Contributed by Chan Stevens
This conversion is for a relatively simple 2-channel V-tail configuration, though the glider itself is designed for 3-4 channel with ailerons, certainly an option for those so inclined, but aileron flight is still well beyond my current piloting skills.
First off, I've got to comment on the amazing quality of the parts in the glider kit. The wing is a foam core. laminated with what appears to be black poplar veneer and very lightly coated with resin. I'm amazed that this nice a wing is available for $99, let alone the rest of the kit (though I subsequently discovered that the wing itself sells for $65).
A friend of mine that is a highly experienced RCRG pilot recommended the Colibri to me back in 2007 when I looked at the NARAM 50 event schedule, saw D-BG on the slate, and felt that it was time for me to step up to something a little more performance oriented than the Edmonds Arcie-II. With a somewhat small field bordered by trees, it really looked like R/C would have too strong an advantage over free-flight models, and so I decided to take the plunge into somewhat serious R/C. The Colibri, he said, would be a fairly simple conversion, offer very good performance, and was a pretty good price as well.
Possibly foreshadowing the luck that would follow, about a month after I purchased the Colibri, internats competitor Greg Stewart posted a terrific and very detailed conversion plan for a slightly smaller and lighter model, the Blue Arrow Venus, but I was "pot committed" to the Colibri at that point and marching onward.
The glider itself was built mostly stock, though with an inverted V-tail to avoid rocket exhaust charring the tail. I'll walk through the main construction steps, not overly detailed, and will include the boneheaded mistakes I made along the way.
The wing is pre-built, but comes in two pieces that must be joined. To join them, there are two wood blocks that slide into the foam cores of each half, very snug for a good tight alignment. In test fitting, they seemed to line up perfectly, so I went ahead and epoxied the two halves together. I stupidly didn't catch that there needed to be a dihedral, since that would have required sanding out some of the foam slot, and actually reading the directions, and actually understanding something about gliders. Bear in mind that at this point, I'd built and flown many boost gliders, and very few had flat wings, but this didn't jump out at me as flagrantly off. Sort of like that teenage driver who at best knows how to operate a vehicle with no understanding of how the power train works.
Should you opt for aileron flight, there are amply detailed instructions in the kit for how to cut out areas for servo mounting, control rods, etc.
The finished wing is then mounted to the fiberglass fuselage/boom by drilling two small holes and inserting threaded nylon bolts. This makes the wing removable for transport, though in my case given the pod mounting approach I was going to use, removing the wing would be problematic and so I mounted it permanently with a little epoxy.
The V-tail consists of two pre-cut balsa tail halves, each of which also has the control surface pre-hinged. All that's needed is to mount the control horns and glue them to the hardwood mounting plate which then slides onto the tail end of the boom.
The supplied pushrod assumes use of ailerons for turning, and so is rigged with a y on the end to connect to the control surfaces of the v-tail, which would make both sides move in the same direction. This would make the tail exclusively up-down control. I wanted to stick with 2-channel for up/down and left/right, which needs each side of the v-tail to be able to move up/down as needed, not forced together. I ditched the y system and used a replacement pushrod set picked up from the local hobby shop.
All that's left of the standard glider construction is to attach the canopy to the fuselage/boom and hook up/test the R/C gear. There's not a lot of room for the gear, especially since I was skipping the ailerons, forcing me to cram (2) micro servos in the fuselage instead of the intended (1). I cobbled together a small mounting plate from balsa, cutting out holes for the servos, and sanding to fit snugly inside the fuselage.
To convert for rocket flight, I made a balsa boom to fit across the chord of the wing and then sanded/leveled the top to run parallel to the boom, maybe a slight angle of attack where the nose is lower than the aft end (pitch down).
Getting the CG right on this was a bit tricky. The glider CG is supposed to be slightly ahead of the midpoint of the wing, and that required nose weight. I didn't have room in the canopy, so added some clay inside the plastic nose cone I used to close off the motor tube. This eventually brought it back to where it needed to be. Note--be sure to trim with an empty motor, in my case a 24mm RC reload case (similar to a regular 24mm case but with a solid/sealed front rather than a screw-on delay cap).
Lacking an actual 4-rod/rail tower for launching gliders, I decided to go with our club's 1/4" rod, so attached a standard lug to the pod. I angled the rod about 20 degrees down, into the light wind. The motor lit right away, but was either too little impulse or there was too much tension/drag, as it never left the pad. It still seemed to slide up/down fairly well, so I went up to a D7.
Now this initial build had a flat wing, no dihedral, and no ailerons, so looking back it was doomed. It hung on the rod a bit, weakly lobbing to about 50 feet before pitching down, at which point I touched it just enough to level it out. It coasted about 50 yards out, level, then burned out. I touched a little left turn to bring it back around, at which point it rolled over and cruised along upside down. Not knowing what to do at this point, I tried turning right, which caused more roll, loss of speed and it cart wheeled quickly down. Ugly, for sure, but it at least survived the flight.
