P-51 MUSTANG. OK; let's admit it. Everyone CONSTRUCTION. A 1.20-size warbird for the sport flier SPECIFICATIONS. by Stephen Scotto MODEL AIRPLANE NEWS - PDF

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MODEL AIRPLANE NEWS CONSTRUCTION A 1.20-size warbird for the sport flier P-51 MUSTANG by Stephen Scotto OK; let's admit it. Everyone wants to build a P-51. It drips power, courage and heroism. It's an
MODEL AIRPLANE NEWS CONSTRUCTION A 1.20-size warbird for the sport flier P-51 MUSTANG by 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 Model: 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 stroke; 1.50 to stroke Engine used: Webra stroke with Slimline Pitts-style muffler Radio req'd: 4-channel (elevator, throttle, aileron and rudder; flaps, retracts and bomb drop optional) SPECIFICATIONS Radio used: Futaba* 9-VAP Retracts used: Robart no. 622 Comments: designed by Stephen Scotto, the plan was drawn using ModelCAD and was developed using Lloyd 3-views from Bob Holman*. The model uses traditional built-up construction and employs balsa and plywood throughout. Building tabs are included on the wing ribs, and they ensure the proper amount of washout at the wingtips. Fiberglass cowl and air scoop, formed canopy and drop tanks are available from the author; ordering instructions are on the plan. Left: the fuselage is built around this longeron framework made from 1/2-inch-square balsa. Note the lite-ply doubter already attached to the balsa fuselage side. Right: aft of the turtle deck, the stabilizer support pieces have been added and sanded to blend into the fuselage sides. Note that the rudder pushrod tube has already been installed. THE MODEL The model is intended to be an attractive and practical airplane that any experienced modeler could build and fly. It has a scale outline, but the fuselage and the wing have been simplified. Standard modeling materials and fittings from normal hobby outlets are used in its construction. To ease wing construction and to produce21/4degrees of washout at the tips, I added alignment tabs to the ribs. The prototype was pulled by the brawny Webra* stroke engine. Four-stroke fans should use at least a 1.20 engine. The engine is side-mounted, and the cylinder head extends out of the cowl. This allows excellent cooling and provides enough room for a Pitts-style muffler. The prototype used 10 servos. Fortunately, you don't need the expensive, oversize units. Each flap and aileron is driven by its own servo while the elevator is driven by two servos linked together. The rudder, bomb drop, throttle and retract valve make do with one servo each. CONSTRUCTION Start with the stabilizer and vertical fin; they are airfoil-shaped, and to ensure warp-free construction, they use the halfshell construction method. Each half is built flat on the board, then the halves are joined to form the final shape. Place the fin parts over the wax-papercovered plans, then add the sub-leading and sub-trailing edges. Add the ribs, and use scrap balsa to form the mass-balance pocket. To eliminate high points, sand the ribs with a 12-inch sanding bar and skin with 1/16-inch balsa. Remove the fin from the board and build the other half (use the mirror image on the plan!). Glue the halves together with aliphatic resin, then add the leading and trailing edges and tip block. The stab is built in the same way: both top and bottom are built over the same drawing. The rudder is built on a balsa core sheet with half ribs added to both sides. Cut the balsa core to shape and mark the position of the ribs on both sides. Glue the balsa leading edge (LE) and the ribs into place on both sides of the core sheet. Add filler blocks on top and bottom, and rough-sand the rudder to shape. Finalshaping should be done when the fin has been attached to the fuselage. Cut the elevators from solid1/2-inchbalsa stock, and taper to shape. WING CONSTRUCTION First, decide which accessories you want to incorporate in the wing. It can be built with flaps, bomb drop and retractable landing gear; it's your choice. To reinforce the Robart* no. 622 retracts installation, ribs W4 and W5 are built from 1/8- inch lite-ply, with 14-inch and1/4-inchaircraft ply doublers. A1/4-inchaircraft ply landing-gear plate provides an extremely secure mount. If you choose to go with fixed gear, use doublers W4F and W5F as shown on the plan. The wing halves are joined with a fourpiece, laminated, 1/8-inch lite-ply brace. Aeroplane Works* cardboard conduits carry the leads to each servo. The flaps are built up with3/32-inchbalsa. If you don't want flaps, do not cut the dotted lines shown on ribs W2 through W7. Make the wing skins from 3/32-inch balsa by edge-gluing the sheets together to form four larger sheets that are approximately 14 inches wide. Sand the joint lines flush, then roughly shape the four sheeting pieces. The separation line for the sheets should be over the centerline of the spar. Build the wing upside-down over the