[ConnClark]

Originally Posted by Frank Lee

The "perpetual motion" thing pops up with some regularity.

Sure there is already internal drag through the engine compartment. I think a prop driven device would only add to it.

A grill block adds drag to engine compartment too. The fact that the turbine adds drag to the internal flow makes it the equivalent of a grill block. This isn't perpetual motion. Its recovery of energy that is going to waste. Smokey Yunick did something similar in stock car racing with a propeller on his alternator before Nascar outlawed it (back then cars didn't have all the electrical load they have today).

Originally Posted by euromodder

The basic squarish wingtip design of the day created vortices and was so inefficient that the wingtip pods bettered it so much, it still reduced drag despite the turbines.

Wingtip Vortex Turbine Investigation for Vortex Energy Recovery

The wing tip pods had nothing to do with it. The plane was tested with the pods and no turbine blades as a base line. To quote the abstract you linked to "The turbine, driven by the vortex flow, reduces the strength of the vortex, resulting in an associated induced drag reduction."

The inefficiency was already built into the baseline vehicle.
This experiment won back some of that energy.

It's better to avoid the inefficiency to start with, rather than try to recover some of the wasted energy later.

A car with a radiator requires an in efficient design to keep the engine cool. You can't avoid it. Its better to recover some energy since your stuck with the inefficiency.

Note: Aircraft manufacturers are still looking into this and still paying people to study it. Why? Because an engine is more efficient if it doesn't have to provide power for auxiliary systems.