Akafleig Braunschweig SB 13 sailplane

G

gery

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Yes very hot.....

(Moderator note: new topic originated from here

http://www.secretprojects.co.uk/forum/index.php/topic,5851.45.html)

Some picts....

http://cadcam.e-monsite.com/album-cat-1-67573.html

My model soon finish...

http://www.rcgroups.com/forums/showthread.php?t=791900

My presentation at "Lyon rhino users" 2009...

http://blog.rhino3d.com/search/label/aircraft


soon

gery
 

flateric

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Re: Horten Ho 229 Documentary -

Gery - fantastic stuff, I'm really impressed
 

shockonlip

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Yes Gery, GREAT stuff.

I need to spend some more time looking at everything you have there.

Is there anything on there on the SB 13 Arcus?

If not, that's OK. I did see a lot of interesting sail plane stuff I need to go through as well.

Regards !
 
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gery

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hi shockonlip and thank ,

It's a "in progress project" of "rhoënsperber", an old german glider of 30'....see here..

http://www.rhoensperber.de/

soon gery
 

shockonlip

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gery said:
hi shockonlip and thank ,

It's a "in progress project" of "rhoënsperber", an old german glider of 30'....see here..

http://www.rhoensperber.de/

soon gery

Thanks, actually I discovered that my 'source' had it wrong.

It is actually the Akaflieg Braunschweig SB13.
It looks like a Horten wing design.
Very beautiful!
 

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gery

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Hi shockonlip,

Very very interesting....can you tel me more..???Like "swift" concept..??


What performances..???Airfoil..??

thank

gery
 

shockonlip

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gery said:
Hi shockonlip,

Very very interesting....can you tel me more..???Like "swift" concept..??


What performances..???Airfoil..??

thank

gery

Hi gery,

Unfortunately I don't have much more information.

I first found the aircraft mentioned in "Tailless Aircraft in Theory and Practice" by
Karl Nickel and Michael Wohlfahrt, translated to english by Eric M. Brown.

After your response I did some more research.

I found out that the glider was probably the work of the Akademische Fliegergruppe Braunschweig
or the technical flying club of Braunschweig (sorry if my translation is poor).

There are references that seem to indicate (for example: http://www.ifl.tu-bs.de/bauteilversucheengl.php)
that the SB 13 was a special project of the Braunschweig club: "Flying Wing SB 13 of the Akaflieg Braunschweig".
On this particular page it shows a photo of structural tests being done on sections of the SB 13 wing
at the Institut fur Flugzeugbau und Leichtbau (sorry - bad german font).

Anyway, it IS very interesting. My original interest was to find out if this glider design was available for purchase.
I actually have a few hours of stick time in a US sailplane, many years ago. I'd be willing to get
back into it to fly a ship like this!

Anyway, I'd like to find out more too!

Regards
 
G

gery

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Hi shockonlip,
I searched some infos about this glider and just found some site...

http://www.sailplanedirectory.com/braunsch.htm
http://www.glide.net.au/on-the-wing1/6SB-13Arcus.pdf
http://www.akaflieg-braunschweig.de/prototypen/sb13/

i think it's a "cantilever" wing concept...the cg is placed upper the wing, and i think it's sensible to drive...a little more hard than a traditionnal concept ...more stable on "fly Back"..made for speed "performance" and "acrobatie"

i can't find a cutaway...but the wing is in composite with a foam core..like the "today's concept" of glider...

i found the airfoil number but not the *.dat...i can't test it..
Airfoil HQ 34 N/ 14,83

May be a little dihedral....4°..i imagine a "washout" ,but with the winglets,it's very difficult to see .

for me just a little problem of visiblity due of wing position...

best regards

gery
 

robunos

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Some info on the SB-13...

Designed by the Akafleig Braunschweig, design began in 1982, with the aim of producing a tailless standard class competition sailplane.
It was expected to deliver superior performance, along with easier manufacture and lower costs.

A 1/3 scale R/C model was first constructed, to prove the concept. This showed several unpleasant flying characteristics,
including poor spinning behaviour with the c.g, aft, and longitudinal 'pecking', at forward c.g. locations. Severe flutter was also present.

A complete redesign was therefore effected. The original straight sweepback was changed to a curved form. This requred a curved mainspar, which led to further difficulties. It was constructed from special, high-modulus carbon fibre, which in turn required special construction techniques.