plan. Attach the landing gear and servo doublers to ribs W4, W5 and W8. Drill the mounting holes for the servos now; it will be much easier than when the wing has been completed. Pin the bottom main spar to the board, and set rib Wl aside until later. Pin ribs W2 through Wll into place, and make sure that each rib is square to the building board. Install the servo conduits as shown on the plans, then use thin Zap* to secure the ribs to the main spar. Do not glue rib Wl into place yet! Install the top main spar in the rib notch, make sure that it overhangs the root rib and Zap it into place. Glue the 1/8- inch lite-ply center-section webs into place on both sides of the spars. Pin rib Wl into place, using the angle of the plywood webbing to set the dihedral tilt of the root rib. To help set the rib in place, put bulkheads W12 and W16 in the notches. When you are satisfied with the fit, glue everything into place and add W15. Glue the3/32-inchsub-leading-edge pieces into place, and use3/32-inchbalsa sheet to make the vertical-grain shear webbing between the ribs. To make it fit under the skin, the landing-gear plate must be beveled slightly at the main spar; after checking its fit, epoxy the plate into place. After the epoxy has cured, drill an 1/8-inch hole through the landing-gear plate about 1 inch into the W4A rib doubler, exactly where shown on the plan. Epoxy a piece of 1/8-inch dowel into this hole. Cut and glue a3/16-inch-squarebalsa spar into the notches at the trailing edge (TE) of ribs W2 through W7. Do the same with a3/32x4i6-inchstick between ribs W7 The Mustang is designed for retracts, but you can build it with fixed gear. Here, the Robart gear have been bolted into place. Access for maintenance is easy. JULY P-51D MUSTANG ISP0100A P-51D MUSTANG SHEET 1 OF 3 TO ORDER THE FULL-SIZE PLAN, CALL and Wll and the1/4x3/8-inchspars that support the bomb drop and form the edges of the aileron and flap servo-access hatches. Shape and sand the sub-le and TE pieces to smoothly follow the contour of the ribs. Use medium Zap to attach the wing skins, and be careful not to distort the wing. Remove the wing from the building board, cut off the building tabs, sand off any overhanging wing sheeting, and cut the access holes for the aileron and flap servos. Pin the wing to the work table, right side up, and sand the sub-le flush with the ribs. Drill a hole through the webbing between ribs W4 and W5 to pass the air lines from the retracts into the conduit. Fit W14 into place next to rib 1. Glue scrap balsa into the TE between ribs Wl and W2, and sheet the top of the wing. Glue the LE into place, and sand it to shape. Add the '4-inch sheet TEs, and make sure that the flap hingesupport blocks are in place before you glue it to the wing. Add the wingtip block, and sand it to shape. Build the other wing half in the same way, then laminate the four center-section brace pieces with medium Zap. Cut rib Wl to form a slot between the spars, and trial-fit the brace into place. Epoxy it into place in both wing halves with 25/8 inches under each wingtip. To ensure a straight wing, make sure that the TEs line up with each other. Epoxy W17 in the wing center section, and make sure that the 1/2-inch hole lines up with the slot in rib Wl. Reinforce the center section with 6-inch fiberglass or nylon tape. Drill a '/2-inch hole at least 3 inches into the wing, keeping the drill bit as square to it as you can. Zap a '/2-inch dowel into place, and leave about1/2inch protruding. Pin the3/32-inchbalsa flap skins over the plan, and mark the location of the ribs. Zap the3/16-inch-squarebalsa spar on top of the sheeting at the LE, and then Zap the flap ribs into place. Glue the top spar into place, then glue the sub-le into place. Add the hinge support blocks and, to provide a base for the flap control horn, make sure the oversize center block fits between ribs FL3 and FL4. Add the top sheeting, then mark the flap's sub-le centerline and drill holes for the Great Planes* Pivot Point hinges. Add the '/2-inch LE, leaving notches for the hinges, and sand the LE to shape (see detailed drawing on plan). Using the hinges as a guide, mark the wing's TE centerline and drill s Aiinch holes for the flap hinges. Epoxy a 1-inch-long piece of brass tube into each hole, and allow the tubes to protrude from the holes about M inch. 62 MODEL AIRPLANE NEWS P-51D MUSTANG to brace them and to set the angle shown on the plan. Glue formers F2, F5, F6, F6A, F7 and F8 to the balsa crosspieces, and I looked at a lot of P-51s before I flew GENERAL FLIGHT make certain that they are square to the this bird. Mustangs are big and solid, CHARACTERISTICS longeron frame. Glue F9 to the top of the and they fly with authority. They were stringers at the tail. Reduce power to about3/4throttle for designed to be stable, solid gun platlevel flight. The big Webra pulls this Using former F2 as a guide, pin (don't forms. They fly straight and make big plane with