Convinced that the poopy boost/flight was because there was too much drag on the rod and/or rod whip, I switched to rail buttons and went back out at our next launch a month later with another D7. That definitely helped the boost, as it now zipped right off the rail with plenty of power. Enough power to pitch down right away, much faster than I was ready to react, so it power-pranged into the ground. The wing had sheared through the nylon screws but was otherwise unharmed. The V-tail had broken off, and the fibreglass fuselage had cracked. It was now just a month before NARAM, and I clearly had no clue how to handle this plane, so I set the carnage aside and decided to make it a winter project.
I had an opportunity to fly with my RCRG buddy that winter, and took the Colibri pieces out to him for advice. He laughed at the flat wing, explained the principles of dihedral and roll stability, which certainly made me feel better, albeit stupid, for knowing what had gone wrong with the first build. I split the wing open, re-epoxied it together with a decent dihedral (one wing flat, the other tip about 3" raised), and mounted it back to the boom/fuselage, using about a 1/4" thick bed of Fix-It epoxy clay to form a nice custom-fit for the dihedral joint over what was a flat surface to bond to.
I then waited for spring to roll around, at which point I took it out for a few hand tosses. It was a much better flyer at that point, and I was able to lightly toss it 5-6 times, getting some left/right action as it slid down, though each toss only carried about 50-75 feet. Just as I was getting comfortable, though, my luck soured, and it landed on a harder patch of ground on short grass rather than in the taller/softer weeds I'd been hoping for. The V-tail cracked and one side broke completely off. Back to the repair shop...
After successfully repairing the V-tail, I brought it back out for another run, on another D7. Similar result--almost immediately after leaving the rail, power-prang. The wing survived, but I had totally trashed the canopy, the servos had broken through the mounting plate, and the receiver was toast, no longer functioning. At this point, having frittered away a full year on/off, I recalled the slogan "if at first you don't succeed...failure just might be your style" and decided to abandon RCRG indefinitely.
Fast forward about 9 months, during which time I'd acquired multiple Estes Sweet Vee's, and built one (mostly) on a lazy Sunday afternoon. The write-up has previously been posted here, but the end of that story is that after building it, I let my RCRG guru buddy break it in on the first flight, he caught and corrected some trim problems, and the path was clear for me to fly RCRG's. With a few successful Sweet Vee flights under my belt, I decided to fix the Colibri and try again.
On a breezy fall day, I had finished the Colibri repairs and was stubbornly determined to get in some flights before winter settled in, so I packed it and my Sweet Vee up and headed to the field, not even bothering to check the weather. When I arrived, winds were puffing a stiff 10-15 mph, but the Sweet Vee is a lumbering giant that could probably handle them, and I decided to at least make sure I got in some hand tosses to trim the Colibri. I started off with a light toss into the wind, and it practically jumped vertically up an instant 30-40 feet. I was able to quickly turn it downwind, raced a bit, then brought it back into the wind to land and try again. Somehow the wind knocked it again, only this time it pushed it into a nose dive I couldn't stop, and I broke the tail off again, cracked another fuselage, and broke loose all the R/C gear (though at least it still worked this time). When even hand tosses end in major structural damage, you know you're in the wrong hobby...
Thanks to an unpaid furlough from work right after Christmas, I had a full week of idle time and decided to clean up a number of broken/damaged models cluttering the basement, and the Colibri kept mocking me as I did so. I finally spent a couple hours with one last effort to rebuild everything, and on a chilly winter day with high temps in the mid teens, trekked three hours west to fly with my RCRG buddy's club, hoping he could work his magic on this cursed bird.
This time, I even decided to mount the V-tail up instead of down, figuring even if it charred off, it might take more than one flight to do so, and certainly would take more than just a hand toss to trash it. He tossed it twice, and quickly pronounced it flight-worthy without any adjustments. We loaded it in the tower (having built one for the Sweet Vee, I abandoned trying to launch gliders off rods/rails). When the D7 lit, it zipped out of the tower surprisingly fast, with some tendency to pitch down but not unmanageable, and by friend tapped the stick just enough to straighten it out. It soared to a good 300-400 feet, at which point he turned the controls over to me, and I had no trouble steering it in and out of the wind, staying aloft for nearly 4 minutes. It was an amazing flight.
I quickly reloaded another D7 for a second flight, this time taking the stick myself the whole way. I had adjusted the trim a couple of clicks to offset the boost pitch issue, but it still faked me a little bit, and in my eagerness to correct I almost overdid it and back flipped it, but I averted disaster and kept it going mostly up. Not nearly as high, maybe 200-250 feet, but certainly respectable and good for another 2 minutes or so airborne.
I'm sure there will be crashes and failures again down the road, but at this point I can say the model is flying wonderfully, and any further mishaps are obviously pilot issues. I'd very much like another crack at one from the beginning, to get the right wing dihedral, to rig the control horns for a little more movement, to get the boost pod mounted a little more forward to reduce the need for added weight, etc., but this flies very well now and I'm quite happy getting my experience on this before messing around with anything nicer.
The only con I'd offer is that I had gone into this thinking it could be a good beginner's model, not as a first RCRG, but as something that someone with as many Arcie II flights as me could handle without much trouble. That was a very flawed assumption. This should not be a first RCRG, but for someone with even a little prior experience controlling boosts, this should be no trouble at all.
What You Can Do