Junior planes

Foreword

^ Twenty'two planes are described in this book. All of 1 ^ 5 ^ them have been built and flown, and all of them have proved themselves to be good performers.

To build one of these models, it is necessary only to read the chapter telling about it, as the descriptions are complete for each one. However, some points are covered more fully in one article than in another; and if more infop mation is wanted on the carving of a propeller or the bend' ing of a shaft, a glance at the drawings for some of the other models will give the needed help.

Although regular airplane model supplies have been specified, there are substitutes that are much cheaper, and just as satisfactory. For instance, instead of the rather expensive papers ordinarily used, wrapping tissue, costing one'twentieth as much, may be purchased; and as to am' broid, or other glues, a home'made cement is equally good. Simply get scraps of old celluloid automobile side'curtain lights, obtainable at any wrecking yard for ten cents a pound, and dissolve a few pieces in a pint of acetone, cost'

ing thirty'five cents. Pour the acetone into a convenient bottle, add the celluloid, and let stand for a few hours, occasionally turning the bottle upside down to help in mix¬ ing. The same glue, when thinned, makes good wing dope.

In building these models, remember that air friction slows up a flight, and consequently reduces duration. If spars and struts are streamlined, cind sanded smooth; and if the paper is tightly stretched, the ciir will flow past with¬ out much eddying, giving the best possible flight.

Dedicated to my little boys, John and James, who all too soon will be old enough to build these planes.

Edwin M. Love

PART 1 GLIDERS Subject Page

1. The Midget Balsa Sailplane ....... 11

2. A ThreeToot Balsa Glider.16

3. A Convertible Glider.21

4. Building a SixToot Sailplane ..25

Part 2 Stick Monoplanes

1. The Rough and Ready Tractor.33

2. The Tumble Bug.38

3. A Hydroplane Tractor.43

4. The Flying Feather Tractor.. . 48

5. The Mayfly Indoor Tractor ....... 53

8. A Twin'Pusher Plane . ....... 70

CONTENTS—Continued PART 3

FUSELAGE MONOPLANES

1. A PushTull Scientific Model Monoplane . . . .78

2. The Teeny Weeny Monoplane.84

3. A Fuselage Low'Wing Monoplane.91

8. An Endurance Tube Monoplane.137

Part 4 Biplanes

1. Building the Biplane Cub

2. The N-Strut Biplane .

. 151 . 157

Part I Gliders

THE MIDGET BALSA SAILPLANE

Can a tiny, all'balsa glider fly well? Build this little sailpleine, and see for yourself. Trim lines it has, with its shapely fuselage and slender wing. It has a very high aspect ratio; that is to say, while the wing spread is 20", the chord of the wing is only and this, together with the fact that the supporting surface is cambered, makes a very efficient flier.

This little plane glides nicely indoors, but of course does better outside. The writer’s model, on a cool day with winds none too favorable, stayed up more than a minute when launched into the breeze from a hill side. On a hot, dry day with a proper wind, it might sail for two minutes.

But few materials are needed. Get a piece of tV" balsa veneer % by 12", for fuselage, stabilizer, and rudder; and for the wing, a piece of *4 by % by 20" balsa. A small ring paper clip, bits of nails, and ambroid cement complete the list.

Make a paper pattern of the fuselage. Notice that the under edge is gently curved most of the distance from the tail end, but rounds upward sharply at the nose. The upper edge is an almost flat curve from the nose to the cockpit, which is wide, situated IV 2 " from the nose.

A straight slope from the cockpit to the tail com' pletes the body of the machine.

To make the wing, carve out the underside with a gouge, and smooth with sandpaper on a round^edged block. Most of the curve, or camber, is near the front edge. When the under side is carved, shape the upper side, reducing the wing to a thickness of less than Wrap the sand' paper around a block of wood when smoothing the wing, as this will help to keep it straight. Cut the tips round, and then round the edges.

You may find, after going to all this trouble to give camber, that the wing has flattened out. If this happens, wet it on both sides with water, and lightly wind it with string, having the loops no more than V/' apart for full length. Draw the string tightly enough to bring back the curvature, and lay the piece aside to dry. Be sure, however, that it does not lie in a twist.

