PT-19 (oz12090)

About this Plan

PT-19. Radio control scale model for electric power. Wingspan 40 on, wing area 300 sq in.

Note this plan is a free download from the Model Aviation website at https://www.modelaviation.com/PT19 where it appears along with full build notes and some good photos. There is also a free Builder's Guide (20 pages) available for download.

Note although this plan was titled by MA as "Speed 400 Pt-19", the model actually uses a E-flite 450 brushless motor.

Note a laser cut short kit is available from Top Notch Kits at http://www.topnotchkits.com/index_files/TN_Kit14.htm

"PT-19. Written by Charles S Pipes. A good gas design goes electric as featured in the October 2013 issue of Model Aviation. Download free plans of the PT-19.

As World War II approached, the US Army Air Corps (USAAC) believed that a low-wing, higher-performance basic trainer was needed. The government was looking for a more demanding basic trainer that would better prepare the fledgling aviators for the high-performance nature of the combat aircraft being developed. This led to the USAAC purchasing the Fairchild PT-19 two-seat monoplane in 1939, and to quote the movie Forrest Gump: That’s all I have to say about that.

I need to begin by thanking Robert Somers and giving him the lion's share of the credit for the development of this model. I converted Bob's good gas design into an excellent electric-powered aircraft. I cannot take credit for how well it flies. The fact that it has evolved into a great-flying airplane is because Bob's initial work produced a light, stable gas model that took minimal effort to rework.

His original design was a trussed structure built around an inverted OS Max .10 two-stroke with a 40-inch wingspan and weighing roughly 30 ounces dry. It had excellent flight characteristics with plenty of power for aerobatics.

As I watched him fly it my only negative thought was that the .10 being inverted tended to be slightly finicky to start.

Shortly after seeing it fly, we decided to convert the design to a Speed 400-size electric. Bob graciously loaned me his original drawings. As a testament to Bob’s original design, the only structural change made was lengthening the nose. This helped achieve the correct CG with the lighter electric motors.

I have an older version of AutoCAD, and decided to use it for the design. Having the CAD program on my laptop allows me to work on models while traveling and to select parts on the drawings and set them up for cutting.

I chose to have John Valentine at Top Notch Product Company cut the parts. He is willing to work with builders going through the learning process of design layout. Because of the amount of travel required for my job, time in my shop is a premium and being able to email a cut file from a hotel and have the parts waiting when I get home is a great advantage.

For the diehard scratch builder, I have made sure the plans show all of the parts so that the short kit is not mandatory.

Going Electric: Having flown only glow/gas models, I have considered electrics as toys. Similar to others of my generation, I carried the preconceived notion that an electric would be heavier and underpowered compared with any glow version.

With this mentality I began working with the idea of cutting weight wherever possible, then learned that Bob is an advocate of light construction. As I made changes to switch to laser-cut parts and ease construction, I added weight to the basic airframe.

As the model neared completion I purchased a set of digital scales and had trouble believing it weighed approximately 22 ounces with a 1650 mAh LiPo. Bob and I have concluded that the weight savings was because of the availability of all the new 'light' electric hardware.

The electric motor, ESC and battery weigh significantly less than the .10-size engine, fuel tank, tubing, and the throttle servo and its linkage. Other weight savings can be attributed to using the lighter microreceivers, servos, foam wheels, and lighter hardware. Using Solarfilm instead of MonoKote also reduced the weight.

Features: The initial effort was a trace of Bob’s design where I laid out the parts in CAD and replaced the .10 OS Max engine with an E-flite 450 brushless outrunner. I carried the fuselage sides past the original firewall and drew the electric motor mounted to a laminated nose block ending in a plywood nose plate.

The motor is accessed through a removable top hatch. The primary advantage to mounting the motor this way is that it eliminates the need for a separate fiberglass cowl. The most significant change at this point was to design the central fuselage into a tabbed and slotted-box design that made it easier to build the fuselage straight.

Not wanting to have to turn the model on its back or take it apart to change the batteries, I designed a removable hatch for the cockpit area, providing access to the flight battery and servos. The motor and battery hatch are held down with earth magnets.

The only other alteration I made was to change the landing gear mount from solid hardwood blocks to built-up plywood assemblies. This was done for those modelers who don’t have a small saw to do the slotting work. The airframe is self-aligning sheet wood with everything included in the short kit but the hardwood blocks and hardware.

Wing: The wing construction evolved from a traditional method of slotted LEs and TEs to a more modern version using all laser-cut parts. Cover your plans with wax paper and pin the lower spar to the plans. If you can’t get hard balsa, use basswood because the strength is worth the slight weight gain. Fit R-1, R-2s, R-3s and R-3T over the lower spar and into false TE notches. (Note R-3T is slotted to accept the wingtip former.)

Ensuring the ribs are aligned to the plans and perpendicular to the spars, pin them to the building board. Glue them to the lower spar and notched false TE using thin CA. Glue the top spar to the ribs and install the notched false LE.

If using the short kit, the bevel for dihedral is already cut and you need to correctly position it. Install 1/8-inch LE and 1/4-inch TE.

Install 1/16-inch plywood R-2As, with the 3/32-inch sheer webbing centered between the upper and lower spar. The grain should be vertical or perpendicular to the spar grain..."

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