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A generous wing area and thick airfoil makethis model easy-flying and aerobaticallycapable. The tail-dragger landing gear setupwith 3-inch wheels makes grass-flying-fieldhandling simple.

AGAIN, I FOUND a reason/excuse tobuild a new model. A Magnum .70 four-stroke that I had bought for anotherproject didn’t work out, so it wasavailable.

The engine was broken in and hadbeen flown a few times, with goodperformance. I figured that a .46 two-stroke-size airframe for aerobatics,sport, and fun would be a good project.

I know; a bunch of ARFs on themarket would work fine for this project.But regardless of the time, work, andmoney involved, I like to build myaircraft from scratch. I like to spendtime in the workshop, making sawdustand wood chips.

If you don’t like to build, ARFs aregreat. However, I consider the workshoptime a good part of this hobby.

I laid out a barn-door wing, whichhad a 52-inch span and 14-inch chord,for approximately 700 square inches ofarea. I like a nice, thick 18% fullysymmetrical airfoil.

For easy, fast building, it’s tough tobeat a foam-core wing. To make it evensimpler, I employed no balsa sheetingon this foam core. Good top and bottomspars, which provide plenty of strength;fiberglass cloth and epoxy around the

center; and a low-temperature, iron-oncovering are all that are needed.

Hey, CL Combat modelers have beendoing wings this way for years. I’vedone it before on similar RC airplanesand it works fine.

If you don’t like the thought of anunsheeted foam wing, make the foam-cutting templates slightly smaller andsheet the wing with balsa. Or cut abunch of balsa ribs and fashion a built-up wing. When you’re building fromscratch, you can make it any way youlike.

I used foam blocks on the wingtips,sanding the material to shape rather thanjust capping the end of the core withlight plywood. It would be less work tomerely cut the cores a few inches longerand cap the ends, if you like thatappearance.

The fuselage is 49 inches longoverall, featuring typical construction:balsa sides and plywood doublers.Rather than look for a suitable plasticcanopy, I laid out a side view I liked,slanted the top fuselage sheeting, andbuilt in the canopy area. This method iseasy and strong.

I prefer a tail-dragger gear setup foruse on the grass fields from which I fly.

Tricycle gear can be troublesome whenthe grass is a bit high.

I didn’t try for extremely lightweight. If you want to, you can cut holesin the plywood doublers and fuselagesides.

After a quick iron-on finishing job, Ihad a new model to fly. This design isnot way different; there are no newaerodynamics or claims of fantasticperformance. But it is easy to build andfly, performs decently, is rugged, and Ilike the appearance.

Are you interested? I’ll zip throughthe construction procedure.

CONSTRUCTIONThere are two ways you can go;

either cut all the parts at once to make akit or cut the parts you need as youprogress in building the airplane. Bothtechniques work fine. On this version, Icompleted the wing before I even startedthe fuselage.

Cut the plans, or a copy of the plans,for the parts templates. I drew aroundthe paper templates with a ballpoint penon the balsa or plywood and cut thepieces with a band saw.

Wing: With my crude-but-it-works hot-

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The author looks pleased with this design. He likes itsfour-stroke engine, small size, and, best of all, flyingcharacteristics. It’s a cinch to build too; turn the page.

by Dick Sarpolus

Fun witha 40-sizeairframe

and foamparts

The overall layout of the Little Fast is conventional, with typical proportions for a nice-flying aerobatic sportmachine—nothing radical. The built-in canopy increases strength.

Tail surfaces, vertical fin, and horizontal stabilizer are sheet balsa. Rudder and elevator halvesare built up for weight savings.

Wing parts including cut foam wing cores and all necessary balsaand plywood parts.

This is the rest of the balsa and plywood parts that need cut out forthe fuselage and tail surfaces. All together, it’s a short list of kitcomponents.

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Root ends of the two wing panels, showing the center plywood riband holes through the foam cores for aileron servo cables. Theplywood dihedral brace is used to support the wing joint.

The wingtip has its foam blocks glued in place on the balsa parts andhas been shaped with a sanding block. The bare foam wing cores arecovered with a low-temperature iron-on film.

The basic fuselage structure begins with balsa sides and plywooddoublers, joined by the first four plywood bulkheads. The next job isto pull the tail together straight.

A Magnum .70 four-stroke engine is located on a molded compositeradial mount. The hole in the cowl side provides access for theneedle valve and choke lever.

Photos by the author

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Type: 40-size RC sport aerobaticSkill level: Novice builder, intermediate pilotWingspan: 52 inchesWing area: 725square inches

Airfoil: Fully symmetrical, 18% thickLength: 49 inchesWeight: 5.75 poundsEngine: .40-.52 two-stroke, .70-.82 four-stroke glowConstruction: Conventional built-up balsa and plywood, foam-core wingCovering/finish: Hangar 9 UltraCote usedRadio: Four channels minimum, five standard servosOther: 10-ounce fuel tank, aluminum landing gear, 3-inch wheels, 21/4-inch spinner

With a wing area of approximately 700square inches, a .40-.45 two-stroke glowengine or equivalent does well.

Foam wing cores have top and bottom spars for strength and are not covered withbalsa; it’s unnecessary. Low-temperature iron-on film does the job.