Horstmann and Quast designed the special reflex aerofoils used on the aircraft.

Finally in 1988, the SB-13 was ready for flight testing. The poor handling exhibited by the model was repeated on the full size. In addition, behaviour while on tow was also poor.

Various fixes, including fences, were tried, which improved the handling, and test glides established that the performance was comparable with orthodox sailplanes of the same class. However, the poor handling counted against the SB-13's general acceptance.

A pioneering parachute based rescue system for the aircraft was designed and fitted, which would bring the entire sailplane to the ground in the event of an emergency, however, this was itself, not without hazard to the pilot.

From 'Sailpanes 1965 - 2000', Martin Simons, pp.49-51.

cheers,
Robin.
 

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gery

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Thank robino,
i'm interested by this concept, i 'm surprise by the final poor performances of this glider....i think it's may be the Cg et Ca position to much advanced and too much hight..???
I found in sb 13 data a very small washout, -1,5...i'm curious to see the "parabolic lift curv" it's the possible effect of "flutter"....i imagine a drag coef very interesting
if i compar with Ho VI, the CG of HO VI is middle of wing due at the prone position of pilot...and placed a little in back
I studied and tested the "swift concept "another flying wing , it's was really nice made....a good airfoil design, total sweeped and -8° of washout...but a cg
lower the wing...very securised...with a good "parabolic lift distribution"...

Can you send me a bigger pict please....i would like redraw the airfoil..

Have you got more infos about it "special construction techniques", and a draw of the airfoil..??

thank

gery
 

robunos

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More on the 'special construction techniques'...

As mentioned before, a curved mainspar was required. This was made from special high-modulus carbon-fibre. This brittle material was difficult to impregnate with the resin, so the Akafleig people designed a special machine to do this job. They had to work in teams, one team working the impregnating machine, another laying up the carbon layers in a precise arrangement and order, and a third placing the laid-up carbon onto the pre-prepared wing skins in their moulds.

I tend to agree with you about the c.g. being too high vertically in relation to the centre of drag...as the mainspar passed through the cockpit it ran below the pilot's knees.

cheers,
Robin.
 

shockonlip

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gery and robuno, you have intrigued me to get deeper into this.
Maybe we need a tailless sailplane thread for this.

I started to read my copy of Nickel and Wohlfahrt. I discovered
near the end of the book a "Discussion of Representative Tailless Aircraft".
I feel somewhat foolish I didn't discover it earlier, but I had been puting
off getting into this book till I finished the number of inlet books I have.
Anyway, there is a 3-page discussion of the SB 13 in that later section.

By the way, Dr. Karl Nickel worked with the Horten brothers during 1942-45
and also worked with Dr. Reimar Horten in Argentina from 1951-55, even flying
some of the designs himself.

Anyway since pecking and flutter were mentioned as "issues" of the SB 13,
I read some of the sections in the book on these, and I will say that the book discusses
the SB 13 in the discussions on pecking and flutter, as well as in other sections
I suspect as well, given the sections I read this evening.

There is also a data section on the SB 13.

So I would suggest getting a copy of this book.

Evidently the German aircraft industry helped with the design of the SB 13 as well and
the authors also mention that the DLR was involved.

Of interest to me, the authors also mention improvements they would make in a SB 13
successor model, and their insight on other tailless gliders, including the Ho's, as
compared to the SB 13, are also useful.

I can confirm the washout of -1.5 deg from this books data.
 
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gery

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Hi shockonlip,

It's confirm that the "ideal calculed concept" and the "reality " are sometime different....
Too, the ideal airfoil does'nt exist...the "lift coef" and "drag coef" are a just balance....when you win lift ...you win drag too..
i think a tailless flying wing must be twisted and dihedral too for a good stability and delete the "flutter"...and the cg placed lower the wing for delete picking..
i remember the "Ho IVb" building with the mustang P51 airfoil for his very good drag coef.....but not adapted for flying wing...

soon

gery
 
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gery

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some infos about Ho IV concept...
 

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robunos

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a good stability and delete the "flutter"...

It's easy in prinicple to abolish flutter, you have to make sure that the centre of mass of the wing, tailplane, rudder, etc. is ahead of the flexural axis [or pivot point].
Take a look at the tailplane of a MiG-21. See the 'antenna' projecting forward from the tip? It's not! It's a tube filled with lead, this brings the centre of mass forward of the pivot, and eliminates any flutter.

