Rebuilding A “Classic” ASW-15 for Slopeless Slope Soaring
Do-it-your-selfers have all experienced the sort of nightmarish project where you start out to fix a leaky kitchen faucet and end up re-plumbing the entire house. This is a similar tale on a (thankfully!) considerably smaller scale and much lower budget.
Somewhere in the dim reaches of my sordid RC soaring past — over two decades ago — an older RC flying friend, Charlie Nelson, willed me one of his toys, a 2-meter, semi-scale (emphasis on “semi”) ASW-15 slope glider that was marketed by Icare (Canada) back in the last decade of the previous century. I wonder if there is any of the old guard left in the Seattle Area Soaring Society who would remember Charlie… or me for that matter?
I had a sister ship at that time, a diminutive ASW-19. Some lucky guy in St. George, Utah probably still has the little beast, which I donated to the local RC club at a time when I was attempting to put RC behind me, which failed miserably — here I am. The only significant difference between the two models was the fiberglass fuselage tail design — T-tail for the -19 and conventional cruciform tail for the -15. The rather thick (airfoil, that is) obechi-sheeted foam core wings were identical. Both were heavy and fast — well suited to soaring the lovely, windswept slopes near Richland in Eastern Washington. I was privileged to maiden Charlie’s glider at Kiona Butte in a healthy north wind. I assume that’s why he left it to me. It flew perfectly — stable, fast and maneuverable. He had a blast with it after that, even flying it off high-starts and winches. The little critters would thermal soar in strong conditions but had to be kept very much “on the step” while circling to prevent a sudden and precipitous tip stall — probably disastrous at low altitude.
Skip ahead a couple of decades+. I was surfing the Internet enjoying RC porn when I happened to notice a “sexy” little 64mm ducted fan complete with outrunner motor for a seemingly very reasonable price at Motion RC:
It occurred to me that I could glue this petite toy onto my old but still quite flyable Boomerang foamie flying wing and have some fun with it again. Back story: I miss slope soaring. There is no slope soaring here in southern Arizona — every hill, ridge, canyon, wash, cliff, arroyo, mesa, and mountain is covered in trees with thorns, bushes with thorns, cactus with needles, sage brush, sharp rocks, scorpions, gila monsters, and rattlers. I placed the order.
A few days later I was opening the small box that the USPS had kindly delivered. Inside was a surprisingly well-made mini ducted fan, shroud and motor, ready to go. After soldering the included connectors to a 40-amp ESC and hooking up a 4S LiPo battery and a servo tester for throttle control, I held on and cranked the fan up..and up…and up until the mad little thing screamed. Impressive! The fan generated a surprising amount of thrust — more than enough to transform the Boomerang into an exciting e-flyer. And, it was very smooth, minimal vibration — well balanced.
Shortly thereafter, I happened to glance up at my overhead storage area and my gaze settled on one of several dusty cardboard boxes that had been following me around for lo these many years. The one containing Charlie’s — now ancient — ASW-15 (gift or curse?) caught my eye. Suddenly, a picture of those full-sized aerobatic sailplanes with jet engines mounted behind the canopy flashed (maybe “slowly materialized” would be more accurate) into my high-mileage gray matter. An epiphany occurred! The Boomerang was immediately forgotten. New plan: ASW-15 + ducted fan = “hotliner” — semi-scale slope soaring without a slope! Ain’t spontaneity great? Let the madness begin!
Truth be told, I already had a pretty hot hotliner, an ancient, like me, RnR F3B Spectrum. It’s a 109 inch wingspan, T-tailed, full-house, fully-molded, heavy and rather sleek glider that I had laboriously (because of the slip-on nosecone style of fuselage) converted to e-power a couple of years ago. It looks great, flies well, goes fast, is tough as nails and, in spite of its high wing-loading, will even gain altitude in the powerful Arizona thermals that frequent the Green Valley area (yes Northerners… even during the “winter!”).
