second image with the combustion chamber more like that in the third image, employing a more rocket-like combustion-chamber/nozzle which would ideally be wrapped around the engine (like an annulus, but retaining the convergent divergent bell-nozzle geometry) and would receive airflow from the fan/compressor.

Sound like a good idea?  


Kendra Lesnick
NOTE:  None of the data I am displaying is to the best of my knowledge classified or is in anyway harmful to national-security to the best of my knowledge

Just out of curiousity, why does the P&W 304 have a combustion chamber and an afterburner?  The exhaust doesn't go directly through a turbine, so I fail to understand why there is any need for an afterburner...


KJ Lesnick

The LAPCAT is a proposed hypersonic airliner design with the ability to fly at Mach 5 @ altitudes of at least 80,000 feet for antipodal distances, and also able to fly subsonically for considerable distances as well.  

I was thinking on coming up with some hypothetical ideas working around the basic LAPCAT design.  Here's the ideas I'd be thinking of:

- Removing the canard, and instead changing it with a long, highly swept leading-edge root extention forming out of the aircraft's delta wing forming an effective double-delta.
- Flattening and widening the fuselage to allow more aerodynamic performance to be extracted from the fuselage (Composite structures don't have the metal fatigue problems that metals do, and even during the development of the BWB they were able to work out to some degree using a non circular fuselage)
- Forming the nose and tail into a flattened blade shape which works better at hypersonic speed generally over a conical nose and helps enable the fuselage to better behave as an airfoil

Anybody interested?


Kendra Lesnick

Okay:

1. Why do you want to remove the canard? How do you propose to control pitch?

2. The fuselage is mostly full of liquid hydrogen tanks which I resume are pressure vessels. As such, they will be more structurally efficient if they are cylinders with hemispherical end caps no matter what material they're made of. Flattening the fuselage would reduce the diameter available for these tanks and to use the new ovoid cross section, you'd either have to have a heavy collection of side-by-side tubes or a heavy non-tubular tank with extra strength at the stress points.

Weaver,

Quote1. Why do you want to remove the canard? How do you propose to control pitch?

I assume the aircraft had elevons for primary pitch control.  Having only a canard for pitch and trim would yield an unstable airplane which for a commercial airliner is something generally to be avoided if you can.  Elevons also generally even on airplanes with canards usually have some trimming functions.  A leading-edge root extension can provide trimming benefits at high speed, especially if sufficiently swept by producing disproportionate amounts of lift up front relative to the rest of the wing which to some degree counteracts the rearward shift in the center of pressure.

Quote2. The fuselage is mostly full of liquid hydrogen tanks which I resume are pressure vessels. As such, they will be more structurally efficient if they are cylinders with hemispherical end caps no matter what material they're made of.

I suppose there is truth to that, but many of the Orient Express concepts often involved flattened tank shapes and I don't recall any problems mentioned regarding the fuel tank set-up.

QuoteFlattening the fuselage would reduce the diameter available for these tanks and to use the new ovoid cross section

The idea was to flatten it, but widen it at the same time so the volume would stay about the same.  The flattened structure would provide more lift especially at hypersonic speed.

Quoteyou'd either have to have a heavy collection of side-by-side tubes or a heavy non-tubular tank with extra strength at the stress points

Of the two which would increase weight the least? 

Do you think LCH₄ would be a preferable fuel-source for a Mach-5 to Mach-6 airliner instead of LH₂?  It's density is lower, it requires less insulation and refrigeration; I don't know if the potential for NOx formation would be substantially greater for LCH₄...

Honestly I think some kind of hybrid of the A2 and a waverider would be a cool idea...

Flattening the fuselage turning the nose and tail into a blade shape (from the overhead view), moving the engines under the fuselage, reshaping the tips a little bit, forming the inboard leading edge into a LERX as it could provide some extra lifting area up front supersonic, some area ruling and blending and such.  

I do have drawing if you need a visual description:

(https://www.whatifmodellers.com/proxy.php?request=http%3A%2F%2Fi763.photobucket.com%2Falbums%2Fxx274%2FKJ_Lesnick%2FLAPCATA3002.jpg&hash=1fefc9487de797ad257248526337e30624a778ed)

I like the wing design as it offers hypersonic performance and subsonic cruise capability, the engines mounted under the wider fuselage could exploit the wave-riding for inlet benefits too, and obviously improved lift when supersonic/hypersonic.

The afterbody shape is the way it is simply because I haven't thought of anything yet.  Truthfully it would probably be smarter to push the wings back a little bit (One odd idea I've thought of would be to widen the tail up a little bit like the X-43 because it could produce a tailplane effect and with a high enough sweep could keep much of the shockwave off the leading edge and provide a reasonable degree of pitch control to augment elevons which would be mounted on the wing's leading edge but I don't know if it'd work)

As the design is drawn it's length is the same as the LAPCAT A-2.  I don't necessarily think the excessive length is practical, but for the time being, I'll stick with it.

What do you all think?

From what I'm reading the LAPCAT A2 can achieve a L/D ratio of 11:1 at Mach 0.9, and 5.9:1 at Mach 5.  Is this considered good, excellent, superb?  Are there any other aerodynamic shapes that can yield a good hypersonic plane and still achieve at least that performance at subsonic flight without using swing-wings?

KJ Lesnick

How much thrust was the Scimitar projected to produce?  I don't recall ever reading any definitive figures even on their website.

KJ Lesnick