Some Tips on Aircraft Woodwork By Arthur W. J. G. Ord-Hume (Copyright reserved) Reprinted by courtesy of Popular Flying Association of Great Britain n aircraft construction it is jften IThere required to bend wood to a curve. are two methods of forming wood to a bow - one is by bending and the other is by laminating several thin strips of wood together in a jig. Both spruce and ash bend readily to a certain degree. Any bend in excess of this amount will result in fracture of the fibres. Also, when bent, the wood is sufficiently elastic to cause it to spring straight again. By softening the wood, however, not only will the timber remain bent but it will be possible to increase considerably the safe radius of the bend. Wood may be softened in two ways - water softening, which may be done either hot or cold, and by steaming. The latter is the most effective but, since it usually necessitates the use of a steam-box if the piece is long, it is more usual to plasticize the wood by saturation in water. Soak the portion to be bent in water for up to two hours until it is soft enough. Bend it very slowly to the shape required, working the bend in with the fingers to prevent sudden stretch of the fibres. The process is speeded up by immersing the piece in boiling water or, if the piece is small enough, actually boiling it in a pan of water for a few minutes. Remove the wood with gloves and again bend it slowly. If the bend is acute or the material thick, repeat the boiling treatment until the bend is completed. It will be found that upon drying there is a tendency for the wood to spring slightly out of the bend. To counteract this, increase the bend from 15 to 20 percent more than is required so that the wood when dry will adopt a "set" just about at the bend required. In steaming wood to be bent, the effect on the wood is similar to that when the wood is treated as above. The fibres soften readily without any loss of strength upon drying. If only a small area of wood of thin section has to be treated, it can be done in the steam from the spout of a kettle. However, for larger pieces a steam-box must be resorted to. This consists of a long metal box or large-diameter tube of sufSPORT AVIATION

ficient size to accommodate the wood to be steamed. It is sealed at one end with a scalable door at the other. The box or tube is connected via a pipe to a water boiler heated by a gas burner. As the water boils, the steam is forced under pressure into the box containing the timber. A suitable safety valve must be fitted into the boiler. Great care must be exercised when exhausting the steam from the box - a scald from steam is a most serious and painful experience. Timber in a steam box should be left from one to two hours before removing. Subjection to longer periods of steaming results in the destruction of the suppleness of the wood after it is dried. Before glueing any wood which has been steamed or wetted in any way, always let the piece dry thoroughly in the open air. On no account try to accelerate the drying by artificial methods. Air drying will preserve the correct moisture content of the timber. Plywood may be bent in the same manner. It is easiest to bend ply with boiling water saturation. Bend the ply as far as it will safely go and, while still holding the bend, get an assistant to pour boiling water from a kettle over the outside of the bend. Immediately the ply will soften and start to fold tighter. Do not hurry the process, for the wood may yet split. By repeated applications of boiling water, gradually work the ply to the curve desired and then clamp it between two boards to dry overnight.

Where it is desired to make a large curve of accurate dimensions with a comparatively thick cross section, the designer will usually call for the piece to be laminated. Formers, wing tip bows, keel members and similar pieces call for lamination. A jig must be made to locate the strips for glueing. Obtain a large flat board of commercial wood sufficiently large to take the curve of the member to be made, plus a margin of several inches. For very large members, a wooden floor may be used. With a hard pencil mark out the curve. Now cut wooden blocks about 1 in. by 2 in. by 3 in. and glue and screw these to the inner edge of the curve at intervals of every 3 or 4 in. If the curve is sharp, these blocks will need shaping. To prevent the adhesion of the glue to the jig, paint the jig with two coats of hot paraffin and allow to dry.

Cut the strips of wood to be laminated and allow several inches more in length than is actually required the excess may be removed later. Glue up the laminations separately on a flat surface, shuffling each strip to the next to exclude air. When the desired number of pieces has been glued up, place the bundle into position on the jig board. On the outside of the bundle, opposite each block, put a piece of scrap wood to use as a clamping block. Alternatively, a strip of steel may be bent into place on the outside

WHO SAYS BIPLANES ARE OUT OF DATE?

Jacksen

This interesting line-up of homebuilt biplanes was seen at the EAA Fly-In held at Riverside, Calif., in January. From left to right the ships are (1) StolpAdams SA-100 "Star Duster"; (2) Smith DSA-1 "Miniplane", and (3) the GlenLee 2 "Special". The "Miniplane" was described in the April, 1957 EXPERIMENTER, and plans are offered in the classified section. Details on the other two craft will appear in early issues of SPORT AVIATION.

