RADIO CONTROL SOARING
Mike Garton 2733 NE 95th Ave., Ankeny IA 50021 E-mail: [email protected]
This month I'll give you some details and flight impressions of three new gliders. The Spinner is an inexpensive expanded polypropylene (EPP) foam discus-launch glider (DLG) kit, the Hyper DL is an inexpensive Almost Ready-to-Fly (ARF) DLG, and the AVA is an ultralight ARF that resembles Mark Drela's Bubble Dancer.
The high-end DLGs reached maturity last year. In other words, last year's versions of the XP-3, the Taboo, and the Encore are still competitive this year. Although contest-driven designs have stabilized, there is still room for improvement in cost reduction and durability.
The $300–$450 DLGs are very durable. Most less-expensive versions are fragile by comparison; it is common to see $250 imported DLGs break on the first day. I have been hoping to find a tough, low-cost model that I can recommend for a first discus glider.
Spinner
Ed Berg of Englewood, Colorado, designed the Spinner. The instructions state:
"The Spinner was designed to fill the need for a plane that could be discus-launched and flown in a wide range of conditions, and survive crash landings in rough terrain. It had to be easy to fly, easy to build, hard to break, and easy to repair."
Ed let me fly one of the prototypes. The Spinner is cheap, strong, and fun to fly. It has straight-taper wings with the AG-44 airfoil at the root and the AG-46 airfoil at the tip. The conservative planform gives friendly handling with no tip stall. The Mark Drela airfoils give it a good glide ratio and a wide speed range. Wing construction uses EPP-foam cores with a carbon-tube spar and carbon-tube sub-trailing edge. The wood supplied in the kit for the flaperons is custom-machined to match the airfoil's thickness. Fiberglass strapping tape reinforces the EPP foam, and Oracover is recommended for covering.
The Spinner's nominal weight is 15 ounces, which makes its sink rate higher than the competition DLGs. On the other hand, this may be the only discus glider available that is both inexpensive—$125—and durable. The Spinner kit is complete except for glue, tape, and covering, and it comes with a 12-page instruction manual. The EPP-foam fuselage pod is preshaped in top and side profiles. Most of the wood in the kit is laser-cut. An experienced builder could complete a Spinner in approximately 15 hours plus glue drying time.
The Spinner's EPP wing and fuselage pod can take a great deal of abuse. I watched Ed crash hard enough to shear both nylon wing bolts. He was playing around inverted and waited too long to loop out. He dug out the old bolts, put in new ones, and continued flying. The flexible wing construction does have a downside: advanced throwers may be able to flutter it with high-power launches. Ed was throwing his Spinner to 80–90 feet with no flutter. I usually throw my XP-3 to roughly 140 feet. With a full launch, I did make the Spinner flutter its wings. Ed said I was the first to do that. I do not hold it against the design.
The Spinner is a good option for a first DLG, a rough-terrain aerobatic sloper, or a sport flier of any type. There is a big niche in the market for an inexpensive DLG that can last through a flying season. The Spinner may be alone in that slot.
Hyper DL (HDL)
The Hyper DL (HDL) is an ARF glider from Art Hobby. It is also inexpensive, at $131 as I write this. The HDL has straight-taper wings with the HN1033 airfoil thinned to 8% thickness. It uses four servos and has partial-span ailerons. Flying weight is 14–15 ounces.
The HDL’s fuselage pod is white gel-coated fiberglass. A canopy hatch provides access to the nose. The pod is small and sleek, but it’s difficult to install gear in. The carbon tailboom is larger than the common kite spars. Tail surfaces are solid balsa sheet.
The HDL wings are white foam with black poplar-veneer wing skins. The poplar is bonded to the cores while the wing is pressed into female molds. This method produces a very accurate wing. I was impressed with the amount of prefabrication in a kit at this low cost.
I helped a friend test-fly his HDL. It started out built stock. My first impression was that it was heavy and fast, with no flaps to slow it down. Compared to a flaperon DLG, it lands like a jet on ice.
The HDL’s wingtips taper toward the trailing edge at almost a 45° angle. These swept, Sagitta-style tips are not a good choice for a DLG. The recommended peg location is near the high point of the airfoil; with each throw the raked-back wingtip would hit my hand at the web between my fingers. The hand strikes can be avoided by making a more squared-off wingtip or moving the peg to the trailing-edge tip. The former is preferable.
