Part 5: Material used in Light Aircraft Construction

l\[OW we come to the material which is used generally in light aircraft construction in this country 1 \ and Europe. This can come under the heading of timber, although ontry a limited number oi types are used in aircraft structure. The Americans generally favour the use of steel tube as the basis of their aircraft structure. This latter form of construction will be dealt with at a later date.

The timbers we are concerned with are spruce and ash, and beech or birch ply. The whole strength of the aircraft relies on the quality of these materials, coupled of course, with the quality of the gluejoints and construction as a whole. These timbers are picked because they possess certain assets from the aeroplane point of view. First a timber is required that is light in weight and yet offers good strength regarding tensile and compression loads. Spruce offers all this and so is an ideal rnaterial for the construction of ribs, longerons, spar booms, etc. Ash is heavier than spruce and is now only used where crushing loads are involved, as this timber is superior to spruce in this respect.

by A. f)euerell

Crushing loads are found where bolts and steel plates are, for instance, at wing to fuselage attachment points and in the vicinity of the undercarriage and tail skid, etc. Hence the reason for the use of ash blocks in the wing box spar at points of undercarriage and fuselage attachment. A11 this is on the drawings supplied but is mentioned in order to avoid any temptation to use spruce in lieu of ash at these points. A bolted up joint will soon work loose unless the timber used resists crushing loads ; a joint allowed to work can soon develop into a serious source of danger. A great deal to do with the strength of spruce and ash, is the way they have been cut off the log, the angle of the grain, its density, moisture content and brittleness. Also, of course, the timber must be free from the many diseases and defects that can affect wood. All this may sound elementary but it is amazing how easily one can overlook some of these. This is one reason why ARB released materials are insisted on in order to keep a safe standard. Plywood is easily obtained to this standard from many reputable aircraft f,rms and suppliers. Spruce is rather more difficult to obtain as the number of firms with approval to convert timber are very few. However, the P.F.A. can supply the name of a satisfactory supplier on request ; we cannot overstress the importance of f,rst class timber for use in aircraft. Therefore, please do not hurriedly purchase a load of timber without flrst conferring with your inspector or the P.F,A.

To delve a little more deeply into the abovementioned requirements of timber may be useful at this point for it is essential to insist on the use of approved timber in the highly stressed structural parts of an aircraft. To achieve lightness, the designer naturally calculates on known timber grades and uses the smallest dimensions practicable, allowing, of course, for a certain safety factor. It follows therefore, that the use of inferior timber could seriously cut down on this safety factor. To quote a yery simple case, if you wanted to fit a new step on a step ladder, you would not dream of making the step with the grain across it or at a very acute angle, because no matter how good the timber condition is, it w_ould collapse immediately under the weight of a child, let alone an adult. Yet, if the grain were running along the step and dead straight, this step could bear the weight of a young elephant. To be continued.

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Popular Flying, Nove mber-De c.enbcr, 196l the F.I.R.'s and upper air regions. The purpose of this pilot census is to determine traffic density. The information required is limited and will be confidential. Postage will be prepaid by the Ministry so that other than your physical effort there is little expenditure-and the possibility of improved facilities.

'Amateur aircraft construction was reprepresented at this year's ' Do-It-Yourself ' Exhibition held at Olympia. Phoenix Aircraft Limited of Cranleigh had a stand on which was displayed the fuselage of the Luton Major which is under construction by Mr. W. G. Cooper of Weybridge. A display of metal fittings for a Luton Minor was lent by Mr. R. F. Tilley, of the Tasmanian Aero Club, and metal parts for a Luton Major were lent by Mr. R. A. Jancey, of Geelong, Australia. A large painting in oils of a Minor by Mr. R. G. Bean of Blackburn & General Aircraft together with pictures of the Luton types formed an attractive background to the stand. A complete Minor undercarriage, built by Mr. Roy Goodwin of Leicester was also on show. Three years ago the P.F.A. displayed its Turbi, G-APFA, at the D.I.Y. show.

Permit applications should now include the following :-(a) Maximum permissible speed of the aircraft. (b) Maximum permissible speed flaps down, ifapplicable. (c) Maximum engine r.p.m. for take otr (d) Maximum cruising r.p.m. (e) Minimum engine oil pressure. There is no need to take any retrospective action on existing Permits, but all concerned should note that the above information is desirable for future recommendations for both issued of or renewals of Permits to Fly.

Ministry of Aviation Census. A census will be conducted during the week beginning December 4th of the aircraft movements in Popular Flying, November-December, 1961.

Each censor's card is for a period of 24 hours and reports should be made on the hour, giving heading, altitude, position, either as a latitude and longitude or as visual fi.x, i.e. 10 n.m. north of Luton, aerodrome of departure and intended landing.

If you are on the ground at the time you make no return or if you are on the circuit you simply state so in the position column.

Several new groups are in the process of getting started and we are waiting to see which will become Group No. 200.

The Luton Wildcats, Group No. 196, has recently been formed following the disbandment of the Hornet Private Flying Group. They are proposing to operate Hornet Moth G-ADKL from Luton. The secretary, Dr. Miles Kingsmill-Moore, tells me that they have several vacancies for new members and hope to caffy out instruction for students from Luton.

From the Lancashire area David Vernon, our area rep., tells me that his group have completed 200 hours flying in the last 16 weeks and that the first of the students to be trained on the Aircoupe are now reaching the end of their course, while membership now stands at approximately 70. West Lancs Group are now contemplating a Beagle Airedale as a replacement for their Tiger Moth.

McAully Group have got their winter programme started and have several winter flying fixtures lined up. As we went to press the Group were due to fly off the Bill Wiggins Memorial Trophy for spot landings, and a short circuit race, followed by flreworks and rum punch on 5th November. The Group has also taken under its wing a junior flying Group comprised of teenagers of 17-19 years who have formed their Group under the auspices of the Norfolk Education Committee.

This followed a successful weekend during r.vhich selected teenagers interestecl in aviation were encouraged to take up the art with the backing of the Education Committee. This is the flrst scheme of its kind in the country and one for which both the McAully Group and Norfolk County Council deserve the highest praise.

At Elstree recently the M.P.M. Group dropped their first paracliutist, much to the delight of the Iocal populace and the constemation of the circuit "bashers." lt is hoped that they will be able to form a parachute section and have a private field over which to carry out their jumps. So far six people have applied for membership and a second machine more suitable for this type of operation is being looked fbr, together with equipment.

Bourne and District Flying Group have now taken delivery of the Auster from White Waltham and have begun operations. This is the first loan to be negotiated successfully with the Private Flying l,oan Trust.

Another Group attempting to get back into the operational status is the Swallow Flying Group at Elstree. Nerv co-owners are urgently wanted and interesled persons should contact D. Bernard.

The Hertfordshire Expenimental Group corltinues to make progress and is now on the hunt for its own private airstrip.

Montgomeryshire Flying Group have now become operational with a Tiger Moth, although the Tipsy still requires a Micron engine.

I understand that the Armstrong Whitworth Flying Group are going to change their name to the Whitworth Gloucester Flying Group. Besides the new narne they are evaluating a stable mate for Weary Willie, now very smart after its respray. David O'Clarey would like to point out that it was their rivals who had the magneto trouble !

ROY MILLS.

Popular Flyins, November-December, 196l