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Old Jan 20, 2014, 01:37 AM
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Australia, WA, Broome
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Build Log
Hobbyking Dragonfly 1800mm balsa composite electric sailplane

I was able to find very little on the internet regarding this airframe though it rates well on the HK website. In purchasing this airframe I was looking for a medium-short range FPV platform, something a little quicker and more interesting in the air than the Radian. Other aircraft I considered for this role were the Phoenix 2000 and HK Cyclone, both 2m wingspan models, unfortunately shipping restrictions makes these models significantly more expensive to freight, to the degree where it's quite ridiculous. Though I would rather the extra 20mm wingspan, I am not prepared to pay so heavily for it.

The glider took 2 weeks to arrive from the domestic warehouse with normal postage, this is pretty standard for our town. She arrived double boxed, well packed and in perfect condition. All surfaces and fuse arrived straight, the quality of the build looks excellent. I've only owned foam or foam composite models and have never handled a balsa but it seems strong and light and looks gourgeous! The wings and horizontal stab are balsa, the fuse and rudder are fibreglass with light ply scaffolding.

All hardware is included and mine was accounted for, only small issue is that the front fastener for the canopy broke off but I was happy to glue it on properly rather than there be any question of ejected canopies! First order or business was to put aside the included motor, a few of the HK reviews mentioned burning out this motor, and replacing it with an NTM 28mm 1800kv outrunner which seems to fit nicely so far.

Building is quite simple and a manual is included, it's quite a nice manual with pictures and good explanations, quite unusual!!! I'm using HXT900s all around, they fit in the wing nicely under the servo covers there (looks very professional) but they were too short for the spaces under the wings for the rudder/elevator servos (nb: The manual advises 18g servos for rudder/ele, hence the large space, seems quite excessive to me!). I used CA to stick some pop sticks in so the servos could be mounted properly. They seem snug but the ply scaffold seems abit soft in this section, time will tell if it's strong enough.

The only real issue I've found so far with this model is that the included screws to attach the prop to the motor shaft are too small, quite a bit too small, I'll have to have a good hunt to find some big enough I expect.

Edit: The horizontal stab is held in with a screw, when done up it pinches the balsa and doesn't seem steady enough, I've added some popstick on the top which seems sufficient at this time.
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Old Jan 20, 2014, 01:42 AM
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The build is complete and Dragonfly is ready for operations!

This was quite an enjoyable build, the quality of the airframe contributes to the enjoyment as I had no real difficulties in putting it together. A few important points for builders: Not all of the interior ply formers in the fuse are glued in and need to be secured before flight. None of the control surfaces are glued in and all need to be properly attached before flight. Though the prop seems pretty well balanced as is, it was a bit rough and needed some sanding.

This is definitely an easy to intermediate build and not for beginners. A few nice points like pre installed servo extensions and included y-cable help and the general finish of the plane is great.

I've installed a 2200 3s pack for balancing and it balances nicely with stated CG 60-70mm, there seems like plenty of room in the fuse for my FPV gear and good access, especially when the wings are off. (wings are removable via screws at the tailing edge and dowel at the leading edge)
AUW exactly 1kg.

The ESC in here is one i'm just using for testing (60A and not at all appropriate for this application) as the 25 I had for this install was damaged.
According to eCalc with 800kv motor and 11x6 with 2200 3s should give me 1.14 to 1 thrust ratio but I will need >30A ESC as she should pull approx 31A.
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Old Jan 20, 2014, 01:42 AM
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Updated flight review:
On this birds fourth flight, I replaced the 1800kv NTM with the stock motor, using 6x4 non folding prop approx 30g lead in the nose and 2200 3s. Took off easily with about 50% throttle and about 10kmph wind, she flies really nicely and I'm really stoked. Probably a bit ungainly at low speeds but no hints of nasty stall characteristics yet (yet, I haven't tested the envelope well yet), glides beautifully, feels really nice with a bit of speed, slips through the air beautifully and looks fantastic!

Despite a bit of down thrust on the firewall (non-stock) the nose really pops up with throttle which, though this is my first real electric glider, doesn't seem disconcerting or surprising. She needs just a little thrust and takes off nicely, with high throttle she seems like she will hold vertical. I can't wait to really put this plane through it's paces.

