Well, HobbyKing managed to suck me in with their Black Friday sale this year. I’ve been teasing myself with the possibility of a Discus Launch Glider (DLG) for the past year, but kept shelving the idea because of the initial cost (even the budget-minded Libelle will be ~$200.00 to get in the air), so when I saw the 2 channel HK Composite DLG ARF on sale for $39.00 I had to jump at the opportunity.
Parts List for this Build:
-HK Mini Composite DLG: $39.25 (on sale)
-2S 300MaH nano-tech: $5.95
-Orange R615X Receiver (Overkill, but I had one on hand): ~$10.00
-Assorted JST connectors: $1.11
-Home-Brew BEC: ~$1.00 in parts
The glider showed up a week later and overall the construction impressed me. Covering was tight, wooden joints appeared to have sufficient glue, and all the aerodynamic surfaces were straight and square. The tail boom appears to be unidirectional wrapped carbon, and the connections to the fuselage pod up front felt sturdy (only time will tell). The wings are one piece with a healthy dose of dihedral (you know, no ailerons and all) and had a finger peg pre-installed for a right handed pilot (they include a second carbon peg for lefties too). The vertical stab is glued into the tailboom out of the box, and the horizontal stab and wing attach with a couple of screws.
After mounting the horizontal stab and connecting the pushrod to the elevator I quickly discovered the biggest flaw with this model: lack of pushrod support. The pushrods for the rudder and elevator are thin (0.020″) wire and are only supported along the tail boom every three inches. With any resistance on the rudder or elevator the pushrods buckle resulting in mushy control throws for up elevator and left hand turns which put the pushrods in compression. This should be an easy fix in the future, however I decided to build the model as-received to see how much of an issue it would be given the low weight of the glider.
One thing HK did right was provide plenty of room up front for the 300MaH battery, de-cased RX, and BEC. RX was attached using some double sided foam tape, and battery was held down using a strip of electrical tape for easy removal during charging.
The 6ch Rx and 3s 300MaH battery (both total overkill for this model) resulted in a slightly nose-heavy model so some paperclips were added to the end of the tail boom to bring the model into the recommended CG range. The paperclips can be easily removed down the road when I add additional weight to the tail to stiffen the pushrods, or swap out the Rx and battery for something more sane (HK Orange R410 Rx).
After everything was stuffed, I powered her up and set the recommended control throws in the radio. I had to set servo throws biased in one direction in order to compensate for the pushrod flex, but it all worked out to get me into a flyable range.
Maiden consisted of a couple of gentle overhand style tosses to make sure the CG was in a flyable location (you never really know what to expect with the recommended CG and control throws from HK) and then some very light discus tosses. The glider felt slightly tail-heavy, which was remedied by pulling one of the paper clip weights from the tail boom. Properly balanced, I attempted a few (more powerful) launches and easily achieved altitudes of ~50-60 feet and glide times of 20-30 seconds. The glider tracks straight during launch, and down elevator and left hand turns did result in the expected mushiness due to the control rods buckling under compression. The quick maiden turned into an hour out in the park experimenting with different launches until my hands went numb from the cold. The model flies great (even in a light breeze) and almost doesn’t want to land; a slight breeze blowing over the trees was enough to create some lift an extend some of my flights by more than a few seconds.
I can’t recommend this DLG enough as an intro into unpowered flight. I’ve had the model out a couple times this winter as weather has permitted and enjoyed each time. In the end, the only downside I see with this model is that people who find out they do enjoy flying DLGs will quickly outgrow this tiny, 2ch, balsa-winged model (I’m already looking into full-blown glass/carbon models). Those who aren’t quickly hooked will be left with a fun model that they can take along anytime and fly anywhere.
Future Improvements to Look For:
-Smaller 3-4Ch Receiver
-Supports for pushrods to prevent buckling.