Ask any scale modeler what his favorite airplane is and you’ll get countless replies. But ask about aerobatic biplanes and only a few favorites come up. At the top of the list, of course, is the famous Pitts Special, but true biplane fans will also check the box for Paul Poberezny’s Acro Sport biplane. President of the Experimental Aircraft Association (EAA), Paul designed his single-place Acro Sport in the 1970s as an easy-to-build homebuilt project plane. Shortly after that, he designed a two-place version, the Acro Sport II, to carry a passenger and help check out new pilots. Over the years, both versions of the Acro Sport have remained popular designs for EAA homebuilders wanting an aerobatic-capable biplane. Construction plans and material kits are still available today.
While filling in as a static judge at the recent National Association of Scale Aeromodelers (NASA) Northeast Scale Qualifier in Goshen, New York, I met Tom Lowrie who flew a beautiful yellow-and-black 40% Acro Sport IIS. I’ve always had a soft spot for the standard Acro Sport biplane, so I asked him more about his beautiful multiwing aerobat. Here’s what I learned.
Model Airplane News: Tom, please tell me about the full-size Acro Sport IIS and its owner.
Tom Lowrie: The full-size Acro Sport IIS (ASIIS) I chose to model was built by a friend, Chris Murley, who I helped teach to fly RC back in the late ’90s when he was a youngster. Chris is from Tunkhannock, Pennsylvania, where he also has a business building and maintaining full-scale aircraft. Chris is part owner of Griggs Aircraft Refinishing and the owner of Wolf Aircraft.
The full-scale ASIIS started out as a standard Acro Sport II, but during the construction, it was “modded” into a single-place aircraft with lots of custom additions. It incorporates a Wolf Pro Pitts canopy, a custom-made carbon-fiber cowl, modified fuselage formers to fit the framework to the new cowl design and cockpit, and lots of custom carbon parts in the wings and fuselage to keep the weight down.
MAN: Tell us about your model.
TL: The ASIIS model is a 40% scale model of the full-scale counterpart and has a top wingspan of 104 inches and a bottom wingspan of 100 inches. The wing chord is 17.8 inches, and I used a 12% fully symmetrical airfoil. The fuselage length is 98.5 inches from spinner to rudder. The ready-to-fly model weighs in at
MAN: What about the power system and radio gear?
TL: I designed the model to use a DLE 170cc twin-cylinder engine with a Walbro carburetor and Bowman rings. The ignition is an IBEC (ignition battery eliminator circuit) by Tech-Aero Designs, and I am using a KS canister exhaust system. For the radio, I use a Spektrum DX20, a 12-channel PowerSafe receiver, and high-voltage digitals servos from Hitec RCD. I use two 5500mAh LiPo battery packs to power the receiver.
MAN: Tell us about building your model.
TL: I had been looking for a “one-of-a-kind biplane” to build for a long time, ever since I designed my own 42% Weeks Solution back 1999. In late-summer 2017, right after I saw Chris’s test flight of his full-scale ASIIS, I knew I had found what I was looking for. It was one sexy aircraft; I just had to model and build a giant-scale version of his ASIIS! On January 1, 2018, I started the design and engineering, and on February 1, I started cutting the first parts. Some 800 or so hours later, the 40% ASIIS was test-flown in June 2018 at Herb Grayek’s private airstrip in Scott Township, Pennsylvania.
The aircraft’s fuselage is standard wood construction with formers and stringers placed in the fuselage as they would be in the full-scale aircraft. Wings are standard wood construction, with ribs placed as they would be in the full-scale [version] as well. The landing-gear wheel pants and cowl are homemade, made of molded carbon fiber. My pilot bust is also homemade, which I did on my 3D printer, along with other small parts on the aircraft. I also pulled the canopy over a foam-and-fiberglass plug that I made.
MAN: What is the basic setup for this biplane design, and what can you tell us about the paint job?
TL: Contrary to standard biplane design, the aircraft is set up with “0-0” degrees on both the wings and the engine thrust line, while the horizontal stabilizer has 0.75 degrees of positive incidence. The color scheme is painted, and it is identical to the full-scale airplane’s scheme, which was developed by Mirco Pecorari at AircraftStudioDesign. I reproduced all the finer markings, and included rib stitching and pinked rib tapes.
MAN: And now for the big question: How does your 40% Acro Sport IIS perform?
TL: As far as flying goes, it is a very neutral-flying airplane, requiring slight coupling for particular maneuvers. Due to the straight wings, it required a little aileron differential to keep the rolls straight and on track. It has plenty of power, and its best maneuvers are takeoffs and landings. Once on final, you keep the wings level and control the sink rate with throttle, and you get a great landing every time.
MAN: How was your time flying here at Danny Carozza’s event?
TL: Well, I did better than I had expected to do. The people I met were amazingly skilled builders, and Jack Buckley is one heck of a guy to talk with; he’s so knowledgeable. The flight judges Rich Roberts and Jim Martin were two of the most helpful guys I have ever met with regards to flying. They really got me going in the right direction as far as scale flight goes.
I would also like to thank Danny Carozza for pushing me to enter my airplane in his scale competition. It opened my eyes to a whole new type of RC competition.
Text & Photos By Gerry Yarrish