Crackerjack (oz4784)

About this Plan

Cracker Jack. Free flight scale rubber model.

Plan is sized at 26in wingspan, and thus can be used at half size for a peanut-sized model.

Direct submission to Outerzone.

Quote: "Here's another two-for-one Peanut or Rubber Scale airplane that will please the free flight modelers among us. The full-size Cracker Jack is a home-built - which just happens to scale down perfectly without any modifications.

Occasionally, comments are made about what it was that inspired the building of a particular model. It was interesting; It was different; It was obscure; etc. This one was built because the designer/builder of the real aircraft sent in a brochure and suggested that a Peanut scale be built. The brochure supplied by Pete Plumb has a three-view that is Peanut scale size, has all the detail and color information needed to make a good scale presentation.

This brochure is available from Wood Wing Specialty, Building H-2 Fantasy Haven Airport, PO Box 1258, Tehachapi, California 93561. The brochure costs $5.00, and if you send him five dollars, Pete will send you one.

This model was drawn up by making a normal and a reverse copy of the three-view, and pasting it up into the Peanut scale format for the magazine. Then, it was blown up to twice-size on a XEROX 2080 machine. The model structure was then drawn in on the blown-up as near to the scale structural arrangement as possible.

The model in the photographs is twice Peanut size, and is powered by Bill Brown's fabulous CO2 twin cylinder engine. As it was built essentially over an original three-view, it has no intentional deviations from exact scale. The color scheme matches that of the prototype. It is all white with red trim and a blue upper stripe and a blue Cracker lack sailor land his dog) on the vertical tail. Luckily, the Sailor on the foil package of a Cracker Jack is exactly the right sizre ffor a pattern for the double Peanut size model.

As I said before, there are no intentional deviations from exact scale, including the rather thick airfoil section used on the real airplane. There are two thread turbulator strips which were added after initial glide tests showed the model with its smooth leading edge sheeting on the scale airfoil wing was suffering from a low Reynolds number laminar separation. Its glide was less than two to one, before turbulation, and is about five to one afterwards. Hence the alternate airfoils shown on the plan for those who want to avoid added thread turbulators. Note that the real airplane does not have this problem because it is flying so much faster than the model and is larger too.

While the original model was built for the Brown twin, the plan will be published as a Peanut in Model Builder magazine. For this reason and because there may be some who even want to build the larger version for rubber power, an alternate nose and a rear peg installation is shown on the plan.

Construction of the model follows tried and true conventional procedures. Keep it light and it has a better chance of flying well.

Laminated wing tips and tail outlines are used. They look more realistic than sheet outlines, but sheet outlines will work OK if laminations seem difficult.

Obviously, the small model uses smaller dimensioned structural pieces than the large ones, so no are called out on the plan. lust match yoursticks to the size shown on the plan you select and the model will turn out OK. The cabane struts on the large model are made from 1/16 diameter birch dowel. On the smaller model, I would suggest using the thin bamboo dowel that is available from Peck-Polymers (see their ad).

The most critical area of a CO2 powered model is the engine installation, and the most critical part of the engine installation in my experience is the support of the CO2 filler valve. Make sure that the support blocks on each side of the filler are hard balsa and they reach clear down to the bottom fuselage planking. It takes considerable force to push the filler down over the valve, and this part of the installation must be strong enough to resist that force..."

Supplementary file notes

Planfile includes article.

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