MODEL AIRPLANE NEWS

CONSTRUCTION

WW II DREW TO A CLOSE just as a whole generation of advanced combataircraft was entering service in the U.S. armed forces. One of the mostimpressive of these was the Grumman F8F-1 Bearcat, which was literally

en route to the Pacific Theater at the time of Japan'ssurrender. Although the family resemblance to itsfamous forebear, the F6F Hellcat, is apparent, theBearcat owed its inspiration to a detailed study ofa captured German Focke-Wulf 190A.

"To surpass the Fw 190, Roy Grummandirected his design team to build thesmallest practical airframe around thesame 2,100hp Pratt & Whitney R-2800that powered the much larger Hellcat.All other factors took a back seat to min-imum weight and maximum perfor-mance, and the result was astonishing.The fighter that rolled from theBethpage plant on August 21, 1944,could take off across a typical runway,and it set a time-to-climb record (10,000feet in 94 seconds) that stood through-out its service life and well into the jet

age. Even today,a modified F8F-2,Lyle Shelton'sRare Bear, holdsthe world speedrecord for piston-engine aircraft with a blistering528mph. For all that, the true geniusbehind the Bearcat was manifested in itsoutstanding handling characteristicsand wonderfully balanced controls. Theresult was an aircraft that could make astrong claim as the finest piston-enginefighter in history.

Many modelers who have built mySpeed 400 Hellcat design (see the July

'97 issue of Model Airplane News) havesuggested that 1 design plans for the

other wartime Grumman fighters, theWildcat and the Bearcat. The productsof the "Grumman Iron Works" providedthe decisive margin in history's greatestnaval war, and these immortal fightershave held a special place in our heartsever since. So with flight operationsCNX'ed by rain one weekend, I sat downat my computer to design a model ofRoy Grumman's masterpiece.

60 MODEL AIRPLANE NEWS

Begin con-struction bycutting a"kit." As youcan see, thetotal partscount is low,and thismakes forquick con-struction.

CONSTRUCTION NOTESThe airframe was designed in AutoCAD.The fuselage is a balsa semi-monocoquestructure, and the wings are foam sheetedwith 1/52-inch balsa. The weight goal forthe empty airframe is 7 ounces. I use regu-lar thin CA for most construction, but thisadhesive will attack foam. For all wingconstruction, I recommend foam-friendlyodorless CA or an aliphatic adhesive.

The foam wing-cores and vacuum-formed canopy are available from me for$24 postage-paid. Send check or moneyorder to Jim Ryan, 6941 Rob Vern Dr.,Cincinnati, OH 45239; (513) 729-3323;email: jimryan@sprintmail.com.

THE WINGThe foam cores are lightly sanded andcleaned with a shop vacuum. The 1/16-inch sub leading edges are installed withodorless CA and trimmed flush. The wingskins are glued up from 1/32-inch balsa; Irecommend Pica* Gluit, which won'tleave hard glue ridges. After sanding andcleaning the skins, attach them with lightcoats of 3M Super 77 adhesive to saveweight. Trim the skins flush with the subleading edges, then install the 1/8-inchleading edge (LE) caps. Trim the roots andtips flush with the cores, then trim thetrailing edge (TE) to the chord shown onthe plans. Finally, install the '/2-inch balsawingtips and sand them to shape.

Cut the ailerons from the wing panelsas shown on the plan and apply 1/8-inchbalsa to the exposed TE. Trim 1/4 inchfrom the LEs of the ailerons and installtheir 1/8-inch balsa LEs. If you wish, youcan trim the ailerons shorter and facetheir inboard ends with 1/32-inch balsa.

Before joining the wing panels, youneed to bevel the roots to the properangle. Align the root of the wing panelwith the edge of your work bench andblock up the wingtip l 1/4 inches. Use asanding block to bevel the root. Repeatwith the other panel. Then, again block-ing each wingtip up 1 1/4 inches, join thewing panels with thick odorless CA.

Apply 1.5-ounce glass reinforcement tapeto the joint with thin odorless CA.

