Slingby Hjordis, scale 1:5 with e-drive

[bocorvin]

Hello everyone,

Why a new glider? I enjoy building, but also because I had some tense moments with slope flying, trying not to land down the slope. Changes to our field had also made towing more difficult. With some mixed feelings, I thought about a scale glider with electric drive. I found that a difficult compromise. Fortunately, there was is coincidence and also Martin Simons' book. It featured the predecessor of the Slingsby King Kite, the Hjordis.
The Hjordis has an almost round fuselage, which I thought would be perfect for a e-drive.
First, a some notes about the real Hjordis, a prototype, only one built. In England, the development of gliders was less spectacular than in Germany. Due to the peace treaty after WW1, a great deal of energy was put into the development of gliders in Germany. In England, this changed in the 1930s, resulting in this more or less successful attempt. Only one Hjordis was built, and it had its shortcomings. For the full story, see the link below.
https://all-aero.com/2025/04/11/slingsby-hjordis/













The designer, Buxton, sought optimal performance and drew an extremely slender round fuselage with a pylon on which the wing was mounted. The pilot just about fits (not 😊) and the cockpit canopy fitted nicely to the pylon. The wing was beautifully slender, with a chord of 117 cm at the root tapering to 30.5 cm at the tip, with a wingspan of 1555 cm and a aspect ratio of 21. However, it had a thick and curved profile, from Gottingen 652 at the root to RAF 32 at the tip. It was a fairly revolutionary aircraft for its time. To be able to reduce speed, Buxton had come up with the idea of making the rudder double, which could then be folded out. There were other gliders (the Elefant) that tried this, but unfortunately it did not work. As a result, it had no spoilers or anything like that, which in hindsight was a great loss. I am definitely going to install spoilers.
Another problem was the very small cockpit. The fuselage was 660 mm in diameter and the pilot, Phillip Wills, suffered from cramps and splitting headaches in that claustrophobic and hot cockpit. By scutting out a few “chunks” out of the fuselage at shoulder height, he was able to sit a little better and the ventilation was also improved






I haven't read anything about getting cold shoulders... Martin Simons' book tells the whole story beautifully.
Now for the model. I am very happy with the size of my Nemere, scale 1:6, wingspan 330 cm. When I build the Hjordis on a scale of 1:5, it will have a wingspan of 311 cm and weigh between 2.5 and 3 kg. Hopefully it will be possible to launch it by hand and it will also be easy to transport. Because the wing is mounted on a neck, a modern profile is not so noticeable. The wing is covered up to the rear spar with ply, then transparent to the TE, as can be seen in this photo.






I started drawing the fuselage, with Devfus, based on the existing drawings. I couldn't get the nose to match the photos. In the photos, the nose looked more pointed than in the drawing, so I decided to make the nose a little more pointed, which also meant that the e-drive with spinner would fit. A little bit of cheeting is allowed now and then.....









A three-dimensional image of the fuselage gives a good impression and, no, it's not a submarine! The internal reinforcements for the pylon, battery and removable cockpit can also be seen here.





I want to make the frames from 3mm light plywood, with 3x3 pine stringers.
I plan to build the fuselage on a jig, like my other models. First sheet the bottom with 0.6mm plywood, remove the fuselage from the building jig and then sheet the top.
I was enjoying myself and decided to draw the wing as well, using Devwing.
For the airfoil I wanted to choose HQ 2.0-9 at the root to the aileron, then tapering to HQ1.0-1 towards the tip, in the hope of avoiding tip stall.










It would be nice if I could get a model that flies well in thermal, it is all flat over here, no slopes.
Since I was sitting at the computer anyway, I used Ecalc to calculate the main spar, 2 mm x 20 mm spruce upper and lower, which would give it a strength to withstand 14G.

I was also able to calculate the wing connector and opted for a rectangular tube that fits nicely into the spar, 12 mm high x 15 mm wide. Made of UD glass with epoxy, it should be able to handle 20G, which will not fail, I presume.

To be continued,

Vincent (DB)

[VincentB]

Salut Vincent
On va prendre du plaisir à suivre ta construction merci de nous la partager

[sebastian92]

Vincent D. l'infatigable
You said : "I enjoy building" : I'm not going to tell you otherwise
ça a l'air vraiment génial ces logiciels devfus & devwing !
Un jour il faudra que je regarde si c'est compatible pour un Mac…
Nice to follow your new building !
Seb

[bocorvin]

Vincent et Sebastian,

Merci pour votre reaction aimable (nice words)

Vincent (DB)

[bocorvin]

Bonjour a tous,

As I planned, I started with the stabilizer and the vertical stabilizer at the same time.
There aren't many drawings of the Hjordis; Buxton left many details that had to be worked out in the workshop, so I can do that too!
I drew the stabilizer in Devwing, making the D-box slightly wider,









I'll adjust the angled root rib manually.