After drying, cut in from the edges toward the center at the middle, until the tips can be bent up 2" for the dihedral angle. Apply cement above and below the break.

THE MIDGET BALSA SAILPLANE 13

then block into position, and let the wing dry thoroughly.

The stabilizer is V 2 by 5". Carefully shave and sand it until it is no thicker than a thin visiting card. When using the sandpaper, lay the balsa on a flat block of wood, and there will be no trouble in thinning it evenly. T rim

Cut a Vi" sht in the tail end of the fuselage. It should follow a line drawn along the center of the body, and must be widened until the stabilizer can be slipped into it. Put ambroid on the edges, and above cind below the stabilizer across the center, before inserting the latter in the slit. Hold it at right angles to the fuselage until the glue has stiffened enough to keep it in place.

The tail, or rudder, is Vi by 1", and the same thickness as is the stabilizer. Ambroid it to the upper edge of the body, above the stabilizer.

Cement the wing to the body, having the leading edge 214" back from the nose, and 14" higher than the trailing edge, measuring from the center line. Fit A" square blocks against the body and beneath the wing, so as to strengthen the joint. After the glue has dried, streamline these blocks.

The glider is now ready for flying. Slip a small paper clip over the nose, and two 14" lengths of nails about ^ 2 " in diameter through the wood under the upper edge of the clip, where they are cemented.

Launch the plane by tossing it lightly forward and a little downward. If it repeatedly nosedives, take off some of the weight, but if it stalls when thrown fairly hard, add a little more. If it turns to the side when fair with the wind, give a little twist to the tail. It may be, too, that the wing is a little twisted, causing one side to drag. If so, breathe on that part, to moisten it, and twist it back.

Long flights must be made from a hill side, where the wind, not too strong, blows toward it. If the breeze is right, the little plane may rise quite high before beginning its final downward glide.

For short glides indoors, remove the bits of nails and try the ship on slow glides. Add a pin if necessary. When

THE MIDGET BALSA SAILPLANE pointed almost straight down and released from a height of seven feet, it should level off and skim away before touching the floor.

The little plane may be decorated by staining it with water colors or rubbing it with wax crayons; but be sure that it is not twisted when drying, or it will remain that way.

A THREE^FOOT BALSA GLIDER

It is said that a condor, high in the air, can come into sight as a tiny speck in the east, soar on outstretched wings overhead, and disappear in the west, without so much as flapping once to supply motive power for his flight.

Flying men nowadays are spending much time studying soaring, and motorless gliders have stayed aloft many hours. Such flights are possible because in many places the wind blows upward with a good deal of force. For instance, a breeze moving toward a hill is turned upward. When a glider is launched by towing it down the hill at the end of a shock cord, it rises like a kite, gaining considerable elevation after being released, for the pilot guides it skillfully in the rising air. Actually, he is not flying upward according to the air, but is gliding downward, at a slower rate, however, than the upward speed of the current. By circling, a great height may be reached, when he can steer toward some distant hill where another rising current will carry him aloft once more.

He may be fortunate enough to fly over a hot, bare stretch of fields and rocks, where the heated air rises almost

A THREE'FOOT BALSA GLIDER as strongly as at a hill. Then his chances for a long flight are very good indeed.

Some wonderful flights have been made by large, welh built model gliders. Durations of half an hour are not unknown. This chapter describes a simple balsa glider that will soar splendidly over a hillside in a fair bree2;e, or will make long, graceful glides above the level after a light toss from the hand.

For this model a piece of Vs by 3 by 36" balsa, and one Vs by 2 by 24" are needed; also two pieces V 2 by V 2 by 3", a piece of lead or solder that can be pounded into a flat strip tV by t® 6 by 2", and some ambroid cement.

Use the 3" balsa for the wing. Gauge it for width along the center, cut it 35 V 2 " long, and square a line across the upper side 13" from each end. Measure back 2" from the leading edge at the ends, connect these points with the width at the cross lines, with straight pencil lines, and trim the taper with a ra 2 ;or blade. Cut the corners of the ends, finishing by rounding them smoothly.

