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Okehampton Aero Tow Sunday 2nd August
Okehampton club has invited us to their next Aerotow on 2nd August. See their website at http://www.okehamptonmfc.org.uk/?page_id=798
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5Metre K7 build update from John
The K7 continues to grow slowly and the bags of laser cut parts are starting to diminish. After doing all I could to the fuselage I started on the tail end. The fin is integral to the fuselage so a rudder was next and fairly straightforward, made of balsa and 0.4. ply. A double horn was made from G10 2mm fibre board, very hard but files well. The closed loop cables will connect to this.
Lots of laser cut parts went together to construct the tail plane and this was covered in 0.4 ply as is the fin, all very strong but getting heavy! Elevators x 2 of built up structure are driven by 2 servos in the tail plane.
I made a mistake with the hinging and got the hinge line in the incorrect axis but hope to address this later.
As it is quite thick at the hinge line and the elevator needs to swivel rather than just move up and down.
I have now begun the first wing, will be in touch! ( Robert: Looking forward to some build clips John)
If anyone subscribes to the forum on Scale Soaring UK, further posts from John on building his Jilles Smits 1/3 K7 Build
Old Phoney – Part 1 ideas taking shape
I thought I’d take a break from designing gliders and build a (powered) vintage classic along the lines of the Junior 60, something light and slow but 4-channel rather than 3.
I found a plan for the 4 channel Super 60 but it’s boxy fuselage shape and angular fin just didn’t ‘do it’ for me so I started wading through the Outerzone plans website. I found the 4 channel PD Parasol and got quite excited about it! But, although it’s tail shapes looked beautiful, its fuselage shape (convex top and bottom) was not my (pre-conceived) idea of a vintage classic. Then I found the lovely curvy fuselage outlines of the Deacon and the Viking and the lovely wing shapes of the Dot I, and Black Magic.
PD Parasol
The Deacon
There were quite a few 3 channel designs that I really liked the look of but my heart was set on having aileron control for some slow, low-energy, aerobatics with half-decent rolls. An aerobatic vintage design called the Over & Under caught my attention but I couldn’t see any way that its fully symmetrical section would give a low sink rate when compared to the flat bottomed Super 60 or the semi-symmetrical PD Parasol. I almost decided to just build a PD Parasol exactly as per plan but I definitely didn’t want a one-piece model and I couldn’t visualise an attractive and lightweight way of adapting the parasol and struts to a banded-on wing. I also want something slightly bigger than 60”.
So, I embarked on producing a new vintage-hybrid design along these lines:
Semi-symmetrical wing section of the PD Parasol with strip ailerons as per the Super 60.
Curvey fuselage of the Deacon/Cardinal but a little extra nose length and diagonal bracing.
Tail feathers copied directly from the PD Parasol which to me look perfect.
Wing shape similar to Black Magic.
Approx. 10” chord, 70” wingspan, 40” fuselage.
Electric power (I found the 4-max website. What a great resource!)
Out of respect for Roger Jones’s RCM&E Forum comment “designing your own ‘vintage’ model is a bit phoney”, I decided to call her the ‘Old Phoney’.
Buying the servos, there was a special offer on five. That got me thinking “what could I use the 5th servo for?” then the penny dropped – a tow release.
The plans are still being tweaked but here’s a recent version:
Inspired by Cliff Harvey’s videos on YouTube, I started by laminating the wing tips and tail:
Then found an old bit of 3mm ali for the u/c:
Old Phoney – Part 2 the wing build
Like most of my designs, the Old Phoney is a combination of ideas gleaned from other designs with a handful of my own thrown in for good measure. The wing shape is a cross between Black Magic and PD Parasol but the construction is completely different. Also the ailerons are much bigger and almost full-length. I figured that large surfaces with small deflections are probably more efficient than small surfaces with big deflections. I also wanted the ailerons to provide variable camber (flaperons) to (hopefully) give a wide range of possible airspeeds from ‘slow half-power vintage-style’ right through to ‘flat-out throwing it about a bit’. The aerofoil section is semi-symmetrical copied from the PD Parasol and Peter Miller’s Peggy Sue II – both very manoeuvrable models. I also wanted a smallish amount of dihedral – partly for looks but also to give me the option of flying rudder/elevator which I still like to do sometimes – but not so much dihedral that manoeuvrability was compromised.
