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After the excitement of finishing The Plan I rather fancied celebratory drink and a sandwich. Not any old sandwich, a rib sandwich – two thick slices of aluminium filled with 13 balsa blanks. Once this aeronautical snack was rasped into shape (and the drink consumed), I finished it off with the sanding block, then repeated the whole process for the opposite wing. Hey presto! Two identical sets of 13 ribs.
‘Back in the day’ carbon spars hadn’t been invented, well at least I’d never seen one. We always used spruce. Seeing carbon amongst the balsa at my local store I thought why not? Not really having a clue, I went for two lengths of 6mm carbon tube with an 8mm joiner which seemed pretty light and remarkably stiff. Back at The Hanger I roughed up and epoxied the carbon tubes, then tapered and assembled the balsa trailing edge. So here we are with the spar, the TE, and two piles of sandwich filling:
I noticed that John said his laser cut K7 ribs had temporary little tabs sticking out that held each rib in perfect position above the building board. I had to devise my own way which was slightly complicated by my wing being not only tapered in both chord and thickness but also having a tip airfoil that’s different to the root airfoil. In the end I pinned tapered strips of scrap balsa to the board and pinned each rib to these. Theoretically this would hold each rib at the right height while the rib-spar joints dried. The aft strips remained pinned to the ribs until after the LE and TE were glued on. To make sure the ribs were equally spaced and vertical I cut all the bits of spar sheeting first and used them as temporary spacers. Just to make doubly sure the wing was ‘true’, at each critical stage I kept weighting it down with lead onto scraps of 18mm ply, packing the TE to take account of the tapers.
Next task was to try this new-fangled idea of sticking servos in the wings (well new to me anyway). In real terms, servos in the 70’s were more than twice the price they are today. More importantly, todays can be less than half the size. There didn’t seem any point using the fixing screws supplied as there’d be no way to access them so I just glued in a few scraps of balsa to hold each servo in place. I reckoned the necessary cuts in the LE sheeting would be weak spots in the wing so I beefed them up with tiny scraps of 1/64” ply. You’ll have realised by now, I ‘have a thing’ about using up scraps.
Looks like those exiting servo leads are going to be very vulnerable. I’ll have to address that later.
Next the center section sheeting went on. Then I ‘slotted’ the ends of the carbon spar to accept those distinctive ‘Peacemaker-style’ wing tips, fashioned the flaperons from 3/8” sheet, and cut the P-style tailplane from 3/16”. There’s something very satisfying about watching your own design gradually turn into reality (even if it was inspired by someone else’s).
Meanwhile, with Christmas looming, I’ve been making two chuck gliders as gifts – one for each of our elder grandsons. I found a delightful little design called the Aleda by Joshua Finn on YouTube which I scaled up to 12” span. I added little bendable rudder trims. Here they are before being sealed and decorated:
The fuselage and the tail end have been put on one side now for some weeks while I began construction of the wings. As with the rest of the kit there are many laser cut parts including false ply LE, all ribs, main spar web ( the 1mm ply sheet glued between top and bottom 1/2 x 1/4 spruce spars) and other ply webs needed around the route section. Tabs as shown are part of the ribs and false LE to allow these parts to sit on your board at the correct attitude, they are cut off later…very clever, makes life much easier. The first wing took a bit of thought and even then I left out a doubler around the joiner…Doh! Too late now. The first job is to make the bottom spar which because of its length needs 2 joints splicing and tapered to 1/4” at the tip. This is then glued to the spar web which the ribs just slot over, grooves pre cut, The top spar is then glued on, nearly done, that’ll be a no then! Still lots of parts to fit and glue. A model this big hoovers up a lorra lorra glue. I have left the aileron attached to save damage for now. The trailing edge construction of 0.4 ply top and bottom with balsa in between is simple enough but I am in thoughts about how to go about building a strong attachment to the wing ribs which also follows the wing section.
As you can see the second wing, which I hope is the opposite and mirror image of the first is well under way with the first hanging above me for reference. There was no plan for the second wing so by pushing a pin through the plan, thanks Joe, I have marked the key outlines on the back of the plan and also laid the first wing on top upside down to double check dimensions. Because the laser cut parts are designed to fit together you can’t get them in the wrong place, well mostly. The K7s wings are angled forwards so I will make a special effort to get the angle of the route rib for fwd sweep and dihedral the same as wing one. Each wing is 2.7mtrs long ( I have measured up the Honda and they just fit) so it will not need to be much out to make a big difference at the tip. Watch this space! Next time I hope to show you the assembled framework, however there are still servos to install in the wing for brakes and ailerons and the canopy to make. Maiden scheduled for late Spring…famous last words!