Still, I thought the ASW-15 would be a kick with its smaller size, quicker control response for aerobatics, and scale appearance. Better portability was an added bonus. Too, it would be somewhat unique sporting the cool ducted fan on its turtle deck. Did I mention the sound? Yes, that might be kinda cool, as well. And, best of all, it would be a “quick and easy” conversion! As old as I am (78) you would think that I’d know better — ever the optimist. How quickly I forget!
Combine that unjustified optimism with an unfortunately high level of negligence in the planning department, and what do you get — this project. Spoiler alert: it turns out all right at the far end, but not without some of those well-known and oft-encountered “trials and tribulations.”
My first thought had been to merely glue the fan shroud on top of the fuse, run the motor wires through a hole, hook up ESC, battery, and receiver and go fly. It looked good on paper… and so simple (the old rudder, elevator and aileron servos seemed to work fine with a new 6-ch. FrSky receiver). Right off I came to the brilliant realization that a pylon would be needed to support the fan shroud because it flares out at the front to guide the incoming air smoothly into the fan. It couldn’t be glued directly to the fuse. Challenged, my now semi-activated imagination started to ponder the myriad of details such as height, width, shape, strength, material, angle of attack, attachment, etc. The pondering is always the time consuming part of these retrofit projects, straining my well-worn neurons to the max. Creativity is after all, difficult! That must be why I love a well-designed model kit with excellent instructions — no thinking required, just start gluing stuff together per the recipe.
Anyway, I cobbled together a little pylon laminated from a few layers of 1/8” basswood that “looks about right” (my primary design methodology) and epoxied it to the fuselage after roughing up the gel coat a bit. I didn’t trust the glue joint to hold the frisky little fan in place for long, so I Dremeled a couple of small holes through pylon, fuse, and shroud and installed small machine screws to solidify things. Three more holes drilled through the pylon and fuse provided a route for the motor wires.
That was pretty simple. Onward to fitting a battery into the cramped nose. Here’s where lack of planning first stung me. Battery-wise, I was thinking way too small. After running the fan on the Watt Meter and finding that at full chat it pulled 37 amps and 547 Watts (almost 3/4 of a horsepower) out of a 4S LiPo (YIKES!) it dawned on me that a lightweight 650 mah battery would provide pretty damn short flights with this little screamer devouring mass quantities of electrons. After looking on-line at battery capacities and dimensions until my eyeballs hurt, I found an 1800 mah 4S LiPo pack which might just be squeezed into the nose ahead of the servos. Theoretically, such a pack would provide three minutes of full throttle excitement before everything goes dark. That’s not a lot of flying per charge. However, since I knew that only partial throttle would be used much of the time, I figured that moderately intense 7 to 10-minute flights would be feasible. Who knows, thermals strong enough to support longer flights might even be encountered. Of course, thermal soaring is not what this mini-hotliner is all about.
With the significant increase in weight of the larger battery now factored in, it became obvious even to me that I had to get rid of the soft metal ballast that Charlie had cast into the nose of the glider. I’ll just say that chiseling that six ounces of metal out of the nose one chunk at a time was not one of the more interesting parts of the project. The alternative of adding weight in the tail didn’t seem like a particularly outstanding idea.
When the new 1800 mah LiPo showed up it did fit into the nose as hoped with zero millimeters to spare — surprised the heck out of me. That almost never happens!
A bit of the balsa cockpit bottom to which the canopy is attached and a bit of the canopy’s front former had to be sacrificed to accommodate the height of the battery. No big deal. The receiver could be squeezed in alongside the battery. The ESC was Velcroed to the side of the fuse aft of the battery.
About ready for flight — let’s assemble the little beauty and check that everything works. Misplaced optimism combined with a continued lack of planning struck yet again. Back in the days of yore when the ASW-15 was produced, designers of small RC model airplanes typically drove the ailerons off of a single servo located in the fuselage and mechanically connected to the ailerons through pushrods and bellcranks. Ah, the dark ages. This was a lousy setup for planes with removable wing halves like the ASW-15. But, the manufacturer used it anyway.