Lightweight slightly aerobatic high-wings often gain rigidity by having struts (e.g. Cub J3). I wanted the rigidity without the struts so I added a bit of weight in the form of a couple of 8mm carbon tubes I had left over from a previous build. The additional weight was about equal to the weight saved by not having metal wing joiners. The tubes were so stiff I thought I’d get away without having LE sheeting. Some strength was gained by having capped ribs which I’d not done before. So here we go…
Started by pinning down two 1/4 sq hard balsa spars with slotted 3/16 sheet at the back
…added the LE and laminated tips
…then built the ailerons in situ, added the TE, and capping strip except where the wing joiners still had to be fitted
I joined the wing halves with 1/8 ply braces, a long one on the center spars, a long one to bridge the weak spots where the center-section sheet ended and the ailerons started, and a very short one epoxied behind the carbon rods. This is the point where I was just about to bury the servo extension leads under 1/16 sheet
I left it at this point and started work on the fuselage but something was bugging me. I’ve never covered a big wing that lacks LE sheeting and started to worry about how much the fore/aft tension of the Diacov 1000 (rather like Solartex) might sag between the capped ribs. It would only have sag by 1/16″ to come into contact with the front spar which would spoil the shape of the airfoil section between all the ribs. In the end I decided to add eighteen short ‘ribs’ as seen below:
Short ribs added, plus LE, TE, and laminated tips roughly sanded. I really like the look of the tip-ribs and with the laminated tips they are really strong but light.
The uncovered wings are plenty stiff enough spanwise but still twist quite easily. Fortunately the info about the covering from Sarik Hobbies says that Diacov 1000 “substantially reinforces all structures to which it is applied without stretching too much”. So all should be well. Now back to the fuselage…
Old Phoney – Part 4 covering and completion
There’s something rather satisfying about the first time it all comes together, wings, fuse, legs, and tail feathers, and pinning the control surfaces on. Pre-covering photos seem to be a bit of a tradition:
I covered the wings in Diacov 1000 from Sarik Hobbies which is an “Extra-lightweight iron-on polyester fabric” probably rather like Solartex or Oratex but I’d never used one of those so it was all rather new to me. It cost £33 for 3 metres by 73cm which John says is expensive but I must say it goes on like a dream. Just stretchy enough to wrap around compound curves when warm but adds tremendous rigidity after cooling, shrinks perfectly and looks great. Slightly translucent and slightly more so when varnished. I used polyurethane spray for the wings and brushed on the tail. Spray looks much better.
I cut the signwriting out of film covering and ironed it on before varnishing. Adhesion was really good.
For the fuselage I used cheap-as-chips transparent dark purple from Ali Express. The roll arrived damaged and their customer service was rubbish but enough of the film was useable and the value for money was great. Covering the stringers was probably the most challenging film covering I’ve ever attempted – curves galore.
I’m hoping that Winnie the Pooh turns out to be a good pilot. Apparently he’s had quite a bit of practice flying balloons with Piglet.
Installing the radio gear was pretty uneventful but the lightweight snakes I’d bought from SLEC weren’t up to the job at all. In the very short distance between the tube ends and the control horns they bent all over the place so I had to use piano wire instead. Fortunately the runs were fairly straight and the wire quite light.
On advice from model designer Peter Miller I went for zero angle of attack, zero tailplane angle, and zero down thrust. Although I did add a bit of right thrust and because of the high wing I have a sneaky feeling I will have to add quite a bit of down thrust so the removable cowl will probably need modifying – pretty easy.
The entire motor set up, the servos, and u/c hardware came from George at 4-max who provided great service and advice. SLEC provided great balsa and plywood. Thanks also go to John Harvey for encouragement and Cliff Harvey for inspiration and tips – particularly on laminating balsa curves, and Martin Tonkins for motor chat.
So there we are, my first vintage model. But in truth, of course. Although she looks old. She has no vintage whatsoever. In fact, she’s nothing but an Old Phoney.
POST-MAIDEN UPDATE
Turns out the u/c legs weren’t up to the job so I made a more substantial pair. The wire braces still broke so I switched over to using bowden cable and steel springs – seems to be fine now.
Here she is with new legs.
Test flights are going well. I’ve added down thrust and mixed elevator with the throttle. Her speed range is impressive from fast enough right down to extremely slow. Even with full down flaps and holding in full up elevator she doesn’t seem to stall, certainly doesn’t drop a wing anyway. Shortest landing roll I’ve managed was 3 metres in still air.
Old Phoney – Part 3 the fuselage
Just as the wing was my first without span-wise sheeting – this is my first fuselage without sheet sides. But, as it turns out, there’s something rather satisfying about longerons, stringers, and all the fiddly bits in between. And when you’re REALLY enjoying a build, anything that makes it take longer just means the pleasure lasts longer.
