Ole Tiger Quarter Midget Racer Article & Plans
August 1973 American Aircraft Modeler

August 1973 American Aircraft Modeler Table of Contents These pages from vintage modeling magazines like Flying Aces, Air Trails, American Modeler, American Aircraft Modeler, Young Men, Flying Models, Model Airplane News, R/C Modeler, captured the era. All copyrights acknowledged.

OLE TIGER

by Don Panek

Having the desire to race and compete is an instinct born in every individual and almost every modeler who has ever watched Formula I or FAI contest. I personally started with an interest in Formula I, but as the years passed by, the event overwhelmed me due to the great amount of time and money required to compete on a near or equal basis.

Recently, the Quarter Midget event has come into its own, and with it a chance for everyone to compete in a racing event without the necessity of devoting all of his resources to only one phase of this great hobby.

The ST-powered version is the original model. A K&B Schnuerle version is shown on the plans. Remember, Q-Midgets must have a stable engine idle, so you can land under power if desired.

The design meets all existing rules plus those presented to the AMA contest board, which were outlined at the Toledo (Ohio) Quarter Midget meeting in February.

Construction has been simplified by using a unique wing design concept utilizing two fiberglass arrow shafts for both structural strength and as the wing building jig. The credit for this concept goes to Don Dombrowski, owner of the House of Balsa, 2814 E. 56th Way, Long Beach, Calif. 90805, who offers the wing kit, complete with shafts, sheeting, die-cut ribs and formed wire aileron linkage for $11.95.

Construction

I personally like to cut all parts out prior to beginning a project. Once completed, the fun of assembling begins. The wing ribs are made by stacking nine pieces of 3/32" balsa cut to lengths noted on plans, placing them between a root and tip 1/16" plywood rib template. Drill the two 1/4" dia. holes, bolt the stack together and sand to shape. Repeat for the other side of the wing by reversing the tip and root template. Be sure to mark ribs with a felt tip or ball point pen to denote top and front to avoid confusion during assembly.

All equipment access is through the bell hatch; it is a one-piece plane. Use those servo trays they provide the best vibration and crash protection.

At this time, drill mounting holes, using plans for proper placement of engine. Sheet metal screws or blind nuts can be used to hold engine in place.

The firewall assembly, consisting of bulkheads 1, 2 and 3, is cut out to the shape noted. Epoxy together with the engine mount in place. The mount will align the assembly, but make sure mount is at right angles to firewall surface, to assure a zero thrust line.

When a K&B 15 is used, it will be necessary to cut out section noted on plan in dotted lines after the assembly has cured. Sand assembly to contour shown on top view.

The basic fuselage sides are cut out to outline shown, stacked together, sanded true and the two 1/4 dia. holes are drilled. Cut slit in forward section as noted. Glue the 1/4 x 1/8" strips to upper and lower edge of the basic fuselage sides. The upper strip ends just aft of bulkhead 5 and the lower one ends aft of bulkhead 9.

Sand rear of sides to angles shown and glue together with bulkhead 9 in place. After curing, epoxy firewall assembly in place, align assembly using top view and clamp sides. Glue bulkhead 4 to 5. Place assembly on a flat surface, bottom side down and proceed to epoxy the landing gear, hatch mount and 3/32" plywood aft hatch cross  cross piece 1/16" off the building surface. Next, epoxy the assembled bulk-heads 4 and 5 to fuselage sides and mount 12. The remaining bulkheads and bottom 1/4 x 1/8" cross pieces are now glued in place. The 1/8" sheet top turtle deck (cut to inside dotted lines) is glued in place and sanded flush with bulkheads.

The upper nose section from 1 back to 8 is now planked with 3/32" strips. Cut strips from a sheet in varying widths to meet your needs. The 3/32" sheet sides of the turtle back are now glued in place, and the assembly is left to dry. The inside of the nose section, forward of bulkhead 5, is now coated with epoxy and glass cloth. The upper 1/4" sheet turtle deck cap is now glued in place. The rear balsa fillets are formed by tack gluing two blocks to two 3/16" sheet spacers which take the place of the fin and stabilizer. This assembly is tack glued in place and left to dry. Rough sand planked area, rear of fuselage and fillet blocks, being careful not to round off edges where front cowl blocks are to be placed.

At this point the wing assembly begins with the two 1/4" dia. fiberglass shafts cut to 32-1/2" length. Shafts can be obtained from sporting goods outlets or plastic supply houses in various lengths. Mark the locations of ribs and centerline on the shafts using a pencil or marking pen. Slide shafts in fuselage and place bottom of fuselage on a flat, true surface. Using two 2-1/4 x 6" (preferably 1/4" thick) sheet spacers, place under outer tips of the shafts. If shafts are out of line and do not lay flat on the spacers, enlarge holes slightly in fuselage sides until they lay flat and true without force being applied. Apply epoxy to shafts from inside of fuselage and let assembly completely cure.

Next, slide down ribs in proper sequence being sure that the top and front of the rib is correctly located. Lay a straightedge against the leading and trailing rib edges to assure proper location. Epoxy root rib to fuselage side, pin or tape to side of fuselage to maintain contour, and wipe excess epoxy from edges of rib.

