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Comment by looping__lui | Hacker News Reader

Funnily enough the SR71 at Mach 3.5 had a better mpg than a Boeing 747 below Mach 1. It’s kind of hard to compare apples to apples here - but at supersonic speed, different engine technology can be used with better fuel efficiency…

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The SR71 was flying at a much higher altitude to achieve lower drag and fits 2 pilots, 0 commercial passengers.

If you want to compare apples to apples, I suggest you refer to the 2 metrics I mentioned: - gallons of fuel per miles flown - fuel used per passenger

One without the other is a useless comparison as you pointed out.

U miss the point entirely that supersonic planes work differently from “traditional” subsonic planes. Just assuming that “faster equals less fuel efficient” is not really correct. Turbofan engines are kind of draggy and not so fuel efficient close to Mach 1. Ramjets change your equation… :-)

The point is poorly made. Would be like talking about how fuel efficient the space station is for it's speed. Can only work if you ignore the trip to that steady state.

So, for the blackbird, how does it do on take off? You know, when it is literally leaking fuel? :)

Maybe you just wanted to understand the point in a certain way so you could argue about it?

Certainly fair. I can't see any world where the comparison is relevant, though. :(

Down thread it was pointed out that sports cars are more efficient than busses. Per vehicle. This is about the same idea, at best.

> Funnily enough the SR71 at Mach 3.5 had a better mpg than a Boeing 747 below Mach 1.

The SR-71 had a maximum takeoff weight of 140,000lbs.

The 747 has a maximum takeoff weight of 735,000-910,000 lbs, depending on model.

That helps quite a bit for the former using less fuel per mile.

And a considerably higher percentage of the 747's weight is passenger/cargo as well.

You also have to compare getting to that speed. And, of course, the comparison is dead when done per passenger. Might as well compare a missile in there, or a drone.

A Ferrari probably has better fuel efficiency than a bus, yeah.

True. An average city bus gets 7 mpg; an 812 Superfast gets 13mpg.

The bus wins when carrying 3 or more passengers besides the driver. And in a city with dedicated bus lanes, the bus may win for route speed, too.

And I guess the brains behind a Ferrari enjoy their work more than engineers designing said bus. And Ferraris will attract more attention than a bus. Maybe some things are just unnecessary. Conquering the useless and doing unnecessary things is what keeps me sane and happy. But our mileage on that topic might vary.

> And I guess the brains behind a Ferrari enjoy their work more than engineers designing said bus

If we want to improve lives of workers, I am game, but can we start by helping all the amazon can drivers that pee in a bottle?

Maybe start with taxing the rich higher taxes, have minimum wage, maximum allowable working hours and all that stuff. The country I live in does that. You unemployed with three kids? Government pays your housing, free education for school and college (which is the same for rich and poor) and free healthcare.

Why does designing a Ferrari have anything to do with your broken society? It’s not about the Ferrari - it’s about middle class upwards being cheap. Pay higher taxes and your problems on “improve live of workers” will go away.

I pay approx. 60-65% on my gross income. Do the same and we can start talking again.

… and don’t be cheap about “oh no, I cant because I can’t change the tax system”. Start tipping everyone rendering you a service until 65% of your gross income is gone every month. That UPS driver picking up your package - here’s 50$. That school teacher staying late at a parent conference. Take my money. The lady in the supermarket - take the $100 because I don’t need it. At least you can feel good about it because you do it voluntarily. You can fix it with (your own) money.

> That school teacher staying late at a parent conference. Take my money.

Oof, I would be carefull eith that, it could be interpreted as a bribe and get you in trouble

Then tip the rest.

okay, you've solved like 10% of the problem.

You what would actuslly help? Start a union, run it well.

Doing what? sat at 70mph, yeh probably. stop/starting chundling around town I guarantee not.

Are you optimizing for throughput or latency?

Probably also because it flew much higher with less air density and drag.

It also only carried 2...

Drag also works differently at supersonic speeds.

Per passenger?

No.

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