If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
Chad Irby wrote in message . com...
In article , "The Enlightenment" wrote: "Chad Irby" wrote in message m... Actually, skip-reentry relies on a somewhat higher initial reentry speed, as compared to the "plunge" method, and while max temps can be higher, the plunge method has some advantages. Note also that the "skip" method relies heavily on radiative heat emission, and that's not very effective for dumping large amounts of heat in a short period of time. Indeed but thats not a problem for winged re-entry vehicles that unlike blunt bodies can fly and control their rate of entry hopefully limiting the rate of hest buildup to that which can be radiated. Nope. Velocity is velocity, and coming in out of vacuum means those steel wings are just little flanges out in the Mach-20 airflow waiting to be melted - or broken off altogether. Nope. There is someting called a hypersonic L/D (lift to drag ratio). You can fly in and limit you rate of decent in a winged or lifting body thus limiting peak heat to the extent that ablatives or even tiles can be dispensed with. You still need some very high-temp metals (Inconel or titanium, to start), instead of the normal stainless steel Sanger proposed. Sangers aircraft the 'silver bird' was made of the high chrome steel (stainless basically as used in the XB70 ) and I expect similar to what was used in Boiler Tubes at the time. That can opperate at 600C without loosing strength and beyond at reduced strength. Stainless is more heat resistant than titanium and but less than inconel. So the Silverbird could have managed about Mach 3 for a short period of time, about 1/5 of the *necessary* speed for suborbital missions like the one it was designed for... and then would have had to be scrapped due to overheating of the structure. It could have managed more than mach 3 easily. The vehicle could have achieved sub orbital velocity at 13,000 mph. Re-entered and slowed to a slower speed say 8,000 mph and skipped to cool of and so on. Sanger never actually worked on the thermodynamic aspect of the Silverbird, and that would have been a potential showstopper for the program, even if he'd had more time to work on it. The plane was a concept/mockup only, and very little actual engineering work had been done when the war came to an end. Sure, sanger didn't know that blunt bodies provide some thermal protection. Here is the Sanger Thermal protection system. The Sanger silver bird is stainless steel. Pilot and critical components such as tires, control and crew cabin are insulted from the over 600C heat of re-entry for as long as necesaary. Insulation of the insides isn't the problem. It's the skin melting off in a very short period that's the issue, combined with the lack of time to re-radiate the heat before hitting the atmosphere again. When a spacecraft hits the atmosphere at Mach 20, the temps reach 9500 degrees. At a "mere" Mach 6, the X-15 skin reached 650 to 700 degrees C, in a minute and a half of powered flight. This would have happened to the Sanger several times per mission, with a skin that didn't have the heat resistance of the X-15's. Sanger is also higher up in thinner atmosphere. It skips up and down and was actualy to cruise at more like mach 10. This is how I think it would have been tested: (Magical handwaving imaginary ten year test program deleted) ...you also left out the two or three Silverbirds that would have been lost due to the control problems inherent in supersonic flight. And then the one or two they would have lost due to the skin peeling off. And then one or two due to not knowing about how to support a man in space... The vehicle had an all moving tail. Either way Sanger was using the first hypersonic wind tunnel in the world to test his model. ...if the program had ever gotten that far. The wedge shapped wing profile shows a keen understanding of supersonic aerodynamics. No, it just showed a basic understanding of high-speed flight. Small wings = high wing loading = higher speeds and lower maneuverability. Landing speeds would have been high, even when empty. It had a flat body to help both hypersonic re entry and landing and braking parachutes. ...and would have come in at 200 MPH or so, like the Shuttle. So add "develop high speed high load tires" to your development program. And "redesign aircraft to really handle hypersonic flight." If you look at the wings they are like triangular wedges like a Sparrow missile. Um, no. They're closer to the F-104 in shape and cross-section in every image I've seen of the Silverbird. Much like the X-15 wings, as a matter of fact. They are triangular wedges. Look closer. The Germans had solved the hypersonic and heat shielding re-entry problems of the V2 ...by not flying it at high hypersonic speeds for very long. The V-2 topped out at about 3500 MPH on reentry, and only managed that for a very short time, in uncontrolled ballistic flight. They had a heat shield. Graphite and plywood that turned to graphite. ...for the minute or two it took to reenter and impact. No doubt other materials were in development. Eg double walled skins, ablatives etc. Replace "were" with would have to be once they started actually thinking about it." They were thinking about it. They apparently had a ceramics heat shield program (for Sanger at least it appear) and more than one hypersonic wind tunnel working on problems. They had a problem defined and thus they could set about solving it. ...in several years. Which they didn't have, and had *not* anticipated in the original idea. Just about everying was anticipated, heat shielding included. Nothing like the 13,000 MPH the Sanger was supposed to hit. Maybe Sanger would only have handeled a lower speed. say Mach 6 or mach 10 instead of Mach 20. ...and been unable to complete its mission, which relied on long periods of coasting in between moderate periods of slamming into the atmosphere at 8,000 to 12,000 MPH and melting that stainless steel skin right off. Then having to be redesigned for massive amounts of fuel to make up for not being able to handle the original mission profile. Getting enough velocity was not the problem. The engines were up to it. A speed of 13000mph is less than 1/2 the energy required to reach 17,000. The biggest problem is heat shielding. Sanger had a hypersonic wind tunnel to test hypersonic L/D. Controll surface effects, stability and propably even heat build up issues could be tested. And a ten-year nuclear program to make a nuke small enough to carry in the darned thing... Off topic but The Germans had 25kg of enriched uranium in 1943, more than the allies. They had developed supersonic centrifuges which is the modern prefered method of enrichment. No huge gaseous diffusion plants. Sanger MkII on the otherhand? Sure, and when they got the Ark of the Convenant out of that secret American storage facility, they would have been unbeatable. |
#12
|
|||
|
|||
"The Enlightenment" wrote in message om... Off topic but The Germans had 25kg of enriched uranium in 1943, more than the allies. They had developed supersonic centrifuges which is the modern prefered method of enrichment. No huge gaseous diffusion plants. Bull**** The Germans only managed to enrich uranium to around 3.7% and that only in small laboratory quantities. They had a centrifuge program which FAILED miserably as did the rest of their nuclear program. Given that the resources allocated were extremely modest this is hardly surprising. The major reason for their failure was the lack of materials that could cope with the extremely corrosive Uranium Hexafluoride the enrichment process required. With Germany critically short of chrome, nickel and other allies the high strength stainless steel alloys required were simply not available. In December 1942 Dr Erich Bagge noted in his diary "Conference in the rooms of the president of the National Bureau of Standards, State Councilor Esau. Diebner, Basche, Clusius, Harteck, Bonhoeer, Wirtz and myself present from the physical side; the chemists Albers, Schmitz-Dumont and a third described their attempts to make volatile uranium compounds [to replace the corrosive uranium hexauoride in the various isotope-separation processes]. Esau is getting ready to throw in the towel in January or February. It seems that they now think the solution of a certain problem can have no bearing on the out-come of the war after all." The Germans basically gave up high level centrifuge enrichment at this point and concentrated on low level enrichment for a power reactor design and they made little progress even on that. The total budget allocated to German enrichment programs in 1944 was 200,000 Reichmarks. The 3rd and final enrichment machine to be built (and the only one to work) was run in July 1944 and managed to produce 2.5 grams of Uranium enriched to 3.7%. This was of course a small fraction of the daily output of the Oak Ridge plant. They were not only behind the American, British and Soviet programs but even the Japanese had a better grasp of the basic physics involved, thats hardly surprising either since most German physicists had either been expelled or had fled the country. I suggest you read The Virus House by David Irving.He's not a historian I'd usually recommend but given that his tendencies are largely pro German you may find his writing more compelling and you can down load it free from http://www.fpp.co.uk/books/VirusHouse/ Keith |
#13
|
|||
|
|||
|
#14
|
|||
|
|||
As I've mentioned several times, not with the materials they had
available in 1945. Repeating this false assumption does not make it suddenly become true. At a "mere" Mach 6, the X-15 skin reached 650 to 700 degrees C, in a minute and a half of powered flight. This would have happened to the Sanger several times per mission, with a skin that didn't have the heat resistance of the X-15's. You obviously don't know much about the SS Technical Branch and their work in metallurgy. Documents recovered at Gottingen and Volkenrode indicate that between 1943-44 the SS were experimenting with a frictionless metal called "Luftschwamm" (Aerosponge) that could withstand 1000 degrees Centigrade. The experimental compound alloy was classified by the US... and probably found its way onto some of the early US replicated disc designs at Wright Field. As I pointed out many threads ago the SS Technical Branch (especially the E-4 Unit) holds the key to much of the amazing technology discovered at the close of the war. The SS were put in charge of developing new manufacturing methods, exotic metallurgy, alternative fuel sources, energy field weapons, development of chemical and biological weapons, advanced jet and rocket aircraft, disc aircraft, and the future of ballistic missile technology. Albert Speer, as armaments minister, talks about this in his lesser-known book "Infiltration". Anyone interested in advanced, little known weapons and all aspects of the SS organisation should read it. Rob |
#15
|
|||
|
|||
|
#16
|
|||
|
|||
|
#18
|
|||
|
|||
|
#19
|
|||
|
|||
Chad Irby wrote in message . com...
