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Mar. 21st, 2016 08:44 amNo flight lesson this weekend. The instructor had to cancel due to family stuff. I spent the time instead studying the chapter of the Pilot's Handbook of Aeronautical Knowledge on flight instruments and how they work.
Here's a thing you should know: instruments suck.
Well, okay. They don't, not really. But the instruments that take up the control panel of your average flying machine- the book is written primarily with fixed-wing craft in mind, us rotorheads have to make do with some adaptations- are all fundamentally approximations. They're crude human attempts at building sensory apparatus based on the phenomena we can manage to measure. The airspeed indicator, for example- that measures differences in air pressure between a tube that pokes out of the side of your aircraft, or occasionally the inside of your aircraft, and the air pressure being forced down the aircraft's tiny, tiny pitot tube of a throat by its forward travel. You can lose the ability to see how fast you're traveling if a single piece of crap happens to wrap itself over one of the openings involved. Your compass only works completely accurately if you're flying straight and level and if you're on a particular heading; if you're heading east or west, and you accelerate, your compass will swear on its very soul that you just turned to the north. If you're flying someplace where the air pressure is high and you fly into a low-pressure air mass it will result in your altimeter lying to you, because as far as it can tell, you just experienced a swift climb in altitude; it does its job based on air pressure differences and it really has no idea whatsoever where the ground is. Same deal if you go from warm air to cold air, since that's 'oh hey, the air's way denser now, we TOTALLY changed altitude' time.
And don't even get me started on the number of places along the coast of Maine with 'yeah, your compass is going to lie to you EXTRA HARD' notations on the map. Seriously, there's a bunch of islands that'll screw your compass up by an extra ten degrees on top of everything else you have to correct for.
Anyway, the point is: humans try to build things that let them perceive the world safely and correctly, but every single one of them has to be corrected in some way, or at least have its many limitations acknowledged and compensated for. It's kind of amazing that our machines let us manage as well as we do.
Here's a thing you should know: instruments suck.
Well, okay. They don't, not really. But the instruments that take up the control panel of your average flying machine- the book is written primarily with fixed-wing craft in mind, us rotorheads have to make do with some adaptations- are all fundamentally approximations. They're crude human attempts at building sensory apparatus based on the phenomena we can manage to measure. The airspeed indicator, for example- that measures differences in air pressure between a tube that pokes out of the side of your aircraft, or occasionally the inside of your aircraft, and the air pressure being forced down the aircraft's tiny, tiny pitot tube of a throat by its forward travel. You can lose the ability to see how fast you're traveling if a single piece of crap happens to wrap itself over one of the openings involved. Your compass only works completely accurately if you're flying straight and level and if you're on a particular heading; if you're heading east or west, and you accelerate, your compass will swear on its very soul that you just turned to the north. If you're flying someplace where the air pressure is high and you fly into a low-pressure air mass it will result in your altimeter lying to you, because as far as it can tell, you just experienced a swift climb in altitude; it does its job based on air pressure differences and it really has no idea whatsoever where the ground is. Same deal if you go from warm air to cold air, since that's 'oh hey, the air's way denser now, we TOTALLY changed altitude' time.
And don't even get me started on the number of places along the coast of Maine with 'yeah, your compass is going to lie to you EXTRA HARD' notations on the map. Seriously, there's a bunch of islands that'll screw your compass up by an extra ten degrees on top of everything else you have to correct for.
Anyway, the point is: humans try to build things that let them perceive the world safely and correctly, but every single one of them has to be corrected in some way, or at least have its many limitations acknowledged and compensated for. It's kind of amazing that our machines let us manage as well as we do.
