Half Pint (oz196)

About this Plan

Half Pint. Free flight sport CO2 cabin model from 1947 Air Trails.

Quote: "At last, a gas model that can literally be carried around in a hat box. Furthermore, it's really the first gas model in the true meaning of the word, as carbon dioxide, the engine fuel is a gas and not a liquid as is used in the conventional type of gas model engine.

The peanut-size Herkimer CO2 engine, which we used for the first time on this model, is not a two-cycle internal combustion engine, nor can it be called a diesel or compression ignition type. Engineers would term it an 'expansion-type reciprocating engine' as it is the energy of the expanding carbon dioxide gas that provides the power for turning over the crankshaft.

Don't be fooled by the small size of this engine. While the overall height is only 1-3/4 in and the displacement is but .0178 cubic inches compared to .099 cubic inches - the displacement of the current smallest Class A engines - the little CO2'er really gives out with much power. Strobotac tests have clocked it at over 7,000 rpm. using a 7 x 3 prop. It has power plus, and will successfully fly models up to 40 in wingspans with wing areas of 140 square inches.

For the experimental-minded modeler, the CO2 engine offers all kinds of possibilities. Because of its consistent performance (each cartridge contains the same charge of gas) many interesting tests can he conducted. By using the same prop for all experiments fuselages, etc.

The small size of this engine lends itself beautifully to completely enclosed cowlings as you don't have to allow for cooling or air intake openings. For radically designed models, the ones you always sketch on paper but never dare build, the CO2 engine is the answer. Flying wings, pushers, canards, or what have you, can be fully exploited in a small economical size before time and supplies are wasted on large 'full-scale' models. This procedure can even be followed by builders of large six-foot Class C models; a half size CO2 powered model can be made of a new design and fully developed in small size before building the big brother. This method of testing is done on real aircraft and now can be done with CO2 powered models to eliminate design and structural defects before going full-size.

It was in line with the above thinking of testing a new proposed design in a smaller size before building the full-scale ship that Half Pint (the full-size model is called Full Pint - that's a pun, chum) was built. We wanted to test our latest Class B brainstorm that had a wingspan of 56 in, so in laying out Half Pint for the CO2 engine, we made the wingspan exactly 28 in and scaled our full-size plans to one-half the original size. Buddy, we found that this new method of testing a 'model of the model' really works. Half Pint, with a few minor adjustments, amazed us with its flying ability and will amaze you too. You will be more amazed at how easily and quickly you can build a model of this size. It is no more complicated than a simple, rubber-powered model.

The plans shown here are exactly half size and can easily be duplicated full size by simply multiplying any dimension by two. A scale is shown on the drawing and all curved sections are 'gridded' for your convenience.

The fuselage is built around a basic square framework of 1/8 in square stringers and is completed by adding the turtle-deck structure and nose faring. Note that the under section of the fuselage, where the cartridge holder is located, is sheeted with 1/8 soft balsa and a hole is cut in this section to house the holder. Finish off the fuselage by adding the firewall which is built up from two 1/32 plywood faces and 1/8 balsa core. Before adding the firewall to the fuselage structure, locate the mounting holes and attach the motor using #3 round head bolts. Now carve the cowl from a solid block of soft balsa and hollow the inside to house the motor. Dress snaps can be used to make the cowling detachable. Locate the cartridge holder within the fuselage before covering and try to avoid any sharp bends in the copper tubing that might cause an unsteady flow of gas while the engine is in operation.

The landing gear is bent from 1/16 in piano wire and cemented securely to a 1/32 plywood sheet backed up by a 1/8 sheet gusset. All landing gear dimensions can be obtained from the drawing by using the enlarging scale.

The tail surfaces are cut from 1/8 cut balsa and follow standard gas model construction. In assembly, the stabilizer must be cemented to the fuselage first and then the rudder placed in position. Cement all joints of both the rudder and stabilizer securely to prevent warpage.

The wing was built by what we call the 'quickie' process. Instead of plotting out a lot of ribs as is usually required in making a tapered wing, we used a method that was introduced to outdoor modelers by indoor builders: A wing rib template is cut from thin sheet aluminum or tin the width of the maximum wing chord. Using this template as a guide, a series of top ribs are sliced from sheet balsa. On a model of this size, the top ribs were cut from 1/16 sheet balsa by 3/32 deep. Lay these ribs aside and now form the wing spar. Place strips of 1/32 x 3/32 balsa on your wing drawing at each wing location and pin in position. This forms the bottom part of the wing ribs. Cement the wing spar in place. Add leading and trailing edges, then the tips..."

Note the plan is complete, the design uses a single rib template, no so further rib drawings are shown (or needed).

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