Pink Lady Formula "40"

Author: B. Wisniewski

Edition: Model Aviation - 1987/12
Page Numbers: 61, 62, 164, 165, 166

Pink Lady Formula "40"

Almost everyone who has worked with high-performance model engines knows who Bill Wisniewski is. He's been a prominent engine designer and control-line (CL) speed flier for years and has twice won gold in the FAI Speed World Championships. This article shares his know-how for the Formula "40" class.

Introduction

Formula "40" (Speed 40) was created to draw pilots of Rat Racers and other control-line racing events into Speed. It is an easy event to fly and epitomizes simplification: no takeoff dollies to build or chase, and contest-supplied fuel under standard restrictions. The Pink Lady was developed from a Class B Speed model and resembles an inverted speed job. With a K&B .40 engine (≈6.6 cc) the finished weight is about 22 oz.

Rules and Fuel

Engine displacement: no larger than 6.6 cc (0.4027 cu. in.).
The airplane and engine must have at least one wheel permanently attached.
Fuel: standard Formula "40" — 40% methanol, 40% nitromethane, 20% lubricant.
Choice of lubricant is left to organizers.
Recommended lubricant: 3/4 synthetic (K&B X-2C or Klotz) + 1/4 castor (Baker's AA).
Clocking: by airplane-mile from takeoff (one mile).
One mile = 14 laps on 60 ft. lines.
Use .018" solid music-wire control lines (see AMA Rule Book, Figure 2, p. 19, for ends).

Design Considerations

Acceleration is very important, so a very light airplane is essential.
Engine torque in racing .40 engines is considerable; to minimize its effect fly clockwise around the circle (instead of the usual counterclockwise). This also eliminates the need for wing tip weight.
The landing gear is bolted on top of the engine head. Advantages:
Places the wheel ahead of the center of gravity.
Acts as a heat sink to improve engine cooling.

Construction

Overview

Construction usually starts with the hardware: landing gear, bellcrank, elevator control horn, fuel tank, and pan. The model uses a Harter's Proto Rat Race pan modified to fit the engine and spinner. Seal and glass the structure with polyester resin and two-ounce fiberglass as described below.

Hardware

Landing gear:
May be made from angle extrusion of hard aluminum alloy 3/32" thick or bent from sheet material.
Drill holes per drawing dimensions.
Axle: machined from 1/4"-dia. steel bar.
Bellcrank:
Cut from 1/16"-thick steel sheet.
Hookup buttons and pulleys: machined from 1/4"-in. steel bar.
Buttons extend through the bellcrank and are silver-soldered on the bottom.
Elevator control horn:
Made from same material as the bellcrank and silver-soldered to a piece of 1/16"-dia. piano wire.
Fuel tank:
Made from .010" tinplate (from a fuel can or K&S).
Fuel pickup line is soldered to the outside of the tank, then drilled through from the inside.

Pan

Use a Harter's Proto Rat Race pan.
Cut off the front at the first rib to accommodate a 1-1/2" spinner.
Remove the other webbing to make room for the engine.
Drill and tap engine-mount holes and screw holes to hold the airplane together (note: five screws hold the pan).
Drill and slot the needle-valve hole; ensure the needle does not touch the pan.
Cut off the back of the pan per the drawing.

Fuselage

Crutch:
Cut two pieces of maple or white mahogany, 1/4" x 1/2", to make the crutch.
Lay out and cut the inside part of the crutch.
Glue the crutch pieces to 1/16" balsa sheet (or 1/8" where noted) using a good slow-setting epoxy compatible with polyester (e.g., Sig or 3M #1838 B/A).
Nose ring:
Make from 1/8" five-ply plywood or laminate two pieces of 1/16" plywood.
Glue to the front with epoxy.
After drying:
Cut wing and stabilizer notches.
Drill pan-mount holes and a 1" hole for the engine cylinder.
Cut away inside clearance for the engine.
Bolt the pan to the airframe, lay out and cut the exterior fuselage outline.
Upper fuselage and cowl:
Make the upper fuselage from balsa, cutting a 5/16" (or 3/16" in alternate text — use 5/16" per earlier layout) slot to accommodate the rudder and tack-glue rudder bottom.
Carve the fuselage contour to fit the pan; aft fuselage is an oval cross section.
Remove the top and carve inside, leaving about a 1/8" wall.
Cut clearance for the control horn and clevis link.
Cowl: cut from soft balsa; drill a 1" hole for the engine cylinder and a 5/8" hole for the mini pipe. Cut and clear engine space.

Shape and Bonding

Laminate 1/4" plywood to the outside using a gap-filling cyanoacrylate (Hot Stuff CA) and accelerator:
Spray balsa with accelerator, spread adhesive on plywood, press on balsa — bonding is nearly instant.
Cowl base: piece of 1/2" balsa extending from the front of the cowl to the wing leading edge.

