MODEL AIRPLANE NEWS

CONSTRUCTIONA 1.20-size warbird forthe sport flier

P-51 MUSTANGby Stephen Scotto

OK; let's admit it. Everyone

wants to build a P-51. It drips

power, courage and heroism.

It's an icon of WW II fighters;

why shouldn't you build one? That's the

question Chris Chianelli asked me, and

it's why he proposed this project. A 1/6-

scale model yields a 74-inch

wingspan—big enough to fly right yet

still small enough to transport. The

new, larger displacement, 2-stroke

glow engines fit this size perfectly.

60 MODEL AIRPLANE NEWS

SPECIFICATIONSModel: P-51 D Mustang

Type: sport-scale

Wingspan: 74 in.

Wing area: 900 sq. in.

Length: 64.5 in.

Weight: 14 1b.

Wing loading: 36 oz./sq. ft.

Engine req'd: 1.20 to 1.50 4-stroke;1.50 to 2.10 2-stroke

Engine used: Webra 1.20 2-stroke withSlimline Pitts-style muffler

Radio req'd: 4-channel (elevator, throttle,aileron and rudder; flaps, retracts andbomb drop optional)

Radio used: Futaba* 9-VAP

Retracts used: Robart no. 622

Comments: designed by Stephen Scotto,the plan was drawn using ModelCAD andwas developed using Lloyd 3-views fromBob Holman*. The model uses traditionalbuilt-up construction and employs balsaand plywood throughout. Building tabs areincluded on the wing ribs, and they ensurethe proper amount of washout at thewingtips. Fiberglass cowl and air scoop,formed canopy and drop tanks are avail-able from the author; ordering instructionsare on the plan.

Left: the fuselage is builtaround this longeronframework made from1/2-inch-square balsa.Note the lite-ply doubteralready attached to thebalsa fuselage side.Right: aft of the turtledeck, the stabilizersupport pieces havebeen added and sandedto blend into the fuse-lage sides. Note that therudder pushrod tube hasalready been installed.

THE MODELThe model is intended to be an attractiveand practical airplane that any experi-enced modeler could build and fly. It hasa scale outline, but the fuselage and thewing have been simplified. Standardmodeling materials and fittings from nor-mal hobby outlets are used in its con-struction. To ease wing construction andto produce 21/4 degrees of washout at thetips, I added alignment tabs to the ribs.

The prototype was pulled by thebrawny Webra* 1.20 2-stroke engine.Four-stroke fans should use at least a 1.20engine. The engine is side-mounted, andthe cylinder head extends out of thecowl. This allows excellent cooling andprovides enough room for a Pitts-stylemuffler.

The prototype used 10 servos.Fortunately, you don't need theexpensive, oversize units. Each flap andaileron is driven by its own servo whilethe elevator is driven by two servos linkedtogether. The rudder, bomb drop, throttleand retract valve make do with oneservo each.

CONSTRUCTIONStart with the stabilizer and vertical fin;they are airfoil-shaped, and to ensurewarp-free construction, they use the half-shell construction method. Each half isbuilt flat on the board, then the halvesare joined to form the final shape.

Place the fin parts over the wax-paper-covered plans, then add the sub-leadingand sub-trailing edges. Add the ribs, anduse scrap balsa to form the mass-balancepocket. To eliminate high points, sandthe ribs with a 12-inch sanding bar andskin with 1/16-inch balsa. Remove the finfrom the board and build the other half(use the mirror image on the plan!). Gluethe halves together with aliphatic resin,then add the leading and trailing edgesand tip block. The stab is built in thesame way: both top and bottom are builtover the same drawing.

The rudder is built on a balsa coresheet with half ribs added to both sides.Cut the balsa core to shape and mark theposition of the ribs on both sides. Glue

the balsa leading edge (LE) and the ribsinto place on both sides of the core sheet.Add filler blocks on top and bottom, andrough-sand the rudder to shape. Final-shaping should be done when the fin hasbeen attached to the fuselage. Cut the ele-vators from solid 1/2-inch balsa stock, andtaper to shape.

WING CONSTRUCTIONFirst, decide which accessories you wantto incorporate in the wing. It can be builtwith flaps, bomb drop and retractablelanding gear; it's your choice. To rein-force the Robart* no. 622 retracts installa-tion, ribs W4 and W5 are built from 1/8-inch lite-ply, with 14-inch and 1/4-inch air-craft ply doublers. A 1/4-inch aircraft plylanding-gear plate provides an extremelysecure mount. If you choose to go withfixed gear, use doublers W4F and W5F asshown on the plan.