THE TACHIKAWA T. S. 1 By John Underwood, EAA 1989

T his

interesting

ultra-light

was

built by the Tachikawa Aircraft Co,. Ltd., of Tokyo, Japan. It was

built during 1937-38, but never went beyond the prototype stage. Although the ship was easy to fly and had no undesirable characteristics, it was not put into production because of the high manufacturing costs and the extremely limited domestic market. The only noteworthy design feature of the T. S. 1 was the

retractable landing gear; most unusual in an ultra-light aircraft. The cantilever wing was built up

entirely of wood. The single box spar consisted of spruce flanges and plywood webs; the ribs were built

Woodwork . . . rather like an additional lamination to take the pressure of the clamps.

Clamp up each block with C-clamps and leave it for 24 hours to dry.

After removal and cleaning up, examine for any signs of de-lamination.

If there is any gap, run thin

glue into the split, working it well in with a thin strip of metal such

as a feeler gauge. Reclamp and leave until dry. When sawing aircraft timber, support it adequately to prevent it from splitting when the saw approaches the other side. Where possible, clamp a piece of scrap wood to

the underside so that the saw finishes its cut in that timber rather than in the required piece of wood.

This produces a clean cut.

Similar-

ly, when cutting plywood, the saw

will leave a rough, split lower edge. It is not always possible to "back up" a cut in plywood as detailed above but by cutting no closer than 3/32 in. to the line, this rough edge may afterwards be removed with plane and sandpaper.

Remember that wood splits easily

and is weakest along the grain when it is being cut. If one is attempting to cut along the grain or at a slight angle to it, take great care for if the saw slips or one tries to hurry the cut, the wood will split, invariably ruining the portion wanted.

up from spruce strips and the structure was covered with a plywood skin.

The fuselage consisted of a rectangular frame of spruce longerons and formers covered with plywood. The tail surfaces were also built

up from spruce and were covered with plywood, except for the rudder and elevators, which were fabric

covered.

The landing gear legs consisted of pairs of shock struts, which folded backwards. When fully retracted the wheels were still partly exposed due

a two-cylinder inverted inline engine of British manufacture. SPECIFICATIONS AND PERFORMANCE FIGURES: Span . . . . . . . . . . . . . . . . . . 25 ft. 5 in. Length . . . . . . . . . . . . . . . . . 19 ft. 6 in.

Height . . . . . . . . . . . . . . . . . . 5 ft. 3 in.

Wing area . . . . . . . . . . . . 107.6 sq. ft. Wing loading . . . . . . . 5.74 Ibs/sq. ft. Power loading . . . . . . . . . . . 22 Ibs/hp Empty weight . . . . . . . . . . . . . 416 Ibs. Loaded weight . . . . . . . . . . . . 616 Ibs.

Top speed . . . . . . . . . . . . . . 105.5 mph

Cruising speed . . . . . . . . . . . . 75 mph

Landing speed . . . . . . . . . . . . 39 mph

to the thinness of the wing.

Service ceiling . . . . . . . . . . 10,824 ft. Rate of climb . . . . 3,280 ft./10.2 min. Cruising range . . . . . . . . . . 303 miles

Planing wood is another operation necessitating care. Always plane

rasp or dreadnaught. These will tear the grain. A coarse flat file is the best thing to use, although it will clog quickly. The file should be used to smooth off wing tips and so forth in conjunction with the sandpaper block. Clean it frequently with a file scratch card. Should

Power for the T. S. 1 was supplied by a 28 hp Scott "Flying Squirrel",

with and not into the grain when surfacing a piece of wood. Examination of the grain will show that,

even on the best boards, it tends to converge slightly to one edge. If one tries to plane toward the grain, the blade will dig into the end of the grain where it meets the surface. Run the plane so that it slices the grain from behind. Should it become necessary to plane the end of a plank or piece

of wood so that the plane is cutting at right angles to the grain, the

blade must be very sharp and set so as to remove the smallest thickness possible, otherwise it will dig

in. The forward edge of the piece of timber should be backed up with a piece of scrap wood so that the plane continues its slice into this.

This is to prevent the edge from being split by the plane blade. The plane may be used for the shaping of a curved member if it is an outside curve. However, it is more usual to make use of the spokeshave with which one may also plane an inside curve. It should be held firmly in both hands and drawn towards the operator. Templates may be made out of plywood to check the shape of the work. To smooth wood or to remove glue that has dried, do not use a joiners

the file become clogged with glue,

immerse the file in boiling water for a few minutes and then clean in the normal way. Store aircraft timber on a rack

or shelf away from drafts and dampness or heat. Never keep wood on a concrete floor. Avoid contamination with oil, dirt or grease during storage and work. Woodwork is clean work. Don't work with dirty

hands. If it is necessary to store incomplete or uncovered components for awhile, protect them from dust and dirt by using dust sheets. The essence of good aircraft carpentry is careful workmanship, the accurate following of drawings and, until experience is gained, an unhurried approach. The best instructor in the world cannot supply the most vital ingredient - experience. Both carpentry and metalwork are subjects which demand practice and experience to gain proficiency. That goal may be reached with patience and care. Remember - sound work is a sure step towards success. A

JUNE 1958