authority. Loops are a delight glue) both fuselage sides to the longerons. loops and rolls; fly this model the same to watch, but remember to reduce Make sure the tabs on F2 fit into the slots way. Don't try to snap and spin it like an power on the downside of the loop. in the doubler. The balsa sides may have Extra; it will just look silly. Rolls are majestic; make sure you have to be trimmed slightly so the ply doubler plenty of speed on entry. fits snugly on top of the longerons. Without gluing, put formers Fl, F3 and F4 TAKEOFF If you lose the engine in flight, get the into place, and use the pins to hold the This is one of the true delights of flying nose down and get back to the runway. sides against the longerons. When you are the model. It's stable, Don't worry about the satisfied with the fit of the formers to the and it tracks rocklanding gear until you are fuselage sides and doublers, glue the sides solid when you treat sure you have made the into place with thin Zap. Use thick Zap to it right. Be sure you field. It's better to secure each former to the fuselage sides know how to fly a scratch the bottom of and to the balsa crosspieces. Remove most tail-dragger before the model than to lose it of the pins holding the longerons to your you attempt to fly this while you fiddle with the work table, then place the antenna tube one. The nose is way switch. and pushrod sleeves through the holes cut up in the air when the in the formers. Glue tailwheel plate F8 to Mustang sits on its tall landing-gear LANDING former F7 and F6A. Use balsa tri-stock to struts, and this plane needs careful For your first landing, leave the flaps up. brace the plate to the fuselage sides, and attention at the beginning of the Remember to drop the gear then turn fit the tailwheel unit into place. It can be takeoff roll. gently onto final and carry some power left in place for the rest of construction. until you have the field made. Cut the Begin the takeoff roll with a small throttle as you cross the runway amount of right rudder and full upcut and glue into place the l^-inch threshold. The plane will run on the elevator. To avoid nosing over, gently balsa tri-stock that runs along the bottom mains before settling down. Remember apply throttle, and ease off the of the fuselage from F4 to F9. It should fit to steer with the rudder on the ground! up-elevator as the model gains speed. snugly against the notches in the formers As you gain more confidence with There shouldn't be any up-elevator left and should bend to match the shape of the plane, you can experiment with when the tailwheel lifts off. Let the plane the sides. Glue into place the M-inch-sheet the flaps. fly off the ground using minimal elevator rear-fuselage bottom, and cut away the for liftoff. Hold right rudder to climb out, tailwheel opening. Do not round the corthis model requires experience to fly and allow the plane to accelerate as it ners of the fuselage yet. Glue into place but rewards careful technique. It looks climbs. To avoid distraction, pull up the the 34-inch balsa tri-stock that runs from and sounds realistic in the air, and it's a landing gear after you have made your Fl to F2A. pleasure to fly. trims and leveled the plane out. Turn the fuselage right side up and use a razor saw to cut away the crosspieces between formers Fl and F2. Use thick Zap to glue top formers FIB, F12, F13, place, and make sure that they F14, F16 and F17 to the crosspieces as operate properly. shown on the plan. Making certain to leave about 1 inch extending forward of FUSELAGE former F14, add the cockpit floor and The fuselage uses 1/2-inchglue the balsa stringer into the notch square longerons to provide on the top of the rear fuselage. Glue in mounting points for the the remaining '4-inch stringers between formers, and the nose is F17 and F13. shaped from 1/2-\nch balsa sheet sanded to shape. To provide glu- The horizontal stab Edge-glue 1/8x48-inch-long ing area to sup- and the fin are airfoiland are built in balsa sheets together, and cut port the turtle shaped Aft of the turtle deck, the stabilizer support pieces have upper and lower deck, an '/6-inchbeen added and sanded to blend into the fuselage sides. out the two sides as shown on halves flat on the square stringer the plans. Glue the lite-ply workbench. Once runs along the Test-fit the flap and hinge parts before you fuselage doublers to the fuselage sides, and the halves have epoxy everything into place. The tubes' be sure to make a left and a right side. Pin top of the '/&been glued inch longeron extensions are necessary to stiffen the together and the1/2-inch-squarebalsa longerons over on each side sheeted, they can hinges. Add the '/4-inch triangular fairing the plan, making sure to follow the be added to the from Fl 7 to strip to the top of the TE, and sand fuselage outline. Join the tail ends of the fuselage. Note F13. smooth. longerons with a small, triangular the fiberglass Cut the ailerons from %-inch