Thursday, April 26, 2018

Free Flight Hand Launch Glider Story

One of the most important things my model aviation hobby teaches me are those tiny little details can make a big difference to an outcome. Last winter I built a really nice looking free flight glider kit with the intention of adding a hook in front to make it a catapult glider. All the parts were included, very nice manual, carbon boom, and it included jigs to set the angles for the polyhedral wing. As I have had trouble getting the glider to fly properly I am not mentioning the kit name.

From the start, and I started flying it over snow, the glide was fine; the issue was getting a smooth transition from launch to glide. Normally with this type of glider if you are right handed you launch with the glider banked to the right and the glider transitions to a left circle at the top of the launch. This glider refused to do that, often it quickly turned around and dove towards me after launch. I kept trimming off the tiny amount of left rudder but any amount of left rudder would cause the plane to spiral in.

Seeking out the advice of people with more experience I tried their ideas and some of my own. First I put in washout in the tips, good idea but did not seem to help much. I thought maybe the vertical fin was too large so broke off part of that, I think that was needed. If you launch it with a very slight left bank it would transition to left circle now. Flying it over some wet ground helped to cushion the crashes but the front of the nose finally broke off from being wet. I taped a dime to the nose and tried launching again and it improved the launch a little more. Now getting more desperate for a solution I broke off some of the rear of the stabilizer, that helped a little more.

Nice Manual

Back home I rebuilt the nose shorter and added a hook for catapult. Fiberglass cloth was used to cover the nose and the catapult hook. After some hand launching it now seemed that the glider would transition from a straight ahead launch to a left circle. Next I started catapult launching and I was having pretty good results but still it would not take a launch to the right. On one flight the glider was circling nicely in a thermal and headed right over where another model had landed on top of a truck trailer; luckily the glider DT’ed just before reaching the truck trailer. When working with trying to get my airplanes trimmed I lose all track of time, finally around 2 pm I took a break for lunch. Just before that I glued a small amount of rudder back on the vertical fin.

Shorter Nose with Hook

After lunch I flew an electric RC glider and found good lift, at least a couple of times it climbed until it was a speck in the sky. With the glue dry on the free flight glider I tried it again, now it was launching more like it should. On a good launch it hooked a thermal, around and around it circled. It was slowly drifting over an area with blacktop roads. The circling glider started to pick up speed and then the glider was circling in a spiral towards the ground. I was sure hoping the DT would trip, but it hit the hard surface before that. Pieces were flying but the damage was easy to repair.

Working with this glider has been a little frustrating but also very fun. It makes me realize that what appears to be a very simple design might be brilliant in that the proportions of the model are closer to optimum. I feel it has forced me to practice more aerodynamic theory than if I had built a model with a string of contest wins.

Bill Kuhl

Monday, April 16, 2018

Viscous DT on Blue Ridge Special Rubber Model

For a long time I have had this idea about installing a viscous DT (dethermalizer) system on a sport rubber powered free flight model. My first experiment installing a DT system was to install a fuse on a Guillow’s Lancer. This worked well and gave me experience handling a fuse but I wanted to try a viscous system because I wanted a system kids could use without playing with fire. Presently I am writing a couple of articles on viscous DT systems so this would be a good time to try a system on a smaller airplane.

Previously I had built a Blue Ridge Special from plans but lost it this winter on a frozen lake, I had the Volare two plane short kit so decided to build one and install a tiny rotary damper system using the E2 style rotary damper, the price is under $3. To keep the weight of the airplane as light as possible I used really light wood, which the instructions caution against. The leading edge started to bow in but I warped it straight, the problem came back when I covered the plane with Esaki tissue. All the covering was ripped off and laminated a piece of 1/16” square to the leading edge. Recovering went better except now the trailing edge was too soft. When I build the second model I think a light plastic will be used.

To make a timer I referred to Manuel Cisneros article; you remove a plastic gear, slip a tube over the shaft, and place a pin through the shaft. My particular rotary damper appeared to take more force to turn it so I slipped another plastic tube over the first tube to increase the torque. On this same model rotary damper on a glider it turned fine without the extra tube. The rotary damper was mounted on top of the fuselage because I was afraid it might interfere with the rubber motor if mounted on the side. Instead of popping up the rear of the stabilizer I decided to pop up the front of the wing. 

Coming Down from DT 

Recently I purchased a couple of small needle nose pliers with rounded jaws, this tool works good for bending wire in nice looking loops. All the wire used was from a common straight pin. The hinge in the rear of the wing would have a good deal of stress on it so I used a small strip of fiberglass cloth over it. Two sides of 1/16” balsa were used to make a small pylon, a short length of 1/8” square balsa under center of the wing in front slides into the groove between the two pylon sides. This should keep the wing from shifting in flight. A toothpick made a good peg for the DT line to wrap around. 

Everything appears to work fine on the ground, waiting for better weather for test flights. The weight of the plane without rubber was 11 grams, the rotary damper only weigh 3/10 of a gram. When I am happy with how this works I will build the other kit and do a better job of covering the wing.

Bill Kuhl

Related Links    Volare Short-kit 2 Pack  First Blue Ridge rotary damper used  Manuel Cisneros article on rotary dampers Fuse on Lancer video of Lancer flying and fuse DT