I participated in one of the early reports of wake turbulence behind the B 747. This was in late 69 or early 70, in Hawaii. I was in a 172 and cleared to land behind Pan Am Clipper One, a brand new 747. Clipper One and Two circled the globe in opposite directions, if I recall correctly.
In any case, there was no such thing as a wake turbulence delay or even caution. Wake turbulence was simply not well understood till the 747 came along.
On short final, my airplane rolled hard to the left, and, being a VERY low time PPL kinda guy, I pulled. Fortunately for me, I just did a knife edge departure from the pattern, didn't hit anything and managed to escape unscathed.....other than having to clean my undies..
Tower asked me "What just happened to you?" in a non threatening manner. They cleared me to re-enter the pattern and land, then asked me to call the tower chief. I was REALLY scared then. But, the chief just listened to my description of "The hand of God smote me" and said that there was information going around about this kind of stuff behind Pan Am's 747s. He thanked me, and later I got a call from someone at NASA. A month or so later the new wake turbulence procedures came out.
Last week, I was instructing in a Cub behind a C 172, on a flat calm (I know, hard to believe here) day, and as the student pitched into the flare, we got a pretty good roll going. Student asked "What was that?" Wake turbulence, that's what. Even a Cub makes a wake, and hit it "just right" and it'll roll you.
A real "heavy" as opposed to a Cessna 172 heavy, will do a little more than a slight roll, however.
MTV