CG seems pretty right, throws as per the manual with lots of expo and small amount of rudder mix. The elevator feels very pitchy, Ill try dialling down the elevator throws. Ailerons seem a bit lazy so I might try adding in more rudder though this plane does't have the roll stability or airframes that I've encountered previously that I was trying to avoid, with a bit of speed it feels quite sporty!
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Old Jan 20, 2014, 05:51 AM
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Thanks for this Matty, I have an interest in getting one of these and looking forward to more reports. Post on the HK review part indicate that the prop may be too large for the motor hence it burning out.
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Old Jan 20, 2014, 08:44 AM
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No worries, she's almost complete now, I'm looking forward to some nice weather for maiden. There isn't a documented power rating for the motor but the 28mm 1800 438w I'm using looks massive compared to supplied motor with its spindly little wires! I'm a bit surprised they're expecting it to pull this plane (not a small park flier) into the air!
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Old Jan 20, 2014, 12:37 PM
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Hi, Matty. I have a general hint for you. Sometimes the ply formers look like they are well glued but they really aren't. A very easy precaution one can take is to add an epoxy fillet to any joints you can reach. I'm looking forward to the flight review.

Cheers!
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Old Jan 20, 2014, 06:33 PM
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Thanks Peter, I'll do that. I did find that out by accident and also that none of the control surfaces are glued in! Good things to know!
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Old Jan 21, 2014, 12:08 AM
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Part 2 of build done and build complete. Storms forecast for next 7 days
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Old Jan 21, 2014, 09:04 AM
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If it makes you feel any better, Matt, it's currently -8F and is not expected to get over 10F before Friday here on the frozen tundra.
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Old Jan 21, 2014, 04:29 PM
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Do those wings have a small angle built in? Looks like the tips are bent a little. That is just what the Dr. ordered for my Specter/PasserX. The plane flies really nicely but the wing is as flat as Kansas. It would be a lot easier to thermal with some small hedral ...

Pete, do you see any similarity between the Spectre wing and the dragonfly? Yes the spectre has the V notch cut in it to fit the fuse, but I have a dremel and I'm not afraid to use it!
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Old Jan 22, 2014, 02:43 AM
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Yikes! That's cold Peter!!

There is a small amount of dihedral in the outer half(ish) section of the wing. It looks very, very similar to the Spectre for sure, maybe this is the V2.
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Old Jan 22, 2014, 08:55 PM
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Maiden done but a bit problematic, reports in post 3. I hope I can advice from you more experienced fliers? I'm suddenly feeling a bit out of my depth...
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Old Jan 22, 2014, 09:41 PM
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The Dragonfly wing doesn't look like an exact match for the Specter but it might be possible. One would have to measure and compare. The Specter has a root chord of 200mm, the notch for the mount is about 11-12mm, and the very thickest part of the wing root is 17mm. (It's a good thing I measured it because I found a small crack in the center section sheeting.) They do have the Specter back in stock with a different color scheme but there's no mention of any modifications.

http://www.hobbyking.com/hobbyking/s...00mm_ARF_.html

I think you are using too much prop, Matt. The HK 2834 1250KV draws better than 30amps and well over 350watts with an 11X6 CF prop. With this prop it gets quite warm in around 20 seconds. HK claims this motor will hold together at 585 watts but I sincerely doubt it would last more than a second or two. I haven't used anything as high as 1800kv but just going with my gut I would think a 9 inch prop, especially if the prop and spinner are heavier than the Aeronaut and aluminum 30mm spinner I'm using, would be about the limit. Do you happen to have a 2 cell battery could could use to see if it gets up to the calculated RPM?

I have also found that all 3 of my 2834s as well as the KD A22-20L, got much warmer for their first minute or so of running. When I got the first 2834 I figured I had a dog because it got too hot with a 10X6. It even got pretty warm with a old 9X5 the first few times I flew with it and then I noticed that it started running cooler. An electric motor certainly doesn't need as much break in as a glow engine but they do seem to need some babying before they run right. If you have a smaller prop, even if it's not a folder, you could use for some bench running that might allow things to free up. I dug out an old Topflite Nylon 9X4 that I drilled out to accept prop adapters and I used it to run in my 2nd and 3rd 2834s and it works very well.

Cheers!
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Old Jan 22, 2014, 09:51 PM
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Thanks Peter, I only have 6x4 props here but will try that as well as some 2s packs. It is a new motor and hasn't been run in, so I will take that into account too, I did consider the run in time but it seems a bit ridiculous that I'm getting so little revs... Oh well, ill keep trying different combos and report my findings!
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Old Jan 22, 2014, 10:21 PM
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Good luck, Matt. Letting her really wind out with a 6 inch prop might be just the ticket! I forgot to mention that I picked up about 1,000 RPM with the bigger props after running in.

Cheers!
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