Cricket

Cricket

Paul F. Denson

A home‑built design suitable for RC modeling as well as for piloted aircraft, the Cricket was developed as the author's own creation (with a little help from friends). It is a three‑channel ship designed to accept roughly .08–.20 two‑stroke engines or a .20 four‑stroke with a slight cowl-ring forward move. The layout was inspired by a Model B Fike and uses a square‑tipped Pietenpol‑style wing and Fike‑style empennage. Chuck Cunningham's design parameters were used to ensure good flying qualities.

Design inspiration and overview

• Inspiration: photo of a Model B Fike (Experimental Aircraft Assn. Museum) showing exposed longerons, cross braces, formers and empennage.
• Wing: square‑tipped, Pietenpol influence.
• Empennage: Fike B style, square‑tipped.
• Controls: three‑channel (rudder, elevator, throttle), optional ailerons for aileron/4‑channel setup.
• Airfoil and dimensions:
• Airfoil: 15% Clark Y
• Chord: 8 in
• Span: 48 in
• Aspect ratio: 6:1
• Prototype weight: ~48 oz
• Wing loading: ~18 oz/sq ft

Cowl and firewall

The most difficult part of the project proved to be the cowl. The following practices were used:

• Engine mounting:
• Prefer mounting the model engine horizontally. Inverted engines have often presented problems and are avoided.
• Standard mufflers may not work; Du‑Bro Slimline (or similar slim mufflers) fit neatly alongside the cowl.
• Two‑firewall trick (learned from Lou Proctor):

1. Build the front former to act as the primary firewall for the fuselage.
2. Build a separate firewall that carries the engine/muffler/cowl assembly and attaches to the first with four 4‑40 machine screws and blind nuts.

• This allows easy removal/reworking of the cowl/engine installation without reconstructing the fuselage.
• Cowl ring and skin:
• Build the cowl ring from 1/8‑in aircraft plywood and support it with narrow 1/8‑lite ply strips while fitting.
• Bevel the cowl ring and firewall edges so 1/32‑in aircraft plywood cowl skin will glue flush.
• Use a paper pattern, cut and soak the 1/32 ply top skin in hot water for easier forming, then clamp and glue.
• Leave lower support at the bottom of the cowl ring removable for engine installation ease.
• Instrument bezels: cross sections cut from brass tubing.
• Throttle: route the throttle pushrod under the fuel tank with a large Z‑bend to the throttle arm.

Tip: remove prop drive washer and needle valve during assembly; the engine will be in and out many times.

Landing gear and wheels

• Gear wire: bend landing gear from 3/32‑in music wire (or per plans).
• Wheels: Trexler wheels recommended; Cricket landing‑gear wire plans fit both 3‑in and 3‑1/2‑in Trexler hubs (cut gear to needed length).
• Bearings: drill wheel hubs with a 5/32‑in bit and insert 5/32‑in brass tubing bearings, add 1/8‑in wheel collars.
• Strut ends: wrap ends with heavy thread and seal with 5‑min epoxy to prevent splitting.
• Landing gear attachment: attach gear to former No. 2 with nylon landing‑gear clamps and screws as detailed on the plans.
• Tailwheel: standard nylon tailwheel bracket attached to a triangular 1/4‑in plywood platform carrying a 1‑in Ace tailwheel.

Wing

Materials and preparation

• Ribs: cut from plan templates.
• Leading edge (LE): Sig pre‑shaped 3/4 x 5/8‑in stock (or equivalent).
• Trailing edge (TE): two 3/8 x 1‑in pieces of light balsa (or rip TE from stock with a power saw or plane and sandpaper).
• Spars: relatively hard 3/8‑in‑square balsa (some builders use 1/4‑in‑sq depending on personal preference).
• Center rib: double with 1/8‑in plywood doublers (strong center rib anchors wing to fuselage).
• Dihedral braces: two 1/16‑in aircraft plywood braces.
• Tip ribs: 3/16‑in balsa.
• Webbing: 1/16‑in sheeting on forward side of spars out to tips.

