This is the newer glass cloth version
|Wing Area:||275 sq. in.|
|Wing Loading:||4.2 oz/sq. ft.|
|Receiver:||FMA Extreme 5|
|Available From:||Mountain Models|
While surfing RCGroups.com one evening, I ran across a post from Doug Binder about a new design Mountain Models was working on, and took a look. It was a departure from Mountain Models' typical offerings, a discus-launched glider (DLG for short), with an expected kit price well below that of most DLG's, kit or composite. I was immediately intrigued, as a DLG was something I wanted to add to my stable for some time, but I had been intimidated by the prices, and the complexity that seemed to go along with the adjustable camber composite ships. Doug's plane was to be a RE only, entry level DLG, and it sounded good to me. I pm'ed him, hoping to talk him into letting this relative sailplane novice "acid test" his design, as it seemed to me I was the perfect target audience for such a plane. He replied and said to come talk to him at SEFF, I did, and soon left the Mountain Models booth with a DL50 kit in hand. Over the weekend at SEFF, I got to fly Doug's DL50, and that little taste only fueled my desire to have a DLG of my own even more.
The plane's wing constisted of a blue foam wing core, reinforced with a combination .060 carbon, .007 carbon tape, 1.5oz glass cloth center reinforcements and finally covered with light glass cloth and water based polyurethane. Earlier versions of the kit were covered with ripstop polyester and 3M-77, and I built both versions. The fuse was a laser cut built up pod, with a wrapped carbon tube for a tailboom. Tail surfaces were balsa, with glass and carbon reinforcements. Carbon pushrods were included, and there was nothing to buy except the adhesives and radio equipment.
NOTE: If I seem to provide a lot of detail on the build here, it's because I felt that many who are interested in an entry level DLG would be unfamiliar with the materials and techniques used. I wanted the review to show the potential kit buyer that there is nothing new and scary here. This kit is easy to build, and the use of glass cloth and carbon make a very, very durable finished product.
The build started with the wing cores. I removed them from the beds and trimmed to the proper chord, then epoxied the .060 spars into precut grooves in the foam. Next, the panels were epoxied together and the .007 tape sub spars were trimmed to length, and glued over the .060 rods. After this came the 2oz glass diamonds, on which I used water based poly-urethane to attach rather than epoxy. I have used the WBPU over foam a few times in the past, I really like the ease that it offers versus epoxy, and I think it is lighter as well. The process is simple, the cloth is cut to slightly oversize, and then layed over the wing panel. The WBPU is then brushed over the cloth, leaving no whitish areas, fully wet but not with any puddling on the surface. The edges of the cloth are brushed down so they overlap the bottom or top, and I kept an eye on mine to make sure they did no lift as they dried, brushing down again as I needed to. After all this, the ply parts were glued to the center of the wing and the bolt holes are drilled. Finally, the 1/16th ply/carbon launch peg was made up, and then attached to the wingtip with more carbon and a little bit of Kevlar thread.
I cheated and started the fuse in between some of the steps on the wing, no sense just watching the epoxy set, right? All the laser cutting was perfect, and the parts fit was excellent. There were no problems encountered here, except I did crack a fuse side slightly while pulling the nose together, with no ill affect on the end product's strength. I glassed my pod with as little resin as I could, which admittedly was all I had left!! I set it aside to dry, and moved on to the tail parts.
Basically, there were just a few balsa and ply parts to assemble here, then the hinging was accomplished with 2oz glass, and some reinforcements made with some of the carbon tape. Then I attached them to the boom, with more 2oz glass to reinforce that joint, making sure I aligned the horizontal tail with the vertical.
Now it was time to bring all these parts together and make an airplane out of them. I fed the carbon boom into the fuse pod, so that the boom just protruded through the last former with a hole in it. Then I bolted the wing to the pod, aligned the tail with the wing and tacked the boom to the pod. Next I removed the wing and fully glued the boom in place, and I was ready for radio equipment.
The DL-50 used .030 carbon for pushrods, run through tubes that were glued to the outside of the tailboom, and small bits of wire and heatshrink for terminations. These worked exceptionally well, I except unfortunately I glued the pushrod in the tube!
I used two FMA PS-20 servos and attached them to the fuse with a little thick CA after wrapping each with a layer or two of masking tape. The RX was Velcro'd just in front of the servos, with the battery taking the forward position. I had enough room to adjust the CG by just moving the battery back and forth, no need to add any weight to acheive CG.
Now the fun really started. I didn't have a whole lot of experience with sailplanes, but I was capable of trimming one to at least some degree of effiecent flight, and playing with this little glider quickly taught me about energy management, finding thermals, and discus techniques. I took it easy on the first few launches, making sure that I used the proper form that Doug had shown me at SEFF, and later began to realize that, just like in most sports, the more natural the movement felt, the better the launch. I was getting consistent launches of about 75 feet, and about 1 minute flights. I have yet to "spec out" my DL50, but I have found some lift from time to time, extending those flights to 2 or 3 minutes.
Discus launching takes some practice. After you tried a toss to verify you are trimmed right, grab the launch peg with the pads on your fingertips. Face into the wind with your launching arm behind you and the outer wingtip resting on the ground. Swing around 360 degrees, keeping your arm behind you. As you get to the end of your spin, rotate your arm forward and release the glider slightly earlier than seems right. You should throw the glider up about 30 degrees and about 10 degrees to the right of the wind (assuming you are right handed). After about 100 throws or so, you'll get the hang of it. Hopefully, you will find this way of flying very addictive.
Mitch Gerdisch's review of the Radio Carbon Art Handlaunch Pro Clinic Video provides a nice overview of this great place to get more info on launching. Another very informative title from Radio Carbon Art is "Secrets of Thermal Soaring". It doesn't deal specificly with DLG flying, but thermal flying in general. I learned quite a bit from both DVD's.
Note: While not absolutely necessary, I found through talking to other DLG flyers and experimentation that I get consistantly higher launches by using an elevator preset on my transmitter. I use about 20% up on my snap roll switch, and get a more vertical trajectory which turns more energy into altitude. I also have noticed I don't tend to launch at a very high angle, so maybe that's why the preset helps me so much. You're mileage may vary.
I think the DL50 flew great, was tough, and was an excellent introduction to DLG's. Having cut my teeth on the this little sailplane, I can see myself getting one of the more specialized composite DLG's in the future, but for now I am content to continue playing with my Mountain Models DL50. I hear there may be a full size 1.5 meter ship coming from Doug and Matthew soon...I think I may have to have one.
I'm convinced! I've got one on order. Actually it was a toss up between the gambler and this one. Looking at the videos, it just seems to track better like it's on rails. But that could be the pilots too. Still, one would almost think it had alerons the way it turns so solidly. I just got to see for myself!
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