Cal Smith's Giant Radio Controlled World War One Flyer Sopwith Pup Article & Plans
December 1962 American Modeler

December 1962 American 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.

'Giant scale' is a relative term - relative to when it is used, that is. In the 1960s, a giant scale radio controlled model was like this Sopwith Pup, by Cal Smith, with a wingspan of 53 inches. In the 2010s, giant scale usually implies at least 1/4 the size of the full-size craft, and more often means at least 1/3 size. A mere .19 size engine was used to haul around its 5½ pounds with 1,000 square inches of wing area, wing struts, flying wires, and a fat cowl producing copious amounts of drag. A single-channel, rudder-only radio control system was used. In a day when radio systems are so reliable that nearly all crashes and mishaps are attributable to pilot error, it is hard to imagine a time when so much manual labor was put into building a model and then it was launched skyward with electronics that often used vacuum tubes and a lead-acid battery.

Cal Smith's Giant Radio Controlled World War One Flyer Sopwith Pup

... for which we've been waiting five years!

PUP SPECIFICATIONS; Span, 26-ft. 6-in; Length, 19-ft, 5"in; Height, 9-ft, 5-in; Chord, 5 ft, 1 1/2-in; Gap, 4-ft, 5-in; Stagger, 1-ft, 6-in; Dihedral, 3°; Wing Area, 254- sq-ft; Loaded Weight, (80 hp), 1225-lbs.

By 1915 the war in the air over the Western Front was beginning to develop the terrible things which were to come. No longer did the airmen on both sides merely wave to or take pistol pot-shots as they passed each other on their observation flights. Thanks to Anthony Fokker's successful development of the fixed forward-firing synchronized machine gun, the Germans were able to gain mastery of the skies over the battlefronts. The. Fokker monoplanes were shooting down Allied aircraft with alarming regularity.

To offset this German advantage, the French, late in 1915, equipped their Nieuport 11 Scouts with guns mounted above the top wing's center section and firing over the prop arc. Thus they were able to meet the German Fokkers on somewhat more equal terms.

During the spring of 1916, a new type airplane, the Sopwith Pup went into action on the English Sector of the Western Front. It quickly proved to be equal to or better than the Fokker monoplanes and Albatros scouts. The Pup was the first Allied aircraft designed specifically to carry a fixed synchronized machine gun. Its design was simple and sound, and it was considered safe and easy to fly. The Pup was fully aerobatic due to its excellent balance and very low wing loading of 5-lbs/sq-ft (glider class). It had a good rate of climb, 650 ft/min, and could maneuver well at altitude.

First Pups powered with the 80-hp. LeRhone rotary engine had a top speed of 106-mph. Landing speed was 40-mph or less, giving it good small-field performance. Later models were fitted with the 100-hp Gnome Monosoupape rotary, which upped performance a bit. Overall the Pup bore a strong resemblance to the earlier Sopwith 1 1/2 Strutter and Tabloid Scout and seemed to have inherited the good features of both of these excellent aircraft.

Pups saw service with R.N.A.S (Royal Naval Air Service) No.3, 4, 8, 9 and 13 Squadrons and R.F.C. (Royal Flying Corps) Squadrons 46, 54 and 66 along the Western Front accounting for a goodly share of enemy aircraft from the spring of 1916 until the end of 1917. By then the little fighter, outclassed by heavier, more powerful, newer German aircraft, was assigned to less vulnerable duties. Since the Pup was originally ordered for R.N.A.S. service it pioneered many experiments in air-sea flying. It became the first type to fly from and land on a ship at sea. Waterborne flying with landplanes was in its infancy in 1916 and 1917 and as a result some unusual operations were run off.

Pups and Camels were put onto flattop barges and towed toward the action at sea. Take-off from the barge was the start of a one-way trip, since the barge was too small to land on. After the mission was flown, the airplane ditched near a friendly ship. Inflatable air bags fitted to the fuselage were blown up just before ditching. If the plane floated - and often they did not - the ship hoisted the plane out of the water. When dried out it was flown again. Pilots had to be good swimmers, too.

In addition ·to flying at the Western Front and in the hair-raising naval program, Pups were used successfully by Home Defense Squadron No. 61 against the Gotha bombers and Zeppelins that raided England. Pup production continued until the war's end and the little ship spent its final active service as a well-liked advanced trainer. Total production reached about 1,300.