Sadly, I don’t have a photo of the Rube Goldberg aileron servo installation located behind the cockpit. It met its demise before I thought about writing this article. Suffice to say that when I attempted to hook up the braided steel cables that were intended to directly connect the servo arms to the aileron control horns it was difficult and inconvenient, requiring the utterance of certain incantations not fit for public consumption. The worst development was that the friction and hysteresis caused by the cables in their old plastic housings with fairly sharp 90-degree bends just ahead of the aileron control horns severely impaired the aileron travel and synchronization. I took my best shot at getting things adjusted and synced until it became obvious that the kind of precise control I wanted was never going to happen with this setup. An additional negatory factor was that after all my fiddling, the Rube G. mounting structure for the aileron servo was beginning to disassemble itself, and would not be easy to repair or replace as it was all so difficult to access in the small fuselage. Not ready for flight. Back to the recliner for more pondering, and a cold beer to assuage my frustration.
The inescapable conclusion from all that sipping and pondering was that the glider really needed servos embedded in the wings to control the ailerons — just like a modern RC sailplane. How bad could it be? Just yank the cables and old servo out, cut a couple of holes in the wings, run some wires through the plastic tubes, glue in servos, make pushrods, solder connectors and all will be far better than new. Again, so simple!
Number 3 bite from lack of planning: after yanking the cables I found that the plastic tubes embedded in the wing cores were far too small to carry the necessary three servo wires. Yes, I did try to pull a tube out thinking that the resulting hole would be large enough for the wires. Unsurprisingly, the brittle old plastic just broke off. What to do now? Wireless servos would have been great! Why don’t we have Bluetooth wireless servos and receivers? No, no don’t tell me!
After the wishful thinking, I bypassed pondering and went directly to head-scratching, a much more intense sort of activity not necessarily yielding better results. OK, so we need a bigger diameter hole from root to servo hole in each wing, about 23 inches. Drill bits do that kind of thing. But, how does one ensure that the long bit goes where it needs to go? Obviously, the bit must follow the plastic tube. That’s not going to happen with a conventional drill bit. Hmm, a piece of brass tubing of the appropriate I.D. and O.D. might just be able to cut through the foam around the outside of the plastic tube and stay on track following it. For lack of any other inspiration… it’s a plan.
As you may have noticed, this quick and dirty project has turned into a slog. But, it has the potential to make some progress in spite of my numerous shortcomings. Perhaps there’s light at the end of the brass tube. And indeed there was.
Servo holes were cut into the wings in front of the aileron control horns exposing the end of the plastic tubing.
The local True Value provided a suitable piece of rigid brass tubing. I cut it to the required length and filed some gnarly sharp teeth into one end.
A piece of music wire was placed inside the plastic tube to prevent the new “drill bit” from cutting through it.
Could this actually work? In spite of my trepidation, after chucking the brass tube into my drill, to my surprise it turned out to be very quick and easy to follow the plastic tube, extract the “bit,” and then pull out the plastic tube and the foam surrounding it, leaving a hole of adequate diameter to run servo wires. Definite progress — whew!
As always, the devil is in the details, and there were plenty to keep me out of the tavern: clean up the servo holes; fill the grooves in the trailing edge that had accommodated the old cables; apply fiberglass and resin to the bottom wing skins to pass the bending loads around the new servo holes; pull wires; solder wires to servos and receiver connectors; glue servos in place with arms properly aligned; and assemble pushrods. Did I repeat myself? Put it down to old age and too many years of exposure as a child to Butyrate dope and model airplane glue. These days, I suppose that would be considered “child abuse!”
