Free Flight Duration - 2009/08
Louis Joyner [[email protected]]
NFFS Sympo 2009
The National Free Flight Society (NFFS) annual Symposium Report, better known as the Sympo, is a source for the latest technical information and provides a historical record of the evolution of free flight. According to editor John Lorbiecki, this year's edition is much less technical than in past years.
"If you are afraid of calculus, this may be the issue for you," he said.
Following are some of the authors and articles scheduled for publication:
- Doug Joyce: Pusher canard F1C concepts
- Jim Parker: Modifying a mechanical bunter F1A to full electronic
- Jeff Hood: Cutting indoor balsa
- Rex Hinson: The other 60% (noncompetition fliers)
- Jim Gerszewski: Tracker radios—what's new
- Nick Aikman: A brief history and tips for cutting indoor balsa
- Bucky Servaites: A high-tech engine-starter assembly
- Paul Seren: A Wiki free-flight Internet site
- Bill Hartill: A lost document on boundary layers
- Brian Eggleston: F1A turbulator theory
- Ron Bennett and Scott Newkirk: Modifying competition engines
- Bob Mattes: .020 engine modifications
- Bob Mattes: National Cup results
- Dan Tracy: A look at NFFS's future
- Lee Hines: F1A development
- Ken Bauer: Using an altimeter to fine-tune an F1A
- Bernard Crowe: An F1Q and electric primer
Free Flight Hall of Fame inductees for 2009 are Art Ellis, Phil Klintworth, Fred Pearce, Lee Campbell, Stan Buddenbohm, and the late Paul MacCready.
This year, the Models of the Year Committee selected nine airplanes for recognition in the 2009 Sympo.
"We decided that each model should represent advancement in the state of the art that will likely be widely adapted in the near future," said Jerry Murphy, committee chairman. "The test for how well the new technology works is the model's competition record."
The selected models are:
- Gil Morris's F1C folder that utilizes a flexible carbon-fiber wing structure to permit a thin, symmetrical airfoil under power and an undercambered, flapped section in the glide. (See the February 2009 Duration column for more information about this airplane.)
- The Excelsior F1P that Cody Secor flew to win the FF Junior World Championships; his father Randy designed it with input from Dave Rounsaville.
- Tiffaney's Coupe, designed by Blake Jensen and built and flown by Tiffaney O'Dell. It features a pop-up wing DT.
- Lutz Schramm's F1D indoor rubber model that employs an all-carbon structure.
- Bernie Crowe's Noah's Quark F1Q that applies off-the-shelf technology to a new high-performance design.
- Bob Mattes' Classical Gas, which brings a unique carbon-capped egg-crate "D-box" construction to the Classic Gas event. The model also features a molded wing spar and screw-adjust stabilizer tilt.
- Two indoor hand-launched gliders: Nifkin by Rob Romash and Pelicatoo by Jim Buxton. Both broke the quarter-century-old Category II record on the same day. These two models represent major breakthroughs in indoor glider technology.
- Chris Starleaf's scale B-47 that utilizes multiple rocket motors. Coincidentally, Phil Klintworth, a Hall of Fame honoree, worked on the full-scale B-47 at Boeing in the early 1950s.
You can order the 2009 Sympo from NFFS Publication Services. The price is $35 for NFFS members and $40 for nonmembers. Postage is $5 within the U.S.; postage for orders from Mexico or Canada is $9. Domestic orders: check or money order only. International orders can be paid by credit card, but a service fee is charged. For more information, contact NFFS Publications Coordinator Bob Stalick.
Free Flight Forum Report
This year marks the 25th anniversary of the Forum series produced by the British Model Flying Association's free-flight members. As its name implies, the Forum Report is a compilation of papers presented at an annual meeting. Like this year's Sympo, the 2009 Forum is focused more on practice than on theory—there are virtually no equations. Chaired by Mike Evatt and edited by Martin Dilly, the 2009 Free Flight Forum includes 13 articles covering a wide range of topics, from model construction to flying-site availability. Lindsey Smith's paper provides a brief history of rubber-scale models and includes plans from World War II–era kits.
Trevor Grey's article about brushless motors covers their advantages and disadvantages, propeller efficiency (bigger is better), and timers. He even describes a simple mechanical brake to assure reliable propeller folds.
Mike Woodhouse describes his experiences as British team manager at the 2008 European Championships. Much of the planning process would carry over to any type of contest.
Chris Strachan's article about sharing flying sites with general aviation, while focused on British airfields, is worth reading for anyone interested in flying-site availability.
Also with a British focus, "A Brief Look at Contest Entry Trends Over the Last 20 Years" by Phil Ball deserves attention in the U.S. One graph shows how total entries and entries per event have decreased at almost exactly the same rate as the number of classes has increased. The British, like the Americans, fly a large number of model classes in addition to the FAI events.
Radio DT is the topic of two papers. Trevor Grey details the policy decisions facing rules makers and contest administrators, while Chris Edge examines the practical aspects of installing and using a system. Radio DT uses a brief coded signal, similar to a garage-door remote, to activate a model's DT. It is especially useful for small-field testing.
