David’s o/d glider build part 3

By | October 7, 2020

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:

Nose view:





Tail view:






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!


12 thoughts on “David’s o/d glider build part 3

  1. John Harvey

    That looks a really nice model David, with good clean lines , well done, seriously! Im guessing the dark blue under colour is so you can see the model at great height. Will you be able to video the maiden? We all love a maiden. It has obviously paid off to get the design details worked out before cutting and glueing, I couldnt quite work out how your swept fwd horns on the flap servo affected the throw of the flaperons when operated left and right, has that been proved yet.
    NW this weekend Dave……. very good luck.

    1. David Ramsden Post author

      Hi John. Thanks for the compliments! “Handsome is as handsome does” my Dad used to say, or “the proof of the pudding is in the eating”.
      Having no prior experience of flaps or flaperons I posted a question about differential on the Model Flying Forum https://www.modelflying.co.uk/forums/postings.asp?th=167572&p=1
      The response seemed to be that both ailerons and flaps need ‘more up than down’ so I raked the horns and the servo arms forwards to do that (more up than down) for both the flaps and the ailerons. It’s worked pretty well. They do go up more than down but the differential (so far) is not quite as much as I was aiming for. However, there’s a weakness in the design that might help. The flaperons narrow towards the tips, they are quite soft balsa , and the film hinges are a bit on the stiff side. Although this doesn’t affect the differential it does mean that the tips don’t deflect as much as the roots. This should help to guard against tip stalling which is a major danger with flaperons on high aspect ratio wings.

    1. David Ramsden Post author

      I thought about that long and hard. I’m used to flat-bottomed wing sections with a positive angle of attack which naturally give bags of lift. This is a different ‘kettle of fish’ altogether.
      I knew that high performance gliders often use semi symmetrical wing sections and aerobatic ones often use a fully symmetrical section with zero angle of attack so they fly well inverted.
      Being rather cautious I took a middle-of-the-road approach – I chose a semi symmetrical section (HQ3-12) and I gave the wing a very small angle of attack.
      So the first launch will be interesting! Will it nose dive? I don’t see why it would. Symmetrical section /zero attack models go up so in theory this one should too. (I hope).

  2. John Harvey

    By the way David I’m no expert in things aeronauticle but have gleened a little knowledge over the years. Reckon you are right to have the wing with a degree or two of positive A of A , with my latest creation the yellow K7, that needed a couple of tweeks of extra attack to stop the tendancy to return to earth. I could alter the tail plane with a slither or two of thin ply at the TE. Even then weight has been removed from the nose and probably could still take more, more experimenting needed yet. With the fapperons up and down (def need more up than down to eleviate ‘adverse yaw’ see I have read the books!) , there is no separate ailerons is there? have you raked the horns there as well?

  3. John Harvey

    ‘Read it’ as the frog said David. Well you can’t complain about the amount of advice. As you said this is an own design and there are no instructions, so if twas me I would test it over forgiving ground. Perhaps just aim initially for hand chuck glides sraight and level, that sorts out Cof G , incidences ect. Then look at small movements of rudder and flapperons or just rudder only to see if your dihedral copes and turns the model. Then perhaps a slope launch.
    With a very new model I have often just held it into wind and with a light push forward let it go before catching to see how it sits in the air, isnt this good fun!

  4. David Ramsden Post author

    Yes it is good fun John! What a great hobby.
    I flew her this afternoon and having just seen your post (above) I did do pretty much exactly what you suggested. Two flat field glide tests on soft and forgiving rough grassland ( a bit of up trim after the first one) then up to Black Hill. There’s a short report here:

  5. John Harvey

    Well done for coming home with a whole model David! I did read your maiden report, did you fly at anytime using aileron combined with rudder and or elevator. Cliff asks about your differential, could be an important point. At least you still have a model to experiment with. Of course BH doesn’t always give good flying conditions, if the air isn’t going up nor will the model, no matter how good. Maybe sometime you may need to consider separate aileron and flap.

    1. David Ramsden Post author

      Hi John, I have increased the aileron throw and the up flap but not the down. Flap function differential is easy to change on the Tx but I can only change aileron function differential by replacing the servo arms and or the flaperon horns. It may come to that but not yet.
      Why struggle one may ask. Why not just stick four surfaces and servos in the wings? It may come to that but I much prefer my mechanical challenge.
      Hope to test the adjustments between 5 and dusk on Chinkwell Tor.

  6. David Ramsden Post author

    One year later…
    I rather fancied having a glider that could be aerotowed so I’ve made some major changes to the DR420.
    I’ve dispensed with the sliding servo and full length flaperons and gone for 4 servos in the wings operating separate flaps and ailerons, increased the span from 2.4 metres to 3.1, added wheels with suspension, and a home-made tow release mechanism based on the one sold by multiplex.


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