In the case of the SB-13, you would need similar things pointing forward from the leading edges at the wing-tips. These of course add drag. Another way is to fill the leading edge with ballast, but this takes more mass.

Dihedral has no effect on flutter, rather it produces lateral stabilty.
You're right about stability, the outer part of the wings must be washed out [twisted leading edge down] to generate a downforce that would otherwise be produced by a tailplane.


cheers,
Robin.
 

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gery

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Very interesting view point Robino

I agree with you....i think that the SB 13 was calculed for "touch the limits" and the "graal research" of "minimal drag"..it's need a good experienced pilot...
We can obtain the "magic airfoil" by morphing like the commercial line airplane and the mechanical's wings...just a little info...B2 for "take off or landing" use a moving tail
....
just type "morphing airfoil" or "morphing wings".....and see the videos on youtube..
I don't tested the airfoil again, but i think the chord of roots can be increased and the wing taper too...
I send you this pict of ho IV...you can see the ballast tube in "nacell"...

Regards

gery
 

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robunos

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Gery, you raise some interseting points, which I'll try to respond to, but bear in mind
I'm approaching the edge of my knowledge here, so shot me down if I'm wrong.... ;D

"morphing wings", It's been tried several times, mostly without success, for example the Akafieig Braunschweig SB-11 (this one worked),
Akaflieg Darmstadt D-40, Akaflieg Stuttgart FS-29, and the british Sigma.
In most of the cases the aerodynamic benefits were outweighed by the extra mass, and complexity of the morphing mechanisms.
In many of the cases, in addition, the aerodynamic improvements were less than anticipated, see below.
The exception to this was the FS-29.
In all of the cases mentioned, the idea was to vary the wing loading, to reduce it for soaring in a thermal, then increase it to fly fast across
to the next one.
The main approach to do this was to use large wing flaps. While these_do_reduce the wing loading, by increasing the wing area,
they also _reduce_ the aspect ratio, such that the increase in vortex drag negates the effect of the wing area increase.
This, coupled with the extra weight of the flap system, produced litle or no improvement in performance.
The FS-29, on the other hand, had telescopic, extendible wings. Now as these extend to increase the wing area, they also _increase_ the
aspect ratio, reducing the vortex drag, and improving the performance.
However the weight, complexity, and hence cost problems are still around.

"wing taper", you're right here, tapering the wing will increase the stiffness at the tip, reducing the tendency to flutter, and also reduces the
tip chord, which in turn reduces the vortex drag. It also increases the aspect ratio, at the expense of reducing wing area, which also reduces
the vortex drag. Increasing the root chord only helps in this case, especially with the SB-13, where you can't reduce the tip chord too far,
or you won't have enough room to mount the fins.

cheers,
Robin.
 
G

gery

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Hello robino,

Very nice debat, and i can see your "extended" knowledge about aerodynamic....and aircraft building..
I thanks you very much for your reply and his many examples which i will study with accuraty...

regards

gery

Ps : i got some problems to find the pictures of your examples...can you please tell me where i can see it...

Akafieig Braunschweig SB-11
Akaflieg Darmstadt D-40
Akaflieg Stuttgart FS-29
british Sigma
thank you
 

robunos

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Apologies, Gery , I was pressed for time when I made the last post.
Here are the images....

Just thought of something else regarding wing taper. Tapering the wing tips reduces the mass concentration there,
which in turn lowers the moment of inertia about the rolling axis, which in turn improves aileron response and control.
It willalso reduce the moment of inertia about the yaw axis, which should have some effect, should the sailplane
enter a spin.

cheers,
Robin.
 

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gery

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Hi robino,

Thank for pictures and your view point....

what better concept for you "telescopic wing or retracting flap"..???

regards

gery
 

robunos

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As I said previously, aerodynamically, the telescopic wing wins out, but all these systems suffer from mechanical complexity,
remember, a modern glass sailplane's wings flex in flight a lot more than a conventional aircraft, which leads to greater design
problems, also remember, there is no convenient source of power on board a sailplane, so ultimately all these systems have to be
manually operated, usually while the pilot is busy with other tasks.
To be honest, I'd rather just have simple camber-changing flaps, or even none at all....

cheers,
Robin.
 
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