Sand the wing on both sides, then taper the thickness of the edges by sanding them down from the upper sides, making the leading edge fairly blunt, with a short taper, and a long taper behind.

Now place a wooden block under one cross mark and another 3 ^/ 2 " from the far wing tip. Press down on the other mark with the edge of a ruler, until the balsa touches the bench. Still holding the ruler there, push the blocks gradually toward the ruler until the balsa cracks beneath, but be careful not to break the tip entirely off. Crack the other tip in the same way. Then fill the ragged under' cracks with ambroid, block the wing with the tips 4^2^ above the center, and let the wing dry.

Make two quarter^streamlined blocks long, using the Vi square blocks. These resemble parts of a cigar quartered lengthwise, but with the thickest parts forward of the center.

When the wing is dry, square a line across the center, on the underside, and glue the blocks each side, with Vs" between.

The fuselage, of neatly streamlined shape, is 13^^" long and VA'" at the widest point.

The tail is Vs by 2". Notch one end to fit around the

SLrLead strip iVx|x2-

RZAK. ELEVATION A THREE " FOOT

BALSA GLIDER trailing end of the fuselage, as the drawing shows, and glue it there. Then shape it up with the razor blade.

The stabilizer remains. Use a piece of balsa Vs by 2 by 8 ". Trim it with the tips sloping back from the center Y&'- Round the comers to a radius of Vs'V and taper the thicU ness. Across the center cut a slit to fit over the top of the tail, where it is glued with the leading edge above the fuselage and Vs"" lower than the trailing edge.

Hammer and trim the lead to shape, bend it into a “U,” cind force it on the nose of the fuselage, where it is glued.

Put the wing astride the body, 3" back of the nose. The blocks should clasp tightly enough to hold it for trial flights.

Glide the plane by tossing it forward and a little down. Move the wing forward or backward, until a good glide is obtciined, and glue it in position.

For soaring, climb a hill on the windward side, cast the ship against the wind, and watch it go.

A CONVERTIBLE GLIDER

Gliders have a great point in their favor—they need no rubber for motors, and so are very inexpensive to fly. Boys who are fortunate enough to live on or near hills can have as much sport with gliders as with powered models.

The Convertible Glider is an eflicient little sail plane that is easy to build, and that can be made into a powered machine simply by adding a bearing, a propeller, and a few rubber bands.

These materials are needed: For spars and ribs, four pieces of tV by Vs by 20''; for the stick, one piece Vs by V4 by 10"; for the saddle, 1 piece Vs by V2 by 2"; for nose weight, 1" of Vs" wire solder; also rice paper 4 by 20", ambroid cement, mucilage, wing dope, and a rubber band of iV" square stock.

Divide two of the 20" spars into spaces for the placing of ribs, measuring 3%" from the ends for the first inner, and the same distance farther on for the next. Cut seven ribs 2" long, and glue these on top of the spars.

Bend the spars at the middle to make a dihedral 2" deep. Roll a pencil along the forward ends on the undersides of 21 the ribs, giving a shallow camber to the wing, and cover the upper side with paper, applying mucilage to the leading and trailing edges, and all ribs. Cover only half the wing at a time.

Sand the stabili2;er spars and ribs to iV' thickness.

Cut two spars 6" long, three ribs IV 4 ' long, and assemble them as the wing was put together. The ribs, however, are left flat.

Build the tail of by Vs" stock. For the base use a piece 2%" long; for the trailing spar, a 2" length, and for the other two pieces such lengths as will shape up the tail illustrated. The projecting front end of the tail base is cemented under the stabili 2 ,er, and the whole assembly is ready for mounting.

The body stick is merely the heavy balsa sanded smooth, with the tail glued beneath.

To carry the wing, a streamlined saddle is shaped, V" form above to fit the dihedral, and rounded below. Cut a slot lengthwise to fit over the stick.