What are they called? Those curved bits that hold stringers in place? I have no idea but they seemed like a good place to start. Cut out of balsa they’d be bound to split, and terribly weak, so I cut the shapes out of 1/64” ply then glued 1/16” balsa copies either side but with the grain in opposing directions. Light, stiff, and strong. Not a bad start:
Next job was to cut out the 1/32” ply doublers. I copied their rather weird outline using the old ‘pin prick’ method. I remember being 13 and getting into terrible trouble for doing that in a school woodwork lesson. “But it works so well” I exclaimed. The teacher wasn’t convinced. Evidently it was not ‘the done thing’. Cutting them out with a scalpel was a bit hard on the fingers but it gives such a clean cut compared to the scroll saw or fret saw:
(The weird bit sticking out above the cabin is because I’d not yet decided how to build that part – just leaving my options open).
Because the longerons had to be ¼” square, but hard balsa and very curved, I laminated two 1/8” x ¼” strips instead. (the ‘Cliff Harvey effect’ again). With the help of a weak solution of household ammonia (to loosen the wood fibres) they bent quite easily and were glued after drying:
All the fiddly bits went together well with soft ¼” sheet infills at the front:
Whilst making the formers I had the idea of incorporating a tow release which I incorporated into F3 so the mechanism terminated just behind the wing:
The cabin top was a bit of a challenge.
I don’t like the look of wing bands that go to a dowel below the cabin so the cabin top needed to be strong enough to cope with pulling quite a bit of G force without the front wing dowels giving way. I tested the strength of a 15mm projection of 6mm dowel by sticking it in the vice hanging a 12kg weight off it. It didn’t break. But whatever they were glued to needed to be equally strong. But the shape was complicated. Hmm…
In the end I carved and sanded a block of 12mm birch ply to shape. It’s curved in two directions; top view to match the screen wrap-around; side view to match the airfoil; and V-shaped in the front view (to match the wing dihedral) and epoxied to three layers of 1/16″ ply on each side, all just 6mm thick:
The diagonal bracing and turtle deck stringers were most satisfying:
…and making the battery hatch and removable cowl:
Almost ready for covering!
Mediator build, part 2 – When is a fuselage not a fuselage?
Since I left the hobby around 1980, glider fuselages seem to have been on a diet – so many these days have extremely spindly bodies with hardly a curve in sight. I must concede, though, that the word ‘fuselage’ does in fact come from the French word fuseler meaning ‘shape into a spindle’. I’m sorry folks but spindly long-thin-stick fuselages just don’t do it for me AND they’re exactly the opposite of what you need for knife-edge flying and slow rolls.
First job was to cut out the 1/8” sides, 1mm doublers, and F1 through to F9. As I don’t have a jig and the fuse was deep and narrow I decided to stick all the formers to one side first before bending the two sides together. Each former had to meet the side at a different angle so each was temporarily held by a bespoke scrap of balsa.
When side two was added I used sash clamps to hold it all straight but it didn’t work well so I think I’ll make some sort of fuse jig for the next one. Any tips?
Before adding the bottom sheeting I put her back in the clamps to try and correct a slightly twisted nose. That worked a bit but I still had to add some balsa to correct it. I then found a slight bend at the tail end! Bit of a pain but not beyond correction later. I really must make a jig.
Then came the top sheeting, nose block, and canopy fashioned from as many scraps of soft 3/8” as I could find. I’d used ½” triangular section all along the top and bottom so I could do lots of rounding off the corners. After lots of work with the palm sander her rather pleasing shape emerged at last.
So here she is, temporarily pinned together in all her naked glory with, (as Kryten once said in Red Dwarf), “all her in and outy bits going all iny and outy”. Not a spindle in sight.
Happy Christmas everyone.
Mediator build, part 3 – completion
I decided to try dyeing the balsa before covering with translucent film and chose pale pink to complement the ‘heather’ pink Solarfilm I’d bought for the underside.
I should have known that pink and yellow makes orange. Will orange and pink really GO together??
Rather than use plastic hinges I thought stitching might be nice.
After covering I dropped the radio gear in and discovered to my surprise that my little 4-cell NiMH battery was too heavy for the nose so it had to go above the switch in the fuse top.
Here’s the radio installation (plus the 2 flaperon servos in the wings). The nose is completely empty!
I avoided unsightly bands going over the fuselage top by adding a (sort of) 3rd wing dowel – so some of the wing bands also hold the top on.
For the finishing touch I simply taped a strip of film to the cutting board, taped a paper print of the word ‘mediator’ over the top, and cut through with a scalpel.
Bottoms up!
Finished weight under 850g/30oz. Wing loading only 9.5 oz/sq’ which is less than my Kloudrider!
For inspiration: thanks to George Aldrich (Peacemaker) and Steve Lange (Le Fish).