DH Comet 88 (oz15234)

About this Plan

DH Comet 88. Control line scale model twin racer. Nationals winner. Wingspan 60 in.

Plan drawing shows detailed retract (and flaps, brakes, throttle) installation.

Direct submission to Outerzone.

Update 16/4/2024: Added article, thanks to Pit.

Quote: "MANY CONSTRUCTION articles for scale models warn the prospective builder that the model is for 'experts' only. Your author does not believe in this theory. In my observations, many relatively inexperienced modelers or even beginners have more natural manual art skill than some modelers of many years experience. If you want to build this model and think you can, go ahead and build it. However, be sure you have the desire to build it. Most scale projects are time consuming, demanding, and reaniire months of work, Without a burning desire to create the model, the builder will never finish the project.

The deHavilland Cornet 88 was a unique airplane in its time. It was designed specifically as a long-range racing aircraft, intended solely for the McRobertsen air race from England to Australia in 1934. Only three aircraft were built. Of these aircraft, the red-and-white racer sponsored by Grosvenor House, a London hotel, was the winner.

The aircraft later experienced a succession of owners who modified the craft in various ways. The aircraft is now on exhibit in the Shuttleworth Museum in England. Comparison of the museum aircraft with photos taken of the craft when first built and flown indicate that major changes were made by subsequent owners and in the last renovation.

These changes have deceived many draftsmen and model builders of the Comet 88, who evidently based their products on the Shuttleworth craft. As a result these efforts do not depict the aircraft as it existed for the McRobertson race.

The author researched the aircraft for three years before enough data was gathered to make a scale project possible, and one having sufficient fidelity to scale. Preparation of a three-view plan was also necessary in order to avoid known errors in available scale plans. The scale drawing was authenticated by the AMA Technical Director as required by the AMA rules.

General Features: The model features retracting gear, flaps, throttle and brakes. Control of these devices, including elevator control, is achieved with only three flying lines, as detailed on the plans. Art optional fixed gear is also shown on the plans.

The model is very fast on twin .35's, having been clocked at 53 mph. The construction, therefore, is rugged so don't be tempted to cut corners to save weight. The author's model weighed 7-1/4 lb complete. The rugged construction is needed to handle twin engines and hard landings, but will also ensure many contest seasons without structural failure or stress cracks, particularly in the wing fillet area, Engines smaller than a .35 are not recommended since a model of this size and weight will not stay airborne on a smaller engine should one engine fail in flight, a common occurrence on twins.

Detailed step-by-step instructions will not be described. Rather, the key elements in fabricating and assembly as well as special parts will be described in order to avoid major errors. A thorough study of the plans and text, however, is a 'must do' chore, after which construction should be no problem.

The construction sequence is not too important, except where noted. The use of cellulose-acetate type model airplane glues is to be avoided in planking and all exterior joints or seams. Glues of this type continue to dry and shrink over a very long period, causing telltale lines in the finish. An aliphatic resin glue is suggested. The glue used must be sandable so therefore do not use white glue.

Money can be saved on planking if the planking strips are cut from sheets. However, this is possible only if the builder has access to a small table saw, such as the Unimat, or other suitable devices.

Use medium-weight balsa for all structure members and use soft, light-weight balsa for planking. Use light (contest grade) balsa for the tail surfaces. The plywood cores in the tail surfaces and the plywood inlay in the wing trailing edge permit sanding of all trailing edges to a sharp edge without the edge crumbling that would occur with a balsa-only trailing edge. The sharp edge is more to scale than thick edges of balsa,

Wing Construction: This should be preceded by fabrication of the landing gear cross shaft and retraction and counterbalance arm, the motor mounts, landing gear bearers and Part A, the main plywood support and connective member (if a fixed gear arrangement is chosen, omit the cross-shaft and its associated parts.) The motor mount, bearing block, and landing gear bearers should be jig-drilled for the cross-shaft bearing sleeve holes and the landing gear strut shaft to ensure alignment and freedom from binding. The cross-shaft and all parts of the retracting gear must operate freely.

Slide the motor bearers and bearing block on the cross-shaft and then silver solder in place the end and center retraction arms and spring counterbalance arms. A jig is recommended during the soldering operation to achieve proper positioning of the arms.

Jig assemble all of the aforementioned members directly on the plans, double-checking all alignments, and ascertaining freedom of cross-shaft rotation before gluee g. Use epoxy glue and 1/2 in no 4 flat-head screws for all joints. Do not add the wheel and strut assemblies until after all sanding is complete.

The wing is constructed in one piece, upside down, utilizing jig ribs in order to create the proper dihedral, wing rib incidence. and to elevate the wing above the work surface for clearance of the center retraction arm.

Start by cutting out all ribs, jig ribs, wing tips, spars. dihedral gussets, and leading and trailing edges. The eight jig ribs are sufficient support, but the trailing edge of the regular ribs will have to be bench-supported to withstand the planking operation. Use a short length of 1/4 in sq balsa for vertical supports, spot glued to the rib..."

Supplementary file notes

Article.

Corrections?

Did we get something wrong with these details about this plan (especially the datafile)? That happens sometimes. You can help us fix it.
Add a correction