The wing is held on with two 1/4-20 nylon bolts. The aluminum landing gear is securedwith three 1/4-20 nylon bolts. Cream and red UltraCote provide good contrast.

wire foam-cutting setup for such a wing, Icut the core and trimmed off the TE. Then,with a separate template, I cut the sparnotches and the LE notch.

If you don’t cut your own foam, PhilCartier at The Corehouse has a computer-controlled setup to do this wing section.And Bob Hunt at Robin’s ViewProductions does a great job on any foam-cutting requirement. You can also ask theAMA Plans Service if it will sell you a setof cores when you order the plans. Thereare many options when you build.

With your cut foam cores, add the slotbetween the top and bottom spars at themiddle for the plywood joiner. Join thewings flat or at a dihedral angle you prefer.

Many builders like a flat wing; on a low-wing airframe such as this, I prefer a fewdegrees of dihedral.

Oh, and make the hole for aileron servocables in the foam cores before you jointhem. I use a piece of 1/4-inch music wirewith a collar on the end. I heat it with atorch and then push it through the foamfrom the root to the aileron servo cutout.

Epoxy the top and bottom spars into thecores, and epoxy the plywood joiner intoone of the wing panels. Epoxy the centerplywood rib in place—it holds the wingmounting tab—and epoxy the two wingpanels together.

I use a light-plywood tip rib to tie theupper and lower spars together at the tips. I

epoxy heavy fiberglass cloth around thewing center-section and use wood fillerblocks to support the two wing boltmounting holes.

On the top and bottom of the balsawingtips, I glued foam blocks in place andcut and sanded them to shape for covering.If those wingtips seem like too muchwork, get the cores a couple inches longerand use light-plywood caps on the tips ofthe foam cores.

I hinged in place the balsa-stripailerons as usual. I made aileron servomounting plates from 1/4 plywood,epoxying them into the foam, flush withthe surface.

Fuselage: This begins with epoxying theplywood doublers to the balsa sides andthe wing-saddle pieces and the stabilizer-area doublers. I’m careful to make a rightand a left side, because I once fabricatedtwo left sides.

With one fuselage side flat on thebuilding bench, add the first fourbulkheads, perpendicular to the side. Theninstall the other side. This is fairly easy tokeep aligned, because the two sides areparallel from the nose to the TE position.

With that completed, pull in the tailends of the sides and add the rear-sectionbulkheads. Now add the upper fuselagesides; there’s a front section and a rearsection. Sand their lower edges to a slightbevel so that they sit flush on the top edgeof the fuselage sides. Sand their top edgesflush with the tops of the bulkheads, andthen add and round the top pieces.

To be sure that the firewall is secure, Iinstall two small screws on each side,through the plywood doublers into theedges of the firewall. The plywood wingbolt mount plate is added to the fuselage,along with the plywood landing gearmounting plate and its reinforcements.

At this point, fit the fuselage to thewing. Where the front plywood wingmounting tab goes through the secondbulkhead, the lower edge of the opening inthat bulkhead can be sanded or shimmedso that the wing fits tightly in place.

With the wing in place on the fuselage,drill the two wing bolt mounting holesthrough the wing TE area and into thefuselage plate, and tap the plywood for the1/4-20 nylon bolts.

Use a nylon engine mount bolted to thefirewall, and add the balsa sides andbottom pieces to the front end of thefuselage. If you want to do more work,you could use balsa blocks faired to blendsmoothly with a spinner mounted on theengine. I didn’t think that was necessary.

Tail Surfaces: The vertical fin and thestabilizer are 1/4 balsa, and I use firm tohard stock to prevent vibration. Thecontrol surfaces, rudder, and elevators arebuilt from 1/4 x 1/2 and 1/4 square stock.The elevator halves are joined by a pieceof 5/32-inch-diameter music wire epoxiedin place.

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Full-Size Plans Available—see page 167

With the fuselage bolted onto the wing,I insert the stabilizer and epoxy it in place,lining it up level with the wing. I insertthe vertical fin and glue it in place, liningit up perpendicular with the stabilizer.

I like either fiberglass-tube pushrods orSullivan’s nylon-tube setup with thecarbon-fiber inner rods, and I use all 4-40hardware. Cut holes in the rear bulkheads,as required. When the rudder and elevatorlinkages are installed, you can install thebottom planking.

Finishing: I used UltraCote for thecovering; it’s one of the easier films toapply. With the equipment located asshown on the plans, the Little Fastbalanced as shown and it works for me.

I’ve always thought that the balancepoint and control-surface movementsshould suit the pilot. There’s a giganticvariation in the way individuals like theiraircraft to “feel,” but today’s radios makeit easy to set up a model to suit you.

I’m happy with the way the Magnum .70four-stroke engine performs and ampleased with this latest building project.

Hey! Make some sawdust and woodchips! MA

Dick Sarpolusrasarpolus2@comcast.net

Sources:

Magnum engines(714) 963-0329http://magnum.globalhobby.com

The Corehouse(717) 566-3810http://home.earthlink.net/~philcartier/

Robin’s View Productions(610) 746-0106

Sullivan Products(410) 732-3500www.sullivanproducts.com

Hangar 9 UltraCote(800) 338-4639www.hangar-9.com

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