Next, apply slow-curing epoxy to remaining ribs. To insure a true wing, rotate tip ribs back and forth until whole assembly will lay flat on spacers, without external pressure. Allow to completely cure.

Glue 1/16 x 1/4" front edge and 3/8" square rear edge in place. After it is dry, sand edges to meet contour of ribs.

The two wing skins, each consisting of three sheets of 1/16 x 3 x 36" medium balsa joined together with Francis resin, are now prepared. This isn't a difficult task if you select the sheets from a common bundle at the hobby shop, making sure the edges are not bowed or unusually rough. Match the sheet edges, sand as necessary for a good fit, and apply the resin to the edge with a pipe cleaner. Pin the sheets down on a flat surface covered with waxed paper and let cure. Sand both the top and bottom surfaces using a 280 grit

The skin is now glued in place over the ribs and butted against the fuselage sides. Lay a straight piece of hard balsa on the front and rear edge of the shim, and use large clothespins to clamp in place. Remember that this whole process must take place with the two wing templates supporting the underside of the fiberglass spars to insure a true wing. After curing, remove the clothespins and apply the lower wing skins. At this stage, the wing assembly is rigid and only requires clamping in place during drying.

Sand the front, trailing edge and tip flush and glue the 3/8 x 1/2" leading edge in place. The trailing edge stock is now cut as shown. Route out the inboard section to receive the aileron torque tube assembly and, using five-minute epoxy, glue tube and trailing edge in place. Be sure not to get epoxy into torque tube during this assembly step.

Next, glue tips in place and apply ailerons to wings. I don't specify hinges because of the numerous types available, and each of us has his own preference, My only comment is to use enough to assure a strong assembly.

With the wing completed, we will now proceed to finish the fuselage. Epoxy a 1/16 x 1/4" plywood strip to the bottom and forward edge of the landing gear mount (12). Next, position formed landing gear on mount and drill two holes for 4-40 screws. Once drilled, place two 4-40 blind nuts on inside and screw down into mount. Glue the forward bottom 1/4" sheet in place. This sheet extends from bulkhead (1) to the leading edge of the landing gear opening.

Make hatch cover from 1/4" sheet and epoxy the two 1/16" plywood cross pieces as shown. Drill the three holes in mount and rear 3/32" cross piece and install 4-40 blind nuts. Undercut hatch to clear the two screw heads holding the gear in place and countersink hatch. Hold down screw openings. Fit nose blocks around engine mount and epoxy left cheek cowl in place. With engine mounted, make right cheek cowl from I" thick balsa, route out section around engine, and extend to cooling opening. After fitting block, glue 3/8" sheet to complete cowl. After rough assembly is complete, epoxy nose ring R in place, leaving approximately 1/32" clearance between ring and nose spinner. Cut cowl aft of area assigned for 3/8" dia. dowel support. (Location noted for K&B 15 or Supertigre.) Epoxy dowel and rear of cowl assembly in place.

Epoxy a 1/16" plywood piece inside removable cowl section where it butts against the dowel. Trim dowel so cowl fits flush. Drill hole through cowl into dowel and fasten with sheet metal screw: Fill in areas around wing and cowl with a mixture of micro balloons and Francis resin to form fillets, and completely sand assembly to contours shown.

Make tail surfaces from 3/16" medium grade sheet balsa and don't forget to use the spruce tips-these prevent warpage and insure against damage. Re-move formed tail fillet assembly from fuselage and break away the two side fillets. Epoxy the hinged tail surfaces, tail-wheel bracket and fillets in place.

Make pants per detail sketch; shape and sand to finished contour. Install radio as noted, engine servo on plywood plate and three servos mounted on tray or directly to two 3/8" square maple cross pieces. After installation of pushrods, horns, etc., glue bottom of fuselage in place. I prefer leaving the bottom off to the last, to assure myself that the rods are free and not touching.

Each of has a preferred method of finishing. I used two coats of Francis resin sanded to a smooth finish and two overall coats of Hobbypoxy white sprayed on with an air brush. The trim is red Hobbypoxy and blue Mylar tape for pin striping. The shield and racing numbers were cut from standard MonoKote. The emblems on the side of the fuselage, Bardahl, Champion etc., were purchased from the House of Balsa. They are Mylar film with adhesive backing and are designed to take hot fuels and meet the scale size required. The tiger decal was made by spraying clear dope on the adhesive side of brown paper tape, hand painting the tiger and words, and then applying by soaking in warm water.

Full details and photos of the real aircraft can be found in Volumes IV and VII of Racing Planes (Aero Publishing).

Flying

Check all controls and be sure balance point is as shown on plans. The surface movements should be as follows: Ailerons-3/16" up and down; elevator-3/16" up and down; rudder-3/8" right and left.

Have your helper hold aircraft, rev up engine and hold a little right rudder and a slight degree of up elevator. Upon release, and when model is tracking true, release right rudder and up elevator, until enough speed is reached for takeoff. The airfoil used in this model will allow you to turn as tight as possible without snapping, with very little drag at high speed, and still allow landings to be made at a very slow speed without fear of stalling. If so inclined, this is a great sport model and with a few added details it could do well in Stand-off Scale.

Posted July 14, 2010