In article , (The Enlightenment) wrote: Chad Irby wrote in message . com... Nope. Velocity is velocity, and coming in out of vacuum means those steel wings are just little flanges out in the Mach-20 airflow waiting to be melted - or broken off altogether. Nope. There is someting called a hypersonic L/D (lift to drag ratio). Yes, there is. And it tells us why those wings would have melted off. To get enough lift to bounce the Silverbird out of the atmosphere again, you have to deal with the drag of having it in the atmosphere for a few minutes. Certainly long enough and hot enough to melt those little steel wings, as demonstrated by the short X-15 flights with even tougher alloys at lower speeds. The USAF and NASA engineers who did the Black Horse SSTO (Single Stage to Orbit) designe study make the following claims: http://www.risacher.org/bh/bh-faq.html "Q: How will the Black Horse protect itself from melting when it re-enters? A:Reentry heating is a strong function of wing loading. The Space Shuttle has a highly loaded wing, at over 120 lbs/ft2. The Black Horse has a 20 lbs/ft2 wing loading. Some at Boeing believe it could be possible to build an all metal aircraft (Applying Inconel, Rene 41, etc.) since their in-house RASV design used all metal integrated structure/tankage/TPS. (And handled cryogens, too!). (Mitchell Burnside Clapp, ) " More info here on Black Horse: http://www.risacher.org/bh/analog.html ****************** The Germans didn't have alloys like inconel, rene 41 or the British Nimonic series because these alloys have an 80% nickel content. (All melt at about 1400C) but they had something close. The Germans used alloys like Tinadur (Chrome,Nickel,Titanium 70% Iron) and Cromadur (Chrome, Manganese, 70% Iron) for the turbine blades of the Jumo 004B-4 Jet engine used on the Me 262. (Both types were were used on the 004B-4 since insufficent production of either alone was avaialble) The reason is that the Germans had a severe nickel shortage. The problem was that without nickel creep strength falls of after 600C more rapidly than the high nickel alloys even though overall strength remains similar and the melting point is still around 1400C. (As a result the Germans had to x-ray and recycle their turbine blades at 25 to 60 hours or about every 16 to 32 missions) Cromadur is interesting in that is is weldable and maleable. Cromadure blades were made by bending and welding along the trailing edge. Thus the Germans had alloys similar to inconel that melted at 1450C and opperated at 750C as turbine blades. These were inferior in creep strength but not melting point. I'd say their metalurgy were good enough for Silverbird. Sanger silver bird re-enters after a few skips at much less than the 17000mph of the all inconel Black Horse and Much less than even its own 13000mph top speed becuase it has skipped to even less speed. Remember that KE = 1/2mv^2 so by halving the rentry speed you 1/4 the heat buildup. Sangers work on re-entry was pioneering and very respectable. He did Hypersonic wind tunnel testing. He had sueprsonic wing profiles and he made use of ligtinn bodies. He build high impulse LOX/Kerosene rocket engines that had the impulse needed to achieve the mission. You can fly in and limit you rate of decent in a winged or lifting body thus limiting peak heat to the extent that ablatives or even tiles can be dispensed with. Up to a point, but you still have to deal with *extreme* temps, in the thousands of degrees range instead of hundreds, and boiler-type stainless is *not* going to do the job, especially in the thicknesses you need to use in spacecraft. The only way to get a decent lifetime out of the stuff at Mach 10 would be to make it prohibitively thick, and replace it after every flight. So the Silverbird could have managed about Mach 3 for a short period of time, about 1/5 of the *necessary* speed for suborbital missions like the one it was designed for... and then would have had to be scrapped due to overheating of the structure. It could have managed more than mach 3 easily. For a *very* short period of time, like the Mig-25. Then it would run out of fuel or melt. Sustained speeds at Mach 3 just aren't feasible with low-temp alloys. The vehicle could have achieved sub orbital velocity at 13,000 mph. ...and melted in extremely short order. Re-entered and slowed to a slower speed say 8,000 mph and skipped to cool of and so on. As I've mentioned several times, not with the materials they had available in 1945. Repeating this false assumption does not make it suddenly become true. At a "mere" Mach 6, the X-15 skin reached 650 to 700 degrees C, in a minute and a half of powered flight. This would have happened to the Sanger several times per mission, with a skin that didn't have the heat resistance of the X-15's. Sanger is also higher up in thinner atmosphere. The X-15 hit Mach 6 and max temp at about the same