Bend the solder into a “U’’ to fit the front end tightly. Cement it there. Also tap the front end lightly with a hammer to mushroom it a bit as an extra help to keep the weight from slipping off.

A CONVERTIBLE GLIDER

Loop the rubber band over the stick and wing, and adjust the saddle so that the leading wing spar rests on its front end, while the trailing spar slips past the saddle end and bears on the body stick.

The ship is now ready for a trial. It will ride about right with the wing IVi' from the front end of the stick, but a little shifting backward or forward will probably be needed to get a good glide.

Launch it with a light forward and slightly downward toss, against the wind. There is much sport in gliding it in the street or any open space, but to get a long flight it is necessary to launch it from a hillside when a soft breeze is blowing up the slope. The thrill of seeing it jockeying in the wind will repay any work expended in making it.

If you wish to add a propeller, carve it from a balsa block Vs by 1 by 7", using a sV' music wire shaft and tail hook, and if a winder is to be used, an S-hook of the same wire.

For a bearing use a re by Vs by IV/' aluminum strip, bent up suitably and cemented to the nose of the stick in place of the solder weight.

BUILDING A SIX'FOOT SAILPLANE

Build the sailplane described in this chapter, and you will have a ship that will stay aloft as long as anyone could wish. The original was designed by Martin Moad, a sixteen' year-old Los Angeles school boy, who has some 200 plane models to his credit. It has made flights of nine minutes— purposely limited to keep the model for measurement.

Use soft balsa for all wooden parts. Cut the wing spars, smooth them with sandpaper, and round the comers. Lay them in position on a bench for a center width of wing of with SVs" at the ends. Hold them with pins at the edges, being careful to make a uniform curve in the trailing edge. Lay out for ribs 5" apart on centers.

Take the rib lengths from the frame, and raise their cambers by rolling the undersides with a pencil. Scarf the ends for cementing to the tops of the spars.

Shape the bamboo wing tips over a candle flame, hold' ing the glossy sides out, and bending gradually. Glue them to the outer edges of the spar ends, flush with the top, and bind with thread, which is drawn across the wing to pre' vent spreading.

For the dihedral, break the undersides of the spars at the middle, so as to raise the wing tips SVz", where they are blocked until the cemented breaks can dry.

Cover the upper side of the wing with rice paper. Mucilage is good for this work, as it dries slowly, giving time for adjustments. It is necessary to paste the tissue to all the ribs.

For the fuselage cut the longerons, and shape the dia¬ mond bulkhead to pattern. Make the notches to fit the longerons, trim the sides, and cut out the center. Break the longerons 6 %"" from one end, as the wing spars were broken, and cement them into the bulkhead notches. Ce¬ ment the ends of the top and bottom longerons together, and miter the other strips to fit against them.

Put in the cross posts, butting them between the longe' rons to hold them straight. Pieces are also mitered between the longerons 3" from the nose, and two such struts, 2" fon ward of the bulkhead along the upper spar, incline backward at the lower ends. Cut away the section of the upper longe¬ ron between these braces and the bulkhead, and glue in the music-wire sides joining the bulkhead, thus trimming the cockpit.

To prevent the paper cover from sagging inward from air pressure, glue a horizontal semicircle of Vs” balsa to the bulkhead, 1" below the side longerons.

A by A" bamboo strip curved upward at the trail¬ ing end and glued to the underside of the fuselage nose acts as a landing skid. The tail skid is a large pin or other short wire stuck into the lower longeron 4" from the end. Make the wing cleat to be glued to the upper longeron to carry the wing.

The towing hook is tied and cemented in a groove in the underside of the bamboo, directly beneath the nose.

Cement and tie in the nose two pieces of solder or lead, one Vs by Vs by IVs”, the other, above it, IVs” long. Both are pushed forward as far as possible.

Cover the fuselage with rice paper.

The elevator stabilizer is next. Draw a pattern of onehalf on a board, remembering that the inner rib fits against the fuselage, and so is at an angle. Notch the inner ends

BUILDING A SIX'FOOT SAILPLANE into a streamlined rib Vs" thick, and the other ends into a semicircular tip Vs" thick. Taper the center spar into the tip, round the leading and trailing edges, and build the other half of the elevator. Cover both surfaces with rice paper.

