It’s time to start the project airplane that I mentioned in my last column, which will take advantage of the E-flite Power 15 motor or an equivalent motor. Such a model should be easy to fly, inexpensive, and could be a competition model as well as an advanced CL Aerobatics trainer. The subject model is Bill Werwage’s Classic Stunt-legal Vulcan. AMA’s Plans Service is the plans source, for anyone who might want to build one.
Converting a glow design of any size to electric power is not difficult. You first need to establish the size of the motor to be used, the ESC, timer, and battery package that will be required, and then redesign the structure of the nose of the model to accommodate the electric components.
I know from experience that the Power 15 motor works extremely well in airplanes that range from 480 to 560 square inches, and weigh between 38 and 50 ounces including the battery. The lower end of the airplane size yields the best performance with this setup, providing that it is built correspondingly light. The Vulcan has a wingspan of 50.25 inches and a 500-square-inch wing area, placing it nicely in the sweet spot of the equation.
Electric motors do not vibrate nearly as much as glow engines do—hardly at all—and put far less stress on the model, especially at the nose. This is where you can save a great deal of weight in an electric conversion. This is where we will start on our project.
The glow version of the Vulcan was designed using normal maple engine-mount beams, and a tank floor plate and former F-2 at the rear of the tank compartment, with a filler piece between the engine-mount beams to increase rigidity.
In the electric conversion, nearly all of that goes away! The nose of the electric version will consist of a motor mount plate, typically made from either 1/8-inch birch plywood or G-10 material, a 1/8-inch birch plywood former that will be installed slightly aft of the motor, a Lite Ply former that will be located at the rear of the electronics bay, and a 1/8-inch Lite Ply fuselage stiffener plate that will run between the two formers. I’ve included three photos that depict the redrawn plan, the new electric components, and a fuselage side with doubler and the parts assembled into a fuselage crutch.
The model is fitted with a front mount. That means that the motor’s shaft is reversed in respect to the way it comes in the box, and the “bell” portion of the motor is bolted to the rear of the motor mount, with the shaft sticking forward through the mount. The front-mounted motor puts less stress on the motor’s main bearing because its load is essentially halved.
The spinning “can” portion of the motor is behind the mount and the propeller, spinner, and any loads applied to the propeller are in front of the mount. I’ve had problems with the bearings in rear-mounted motors, so I highly recommend front mounting for all CL electric models.
I made a new drawing of the Vulcan’s nose, depicting the shapes and locations of the various parts needed for the electric conversion, as well as the necessary modifications to the landing gear mount, because the stock mounting didn’t fit with the electric-system component placement. I can supply copies of the drawing to anyone who wishes to do this conversion. I’ll supply the prints at my cost plus postage. Email me for ordering details if you are interested in receiving a copy of that conversion plan.
I prefer to use a motor mount plate that is made from G-10 material. This is the material from which printed circuit boards are made. It is an epoxy/fiberglass laminate that is extremely tough and crush resistant. Plywood can be used for the mount, but it is more prone to crushing over time from the mount bolts and washers. Be sure to wear a dust mask when working with the G-10 material.
G-10 is tough to cut with a normal scroll-saw blade; it will dull the blade in seconds! I use a hand tool, fitted with a 1/8-inch diameter carbon bit to rough out the mount plate, and then use a disc sander to bring the mount to the final shape. The surface of the G-10 mount should be scuffed with sandpaper to remove any mold release from the manufacturing process, and notches should be made every 1/8 inch or so along the edge of the mount plate to allow the epoxy to get a better grip on the piece.
When gluing the mount—or any of the nose parts—in place, be sure to use a good dash of micro balloons in the epoxy mix. The micro balloons add tremendous strength to the joint between the mount and the fuselage side. The mount plate will receive additional gusseting when the nose takes final shape.
The fuselage is built to accept batteries that are loaded from the top of the model. It’s a pain to have to place the model on its back to change the battery. In the case of this design, it’s difficult to position the ESC and the timer above the battery in the model; there’s insufficient room in the top block area. There’s more room below the battery in the top-load configuration, and you can make a neater-looking installation as well.
The photos should help to clarify the nose construction. I’ll not go into much detail about building the rest of the fuselage, because it is done according to the original plans aft of the electronics bay.
Tucker Special
I’ve finished converting the Tucker Special that I built in 1991 to electric power. That model flew very well and I even won a Vintage Stunt Championships crown with it in 1993. I installed an E-flite Power 15 motor, a Castle Creations Phoenix 45 ESC, a Hubin FM-9 timer, and a Hyperion 4S 2500 mAh battery. An APC 11 x 5.5 tractor propeller was used—it was all I had in the right size range—and it was off to the field.
The model still flies well, but has a slight “hunt” in level flight. I checked the thrustline and found that I’d inadvertently put in approximately 1° of downthrust. I fixed that and am looking forward to my next flight session.
The big surprise was that in a full pattern run, it used only 1350 mAh! I can easily drop to a Hyperion 4S 2100 mAh battery and be safe. With the battery, the model weighs 44 ounces. It’s going to be a fun airplane when all of the trim bugs are worked out.
