Andrew M emailed me with a strange factoid.
Apparently a Nimitz-class aircraft carrier weighs about 102,000 tons and generally cruises using about 260,000 horsepower. Horsepower is a difficult thing to measure when you’re talking about a nuclear reactor that’s pushing a bunch of turbines and rotating several (4) propeller shafts. No matter how you slice it, though, that’s a hell of a lot of horsepower and it’s pushing a lot of tonnage and about 6,000 people and food and water and ass-kicking stuff at a fairly high speed.
Apparently each of the engines of an SR-71 outputs about 160,000 horsepower. So the SR-71, during a speed run, is putting out more horsepower than a Nimitz-class aircraft carrier.
As Andrew observed, “pushing things through air gets difficult as your speed goes up.
I still believe that the Saturn V’s F-1 engines are the king of horsepower – a bit more than 3,000,000 horsepower each and the rocket had 5. It was also bigger and faster than an SR-71. So, there’s that. I wonder if an F-1 engine could get a Nimitz-class aircraft carrier to water-plane? Briefly. I believe I read somewhere that you could water-ski behind an aircraft carrier; they are ridiculously fast for something that big.
Time is a factor to consider. As Andrew pointed out, an SR-71 needs to refuel frequently, but a Nimitz-class aircraft carrier’s fuel supply is rated at 90 years. And let’s not talk about the F-1, the great gas-guzzler.
And, just in case you haven’t heard this story before, it’s a tale of SR-71 awesomeness.
A Boeing 747 at cruise speed is loafing along on 19,000hp of thrust. The in-cabin entertainment system of an SR-71 probably made more horsepower than that! If they had one, that is.
Back in 1997 when we were prepping for the V-One IPO roadshow, the investment bankers brought in a motivational speaker/speech coach for the management team. It was a horrible waste of time for all of us. The only part I remember was when the guy was talking about The Power of Marketing and Branding and said (in that tone that one uses when one is being very clever) “Do any of you know what Rolls Royce makes?”
Without opening my eyes I muttered, “Jet engines.”
Obviously he expected us to say “cars.” Memo to motivational speakers: know your audience.
I suppose SR-71s make carbon dioxide.
Remember the story about how the tooling for SR-71s was destroyed at the order of a congressman from a district where Raytheon was making satellite systems? That gets brought up now and then when someone asks “why don’t we resurrect the SR-71?!” The same can be said about the F-1 engine. But the situation is more complicated – entire manufacturing processes don’t exist in the same way, anymore. First off, nobody can weld like the welders who hand-welded the oxygen feed-pipe on the F-1. It takes a lifetime of welding to learn how to weld like that; we’d have to gestate a welding cult. The same goes for the machinists who made SR-71s. Nobody uses those methods to make things anymore because, adjusted for inflation, they’d be insanely expensive fine art. We could use modern CAD, composite ceramics, and CNC to make a new version of an SR-71 but it would behave differently. For one thing, it would probably be made of carbon/carbon like the leading edge of a space shuttle’s wing. That would be easier to form using today’s technology than to resurrect the titanium fabrication process used in the SR-71’s airframe. Synthetic diamond is cheaper than training a captive generation of fabricators. The wing-edge tiles on a shuttle cost about $250,000 apiece. So the new SR-71 would cost about half as much as an F-35. Just kidding about that last bit.
This is a pretty cool video: an SR-71 pilot does a walkthrough of the monstrous, unique, incredible engine of the blackbird.
But how did it work? If I understand correctly, it was a blend of a ramjet and a scramjet and a whole lot of inspired engineering. It must have been quite a thing for a bunch of people to sit down and design something like this using slide rules and paper blueprints.
Burt Rutan did a talk many years ago about how it is unlikely humans will bother to build anything like an SR-71 ever again. It’s just not a problem we have to try to solve anymore. He drew a chart that was sort of like the opposite of Ray Kurzweil’s “singularity” chart, arguing that we got really good at airplanes, built SR-71s, and since then the progress has all been directed toward efficiency. It’s an interesting meditation on what “good” means.
2000 knots is 2300 mph.
Extra credit question: how much horsepower would it take to get a S.H.E.I.L.D. helicarrier into the air?
