Small-Field Flying
Paul Bradley | [email protected]
FF designs, small brushless motors, and small-field flying
There is a trend I like. The makers of motors for model aircraft have been delivering more suitable options for those of us who like to fly in smaller spaces.
Within an increasing array of motors are some nice brushless outrunners that are perfect for small-field models in the 20- to 35-inch wingspan range. That size model makes the direct conversion of many wonderful FF designs practical and works well for some of the classic .010- and .020-inch glow-powered RC models of yesteryear.
Some of the suitable motors include the AXI 2203 and 2204 series and the ELE C20 (see the source listing). The motors weigh 18–26 grams and will fly models weighing 3.5–8.0 ounces on a two-cell Li-Poly battery pack—just right for that FF conversion or vintage 1/4A glow RC project.
I'm going to share several small-field projects submitted by readers who use these motors. The first one comes from Glen Allison of Tucson, Arizona.
Glen Allison — Baby Playboy conversion
In 1948 Glen's friend Rodney Taylor built an Arden .099-powered Baby Playboy. During that era that model was a popular engine-powered FF design. Glen decided to build a current-day Baby Playboy but use RC assist and an electric motor for power.
The model has a 33-inch wingspan—perfect for one of the newer, smaller brushless outrunner motors. Glen chose the AXI 2204/54 turning a GWS 8 x 4.3 propeller as his power plant and a two-cell, 720 mAh Li-Poly battery pack as the energy source. The Baby Playboy's all-up weight is 6 ounces.
Glen reports that he is having a ball flying the model as though it were an FF aircraft. He lets it climb in a tight, right-hand spiral pattern with no control input. It reaches good altitude after 20–30 seconds of motor run, and he cuts the power and lets the airplane transition into a nice left-hand circling glide. He flies hands-off with only occasional steering to keep the model on the field. Very nice, Glen!
Bob Aberle — Ranger 30 conversion
Another great small-field model taking advantage of the less-than-1-ounce brushless outrunner motors comes from Bob Aberle. He is a Model Aviation Hall of Fame member, an MA author, and writes for a number of other publications. As do many of us who were doing this model-airplane thing a number of years ago, Bob has some fond memories of aircraft that were popular in a past era, one of which is the Carl Goldberg Ranger 30.
With a 30-inch wingspan, the Ranger 30 was sold as a sport model for FF or CL flying. The intended power plant was a .020 when flown as an FF model and a .049 if flown as a CL aircraft. Through the AMA Plans Service, Bob acquired a copy of the Ranger 30 kit plans and set about developing a modern small-field flyer. Bob powers the Ranger 30 with an AXI 2203/46 turning a GWS 5 x 3 propeller. His battery is a two-cell, 300 mAh Li-Poly pack. The model's all-up flying weight is 6 ounces.
Not all the vintage FF designs fly right off the board when we add the ability to control them from the ground or alter their original source of power. The tricks Bob applied to his Ranger 30 project to get it into the category of "nice flyer" are a good lesson for us all.
On its first flights the Ranger 30 displayed an annoying tendency to roll on its back when rudder input was applied. That can be slightly unsettling. Fortunately Bob was able to wrestle the model down in one piece and set out to correct the problem.
First, he enlarged the fin area. The original model had a vertical fin area of 5% of the wing area. Bob doubled that value to 10%, but the next flight revealed that the problem still existed.
Next, Bob increased the wing dihedral. The original value was slightly less than 6% and he raised it to 9.5%. The combined increased area of the vertical fin and dihedral went a long way to help get the model to turn properly.
Things were not perfect yet, so Bob applied one more adjustment. Because FF designs need much positive stability, they often use more angular difference between the wing and stabilizer. That can be an issue when you want to control the model from the ground. Bob reduced the angular difference by placing a 1/8-inch shim under the wing's trailing edge. Rubber bands hold the wing on, so that was not a major structural rework. Reducing the angular difference in combination with the other changes transformed the model into a well-behaved small-field flyer.
Thanks for sharing your nice project, Bob, and I appreciate the important lessons on taming a poor-handling model. You will find a nice construction article about this model in the September 2007 issue of RC Micro World (see the source listing).
Micro and near-micro models — Plantraco gear examples
While on the subject of small models for our small-field-flying venues, I'm going to spend time in the region between micro and small. I occasionally get into the smaller end of our small-field spectrum. There are two readers' models that struck my fancy that I would like to share with you.