altitude the Sanger was supposed to be at when it "skipped." It skips up and down and was actualy to cruise at more like mach 10. And when it reentered the atmosphere, it would melt unless they redesigned it with better materials. ...you also left out the two or three Silverbirds that would have been lost due to the control problems inherent in supersonic flight. And then the one or two they would have lost due to the skin peeling off. And then one or two due to not knowing about how to support a man in space... The vehicle had an all moving tail. An all moving tail is nice, but it's not a prerequisite of super- and hypersonic flight, and it certainly would not have made the rest of the design workable. Either way Sanger was using the first hypersonic wind tunnel in the world to test his model. And I'm sure that foot-long model would have showed all of the issues I've mentioned. Oh, wait, it wouldn't. All it did was show how the air flowed around a solid machined model of the Silverbird. No doubt other materials were in development. Eg double walled skins, ablatives etc. Replace "were" with "would have to be once they started actually thinking about it." They were thinking about it. Not in any reference I've ever seen. Most of the books I've seen on the Silverbird are quite adamant that Sanger didn't spend much time on the bomber after the initial concept, and spent *no* time on heating issues, other than "it's going to cool off between skips." It was a concept with a tiny bit of research after the fact, but nothing like what you imagine it to be. Sanger spent a lot more time on his design for a ramjet-powered interceptor (which also never flew). They apparently had a ceramics heat shield program (for Sanger at least it appear) and more than one hypersonic wind tunnel working on problems. Nope. They had *one* hypersonic tunnel in use in 1944, and it had a very short (~30 sec) operating period (vacuum-operated). The Sanger model was only tested for general ariflow, and they had *no* facilities at the time for extended hypersonic flow runs. There were plans to build a sustained hypersonic tunnel towards the end of the war, but the Germans never finished it. Just about everying was anticipated, heat shielding included. Sanger spent no time studying the problem before the end of the war. The biggest problem is heat shielding. Sanger had a hypersonic wind tunnel to test hypersonic L/D. Controll surface effects, stability and propably even heat build up issues could be tested. No, they couldn't. While small hypersonic tunnels are good for general airflow testing, they're lousy for extrapolating up to full-size machines. |
#20
|
|||
|
|||
In article ,
(The Enlightenment) wrote: Chad Irby wrote in message . com... In article , (The Enlightenment) wrote: Chad Irby wrote in message . com... Nope. Velocity is velocity, and coming in out of vacuum means those steel wings are just little flanges out in the Mach-20 airflow waiting to be melted - or broken off altogether. Nope. There is someting called a hypersonic L/D (lift to drag ratio). Yes, there is. And it tells us why those wings would have melted off. To get enough lift to bounce the Silverbird out of the atmosphere again, you have to deal with the drag of having it in the atmosphere for a few minutes. Certainly long enough and hot enough to melt those little steel wings, as demonstrated by the short X-15 flights with even tougher alloys at lower speeds. Thus the Germans had alloys similar to inconel that melted at 1450C and opperated at 750C as turbine blades. These were inferior in creep strength but not melting point. So in other words, even if they used those alloys, the plane would have come apart or deformed, or he would have had to build them out of much thicker pieces of metal. I'd say their metalurgy were good enough for Silverbird. Too bad they never got around to using it. Once again, the design for the Silverbird had *nothing* in it about high-temp metals - just plain old stainless steel, which you finally admit is not good enough, after trying to claim that boiler-type stainless was good enough. Sangers work on re-entry was pioneering and very respectable. He did almost *zero* work on re-entry. With the machinery he had available, all he could do was very short tests on shockwave formation. He did Hypersonic wind tunnel testing. ....on tiny little models of the Silverbird, for less than 30 seconds at a time, with *no* heat testing, and could not have done any different with the equipment he had during the war. -- cirby at cfl.rr.com Remember: Objects in rearview mirror may be hallucinations. Slam on brakes accordingly. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Squadron formed to test Osprey for combat readiness | Otis Willie | Military Aviation | 0 | August 30th 03 07:33 PM |
Osprey vs. Harrier | Stephen D. Poe | Military Aviation | 58 | August 18th 03 03:17 PM |