Building the wing

1. Shape the TE stock and cut notches in TE for rib ends.

• Tape three thicknesses of hacksaw blades together to saw accurate notches for 3/32‑in ribs; a snug fit is desirable.
• A small drop of cyanoacrylate (CyA) will anchor ribs in place.

1. Fasten bottom spar to the workbench so TE and ribs fit snugly into notches.
2. CyA the ribs to the bottom spar in place, then glue the top spar. CyA the center rib (some sequences pin center rib later; follow the plans you are using).
3. Pin the LE tight against rib fronts; add a drop of CyA at each joint.
4. If building with ailerons: modify outboard ribs accordingly, cut and hinge ailerons and reinforce hinge lines.
5. Bevel the ends of spar, LE and TE so the two wing halves fit together. Block up each tip 2 in (1‑1/4 in for aileron wing) when joining.
6. Dihedral braces:

• Remove 1/16 in behind the spar of the first rib outboard of center, slip the dihedral brace into this space and epoxy.
• Repeat for the forward side, clamping until cured.

1. Double the center rib with 1/8‑in ply and epoxy into the center of the wing.
2. Add diagonal corner braces and sand smooth. The wing is then ready for covering.

Strut anchors and reinforcement (three‑channel wing without ailerons)

• Cut strut anchors from 3/8‑in lite ply and epoxy fore and rear anchors in place.
• Notch short spar tabs into the bottom rib of the outboard ribs as indicated on plans; epoxy anchor between ribs and tack against short spar.
• Sand underside true and install/epoxy dihedral braces.

Cabane, wing struts and anchors

• Cabane struts:
• Make from piano wire legs fitted into 1/8‑in brass tubing fittings.
• Tubing: cut four 1‑1/8‑in pieces of 1/8‑in brass tubing and four 5/8‑in pieces of 3/64‑in brass tubing as doublers for outer ends.
• Squeeze flush, insert piano‑wire legs, form an upside‑down V (lambda) and round ends with a ball‑peen hammer.
• Support posts: 1/8‑in ply, 5/8 in wide, 1‑1/8 in long; drill 1/8‑in holes and glue to cabin top.
• Tie installed cabane tubing to fuselage with safety wire wrapped and soldered.
• Wing struts:
• Make from 3/64‑in piano wire or 1/16‑in‑thick spruce strips (some builders use spruce with aluminum insert).
• Reinforce outer ends with short pieces of 1/8‑in brass tubing; slot inner ends and insert small sheet‑aluminum anchor plate, epoxy.
• Outer ends fasten under nylon landing‑gear clamps on outer wing anchors with small L‑hooks and inner Gold‑N‑Rod sleeves to bring diameter up to 1/8 in where needed.
• Underfuselage strut anchor:
• 3/8‑in strip of aluminum long enough to protrude 1/2 in on each side; drill holes for anchor screws, bolt to inside of fuselage and solder strut tubes in place.

Wing alignment and washout

• Assemble the skeleton plane (wing, cabane, struts, gear) for easier handling and to ensure screw holes are aligned.
• Mount wing and struts, then determine dihedral and washout:
• The two front struts set the dihedral; the rear struts determine washout.
• With the tail propped and fuselage level, measure from the workbench to the front corner and rear corner of each wing tip. Adjust L‑hooks to equalize distances and avoid warp.
• Leave the wing flat during covering, then add washout after covering:
• Put a 1/2‑in block under the outboard trailing edge corner while holding the wing center flat.
• This creates diagonal wrinkles in the film; iron out and shrink, then hold until cool.
• Final washout should be approximately 3/8 in at the tip.

Fuselage

Formers, longerons and skin

• Formers:
• Cut from ply per plans. Former No. 1: 1/8‑in aircraft ply. Former No. 2 (landing gear attachment): 3/16‑in aircraft ply. Firewalls: 3/16‑in ply.
• Longerons:
• 1/16‑in square spruce for main longerons and cockpit door frame. Station No. 3 just aft of cockpit is spruce. Other vertical/diagonal members are 3/16‑in‑sq balsa.
• Side construction:

1. Cover plans with wax paper and build left side first.
2. When glue has set, apply 1/32‑in ply skin from firewall aft to the former just behind the cockpit.
3. Duplicate for the right side (except cockpit door) taking care to make distinct left and right halves.