The wing halves are joined with a four-piece, laminated, 1/8-inch lite-ply brace.Aeroplane Works* cardboard conduitscarry the leads to each servo. The flaps arebuilt up with 3/32-inch balsa. If you don'twant flaps, do not cut the dotted linesshown on ribs W2 through W7.

Make the wing skins from 3/32-inchbalsa by edge-gluing the sheets togetherto form four larger sheets that are approx-imately 14 inches wide. Sand the jointlines flush, then roughly shape thefour sheeting pieces. The separation linefor the sheets should be over the center-line of the spar.

Build the wing upside-down over theplan. Attach the landing gear and servodoublers to ribs W4, W5 and W8. Drillthe mounting holes for the servos now; itwill be much easier than when the winghas been completed. Pin the bottom mainspar to the board, and set rib Wl asideuntil later. Pin ribs W2 through Wll intoplace, and make sure that each rib issquare to the building board. Install theservo conduits as shown on the plans,then use thin Zap* to secure the ribs tothe main spar. Do not glue rib Wl intoplace yet!

Install the top main spar in the ribnotch, make sure that it overhangs the

root rib and Zap it into place. Glue the 1/8-inch lite-ply center-section webs intoplace on both sides of the spars. Pin ribWl into place, using the angle of the ply-wood webbing to set the dihedral tilt ofthe root rib. To help set the rib in place,put bulkheads W12 and W16 in thenotches. When you are satisfied with thefit, glue everything into place and addW15. Glue the 3/32-inch sub-leading-edgepieces into place, and use 3/32-inch balsasheet to make the vertical-grain shearwebbing between the ribs.

To make it fit under the skin, the land-ing-gear plate must be beveled slightly atthe main spar; after checking its fit, epoxythe plate into place. After the epoxy hascured, drill an 1/8-inch hole through thelanding-gear plate about 1 inch into theW4A rib doubler, exactly where shownon the plan. Epoxy a piece of 1/8-inchdowel into this hole.

Cut and glue a 3/16-inch-square balsaspar into the notches at the trailing edge(TE) of ribs W2 through W7. Do the samewith a 3/32x4i6-inch stick between ribs W7

The Mustang is designed for retracts, butyou can build it with fixed gear. Here, theRobart gear have been bolted into place.Access for maintenance is easy.

JULY 2000 61

P-51D MUSTANG

ISP0100A P-51D MUSTANG SHEET 1 OF 3

TO ORDER THE FULL-SIZE PLAN, CALL 1-800-537-5874. www.rcstore.com

and Wll and the 1/4x3/8-inch spars thatsupport the bomb drop and form theedges of the aileron and flapservo-access hatches. Shape and sandthe sub-LE and TE pieces to smoothlyfollow the contour of the ribs. Usemedium Zap to attach the wing skins,and be careful not to distort the wing.

Remove the wing from the buildingboard, cut off the building tabs, sandoff any overhanging wing sheeting,and cut the access holes for the aileronand flap servos. Pin the wing to thework table, right side up, and sand thesub-LE flush with the ribs. Drill a holethrough the webbing between ribs W4and W5 to pass the air lines from theretracts into the conduit.

Fit W14 into place next to rib 1.Glue scrap balsa into the TE betweenribs Wl and W2, and sheet the top ofthe wing. Glue the LE into place, andsand it to shape. Add the '4-inch sheetTEs, and make sure that the flap hinge-support blocks are in place before youglue it to the wing. Add the wingtipblock, and sand it to shape.

Build the other wing half in thesame way, then laminate the fourcenter-section brace pieces withmedium Zap. Cut rib Wl to form a slotbetween the spars, and trial-fit thebrace into place. Epoxy it into place inboth wing halves with 25/8 inches undereach wingtip. To ensure a straightwing, make sure that the TEs line upwith each other.

Epoxy W17 in the wing center sec-tion, and make sure that the 1/2-inchhole lines up with the slot in rib Wl.Reinforce the center section with 6-inchfiberglass or nylon tape. Drill a '/2-inchhole at least 3 inches into the wing,keeping the drill bit as square to it asyou can. Zap a '/2-inch dowel into place,and leave about 1/2 inch protruding.

