Can X-plane be used to design aircraft?

I've been trying to design aircraft in it, but most of my designs just
crash immediately as it starts in a fraction of a second, even though
most of the details are pretty reasonable (if the engine horsepower is
0, it just sits there, if its 1, it crashes immediately even though the
aircraft weight is 100-1000lbs).

I've been trying to check designs that I could use for RC airplanes.
The airplanes I've tried to design are of reasonable size; 20ft
wingspan, dihederal wings, 500lbs total weight with the CoG at the 25%
from leading edge of the main wing under the fuselage. Also the CoG is
well within the landing gear triangle (including fuel weight). How
realistic is designing aircraft in X-Plane? Can I trust it enough for
simple slow flight in a reasonable-size prop airplane?