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Oct 04, 2019, 04:13 AM
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A new 3 meter plank for slope flying

Dear all

I tought, that it was time for something new and updated. So here it is:
A 3meter plank intended for fast slope flying (alla F3F) - so make it decently tough, but light!

First of all I would like to say thanks a lot to many people who have dedicated time to work on this plane as well - Tobias Schill and a lot of others, that have experimented, designed and have shared their knowledge - Uwe Heuer, Tim Harris and so on. Thanks a lot! We would not be there, where we are now.

The main profile is only 7.9% thick and is surprisingly re-number insensitive (down to 100k) and is therefore present trough the largest part of the wing (so no problems with different angle of attack at 0 lift with different airfoils). Only towards the tip, there are 2 more airfoils, which are slightly thinner and the last one less cambered.The main profile shows its best performance in high-speed flight (flap 0), but still has a very high Cl max for tight turns and thermal flights. In between (ie fast glide - best glide ratio ----- there I have made some compromises, but it is still quite good, especially because you have 3m wingspan and a aspect ratio of 14.3 :-)
The main airfoil looks quiet promising and will work - guaranteed.

The profiles are smoothed and can therefore be used in CAD, if one wants to cut out the wing in moulds. In the german forum, some people are already workning on CAD files - so probably we all can profit from the work of others. Here is the link:

The hinge line at 25% is unswept and the lift distribution is elliptical - so the wing looks similar to today's F3F counterparts (except for the smaller aspect ratio). Due to the smaller Ca max of the plank you do not need the bigger aspect ratio and because of the rather low thickness and the very thin trailing edge (!!!) you are sure glad to have a bigger chord depth.

The flap layout is: 6 Flaps!!!! 35cm for the inner one, 35cm for the middle one and 80cm for the rest - this should make it possible to brake fine - more on that issue later. The 3 flaps per wing also helps to make the flap not so long and soft.

Dihedral is 1,5 degrees per side.

Enclosed so the Ranis file with all data (depth distribution, airfoil distribution, etc.) and the airfoils and some overview of the looks. Later I will come up with sizing the vertical stabilizer and its airfoils. The free Ranis Program is available here:
It hink there is also english version somewhere...(another thank you :-)

For the Ranis file (NF3m v7) please change from: .txt to .flg
and for the airfoils: from .txt to .dat
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Oct 04, 2019, 04:34 AM

Very wild indeed ...

I don't think I have ever seen an elliptical plank before Peter - maybe on one with a separate 'fuse with fin' arrangement (like the Rubicon, Warhead etc.)

When you say "light" do you have a target loading in mind?

Awesome looking project - sounds like another great collaboration.

Regards, Steve.
Oct 04, 2019, 05:58 AM
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Thread OP
Dear Steve

I used 2,5 kg for the analysis, but as the main airfoil is rather insensitive to drag rise at lower re, I think it would make a very fun plane (slippery at low cl´s and nice to thermal) also at 1,8kg. For higher usual use ballast, build strong and tips light :-)

Yours Peter
Oct 04, 2019, 07:32 AM

Foils ...

For those who don't have the ability to read the foil files, here's a visual of the three.

They do look pretty sweet Peter - as always
Oct 05, 2019, 12:01 AM
Auzzie built planks
timbuck's Avatar
Very cool mate , perfect for manilla slop feet 2020
Latest blog entry: More colours
Oct 05, 2019, 09:59 AM
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Brake modes

These are the suggestions for the flap settings that can be used as a starting point:

Brake mode;inner[degrees];middle[degrees];outer[degrees]
hard;45 up to 90;-30;-8

The flaps in the middle is always deflected upwards by 30 degrees. Just the deflections of the other flaps change with the brake mode. This should also simplyfy flap programming a bit.
Limiting the upward deflection of the middle flap to 30 degrees also enables to have a bottom hinge line throughout the wing.

Oct 06, 2019, 03:57 PM
Living on the Dark Side.
guitarcher's Avatar
Interesting looking project Peter, I look forward to following the progress.

