On Sat, 21 Mar 2015 13:02:34 +1300, Dave Doe wrote:

In article ,
, Larry Dighera says...

Mentioned in the NASA video at the YouTube link below are the reasons this
revolutionary technology are an exciting step forward for aviation.

* Four horsepower per pound are achievable with electric systems. This is
comparable to turbine engine performance.

* Ninety-five percent efficiency is possible with electric propulsion
systems compared to 45% turbine engine efficiency. This translates into
reduced fuel costs and emissions.

* The technology aims to achieve an 80% reduction in energy requirements.


Notice the rear-facing wing-tip engines on this concept drawing:
http://www.aero-news.net/images/content/aerospace/2015/Airborne-NasaLeapTech-031915.jpg.
Is this a means of overcoming the drag produced by counter rotating wing-tip
vortices inherent in virtually all current aircraft?

I don't think so. Have a look at this...
https://www.youtube.com/watch?v=QKCK...PLCdGBvDMYlr8-
tm7kQibn0iDCBbgpLbX6

https://www.youtube.com/watch?v=QKCK4lJLQHU

Dr. McLean, who earned a Ph.D. in Aerospace and Mechanical Sciences from
Princeton University, is discussing aeronautics in terms far beyond my ability
to comprehend. That said, at 39:50 minutes into the video Dr McLean does
mention that a propeller placed at the wing tip is capable of reducing drag to
a limited extent. Therefore, if one is using the propeller to produce thrust,
and is able to also reduce drag to some extent at the same time, I'd say that
is a win with little cost.

Perhaps you have a deeper understanding of the issue, and are able to provide
an alternative explanation for the rear-facing propellers NASA has chosen to
place on the wing tips.