(no subject)

[camwyn]

This week's ground lesson for the helicopter was focused on parts. I hadn't memorized them all just yet, but I had a good grasp of most of the important ones, so I've got some studying to do before next week. I did, however, get handed a freewheeling unit that had been taken out of service so I could appreciate it properly. The freewheeling unit surrounds the driveshaft at one point; it looks like this:



Those metal parts are pressed outward by centrifugal force when the driveshaft spins, allowing the engine to transmit torque to the shaft that drives the main rotor. In the event that something goes horribly wrong and the engine stops or drops below an acceptable amount of RPM while you're in the air, the metal parts drop back down into the unit and no longer engage the rotor shaft. This allows the rotor to spin freely, which it's gonna do because if your engine's stopped, you're going to start going down- and that means air is going to be pushing upward through the rotor blades- and if you listened to your instructor you know that the instant your engine craps out you have to slam the collective control to the floor so that your rotor blades all change their pitch the appropriate angle for a controlled descent. If you didn't slam the collective, they're probably still angled for ascending flight or hovering, which means you're not going to get enough lift out of them, which means you're going to stall- anyway, the point is that if you did lower the collective when your engine crapped out, your rotor will be able to spin in the wind being pushed up through the blades and thereby generate a basic amount of lift. Not enough for you to go upwards or to stay level, but enough for you to glide downwards at an acceptable angle, assuming you have enough height vs. airspeed to do it safely. (There are charts of this ratio. you probably don't want to see them.) Without the freewheeling unit you'd just have the rotor blades lock up along with the engine and pretty much kinda plummet like a brick.

That bracelet-lookin' thing there is very literally the part that makes you not die.

Comments

[laudre]

If there's an engineering gene, it runs in my family: my grandfather was an electrical engineer (worked for IBM, in the era of computers that took up vast chambers and were distinctly less powerful than the TI graphing calculator I got in 1994), my uncle is also an electrical engineer; two of my cousins (one of that uncle's sons, and one of my youngest aunt's sons) are software engineers, as is one of my aunts (and, ; the younger of that electrical engineer uncle's sons is finishing up his mechanical engineering degree at Clemson (if he hasn't already? I think he added a semester, but I'm not totally clear -- suppose I'll find out at the next reunion), yet another cousin is making at least part of his living fixing smartphones and tablets... you get the idea. (And that says nothing about the parts of my own work that are rather like engineering anyway, what with all the programming and algorithm design...)

All of which is a very roundabout way of saying that the above image and its accompanying description have approximately the same effect on me as looking at a bit of elegant prose, or a subtle and evocative sculpture. It's engaging, yet calming and soothing, despite the situation it's designed to address; I think it's a bit like when I was having a conversation about firearms and the challenges they present to designers with the nascent mechanical engineer cousin I mention above. He found every bit of it intellectually fascinating, because of the ingenuity involved in solving many of the problems, even as his strict pacifist father described such intellectual effort as misguided.