Wing

Use 3/8" balsa for the wing.
Taper the bottom to 3/16" thickness at the tips, leaving a flat portion to mate with the cowl.
Cut the wing outline.
Cut a .020" x 3/16" deep groove at the leading and trailing edges, parallel with and 3/32" from the bottom.
Fill these slots with 1/64"-thick plywood and glue with thin CA to give a hard line for shaping the airfoil.
Bellcrank mount:
Cut from hard maple (do not glue to the bellcrank yet).
Cut the wing to accept the bellcrank mount and to clear the bellcrank.
Control-line grooves:
Cut grooves in the bottom of the wing for the lines and caps to cover them.
Seal the grooves with polyester resin.
Tip guide: made from a piece of 3/64" brass tube, flattened to 3/32" inside dimension using short pieces of 3/64" wire. Both lines go through one tube. Glue in place with slow-setting epoxy.
Airfoil:
Shape with a lifting section in the center and symmetrical tips.
Finish:
Glue the bellcrank mount in place (ensure bellcrank and pivot pin can be removed to install pushrod).
Leave the wing flat where it joins the fuselage and cowl.
Cover the wing with two-ounce fiberglass and polyester resin.
Drill the bellcrank mount pieces 1/8" for the bellcrank pivot; glue the mount pieces together with slow-setting epoxy with the bellcrank in place.

Stabilizer and Elevator

Use 3/16" balsa sheet for the stabilizer.
Cut the stabilizer outline.
Cut a .020" x 3/8" deep groove in the leading and trailing edges and in the center of the 1/16" thickness; fill slots with 1/8" plywood and glue.
Shape a symmetrical airfoil, leaving the center flat where it joins the fuselage.
Cut the elevator from the stabilizer.
Drill 1/16" and 5/32" holes for the control horn and end hinge-pin.
Groove the elevator so the control horn wire and hinge-pin wire fit flush; glue with slow-setting epoxy.
Cover stabilizer and elevator with two-ounce fiberglass and polyester resin, wrapping the glass around the elevator.
Cut pockets in the stabilizer to accept the control horn wire and hinge-pin wire; wax the wires with paste wax, place them in pockets, fill with slow-setting epoxy to form hinges. When set, file or sand epoxy flush and cover with small fiberglass patches.

Assembly

Seal all inside areas with polyester resin before final assembly.
Pushrod:
Make from 1/16" music wire.
Rudder and tail-skid:
Make mounts from 1/16" plywood; glue in place with slow-setting epoxy.
Bellcrank and pushrod:
Install the pushrod in the bellcrank and replace the pivot pin.
Cover the ends of the pivot pin with two-ounce fiberglass and slow-setting epoxy to retain the pin.
Wing and stabilizer:
Use a solder "quick link" to establish elevator neutral while fitting into fuselage notches.
Glue wing and stabilizer in place with slow-setting epoxy, maintaining zero incidence between them.
Pan and engine:
Glue the rear pan mount into the back of the fuselage.
Disassemble the engine and mount the crankcase in the pan; wax the pan so final-glue won't stick to it.
Wrap three layers of masking tape around the crankcase fins as needed.
Bolt the fuselage to the pan after drilling mount holes through the wing.
Cowl and hold-down:
Glue the cowl in place.
Glue a piece of 3/32" aluminum in the upper fuselage to act as a rear hold-down; drill and tap in line with pan holes for a 4-40 screw.
Final shaping:
Finish shaping and sanding the fuselage smooth.
File the notches near the break at the pan with a small round file; do not file more than 1/16" deep.
Fill the notches with strands of fiberglass and polyester resin; file and sand smooth.
Fuel tank installation:
Install the tank in the pan using silicone rubber (RTV).
Notch the fuselage to clear the fuel-filling tubes.
Seal the entire fuselage with polyester resin and sand smooth.
Cover all seams and fillets with two-ounce fiberglass and polyester resin; sand smooth.
Controls:
Drill the air-supply hole through the cowl and install the throttle arm and throttle-arm shaft.
A sewing-machine needle makes a good fuel pickup tube; ensure the needle does not project into the tank.
Mount the bellcrank and check full movement of elevator and rudder.
Install pushrod clevis and set control throws to approximately 1/4" up and down for elevator and 1/4" each way for the rudder.
Final:
Mount the engine and balance the model; finished weight should be about 22 oz.

Flying

Balance the model about 3/8" aft of the wing leading edge.
For first flights:
Use about 18% nitro in the fuel, rich mixture.
Trim for gentle climbs and turns.
Run the engine in and gradually lean the mixture for best performance.
Use a 60-ft. line and the starting procedure given in the rule book.

The Pink Lady has proven fast and competitive in club races. Its inverted appearance and simple construction make it a good choice for newcomers to Class B racing.

Plans and details are available from the author.

Transcribed from original scans by AI. Minor OCR errors may remain.