"While climbing through 8,000 ft above mean sea level, the UAV experienced a series of uncommanded turns. The UAV self-recovered from the first two uncommanded turns however, the third upset resulted in the aircraft entering an uncontrolled spiral descent. Despite attempts to return to controlled flight, the UAV sustained an in-flight break-up."
I can only imagine the control systems that go into these gliders.
> I can only imagine the control systems that go into these gliders.
Fun fact, most planes are inherently stable, just like paper planes. If there is a disturbance, they will self correct most of the time.
For example, glider pilots, if they do something stupid, are instructed to just let go of the controls, and the glider recovers on its own very quickly. Few ways this can go wrong: the wings start to "flap" by vibrating to a resonant frequency, in which case they need to change something, and also spiraling down towards the earth: not because the plane would not recover eventually, but because it might experience high forces that destroy them before recovery can happen.
Few planes are inherently un-stable: meaning they cannot keep flying without constant input, only examples I know of are fly-by-wire modern fighter jets (4th generation onward) and planes with weird shapes like the B2 bomber.
I don't think there is too much control put into these gliders for second to second operations, they are probably just letting it fly forward, with the control being: point it in a very general direction and don't lose contact with it.
Almost all gliders are fairly strongly spiral unstable. Because of the long wings the outer wing in a turn is moving significantly faster than the inner wing. As a result the outer wing generates more life than the inner and the bank will increase until the glider is in a spiral dive. It is normal during a steep bank in a glider to have to apply a significant roll input to prevent the bank from increasing. So not only will a glider not spontaneously recover from a spiral dive, it will put itself into one by itself.
That is why recovery from a spiral dive is something that a glider pilot usually has to do as part of a demonstration of proficiency. I get to do one every year as part of my seasonal check flights.
These high altitude, long duration UAVs have really long wings. So the control system would have to work to overcome the tendency to overbank. At some point the tendency to overbank might overcome the authority of the controls.
As you said, stable is not necessarily good. A fully developed spin is incredibly stable to the point where you might not recover from it even if you try, but it also reliably takes you into the ground with too much vertical speed.
For conventional layout aircraft, with a suitably sized tail, stable mostly means nose-heavy. Which implies constant negative lift on the tail, and corresponding excess positive lift on the wings. Which means additional induced drag. All of which adds up to an efficiency and performance penalty.
And if the tail controls aren't suitably sized, then the pilots won't have enough control authority to move of of the very stable ballistic arc the plane wants to travel on.
I guess what I was trying to say is that a conventional aircraft has multiple stable lift-generating modes. Aside from going forward at the front side of the power curve there's also the spin. Both of these are implied by the design. One is desirable and the other is not.
For what it's worth I found your whole comment easy to understand because it was well constructed and very logical, so much so that I didn't even notice the typo because your intent was so clear that I subconsciously auto-corrected it.
Fighter jets and the B2 are by no means inherently stable, in fact they're inherently extremely unstable relative or to earlier designs. It's just that the fly by wire systems make them fly stable.
It was two typos in a row. Mysteriously missing "un"s, "il"s, "im"s, "in"s, "ir"s, "non"s and "not"s change the intended meaning to its opposite unintentionally. Happens to me all the time. Touchscreen kb?
"While climbing through 8,000 ft above mean sea level, the UAV experienced a series of uncommanded turns. The UAV self-recovered from the first two uncommanded turns however, the third upset resulted in the aircraft entering an uncontrolled spiral descent. Despite attempts to return to controlled flight, the UAV sustained an in-flight break-up."
I can only imagine the control systems that go into these gliders.