Base Actor Components are not affected by gravity.
Actor is simple StaticMesh.
Perhaps you mean that the actor owns a Static Mesh Component - a highly specialised actor component that can simulate physics? If so, with both Simulate Physics and Simulation Generates Hit Events, you can have the OnComponentHit fire when collision is detected:
Do note that you may need to follow it up with a resettableDoOnce node, otherwise the hits will fire rather rapidly. And, of course, the simulating mesh must have blocking collision.
Sadly, onLanded is something only characters can utilise.