Recent content by cjl

In addition to Flyboy's excellent answer, the final part of it is that gas turbines have atrocious idle and part throttle fuel consumption. They're actually quite efficient at high power, but the amount of fuel they burn just to stay running at low power levels is much, much more than what is...

OK, let's take a look... OK, true enough, but I'm already having my woo senses start to tingle. Let's see what this Betz discussion is... Betz applies to *all* incompressible external flows that you're trying to extract power from. This "gotcha" that he's trying to claim here is false - any...

Yes and no? Higher velocity doesn't actually necessarily mean more penetration. Extremely high velocity can cause massive hydrostatic shock on impact, causing pressures that can break up the bullet or cause it to tumble and that can also cause it to dump energy much faster than a lower velocity...

Sure, this should be totally possible. Obviously, once the tow vehicle leaves the water, you've got a glider, so the parasail will move slightly in front of the dangling weight and will be losing altitude until the vehicle reaches water again, but with a reasonably long cord, you could certainly...

You use disk area because the only air you can harvest is that which flows through the disk. Yes, there's much more total air power, but you don't care about the air flowing around the disk, you only care about the air that you could theoretically capture.

This is true for large orbital launch vehicles, but for smaller rockets like sounding rockets and missiles, it's far more typical for the rocket to just be on a guide rail or in a tube and for motion to start as soon as thrust exceeds weight. The ignition transient of a modern solid rocket motor...

Around a 4-5% increase in density vs surface. Again, certainly measurable, but not particularly large.

Whether ocean water is compressible or not really depends on how much compression you deem to be significant. It compresses even just between the surface and a few feet down, but the amount of compression is really quite small. Seawater has a bulk modulus of around 2.3*10^9 Pa, so at 3km, with...

So with AC power, and particularly grid-scale AC power, it's a little different. You can't look at a single "impedance" at a substation, at least not in the sense of "you feed in a particular voltage and the current is deterministically based only on that voltage". To an extent, that's somewhat...

No, it's a necessary reaction force to the torque being applied to the crankshaft. The caveat here is that a bore offset means some of the reaction torque comes from the pressure force on the head instead, so depending on how much bore offset you have, this sideloading will contribute more or...

I'd never thought about it much before, but yeah, this kinda has to be the case. During the power stroke, the rod is not parallel to the cylinder bore, it's angled, and therefore is transferring a significant side load that must be the primary torque acting on the block. You could mitigate this...

It's worth noting that PAC-3 is almost an entirely different weapons system than the Gulf War era Patriot. It follows the US tradition of keeping the same name for a system even when basically everything about it has been redesigned. Unlike Patriot Classic, Pac-3 has an active radar seeker (in...

That's not really a hole for drag purposes though, that's just where they decided to put the engine inlet. You need to intake air somewhere, and for a single engine supersonic jet, the nose is as good a place as any other*. Also, as boneh3ad said, it wouldn't really help you with drag or noise...

As stated above, most small model rockets use an internal ring that the front of the motor butts up against to prevent exactly this from happening. For larger model rockets, it's much more common for this to be missing, and instead the motors are designed with a slightly larger diameter section...

No, that's just where you're going fast enough to have a decent amount of drag-induced acceleration, giving you fairly clean data. Cd should be (largely) independent of speed in the subsonic regime for a rocket-shaped object, and that's just where your data is good enough to observe that. (For...