Tiny Toni

By David Boyll [email protected] Photos by the author

The Volunteer Aeromodelers club of Knoxville, Tennessee, developed a minimal set of criteria for a novice-level Pylon Racing class for fun-fly events. The racers would be small, with top speeds of roughly 70 mph to accommodate a small, triangular course measuring 300 x 60 x 300 feet. The racers would be simple-to-build, electric-powered, profile models made primarily of foam board. 

Power would consist of a nominal 25-gram, 1,900 Kv brushless motor using a 3S LiPo battery to limit the model’s size and speed. The models would resemble full-scale pylon racers. An internet search found nothing like this, so I developed this racer, patterned after the Cosmic Wind Little Toni Goodyear racer that was flown in the 1940s and 1950s.

The sixth revision is shown here. The basic airframe can be built for approximately $5 in raw materials, plus half a roll of EconoKote or a similar covering film. These models have turned out to be a real hoot to race, are inexpensive to build, and are relatively crash resistant. The first two racers were red and white, like the full-scale Cosmic Wind Little Toni. These looked nice but were hard to see in anything less than full sunshine, so the non-scale, yellow-based color scheme was adopted to enhance visibility.  

Tiny Toni is a small, one-piece, overpowered, easy-to-transport racer. It is wicked fun but definitely not for beginners or the faint of heart. If a lightweight ESC and battery are chosen, it is possible to come in under the 250-gram weight limit imposed by the FAA that requires registration.

General

To print the plans, select 8.5 x 14 legal-size paper and portrait mode for the printer. Print it at 100% scale. Do not select the printer’s “fit to page” option. Measure the print size against the scale shown on the plans. The printer’s scale settings might need to be increased or reduced a few percentage points to print to the correct size.

Some foam board is warped, so make sure to hunt through the store stock to select a really flat one. All foam parts can be cut from a single sheet of foam board if the templates are properly arranged.  

Motor

The key to equalizing speed is for all racers to use nominal 25-gram 1,900 Kv motors. The 1,900 Kv SunnySky X2206-14 motor, pulling 11.5 amps (131 watts) with a 15-amp ESC and an APC 5.2 x 5.5 propeller, is the preferred racing motor. If extra performance is desired, an 1,850 Kv SunnySky X2305-13-V3, pulling 14.5 amps (163 watts) with a 20-amp ESC and an APC 5.2 x 6.0 propeller, can be substituted because the motor mounts and weights are the same.  

An APC 6 x 4 propeller with the X2305 motor provides the extra grunt needed for pulling streamers for Combat flying. The plans presented here are drawn based on the dimensions of the SunnySky X2206 and X2305 motors. If a different size or brand of motor is used, the firewall location and diameter might need to be modified accordingly to fit it. Note that using the X2305 motor with the heavier 20-amp ESC and larger battery will likely exceed 250 grams flying weight and the model will require FAA registration.

02. The Tiny Toni is constructed of foam board and 3/16-inch sheet balsa, making it an inexpensive model to build. Here is the model with all of the parts cut before covering.

Fuselage Construction

The fuselage is laminated from three layers of 3/16-inch thick Adams Redi-Board white, paper-backed foam board, which is commonly available from Dollar Tree stores. Trace the fuselage outline (including the wing and stabilizer cutouts and the correct firewall location for your motor) onto the foam board, once for the center panel with the vertical fin and twice more without the vertical fin for the outer panels.

Cut out the three panels. Measure the largest battery to be used then cut out the rectangular hole for the battery compartment in all three fuselage panels to accommodate the battery. The three panels are laminated with Elmer’s Glue-All white glue, thinned three parts of glue to one part water. Use an old credit card or gift card to squeegee the glue to a thin film on both surfaces that are to be laminated. 

Laminate the center and left sides first, place them on a flat surface, put some weights on the assembly to hold it flat, and let it dry overnight. Cut the slots for the top and bottom battery compartment, insert popsicle sticks as stiffeners, and glue in the stiffeners. Laminate the right fuselage panel as before, hold it flat, and allow the assembly to dry. 

Cut the firewall to fit the motor to be used from a piece of 1/8-inch aircraft plywood. Mark and drill 1/16-inch holes in the motor mount for the 2mm mounting screws and drill a 5/16-inch hole in the center to clear the motor bearings. Epoxy the firewall to the fuselage with 2° of downthrust and 2° of right thrust.

Using Elmer’s glue, laminate each cheek cowling from balsa or from multiple layers of foam board with the paper removed. Carve and sand the cheek cowlings to blend into the fuselage/firewall and glue them on. Glue the 1/16 x 3/8-inch basswood keel stiffener to the fuselage bottom from the nose to the point shown aft of the wing’s trailing edge (TE). Cut servo mounting rails from sections of popsicle sticks and glue them in place to fit your servos. Cover the right side of the battery bay cutout with card stock (poster paper or a business card will do). Cover the fuselage with low-temperature, iron-on film and apply trim markings as desired. Keep the iron temperature below 240° F and keep the iron moving to avoid damaging the foam.  

