Ken Kochanski wrote:
A couple of recently read articles described different sources for
induced drag.

One attributed the drag to the wingtip vortices ... increased angle of
attack created bigger vortices.

Another said the drag was the result of the lift vector tilting
backwards at higher angles of attack ... creating a rearward 'induced
drag' resultant.

I have heard the tip vortex explanation before ... the induced drag
vector seems plausible ... does it have any merit.

If induced drag is a result of both of these effects ... what is the
relative weight of each?

They are pretty much two different explanations of the same effect. The
tip vortex creates a downwash on top of the wing, which means it has to
tilt back to fly in the downward flow, which tilts its lift vector aft...