Pin the 3/32-inch balsa flap skins overthe plan, and mark the location of theribs. Zap the 3/16-inch-square balsa sparon top of the sheeting at the LE, andthen Zap the flap ribs into place. Gluethe top spar into place, then glue thesub-LE into place. Add the hinge sup-port blocks and, to provide a base forthe flap control horn, make sure theoversize center block fits between ribsFL3 and FL4. Add the top sheeting,then mark the flap's sub-LE centerlineand drill holes for the Great Planes*Pivot Point hinges. Add the '/2-inch LE,leaving notches for the hinges, andsand the LE to shape (see detaileddrawing on plan).

Using the hinges as a guide, markthe wing's TE centerline and drill sAi-inch holes for the flap hinges. Epoxy a1-inch-long piece of brass tube intoeach hole, and allow the tubes to pro-trude from the holes about M<> inch.

62 MODEL AIRPLANE NEWS

P-51D MUSTANG

FLIGHT PERFORMANCEI looked at a lot of P-51s before I flewthis bird. Mustangs are big and solid,and they fly with authority. They weredesigned to be stable, solid gun plat-forms. They fly straight and make bigloops and rolls; fly this model the sameway. Don't try to snap and spin it like anExtra; it will just look silly.

• TAKEOFFThis is one of the true delights of flyingthe model. It's stable,and it tracks rock-solid when you treatit right. Be sure youknow how to fly atail-dragger beforeyou attempt to fly thisone. The nose is wayup in the air when theMustang sits on its tall landing-gearstruts, and this plane needs carefulattention at the beginning of thetakeoff roll.

Begin the takeoff roll with a smallamount of right rudder and full up-elevator. To avoid nosing over, gentlyapply throttle, and ease off theup-elevator as the model gains speed.There shouldn't be any up-elevator leftwhen the tailwheel lifts off. Let the planefly off the ground using minimal elevatorfor liftoff. Hold right rudder to climb out,and allow the plane to accelerate as itclimbs. To avoid distraction, pull up thelanding gear after you have made yourtrims and leveled the plane out.

Aft of the turtle deck, the stabilizer support pieces havebeen added and sanded to blend into the fuselage sides.

Test-fit the flap and hinge parts before youepoxy everything into place. The tubes'extensions are necessary to stiffen thehinges. Add the '/4-inch triangular fairingstrip to the top of the TE, and sandsmooth.

Cut the ailerons from %-inch balsastock, tack-glue each into place, and shapewith a plane and sandpaper. If you installretracts, make a cardboard wheel-welltemplate, and cut open the bottom of thewing to install them. Line the wheel wellswith 1/16-inch balsa. Fit the retracts into

64 MODEL AIRPLANE NEWS

• GENERAL FLIGHTCHARACTERISTICSReduce power to about 3/4 throttle forlevel flight. The big Webra pulls thisplane with authority. Loops are a delightto watch, but remember to reducepower on the downside of the loop.Rolls are majestic; make sure you haveplenty of speed on entry.

If you lose the engine in flight, get thenose down and get back to the runway.

Don't worry about thelanding gear until you aresure you have made thefield. It's better toscratch the bottom ofthe model than to lose itwhile you fiddle with theswitch.

• LANDINGFor your first landing, leave the flaps up.Remember to drop the gear then turngently onto final and carry some poweruntil you have the field made. Cut thethrottle as you cross the runwaythreshold. The plane will run on themains before settling down. Rememberto steer with the rudder on the ground!As you gain more confidence withthe plane, you can experiment withthe flaps.

This model requires experience to flybut rewards careful technique. It looksand sounds realistic in the air, and it's apleasure to fly.

place, and make sure that theyoperate properly.

FUSELAGEThe fuselage uses 1/2-inch-square longerons to providemounting points for theformers, and the nose isshaped from 1/2-\nch balsasheet sanded to shape.

Edge-glue 1/8x48-inch-longbalsa sheets together, and cutout the two sides as shown onthe plans. Glue the lite-ply

fuselage doublers to the fuselage sides, andbe sure to make a left and a right side. Pinthe 1/2-inch-square balsa longerons overthe plan, making sure to follow thefuselage outline. Join the tail ends of thelongerons with a small, triangularpiece of balsa, then, startingfrom the front, cut and glue intoplace the balsa crosspieces. Makesure that the first crosspiece is recessed1/4 inch from the front edge. Laminateformer F2A to F2 and glue F4A to F4together, using the two F4B pieces

to brace them and to set the angle shownon the plan. Glue formers F2, F5, F6, F6A,F7 and F8 to the balsa crosspieces, andmake certain that they are square to thelongeron frame. Glue F9 to the top of thestringers at the tail.