Construction articles in this year's Forum include Ray Monks' article about rolling F1C and F1J tailbooms using carbon cloth, and Phil Ball's step-by-step instructions for making carbon-capped ribs. Basically, a thick block of balsa is cut and sanded to airfoil shape, unidirectional carbon is added to the top and bottom, and individual ribs are sliced off deli-style. For the undercambered aft ribs on F1A gliders, Phil laminates the block from thinner, prebent sheets so that the wood grain follows the curve of the lower surface.
For quicker ribs, Leon Cole details the use of laser cutting. Mark Croome shows how he makes lightweight D-boxes from Rohacell foam sheet: he heats the 1/16-inch-thick material on an electric griddle and then bends it around a form.
Roger Wilkes provided two articles. One details his "Torqueback" system for F1B and F1G rubber models. Using motor torque to control auto surfaces has been used off and on for many years, though more recently it has been supplanted by mechanical or electronic timers. Using torque rather than time has the advantage of automatically adapting to variations in rubber quality. The system utilizes a chrome-plated rear peg that rotates through about 16° as the motor unwinds. A spring attached to one end of the peg counteracts the torque; the other end of the peg moves a pivoted carbon-rod lever, which in turn moves the wing trailing edge up during the motor burst. Variations include differential wing movement (wing wiggler) and flaps.
Roger's other article shows a variety of wing and stabilizer structures for F1B and F1G models that combine balsa and carbon rods and tubes in unusual ways. They are not the now-familiar composite structures with molded carbon-fiber D-box and carbon-capped aft ribs. One stabilizer structure consists of a balsa front section carved out for lightness, connected with a carbon rod back to a carbon-strip trailing edge; the covering provides the aft airfoil shape. An F1B wing structure uses a large-diameter carbon-tube spar for torsion and bending strength with balsa riblets and leading edge providing the desired airfoil shape forward of the spar. The aft portion of the wing consists of a bent carbon micro tube on the top surface and a bent carbon–balsa–carbon laminate forming the bottom surface; both connect to a carbon-strip trailing edge. Warren-truss–style diagonal bracing in between helps preserve the aft airfoil's shape.
The 2008 Forum Report is available from Martin Dilly. The price, including airmail postage to the U.S., is £14.00 (approximately $21, exchange rate fluctuates). Make checks payable to "BMFA F/F Team Support Fund." Since checks must be in pounds sterling and drawn on a bank with a branch in the United Kingdom, it's much easier to pay by credit card. Back issues of Forums are available. The 2008 edition is also available from NFFS Publications (Bob Stalick) for $25 plus $5 postage. Domestic orders: checks or money orders only; international orders: credit card payment accepted (service fee may apply).
Rubber Bands
Rubber bands used to attach wings and tails can fail at the most inopportune times. They are an easy, light way to attach surfaces to the fuselage and provide a measure of safety in the event of a crash—the bands break rather than the model. For wing and stabilizer hold-down bands, it helps to standardize on a few widely available rubber-band sizes rather than keeping different sizes for each model.
To be effective, rubber bands need to be tightly stretched. Hooks should be located on the model so that standard-size rubber bands can be used at the optimum stretch. However, optimum stretch is not necessarily maximum stretch. A new size 8 band measures roughly 3/4 inch long relaxed and will stretch to nearly 5 inches. After a few minutes at maximum stretch, it provides significant tension only in the 4- to 5-inch range. Allowing the band to completely relax for a few minutes improves things somewhat, just as allowing a rubber motor to rest between windings improves performance, but removing and reinstalling bands between flights is generally impractical.
Instead, space hooks so that the band is stretched less than the maximum but enough to provide the needed tension. Something approximately 80% of maximum, or close to 4 inches for a size 8 band, works well.
Heat, sun, and time will cause bands to weaken during a day of flying, which can have serious effects. Weaker bands can allow wings to lift or shift slightly, especially under power, affecting trim. Weakened bands may not have sufficient strength to pull the stabilizer up on DT, resulting in a lost model. Replace bands several times during the day and discard used bands. It is a good idea to use at least two bands for wing or stabilizer hold-down.
Pay attention to the hooks to which the bands attach. A wire hook should have the exposed end rounded to prevent nicking the band (or your finger) when installing it. Hooks should be well anchored to prevent pulling loose. If possible, use a thin-plywood reinforcement to anchor the hook, then sew it in place with Kevlar thread and apply epoxy. Consider using dowels instead of wire for hooks; thin-plywood washers can be combined with the dowel to maximize gluing surface on sheet-balsa structures.
For gas-model wing mounts, use a spruce strip set between the top of the balsa pylon and the wing mount, extending fore and aft. Add a piece of trailing-edge stock on either side for reinforcement. Slightly round the projecting spruce strip's edges to avoid cutting into the wing hold-down rubber bands.
Sources:
- NFFS: www.freeflight.org
NFFS Publication Services: Bob Stalick Box 1775 Albany, OR 97321 [email protected]
2008 Forum Report: Martin Dilly 20 Links Rd. West Wickham, Kent BR4 OQW UK [email protected]
Transcribed from original scans by AI. Minor OCR errors may remain.
