their refineries kept having bombs fall on them
I hate it when that happens.
their refineries kept having bombs fall on them
I hate it when that happens.
The use of "y" at the end of a word and "i" in its place in the middle of a word was a convention by printers which made it easier to deal with the "y" descender in a stylish way.
I would not say this in many forums, but this is slashdot....
*I* find it convincing and interesting though a reference would be nice. And this is
A pet hate of mine is faux archaic signs like "Ye olde cheese shoppe". The "ye" is just a misunderstanding AFAIK of "the" written with a slightly open, regional form of the letter thorn which vaguely looks like a "y" though it just means "th".
but on the same not do the engines actually stop spinning? I would have thought the air naturally moving through the off engine would cause it to spin too.
Yes and no. Turbojets and turbofans as well as fixed-pitch props do free-spin in the air. However, they do so at a very low rpm, usually in single-digit percent of their rated speeds. If anything, this is more of a detriment to performance because it actually acts as a big air brake. All turboprops (as well as some of the higher performance piston props) I know are equipped with variable pitch full-feathering propellers, so they actually do come to nearly a complete stop - this helps reduce their drag and increases performance in engine-out conditions. Turbojets and turbofans do have an in-flight minimum restart rpm. This can be achieved either by flying very fast, by cross-bleeding compressed air from the compressor of the working engine, or by using an auxiliary power unit (a small turbine engine designed to start the aircraft without ground assistance and to provide power when the main engines are off or failed) to feed compressed air to the air turbine starter of the failed engine.
Regardless, irrespective if the engine's internal turbo machinery remains spinning at some small fraction of rated RPM, the hot section of the engine cools off pretty quickly, since the heat source is gone and you've got very cold air going through there (not at a very high rate, but still after a few minutes of -50C air flow, it's going to be pretty much chilled). As a further example, here you have a Boeing 747-400 APU (a >1000 shp beast) starting up and going from zero to 100% rated output power in about 30 seconds. The APU is fully automatically controlled, the crew literally just flips a knob in the cockpit and that's it (here it is, near the center of the picture).
Apparently it was the turbine of an old 737-300 with the turbofan removed so one of the mech engineers told me.
Possibly an industrial variant of the CFM56. Don't know what they're called in industrial versions, I'm only familiar with GE's and some of RR's products. Industrial conversions of aviation engines do occasionally happen.
the engine was attached to a large gearbox. Maybe that's where the warm-up requirement came from
Not sure either. Gearboxes don't really need warmup either, they just need lubrication. It's mainly large castings (as occur in piston engines) that are susceptible to heat stress. Turbine engine oil has very low viscosity (far lower than automotive engine oil), so I don't think viscosity of the oil is much of a factor either... I dunno, maybe the manufacturer just wanted you to really baby the engine.
That's the strange part, it was an aviation engine.
What was it? Just out of curiosity.
Anyway, all I can say is I've never seen a warmup requirement in the operating manual of any turbine engine-powered aircraft, but maybe it's because the operational procedures were designed such that it's averted. Warmup is definitely required in piston aircraft (e.g. DA-40; after startup 2 mins idle, then 1200 rpm until oil in green; no takeoff before that). However, in-flight restart procedures don't mention warmup either. You can shut down an engine in flight, leave it off for as long as you like, restart it again and immediately apply full power. One would think if component temps were an issue that the designers of the procedure would warn about it, but apparently they don't. I don't know about industrial applications. I've seen an engine overhaul tech once mention that when they test out industrial engines they do run them up slowly, but that it's not really required.
Still not a good idea to run up to full power before ensuring that every surface is lubricated.
Curiously enough, since in turbine engines there's no sliding of surfaces going on (everything is on ball and roller bearings), oil is primarily used as coolant, not as lubrication. That's why it's okay to let a turbine engine freewheel in the wind on the ground. You won't see that happening with turboprops or helicopter rotors because these guys are using a gearbox between the engine and the prop/rotor (and a pretty aggressive one at that, usually in about a 10:1 ratio). In fact, first thing after parking you'll often see ground crew running up to tie the props and rotor down.
high density users (more than 250kW per square foot)
Holy shit! That sort of power density puts a nuclear power plant to shame. Or has some journalist again mixed up their units?
Less sexy would be to develop a tug that could not only push the plane back, but also perform taxi duties.
This is already done. The pushback tugs are also used for repositioning aircraft between gates and/or hangars. There are many reasons why aircraft start their engines at the gate. This serves primarily as a checkout of the aircraft systems. If an engine behaves oddly, or has trouble starting, pulling back into a gate is simple. Doing it at the runway would be a lot more complicated, as it would require a full back-taxi, which on congested airports is already a major PITA. In addition, many of the internal systems such as flight control hydraulics are powered by the engines, so for example you won't have all flight controls fully functional (meaning, you can't perform a F/CTL check) and you can't fully extend flaps for takeoff unless you have at least one of the engine-driven pumps running. Secondly, the air conditioning packs inside the cabin are engine-powered and they take a lot of juice as well as compressed air (or you'd have to carry a sizable battery just to keep them running for the 20-30 minutes on the ground). On very long taxis to takeoff or after landing, many aircraft already do reduced-engine taxi. 747s routinely shut down 1 or 2 engines right after landing. Twins routinely do single-engine taxi. When there is a long queue for takeoff, similarly, engines get shut down. But doing the whole taxi completely shut down and only starting once close to lining up would probably result in tons of operational complications and possibly safety issues.
More importantly: a there are thousands of devices that monitor the beam. Plus the actual detectors, which generate multiple terabytes of data PER MINUTE. I'd like to see the wireless hub that can keep up with that.
Yes, but there's a point that doesn't work any more. The original injectors at CERN are more than thirty years old; some sites are probably 40 or 50. You find me a cheap and effective way of labelling cables that doesnt' fall apart over that time span...
Sounds great, except:
- Are the cables transparent along a run of 100 meters or more? I doubt it.
- Do they STAY transparent for thirty years?
That's the case with CERN: long old cables, covered in dust. Some are probably quite brittle from heat or radiation damage.
Mirrors should reflect a little before throwing back images. -- Jean Cocteau