Attach the elevator halves to the fuselage by means of two sV' wires thrust through the body and projecting Vz" into the leading and center spars, and cement.

The rudder is much like a halhelevator. The lower rib.

however, is in two parts, the forward end inclining upward to fit the fuselage, and the rear half at 45 degrees with the center spar. Push a wire dowel into the end of the center spar end and the fuselage longeron, and nail the leading spar with a pin. Brace the rudder with a fine thread through the tip, connecting with the elevator tips.

Cement the wing to its cleat, further securing it with pins having celluloid washers under the heads. Then make the two pairs of streamlined struts, cementing and pinning one end of each to the fuselage under the bulkhead and the other end to the wing, the front one under the third rib from the center, the trailing one 1" beyond that rib.

Test the plane on the level, casting it a little downward. The weight in the nose may need increasing, or the angle of the stabili2;er may need changing.

This plane has a remarkably flat gliding angle. It will make excellent flights if launched from the hand on a hill side, but for real endurance and altitude it should be towed with a shock cord. Use two strands of tV'' square rubber with a small metal ring tied at one end to go over the towing hook. With a boy to launch the plane, and one to tow it against the wind, it rises quickly. When enough elevation has been gained, the one towing should stop and twitch backward on the cord to release it from the hook.

Part II Stick Monoplanes 1

THE ROUGH AND READY TRACTOR

The Rough and Ready Tractor is a solid little plane, with wheels on the Itinding gear permitting it to take off from the ground. A staunch little flier it is. It whistles through the air in a steady climb, and if it perches in a tree or collides with a telephone pole, more likely than not it re' ceives no other damage than a bent propeller shaft.

For this ship have the following materials: For motor stick, one piece of balsa by 14 by 13%"; for wing spars, ribs, etc., 614' of 14" square balsa; for the propeller, a piece of % by 1 by 6"; for landing gear, etc., sV" music wire about 2 ft.; for propeller shaft bearing, a fine 1 or 114" brad; rice paper 6 by 14"; for the wheels, stiff paper 1 by 4"; also thread, ambroid cement, wing dope, and 4 ft. of 14" flat rubber.

To make the wing, cut two spars llVi" long, and seven ribs 3" long. Mark the spars for the ribs, spacing them IVa apart, and cement them to the rib ends, the ribs lapping 33 above. When the cement is hard, glue rice paper over the frame, drawing it tight. Smear a thin coat of glue or paste on the wood, including all the ribs.

Partly break the spars at the center, coat the breaks with cement, and bend the wing so that the ends are 1" above the center, blocking the part in that position for drying. The right end should be twisted slightly upward toward the front, so that the rubber motor will not whirl the plane.

Bend the two wing stirrups as shown, so that the ‘'"U” centers will clasp the motor stick firmly. Cement the ends to the upper sides of the spars, and bind them with a few turns of thread.

The motor stick is sandpapered smooth, with the cor¬ ners a little rounded. Make the tail hook as shown in the drawing. Push the other end through the motor stick 2" from the rear end, sloping it backward, and bend the wire to form a skid. If the motor is to be wound by turning the propeller, slip over the hook a bit of rubber tubing; but if a winder is used, make an ''S’' hook to join the rubber with the tail hook, and put on the tubing.

Heat the brad red hot to soften it. Cut off the head, bend the nail around a piece of the wire, and y% from the

THE ROUGH AND READY TRACTOR 35

eye bend the point back nearly at right angles. Flatten this part by hammering, cement it to the forward end of the motor stick, on top, and wrap it with thread.

The stabili 2 ;er is made of two 5" spars and four PA" ribs. This is cemented across the under edge of the motor stick at the rear end, with the paper side down.

tween two ribs, with sides flush. It is covered on one side with paper, and is cemented to the top of the motor stick, over the elevator.

Paint all paper covering with wing dope.

