Spinoff from a thread mentioning the HP of the propeller engines on aircraft carriers.
As to the query, would the number one spot, perhaps by cheating of some semantic sort, go simply to power electric plants (nuclear, coal, hydro, etc)?
But I was actually thinking of pride-of-place ranks for massive machinery engines, including rockets (Saturn V?), ships, cars, combines, and perhaps types of machinery I’ve never heard of.
Most powerful hedge clippers, meat grinders, and the like can be excluded.
Confusing thread title. “App” is short for software application (or sometimes an application to college, for example), but not the the broader meaning of application.
Absolutely, it’s big rocket engines, by far. To clarify the link though it’s confusing in listing the thrust of one F-1 engine on a Saturn V but giving the effective hp of all 5, sometimes quoted similarly as 190 mil hp. Assuming the F-1 had a vacuum thrust of ~1.8mil lbs then that oft quoted number, 38mil hp per engine, would be at a first stage burnout speed of around 11,600 ft/sec. That actually seems high, since a NASA publicity data sheet gave 6,000 mph (8,800 fps) as first stage burn out speed. But that would still be almost 30mil hp per engine*, an order of magnitude more than any other thermal engine. Rockets are generally just quoted in lbs of thrust, because that’s almost constant with speed and rises only somewhat as the rocket leaves the atmosphere and so hp depends almost entirely on speed. It’s zero effective horsepower as the engines throttle up with the rocket standing still, only 10,000’s of effective hp as the rocket slowly rises past the launch gantry, but millions of effective hp at first stage burnout on a big rocket.
As links says there are now nuclear shore power stations with individual steam turbines of around 2mil hp each whereas the biggest diesels are around 100k hp. The biggest industrial gas turbines in power plants are several 100k hp.
Yeah I wondered about that myself. Before I PM a mod to ask to change it most easily, is there a proper single word I could I use? (Not the most pressing question…)
Rating rocket engine horsepower on the basis of force times engine speed isn’t really right, because the engine isn’t pushing against something stationary, like a locomotive or car engine. It would be more meaningful to rate it on the basis of force times exhaust exit velocity.
Your description actually makes this clear. The engine isn’t getting more powerful as the rocket gets further. In fact the engine could go fast enough that the exhaust is actually traveling forward when it leaves the engine, rather than backward. That extra apparent horsepower got built into the system earlier on, when the fuel tank was slowly being accelerated.
I agree, though, that rockets are enormously powerful. 55,000 horsepower, for example, on an F1 engine, just to power the fuel pump.
The engine is in fact pushing about equally hard* on the rocket when it reaches 6000 mph at first stage burnout (say) as it was at launch.
So the effective hp (note I said) actually is 10’s of millions hp at burnout in terms of what horsepower means, thrust*speed, which is always what it has meant**. The fuel pump while impressive is a relatively tiny fractional parasitic loss not directly related to the horsepower of the whole engine. True the nature of the engine and its thrust hasn’t changed, the propulsive efficiency is what has changed, from zero at the instant of launch to pretty good.
*more because of the lower atmospheric pressure, slight variation just due to speed.
**back to, exerting a 550 lb ‘thrust’ over one foot in one second is a rough measure of the ability of a typical horse.
The F1 engine’s specific impulse is 263s at sea level, with a thrust of 6770 kN. Specific impulse is exhaust velocity divided by 1G. So are we saying the effective horsepower is 263s * 9.8 m/s/s * 6770kN = 17.5 gigawatt = 23 million horsepower?
Actually the Shuttle solid rocket boosters are even more powerful, but I’m not sure if you can call a solid rocket an “engine.”
The GE90 is the most powerful aero engine at 115K lbs of thrust in the most powerful sub-model: General Electric GE90 - Wikipedia. It was created for the 777.
Perhaps paradoxically, the newest variant 777 that has not yet flown is more efficient and will use smaller, less powerful engines. There’s some chance this is the most powerful enclosed fan + gas turbine aero engine that ever will be built. Aero powerplant tech is now going in other directions; like the famous Pratt 4360 piston aero engine Pratt & Whitney R-4360 Wasp Major - Wikipedia, this may represent the high water mark of its breed.
Aside:
Agree that HP is a stupid measure to use for thrusting devices such as jets and rockets. The physics is 100% correct, but the result is absurd vs. ordinary people’s intuitive = vague concept of what a “horsepower” means. IMO the right answer is thrust force, whether that’s lbF or Newtons or …
in those terms it would be saying some kind of theoretical hp was more like 304s9.8m/s7,770=23gw=31mil hp, using the vacuum rather than s/l values of specific impulse and thrust since near first stage burnout when the engine is accomplishing massive amounts of useful work by moving the rocket rapidly it’s almost in a vacuum. Again at s/l the ‘effective’ hp as I’d call it in terms of the thrust*rocket speed is near zero since the rocket speed is, or again IOW the propulsive efficiency is close to zero. At first stage burnout the propulsive efficiency is high, and effective horsepower is gigantic whatever the exact number.
I agree ‘horsepower’ is not a useful way to compare one rocket, or jet engine (gas turbine in a true ‘jet’ not turbo-shaft application) to another, but it can’t really be avoided if the question is how powerful are big rocket engines compared to the biggest steam or gas turbines generators, the answer being: way, way more powerful. It also comes up in comparing for example the power of late prop fighters to early jet fighters, since they coexisted. You can’t just say one engine is measured by hp and another by static thrust and that’s it. There is a hp comparison, it’s just a function of speed, with the early jets producing more effective hp at high speed.
No, they are “motors”. A mechanical contrivance that burns chemicals to make thrust would have to include solids. Lack of moving parts perhaps makes them less an “engine”. SCRAM jet could be considered to have the same problems. What about hybrid solid motors?
In terms of doing its job a rocket engine can (I think) reasonably be measured in power. Its job is to accelerate gasses into the nozzle throat. After that it is up to the user to work out how to set things up for best effect. The engine is doing its job whether the stack is motionless at sea level or in near vacuum just before engine cutoff, and whether the nozzle has a sensible expansion ratio or not.
In terms of the silly power levels required, recently an F-1 engine was disassembled and the gas generator tested. The gas generator creates the hot gas that drives the turbine that drives the fuel and oxidiser pumps. There is a video here. This is just the power unit that drives the fuel pump.
But looking at this specific comparison, is it appropriate to measure the piston engine’s HP at the crank, or is it more appropriate to measure the thrust produced by the prop? If the prop falls off, the engine may still be producing torque, but the airplane isn’t being moved.
If it is appropriate to measure prop thrust, then the speed term enters into the [piston engine + prop] system’s calculations as well.
In fact, much of the progress in aero propulsion from 1903 to 1925 was not in creating more powerful engines, although they certainly did that. It was in creating more efficient propellers that used more, and wasted less, of whatever engine power was available. A similar thing is going on now with gas turbine fan design and will probably be going on with so-called propfan design for the next 20-30 years.
Implicit in the layman’s (mis-)understanding of horsepower is a non-slip coupling to increasing motion. How much horsepower does a dragster put out during the stationary burnout?
I suggest we need a new cartoon physics concept to bridge this conceptual discrepancy. Let’s call the thing “oomph” and the SDMB unit of oomph is the Bloom.
Late edit: Insert this paragraph after the first body paragraph ending "… but the airplane isn’t being moved"Compare the power output of the turbopumps in an F-1 with the power output at the crank of a piston aero engine. Both are essential to making the vehicle move, but neither move the vehicle without more downstream machinery.