But the story of the valiant Pup did not end with WW-I's end. In 1919 Sopwith produced a modified two-place version for the civilian market. This airplane was called the Dove and eighteen were built. One of these somehow survived the rigors of the years, including another World War (2) in England. Just after V J Day this plane was completely restored and converted into a replica of the original 1916 Pup. Today, a part of the famous Shuttleworth Collection of vintage aircraft, it is in full flying condition.

In the U.S.A. an accurate reproduction Pup has been scratch-built and flown by Californian Joe Pfiefer. Several other Pups are under construction by experimental aircraft home-builders.

The Pup Model: Simple construction and its many straight lines make the design most appealing for a model builder. She has enough scale dihedral for good inherent stability. Both wings are equal chord, thus we need only a single basic wing rib pattern. The model is scaled at 2-in to the foot. Every effort was made to simulate the construction of the full size airplane ... you will find fabric cover and planked surfaces in their proper places.

We do not claim the model to be a 100% Smithsonian-type non-flying scale version since some departures were made as noted for simpler building and better flying. For those interested here are the changes; Wing rib spacing is uniform which differs slightly from scale; however, there is the correct number of ribs. Leading edge is planked rather than having a false rib between each full length rib. Wing spars are in scale position; wing ribs, which scale thickness, are flat-bottomed rather than undercambered. Certain rigging omitted includes the flying and landing wires between wing struts and fuselage. Dihedral is increased to 40 - but the scale 30 should be adequate. Horizontal and vertical tail areas are increased and stab has thick symmetrical airfoil rather than thinner scale section.

Span is 53 inches. Length is 39 3/4 inches. Wing area is 999-sq-in, stab area is 200-sq-in (20% of wing area), fin area is 50-sq-in (5%). While weight may appear high at 5-lbs, 8-oz, we still end up with a relatively light wing loading. Nearly one pound is in nose ballast, a necessity for a model with such a short nose moment arm. This is the one unfortunate feature of most WW-I scale planes. Their snort noses pose a knotty design problem - how to get proper longitudinal trim? Answer: via ballast or a lifting tail surface. We prefer ballast to gain a normal C.G. position, since the lifting tail tends to make a model tuck-under in a high speed dive.

Full size drawings for Cal's Pup are part of Group Plan #1262 available from Hobby Helpers.

Our Pup is not a roar-and-zoom crowd-scattering type. Since the lower wings plug-in and are rubber band retained, excessive speed might set them adrift ... we haven't attempted to find out. The Pup is a fine pattern maneuver model - with throttle control circuits and bumps would be a delight. The biplane makes R.O.G. take-offs as though on rails and in most realistic fashion. The tail slowly comes up to near level attitude before the model breaks ground. Those big wheels roll over rough ground easily. The landing gear has rubber band shock absorbers at the axle similar to the prototype. Entire gear which can pivot backward at the fuselage about rear leg crosspiece is held at front with bands passing upward into fuselage.

Our model operated with rudder-only control, but there is ample space in the fuselage for more R/C equipment. With more controls and a throttled .29 size engine, performance would be very lively!

A .19 engine as illustrated is adequate for rudder-only control. Due to that short nose things do get a bit crowded up front ... the cowling is filled with engine, fuel tanks and ballast. The cross-feed fuel pick-up from two tanks works well. A single small tank can be used for short test flights.

The Pup flies fine. About the only problem to concern yourself with is a tail-heavy tendency so keep that tail structure light!

An attempt was made to fly the Pup free-flight when it was first built. We had fitted wagon wheels because of their scale-like appearance, With a 1/4"-dia steel axle and those steel wheels nearly a pound hung below the airframe. As a turn developed in flight, centrifugal force on this low slung weight seemed to increase turn and every flight ended up in steep bank into the ground. The Pup successfully resisted a half dozen nifty cartwheels with only minor damage. When the lightweight wheels shown were fitted this turn tendency dropped off considerable. Now with only rudder control, turns are tight but stable and recovery to straight flight is good. A quick blip of opposite rudder is helpful to turn recovery. Numerous flights have unveiled no bad trim characteristics.