This model is intended for operations from grass fields. If flying from pavement, plastic skid strips must be added to the fuselage keel and wingtips. Skid strips can be cut from a plastic milk jug and attached to the keel and wingtips with double-sided foam tape after the model has been covered. Cut slits through the fuselage above and below the battery compartment stiffeners and thread a Velcro strap through the slits to secure the battery and the ESC, as shown in the photos.

Stabilizer and Elevator Construction

Cut the horizontal stabilizer from 3/16-inch foam board and glue on the rear 1/4 x 3/16-inch basswood spar. Round the leading edge (LE) and tips of the foam stabilizer and sand lightly around the back edges of the basswood spar.  Reinforce the stabilizer’s LE with a 3/4-inch strip of printer paper and some Elmer’s glue that is thinned three parts glue to one part water. Cover the stabilizer’s LE with a 1/2-inch strip of the base color EconoKote, and then iron on the EconoKote hinges and cover the stabilizer with iron-on film, leaving the center 9/16 inch uncovered where it will glue to the fuselage. Fit the fuselage stabilizer slot depth as needed to hold the stabilizer snugly and squarely.

Elevator Option 1: Cut the elevator halves from 3/16-inch sheet balsa and splice them together with a piece of 3/16-inch wood dowel. Sand the elevator LEs round and taper the elevators from 3/16 inch at the front down to 1/16 inch at the TE. Shape both elevator halves only on the top side to keep them in alignment. The elevators cannot be hinged to the stabilizer until after the elevators and stabilizer have been slipped through the fuselage stabilizer slot. YouTube has videos on how to make hinges from plastic covering films. Elevator Option 2: If you need to keep the all-up weight below 250 grams, cut the elevators out of foam board instead of balsa to save roughly 5 grams. Use a full-span 3/16 x 9-3/16-inch dowel to join the elevator halves. Remove the paper from only the top side of the elevators and sand them to the tapered cross-section of the balsawood elevators as previously described. 

Glue the elevators to the dowel. When dry, cover the entire elevator with printer paper and thinned white glue, as previously described. Starting at the elevator’s top TE, wrap the paper forward around the LE dowel, and then continue it aft to the bottom TE. This provides adequate torsional rigidity and eliminates approximately 5 grams of weight.

Wing Construction

The wing is made from two layers of 3/16-inch foam board for a total thickness of 3/8 inch at the spar location. Cut out the top panel to the full wing outline (including the balsa TE) from a sheet of foam board. Remove the paper backing from both sides of only the top panel. (Note: Redi-Board peels easily, but Ross and Elmer’s foam board is hard to peel.)

Cut a second panel for the bottom minus the balsa wood TE. Cut the 1-1/4 x 3/16-inch balsa wood TEs and glue them onto the lower wing panel with Elmer’s glue. The outlines of both top and bottom wing panels should now match. Laminate the wing panels together with Elmer’s white glue in the same manner as the fuselage laminations, being sure to weigh the wing down on a flat surface while the glue dries overnight. Cut the 12-inch wing spar from 1/8 by 3/8-inch basswood. Locate the wing spar, as shown on the plans, and cut a 12 x 1/8-inch slot the full depth of the wing. Glue the spar into the slot with Elmer’s glue and let it dry. 

Shape the airfoil with a drywall sanding block fitted with 120-grit, open-screen sanding cloth. If available, use a razor blade planer to speed up the shaping process. The airfoil remains 3/8-inch thick at the spar line from wingtip to wingtip. The airfoil tapers toward the TE to a final thickness of roughly 1/16 inch. Foam board sands quickly when the initial glue/glaze is removed. Be careful not to sand off too much foam.

Round the LE to the airfoil shape that is shown on the fuselage plans. Make all of the sanding passes parallel to the wing spar. The top foam layer will slightly overlap some of the balsa TE on the outer 5 to 6 inches of each wingtip. Cut two 11 x 1-inch strips of printer paper for the wing’s LE reinforcement and apply them with thinned Elmer’s glue. 

Cut the 3/4-inch wide single aileron out of the right wing’s TE. Attach the aileron with EconoKote hinges during the covering process for the wing. Other hinging methods can be used, but the EconoKote hinges are the lightest, minimizing the aileron gap and preventing flutter. While covering the wing with EconoKote, leave the center 9/16-inch strip uncovered where the wing will be glued to the fuselage. Trim and sand the fuselage wing slot to fit the wing’s airfoil. 

03.  The Tiny Toni can be flown with only three channels. A battery bay is used to better secure the battery to the aircraft.

Final Assembly

Glue the wing to the fuselage with white glue and let it dry. Any large gaps can be filled later using a hot glue gun. Cover the elevator’s LE with a 1/2-inch strip of the base color EconoKote and insert the elevator into the fuselage stabilizer slot first then slide in the stabilizer and glue it in place. When dry, iron on the EconoKote hinges to the elevator and finish covering the elevators. This seals in the hinge strips.

