Vickers-Supermarine Spitfire Mk IIA
Article & Plans
December 1972 American Aircraft Modeler
Website visitor Garry O. wrote to request that I post this article featuring the Vickers-Supermarine Spitfire Mk IIA. With its elliptical wing planform and outward-retracting landing gear, is considered one of the most attractive airplanes ever to come out of England. It, along with the North American Mustang, are probably the two most modeled fighters from World War II. This .61-powered control-line model by Malvin Meador won the 1971 Nationals for control-line scale. It has operating retractable gear, flaps, sliding canopy, navigation lights, and drop tanks. |
Vickers-SupermarinePlane on the Cover
Spitfire Mk IIA
Model that won the '71 CL Nats and was 6th at the '72 CL Scale World Champs is patient project of a great plane. Has many operating features and flies quite well.
By Malvin Meador
Photos by Bill Boss and the Author
Every Scale builder has a favorite airplane or type of airplane; I've always been inclined toward World War II military aircraft. After moderate success in local scale contests, I decided to build a ship for entry in the 1971 Nationals. To do this, I needed a subject which inspired me to invest the amount of time required to complete a competitive scale model. Retractable landing gear - an operating feature having good spectator appeal and a high scoring flight demonstration option - was a must. Another point relevant to selecting a subject was additional operating features such as flaps, sliding canopy, navigation lights, drop tanks, etc., which could be incorporated. Also, I wanted to stay away from subjects which had been overdone.
One aircraft kept coming to mind, the Supermarine Spitfire. It was one of the most famous World War II fighters, plenty of reference material was available and, despite its fame, it didn't enjoy much popularity with modelers. The Spitfire had enough operating features to insure a respectable scale flight score, and it featured very simple retractable landing gear which could be easily adapted to Bill Johnson's efficient, lightweight Centrak gear retraction unit. Using this system would eliminate the mess of batteries, extra control lines, electrical wiring, and other assorted headaches which go with retractable gear in control line models. Also, the simplicity of the landing gear would make it fairly easy to machine scale shock absorbing gear struts for added realism.
While considering the positive and negative aspects of the Spitfire as a flying scale project, one nagging thought kept coming to mind: The extremely short nose moment, small empennage areas, and fore and aft placement of the landing gear on the prototype could make the model's flying characteristics less than satisfactory. However, after reading a very scientific conclusion that "anything will fly on control lines," I decided to proceed with construction. The resulting model did fly satisfactorily, but it is definitely not a beginner's ship-the Spitfire demands the flier's undivided attention from takeoff to the end of the last taxi lap.
Nice facet of real plane was its plywood covered wings. Detailing is complete without yards of rivet lines.
A Bill Johnson Centrak gear is used. At speed in flight, centrifugal force working against a spring raises the gear. Very reliable.
With flaps down one sees even more detail, including flap position indicator finger which lifts through a coyer on wing top surface. Oil cooler door also operates.
All smooth areas of the model are fiberglassed, including some detail items such as simulated exhaust stacks.
Before surface finishing, cockpit interior is completed. Door hinges open to reveal many more details, note canopy slides back.
All control surfaces have simulated fabric covering. Note full swiveling tail-wheel.
Which variant of the Spitfire to build was the final problem. The solution was dictated by the availability of reference material, and I settled on the Mark IIA depicted in Profile Publication, No. 41. Several variants of the Spitfire shared a basic airframe; it is simple to convert the Mark IIA to a Mark I, III, or V, and substitution of four 20mm cannons for the inboard .303 caliber machine guns converts the model to a Mark IIB.
Before beginning construction, study every available publication on the Spitfire to become familiar with details of the prototype. I found the following references to be particularly helpful: Bruce Robertson's Spitfire: The Story of a Famous Fighter, and Aircraft Camouflage and Markings, 1907-1954 both available from Harleyford Publications; Profile Publications, Nos. 41 and 166; Aero Publisher's Supermarine Spitfire; and Willis Nye's excellent drawings of the Spitfire. These publications contain many drawings and photos invaluable for detailing the model and preparing the proof of scale presentation which must accompany it in competition.
Construction may be greatly simplified with installation of conventional non-retractable gear. However, the satisfaction of seeing the wheels disappear into the wings shortly after takeoff makes the extra effort worthwhile. If you use the Centrak installation, contact Bill Johnson, 2504 Charwood St., Charles, Mo. 63301. Bill is familiar with the model and can supply the retract unit and complete instructions for installation and operation.
At Nats, Malvin won scoring 517 points. He also won Sterling Award for highest static points.
The landing gear is the most complicated component and is a good place to begin. The gear struts are turned from aluminum stock and a 7/32" diameter bore drilled and reamed for the oleos. Drill holes for the oleo retaining pin and the gear support rod, making sure the centerline of each hole is at the proper angle (see plans). This is necessary for correct tracking of the wheels and for maintaining correct gear geometry during retraction.
The oleos are machined from mild steel (I used 5/16" steel bolts). and the axles are 1/8" music wire threaded on both ends and silver soldered into tapped holes in the oleos. Exercise caution when drilling the holes in the oleos to insure correct alignment of each component. File the top of each strut to the shape shown, and assemble the struts and gear support rods, keying in place as illustrated in the plans. Fabricate the spacers, bushings, and mounts from brass tubing and sheet and the gear actuating arms from mild steel; assemble, making certain that the gear mounts rotate freely on the support rods and that the actuating arms are silver soldered in place at the correct angle. Selection of springs for the oleos depends on the final weight of the model and the amount of shock absorbing action desired. The oleos can be removed easily, so experimentation with various springs presents no problem.
