|Mar 10, 2012, 06:23 AM|
Back home - and several days later - I knew what had gone wrong.
Certainly I had burned out the ESCs - but they were not relevant to the crash as it would have happened with or without power - and they were only cheapies anyway so I wasn't bothered about ditching them.
The lack of right aileron control was due to a problem in building. The plug that was supposed to seat firmly in its socket in the fuselage had not been fully inserted during the operation when I glued it into the wing root. It therefore made connection sufficient for it to appear to operate properly while static, but running across the deteriorating runway had shaken it free so that one of more pins had lost contact and the servo failed to work. I had included quite a lot of differential in the ailerons so that most of the work was done by the up-going aileron and the loss of one servo had therefore lost the turning ability one way (right) only.
Coupled with the fact that I was not happy with the skimpy wing construction in the first place, the twisted and shattered wing decided me to build a new set of wings. But as all the Cyparis spars had survived because of their flexibility they and all other reusable bits would be rescued and pressed back into service.
I stripped bits of shattered ribs off spars and leading edges, rescued the struts and wing roots in their entirety and devised a new method of building the wings based on laying down the underside capping strips first, gluing the spars to them then cutting out the ribs slotted over the spars.
A couple of days per wing and I was well on the way to recovery - or the model was anyway!
It proved to be so easy I wondered why I hadn't thought of doing it this way before...
|Mar 10, 2012, 10:59 AM|
There was also damage to the wing centre section, the nacelle that had hit the ground first hanging forlornly from the rest of the model on retrieval. The balsa spars were both broken and the fairing on the port side shattered.
I decided that having withdrawn the two ESCs from their coffins that I would have to cut the underside of the wings away so that their replacements would have the benefit of plenty of airflow over them - by becoming part of the underside of the wing section themselves.
So, as I could not reasonably hope to insert Cyparis spars into the wing from the side of the missing nacelle, I might as well save myself some bother by cutting away the underside sheeting so that I had as easy access as possible.
Having done the repairs I then adjusted the drawings to show the stronger arrangement. At least I would know that no other builder would suffer a broken centre section due to a heavy landing.
Inside a couple of weeks the structure was all repaired and the glue well dried out so covering could be completed. At the end of the process nobody would know that such an extensive repair had been required.
But the weather had deteriorated - so while waiting for it to clear I fussed about with a few details - like painting the props and carving a foam pilot (or part of him, the installation of his lower part being prevented by one of the sets of batteries) so that he bore a passing resemblance to what little I knew of the appearance of Torquil Norman - which was gleaned from this photo...
|Mar 13, 2012, 04:31 AM|
It was late June 2010 when the repaired Dragonfly arrived on the field for another photo shoot in the spacious setting of Bassingbourn (or what is left of it's former glory these days).
She looked as good as ever, but now the props did not stick out as non-scale - and there was now a pilot in the cockpit - although, in keeping with my normal philosophy of 'if it looks right on a slow fly-by that's good enough for me' he did not stand up to close scrutiny... Come to that he didn't stand up at all!
And on that general theme I was to be seen laying down on the grass to get my low-down and dirty shots.
|Mar 14, 2012, 06:43 AM|
Ground checks complete... I don't waggle the sticks - that only tells you the controls are working and NOT that they are working in the right sense. I give them a definite push each way checking that the surface moves the right way to give the expected response.
A short taxi and it was time to open the throttles.
Even with a large amount of washout at the wingtips I always prefer to let the model fly itself off the ground - it looks so much more scale. Off the ground in about 15 yards there was immediately the need for a lot of aileron trim. I soon ran out of trim and held the aileron on the stick while I completed the circuit and landed to make adjustments. I had obviously got a bit of a twist on one of the wings.
I adjusted the position of the output arm on the servo - and was glad that I had used a hinged servo plate so it only took one screw to undo it then the servo dropped down from the wing so the adjustment could be made quickly.
Next flight I found I now had plenty of trim available to fly straight and level - and that she would happily potter about on half throttle.
In fact even on these old 10C cells I could take off on three quarter throttle and even back off a little on the climb-out.
Turns were a little flat on the first flights and I soon got some rudder coupling dialed in so that I did not have to use manual rudder to get them looking nice.
