The Aeroplane Speaks [44]
as they may not have been placed quite accurately by the manufacturer. The lines AC and BC must be taken from both top and bottom spars--two measurements on each side of the aeroplane.
The two measurements FD and FE should be equal to within 1/8 inch. F is the centre of the fuselage or rudder- post. D and E are points marked on both top and bottom rear spars, and each must be the same fixed distance from the butt of the spar. Two measurements on each side of the aeroplane.
If these over-all measurements are not correct, then it is probably due to some of the drift or anti-drift wires being too tight or too slack. It may possibly be due to the fuselage being out of truth, but of course the rigger should have made quite sure that the fuselage was true before rigging the rest of the machine. Again, it may be due to the internal bracing wires within the lifting surfaces not being accurately adjusted, but of course this should have been seen to before covering the surfaces with fabric.
FUSELAGE.--The method of truing the fuselage is laid down in the aeroplane's specifications. After it has been adjusted according to the specified directions, it should then be arranged on trestles in such a way as to make about three- quarters of it towards the tail stick out unsupported. In this way it will assume a condition as near as possible to flying conditions, and when it is in this position the set measurements should be confirmed. If this is not done it may be out of truth, but perhaps appear all right when supported by trestles at both ends, as, in such case, its weight may keep it true as long as it is resting upon the trestles.
THE TAIL-PLANE (EMPENNAGE).--The exact angle of incidence of the tail-plane is laid down in the aeroplane's specifications. It is necessary to make sure that the spars are horizontal when the aeroplane is in flying position and the tail unsupported as explained above under the heading of Fuselage. If the spars are tapered, then make sure that their centre lines are horizontal.
UNDERCARRIAGE.--The undercarriage must be very carefully aligned as laid down in the specifications.
1. The aeroplane must be placed in its flying position and sufficiently high to ensure the wheels being off the ground when rigged. When in this position the axle must be hori-
nontal and the bracing wires adjusted to secure the various set measurements stated in the specifications.
2. Make sure that the struts bed well down into their sockets.
3. Make sure that the shock absorbers are of equal tension. In the case of rubber shock absorbers, both the number of turns and the lengths must be equal.
HOW TO DIAGNOSE FAULTS IN FLIGHT, STABILITY, AND CONTROL.
DIRECTIONAL STABILITY will be badly affected if there is more drift (i.e., resistance) on one side of the aeroplane than there is on the other side. The aeroplane will tend to turn towards the side having the most drift. This may be caused as follows:
1. The angle of incidence of the main surface or the tail surface may be wrong. The greater the angle of incidence, the greater the drift. The less the angle, the less the drift.
2. If the alignment of the fuselage, fin in front of the rudder, the struts or stream-line wires, or, in the case of the Maurice Farman, the front outriggers, are not absolutely correct--that is to say, if they are turned a little to the left or to the right instead of being in line with the direction of flight--then they will act as a rudder and cause the aeroplane to turn off its course.
3. If any part of the surface is distorted, it will cause the aeroplane to turn off its course. The surface is cambered, i.e., curved, to pass through the air with the least possible drift. If, owing perhaps to the leading edge, spars, or trailing edge becoming bent, the curvature is spoiled, that will result in changing the amount of drift on one side of the aeroplane, which will then have a tendency to turn off its course.
LATERAL INSTABILITY (FLYING ONE WING DOWN).--The only possible reason for such a condition is a difference
The two measurements FD and FE should be equal to within 1/8 inch. F is the centre of the fuselage or rudder- post. D and E are points marked on both top and bottom rear spars, and each must be the same fixed distance from the butt of the spar. Two measurements on each side of the aeroplane.
If these over-all measurements are not correct, then it is probably due to some of the drift or anti-drift wires being too tight or too slack. It may possibly be due to the fuselage being out of truth, but of course the rigger should have made quite sure that the fuselage was true before rigging the rest of the machine. Again, it may be due to the internal bracing wires within the lifting surfaces not being accurately adjusted, but of course this should have been seen to before covering the surfaces with fabric.
FUSELAGE.--The method of truing the fuselage is laid down in the aeroplane's specifications. After it has been adjusted according to the specified directions, it should then be arranged on trestles in such a way as to make about three- quarters of it towards the tail stick out unsupported. In this way it will assume a condition as near as possible to flying conditions, and when it is in this position the set measurements should be confirmed. If this is not done it may be out of truth, but perhaps appear all right when supported by trestles at both ends, as, in such case, its weight may keep it true as long as it is resting upon the trestles.
THE TAIL-PLANE (EMPENNAGE).--The exact angle of incidence of the tail-plane is laid down in the aeroplane's specifications. It is necessary to make sure that the spars are horizontal when the aeroplane is in flying position and the tail unsupported as explained above under the heading of Fuselage. If the spars are tapered, then make sure that their centre lines are horizontal.
UNDERCARRIAGE.--The undercarriage must be very carefully aligned as laid down in the specifications.
1. The aeroplane must be placed in its flying position and sufficiently high to ensure the wheels being off the ground when rigged. When in this position the axle must be hori-
nontal and the bracing wires adjusted to secure the various set measurements stated in the specifications.
2. Make sure that the struts bed well down into their sockets.
3. Make sure that the shock absorbers are of equal tension. In the case of rubber shock absorbers, both the number of turns and the lengths must be equal.
HOW TO DIAGNOSE FAULTS IN FLIGHT, STABILITY, AND CONTROL.
DIRECTIONAL STABILITY will be badly affected if there is more drift (i.e., resistance) on one side of the aeroplane than there is on the other side. The aeroplane will tend to turn towards the side having the most drift. This may be caused as follows:
1. The angle of incidence of the main surface or the tail surface may be wrong. The greater the angle of incidence, the greater the drift. The less the angle, the less the drift.
2. If the alignment of the fuselage, fin in front of the rudder, the struts or stream-line wires, or, in the case of the Maurice Farman, the front outriggers, are not absolutely correct--that is to say, if they are turned a little to the left or to the right instead of being in line with the direction of flight--then they will act as a rudder and cause the aeroplane to turn off its course.
3. If any part of the surface is distorted, it will cause the aeroplane to turn off its course. The surface is cambered, i.e., curved, to pass through the air with the least possible drift. If, owing perhaps to the leading edge, spars, or trailing edge becoming bent, the curvature is spoiled, that will result in changing the amount of drift on one side of the aeroplane, which will then have a tendency to turn off its course.
LATERAL INSTABILITY (FLYING ONE WING DOWN).--The only possible reason for such a condition is a difference