Michel,
-> I've been to Pleso for about half an hour last year. There is a dirt road running along the airport fence and
runway. From there you have an overview of the military platforms on the left side and the civil apron on the right. If a hangar is open you
could read something with binoculars. I didn't have any problems there.
But you are in very open terrain. This is past the bridge over the highway Stefan was talking about.
-> Zagreb Lucko was a different story. I was send away there only seconds after I parked my car. But from the flying club you can look onto the platform.
-> Zadar: One serious advise: stay on the roads. Mines!!!
I was there in the weekend. There is a road running through the airfield. But there was nothing to see except for some Piper-like stuff...
Don't know about flying-activities in the weekend in general. But with the increasing chance of forestfires...they have some of those brave yellow fella's, you know...
regards,
Arco