On Wed, 13 Dec 2017 11:46:30 +0000 (UTC), Kiwi User
wrote:

On Wed, 13 Dec 2017 01:27:16 +0100, Andreas Maurer wrote:

Hi Andras,


I'm rather worried about spanwise flow originating at the wing root
(similar to the SB-13) - but let's wait and see. The guys (and gals)
know their stuff.

I notice that initial drawings put the wing at the bottom of the pilot's
pod, but in the 1:2 model its just below the canopy rim. Was this for
wing clearance or aerodynamics?

Several causes:
- mainly wing tip clearance: The wing tips are far behind the landing
gear and dihedral is only 2 degrees, they come down when the nose goes
up, creating ground clearance problems

- with the wing out of the way lots of space for a really strong nose
gear (one of the famous weak points of the SB-13)

- the wing spar is now over the knees of the pilot, leaving plenty of
easily accessible space for the controls, mixer and Haenle-type stick
between wing spar and instrument panel

- lots of space for the pilot (I'm 6'7" and fitedt comfortably in the
prototype fuselage on the Aro aviation fair)

In their own (German) words:
https://akaflieg-karlsruhe.de/ak-x/aerodynamik/



I'm a little surprised, too, at the quite minimal root fairings. Is this
what you were referring to when you mentioned spanwise flow at the root?

Well, aerodynamically speaking there is no need for wing root fairings
as long as the complete wing root is in an area of pressure rise.
On a conventional glider the wing is in the area of pressure loss
(aka: where the fuselage gets thinner), resulting in the need for a
wing fairing.

I'm not the designer of course, but I think you can be sure that we'll
get to know all the details in the future.

What I'm referring to can be seen on the SB-13:
http://www.airport-data.com/aircraft...00724103.html#

Look at the little red wing fences - afaik they had to be intruduced
to tame handling (stall?) characteristics.

(Bert: Dein Auftritt! Habe das SB-Buch gerade nicht vor mir, wo der
genaue Grund beschrieben wurde).


It would be interesting to see flow visualisation round them. Though, as
you say, the guys and gals know their stuff, so maybe cleaning up the
wing roots is being left for full size detailed design. After all, the
1:4 model had nothing except a couple of sensor probes at its root, so
just adding the pod was quite a big step aerodynamically.

Definitely.

BTW:
This is the project page of the AK-X 1/2 model:
https://akaflieg-karlsruhe.de/tag/12-modell/
On the spin onboard video you can nicely see how the inner flaps work
as elevator.