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Comment Re:What about hydrogen fuel cells? (Score 1) 87

That's probably true, I don't know much about piston engines at high altitude because they are rarely used there. A supercharger does lose energy. I think in principal a turbocharger doesn't lose energy, but in practice the intercooler is inefficient (throws away energy). I don't know how that balances against the higher combustion temperature in a piston engine.

I guess in some ways a turbo-compounded engine (supercharger and expansion turbine coupled to the main drive) smoothly blends into a turboprop where the piston engine acts like a combustion chamber. In practice no one uses these any more since the turbines are so much lighter. Some of the last generation turbo-compounded piston engines were pretty impressive machines. https://en.wikipedia.org/wiki/...

In practice turbo-props are clearly the best solution for all but the smallest planes.

Comment Re:What about hydrogen fuel cells? (Score 1) 87

The turboprop aircraft is more efficient, the turboprop engine is less efficient when you remember that kerosene is higher density than gasoline but its pretty close. The Wikipedia link doesn't have recent engines of either type, but gives a hint: https://en.wikipedia.org/wiki/...

My copy of Raymer (Aircraft design, a conceptual approach) gives a typical specific fuel consumption for a turbo prop as 0.5lb/hr-hp, and 0.4 for a piston. The detailed charts I have for a modern light aircraft piston engine (IO550) gives about 0.36. I don't have detailed numbers for a turboprop.

It doesn't really matter, the turboprops are so much lighter for the same power that they result in higher efficiency aircraft for all but the smallest planes. (turboprops don't scale well below about 1000hp).

Comment Re:What about hydrogen fuel cells? (Score 1) 87

The power density of present day fuel cells isn't very high. Power density is very important for aircraft because carrying extra weight uses more fuel. Its surprising but old fashioned aircraft piston engines are more efficient than modern jets (eg, more power produced per fuel burned). Modern planes use jets because they are very much lighter for the same power, so the overall aircraft efficiency is better (and the planes can fly faster).

I remember seeing design studies of hydrogen fueled aircraft where the hydrogen is burned in conventional engines. Even though the hydrogen is very light (which should be a big win for aircraft) the weight of the tanks and the extra volume (liquid hydrogen is very low density) made it not competitive with jet fuel.

Of course as technology changes these trade-offs could change.

Comment Re:The Discrimination is about wages, not age (Score 1) 207

It may also be about the expected level of responsibility. A talented older worker will be in a position of considerable technical and / or managerial responsibility. If he / she tries to move out of their narrowly defined career, it may be difficult for a new employer to take the chance of giving them that much responsibility, but at the same time can't reasonably them as well for a position of less responsibility.

From what I've seen, moving within the same industry is not that difficult, but moving to a new industry is very tough for older workers.

An older worker who has lost their job (for any reason) can also be viewed as a risk. Sometimes "layoffs" really are about money but sometimes its a way of nicely firing someone. Do you trust that person to make critical decisions on your project?

Note, I'm one of those "older" workers and I don't like the idea that its very difficult to find different work, but I think I understand it .

Comment Cool but will teh economics work? (Score 1) 222

Its a neat idea, even if it is a very watered down version of the 60's vacuum train concept that ran at near orbital speed. https://en.wikipedia.org/wiki/...

No fundamental physics issues, the big question is economics. The cars are pretty small and at those speeds you need a lot of spacing between trains. Curves need to be large radius and if track switching is even possible, the switches need to be very large. Its not clear that its less expensive than 350km/h high speed rail - which itself is often not cost effective.

The higher speed than high speed rail is nice for long trips (>150KM). but otherwise the boarding and accelerate /decelerate times will hide most of the difference. It will need airport like security since a relatively small bomb would kill a lot of people - sort of like an airliner, so it may be slower to board than high speed rail.

Not crazy but there isn't an obvious niche where it is cost effective (similar problems for maglev).

Comment Re:Now we know where the moral compass is pointing (Score 4, Insightful) 244

Considering that the argument for why distributing and owning (as opposed to producing) child porn is that the images actively harm children, I do not think there is any way to justify the FBI's behavior. I think its been generally established that law enforcement cannot commit felonies in order to gather evidence. Otherwise we could have police informants carrying out gang hits in order to capture higher level crime bosses. This is not the start of a slippery slope, it is well down the slope.

They can't have it both ways. If the images don't do actual harm to children, the people who posses the images are only guilty of a minor crime. If the images do harm children, then the FBI should destroy them as soon as they are discovered to prevent continuing harm .

On the central topic there need to be clear rules about what capabilities we want law enforcement to have. It is probably technologically possible for law enforcement to scan all of the records of the great majority of citizens to look for criminal activity. Is that what we want?

Personally I would vote to reduce surveillance and accept a higher rate of criminal activity.

Comment Re:Why stop at $50? (Score 1) 248

I assume they have done some market research and think that $50 would be the price point that would make them the most money. Fair enough - they are a business, they have every right to set prices where they want, and consumers have every right to choose to purchase or not at that price.

$50 is more than some people can afford, and insignificant to others.

Comment Re:Cake or death (Score 1) 917

There *should* be zero tolerance for some behaviors. If someone is harassing one of their workers, in addition to behaving immorally and illegally, they are driving away talented people, and exposing the company to huge lawsuits.

Why should anyone ever be given a pass for this sort of behavior?

More minor offenses are a different matter, but a manger asking a direct report for sex is not a borderline case.

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