Author: Louis Joyner

Edition: Model Aviation - 2011/05
Page Numbers: 119,120,121,122
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Free Flight Duration - 2011/05

E-36 was introduced as an event for rubber-power-size models but originally limited projected wingspan to 36 inches and restricted power to four nickel-based cells and a brush-type motor. With power so limited, E-36 performance was closer to that of an underpowered Rubber model—hardly the exciting stuff needed to draw large numbers of modelers to a new event.

A year ago, the National Free Flight Society (NFFS) formed a committee to investigate ways to improve performance, take advantage of technological advances in motors and batteries, and make E-36 more attractive to both beginners and experienced modelers. The Electric Power Subcommittee, chaired by David Mills with members Jim Jennings Jr., Dick Ivers, Bernie Crowe, and Mark Covington, came up with new rules.

The process was open: the committee solicited comments on the NFFS forum and discussed suggestions on the Internet. Committee members and other modelers also built and tested models to fit the new rules. This approach allowed people who actually fly the event to participate in developing and voting on the rules. "At some point an effort will be made to make E-36 into an official AMA class," said David Mills. "Hopefully we'll have a couple of years experience to finalize the rules."

New E-36 rules (summary)

  • Wingspan: 36-inch projected limit retained.
  • Motors and batteries: any type of motor allowed; either six nickel cells or two lithium cells permitted.
  • Propellers: geared and folding propellers allowed.
  • Auto surfaces: not allowed.
  • Minimum flying weight: 120 grams.
  • Motor run times:
  • First three flights: reduced from 25 to 15 seconds.
  • Maximum remains 120 seconds for all flights.
  • First flyoff flight: 10-second motor run; subsequent flyoff flights: 5 seconds.

More detailed information about the new rules is available on the NFFS website.

The Electric Power Subcommittee is supporting the event with articles, plans, and technical information. Bernie Crowe wrote an article about his Slick Willie E-36 design for the January 2011 Free Flight Quarterly; the piece includes detailed drawings, construction tips, and a rundown of all the electrical components needed.

David Mills commented: "I suspect E-36 will function much like P-30 has, as a good entry-level class. We can give credit for this stair-step approach in cost and complexity up through the electric classes (E-36, A Electric, B Electric and F1Q) mainly to Jim Jennings. Maybe we'll look back on 2011 as the year electric power in free flight really took off."

John Oldenkamp and the Joule Box

John Oldenkamp, one of the fathers of the popular P-30 Rubber event, has been very active with electric power. His Joule Box design, recently featured in the NFFS Digest, offers an easy entry into electric flying. The all-balsa model features full-depth spars and diagonal ribs to stiffen both wing and stabilizer. Flat-bottomed airfoils and squared-off lines make it quick to build. The wing area is approximately 190 square inches.

America's Cup

The America's Cup, created by the Southern California Aero Team and administered by Jim Parker, offers a multicontest format encouraging modelers from the US, Canada, and Mexico to compete in FAI free flight events.

  • Points are awarded at each contest: first = 25, second = 20, third = 15, fourth = 10, fifth = 5. Additional points are awarded depending on the number of contestants flying in the event.
  • The best results from four contests are counted.
  • To encourage travel, only two contests at any one site can be counted; the other two results must be from two other sites.
  • In case of a tie, results from more contests are counted.

Detailed rules for the America's Cup are available on the NFFS website.

2010 Winners

  • F1A Towline Glider: Jim Parker
  • F1B Wakefield Rubber: Brian Pacelli
  • F1C Power: Don Chesson
  • F1P Power: Bob Hanford
  • F1G Coupe: Ed Vanlandingham
  • F1H Towline Glider: Brian Van Nest
  • F1J Power: Austin Gunder
  • F1Q Electric: Julie Parker
  • F1E Glider: Peter Brocks

Brian Pacelli, in addition to winning F1B, placed second in F1P. He is a three-time member of the US Junior FF team and, at age 17, is eligible to try for a fourth team spot for the 2012 Junior World Championships. At the 2010 Junior World Championships, Brian placed second in F1B and third in F1P.

"Not bad for a kid who picked the event [F1B] simply to ensure a full US Junior Team in Romania," said his mother, Lisa. "All I had to do was drive and fly him around the world for competitions, time him, and be proud, so it wasn't that much of an effort for me."