Automation has gotten better, and the huge portion of space, effort and thrust used to keep a human being alive in such a craft became unnecessary.
To answer my own question, based on max take-off weight specs for the CH-47F Chinook helicopter and assuming it weighs about as much as a Nimitz-class carrier (AROOGA! Questionable assumption alert!), somewhere north of 44,000,000 hp, or 33 GW. To produce that using A4W reactors, you’d need around 60 of them, as opposed to the 2 carried by a Nimitz-class carrier, so our weight assumption starts to look a bit iffy, to say the least… I can’t find how much an A4B weighs, so I can’t figure out if one could even lift itself.
OK, let’s take another tack… I can find both weight and power specs for the S8G submarine reactor, which produces 220kW and weighs 2750 tons, giving a power to weight ratio of 80 kW/t. At maximum take-off weight, a CH-47F Chinook has a power to weight ratio of 311 kW/t. So, there’s no danger that an S8G reactor could even get its own weight off the ground.
Long story short, building a S.H.E.I.L.D. helicarrier (or any other kind of nuclear-powered helicopter) probably isn’t practical. Who could have guessed?
I think I might have too much time on my hands today.
Generally speaking, things that are longer and thinner travel faster on the surface of water (fluid dynamics, man), as I’m sure you know. Aircraft carriers have extremely long and thin waterline profiles. This means that yes, you probably could ski behind an aircraft carrier traveling at speed. Just about anything would plane behind an aircraft carrier.
Actually, how fast a ship travels is a property not only of its wave-making resistance (usually decreased by increasing the waterline length compared to total displacement, among other things), but also how much power you put in. So it’s not really correct to say that these longer and thinner ships travel faster, but that they travel faster for the same amount of energy expended. A short, squat aircraft carrier could travel just as fast as a long thin one, given the same energy input.
So really, the reason you can water-ski behind an aircraft carrier is just because it can go fast. That’s the key component of the design, and that it uses a hull design that requires less energy to achieve that speed is just an engineering decision that reduces the cost of maintaining that speed.
“It takes a lifetime of welding to learn how to weld like that; we’d have to gestate a welding cult.”
Interesting. I am reminded of a bit in the “magic in the Real World” fantasy novel The Case of the Toxic Spell Dump: The US military had a small cult of Hermes-worshippers, for the express purpose of creating hermetic seals on things.
cubist@#6:
I am reminded of a bit in the “magic in the Real World” fantasy novel The Case of the Toxic Spell Dump: The US military had a small cult of Hermes-worshippers, for the express purpose of creating hermetic seals on things.
That’s pretty funny!
There was a story I read somewhere about Larry Ellison spending a huge amount of $ to renovate his house with a Japanese-style interior; the problem was that the craftspeople who do such things are mostly old and not interested, anymore – so he financed training a new generation. That’s what I imagine would be necessary to create a team with old-school fabrication skills. You’d need to find people who wanted to learn how to do it – “retro” artists – who were not interested in the modern powdered metal and CNC processes.
Besides, making a new engine that was a reboot of the F-1, using modern processes and materials – would result in an engine that was better and cheaper to manufacture, but it’d be a whole new design process and development/testing cycle. Start from the beginning, in other words.
There are schemes in the UK that the various charities that conserve buildings set up to train up a new generation of craftspeople in skills like making and using lime mortar and plaster, building walls with uneven stone, the joinery involved in a cruck roof (ie one made by splitting an appropriately curved oak tree and leaning the two pieces against each other to make the main support of your roof). There are also similar schemes run by the preserved railways for the skills to maintain steam engines, by the people that preserve and fly old planes etc but I don’t think anyone has got to conserving an SR-71 yet …
“I wonder if an F-1 engine could get a Nimitz-class aircraft carrier to water-plane?”
I suppose it could. Briefly. Then it would break, I highly doubt it was engineered to withstand that kind of stress.Interesting mental image at least.
That’s basically what SpaceX is trying to do with the Merlin engine.
Ewout@#9:
Interesting mental image at least.
I don’t know how to say in Russian, but it would be something like “OMG look at the after-burner on that thing!”
Thank for the LA Speed Story – very good!