[dpansier]

Anyone familiar with the drag reduction work of David Birkenstock?

His patent (7,614,588) and patent application (US 2010/0078522 A1) describe methods to reduce drag on small personal aircraft.
Figure 13 and 14 appear to be a RV-8 aircraft.

From the patent application:
[0048] FIGS. 13 and 14 show two exemplary embodiments of the present invention. One such embodiment incorporating pressure thrust pressure could be utilized in aircraft focused on climb performance. In such designs as the RV-series, Nemesis NXT and/or Lancair IV, for example, the existing aircraft could be optimized for pressure thrust with minimum difficulty. For example, in FIG. 13, concave-shaped steps 1300 and 1310 may allow for 100% of fuselage 1320 Width to be devoted to pressure thrust. In such an example, modifying wings 1330 and 1340, empennage 1350 and fuselage 1320 can yield a phenomenal total power savings.

Any thoughts on this?

 

[scsmith]

Good Grief!

Don't get me started!

For relevant science in the technical literature, see the following:

Stratford pressure recovery

Active flow control

Coanda jet

Goldschmied propulsion


Summary: In the absence of any active flow control to prevent separation, the Stratford criterion describes the steepest (most abrupt) closure on the aft portion of an airfoil (or by conceptual extension, any body) that can be achieved without flow separation. Shapes that approach the limit defined by this criterion achieve a large degree of pressure recovery. The steepness of the closure that can be achieved is dependent on the Reynolds number of the flow, with higher Reynolds number flows tolerant of more aggressive or abrupt closure. Also newly formed turbulent boundary layers, with laminar transition occurring just upstream of the beginning of the recovery region, are capable of more aggressive closure without separation.

Goldschmied propulsion is one scheme of achieving greater pressure recovery by active flow control. Generally either jet blowing near the onset of the steep closure region (a Coanda jet) or suction over the actual closure region can be used to maintain attached flow where it would otherwise separate. Goldschmied used the accelerating flow on the intake side of a ducted fan to provide the favorable conditions to prevent separation, and at the same time, allowed the ducted fan to operate without the normal intake momentum loss (usually called ram drag). The result has the potential for low fuselage drag and high propulsion efficiency. Real-world applications are fraught with difficulty.

 

[PCHunt]

In English please!

 

[chazking]

It's a brilliant idea, but near impossible to achieve (particularly, for the laity!).