All the best and trust everyone is coping with this awful situation
Back in ‘71/72, we used to fly control line models for three hours every Sunday morning in a field next to The Rowdens at the top of Eastcliff Lane in Teignmouth. Not a silencer in sight. How the neighbours stood the noise I will never know. As far as combat flying and aerobatics were concerned, the model that really stands out in my memory was the ‘Peacemaker’ designed by George Aldrich. Wow. What a great flyer that was! A legend in its own lunchtime. Not many 50 year old designs have their own Facebook page! https://www.facebook.com/George-Aldrich-Peacemaker-411836712594945/ Maybe I could I create a slope soaring version of the Peacemaker?
Whilst researching a previous creation, I accidentally came across VTPR high performance aerobatic gliders (VTPR is French for “aerobatics very close to the ground”). If you’ve not seen it before take a look at this https://www.youtube.com/watch?v=_oBuqhEg0xU. I was amazed(!) and set myself the task of creating a new design that combined three things; the shape of a Peacemaker, some of the principals of VTPR design, and my own ideas.
I stretched the Peacemaker’s wing-shape spanwise but kept the aspect ratio still quite low at 1:6.5 rather than 1:4.3. Used a completely different wing structure and airfoil – semi-symetrical SBV96V at the root and symmetrical at the tips – and made the ailerons pretty huge (as per VTPR). I retained the characteristic Peacemaker wing tips and tailplane shape but moved the elevator hinge line forward which dramatically increased the elevator size. I designed the fuselage profile pretty much from scratch. Its wing position is as per VTPR and its canopy and fin shape reminiscent of the Peacemaker but that’s where the similarity ends. I played around with it for ages. The “if it looks right it is right” theory only works if it actually does look right. In the end I’m very happy indeed with its nice curvy outline.
Rubber banded wings are great – delightfully simple and very forgiving in crash – but not so easy with a mid-wing design. After much head scratching I came up with a simple three-piece design. The one piece 54” wing will be banded onto the lower half of the fuse and then the top half of the fuse will be banded over it. Two of the servos will be in the wings – that’s a first for me – which means the fuselage can be unusually narrow (another VTPR design feature) which apparently aids knife edge flying, not that I’m capable of doing it(!) but at least the model might be. So here’s my Plan for the ‘Mediator’…
Although the breeze was from the North East and unfriendly for gliders, it was good to get out and enjoy the really calm and clear air this morning. I decided to get out the thermal clothing and take my Riot up for a few circuits and try out my new Runcam2 camera for some area clips. Sidmouth Martin had made an early start but had not found any lift for his glider (sorry Martin, I cant remember the model name). Exeter Bob arrived with his Vintage Models – Balsa Basics Cub for a maiden flight that went very well and I think the aerobatics were intentional. My Riot bumbled around the sky and recorded some aerial clips but I must remember which side the camera is pointing when I fly past our group. Duh!
Welcome to our first newsletter for a very long time. We thought that with winter looming and opportunities looking limited to meet up inside or out for a while that a Newsletter would help to keep everyone in touch. As John said in his covering email, the frequency of issuing future newsletters will depend mainly on having something to report. We have had a couple of suggestions already, including highlights from our Facebook page, for a subsequent edition, so if anyone has any ideas or has anything to report from the building board, just drop Robert or John an email.
By today’s standards my new ‘DR420’ is a blast from the past – balsa and ply, with spruce spars, full length flaperons, and mechanical mixing. She’s also the first model aircraft I’ve designed in over 40 years!
Maiden – test flights 1 & 2 – Black Hill
Her ‘maiden’ consisted of two flat field test glides and two 40 min test fights in a gusty 6-12 mph:
I didn’t touch the flap function for the first 20 mins just used aileron and elevator and struggled to get above 30-40 feet in less than ideal conditions. Applied about 30% down flap and she was 80 feet up quite quickly.
Stalling straight showed no tendency to drop a wing and recoveries were easy and with little loss of height. She did sometimes drop a wing in turns but usually not. I couldn’t establish exactly why but suspect that variations in wind speed caused the inconsistency. Mostly she flew pretty well for a first attempt. I found that:
- Flap function made more difference to airspeed than altitude and no constant elevator input was needed. With full up flap she does come down gradually but gains considerable energy. At full down flap she flies close to stall speed but with careful handling is still well behaved. 25-35% down flap was best for climbing.
