Viking (oz4911)


Viking (oz4911) by Tom Williams 1978 - plan thumbnail

About this Plan

Viking. Radio control sailplane. One sailplane with 2 wings: one designed to be best in light air thermal events and one wing designed to be best at the combined FAI tasks.

Quote: "No one has ever developed an airfoil that would turn 13 seconds on an FAI speed run and then fly in 20 ft diameter circles at 10 mph, climbing out from 50 ft. In other words, sailplanes which are best in light air thermals are not best in speed events.

Well then, how about one sailplane with two wings - one wing designed to be best in light air thermal events and one wing designed to be best at the combined FAI tasks.

Now you can go to any contest prepared for any task under any wind conditions and not have to decide until 2 minutes before your 1st flight which wing to fly. It's like having two entirely different sailplanes yet only having to invest in one radio, one fuselage and tail feathers; also, there is a growing pressure to revise the rules to allow changing wings etc between rounds.

The flat bottom airfoil I designed in 1974 for the Windrifter (oz6700) is known to be the best for light air thermalling. That takes care of one wing. Now I have a semi-symmetrical airfoil which (those who have flown it believe) is the best yet compromise for the combined FAI tasks.

The history of the design of the airfoil is in itself interesting. It all started about 3 years ago when Bill Watson, then working for Hi Johnson, was developing an aerobatic slope ship (Rubber Ducky). Bill asked Hi’s advice on the selection of an airfoil. Hi suggested the NACA 2R,12. So it was. Later Bill used this airfoil on his Goose, a big machine. It is very fast, but is marginal in thermals and really suffers on the launch.

Blaine Rawdon decided to try a compromise between the 2R,12 and a Paragon airfoil (similar to the Windrifter). He split the difference in camber between the two. The result was an excellent airfoil. His Mirage, built light (5oz/ft) launches well, thermals well and is fast, but in my opinion is not forgiving enough to make consistently good landings so necessary in today's contests.

I modified the Rawdon airfoil by dramatically increasing its sharp leading edge radius. The Viking Mark II airfoil is much thicker at 5%, 10% and 15%, but is the same from 30% back. The result - excellent launches (as good as a Windrifter), competitive in thermals and fast, yet easy, to fly and make consistently good landings.

To win in FAI events, the sailplane needs to be:

(1) Large but not too large - I selected 3 meter span.
(2) The aspect ratio should be moderate so as to keep the Reynolds Number about 12:1.
(3) The tail surfaces should be designed to just achieve stability - not like a free-flight.
(4) The weight must be kept down to keep the wing loading below 7 oz/ft.
(5) Large, effective rudder.
(6) Effective spoilers.
(7) Flaps are not needed with 12% high lift airfoil.
(8) It should be attractive - pretty sailplanes fly better.

I proudly present to you the Viking. I hope you enjoy building it - I know you will enjoy flying it. Use the Mark I wing in light air thermal contests and for sport flying. It will go up when nothing else will. When the wind is up and you want to penetrate or go fast, fly the Mark II wing. You will be pleasantly surprised at its performance..."

Quote: "Here is another for the OuterZone, the Craft Air Viking. I reworked the plan for smaller sheets and included the article publisher in RCM May 1978... thank you for providing this wonderful vault for all these old plans."

Direct submission to Outerzone.

Update 12/06/2019: The rights for the Vikiing Mk1 and Mk2 rest with Sky Bench Aerotech, see their site at for more details. As of June 2019 Skybench (under new owner Scott Black) are hoping to have Viking kits available this summer. Scott asked us to add a link to his site here.

Quote: "Certainly, there is no problem with people scratch building a Viking. Is it possible for you to let people know the kit will again be available through Sky Bench? Thanks, Scott"

Update 21/12/2019: Added main model pic in colour, thanks to Rob at SkyBench.

Supplementary file notes

Article pages, text and pics.


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Viking (oz4911) by Tom Williams 1978 - model pic

  • (oz4911)
    by Tom Williams
    from RCMplans (ref:726)
    May 1978 
    118in span
    Glider R/C
    clean :)
    all formers complete :)
    got article :)
  • Submitted: 10/10/2013
    Filesize: 872KB
    Format: • PDFbitmap
    Credit*: JoeHayes
    Downloads: 7937

Viking (oz4911) by Tom Williams 1978 - pic 003.jpg
Viking (oz4911) by Tom Williams 1978 - pic 004.jpg
Viking (oz4911) by Tom Williams 1978 - pic 005.jpg

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User comments

There's nothing on pages 1 and 2 of this plan.
David - 26/09/2022
Is that so? Really? Strange how we all never noticed that, at any point between 2013 and now. Oh, wait. It's ok. I've just opened it again, had a look at it, one more time. Works fine. Great plan. So I guess the problem must be at your end, right?
SteveWMD - 26/09/2022
Hey David, I have windows 10 on a desktop computer and I prefer to use "firefox" browser and I had the same problem as you. when I saw your comment I tryed again to find the cause, and I think I found it. When you download a plan and open it you have to configure it to open in Adobe AcrobatDC and not in firefox as it seems to be the default.
KLH - 28/09/2022
What you have to do is to right click on the link for the plan and, in Firefox, 'save link as'. That will download the plan and you can then open it with whatever .pdf app you are using.
The same approach will work in other browsers - not opening the plan 'on site, but to right click and use the download option.
Daithi - 29/09/2022
Yes indeed. I would suggest first port of call, for people with an issue like this, is the FAQ page at then reading that section which links in turn to the Download Help page at which has a few useful points, starting with: "First, we seriously recommend not using a browser plugin. Use a PDF viewer." Then it covers doing right-click and save as. What really surprises me is when people don't explore the issue they have, or read the help available. Instead they post a comment saying: this file is empty.
SteveWMD - 29/09/2022
Actually, that doesn't surprise me at all.
Jan Novick - 29/09/2022
Terry in Belgium at the F3B contest, I was building the Viking, both wings! He advised me at the time. It flew very well in thermals indeed, also with both wings!!!
Loved it very much!
Noël Rumers - 15/12/2022
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