balsa piece of balsa, then, starting reinforcing at stock, tack-glue each into place, and shape from the front, cut and glue into the center joint with a plane and sandpaper. If you install place the balsa crosspieces. Make of the horizonretracts, make a cardboard wheel-well sure that the first crosspiece is recessed tal stab. template, and cut open the bottom of the 1/4 inch from the front edge. Laminate wing to install them. Line the wheel wells former F2A to F2 and glue F4A to F4 with1/16-inchbalsa. Fit the retracts into together, using the two F4B pieces FLIGHT PERFORMANCE I 64 MODEL AIRPLANE NEWS P-51D MUSTANG The Webra stroke engine has more than enough power to fly this fighter. A Slimline Pitts-style muffler easily fits inside the fiberglass engine cowl. the1/2-inch-squarestringer into the notches on F12 and FIA, then cut two, te-inchsquare stringers lite inches long. To make them easier to bend, make a series of cuts about halfway through each stringer and 1 inch apart, and with the cuts facing downward, Zap them into place between formers F12 and FIB. Use a razor plane to trim the stringers to follow the sides of the formers. Glue rear-cockpit deck F15 to the tops of former F14 and F13. The top turtle-deck stringer fits into the notch in F15. TURTLE-DECK SHEETING Cut two, 1/8-inch, contest-grade balsa pieces 22 inches long, and glue together. One end should be 31/4 inches wide, and the other end should be51/2inches wide. Soak one side of the sheeting in warm water for about 10 minutes; with gentle pressure, it should easily wrap around the formers. Wrap the fuselage with an Ace bandage to hold the sheeting in place while it dries (this takes about an hour). Remove the bandage, trim the turtle deck to fit, and glue it into place. Glue the te-inch balsa stab supports to the tail with a scrap of '/4-inch balsa between them. Next, sheet the nose with 1/8s-inch balsa sheet from formers F12 to FIB. Use 30-minute epoxy to laminate firewall Fl to FIA and FIB. Using the longerons as guides, align the motor-box opening with formers FIA and FIB. Clamp Fl into place, and allow the epoxy to cure thoroughly. Cut and glue into place the teinch, balsa-sheet chin pieces. They should fit between formers FIA and F2A. Rough-shape the nose with a razor plane and coarse sandpaper. Leave some material for the final shaping with the cowl in place. Fit the te-inch balsa cockpit side pieces into place, and bevel the edges to follow the curves of the fuselage. The motor box is built from!4-inch aircraft ply and is set up to fit your own engine/ engine-mount combo. Measure your engine, and adjust the box accordingly. Assemble the box with thick Zap, and reinforce all the corners with Vi-inch tri-stock. Epoxy the engine box to Fl with 30-minute epoxy. Glue the cowl-retaining blocks into place, and trial-fit the cowl. When you are satisfied with its fit, screw the cowl into place and finish shaping the fuselage. Trial-fit the engine and mount combo, and make the cutouts for the required cylinder head, exhaust, needle valve and cooling clearance. FINAL ASSEMBLY Zap the wing-mounting plate doublers forward of former F4, and epoxy the '4-inch-ply wing-mounting plates into place. Reinforce them with3/4-inchtri-stock. Secure the fuselage upside-down, and fit the wing into place. Measure to ensure that the wing is square to the fuselage, and tack-glue it into place. The wing scoop is held in place by a hook that's built up from plywood. Glue both SCI pieces into place at the wing TF. centered on the fuselage. Drill a Md-inch hole at each mark into the '4-inch-ply mounting plate. Pop the wing off, tap the mounting plates with a '4x20 tap, and enlarge the hole in the wing to '4-inch diameter. The fiberglass air scoop is latched onto a small hook formed by the SC2 and SC4 pieces at the LE of SCI. The air scoop hides the wing hold-down bolts and the radio charging plugs, which are installed in former F4A. With the scoop in place, sand the bottom of the fuselage to match. Fit scrap balsa between the wing LE and the fuselage, and sand to shape. With the wing in place, epoxy the stab and vertical fin into place. Saw, carve and sand two filler blocks to blend in the stab/fin joint. Cut and rough-carve the wing fillets to shape, then fit and glue them into place. Attach the dorsal fin and smooth it out with filler. Tack-glue the rudder into place, and sand it to shape. Detach it, and bevel the rudder's LE. COVERING AND FINISHING There are hundreds of well-documented paint schemes for the P-51D. I chose a scheme that I felt was attractive and practical. I got the photos of the Ridge Runner III from Scale Model Research*. I used silver MonoKote* for most of the model, with white and dark red trim. I sprayed parts that needed to be painted with Top Flite* LustreKote to match the MonoKote. The photos of the nose art, kill markings and spec plate were scanned into a computer art p
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