Tadpole (oz676)


Tadpole (oz676) by Howard McEntee 1948 - plan thumbnail

About this Plan

Tadpole. Free flight sport flying boat model. All-sheet design. For CO2 power with Campus A-100 engine.

Quote: "Try this miniature flying boat for real fun. Tadpole, by Howard G McEntee.

MODELERS who have built and flown model seaplanes insist that flying over water has all other types of modeling beat. After hours of experiment with our Tadpole we certainly agree. Land flying surely offers no such thrill as can be had from the sight of a model seaplane skimming over the water with foaming wake trailing behind, then climbing smoothly upward, motor humming quietly. And of course the climax is a smooth landing (preferably downwind, as the added speed causes the model to skip over the surface in the most realistic fashion) without turning upside down!

The little model was designed strictly for sport flying and realism. The only departure from present day seaplane practice was the use of sponsons instead of the more common wingtip floats. The latter are a liability in models; they are easily damaged, and moreover their action on the water is poor because they tend to dip in as the model taxis and cause 'water loops'. Sponsons on the other hand are very rugged and, more important, they aid rather than hinder the model's seagoing qualities.

It goes without saying that a model of this sort should be thoroughly waterproofed, in our case we went the limit in this direction. The model is built entirely of sheet balsa without any framework. This style of construction, long our favorite for such little planes, is fast to make and is puncture-proof. After the woodwork was finished and smoothed with the finest sandpaper, the entire model was covered with the lightest weight model tissue obtainable. Everyone to whom we show the model asks: Well, why not cut some of the wood away and save weight? Save weight it certainly might, but we would then lose the ruggedness and freedom from punctures, splits and tears which we sought.

The object of the tissue covering, of course, is to make it possible to waterproof the model with only a few coats of thinned dope. Balsa wood soaks up dope like a sponge, especially in the very soft grades required for a model like this. Using the paper, however, only three coats of dope will do a fair job of waterproofing, and all dope we used was thinned 50- 50 so it would brush on smoothly.

The finished model weighs exactly 1.5 oz, and at a rough estimate probably .3 oz of this is waterproofing - quite a weight penalty but a necessary one if you wish to fly your plane off water for several hours as we have done on occasion, suffering the inevitable dunkings, yet have a model which can stand such treatment without soaking up water and becoming unflyable.

Wood used throughout the model should be of the lightest grade you can obtain, but the wood must of course be selected with care, as pithy or punky wood, while light, has practically no strength. Even though this light material is used the paper covering adds a great deal to the strength: if the paper is not used the wood must be either thicker or of a stronger and heavier grade.

Since this could hardly be called a beginner's model, we will not go into detailed building instructions but will use the space available to describe construction tricks used, and of course to cover operation and flying details.

Before starting we must caution those who have little experience with thin sheet balsa to use slowdrying model cement, and one that dries with no tendency to bubble. Fast drying cement doesn't give you time to align the various parts properly; also, it tends to warp the thin wood.

The fuselage is started by cutting the two sides from sheet about 1/32 thick. Since most standard wood in this thickness is only 3 in wide, glue an extra 1/2 in wide strip (a butt-joint is satisfactory) where the cabin comes. It is advisable not to cut the windows yet, but the slit X-Y can be made before assembly. Glue formers 1 and 2 to the sides and block the assembly up so it will be true when dry. Next add formers 3, 4 and 5 and join the sternmost ends of the fuselage together with the rudder between. Following this, cut and install the nose block, the hull step and the cabin rear edge.

The sponsons are built up on a solid center spar 1/16 x 3/8 and a solid trailing edge trimmed down from 1/8 stock, while 1/4 square forms the nose. Build the rough framework up, including the tips, then sand down to the finished shape and cover; use 1/16 stock on bottom and 1/32 on top, and when dry sand all edges smooth.

Our original plans called for addition of wheels to the model. The idea was to bind partially flattened lengths of aluminum tubing to the outer tips of the main sponson beam. Wheels on short music wire struts could then be added if we wished, and the water rudder would serve as a tailskid. In our rush to finish the model, however, we forgot to install the aluminum sockets so the wheels have never been tried. Subsequent flying experience indicates that the model would fly and ROG nicely with wheels since it has ample power to take off from grass, sand, or even the living room rug!

After completing the sponsons, cover the hull top and bottom. Forward of the step, we used 1/16 stock on the bottom, while to the rear, 1/32 wood was employed on both top and bottom. Note that the fuselage top behind the cabin is slightly rounded to help it shed water faster.

The flare on the fuselage bottom from nose back to step is made by allowing the bottom sheeting to extend 5/16 out beyond the fuselage sides. After trimming to shape, cement pieces of 1/32 sheet from the outer edges of the extended bottom sheet, upward at an angle to the fuselage..."

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