Make two control horns from a plastic gift card or credit card.  Cut full-depth slots in the elevator and aileron for the control horns and epoxy the control horns in place with each control horn pointing up. Attach the motor to the firewall with 2mm sheet-metal screws and install the propeller. Install a lightweight, 15-amp ESC (with a BEC) on the right side of the fuselage and hold it in place with the Velcro battery strap. Attach a full-range, lightweight end-pin receiver (4.54-gram Lemon six-channel receiver is shown)  

04. Because it is a profile model, all of the radio gear is attached to the side of the fuselage.

Pushrod and Control Linkage

Make the elevator and aileron pushrods from 0.039-inch music wire with Z-bends, as shown. The elevator is very powerful and should be initially set for no more than 1/4 inch up and down, as measured at the elevator’s inboard TE. With equal aileron throws, the airplane will roll faster to the right than to the left, so differential aileron throws are needed to keep the left and right roll rates even. Start with 3/16 inch up (right) and 1/4 inch down (left). Offsetting the neutral position of the aileron servo, as shown, is an easy way to provide the needed differential throws. 

Adjust the final control throws during your test flights to suit your flying preferences. (Note: The small control surfaces do not need large servos. Eight ounce-inches of servo torque is more than sufficient.) The model should balance without any additional weight if nominal 3.5- to 4.1-gram servos are used (such as the EMAX ES-9051). 

Balancing

The model should come close to balancing with a 500 to 1,000 mAh 3S LiPo battery. The correct balance is primarily achieved by adjusting the location of the battery, receiver, and ESC. The battery can be moved slightly fore or aft in the battery compartment until the model balances on the wing spar. Mark the battery location. Foam spacers might be needed to keep the battery from sliding when it is strapped in place. 

Flying

This model can fly sub-10-second laps around a 660-foot racecourse. A 10-lap race takes approximately 2 minutes, including landing. A 500 mAh 3S LiPo battery will run the motor at full power for roughly 3 minutes with a 5.25 x 5.5 propeller. The more powerful 163-watt SunnySky X2305-13-V3 with a 5.2 x 6.0 propeller needs an 850 to 1,000 mAh battery. To keep the total weight below 250 grams, it will be necessary to limit the battery weight to 56 grams or less, which means a 500 to 600 mAh battery.  This model is intended for smooth, low-cut grass runways. It has neutral roll stability because there is no wing dihedral and it does not right itself. It is hand-launched, and initial control inputs might be needed quickly. The first flight should be made with a helper launching the model so that the pilot can concentrate on applying instant corrections and begin trimming out the model. 

After it is trimmed, using a transmitter neck strap can facilitate maintaining aileron and elevator control throughout the hand launch. Grasp the fuselage at the canopy with your left hand, go to high throttle, place your right hand on the transmitter stick, and launch the model underhanded with the nose pointed up at roughly 30° at the point of release.

Landings are made using a little power down to 1 foot above the ground. Chop the throttle and hold it off as long as possible until it settles onto the grass and slides to a stop. This model grooves well and is not particularly difficult to fly, but it does require a pilot’s undivided attention. Don’t look away from the model for even a second because its small size makes it hard to see if it gets too far away. Although definitely not for beginners, it is suitable for intermediate-level pilots who are comfortable flying 70 mph airplanes.  This model was designed to go fast and turn left, and therefore, it has no rudder, which means it will not do spins, snap rolls, knife-edge flight, or 3D maneuvers. The aircraft has an unlimited vertical climb capability, flies well both upright and inverted, easily performs inside and outside maneuvers, and has a fast but decent glide ratio.  

Start racing and enjoy the adrenalin rush! 

Specifications

Wingspan: 22.75 inches

Wing area: 106.6 sq. in. 

Wing loading: 11 to 13 ounces per square foot

Weight: 8.1 to 9.5 ounces (including battery)

Power loading: 258 to 274 watts per pound, depending on motor, battery, and propeller 

Radio required: Micro, full-range, three-plus-channel receiver; two micro (4-gram) servos

Battery: 500 to 1,000 mAh 3S LiPo  

Top speeds: 68 mph with a SunnySky X2206-14 25-gram, 1,900 Kv motor and APC 5.25 x 5.5 propeller (131 watts); 73 mph with a SunnySky X2305-13-V3 25-gram, 1,850 Kv motor and APC 5.2 x 6.0 propeller (163 watts)

05. Several people in the club have built the Tiny Toni and race them. Some have even selected a different color to better tell them apart while racing. 

SOURCES:  

Dollar Tree 

www.dollartree.com

HobbyTown USA 

(844) 714-3445

www.hobbytown.com

Buddy RC

(614) 808-4488

www.buddyRC.com

SunnySky USA

(614) 465-6688

www.sunnyskyusa.com

MotionRC

(224) 633-9090

www.motionrc.com

Altitude Hobbies

(970) 412.7303.

www.altitudehobbies.com

Harbor Freight

(800) 444-3353

www.harborfreight.com

Tower Hobbies

(800) 338-4639

www.towerhobbies.com