Scale kit

CAP 21

The Scale Aerobatic Model with Character

Our CAP 21 is designed for large model aerobatics and is especially light, but in spite of this is very strong. It can be best described as being of simple construction. Nevertheless our CAP 21 is scale in every detail.

Quick to build

Due to this simplicity the model goes together in a surprisingly short time. The wing is of conventional construction. That is to say, spars, ribs and fully planked with 2 mm Balsa sheeting. The wing is built in one piece, a two piece wing of the same strength would increase the weight to an unacceptable level. The full-size CAP is an all wood airplane, our CAP also, with the fuselage being a simple Balsa box construction with a half round Turtle deck. The CAP is totally unsuited for Fibreglass with it’s flat fuselage sides.

Image: Ready for take off. My CAP 21 is waiting for the next flight.

Lightweight Epoxy/ Glassfibre Parts

The motor cowl, wing root fairings, the wheel spats and tailplane centre section fairing are made with very lightweight epoxy and glass cloth. As with the full size CAP all the control surfaces on this model are shrouded. The ailerons have spindle moulded leading edges with matching wing trailing edges. The leading edges of the rudder and the elevators are vacuum formed. The elevator servo is built into the tailplane, the tailplane is removable. The rudder can be taken off by withdrawing the piano wire hinge pin, all this to ease transport.

Carefully selected Balsa throughout

Apart from these aforementioned points the kit is made to our exacting standards. There are shaped jig strips to ensure accurate assembly of the wings and tailplane. All Balsa used in the kit is selected first at the log stage, and again when fully machined and sanded.

Image: Karl Paul´s latest CAP 21. Using the shape of Catherine Maunoury’s CAP 21 colour scheme in Charly’s favourite colour red.

Perfect Harmony between Engine Unit and Model

Without doubt the best choice is the Titan ZG 62. Without a tuned pipe this engine has more than enough power for any form of aerobatics and has the added advantage of a saving in weight. The 62 can turn larger propellers without losing power, a prerequisite for scale maneuvers where the model flies slowly and with constant airspeed. The Titan ZG 62SL fitted onto the CAP 21 Hydro Mount System #6706 designed specially for our CAP 21 combined with the Stainless steel silencer #6660 makes the CAP 21 into a super show model but without the usual noise and maintenance. The engine and silencer fits inside the scale motor cowl.

Image: The perfect power plant for the CAP 21: Titan ZG 62SL with 21 x 12″ CF-three blade propeller, HMS-CAP 21 #6706, stainless steel silencer #6660.
The intake bend is fabricated from the parts #6577, 6578 and #6579 and silver soldered together and of course Charly has painted this bend red. The mounting of the Easy-Start socket is clearly shown here, as well as the perfect layout of the Hydro-Mount shock absorbers.

The Flight Characteristics are unbelievable

The scale fuselage without a slimmed down nose allows knife edge looping big and small. The slimmed down nose is a widely held fable due to the mistaken idea that a slimmed down cowl offers less resistance. But the engine parts such as the cylinders being exposed to the airstream cause considerably more resistance and therefore causing the need for more engine power which leads to more noise.
The wing section used is from Eppler which is very similar to the one used on the full-size aircraft. This Eppler section, as apposed to the more usual F3A sections, gives approximately 20 per cent more lift. At the same time it shows an almost constant airfoil drag over a wide speed range. The result is, the model when diving, does not accelerate unduly, also does not cause the speed to drop off markedly in tight turns.

Image: This view showing the stainless steel silencer. All photos of this Red CAP 21 by Charly Paul.

The very uncritical stalling characteristics of this Eppler section combined with the wing planform (high aspect ratio and tapered) is an ideal combination for safe flying characteristics and precise, predictable flick maneuvers.
To summarize, the CAP 21 is a model that any average pilot can fly the modern Aerobatic schedule, with any amount of tight turns and landings, and without a racing pulse.

CAP 21 30% scale (1:3.4)

Airplane Specifications

Wingspan: 2.38 m
Weight: 7.5 – 8.5 kg
Length: 1.90 m
Wing loading: 90-102 g/dm2
Wing area: 0.83 m2
Engine: 50 – 62 cc

Image: My CAP 21 with the town Göttingen in the background, knife edge flight with quarter throttle. Photo: Rüdiger Dorow.

Three View Drawing

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