Next, install the aileron torque rods.These are made of 1/16-inch music wireand 3/52-inch brass tube. Note that thetorque rods mate with the ailerons at thevery end, forming the inboard hinge forthe surface. The easiest way to install thetorque rods is to cut through the bottomsheeting, remove the underlying foamand then install the torque rods withthick odorless CA, being careful not to getany glue inside the brass tubes. Next, fillin the slot with 1/8-inch balsa and sand itflush. Cut the hinge slots and dry mountthe ailerons. I recommend installing the'/i6-inch-ply aileron servo mount aftercovering the wing.

THE FUSELAGEThe fuselage is built over a crutch, whichmakes it easier to ensure a light, straightassembly. The crutch shown in the plansis cut out of 1/8-inch hard balsa andmarked as shown. Note that thecrutch is to be removed when thefuselage is complete. Do notglue any of the formers to thecrutch!

Slide each former over thecrutch into its marked position. Dry-fit the 3/16-inch square top stringersinto place and, after making sure eachformer is exactly perpendicular to thecrutch, glue the top stringers to the form-ers with thin CA. Repeat this step for the3/16-inch square bottom stringer, againmaking sure the formers are square to thecrutch. Note that F-6A and F-6B must bebeveled and joined at the proper 30-degree angle to allow removal of thewing. You'll also need to trim the slot inF-6B for the 3/16-inch stringer to seat prop-erly. Finally, dry-fit the 3/32xVi6-inchupper and lower side stringers and CAthem into place. You should now have alight and straight framework.

Secure the lower fuse sides to the lowerside stringers with thin CA. Make sure thelower sides overlap exactly half of the side

SPECIFICATIONSModel: F8F Bearcat Speed 400

Type: 11/4-scale electric warbird

Wingspan: 30 in.

Length: 22.25 in.

Wing area: 170 sq. in.

Weight as flown: 18 oz.Wing loading: 15.3 oz./sq. ft.

No. of channels req'd: 3 (throttle,elevator and aileron)

Power: 6V Graupner Speed 400, 7 or 8Sanyo 600AE Ni-Cds, Micro BECspeed controller

Features: thinned Clark Y airfoil, foam-core wing, simple balsa construction.

Comments: while simple in structure,the Bearcat is very true to scale; thethinned wing and the lack of LE "crank"are the only significant deviations.Weight is critical, and the builder mustresist the temptation to add surplusreinforcement. Because of its small sizeand short coupling, it's targeted toexperienced modelers, preferably thosewho have some electric experience.

stringers as shown on section F-3 in theplans; the stringers will make it easier toglue the upper fuse sides to the lower sides.

If necessary, wet the lowerfuselage sides so they'llbend, then carefully *'**"trim them so

Fuse constructionbegins by mounting all for-

mers on the removable con-struction crutch and installing all

stringers. Make sure that each for-mer is square to the crutch before glu-

ing the stringers. Also install the cockpitfloor at this time.

\

With the fuse assembly inverted, the lowerfuse sides are glued in place. Wet the sides,push them together and glue them in place.

JANUARY 1999 61

CONSTRUCTION: F8F BEARCAT

FLIGHT PERFORMANCEBe very careful checking the CG; thismodel is short-coupled, and it's toughto handle in an aft CG condition. I sug-gest you start with the CG 2 inchesbehind the LE of the wing where it exitsthe fuse and adjust it to suit your tastes.If you keep the weight at around 18ounces, the Bearcat should fly just fine.

• TAKEOFF AND LANDINGI strongly recommend getting a capableassistant to hand-launch the model onthe first flights. The model needs to bethrown straight and level. If the launcherlobs it upward, it's likely to stall. Holdthe wings level and let it climb slowly asthe speed builds up.

Landings are made with a straight-inapproach, and the model is simply heldjust off the ground until it settles in. TheBearcat has very little tendency to tip-stall, but don't tempt fate with tightturns onto final.

• FLIGHT CHARACTERISTICSThe model does a good job of mimick-ing the handling characteristics andclimbing performance of the original.

For your first flights, I recommend 7cells. I use 8 cells to improve the verti-cal, but I spend most of each flight at 1/2to 2/3 throttle. Running 8 cells wide openshortens motor and battery life consid-erably.