I was fortunate to have Alan Florence in attendance with his camera, so the photos below are thanks to him...
|Mar 14, 2012, 12:17 PM|
Thank you very much Yel914, glad you like her.
I do too! Such a gentle flier - she gives the pilot too plenty of time to enjoy the sight of her in the air.
Here are some details of the model:
Wing span: 86 inches
Length: 63 inches
Wing area: 7.6 square feet
A.U.Weight: 8 pounds 4 ounces
Wing loading: 17.4 ounces per square foot
Motors: Towerpro 2915/930
ESCs: Hobby King SSH50A
Batteries: 2s 6,000 mah 10C (2)
Propellers: Zinger 12”x8” (modified to rounded tip)
Max current: 31 amps static at full throttle
|Mar 15, 2012, 06:04 PM|
Here's a little story for you.
Our club had an evening meeting out on the field in the middle of last summer and I took the Dragonfly. As the sun began to go down and the sky reddened I put a couple of 25C packs in and took off in my customary scale manner at a little over half throttle and did quite a few circuits. The Dragonfly purred around the sky and, aware that the club chairman was taking photos I flew her in front of the sunset a couple of times. It was a balmy evening and the last thermal of the day hardly bothered to generate a breath of wind. I got a bit bored with slow circuits and had done one or two passes with the flaps down - when she flies at about half normal speed - so I decided to open her up. At full throttle the note of the motors changed to a growl and I pulled her up into a nice loop from level flight.
Chairman said 'Whoa I wasn't expecting THAT!'
I suppose one really wouldn't expect that kind of thing from a model that flies at 32 watts per pound - but that's just one of the perks of building light.
|Mar 19, 2012, 04:08 AM|
By September 2010 I was in need of some more photos for the publication of the design and Chris Bramwell took another batch for the purpose, some of which are below.
I had by this time also flown with more modern 25C 3S LiPos and found that they made very little difference to the flying of the Dragonfly in practical terms as there was already plenty of top-end performance available using the 10C 2S batteries originally used. As the newer batteries were lighter I just had to remember to fix them to the Velcro a little further forwards as they were quite a bit lighter.
I also tried 25C 2S batteries - which also gave me the freedom of taking pairs of different batteries to any fly-ins attended so that I did not have to recharge batteries on the field. Same balance requirements applied for these - although it seemed that the balance point was quite flexible.
I never felt the need to explore the range of acceptable balance points as the Dragonfly flew perfectly well without adjustments from the start and no balancing weights were required.
|Mar 19, 2012, 04:30 AM|
Here are some more...
The tail areas are all scale sizes - as have all my models been for the last ten years or so and I think that the long tail of the Dragonfly assists very much in the achieving of scale flying as it reduces the effect of elevators and rudder making flight smoother. Of course this means that for co-ordinated turns more rudder is requires to be programmed in with the ailerons but once that is programmed in it can more or less be forgotten and the model flown very lazily.
|Mar 19, 2012, 06:14 AM|
Your Dragonfly is one great looking aircraft doing what it does best. I have noticed that in this family of planes, the Dragonfly seems to have much more dihedral really giving it the appearance of the dragonfly insect. Watch their wings in flight the next time you see one, you'll know what I mean.
|Mar 19, 2012, 07:07 AM|
I do indeed know what you mean Dan.
Geoffrey DeHavilland was, I believe, a lepidopterist, who transferred his love of moths to his aircraft by naming them as he did.
I am a bit puzzled as to why damselflies were not also honoured - since his designs so frequently featured wings that folded back in line with the fuselage.
I think I probably speak for all when I say that we are still staying tuned for further reports on your progress...
Perhaps while you are relaxing after your first day at the new job?
|Mar 19, 2012, 08:46 AM|
Mike, thank you!
Do you ever get across this way for fly-ins?
If you fancy a day out sometime the North London club's scale fly-in in June and the electric day in September are well worth a visit. They are at their field East of Baldock. I usually try to attend - if the weather is gentle!
|Mar 19, 2012, 04:36 PM|
Whatever time I do get, I tend to spend flying aerobatics and 3D.
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