Small-Field Flying — August 2011
Paul Bradley | [email protected]
There is a P-39 lurking inside that ParkZone Micro P-51
You may have heard a quote by Michelangelo that goes something like this: "Every block of stone has a statue inside it and it is the task of the sculptor to discover it." I think Ron Sims of St. Joseph, Missouri, has a similar feeling about what's lurking inside RTF foamie model airplanes.
You may recall that in the August 2010 edition of this column I shared what Ron, owner of a Hughes Racer model, discovered inside his ParkZone Sukhoi. Guess what? He acquired a ParkZone P-51D Mustang and discovered there was a Bell P-39 Airacobra hiding inside the foam.
Ron has performed another of his masterful conversions of an existing model from one format to another. Here is his transformation of the ParkZone Micro P-51 into a P-39.
Fuselage modifications
Most of the effort was reworking the fuselage from the classic P-51 shape to the slim-nosed P-39. This involved cutting away the belly air scoop, reshaping areas with judicious sanding, and adding pink foam. Ron found he could not fit the P-51 motor/gear-drive power unit in the nose because of the slim P-39 profile, so he elected to use an AP05 brushless motor.
The wings required a little work, including tip reshaping and removing the dogleg at the leading-edge root. The wing saddle was moved 1/4 inch on the fuselage to maintain the scale geometry.
The tail surfaces were made from foam sheet obtained from take-out box lids. The texture of that foam closely matches the original P-51 tail surfaces. For the fin and rudder, Ron laminated two layers of the foam with a 1/64-inch plywood strip tucked in the hinge line. The plywood holds a 3M Blenderm tape hinge.
The overall finish is olive drab and gray paint. The star roundels were made from the P-51 decals with the bars cut off. After the decals were applied, a final top coat of Testors Dullcote was sprayed.
Power and propeller
- Motor: AP05 brushless.
- Battery: two ParkZone-compatible Li-Poly cells in series (required an ESC).
- Motor, ESC, and two-cell adapters were obtained from Bob Selman Designs.
- Propeller: GWS 5030 cut down to a diameter of 4½ inches; blades were narrowed to create a more scale look and to keep the load on the motor in range.
- Final flying weight: 50 grams.
Ron reports the model performs nicely. Great effort, Ron — I look forward to discovering what you find hiding inside other RTF foamie models.
Fly Baby biplane — a small-field flyer
The Fly Baby is a small-field flyer based on a classic home-built aircraft. Home-built designs make great subjects for scale models; some look as if they could be scaled-up model airplanes. Peter Bowers' Fly Baby, designed in 1962, is one such example.
Although the original design started as a low-wing monoplane, biplane versions have also been developed. Biplanes excel as small-field models, especially when built light. Pat Tritle has developed a number of lightweight biplanes favored by the small-field flying community.
Pat selected the Fly Baby biplane for his latest offering. With a 33-inch wingspan and a flying weight of slightly less than 15 ounces, it makes a perfect scale small-field flyer.
Specifications and power
- Wingspan: 33 inches.
- Flying weight: slightly less than 15 ounces.
- Motor: E-flite Park 370 brushless outrunner.
- Battery: two 1320 mAh Li-Poly cells.
- Propeller: 9 x 5.
- Controls: all functions included; dual servos for the ailerons.
Flying qualities (Pat Tritle)
Pat commented on its flying qualities:
- "The Fly Baby flies a lot differently than I expected. I thought it would be a bit of a floater, similar to the Tiger Moth, but it turned out to be a far more solid flyer.
- Control input is crisp and very positive; the model grooves really well.
- Surprisingly, there was no adverse yaw from aileron input, so no rudder is needed in the turn, though it turns equally well on either rudder or ailerons, and the Fly Baby will sideslip nicely.
- On takeoff, ground handling is no problem. The rudder is effective but not overly aggressive, so tracking a straight line is easy.
- Landings are easy: the model floats a little in ground effect and touches down and sticks to the runway in a perfect three-point attitude with no tendency to bounce."
Pat is offering short kits for the Fly Baby biplane.
Converting a Mambo to electric while keeping a vintage look
My brother Ralph acquired a partially built Mambo that had originally been flown with glow engine power. Ralph wanted to convert it to electric while keeping the original look, which presented two challenges: the appearance of a glow engine and the original use of an escapement for rudder control (which used a torque rod rather than a pushrod).
I want to share Ralph’s approaches for achieving a vintage look with modern components.
Simulating the glow engine
Other modelers fabricate dummy engines to create the illusion of a fuel engine. Ralph and I still had a Fox Manufacturing .15 engine from the early days, and he decided to use it without making any permanent alterations so it could be returned to glow use if desired.
- He removed the piston, crankshaft, and backplate.
- A bearing was placed in the forward end of the crankcase and secured with Loctite Removable Threadlocker.
- A 4 mm drill rod was used to make a propeller-shaft extension for the electric motor.
- The electric motor was mounted behind the Fox .15 with a homemade shaft coupler.
The result is a Fox .15 mounted in the proper place, looking like the power source for the propeller. The setup runs smoothly; the only external giveaway is the lack of engine compression.
Simulating escapement-driven rudder control
To simulate escapement-driven torque-rod rudder control, Ralph built a rig that uses an actual torque rod driven by a servo. The control surface is actuated as it was in the early days of RC, but with the benefits of proportional control.
Great work, Ralph — I hope this gives others ideas for small-field flyers based on early RC models.
Notes
Diels Engineering has moved. Some modelers like to convert rubber-powered free-flight models to small-field RC aircraft; Diels Engineering is a great source for such kits. See the Sources listing for updated contact information.
As always, let me know what you are up to in the wonderful world of small-field flying. — PB
Sources
- BSD Micro RC
(417) 358-9521 www.bsdmicrorc.com
- Fly Baby by Peter Bowers
- Pat’s Custom Models
(505) 296-4511 www.patscustom-models.com
- Diels Engineering, Inc.
[email protected] www.dielsengineeringinc.com
Contact
Paul Bradley 10201 Scarlet Oak Dr. Independence, KY 41051 www.parmodels.com
Transcribed from original scans by AI. Minor OCR errors may remain.
