Prevailing lack of inertia in the flight model, opinions?

Since helicopters came out I almost stopped flying planes.
But twice now I have started propellerplanes on a runway and the planes behaves crazy!
Its like the flightmodel has changed since I drive them last!
And this paperplane is a good metaphor for the behavior.
Yesterday a plane flipped over during take off because it was so twitchy!
Never happend before!