Right so it goes like this. I can't claim that what I saw was Aliens or anything significant for that matter. It could have been my eyes playing tricks on me, or it was eye fatigue, or maybe I made a mistake and identified one common place thing as unusual when it wasn't. That disclaimer said..
I have a lot of hobbies and sometimes they shift around depending on my level of interest at the time. At this particular point in my life I had just discovered RC planes and was on a serious kick about them. It was a nice Saturday and that previous week I had just gotten in a Parkzone Micro-Cessna, it's a tiny little plane made for indoors but you can fly it outside if the wind isn't that heavy. Anyway, so I took this plane to my local park. It has a lot of grassy open space, miles of forested trails, a lake and a few gazebos scattered here and there. It was a bright sunny day without a cloud in the sky, deep blue sky and a light breeze.
I was flying the plane around in a lazy circle and I passed it over my head. That's when I saw a tiny little white sphere. It looked like a white BB way up in the sky. I thought to myself, that's really strange, and I put my attention back over to the airplane. I flew it back around and landed it. I then tried to reacquire the little white sphere. I found it after a lot of looking, it had moved (I think, it's hard to tell when things are almost directly over you) North to my position. Then, it started to do the weirdest thing - it started to do loops, each loop was wider and wider than the other one. These loops were horizontal, not vertical (just to clarify), it performed about 5 of these loops when suddenly at the top of the arc the little white sphere shot up at a great velocity straight up into the sky and vanished from view.
My then girlfriend (now wife) was there with me and couldn't see it. It was difficult to see so I'm not surprised she missed it.
Still, it could have been my tired eyes coming up with something - staring at a tiny airplane against a bright blue background isn't easy on the eyes, maybe it was a puffball from a plant caught in an air-current? perhaps it was a white balloon from some kids party that got loose? I have no idea.
Bottom line is that I had a weird "UFO" experience. I wouldn't believe it if you had told me about it until I experienced it myself.