Lay out the propeller carefully. Draw diagonals on both faces, and circles at the centers. Saw along the diagonals.

leaving a little wood each side of the marks to strengthen the hubs, and whittle the backs of the blades. Sand them smooth, a little hollowing, before carving the fronts. When well shaped, trim the comers of the tips round.

Bend a V 4 ' hook on a piece of wire, leaving a straight shaft 2" long. Press the end through the propeller hub, bend over the end, and cement.

Before adding the rubber tubing to the hook, slip on two glass beads for thrust bearings, and put the hook through the brad eye.

The landing gear stmts are bent up as shown, so as to clasp the motor stick as do the wing stirmps. As they spring apart a little when carrying the weight of the plane, the

THE ROUGH AND READY TRACTOR wheel spindles are bent downward somewhat at the ends, so that, when standing on the ground, the wheels will be upright. The struts are pressed on the motor stick 3" from the front end.

Make the brace. It clasps the stick IV 2 " in front of the struts, and the ends wrap around the struts about half' way down.

To make the wheels, cut four 1" circles from stiff pa' per, and cut each radially to the center. Fold a little Ys" from the cut, spread glue on this flap, eind close the cut edge over to the fold, pressing the flap behind. This makes a cone.

Cement two cones, at the edges, to form one wheel, and thread the strut ends through the centers. A little blob of cement each side of the wheel, on the wire, keeps it from slipping sidewise.

Put the wing in place on the motor stick, the front edge about 5" from the front end. Loop a rubber over the motor stick before and behind the plane and under the wing, to prevent its working off.

Put on four strands of Vs" flat rubber, short enough to hang rather straight without being stretched. Before launch' ing, wind the propeller backwards until two rows of knots are seen. If the ship settles on the tail, move the wing back a bit; and if it nosedives, move it forward.

THE TUMBLE BUG

The Tumble Bug is a little tailless plane, and a pusher. A regular clown it is, for it just can’t behave. It darts away from the hand of the launcher, looping and zooming, cir¬ cling and zig'Zagging, as likely as not returning to give a peck at one’s head. If a thrilling flight is wanted, this plane is certainly the one to give it.

To build the Tumble Bug, these materials are needed: One piece of balsa 3 % by A by 7"; for the wing, balsa % by 12"; for the propeller, balsa V 2 by % by 4%"; for the shaft, etc., 5 ?" music wire 8 " long; also two small washers, a glass bead, ambroid cement, wing dope, rice paper 3 by 15", and 14" of Vs" flat rubber. For the bearing, have a piece of aluminum 3*2 by Vs by Vs".

In laying out for making the wing, draw on a board two lines 2*4" apart, and a third P/s" from the second. Square a center line across them, and 5 V 2 " each side make two other lines. From the balsa split off two spars gV" wide. Cut two halves for the front spar, fitting them to¬ gether to sweep back from the center at the first line to the second at the ends. The rear spar sweeps back from a point 38

THE TUMBLE BUG at the center 1 }/% behind the leading spar, to the back line

at the ends. Cement the center ends, and ambroid a 1^6 by 3 ^ 2 " rib there.

Also cement ribs between the ends. When nearly dry, bend the spars at the center until a dihedral angle ly/i deep is formed.

Cement again, and let dry. Finally cover the upper surface with rice paper glued both to the spars and the ribs, but do not dope yet.

Two rudders are to be made next. The detail in the drawing clearly shows their form. They are 2" high, iVs' wide at the top, and iVs" at the bottom. The frames are of T6 by Vs" balsa, with the top butted between the sides, and the sides butted against the lower rib. The lower ribs are cut long, so that they can be fitted between the rib spars. Cover them on one side with paper.

Draw a pencil line IV 2 ' from each end, and parallel to it, on the wing. Carefully slit the paper along this line. Fit the rudders between the spars at these points, coat the sides and ends of the lower ribs with cement, and glue the tails in place. Be sure to get them parallel to each other, and upright in relation to the wing. Paste the wing covering neatly to the lower ribs. When dry, dope the paper. Twist the right end slightly to prevent the motor rubber from turning the plane over sidewise.