Building The Pup: Construction starts with the wings - since there are so many of them! One-piece upper wing is built in three sections: two outer panels and a center-section which are joined to complete assembly. Plans show only one right and one left panel because these are used to make both upper wings and lower wings. Note that lower wings, though of similar construction, are a few inches longer than upper wing outer panels.

Sopwith Pup Bill of Materials

Balsa, unless noted otherwise

Eleven pieces of 1/16" x 1/8" x 36" for wing rib, fuselage, cap strips; (six) 1/16" x 1/4" x 36" for fuselage cap strips; (ten) 1/8" x 1/4" x 36" for stringers, diagonals, tail spars; (one) 3/16" x 3/4" x 36" for T.E. stock; (fifteen) 1/4" x 1/4" x 36" for longerons, spars, tail L.E.; (four) 1/4" x 3/8" x 36" for wing spars; (four) 1/4" x 1/2" x 36" for L.E. fin spars; (four) 1/4" x 1" x 36" for T.E. stock; (four) 1/16" x 3" x 36" for wing, fuselage, planking; (six) 3/32" x 3" x 36" for wing, stab ribs, fairing; (three) 1/8" x 3" x 36" for wing, stab ribs, formers; (two) 1/4" x 3" x 36" for wing tips, formers, tail edges; (one) 1/2" x 3" x 36" for cowling.

Also, three pieces 1/16" x 6" x 12" plywood for doublers, ribs, joiners; (two) 1/8" x 6" x 12" plywood for firewall, bulkheads; (one) 1/4" x 1/4" x 24" hardwood for corner braces, wing hook mounts; (one) 1/4" x 1/2" x 24" hardwood for bulkhead braces.

Also, three pieces 1/32"-dia x 36" steel wire for strut bracing; (one) 3/64"-dia x 36" steel wire for strut bracing, hooks, rigging; (two) 1/16"-dia x 36" steel wire for hooks, interplane struts; (two) 3/32"-dia x 36" steel wire for cabane struts, wing platform; (two) 1/8"-dia x 36" steel wire for landing gear and axle.

Also, tinned iron or copper wire for strut binding and rigging. Scrap steel for axle plates. Eight J-bolts for cabane strut mounting. Three 4-40 blind nuts for engine mounting. Wedge fuel tanks. One pound lead ballast. Nylon control horn. Du-Bro Kwik-link control yoke. R/C batteries, receiver, escapement or servo, switch, plug, etc., as required. Cement, glue, clear dope, colored dope, nylon.

Let's tackle the lower wing first. Cut required number of balsa ribs and two plywood ribs for root faces. Cut notches in trailing edge stock. Pin down leading edge, bottom front spar, rear spar and trailing edge over plan. Cement ribs in then add top front spar and corner braces at trailing edge tip and root. Cut tip outline from 1/4" sheet, bevel and cement to tip rib. Add brace to tip plate at front spar and 1/16" sheet to leading edge. Also plank top of space between root and next rib outboard. Cement 1/16" x 1/8" cap strips to all other rib tops from front spar to trailing edge. Set diamond-shaped plywood gussets for strut ends in place on top surface . These are inlaid flush with surface. Add scrap 1/4" sheet to top of rear spar to help support plywood. Bend strut end hold-down wire hooks to shape, drill plywood and cement hooks in place over spars ... double cement these. Prepare wing mounting wire hooks by binding and cementing to 4 1/2" lengths of 1/4"-sq hardwood, Notch inboard ribs and cement these strips to front and rear spars. Add 1/8" x 1/2" stiffeners along root rib bottom.

Carefully drill plywood root face ribs for 1/4" dowel alignment pegs. Cement plywood rib to balsa root rib, then drill balsa and cement dowels in place ... they should project 1/4" from root face. Thread-wrap dowels to spars if desired and cement liberally. To complete wing, carve leading edge to shape and sand all surfaces smooth. Wing can be covered now or later as you wish. Apply two coats of clear dope to all balsa that will touch any covering. Sand smooth then cover with nylon.

Build upper wing outer panels over plan following same procedure as described for lower wings ... with these following exceptions: Omit inboard rib until outer panels are joined to center-section.

Sopwith Pup Fuselage Plans

Sopwith Pup Wing Plans