Flying a pair of Stefanchuk F1B models, Brian scored four firsts and a third to garner 109 America's Cup points, edging out Open flier Blake Jensen by 2 points.

Other recent US Junior team members did well in the America's Cup: Timothy Barron placed second in F1A; Taron Malkhasyan earned fifth in F1P. Former Junior World Champion Austin Gunder, who has graduated from Stanford and is working at AeroVironment, placed second in F1C in addition to his F1J win.

Lightening Up (building lighter F1G Coupes)

After years of building F1B Wakefields, I started working on some F1G Coupes. Size-wise they aren't too different: a typical F1B has approximately 250 square inches of wing area; a typical Coupe's is roughly 170–210 square inches. But the minimum airframe weight for an F1B is almost triple the 70-gram minimum weight for a Coupe. It has been a challenge to build down to that weight; here are lessons learned.

  • Begin with a budget. Weigh all purchased parts first (front end, motor tube, tailboom, timer, tracking transmitter) and include small bits such as the bobbin, rear peg, timer mounting screws, and hold-down rubber bands. Total those numbers and subtract from the required minimum weight to find how many grams you have to spend on the rest of the model.
  • Use your scale. Weigh each sheet of balsa and write the mass in grams and the density (lb/ft³) on the label. Weigh each piece of wood before it goes on the model—choose the lightest piece that is still strong enough. Use lighter wood for wingtips, tails, and other extremities and heavier wood for more highly stressed areas.
  • Keep notes. Accurate, detailed records will build a database useful for designing and building subsequent aircraft.
  • Calculate carefully. For example, when using a carbon-fiber D-box, calculate weight per unit area from existing skins. Reducing D-box chord by 1 mm saved 0.7 gram in one case; reducing chord from 25% to 20% of wing chord saved almost 7 grams.
  • Easy on the glue. A heavy fillet isn't necessary for a perfectly fitted joint. Apply a coat of epoxy or Titebond and blot off excess (wedge-shaped foam makeup sponges work well).
  • Consider alternatives. A 36-inch piece of 8 lb/ft³ 1/2-inch TE stock weighs ~3.6 grams. A similar length of 1.6 mm trapezoid carbon-fiber pultrusion weighs ~1.2 grams. For full-depth spars and ribs, build with light balsa and add thin carbon-fiber caps; the result can be lighter and stiffer than all-balsa structures.
  • Think small. Don't make components larger or heavier than needed. For stabilizer mounts, printed circuit board can be stiffer than plywood and lighter; reducing a mount from 11 x 30 mm to 7 x 26 mm saved 0.1 gram. Switching from a 2-56 nylon stabilizer adjustment screw to a smaller steel version in an aluminum fitting saved another 0.1 gram.
  • Sand and then sand some more. Keep a scale handy while sanding; dust adds up.
  • Choose coverings carefully. Covering choices for small models range from ~2 g/m² to >30 g/m². On a 200-square-inch wing (total area ~400 in²) that can mean a weight range from ~0.5 gram to >7 grams. Remember covering weight includes adhesive and dope as well as the film. I find grams per square meter easiest to work with; conversion: 1 m² = 10.7639 ft², 1 ft² = 0.0929 m².

Carbon Pultrusions

Tim Goldstein's A2Z Corp offers a selection of carbon-fiber pultrusions from Van Dijk Pultrusion Products (Netherlands). The most useful shapes for free flight are rectangular and trapezoid.

  • Rectangular shapes: thicknesses from 0.12 mm to 1.1 mm and widths from 1.0 mm to 8.0 mm. Most pieces come in 1-meter strips. The thinnest stock (0.12 mm) comes in 10-meter rolls in widths of 1.0 mm, 1.5 mm, 2.0 mm, and 3.0 mm—useful for rib caps or spar caps on small models like P-30s.
  • Trapezoid shapes: 1-meter lengths in widths of 1.6 mm, 3.0 mm, and 3.8 mm—perfect for trailing edges.

The 2005 NFFS Symposium featured a presentation by Maarten Van Dijk about the pultrusion manufacturing process. The Van Dijk website contains information about both process and product. Free Flight Supplies also sells Van Dijk pultrusions.

Sources

Transcribed from original scans by AI. Minor OCR errors may remain.