Using former F2 as a guide, pin (don'tglue) both fuselage sides to the longerons.Make sure the tabs on F2 fit into the slotsin the doubler. The balsa sides may haveto be trimmed slightly so the ply doublerfits snugly on top of the longerons.Without gluing, put formers Fl, F3 and F4into place, and use the pins to hold thesides against the longerons. When you aresatisfied with the fit of the formers to thefuselage sides and doublers, glue the sidesinto place with thin Zap. Use thick Zap tosecure each former to the fuselage sidesand to the balsa crosspieces. Remove mostof the pins holding the longerons to yourwork table, then place the antenna tubeand pushrod sleeves through the holes cutin the formers. Glue tailwheel plate F8 toformer F7 and F6A. Use balsa tri-stock tobrace the plate to the fuselage sides, andfit the tailwheel unit into place. It can beleft in place for the rest of construction.

Cut and glue into place the l^-inchbalsa tri-stock that runs along the bottomof the fuselage from F4 to F9. It should fitsnugly against the notches in the formersand should bend to match the shape ofthe sides. Glue into place the M-inch-sheetrear-fuselage bottom, and cut away thetailwheel opening. Do not round the cor-ners of the fuselage yet. Glue into placethe 34-inch balsa tri-stock that runs fromFl to F2A.

Turn the fuselage right side up and usea razor saw to cut away the crosspiecesbetween formers Fl and F2. Use thickZap to glue top formers FIB, F12, F13,F14, F16 and F17 to the crosspieces asshown on the plan. Making certain toleave about 1 inch extending forward offormer F14, add the cockpit floor andglue the balsa stringer into the notchon the top of the rear fuselage. Glue inthe remaining '4-inch stringers betweenF17 and F13.

The horizontal staband the fin are airfoil-shaped and are built in

upper and lower

To provide glu-ing area to sup-port the turtledeck, an '/6-inch-square stringerruns along thetop of the '/&-inch longeronon each sidefrom Fl 7 toF13.

I

halves flat on theworkbench. Oncethe halves havebeen gluedtogether andsheeted, they canbe added to thefuselage. Notethe fiberglassreinforcing atthe center jointof the horizon-

tal stab.

P-51D MUSTANG

The Webra 1.20 2-stroke engine has more thanenough power to fly this fighter. A Slimline Pitts-stylemuffler easily fits inside the fiberglass engine cowl.

the 1/2-inch-square stringer into the notch-es on F12 and FIA, then cut two, te-inch-square stringers lite inches long. To makethem easier to bend, make a series of cutsabout halfway through each stringer and1 inch apart, and with the cuts facingdownward, Zap them into place betweenformers F12 and FIB. Use a razor plane totrim the stringers to follow the sides of theformers. Glue rear-cockpit deck F15 to thetops of former F14 and F13. The top tur-tle-deck stringer fits into the notch in F15.

TURTLE-DECK SHEETINGCut two, 1/8-inch, contest-grade balsapieces 22 inches long, and glue together.One end should be 31/4 inches wide, andthe other end should be 51/2 inches wide.Soak one side of the sheeting in warmwater for about 10 minutes; with gentlepressure, it should easily wrap around theformers. Wrap the fuselage with an Acebandage to hold the sheeting in placewhile it dries (this takes about an hour).Remove the bandage, trim the turtle deckto fit, and glue it into place.

Glue the te-inch balsa stab supports tothe tail with a scrap of '/4-inch balsabetween them. Next, sheet the nose with1/8s-inch balsa sheet from formers F12 toFIB. Use 30-minute epoxy to laminate fire-wall Fl to FIA and FIB. Using thelongerons as guides, align the motor-boxopening with formers FIA and FIB. ClampFl into place, and allow the epoxy to curethoroughly. Cut and glue into place the te-inch, balsa-sheet chin pieces. They shouldfit between formers FIA and F2A.

Rough-shape the nose with a razorplane and coarse sandpaper. Leave somematerial for the final shaping with thecowl in place. Fit the te-inch balsa cockpitside pieces into place, and bevel the edgesto follow the curves of the fuselage. Themotor box is built from !4-inch aircraft plyand is set up to fit your own engine/engine-mount combo. Measure yourengine, and adjust the box accordingly.Assemble the box with thick Zap, andreinforce all the corners with Vi-inch

tri-stock. Epoxy the engine box toFl with 30-minute epoxy.