One further note on the landing gear: If the Banner wheels shown on the plans are used, the aluminum hubs must be faced off on each side to give a thinner contour and allow the gear to retract fully into the wheel wells.
The wing contains almost all the gear, flap, and other control operating mechanisms and is the next component to build. Cut ribs R-2, R-10, and R-15 to shape and drill 1/8" holes in each one at the location shown on the plans. Stack the correct number of 1/8" balsa rib blanks in sequence with the pattern ribs, using 1/8" dowels to maintain alignment. Shape the stack of ribs in the usual manner, with one exception: The stack should show a curve, top and bottom, from the root to the tip rib. This is because the upper and lower wing surfaces are curved as viewed from the front.
Join the balsa wing spars and plywood doubler, and glue the ribs in place on the spar. Use two 20" lengths of 1/8" doweling in the holes previously drilled in each rib to maintain rib alignment until the glue dries. When dry, notch the ribs and install stringers for the flap wells and aileron cutouts.
The bottom surface of the outer wing panels should be sheeted next. Leave the bottom center section open until the wing is in place on the fuselage and all control linkages are hooked up and operating properly. The flap and aileron wells should not be cut out until the tops of the outer wing panels have been covered and the wing sanded to shape.
Cut the openings for the landing gear wells in the bottom of each wing and remove sections of ribs as required. Then line the wells with 1/16" balsa. To install the landing gear, it is necessary to cut a small hole in the wing bottom sheeting between the leading edge and front spar. Before final gluing of the plywood landing gear mounts, check gear alignment carefully both in the extended and retracted position.
Mount the Centrak unit with the Roberts Flight Control, control line leadouts, and control linkages attached. Bend and install the 3/32" music wire gear actuating arms. Be certain that e rods are the correct length to actuate both gear simultaneously-they m s: both be full up and full down at same time. Install the Centrak spri leaving the end which attaches to control unit free. This will allow ' r movement of the landing gear to check for proper fit in the wheel wells as construction progresses.
Now is the time to install linkage for moveable ailerons, navigation lights and wiring, flaps, etc., if you wish. The wing tip lights on the original were left hanging from the end of the wing until the tips and top covering were in place and the wing shaped. They were then epoxied in place, covering the bulb completely with epoxy. When dry, the epoxy was filed and sanded to form the lens and housing, and the entire area was painted the color of the lens. (Red on the left wing and green on the right wing. Mask the lens area, and paint the surrounding area silver. The silver dope is covered by the finish coat later and allows light to shine through the lens but not the surrounding area.
The fuselage is constructed of balsa blocks glued to a built up crutch. The various blocks are tack glued in place and the entire fuselage is carved a sanded to shape, using cross section templates. After shaping the fuselage, remove the blocks and hollow as much as possible without sacrificing strength, particularly in the aft sections of the fuselage. Shape and glue 1/16" formers inside the blocks in the positions shown on the plans. This provides stiffness without adding excessive weight.
Epoxy the fuselage crutch to the wing, lining the wing up carefully to insure correct incidence and planform alignment.
The horizontal and vertical stabilizers can be built up, or made by laminating two 1/8" balsa sheets with a hollow 1/4" balsa core. I tried both methods, and the weight difference using the latter method is negligible if you choose your wood carefully (Sig contest balsa was used on the original). The elevators and rudder are solid contest balsa, hinged as shown on the plans. This type of hinge is slightly difficult to construct, but it closely approximates the hinges used on full scale aircraft.
Glue the empennage in place, complete all linkage hookups, and install all lower fuselage blocks and wing center section sheeting. Note that the bottom center wing covering is flat at the front and blends to an inverted gull section at the flaps.
Most of the cockpit details on the original were finished prior to installation of the upper fuselage blocks. When the cockpit area is finished to your satisfaction, glue these blocks in place, add the wing fillets, and the model is ready for finishing. I used Sig polyester resin and fiberglass cloth on the original. I have tried many finishing methods, and found that the use. of fiberglass results in an extremely tough model, requires less time than dope and silk, and makes detailing (such as scribing panel outlines) much easier. The finished model, ready to fly, weighed in at six lb. 12 oz. which compares favorably with other models of this type. The use of fiberglass doesn't present a weight problem if it is applied sensibly.
To finish the model using fiberglass, give the airplane a final sanding, making certain that all contours and shapes are correct. Cut a piece of glass cloth slightly larger than the area to be covered, lay it in place, and coat liberally with polyester resin. The cloth to cover the adjoining section should overlap with that already applied. Sand the resin in the overlap area to insure good adhesion.
After completing the first coat, sand the entire coating with coarse paper (80 grit aluminum oxide paper works well) to remove gloss and rough edges. Use a sanding block where possible to maintain the basic contours of the model. Apply a coat of resin only, and wet sand with 220 and then 320 wet or dry paper. The model is now ready for a coat or two of clear dope followed by color. I used Pactra military flats with excellent result.
One final note on finishing. Component parts such as ailerons, flaps, elevators, rudder, etc., should be as nearly finished as possible before installation. I try to have them ready for the final color coat before attaching them to the model. This requires the builder to apply the finishing steps outlined above to certain parts of the model such as aileron wells, flap wells, and horizontal and vertical stabilizer trailing edges before finishing the adjacent area. Care must be exercised when fiberglassing and painting to prevent spoiling an already finished area.
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Posted January 21, 2012