I flew the wing off on one of the first moderate-power launches. It had been held on with one wire pin at the leading edge and one nylon bolt near the trailing edge. The fuselage pod gained some cracks in the crash. After that incident we removed the wire wing pin and added a second nylon bolt. Later we cracked the balsa rudder when it air-loaded on launch. More fiberglass took care of that. High-dollar DLGs come with fiberglassed wooden tail surfaces.
Even with a gyro, the yaw oscillations on launch are a little larger than on most DLGs. This is because the relatively heavy hardwood-sheeted wing creates more inertia in the yaw axis. More vertical fin height should help.
Built with the stock nearly-flat wing, thermal turns required constant attention. If I stopped actively controlling the model for three seconds, it would be in a vertical dive. A visit to the table saw and adding 6° of dihedral per side fixed that problem. It did require us to make a new saddle for the wing using a bit of epoxy and cabosil filler.
Handling is much improved with the higher dihedral. It is still difficult to get a good thermal climb rate out of the glider. The weight and lack of camber control force a pilot to make large, fast circles compared to flaperon-equipped gliders.
A redeeming quality of the Hyper DL is the availability of inexpensive replacement parts. A new fuselage with pod and boom is $46. Wings are $70.
I called Andre of Art Hobby and gave him my feedback: two bolts for the wing, flaperons, 6° per side dihedral, square off the wing, and more vertical fin. Builders may also want to fiberglass the vertical fin and rudder. Replacing the pushrod system and not using metal tail fasteners will reduce the need for nose weight.
Hopefully many of these changes will make it into production by the time you read this. If they do, they are easy for the builder to make. With the tweaks listed, the Hyper DL is still a good value.
AVA
The AVA is imported from Ukraine and is made by Vladimir, the maker of the Graphite and Organic series. As this is being written, it is available exclusively from Barry Kennedy.
The AVA is unusual in that high-tech materials and methods were used to make a rudder-controlled floater. The aerodynamic design is a direct knockoff of Mark Drela’s Bubble Dancer. The 127-inch-wingspan AVA weighs approximately 38 ounces ready-to-fly. With 1,100 square inches of wing area, the wing loading is just under 5 ounces per square foot.
The AVA has a 36-inch-wide single carbon spoiler across the center section. The three-piece wing is carbon/Kevlar D-box, Kevlar-wrapped spar, carbon-capped ribs, and carbon trailing edge, all wrapped in Oracover. The leading edge (carbon/Kevlar on a 45° bias) D-box is also made in a mold. The fuselage has a slide-on nose cone; all major parts are prepainted in a mold and then postcured.
The AVA is $705 shipped. Kevlar ballast tubes are available for $10 each. The ballast tube mounts in the fuselage and holds 14–18 ounces. The sailplanes are shipped in returnable Series 3 Sport Tubes.
The generous three-panel-per-side polyhedral makes for beautiful thermal turns. Although the handling is extremely good, nothing happens quickly because of the slow (unballasted) speed. Jim Porter had not tried his AVA's towhook yet because "you don't need to." A firm toss was enough launch to catch thermals each time he went out.
Jim positioned his servos at the front of the compartment to minimize nose weight. In the end he found that he needed 1/2 ounce of weight at the tip of the tail. In hindsight, the servos should have been placed rearward.
A pushrod trick is visible in the detail photo of Jim Porter's AVA. Putting the servos forward left them potentially unsupported for 4–5 inches. To solve this problem, Jim drilled a small hole in the servo tray directly under the pushrod and pushed a small carbon rod into the hole.
The carbon rod should be long enough to extend from the floor of the fuselage through the servo tray and up to the pushrod. It is glued to the fuselage floor and to the servo tray, then a small piece of pushrod housing tube is fit over the pushrod and aligned over the carbon rod. Thread or string is used to lash the pushrod housing piece onto the carbon rod. Some cyanoacrylate (CyA) glue is used to harden the thread. The support is light and strong.
You may also notice a pushrod splice exposed in Jim's AVA; 48-inch carbon pushrods were not quite long enough for the forward servo position he chose. Spare nylon tail bolts are also visible, screwed in between the servos and the switch.
Sources
- Spinner:
Ed Berg (303) 762-9085 [email protected] http://upslopesoaring.com/
- Hyper DL:
Art Hobby (406) 256-1224 www.arthobby.com
- AVA:
Barry Kennedy (972) 602-3144 [email protected] http://kennedycomposites.com
Transcribed from original scans by AI. Minor OCR errors may remain.
