The XMEN Clan Forums

Posted: **Fri Nov 19, 2004 11:05 pm**

Yes, I know this is several days old by now, but I was expecting Asha to post something on it. <a href="http://www.nasa.gov/missions/research/x ...  I heard about this X-43 test flight, and one of the first things I thought of was the effect the heat would have on the thing. One of the other stories linked to on that page said that they estimated only about 3600 degrees F for the leading edges from friction, even in the thin air at that altitude. YIKES. That X-43 is hot stuff! <img src="http://www.xmenclan.org/xmengambit.gif"/> XMEN member Card-carrying DTM OKL Fish-napper Though a program be but three lines long, someday it will have to be maintained.  The Tao of Programming

Posted: **Sat Nov 20, 2004 6:15 pm**

Was gonna post something... but I've been kind of busy. Plus... they didn't fly it on their scheduled day! (The weather out over the ocean wasn't good.) Get this... back in May/June... I actually touched this one! My direct boss (he's called a branch chief) within EW, knew the lead propulsion guy for the X43. So he got myself and a few other people a tour. I was kind of suprised because I had just stopped by his office to drop off some paperwork. We drove over to Dryden, went inside, and went back to the hangar where they had the thing hidden in an area that had black curtains all around it. It was really cool! The only difference between it and the previous ones were some slight modifications to improve the flight software and some rerouting of the gas lines. But the major thing was that the spacing of the injector nozzles in the engine was slightly different (the spacing dictates what speed the engine is capable of... due to the mixing time change for the fuel, air, and flame). Oh and get this... the thing had leading edges of... guess what? CORK! That's right. I personally was expecting some exotic form of titanium or something. (Maybe a ceramic aluminate or something too.) But everyone there except the propulsion guy was like, WTF!? It turns out that they do it so that the leading edges ablate during flight and keep the boundary layer, which is a region of air that sits right next to the skin and has no velocity at the skin and transitions to full, free-stream velocity at the outer part (think of it as a transition layer), from warming the skin up too much. The cork actually melts / catches fire, but it's one of the few materials that retains its shape as it does so. So they don't have to worry about funky aerodynamic effects, which can be catastrophic at supersonic velocities. The rest of the skin is kept relatively cool by the boundary layer using the same principle as ballistic missiles during reentry. It's called the blunt-body effect and was actually classified top secret to keep the Soviets from learning how to get around the highspeed heating problems associated with a sharp-nosed vehicle. That's why the Gemini, Mercury, and Apollo capsules were all blunt-bodies. What happens is a sharp body will allow air to move faster over the skin at high speeds than a blunt body would. The effect is that there is more friction on the skin and the skin will heat up tremendously. With a blunt body, the boundary layer doesn't move as fast, so instead of the skin heating up tremendously, the boundary layer absorbs most of the heat and acts like an inulator to the skin. It still gets hot, but not as hot. To get an idea of what temps: slender body (think needle-nosed aircraft screaming in from space at 10,000 mph) ------ 7000 degrees on the skin. blunt body (think Apollo modules, space shuttle) ------- 4000 degrees on the skin. There are no materials that can withstand 7000 degree temps and still maintain their structure (or not be instantly ionized... we're talking ionization temperatures here). The other thing that a blunt body does is it keeps the shock that forms off the front of the vehicle from ever actually being in contact with the vehicle. For a sharp-nosed body, the shock will eventually touch the tip as the vehicle slows down and that tip will get VERY hot when the shock touches it. It's only when the vehicle slows to about Mach 9 (give or take .3 Mach) that the shock will jump to the surface. You can see this effect on your next commercial airline flight if you sit near where you can see the wing, and if the lighting, air temperature, and humidity are correct. If you look out, you'll be able to see what looks like a line dancing on the wing. It can be a fat line or a thin one, but you should be able to spot it. The line will be moving back and forth (kind of vibrating I guess). This line is the exact place where a shock is formed. You'll see it curve over the wing and reattach at the back edge somewhere. This happens because the curved part of the wing (usually the top) accelerates the air moving over it and can cause the air to accelerate past the local speed of sound. When this happens, a shock forms, and because of the shock, the density, temperature, and pressure of the air changes. The density change actually bends the light passing through it and you see the distorted light as a line. If it's humid out, you'll be able to see a sort of cloudy thing which corresponds to the water vapor in the air suddenly condensing due to the pressure and temperature changes just before and across the shock.

Posted: **Sat Nov 20, 2004 10:55 pm**

According to that article I mentioned (which was written after the last flight, not this one) they made some leading-edge changes between this one and the previous models. One of the differences was horizontal vs vertical stabilizers on the tail. It also said the leading edges were covered with a carbon-carbon material, but I didn't look into that any further. The stuff about cork was interesting.

