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Air Force Builds Quiet Mach 6 Wind Tunnel
An anonymous reader writes "To help design 'scramjets' -- vehicles that'll travel thousands of miles per hour as they leave the atmosphere and zip around the globe -- the U.S. Air Force has just funded a wind tunnel that operates quietly at Mach 6. To get a quiet flow, the throat of the Mach 6 nozzle must be polished to a near-perfect mirror finish, eliminating roughness that would trip the flow."
Wikipedia on Scramjets. AC to avoid karma whoring..
neat scramjet pictures here.
The theory of relativity doesn't work right in Arkansas.
proper lockout/tagout procedures would involve the person doing the work personally putting a padlock on the circuit breaker (in the off position), one to which the only key is in the posession of the person working inside the device, along with a tag stating who he is, what he's working on, and when he expects to be done, after which he would personally test that the equipment is not capable of powering on before climbing inside.
Removing a fuse is no more effective then turning off the switch if some idiot comes along and puts it back together (the same idiot who first tried the switch and found it didn't work) always LOCK it out.
ok... so there's always some moron with bolt-cutters... but I'd love to see him claim THAT was an accident when he goes to trial...
This tunnel works in a fashion opposite most wind tunnels. Instead of pressurizing one end, they create a vacuum at the other. That means they only get a run time of 8 seconds, but they use computers to get all the data they need in that short of a time frame.
So, yeah, it really does suck.
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Yep. For those that don't know, there hopefully are archives of teh Skunkworks-L mail digest on the net, where several people who were associated with the SR-71 programs (USAF and NASA) have some great stories about this incredible aircraft, and how bad engine unstarts were when zipping along at Mach 3, with the typical reason being that the shock wave entered into the engine inlet faster than the inlet spike system could respond to it. IIRC, more than one SR71 was lost operationally because the restart didn't go well or the plane broke because of the violence of the yaw caused by the unstart.
Turbo-Props (propeller driven by jet like turbine power) is good up to a few hundred mph. Then the tips of the prop start going supersonic and cavitating. Highest efficiency
Turbo-Fan (same turbo jet power like a turbo-prop, but with an enclosed fan rather than a prop. Most of thrust still comes from the air driven by the fan. think 747) is capable of working in a faster regime up to somewhere near sonic speed (~780mph). Used for most commercial aviation because it is still fairly efficient, but faster than turboprop.
Turbo-Jet (same turbo jet power as turbo-prop, but little or no "bypass" air. The main purpose of the intake fan is now to pressurize air at intake for combustion with jet fuel. Thrust comes from) can provide substantial power at high velocites. TurboJets are the big muscular loud as hell engines used on fighter planes. They are several times less efficient than the TurboFans used in commercial airliners, but they produce many times more thrust and can run well in super-sonic regimes. More power + less efficiency = burns lots of fuel. Fighters can chew through thousands of gallons of jet fuel each hour just cruising. Temperature (melting point of metal) is a huge limit to the perf of these engines. Afterburners burn even more fuel in a way that isn't as temperature constrained, but is even less efficient. Modern fighters can burn through their fuel in something like a half hour of combat.
RAMjets work by using a constriction at the intake (rather than a fan) to pressurize the air. RAMjets don't work at low speeds, and are better designed to operate at a single design point. They typically run in the low mach numbers, although to operate, the intake air must be slowed to subsonic speeds. They are fast and efficient, but not very flexible. Typically used on missiles (due to their tendancy to operate in a single regime).
SCRAMjets are the same basic idea as a RAMjet, but the intake air remains supersonic.
Rockets do not burn any atmospheric O2 at all. For this reason, they operate equally well (or poor) at all speeds and air densities, providing a consistent predictable thrust. Due to the need to carry O2 around (which is far heavier than most of the fuels), their efficiency is appalling when compared to air-breathing engines. The uber-efficient space shuttle engines (2H2 + O2 -> 2H2O) have a specific impulse of ~440s. Solid rockets are more like ~200s. Kerosene rockets are in between. Air-breathing engines are in the thousands.