I would like to contribute with some facts about the wake turbulence. I refer to Spanish regulations, but to my understanding they closely follow ICAO recomendations, so they should be about the same everywhere.
Wake turbulence is a by-product of lift, so the most important factor that influences it is weight. Wake turbulence categories are as follows:
Heavy: MTOW of 136.000 Kg (300.000 lbs) and up
Medium: 7.000 Kg (15.400 lbs) to 136.000 Kg (300.000 lbs)
Light: 7.000 Kg (15.400 lbs) and less
Controllers aply a number of separations based on these categories. A typical one is waiting 2 minutes after a take-off/landing of a heavier ACFT.
But the importance of wake turbulence varies greatly with the shape of the wing. That's why some Medium weight ACFT are actually considered Heavy for wake turbulence. The most known of them is the B757, but others have been added to the list recently, like the B737-800.
Recently they have also added a new category "Super Heavy" for the A380. I am inclined to believe Airbus' claims that the A380 wake turbulence is no worse than the B747, because this was one of the requirements they set before they even started to design the new airplane.
So, what is wake turbulence?
Wake turbulence is composed mainly of jetwash and wingtip vortices. Jetwash is strong but has low range, so it is a hazard in the Apron, when you walk or taxi behind a jet. When in flight, we are speaking about the wingtip vortices. They are generated by the pressure gradients between the intrados and extrados of the lifting surfaces, and form a counter-rotating vortex pair that can persist for over three minutes. A small airplane caught inside one of these vortexes can be easily put upside-down, and full aileron deflection will not be enough to counter it.
Vortices are stronger with heavier weight, slower speeds and clean configurations. Helicopters generate stronger vortices proportional to their weight. They depend on lift, so they start with the rotation and end with the front gear touchdown. They move with the air mass and tend to dissipate quiclky in strong winds, but they will persist for a long time in calm wind. They descend at 400-500 fpm and stabilize about 1.000 ft behind the flight path.
So what should pilots do? Take off and land always 2 minutes after heavier aircraft, more if the wind is calm (controllers will understand) or if taking off from an intersection (more forward than the previous ACFT). Take off before the point where the previous ACFT did and with a higher climb angle. Land beyond the point of the previous ACFT and with a higher glide angle. Try to be higher and/or upwind of the flight path of the previous heavier aircraft.
P.S. Dave, I am a fan of you. You know a lot about airplanes, you take beautiful pictures, you definitely can write, I laugh out loud listening to you irony and you pass on your joy of life. I want you to be around for a long time. So please, don't try to land behind a heavy aircraft. Always fly higher than their path. Take off behind and land beyond where they did.