Oct 06, 2019, 04:10 PM
Entropy is happening!
Jim.Thompson's Avatar

Thanks for starting this thread and working on another big plank. I am a definite plank convert!..................

Reading this inspires me to get back to working on my 4 mtr. built up (part elliptical) plank too.

It would be nice to have it flying for the Borah festival 2020.

Oct 07, 2019, 02:55 AM
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Thread OP
Dear all

There might come some small changes at the give me / os a few days more and then there will be a better version. I think some guys will make the CAD available for everybody - cool!!

vh Peter
Oct 07, 2019, 08:55 AM
Have Wings, will Fly!
dont's Avatar
Fantastic Peter, a slippery 3mt F3F slope ship, can’t wait to build one, I hope the cad files are available when complete, I might warm up the CNC and be able to coax a few to get involved.
Should be good for a fun DS ship as well.

Last edited by dont; Oct 07, 2019 at 09:06 AM.
Oct 08, 2019, 04:21 PM
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Thread OP
Hello everyone

as promised here the final version: The outlines are the same, the main profile also - only the two Strak profiles outside are changed. I incorporated some hints from Franz Heindler and Eberhard Mauk. The position of the airfoils - spanwise - is the same. The tip profile is now a customized one by me and is based on a PW RES, which Eberhard smoothed very well, it is still a little more Rezahl insensitive. Overall, not too big changes, but everything is a little more harmonious. Many thanks also to Tobias Schill for the ongoing sparring and all the others who joined the discussion.
The airfoils and the new files for the ranis programs are available her:

We've already worked on the vertical stabilizer - more on that later.

Now I have a week's holiday!
Oct 09, 2019, 07:11 AM
Have Wings, will Fly!
dont's Avatar
Hey Peter,
thanks so much for your efforts, I’ll see how my German goes with the other thread, Google Translator is your friend!

Have a great weeks holiday

Oct 09, 2019, 08:49 PM
A dream will find you
StevenSeim's Avatar

Not necessarily CAD/CAM ready...

Thank you for making this airframe and data available.

The profiles are not really smoothed and/or CAD/CAM ready. .dat formatted curve sets are not parametric. They consist of straight line segments between fixed coordinate points. Any computer process that averages, truncates, branches and breaks can produce a curve good enough for a hot wire, but not necessarily great for CAD/CAM.

Presented is the posted .dat file curve analyzed as imported, and again on optimizing. The optimized curve is what I would build a surface from.

That said, the wing with optimized profiles and surfaces is posted in .IGES format to the Goodies page of Help yourself. I did not render the fuselage and fin, as that is often personally interpreted.

On the machine now is a super ultra speed slope/DS wing 64" span. 19" root chord 6% thick. 7% thick tip with elliptical (not linear) washout. Top aligned wing with irregular leading edge.
Last edited by StevenSeim; Oct 09, 2019 at 09:17 PM.
Oct 10, 2019, 12:42 AM
Entropy is happening!
Jim.Thompson's Avatar
Originally Posted by StevenSeim
......................... elliptical (not linear) washout. .......................
What is this please Steven?
Oct 10, 2019, 03:35 AM
A dream will find you
StevenSeim's Avatar

Non linear washout...

Washout plotted as a curve instead of a straight line. This Horten IV scale model leverages elliptical washout. Somewhat easy to present as this airframe leverages a lot of washout. (6.7 degrees plus V-angle)

In the lower of the three planform views viewed from the top you can see the washout schedule as originally plotted by the brothers. As opposed to that schedule being a straight line (airfoil station) end point to end point, the entire trailing edge is a single curve plotted through those declared points. The result is a curve when viewed from the front or an oblique angle. If linear washout, the trailing edge curve would appear faceted.

Somewhat difficult to present in a wing with only a small amount of washout, but it can be seen in the third wireframe of this specific example, in yellow seen in perspective view. With the trailing edge plotted, the station sections are positioned and aligned accordingly.

You can see it in the side view if you stare long enough. It is subtle.
Last edited by StevenSeim; Oct 10, 2019 at 05:51 AM.

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