The first comes from Lyn Coon of Arkadelphia, Arkansas. When we think of a Randy Randolph design, our mental image is probably of an RC model that typically fits well in the small-field arena. Randy was also a great FF model designer. One such design is a rubber-powered profile (No-Cal) model of the J-3 Piper Cub. Lyn's father has been flying one. Watching its performance, Lyn reasoned that it would be a perfect RC conversion subject using the micro gear from Plantraco. I have converted a few No-Cal FF designs of my own to RC with the Plantraco gear, and Lyn was right on target.
Lyn used the 0.9-gram Plantraco three-channel receiver. He also used the Plantraco-supplied 90 mAh Li-Poly cell that includes magnetic contacts to hold the battery to the receiver. This is a slick setup and makes battery changes a snap.
Control functions include rudder and elevator handled by Plantraco magnetic actuators. All-up flying weight for Lyn's No-Cal J-3 is 16 grams. I can see that beauty in the photo floating slowly around the back yard late in the evening.
Another Plantraco-equipment-based model shown is the aircraft with the V-tail and nice elliptical-planform wing from John Krouse of Rockville, Maryland. John used the Plantraco 0.9-gram receiver and 90 mAh Li-Poly cell, as Lyn did.
John's model has rudder and throttle control, so he used only one magnetic actuator. The wingspan is 16 inches and the airplane has a flying weight of 18 grams.
What sets this aircraft apart from many others is the use of a V-tail. John's use of only rudder input to control the model's flight direction works by setting up the "ruddervators" to move differentially. This is done easily with the magnetic actuator.
The actuator pivots inside the electromagnetic coil so the output arm moves the way a typical servo does. The control is fully proportional, and you get the differential surface movement needed to create rudder action from a V-tail setup. John reports that the model has excellent turn control with this arrangement. Very cool, John.
Pat Tritle — 60-inch Curtiss Jenny
Where is the Pat Tritle installment? Pat is such a prolific designer and builder that I almost expect something new each time I prepare a column. My last one did not include anything from Pat, but I'm most pleased to report that he is back.
Not only does Pat have a new offering, but it is special. How about a 60-inch-span Curtiss Jenny that weighs only 23 ounces? Pat is completely redefining the term "slow flyer." As you can see from the photos, this model is a real looker.
The Jenny is powered with the low-cost, 1,000 rpm-per-volt outrunner motor from RC Hot Deals (Tower Pro 2409-18), turning a GWS 10 x 4.7 propeller, and a two-cell, 2100 mAh Li-Poly battery pack. Control functions include aileron, rudder, elevator, and throttle.
The design was set up with 1° of dihedral so the wings don't look "droopy." The wings are removable for easy transport and can be assembled at the field in less than a minute with only two screws.
Nelson LiteFilm covers the model and Pat added details with an airbrush. A light coat of Krylon Satin Clear gives it that aged look of an old barnstormer. Keith "Sparky" Sparks of Park Flyer Plastics did the plastic detail parts. The fuselage script was worked up in Microsoft Word, printed on Avery clear label material, and applied before the weathering wash was added.
Pat indicates that flying the Jenny is the fun part. It is smooth, honest, and predictable, although it still exhibits the Jenny’s distinct flying qualities. With the long, slender wing, it doesn’t like steep banks, but by adding “top aileron” in the turn to maintain a shallower bank, the distinct skidding turn looks just right.
Pat reports that the ailerons are effective and the rudder has a “soft” feel. As with any of these old airplane designs, there is a small amount of adverse yaw. The model will turn on ailerons alone, but it looks slightly sloppy.
With the limited dihedral, a rudder turn is possible but recovery is sluggish. However, with rudder/aileron coordination the model will do anything a Jenny is supposed to do. The model is fun to fly and even shoots nice touch-and-goes although landings are slightly “floaty” in ground effect.
Watch Model Airplane News for a construction article about this lovely model. Pat indicates that short kits will be made available when the article is published.
Here we are again at the end of another column. As always, don’t be bashful about sending me a picture or two of your latest project. In addition to the e-mail address in the column header, you can reach me via regular mail at:
32238 Spinnaker Run Magnolia, TX 77354
Sources
- Brushless motors less than 1 ounce:
- Hobby Lobby International, Inc.
(615) 373-1444 www.hobby-lobby.com
- BP Hobbies
(732) 287-3933 www.bphobbies.com
- Plantraco micro RC gear:
- Bob Selman Designs
(417) 358-9521 www.bsdmicrorc.com
- Pat Tritle’s 60-inch Curtiss Jenny:
- Pat’s Custom Models
(505) 296-4511 www.patscustom-models.com
- RC Hot Deals:
- (302) 250-4611 or (503) 708-2214
- RC Micro World:
- (703) 273-0607
Transcribed from original scans by AI. Minor OCR errors may remain.