Posted: **Sat Nov 20, 2004 11:22 pm**

It's so cool having smart geeks here. <img src=http://www.ezboard.com/images/emoticons/happy.gif ALT=":D"> <hr /><div style="text-align:center"> "Never, Never, Never Quit" -Winston Churchill</div>

Posted: **Sun Nov 21, 2004 9:14 pm**

Asha - you rock! I wish I had your style of intelligence. Sure would be fun to work around that stuff. Ahh well, I will just abuse my gnome-mage and pretend I can pull some of your stunts. <img src=http://www.ezboard.com/images/emoticons/smile.gif ALT=":)"> "Death is not the end."-Ravok

Posted: **Sun Nov 21, 2004 9:21 pm**

Asha, Do you know much about single-crystal turbine blade formation? I am extremely interested in how they get a single crystal of nickel to form. Also do they still bleed air over the blades through tiny holes to keep them cool at very high speeds? I also assume that all hypersonic scramjet engines will have to use some type of rocket booster to get the vehicle up to speeds in which the scramjet can generate enough pressure in order to ignite and operate? My next question for discussion here is can the scramjet theorically not need to carry ANY fuel and scavenge the hydrogen and oxygen needed from the thin atmosphere in which it operates? Thanks! <table border=0><tr><td><embed align=left src=http://www.thzclan.com/avatars/ezice.swf menu=false quality=high bgcolor=#000000 width=217 height=166 type=application/x-shockwave-flash pluginspage=http://www.macromedia.com/shockwave/dow ... <td><table border=0 style='Filter: Shadow(Color=#BB1403,Direction=255)'><tr><td>XMEN Iceman [DTM] Founder and Leader of the Base Tribes XMEN Clan Proud member of the Dragon Talon Mercenaries teamplayers Guild Citizen of New Fenecia You weren't much of a challenge - T2 bot after killing Iceman - click on avatar for links - no, not sausage links!</td></tr></table></td></tr></table>

Posted: **Mon Nov 22, 2004 10:37 pm**

Hoo boy! <blockquote>Quote:<hr> Asha, Do you know much about single-crystal turbine blade formation? I am extremely interested in how they get a single crystal of nickel to form. <hr></blockquote> They get a single crystal of nickel to form just like you would with any other metal: EXTREMELY, ULTRA pure forms of the element, and slow crystal growth. I think they use vapor deposition... just like with silicon crystals, but using a metal in a clean environment. The metal could also be done as a liquid, but would have to a much purer form of nickel. Just one purity causes a discontinuity as the crystal forms and will cause cracks/shear planes to form. In other words, you will limit the size of the physical structure of the crystal by having just one errant atom. <blockquote>Quote:<hr> Also do they still bleed air over the blades through tiny holes to keep them cool at very high speeds? <hr></blockquote> Yep. They don't exactly use tiny holes. They're more like channels internal to the blade itself that take un-combusted air and flow it through the channels. The exits of the channels are specifically angled so that the cool air mixes with the hot gases directly near the surface of the blades. These types of blades are only used in the turbine section of a turbojet (military aircraft) or turbofan (commerical airliners, transports, and cargo planes). The compressor blades and stator blades are not the same. In a turbojet, they are purely used to compress the air and direct it in the proper direction (this matters with how the mixing of the fuel and air is done, as well as keeping the flow velocity in the mostly axial direction). In a turbofan, only a small percentage of the air is compressed and used in the combustion process (about 10 percent for modern turbofans). The other 90 percent of the air is forced around the central column of air inside the engine. This is done for two reasons: as a source of cool, bleed air, and it gives you a HUGE mass at the exit of the engine. That central column of air that goes through the combustion process and is spit out the ass-end of the turbine section, is used to push the much larger mass of air. In engines, the amount of thrust is ALWAYS going to be mass per unit time multiplied by the exit velocity. That means for a turbojet you have a high-speed flow, and for a turbofan, you have a high speed flow pushing a huge mass. <blockquote>Quote:<hr> I also assume that all hypersonic scramjet engines will have to use some type of rocket booster to get the vehicle up to speeds in which the scramjet can generate enough pressure in order to ignite and operate? <hr></blockquote> True. Scramjets won't work below Mach 5 or so. Ramjets (as used on the SR-71 blackbird) can get you up to Mach 5, but they have to be designed for that range of speeds. Which means you have REALLY REALLY long engines to be able to keep the shock coming off the cones' tips in each engine, contained within each engine. Those cones have to move to keep the shocks coming off of them hitting the inside cylinders of the engines. It's these shocks that slow the flow properly (to subsonic speeds) so that the fuel-air mixture inside can mix and burn at the proper times. The faster you go, the more the shocks angle back. (The angle between the shock and the surface of the vehicle is called the shock angle.) The shock angle gets smaller as you go faster, so to keep the shock impinging (hitting) the inside wall of the engines, you have to move the cone farther and farther forward. The only realistic option right now is to use a rocket to get up to the speeds required for a scramjet to operate. Technically, you could use a ramjet engine to get you up there, then switch where and how you inject the fuel into the engine, and you should be able to use a similar design all the way up to the limit for scramjet flight (which at this point is only limited by how fast and how hot things get when they move that fast). <blockquote>Quote:<hr> My next question for discussion here is can the scramjet theorically not need to carry ANY fuel and scavenge the hydrogen and oxygen needed from the thin atmosphere in which it operates? <hr></blockquote> Scavenging hydrogen from the atmosphere is DAMN hard at high altitude. There is not much hydrogen up there (it floats off into space), and what little hydrogen there is is usually locked up in the form of water vapor. You can find very small trace amounts of hydrogen very high up. And if you find such small trace amounts, you need to either cool the incoming atmospheric gases to cryogenic temperatures, or compress them to very high pressures. The problem with this is that air is a mixture of gases, and you have to have a way to separate the different gases after freezing/compressing them. If you find a way to do that, you'll have to process insane amounts of air to get the hydrogen fuel you'd need. Which implies either a HUGE inlet, or an insanely efficient engine. Scramjets are VERY efficient, but they'll use fuel faster than you can replenish it. <blockquote>Quote:<hr> Thanks! <hr></blockquote> No problem!

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