• AEROBATICSWhat's the point of a model that lookslike a Bearcat if it doesn't fly like aBearcat? This model is remarkably aero-batic for its small size and modestpower. Huge loops and Cuban-8s are noproblem, and the roll rate is very fast. Ilike making an overhead pass and thendropping through a split-S into a straf-ing run. The inverted performance issolid and predictable. It's a model you'llget comfortable with very quickly. Thankyou, Roy Grumman!

they'll join tightly over the -Vi6-inchkeel stringer. Apply thick CA to theformers and push the fuselage sides intoplace, running a bead of thin CA downthe seam.

Laminate the wing saddle doublersonto the lower fuselage sides as shown onthe plans. Trim or block-sand the edges ofthe lower fuse sides flush with the form-ers around the wing saddle.

After making certain that they'restraight (the pointed tail of the crutchhelps here), glue the tail pieces together.Tack-glue the '/5-inch balsa tail block inplace with thin CA and carve it to shape,then remove it and hollow it out beforegluing it back in place permanently.

At this point, I recommend you care-fully slide the crutch out of the fuseassembly and apply 2 1/2x2 1/2-inch "dou-blers" made of 1.5- or 2-ounce fiberglasscloth to the inside surface of the lowerfuselage sides between F-2 and F-3.Simply fit the patches in place, smooththem down and then saturate them withthin CA. You might also apply glass clothdoublers to the area right behind F-6 atthe TE of the wing, since this is whereyou grip the model to hand-launch it.Also, install 1/4-inch triangle stock to thejoint between the wing-saddle doublerand F-3 at the LE of the wing to help rein-

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62 MODEL AIRPLANE NEWS

The lower tail block is carved to shape,removed and hollowed out before beingpermanently glued in place.

force this high-stress area. Finally, careful-ly slide the crutch back into place.

Edge-glue the mid-upper sheeting tothe bottom sheeting and lower sidestringers. If necessary, wet it so that itwill conform to the upper formers.To minimize the chance of itbecoming warped, I recommendyou glue the lower edges of bothsides into place and then tack-glueboth sides into place at the same timeby pinching them down against the for-mers, starting at the middle and workingtoward the ends.

At this point, you should remove thecrutch before installing the top sheeting.By now, the fuse should be very stiff. Gluethe lower edges of both pieces of topsheeting into place against the mid uppersheeting, then trim the pieces so they jointightly over the 3/16-inch top stringers. Ifnecessary, wet the top sheeting to push itinto place, and CA the joint. The mainfuse construction is now complete.

WING INSTALLATIONAND BELLY PAN

Block-sand the LE of the wing at the rootso that it will have a flat faceagainst F-3, then trim theTE at the root so it will

The mid-upperfuse sides are

edge-glued to thelower fuse sides and are

then pressed and glued intoplace. If necessary, wet them to

make them bend more readily.

fit into the wing saddle. Tap the 1/16-inch-ply wing mount for a 6-32 nylon screw,glue the mount in place in the fuselageand reinforce the joint with 1/4-inch-balsatriangle stock. Drill the screw holethrough the wing and install the 6-32nylon wing screw. Square the wing withthe tail of the fuselage, pinning it in placein the proper position. Drill the LE of thewing to accept the 1/8-inch locator dowel.Remove the wing, install the dowel andre-install the wing with a sheet of wax

paper sandwiched betweenthe wing and fuselage. Installthe belly pan formers on the

bottom of the wing, beingcareful not to glue them to the

fuselage. Glue the front and backformers (F-3A and F-6A) in place

first, and then dry-fit the keel stringerin place. Then trim the middle two form-ers (F-4A and F-5A) until they can fit inplace without bowing the keel stringerupward; this makes the belly pan mucheasier to plank.

Remove the wing from the fuselageand install the 1/16-inch belly pan sheet-ing. It's easiest if you do this with sepa-rate halves and trim them so that theyjoin tightly over the 3/16-inch keelstringer. Trim and sand the front and rearedges flush with the formers. Cut an 1/8-

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CONSTRUCTION: F8F BEARCAT

FSP01991 To order, (F8F BearcatThis Speed 400 model was CAO-designed by Jim Ryan and features a thinned Clark-Y airfoil, foam-core wing and simple balsa constructionweight of only 18 ounces, is remarkably aerobatic. WS: 30 in.; L: 22.25 in.; motor: Speed 400; 3 channels; 1 sheet; LD 3. $14.95.

To order, call (800) 537-5874.