• Landing gear fitting:
• Drill holes in 1/32 ply skin for landing gear, slide each side over gear wires until flush against former No. 2, glue and erect upside down over top view of plans.
• Cross braces and diagonals:
• Add two cross braces at station No. 3 (one in line with vertical components, the other set aft to receive cabane strut), then install top/bottom cross braces and diagonals.
• Turtledeck:
• Cut turtledeck formers from 1/8‑in medium balsa, transfer longeron location marks, glue formers and check with a straightedge. Sand where necessary and notch longerons to allow the turtledeck to flare into place.
• Fill gaps between longerons with individually fitted 1/8‑in soft balsa fillers.

Tank and cowl platform

• Build a platform of 1/8‑in sheet balsa between formers No. 1 and No. 2 to support the fuel tank.
• Route silicone tubing to extend about 4 in beyond former No. 1; tubing holes must be above and to each side of the engine mount.
• Pad tank with foam and check that it can be removed through the cutout in former No. 2 before final installation.
• Plank the cowl area in front of the cockpit with 3/8‑in‑wide strips of 1/8‑in sheet balsa, working from top center out each side and fitting the center strip last.

Firewall and engine mount

• Make the separate firewall that carries the engine mount and attaches to former No. 1 with 4‑40 machine screws and blind nuts.
• Before final assembly:
• Reverse the screws through the mount so they protrude slightly into former No. 1; use these to mark indentations for blind nuts.
• Enlarge indentations to ~3/16 in diameter and 1/16 in deep so blind nuts sit flush.
• Check that firewall is about 1/8 in smaller all around than former No. 1 so cowl skin will fair in.
• Drill fuel‑tubing holes and the four screw holes while surfaces are in register.
• Attach engine and mount with machine screws; the engine mount should be removable for service.

Tail assembly

• Standard construction from 3/16 stock sized per plans.
• Elevator joiner: 1/4‑in piano wire epoxied into forward grooves of each elevator half.
• Pin tail surfaces in place and fit pushrods from servos to facilitate locating horn positions before covering.

Covering and finishing

• Covering sequence:

1. Cover turtledeck top first; cut and use pieces to cover the cowl and sides as needed.
2. Cover bottom in two pieces starting at end of ply skin, overlapping about 3/16 in and working aft to tail.
3. Allow covering to bend around former No. 1 about 1/2 in and seal; coat front of cockpit with epoxy for fuel proofing.

• Washout: put washout in after covering as described in Wing Alignment section.
• Painting:
• Cowl: two coats primer, two coats gloss white, one coat clear; paint back of firewall and inside cockpit flat black (two coats).
• Paint struts, rear ends of pushrods, landing gear, cabane struts and wheel hubs as desired.
• Cockpit hatch:
• Optional, made from 1/32‑in aircraft ply with an inside 1/4‑in‑sq balsa frame to make it flush. Overlap hatch 1/8 in each side.
• A length of 1/16 O.D. copper tubing with a piece of music wire can be used for hatch hinge/retention.
• Antenna: run antenna wire through a length of plastic tube so it dangles free in flight (old roll‑up window shade tube works well).
• Latches for cockpit door: small plastic pieces screwed in place.

Final assembly and flight preparation

• Fully assemble skeleton plane to confirm screw locations and alignment.
• Install wheels and check wheel bearings and collars.
• Balance model as shown on plans, check control throws and radio installation.
• Make a few glide tests before attempting powered flight.
• Recommended powerplants:
• .08–.20 two‑stroke
• A .20 four‑stroke works well if the cowl ring is moved forward slightly.

Notes and tips

• The two‑firewall arrangement permits trials and changes to the engine position or cowl without rebuilding the fuselage.
• Be careful when epoxying strut anchor blocks and positioning—one builder accidentally epoxied a block on the wrong side; check alignment before final glue.
• When fitting brass tubing into strut ends, clean, fit, and solder where required to prevent movement.
• Use clamps and protector strips when gluing thin ply skins to avoid crushing and to keep edges flat.
• After covering, check the tailplane and wing incidence and make final control adjustments.

End of article.

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