A while  back I proposed using excess energy in the exhaust stream to
drive a  turbine which would provide boundary layer control (suction)
for  better takeoff and landing performance.  I still think this  isn't
a bad idea as it might be quite a bit simpler than a turbo  compound to
construct and implement.  I admit that it would be  important to think
out what would happen if there were an engine  failure while utilizing
such a system..

Similarly, I  think it would be worth exploring what cruise drag
reduction might  be afforded by applying active boundary layer control
for parts of  the airframe that are difficult to streamline properly.
We were  looking at a pusher design recently on here which had the prop
mounted too close to the widest part of the fuselage for airflow
without separation.  Active boundary layer control could improve  the
ability of the air to stay attached as it follows the contours  of the
fuselage.

The consequences of a turbo failure  would be poorer cruise efficiency,
but nothing  dangerous.


Regards,

Matt-

You  can do the same thing by adding Fowler flaps, leading edge
slats and  cutting down the wing area. Safer as they will not go
out if the  engine dies. The best example is the Mitsubishi Mu-2.
http://en.wikipedia.org/wiki/File:Mitsubishi_Mu-2.jpg


The  ultimate is VTOL. No wing area to speak of.
http://www.rotaryeng.net/VTOL.html Least safe :)

Paul  Lamar

Fowler flaps don't help cruise speed except in that they  might allow
for lower overall wing area.

The MU2 doesn't exactly  have an exemplary safety record..  Part of the
reason is that it has  such low wing area that it's easy to get behind
the power curve - where  induced drag is rising rapidly.  I recognize
that part of the MU2's  problem has been pilot training - I'm not
calling it unsafe outright, just  unforgiving.

Fowler flaps add significant weight and complexity to wing  design.
However, if there were a targeted location on the airframe that  would
be difficult to clean up (fair) but which would benefit from  boundary
layer control, driving it with the turbo gives you the opportunity  to
use some of the horsepower in the exhaust stream without having  to
design a complex reduction unit.


Matt-

I understand  Matt. Historically suction devices on wings get
plugged up. Blowing is  another option and the F104 had that.

Paul Lamar

Jim Bede With the XBD-2 and others have done the suction wing idea for
boundary layer control. The plane also had twin engines driving a ducted fan
and  fiberglass main gear legs

_http://www.bedecorp.com/designs/xbd2.htm_


The F-4 used compressor bleed air blowing from manifolds exposed when
leading edge droops extended.  Also from the trailing edge, blowing down  the
back of the flaps that extended to almost 90 degrees. So if you are  short on
wing area, and weigh 74,000 pounds, its a good idea.

Lynn E. Hanover