Part 13 (1/2)

If it is necessary to bore holes in the spars for the purpose of receiving, for instance, socket bolts, then their places should bebored and their positions confire of the workshop All is now ready for the sail-maker to cover the surface with fabric

ADJUSTMENT OF CONTROL CABLES--The adjustment of the control cables is quite an art, and upon it will depend to a large degree the quick and easy control of the aeroplane by the pilot

The ed the controlling surfaces, and as far as possible secured the correct adjust which has kept the control levers rigid Then, sitting in the pilot's seat, move the control levers _smartly_ Tension the control cables so that when the levers are s Be careful not to tension the cables more than necessary to take out the snatch If tensioned too much they will (1) bind round the pulleys and result in hard work for the pilot; (2) throw dangerous stresses upon the controlling surfaces, which are of rather flimsy construction; and (3) cause the cables to fray round the pulleys quicker than would otherwise be the case

Now, after having tensioned the cables sufficiently to take out the snatch, place the levers in their neutral positions, and move them to and fro about 1/8 inch either side of such positions If the adjust surfaces move

If they do not move, then the control cables are too slack

FLYING POSITION--Before rigging an aeroplane orany adjustments it is necessary to place it in what is known as its ”flying position”

Iposition”

In the case of an aeroplane fitted with a stationary engine this is secured by packing up the ine foundations are perfectly horizontal both longitudinally and laterally This position is found by placing a straight-edge and a spirit-level across the engine foundations (both longitudinally and laterally), and great care should be taken to see that the bubble is exactly in the centre of the level

The slightest error will assunitude towards the extremities of the aeroplane Great care should be taken to block up the aeroplane rigidly In case it gets accidentally disturbed while the work is going on, it is well to constantly verify the flying position by running the straight-edge and spirit-level over the engine foundations The straight-edge should be carefully tested before being used, as, being generally htly in a vice, and in such a position that a spirit-level on top shows the bubble exactly in the centre Noly e, and the bubble should remain exactly in the centre

If it does not do so, then the straight-edge is not true and must be corrected _This should never be oines of the rotary type, the ”flying position” is some special attitude laid down in the aeroplane's specifications, and great care should be taken to secure accuracy

ANGLE OF INCIDENCE--One le of incidence is as follows:

[Illustration]

First place the aeroplane in its flying position The corner of the straight-edge ainst the _centre_ of the rear spar, and held in a horizontal position parallel to the ribs This is secured by using a spirit-level The set e to the centre of the bottom surface of the e to the lowest part of the leading edge Care should be taken to measure from the centre of the spar and to see that the bubble is exactly in the centre of the level Remember that all this will be useless if the aeroplane has not been placed accurately in its flying position

This le of incidence must be used under every part of the lower surface where struts occur It should not be used between the struts, because, in such places, the spars ht permanent set up or down; not, perhaps, sufficiently bad toof the le of incidence, which cannot be corrected at such a place

If the angle is wrong, it should then be corrected as follows:

If it is too great, then the rear spar ht, and this is done by slackening _all_ the wires going to the top of the strut, and then tightening _all_ the wires going to the bottole is too s to the botto to the top of the strut, until the correct adjustle by warping the main spar

The set measurement, which is of course stated in the aeroplane's specifications, should be accurate to 1/16 inch

LATERAL DIHEDRAL ANGLE--Onethis is as follows, and this le of incidence:

[Illustration: FRONT ELEVATION and PLAN]

The strings, drawn very tight, must be taken over both the main and rear spars of the top surface They must run between points on the spars just inside the outer struts The set measurement (which should be accurate to 1/16 inch or less) is then fros down to four points on the main and rear spars of the centre-section surface These points should be just inside the four centre-section struts; that is to say, as far as possible away from the centre of the centre-section

Do not attempt to take the set measures should be as tight as possible, and, if it can be arranged, the best way to accomplish that is as shown in the above illustration, _ie_, by weighting the strings down to the spars by ive a tight and

However carefully the above adjustht error This is of no great importance, provided it is divided equally between the left- and right-hand wings In order to make sure of this, certain check measureonally measured, and such measurements must be the same to within 1/16 inch on each side of the aeroplane As a rule such diagonal measurements are taken from the bottom socket of one strut to the top socket of another strut, but this is bad practice, because of possible inaccuracies due to faulty onal measurements are taken should be at fixed distances fro the same on each side of the aeroplane, thus:

[Illustration: Points A, B, and C, must be the same fixed distances from the butt as are Points D, E, and F Distances 1 and 2 must equal distances 3 and 4]

The above applies to both front and rear bays