About this Plan
Mandrake. Radio control sport model, for electric power.
Quote: "THE ORIGINAL Mandrake dates back some twelve years, and was a semi-scale model based on the Russian YAK high-altitude reconnaissance aircraft. This aircraft was a modification of the Yak 25 Firebar [Yak-25RV], and was allocated the NATO codename of 'Mandrake'. This 65in span model, of which two versions were built, was powered by a 2.5cc diesel and was controlled by four-channel reed equipment on aileron and elevator.
In 1977 I became interested in electric powered flight, and started looking for a suitable design. The Mandrake, with its powered-glider configuration appeared to have possibilities. The plan was redrawn, with a longer span, less sharply tapered wing, an all-moving tailplane, and built-up instead of sheet tail surfaces. The tandem-style undercarriage was eliminated as a weight-saver.
The first flight was approached with considerable misgivings, as the weight of 54 ounces seemed far too much for the Cyclone motor fitted. However, noise and efficiency are apparently not related, and a steady climb away from a hand launch, followed by some mild aerobatics established that the basic design was right, although the roll rate was modest.
This model was followed a year later by the Mark 2. Changes to the design included a thinner wing section (flat-bottomed Eppler 387) to give a cleaner line to the top of the fuselage, larger ailerons, and as an experiment a glassfibre fuselage. This was a single lamination of 175 gm/sq.m glass cloth, and even with the internal formers and crutch system of the Mark 1 retained, was the same overall weight.
The Mark 3 version uses a single layer of 300gm/sq.m glass mat which, although heavier, is much stiffer and has allowed some reduction in internal structure. The Mark 2 met an embarrassing end by folding its wings in the rather turbulent conditions at the Radio Modeller 1978 Electric fly-in. A stronger dihedral brace, and the substitution of spruce for the spar material has cured the problem, and the wing structure should give no cause for concern.
The plan shows the conventional balsa fuselage construction, which, unless you fly off extremely rough terrain, should be entirely adequate. A useful feature if you do happen to damage the fuselage, is that the building jig can be slipped back in place, new formers threaded on and some fresh sheet covering applied with no fear of warping or distorting the fuselage.
Construction of the fuselage is quite straightforward, if a little unusual. All the formers are cut out and carefully drilled on the centre line to suit the jig used. This jig may be of any material, as long as it it stiff enough to resist bending whilst the sheeting is being applied. On the first prototype I used 12mm square obeche, and for the glassfibre versions a length of 6.5mm diameter aluminium rod..."
Mandrake, Radio Modeller, July 1979
Direct submission to Outerzone.
Note: for a modernised version of this plan, see Mandrake Mk4 (oz9810)
Update 17/02/2018: Added complete article, thanks to JeremyCollins.
Supplementary file notes
Did we get something wrong with these details about this plan (especially the datafile)?
That happens sometimes. You can help us fix it.
Add a correction
Do you have a photo you'd like to submit for this page? Then email email@example.com
User commentsNo comments yet for this plan. Got something to say about this one?
Add a comment
* Credit field
The Credit field in the Outerzone database is designed to recognise and credit the hard work done in scanning and digitally cleaning these vintage and old timer model aircraft plans to get them into a usable format. Currently, it is also used to credit people simply for uploading the plan to a forum on the internet. Which is not quite the same thing. This will change soon. Probably.
This model plan (like all plans on Outerzone) is supposedly scaled correctly and supposedly will print out nicely at the right size. But that doesn't always happen. If you are about to start building a model plane using this free plan, you are strongly advised to check the scaling very, very carefully before cutting any balsa wood.
© Outerzone, 2011-2020.
All content is free to download for personal use.
For non-personal use and/or publication: plans, photos, excerpts, links etc may be used, provided that full and clear credit is given to Outerzone with appropriate and specific direction to the original content i.e. a direct hyperlink back to the Outerzone source page.
Unauthorized use and/or duplication of this material without express and written permission from this site's owner is strictly prohibited. If we discover that content is being stolen, we will consider filing a formal DMCA notice.