- The aileron response is disappointingly slow even at high airspeed. Increasing aileron throw a bit made little difference. I couldn’t roll her past about 80 degrees no matter what I did and even that took ages and height was lost. I expected to be able to do quick 90 degree banks and turns using up elevator but she was having none of it. Most turns were fairly close to flat.
- When I flew her rudder/elevator the flight characteristics were almost identical (even with very little dihedral).
- Remarkably, flap position made no difference to aileron authority and no difference to the likelihood of dropping a wing. That’s good.
- She looked majestic in flight and sounded great in passing.
Next Day – test flights 3 & 4 – Chinkwell Tor
Beforehand – I increased and aileron throw AND the up-flap throw but decreased the down flap (bearing in mind that these are full length flaperons not separate control surfaces). Conditions were far better, a much steeper slope with a much stronger wind than yesterday gusting 7-17mph at eye level .
In these conditions she flew like a different bird possibly because of the overall higher airspeed but the increased aileron throw was obviously making a huge difference. Mostly I just tested her responses and watched for tip stalls:
1) Aileron response was good at a wide variety of airspeeds and was not affected by up or down flap input. She still won’t do a complete roll but did pretty fast 80 degree banked turns (both into wind and downwind) and half rolls from inverted were no problem. She even did a half-decent Cuban 8.
2) Up flap (now about 30 degrees) response was much stronger and looked identical to down elevator input (it had zero braking effect – quite the opposite!). It worked brilliantly when more penetration was needed but for bringing her down I guess the next thing to try is up flap and up elevator at the same time(???).
3) No sign of tip-stalling in any sort of turn or at any groundspeed (but probably the airspeed was constantly higher than yesterday).
4) Rudder response is great. She can be flown rudder/elevator and does great stall turns.
She really was a great pleasure to fly in these conditions. To anyone reading this who has not had a go at ‘designing your own’ I would say have a go.
With traditional spruce spars, her thin wings are pretty flexible and at speed she literally ‘wriggled’ her way though strong gusts – like a falcon rousing her feathers in flight – quite something to watch. In recoveries from failed manoeuvres I pulled far more G than intended which greatly increased my faith in the light balsa wing structure.
I hope to further improve the aileron response by increasing the flaperon differential (reduce the amount of down aileron). Mind you, if it doesn’t work I’m still a happy chappie. If I’d wanted an out-and-out aerobatic glider I would have designed her differently.
I guess that’ll be my next project.
I um’d and ar’d over how to hinge the flaperons and eventually decide not to – to just let the film be the hinge. Multi-tasking was never my strong point so rather than try and wing-cover and hinge all in one go I decided to top-hinge the flaperons with a narrow strip of film first, I also covered the fuselage fairings before the whole wing:
Covering went well. The wing and tail undersides are dark blue. I was surprised to find that the cheap white Hobbyking went on better than the expensive dark blue Oracover. The winglets had 2 coats of sanding sealer, 2 of white enamel, and 2 of red:
The radio installation had been planned for from the outset so seeing it all fit – and the servo slide working – was all very satisfying. Working out all the angles to achieve ‘more up than down’ was fun too:
The flaperon horns needed to sweep forward:
…and the elevator horn had to sweep backwards to be 90 degrees to the control cable:
I was pretty pleased with my first attempt at signwriting with Oracover after asking for advice on the Model Flying Forum.
Close-up of my first attempt at function mixing with a sliding servo:
The wing-mounted fuselage fairings hold the wing halves together:
And the finished model – the DR 420 – ready for her first test flight. She balanced at 1/3 of her root chord without any ballast needed – pure luck!
From John H.
Hi Everybody, here is a forwarded message from Rob Oats of the Okehampton Model Flying Club. It would seem the best option as suggested, is to just hold just one event at the most suitable venue Sunday the 11th Oct.
Good Morning Everyone,
Storm Alex has scuppered our plans for the aerotow at 18 Acre this
Sunday. We have next Sunday as the reserve, however this clashes with
the aerotow at Little Haldon. If the weather conditions favour Little
Haldon we will cancel. If weather conditions mean an aerotow in Exbourne
is more favourable than Little Haldon then we will consider holding the
event in Exbourne.
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 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: I look forward to seeing more pics of this stage John)
If anyone is subscribed to Scale Soaring UK, more pics of John build can be found. Click here – UKJilles Smits 1/3 K7 Build
Stuart Chambers recently sent in a photo of this build by his No. 1 son. Does anyone recognise it? (of course Stuart knows the answer) Feel free to post your answer comment here or if more convenient over on our Facebook page.