Maybe a simple comparision is in order: ask "What makes a Ram Air Turbine function?" Answer: "A transfer of energy". The aircraft's kinetic energy is being transfered into keeping that prop and all its associated hardware rotating. It's got to come from somewhere, right? No energy transfer, no rotation.
Dan Winterland: That was an outstanding explanation on the merits of doing forced landings the military way. I saw that same method in some USAF flight training manuals I got hold of a few years back (I've never heard it called the "Constant Aspect" technique until you mentioned it, but the concept's the same). Definitely beats the hell out of the "square corners" technique the FAA's Flight Training Handbook teaches. Simple enough that I was able to figure it out from the text and then use it the next time I had the power pulled during a dual session.
The military 360º Overhead Approach seems to work pretty well for light aircraft also. For the Citabrias and Decathlons I used to fly, I personally felt more comfortable using this method than the civilian Rectangular Pattern.
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Contrabanderos may run, but they can never hide!