RADIO CONTROL SOARING
Mike Garton 506 NE 6th St., Ankeny IA 50021 E-mail: mike@iastate.edu
The theme of this column is Rudder–Elevator–Spoiler (RES) class gliders. Below is a brief explanation of the class, an update on the rekitting of the Sagitta 900, details of Rich Burnoski’s RES offerings and his new company, impressions of the Two‑Meter Chrysalis, and an introduction to Mark Drela’s Allegro‑Lite RES design.
RES Class Overview
In RES class the controls are limited to rudder, elevator, and spoilers. This competition class is intended to let relatively simple and inexpensive gliders compete on a level playing field.
- Computer radios are not needed, so the initial investment can be three to four times lower for an RES glider.
- RES gliders are generally easier and faster to build than flaperon-equipped "full-house" gliders.
- They are also easier to thermal than flaperon models because turns are automatically coordinated.
Sagitta 900
The Sagitta 900 is an excellent choice for RES. Designed by Lee Renaud, it is a built-up model with a 100‑inch wingspan and a conventional tail. The Sagitta was a breakthrough partly because of its computer-designed semisymmetrical airfoil (an Eppler 205 variant), which provides high lift for launching and thermaling, good penetration, and a high lift-to-drag ratio.
As of mid‑October, Roy Simpson of Dream Catcher Hobbies had "short kits" for the Sagitta 900. These kits include plans, photo-illustrated instructions, laser-cut wing ribs, wing-rod receiver blocks, and preshaped spruce trapezoid leading-edge pieces. Dream Catcher also offers fiberglass Sagitta 900 fuselages and short kits for several other polyhedral airplanes. Roy plans to upgrade many of the short kits to full kits as time permits.
Dream Catcher: Aquila XL
The Aquila XL is another good RES kit from Dream Catcher. The Aquila XL is a 150‑inch‑span variant of the Aquila, which had a short production run before 1980 and is Nostalgia‑legal. It uses a larger span for improved performance; I expect to complete mine soon and will report more on it later. More information is available on the Dream Catcher web page.
Chicago Style and Chicago Sky1 (Rich Burnoski)
Rich Burnoski of Chicago has started a glider business, Chicago Sky1. One airplane he will sell is his RES design—the Chicago Style.
- The Chicago Style is a modern RES design with a 120‑inch wingspan and a modified SD7037 airfoil.
- The fuselage is fiberglass with a slip-on nose cone.
- The wing is vacuum-bagged carbon and glass over foam.
- Weight is about 72–74 ounces.
- The design is strong enough for zoom launches and has the glide ratio to reach distant thermals. Rich placed fifth in RES at the 2000 AMA Nationals with the prototype.
The Chicago Style’s spoiler design is notable. The blade was made by vacuum-bagging carbon and fiberglass between two pieces of Mylar in a wing-core bed; it is only 0.015‑inch thick. This allows it to lay nearly flat on the existing wing skin without disturbing airflow much. Only a small hole is cut in the top wing skin for the linkage, creating very little stress concentration. A servo is installed from the bottom side of the wing to direct-drive each blade. This short direct linkage prevents the spoilers from opening on launch — a common problem caused by suction above the wing.
Rich also plans to be a stocking dealer of molded composite airplanes and accessories. By having airplanes in stock, he expects to deliver them within a couple of days, versus the typical six to ten weeks many molded-airplane vendors require.
Paul Wiese's RES and Handling Notes
Paul Wiese's RES airplane could have fit well in a discussion of Mantis variants. The bulge on the tailboom behind the wing serves as a hand grip—holding a large airplane by a small-diameter tailboom is difficult in wind.
When winch-launching, it is critical that polyhedral models are released with the fuselage in the plane of the line. A crooked release can cause the airplane to dart off to the side at high speed and low altitude. This problem is most severe on airplanes with large amounts of polyhedral; narrow tip chords aggravate the situation.
Two‑Meter Chrysalis (DJ Aerotech)
DJ Aerotech's Two‑Meter Chrysalis is a relatively new RES kit that uses proprietary airfoils and typically weighs about 26–27 ounces.
- Handling and penetration are good for the Two‑Meter Chrysalis; I was surprised by its penetration compared with the Hand‑Launched Glider (HLG) Chrysalis, which does not penetrate as well.
- Don Stackhouse put a great deal of engineering and innovation into the Chrysalis structure. An experienced builder can assemble the wing in one evening. The leading edge is a dowel, requiring no shaping, and the shear webs are precut and preglued on tabbed wood.
- Parts are provided to build either a V‑tail or a conventional tail; I recommend the conventional tail for beginners since V‑tails are harder to set up perfectly.
- Common owner modifications include converting to a bolt-on wing and adding a vertical plywood blade across the wing center joint.
The Chrysalis Two‑Meter was touted as a replacement for the Carl Goldberg Gentle Lady. It’s a nice kit, but the Gentle Lady is prettier in the hobby store and costs about one-third as much, so newcomers often choose the Gentle Lady. Either model is a good field choice.
Mark Drela’s Allegro and Allegro‑Lite
Mark Drela, a professor of aeronautics and astronautics at MIT, designed the Allegro RES series. Drela was Senior Design Engineer for the Daedalus human-powered airplane and has authored the XFOIL airfoil design software. He also held several Indoor Free Flight and HLG records.
The Allegro was first built as an all‑composite Two‑Meter RES glider. Mark designed six different airfoils for the model—four for the wing and two for the tail—so each wing section uses a different airfoil optimized for local requirements.
The Allegro‑Lite is a similar design with a built‑up wing. Mark designed new airfoils tolerant of rib sag for the light‑built wing. The Allegro‑Lite is a few ounces lighter than the original composite Allegro.
Mark supplied a detailed graphic with structural analysis. He calibrated his breakdown by building spar samples and instrumented destructive tests. The wing is stressed for 150 pounds of winch‑line tension; it is remarkably strong for an 18‑ounce Two‑Meter — Mark has flown it and can stand on the winch pedal.
He lists component weights and can predict final model weight, strength, and performance during the design stage. This is an example of thorough engineering backed by real experiments.
A couple of terms from his drawing:
- Neutral Point: an aeronautical engineering term roughly representing the aft limit of the center-of-gravity (CG) range. The practical CG range lies ahead of the neutral point; the drawing shows Mark's recommended CG.
- "Re sqrt(CL) = 70K (100K)": a function giving the local Reynolds number at that wing station for a given lift coefficient, assuming the model is at design weight. The number in parentheses refers to the ballasted weight. These are reduced Reynolds numbers used by aerodynamicists.
Although the Allegro designs incorporate a lot of technology, they are relatively inexpensive to build and equip and should be easy to fly. More information about the Allegro and Allegro‑Lite is available on the Charles River Radio Controllers site, including details about carbon‑spar construction, structural analysis, airfoil coordinates, and pictures.
Vendor Contacts
- Dream Catcher Hobbies
Box 77 Bristol IN 46507 (219) 523-1938 www.dchobby.com/
- Chicago Sky1
751 N. Bolingbrook Dr. Link 3B Bolingbrook IL (630) 759-8610 www.chicagosky1.com/
- DJ Aerotech
719 Fisk St. Piqua OH 45356 (937) 773-6772 www.bright.net/~djwerks/
Transcribed from original scans by AI. Minor OCR errors may remain.
