[Headline: New E-20 event is inexpensive and fun]
The popular E-36 Electric event now has a little brother. Developed by Bob Stalick and the Willamette Modelers Club in Oregon, this unofficial event, called E-20, provides an inexpensive introduction to electric FF.
As the name implies, the wingspan is limited to 20 inches. Biplanes are prohibited. Minimum model weight is 30 grams (roughly 1 ounce). Power is limited to a single-cell 160 mAh LiPo powering a ParkZone Ultra Micro P-51, UM T-28 (PKZ3616) motor. The propeller diameter can be no larger than 2.6 inches, and gears are not allowed.
A simple, inexpensive electronic timer developed by Luke Napier controls the motor run, which is 20 seconds with a 90-second flight maximum. For flyoffs, there is a 10-second motor run and 2-minute maximum.
To encourage participation in the E-20 event, the Willamette Modelers Club offers a motor, propeller, and timer package for approximately $30, plus postage. (Ordering information is on the club’s website, listed in “Sources.”) Also included are detailed three-views of two E-20 models and instructions for setting up the motor and timer.
The only other component needed is the battery, which is available at many hobby shops. Because of the E-20’s small size, most modelers should have enough scrap wood to build the airframe.
Because the propeller, motor, and battery are limited, everyone is flying essentially with the same amount of power. This puts emphasis on accurately designing and building the model down to the minimum weight. Adjusting the model for the best climb, transition, and glide are also important.
A typical E-20 aircraft resembles a scaled-down Power model and is flown similar to most locked-up (i.e. no auto surfaces) 1/2A models with a rearward CG, minimal decalage, and washin on the right main wing panel. The climb is spirited, although not as fast as a “hot” Power model.
The performance is good enough to be exciting, but does not require much space to fly. E-20 would be an excellent event for a small-field contest and a great way to make FF more visible to the public.
Ross Jahnke’s E-20
A salvaged carbon-fiber tailboom provides the impetus for Ross Jahnke’s elegant E-20 model. “It’s an old piece of tailboom,” Ross said. “I can’t remember where I got it.” The white stripes that Ross added to the boom are an homage to Hardy Brodersen’s similarly decorated Salt Peanuts series of F1C Power models.
The electric motor is epoxied into a two-part aluminum mount that Ross turned on his metal lathe. Three screws allow for thrust adjustment. The wing features a 4mm-diameter carbon-fiber tube spar and narrow carbon-fiber TE. The wing tapers from 4 inches in the center to 3.125 at the tips. Covering is clear Mylar with floral spray accents for visibility. A pop-up wing DT is used. It is operated by a viscous timer mounted on the pylon.
New P-30 Propellers
The popular P-30 Rubber event also places limits on model size, with maximum wingspan and length set at 30 inches. Minimum model weight is 40 grams and maximum motor weight is 10 grams. The propeller must be an unmodified, commercially produced plastic propeller with a maximum diameter of 9.5 inches.
In the past, the choices were limited to the IGRA propeller from the Czech Republic, the Peck-Polymers propeller from Japan, and the GizmoGeezer Products propeller from Canada. (For a detailed analysis of these blades, see Paul Rossiter’s original article in Free Flight Quarterly, “P30 Propeller Analysis,” April 2005. This is a must-have book for anyone interested in the P-30 event.)
Two new P-30 propeller options were introduced at the 2014 Nats. The orange propeller, made in China, is available from Shorty’s Basement, and the white propeller, molded in Chicago, is offered by Campbell’s Custom Kits. Both blades are available in 9.5 inches for the P-30 event, as well as other sizes suitable for scale or sport models.
A comparison between the orange and white 9.5-inch propellers revealed some similarities and a few differences. Both sell for $2, plus shipping, and both weigh nearly 7 grams, with the orange one roughly 1/10 of a gram heavier. The maximum chord for the white blade was 36mm, but the orange blade was 33mm.
The white propeller’s measured blade angle at 0.7 radius is approximately 26°, giving a pitch of roughly 260mm and a pitch-to-diameter ratio of 1.07 to 1. The blade angle for the orange propeller is roughly 30°, which gives a pitch of approximately 306mm and a pitch-to-diameter ratio of 1.27 to 1. The obvious difference is the scimitar tip of the orange propeller. I’m not sure if this offers any aerodynamic advantages, but it looks good.
Both propeller blades have a molded-in freewheeling ramp on the front. Although easy to use, this is not the best way to set up a freewheeling propeller. A better system is to use a wire lever pivoted on a piece of square brass tubing soldered to the shaft behind the propeller. This allows a positive propeller drive under power, works regardless of the amount of tension on the motor, and permits propellers to be quickly and easily interchanged. (The drawing originally appeared in Vol Libre Trimestriel and was featured in Free Flight Quarterly P30 Survey 2010.)
John Diebolt, who told me about the orange blades, said he intends to make two P-30 front ends—one with the standard 9.5-inch propeller and the other with the 9-inch propeller. The front end of the smaller propeller will be weighted to match the front end with the standard propeller. The propellers could be interchanged without affecting glide trim.
The smaller-diameter propeller could be used in windy weather to generate extra speed in the climb to help the model get up through ground turbulence. This way, the same cross-section motor could be used with either propeller. (The other way to speed up the climb is to use a shorter motor with more strands.)[dingbat]
Willamette Modelers Club
Volaré Products/Shorty’s Basement
Campbell’s Custom Kits
Free Flight Quarterly
National Free Flight Society (NFFS)