64 MODEL AIRPLANE NEWS

inch access hole over the wing hold-down screw (this will leave the screwtrapped in place so that it won't get lost)and re-install the wing on the fuselage.Sand the joint between the belly pan andfuselage sheeting flush, being careful notto sand through the sheeting.

EMPENNAGEFit the triangular stab base into placebetween the fuse sides and secure it withthin CA. Assemble the wing to the fuseand trial-fit the stab on the stab base.Make certain the stab is parallel to thewing, and if necessary, sand the base oradd shims to correct any error. Removethe wing and stab and glue the tail filletblocks into place using a T-shaped 1/8-inch-balsa spacer as a guide (be carefulnot to glue the spacer in place). Carveand sand the tail fillets to shape.

The tail feathers are simple 1/8-inchbalsa sheet stock. Glue the vertical finpieces together and let them dry. Cut theelevator hinge slots and test-fit them.Now remove the balsa spacer from thetail fillet. If you've been careful with theglue, it should slide right out. You canadd an 1/8-inch-balsa spacer to supportthe tail fillets behind the stab, but makesure you leave room for the music wireelevator joiner. Cut a slot in the turtledeck to accept the key at the forward endof the fin fillet. Dry-fitthe vertical fin andstabilizer and test-install a 1/16-inchmusic wire elevatorjoiner (you can usean 1/8-inch doweljoiner if you prefer). Ifound it easiest towait and permanentlyinstall the vertical finand stabilizer afterfinishing.

After the fuselage has been completed,slide the construction crutch out the frontand discard it.

The cowl block is glued in place and thencarved and sanded to shape. It also pro-vides the mounting surface for the plywoodmotor mount, making the nose very strong.

The tail fillet blocksare glued in placewith the help of an1/8-inch balsa T-shaped spacer. Thefillet blocks arecarved and sandedto shape, then thespacer isremoved anddiscarded.

COWL BLOCK ANDLAST DETAILS

The cowl is a block ofend-grain balsa that iscarved to shape.Vacuum-forming itor carving it fromblue foam would beeasier and cheaper, but nei-ther would have the neededcombination of light weight andhigh strength (remember, the Bearcat isgoing to take landings right on its bluntchin). Note that the block is bored for themotor opening and a 1/4-inch-wide stripof cross-grain balsa is glued in place toprovide a shoulder for positioning themotor mount. Draw datum lines on thefront of the block and use them as aguide for installing F-l, which is reallyjust a sanding guide. Then glue the block

The completed airframe is ready forcovering. At this point, the prototype

weighed 4.3 ounces.

The belly pan formers are glued to the bot-tom of the wing, and then the 1/16-inchbalsa belly sheeting is added. Make surethat you install the nylon wing-mountingscrew before building the belly pan so itwill be trapped in place.

in place onto F-2 and carve and sand it tofinal shape. I recommend waiting untilthe model has been covered to install the1/16-inch-ply motor mount with thin CA.

Install the elevator servo mount withthin CA. I recommend installing theaileron servo mount after covering. Cutthe battery mounting plate out of 1/16-inch balsa and install it on F-3 and F-4,using V4-inch triangle stock to reinforcethe joint. Apply a strip of Velcro® to themounting plate so that the Ni-Cd packcan be secured. I use .038-inch musicwire for the pushrods to keep weight to aminimum. Another option for the eleva-tor is to install Kevlar pull/pull cables. Ifyou opt for music wire, I've found thatSullivan* 2-56 brass couplers (no. 512)are perfect for these small models; justsolder them in place and add a smallnylon clevis.

FINISHINGAlthough I like painting my models, I rec-ommend film covering for a small navalfighter such as this. After covering themodel with dark blue film (I preferCorsair Blue Ultracote*), cut the nationalinsignias and ID markings out of whitefilm using the patterns on the plans for a

quick and very scale finish.The canopy framing can be

painted easily using the frisketmasks shown in the plans forthe windshield and tape for

the bubble. Make sure you mask off theinside surface of the canopy; overspraygets everywhere. After painting the fram-ing, remove the masks and glue thecanopy in place with RC-56 or equivalent

canopy glue. Install the hardware, andyou're ready to go fly.

'Addresses are listed alpha-betically in the Index of

Manufacturers onpage 174.

JANUARY 1999 65