Glue the cowl-retaining blocksinto place, and trial-fit the cowl.When you are satisfied with its fit,screw the cowl into place and fin-ish shaping the fuselage. Trial-fitthe engine and mount combo, andmake the cutouts for the requiredcylinder head, exhaust, needlevalve and cooling clearance.

FINAL ASSEMBLYZap the wing-mounting plate dou-blers forward of former F4, andepoxy the '4-inch-ply wing-mount-ing plates into place. Reinforcethem with 3/4-inch tri-stock. Securethe fuselage upside-down, and fitthe wing into place. Measure to

ensure that the wing is square to the fuse-lage, and tack-glue it into place. The wingscoop is held in place by a hook that'sbuilt up from plywood. Glue both SCIpieces into place at the wing TF.centered on the fuselage. Drill aMd-inch hole at each mark intothe '4-inch-ply mounting plate.Pop the wing off, tap the mount-ing plates with a '4x20 tap, andenlarge the hole in the wing to'4-inch diameter.

The fiberglass air scoop islatched onto a small hookformed by the SC2 and SC4pieces at the LE of SCI. The airscoop hides the wing hold-downbolts and the radio chargingplugs, which are installed in for-mer F4A. With the scoop inplace, sand the bottom of thefuselage to match. Fit scrap balsabetween the wing LE and the fuselage,and sand to shape.

With the wing in place, epoxy the staband vertical fin into place. Saw, carve andsand two filler blocks to blend in thestab/fin joint. Cut and rough-carve thewing fillets to shape, then fit and gluethem into place. Attach the dorsal fin andsmooth it out with filler. Tack-glue therudder into place, and sand it to shape.Detach it, and bevel the rudder's LE.

COVERING AND FINISHINGThere are hundreds of well-documentedpaint schemes for the P-51D. I chose ascheme that I felt was attractive and practi-cal. I got the photos of the "Ridge RunnerIII" from Scale Model Research*. I used sil-ver MonoKote* for most of the model,with white and dark red trim. I sprayedparts that needed to be painted with TopFlite* LustreKote to match the MonoKote.The photos of the nose art, kill markingsand spec plate were scanned into a com-puter art program, cleaned up and sent toa commercial vinyl shop, which producedthe marking shown here—expensive, but

worth twice the price when you realizehow much work they save you.

Before applying the markings, I scuffedall the MonoKote with a Scotch-Brite padto give it a weathered appearance. Thepanel lines are made from '/42-inch drafts-man's tape. 1 sprayed flat, clear LustreKoteover everything to seal the tape andenhance the weathered appearance. Sincevery few Mustangs were polished like mir-rors during WW II, the Ridge Runner III isquite realistic. You can make the cockpit asfancy as you want; the plan shows a scalelayout for the instrument panel. I used 1/5-scale instruments from J'Tec* and a 1/6-scale, Hangar 9* pilot figure.

There's nothing fancy about the radioinstallation, but it is a big job; workneatly. One of the flap servos needed to bereversed, so I used an ElectroDynamics*EDR-106 Pro Servo Reverser. I used a sim-ple, homebuilt servo doubler for the eleva-tors so if one servo fails, the other can stillmove both elevator halves equally. The

There is plenty of room for the radio gear in the fuse-lage. The RX is secured in a padded plywood box builton top of the removable servo tray.

doubler is shown on the plan. The1200mAh battery is packed in foam andplaced under the fuel tank. The receiver issecured in a Great Planes Receiver Guardmount box for security.

Installation of the Robart 622 retracts isstraightforward. The air tank fits underthe radio tray, while the servo and controlvalve sit on top. I used a UP-1 controlvalve from Ultra Precision*, which givesslow, realistic landing-gear motion.

When I installed the engine, I used aheavy-duty Davis Model Products* IsoMount to secure it. I fitted the engine witha Slimline* Pitts-style muffler. After the firstfew flights, I added an on-board GlowLiteglow igniter to provide a little extra securityat low throttle settings. The Spinner is a4.5-inch-diameter unit from Zinger*.

That's it for the building. I know you'lllove this Mustang, as it is an honest andgood performing model. If you've alwayssaid you want to build a P-51D, now isyour chance; go for it.

* Addresses tire listed alphabetically in "FeaturedManufacturers" on page 134.

66 MODEL AIRPLANE NEWS

and Saw, carve and