The stabilizer moves entirely on two pins. I still had some thin-walled 3 mm stainless steel tubing, which I'll use as a holder for the two "wing" joiners : the rear one as a pivot point and the front one to adjust the stabilizer.

I chose the HQ-10 symmetrical profile, and Adri milled beautiful balsa ribs










I immediately applied Maarten's tip for the LE (from the Dutch forum). The TE is constructed of 0.6 mm plywood top and bottom, with a 1 mm spruce strip between them at the front, which is quite sturdy. The ribs are quite fragile, but that's improved after gluing on cap strips. The tips have a balsa core, then covered with plywood. I can sand without any worries, because this plane is painted, not clear-coated.









The stabilizer still needs some finishing, but I'm going to make the vertical stabilizer first.


The vertical stabilizer consists of a small fin that extends under the fuselage into the tailskid. The top section houses the mounting and controls for the stabilizer.
I tried to draw it in Devwing





I adjusted the thickness of the HQ symmetrical profile so it could be properly positioned in the tailboom.
I also drew only the 1mm holes for the continuous hinge pin in the ribs, not the semicircle that should be used for a round leading edge. This resulted in too many loose parts, and I couldn't find anything in the program to solve that.
I made the base on a modified building board.





I made the tip and D-box of the rudder in the same way as I did for the stabilizer.
Then I glued 1.0mm plywood reinforcement plates to the ribs to form the hinges.





Now I could cut the rudder loose and make the round the nose. I bent plywood around a round pipe with boiling water to make the it. I first glued that to one side with cyano





and once that was hard, the other side.

I did the very tapered bottom part separately with





Then I cut slots for the hinges and fittings.





Before I sheeted the fin, I made the elevator lever. I sawed it from 1.5mm epoxy sheet, but unfortunately, I had to modify it to allow for 10 degrees of up and down travel. Here's a picture of the botched version. I used the thin walled 3mm stainless steel tube as a hinge for the lever.





Now I could cover it, using lots of clamps.





The tail surfaces completed









This whole thing weighs 115 grams

Vincent (DB)

[sebastian92]

ah super Vincent !
tu as commencé ta construction, ça fait plaisir de voir de nouveaux projet à l'œuvre
à suivre avec plaisir

[bocorvin]

Merci Sebastian pour ton comments.

Et oui, j' aime la forme des empanages aussi!


Vincent (DB)

[bocorvin]

Bonjour a tous,

I went on with the fuselage

I drew the fuselage (some time ago already) using Devfus. I have already drawn a few fuselages with this programme, but this one was a bit different because of the pylon for the wing.
Back to the information about the original. In the drawings I could find, the Hjordis has a fairly blunt nose, but in the photos it looks much more pointed.





So when drawing it, I made it a little more pointed





It looks nice and sleek





The slightly more pointed nose also made it easier to install an engine, an outrunner with an extended neck (Hacker A30-8XL-LN). With a Z spinner, I hope the propeller blades will fit nicely.

The cockpit of the Hjordis is very small, so I had to make a larger aperture. I drew the top of the battery box on the centre line and made the upper half of the fuselage removable. This had to be done in two pieces, as there was no other option due to the pylon. The front piece can then be removed straight upwards and the rear piece first forwards and then upwards. The motor can then be slid in through the battery box.

To be on the safe side, I drew two more boxes in the removable pieces to make them sturdy.

[133 420-001



Adri did some nice CNC work in poplar ply (obtained thanks to a very nice fellow modeller).





I cut the frames in half to make the top removable and temporarily glued them together with pieces of scrap wood.





In the pylon, I thickened the plywood and inserted four insert nuts, to which the wing centre section will be attached with (nylon?) shear bolts.





Because the battery box also rests on the centerline, I was able to assemble it separately from the building frame. That went very smoothly, as did the holes for the servos and a small board under the battery box for the decoupling servo, so it must be able to be towed.





I had already made the building frame, a sturdy board with 10X10mm slats at right angles and at frame spacing.

I am leaving out the boxes for the removable fuselage halves for now, so that the whole thing fits on the slats of the building board.





I put in some stringers to see if everything fits, which fortunately was the case.

Vincent (DB)

[sebastian92]

Hi Vincent,
wonderfull building !!
What a so facility to draw all the elements with those logiciels…
It d'ont turn on MAC… my next computer will be a PC, absolutely !
I could charged it on the PC of my wife… but it is full of cracked
Wait and see for me in the future…

To be continue like this your building with lot of pictures and details

[bocorvin]

Hi Sebastian,

Thanks and yes it is nice software, it took me some time to work with it

Cheers,
Vincent (DB)