Originally Posted by Sparky Paul
I've had a Hershey bar plank that would pulse in flight, but it was deliberate, I could do it on command. No motor at all.
Slowed it up, and it would "pulse" in a semi-stall.
That's called a hyperstall. It's usually caused by the CG being too far forward but can also be caused by excessive control throw. Plank wings are particularly susceptible. They are sensitive to extremely small CG changes. Just a couple of millimeters change in CG could cause it. What happens is that the elevon stalls repeatedly while trying to pull the heavy nose up. It should happen more easily at slower speeds or during positive G commands, however the slow speed hyperstall will happen at higher speeds the further forward the CG is and thus can happen at fairly high speeds. I could see the prop noise on a hyperstalling wing make a pulsing sound as the airflow through the prop rapidly changes angle.