Dummy Lifter (oz2128)

About this Plan

Dummy Lifter. Free flight PAAload model, .049 Wasp motor shown.

Update 26/6/2022: Added article, thanks to RFJ.

Quote: "Simplified cabin design for Half-A PAA-Load or Pan_Am's new Clipper Cargo event. Dummy Lifter, by Bob Buragas.

In designing a model for the Half-A Payload Event, it should be kept in mind that the take-off distance must be short. This means the model should produce a good amount of lift at low speed. Due to the high power output of Half-A engines, it was found that a model. of Wakefield proportions would best suit the requirements. Flight test durations were over two minutes fully loaded—unloaded this model makes a fine free-flight competitor. The large cabin can be put to good use in carrying the necessary large loads for the new Clipper Cargo event, also.

Rather than employ the ultra-fabrication which many call simple, it was decided to be old-fashioned and have simple longeron, box construction. By using hard 1/8 balsa throughout the fuselage, adequate strength is supplied. Use of sheet fill-in at nose and tail adds much strength at the key points of impact.

Since the entire model is built around the occupant, this item should be made before fuselage sides are joined into a box. Choose pine wood for an occupant as it minimizes the amount of lead required to bring it up to weight. Weight is added by drilling a series of 1/4 in holes in bottom of the occupant and filling them with melted solder.

Use rubber-bands, or pins, to fasten temporarily the fuselage sides to dummy. Cross-braces and formers are added to complete the body structure. You will find that by doing this you will have a jig which holds fuselage square and assures a snug fit for dummy. Liberal cement gussets at this stage will eliminate a lot of future trouble.

The landing gear wire is mounted between a balsa sandwich consisting of two sheets of hard 1/8" and 1/16" sheet filler. If the wire you use is slightly smaller, you should sand filler sheet down to match wire thickness.

Medium hard, straight-grained sheet balsa is selected to form tail platform. Use two or three pieces of sheet to get proper width. The dethermalizer hinge is cemented. to upper rear of this platform. Make this hinge from a piece of tubing and a length of paper clip wire which is soft and easy to align. Strengthen the hinge mounting by covering it with cloth or silk.

While fuselage sections are drying it is wise to save time by marking and cutting all parts needed to build the flying surfaces. Ribs can be marked, using a ball point pen and balsa template. This method leaves dark, clean lines which are easy to follow during cutting process. After trimming, ribs should be sanded to their completed shape by stacking them into one pile and using a straight sanding block.

Forget about dihedral and build the wing frame flat. All spars are added in final stage. Only variation in the construction of stabilizer is use of a 1/4 in rib as indicated on plans. This serves as the sub-rudder mount. When wing structure is dry it is cut apart at the dihedral points. Mount center section of one wing fiat on a board and add the tip, following the indicated dihedral. When this is properly aligned, other wing panel is placed so that it is leading edge to leading edge with the first. Pin and glue this panel so that it aligns with the first. In this manner both wings are set at exactly the same dihedral. Both panels will be joined to complete the assembly, and then the spars will be added.

What happened to the half-ribs? These are added after the spars are dried into place. In making them fit do not exert pressure on spars as this will put irregular tension into wing and prOduce warps at a later stage. Tip blocks of soft 1/4 in sheet are glued onto outer ribs. These blocks need not be pre-shaped as they can be easily carved after mounting. The necessary balsa gussets and cloth reinforcements are now added.

There is little to say about the rudder construction. Cut rudder and sub-rudders out of 1/8 sheet and sand them into airfoil shape. One of the sub-rudders has a short length of 1/16 dowel built into it. This dowel acts as the pivot for the variable sub-rudder adjustment.

For a firewall it has been found best to use at least 3/32 plywood. Cut and mount this onto the front of fuselage. A little sanding will bring it to proper size after glue has set. By using two pieces of 1/16 sheet and a soft balsa block you can build up a neat, simple cowl for your engine. Tack-cement this unit to firewall and then shape it with a sanding block..."

Supplementary file notes

Article.

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