From John Henson
This little American Kestrel came flying straight at me, and for a split second I wasn't sure if I was about to get the shot or get buzzed!
They're tiny, unbelievably fast, and almost impossible to predict. Capturing one head-on like this takes a little luck, a lot of patience, and complete trust in your autofocus.
Those little nubs sticking out of our bird friend's wings here are something very special. Those are the alulae, also called "bastard wings", and they are the birds equivalent of thumbs, with 3-5 flight feathers on them.
This may seem somewhat insignificant, but they serve a very important purpose. They are so important that we humans stole the idea.
I'm no aviation expert, so perhaps someone may be able to provide more details, but the alulae are used during takeoff, landing, and certain aerial maneuvers where the main wings no longer produce enough lift, what would be called a "stall" in an aircraft. It basically keeps them from just dropping out of the air when they're moving too slowly to maintain adequate air passing over the wings.
So stability in this case means the force trying to make the plane fly straight and level; stability greater than 0 means if the controls were locked in place, the plane would try to fly straight and level. Less than zero means it's constantly trying to turn. This is good if you want maneuverability and making constant minor corrections is fine.
That makes sense. Refreshing myself on the X-29, I remember its inherent instability being something of note. Thinking about it now, I can understand that being something desired or undesired depending on the outcome one wants. I recall learning about countersteering a bicycle to get better turning by inducing instability, which sounds bad on its own, but otherwise one doesn't get the maneuverability to not crash on sharp turns. Meanwhile, the X-29 wiki said that should the stability systems that make 40 adjustments per second suddenly fail for some reason, basically the thing would become so unstable it would disintegrate before the pilot could even think of ejecting.
Yes, as long as you are holding the handlebar forward, the bike's stability is negative; it wants to fall over. If you release the handlebar, assuming you're going fast enough, the bike will pick itself up. This is easier to feel in motorcycles where the forces are greater.
I remember a number of people referring to even walking as just controlled falling. Thinking about all these examples really makes me consider how much we purposefully lose balance without even considering it! Next time I'm clumsy, I will have to say I'm just working on experimental forms of stability control. ๐