About this Plan
Crackerjack. Control line stunt model.
Direct submission to Outerzone.
Quote: "Crackerjack. A 32 inch control line stunt model by Harry Hundleby and John Coasby, for 2.5 to 5 cc motors. Mostly redrawn. Aeromodeller October 1948. My scan, originally uploaded in 2012."
Update 11/09/2020: Added article, thanks to JohnL.
Quote: "HAVING learnt our control-line flying the hard way and having tried for some considerable time to develop a really successful stunter suitable for a popular size of British engine, we were more than gratified at the performance of Crackerjack. The prototype, powered with an ED Mark III performs the most difficult of stunt manoeuvres with an ease and reliability that make it a pleasure to handle. The model is extremely sensitive to control and less experienced flyers should watch out when the undercarriage releases We found 50 ft. the most satisfactory line length, although in calm weather this can be extended to 60 ft. with beneficial results.
Wing: Commence by building the wing, cutting all ribs from hard 1/16 sheet. Utilise a template of thin sheet zinc or aluminium for this job, it saves time and ensures accuracy. Sand and shape leading and trailing edges before pinning down and note that packing will be required in view of the symmetrical section. Cement ribs in position and also wing tips, lift from plan, and apply top and bottom sheeting as shown. Finish by sanding lightly and then cover with rag tissue and dope. Cut through the covering over the slot that takes the ply guide plate and cement plate into wing.
Fuselage: Commence by cutting bearers to shape and drill engine bearer holes and the hole for the control plate. Glue the bearers to the top and bottom fuselage sheeting with Durofix and when dry cement bulkhead F.1 and formers FAA, F.4, F.5 and tail-block in position. Do not insert formers F.2 and F.3 at this stage. Remember also to screw undercarriage tubes to F.1 before inserting. Fit control plate and also engine bolts together with their back plates. Check assembly at this stage for accuracy and leave to dry thoroughly.
Cut out fuselage sides slightly oversize and construct tail surfaces and fin whilst you are waiting. Fit all control wires to the control plate and then cement the port side of the fuselage in position. When dry slide wing into place remembering to thread the control leads through the wing guide plate. Now is the time to cement formers F.4 and F.3 in position and the wing should be accurately aligned at right angles to the fuselage. Any adjustment necessary can be made by lightly sanding these formers before glueing. Complete the tailplane and cement in place. With the wing and tail surfaces in position the starboard fuselage side can now be passed over the wing and cemented in place, remembering to thread the control lead through the side at the same time. Lightly cement the front nose block in place and thoroughly sand fuselage with block in position. When sanding is completed remove nose block, which can be finally positioned when the engine is installed.
Cover fuselage with rag tissue using thick dope or banana oil and finally apply finishing coat of clear dope. Cut tissue carefully away from fin and underskid positions and cement these two items in place, also the tailskid. Note that the tail surfaces are left uncovered and finish with clear dope. A final finishing coat of coloured dope may be applied although this was not done on the prototype in order to save weight. Construct the fuel tank and also the undercarriage remembering that the latter item should be a loose fit in the undercarriage tubes. The inside of the fuselage front should be given a coat of shellac as a proof against fuel residue. Bend the necessary clips at the end of the lead-in wires and carefully adjust the length of the elevator control wire before cutting and bending through control horn.
The prototype came out at 13 oz complete with motor and it is not advisable to exceed an all-up weight of 14 oz. The model should balance at a point half inch back from the front wire measured at the guide plate."
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