A niggling little problem that had become apparent was that the plastic covering on the wings under the tape hinges for the ailerons had come loose and refused to be ironed back down — the glue yet another victim of old age. I decided to remove this covering and paint the area white to more or less match the white plastic film. After cleaning off the residual adhesive, a couple of coats of white from a rattle can were applied. The paint isn’t actually noticeable, and provided a good base for the Scotch cellophane tape I used to hinge the ailerons. Yes, cellophane tape — it sticks well, is fairly durable, and is nearly invisible. I prefer it to hinge tape.
At the time I was doing this project, UltraCote was in very short supply, due to pandemic-related supply chain issues, and color choices were nil. So, I took the quick and cheap way out by using scraps of the 10-year old yellow UltraCote hidden in a bottom drawer to cover the bare areas around and over the servos. This late in the game, aesthetics were definitely not a high priority! Well, truth be told, they never were, as this glider to begin with was far from flawless in appearance.
So, the house is mostly re-plumbed and the system is nearly ready for pressurization — only a few of those devilish details still left to conquer like installing cockpit hold-down magnets, aligning servos, programming the transmitter, and figuring out how to squeeze battery, receiver and wiring into the fuse.
Those tasks laboriously accomplished, the dripping faucet drips no longer. The simple and quick project that was neither simple nor quick is complete. The plumbing is whole again. Let’s fly!
Here’s what the little “beauty” looks like ready to rock and roll.
After all that unplanned blood, sweat and tears the diminutive ASW-15 ducted-fan hotliner fortunately turns out to be a hoot to fly, although not without certain challenges. I like to launch left-handed so that my right can remain on the main control stick. Unsurprisingly, being right-handed I “throw like a girl” with my left hand (sorry ladies). This is fine for slow flying F5J gliders but it got me into trouble a couple of times when there was no wind to help augment the launch airspeed, a critical factor for this heavy (3lb.-3oz. all up), high wing-loading little bird that likes to tip stall.
One of the more extreme insufficient-airspeed incidents on launch resulted in the glider flip-flopping back and forth from tip to tip until contact with an inappropriately located immovable object (Ma Nature at work) resulted in a broken wing. The wing structure is so basic — no spar, just foam and skin — that the repair was completed quickly, barely interrupting the fun.
After those incidents I gave in and switched to a right-hand toss — throwing “like a boy,” I guess — per NTSB’s accident investigation recommendation. That works much more reliably — no problems since.
After my now “supremely powerful” toss the little bird moves out smartly with its “turbine” whining at full chat. It climbs steeply but is just a smidge short of having enough thrust to sustain unlimited vertical. It does have more than adequate power for any sort of normal (2D) aerobatics that the airframe and pilot are capable of performing. It is quite stable, flies smoothly, and retains energy well. The glide with power off is actually pretty flat, which surprised me. I had assumed that the relatively large fan and shroud would make the glider fall out of the sky when powered off. Not so. With the throttle closed it has even managed to gain a little altitude in a couple of our Arizona hat-sucker thermals. The fast flat glide makes landing without glide path control a bit challenging, requiring a long low final approach with the airspeed kept up to prevent that wicked tip stall. Once in ground effect the little beast doesn’t really want to settle in at all. It eats up a lot of the dirt runway at our local field. Grass works better but is scarce in these parts.
Its forte, though, is speed. Because of its small size the little screamer appears to fly extremely fast — generating plenty of excitement for these well-aged reflexes! I still miss being able to fly the glider far down the slope below me then zoom back up the hill. But, at least I can do most of the other stuff that a good hill and a stiff breeze support, just not for very long given the e-motor’s feeding frenzy when pushed hard. Still, intense “sloping” for 7 or 8 minutes is about all the adrenaline rush this old guy can take anymore.
Dave Nutt gets the credit for these flying photos. We were aviating at Maxwell School’s soccer field in Tucson one fine weekend day during the so-called “winter.”
All-in-all the ducted fan conversion was a worthwhile project with a happy ending and a few lessons learned. Slope on!
