CHAPTER XI
INSPECTION OF AIRPLANES
Mechanics in charge of airplanes, who are primarily responsible for their safety while in their care, should constantly think of new methods for insuring greater safety and reliability. They should invariably bring any fresh points they think of to the attention of their Flight Commander, in order that the rest of the Corps may benefit by them. They should always try to find out the cause of anything wrong, and inform the officer in charge of the machine of their opinion. They should bear in mind any particular incidents which may have happened to their machine while under their charge during each flight, and be on the lookout for signs of stresses that may have occurred to the machine in consequence of these incidents. For example, a steep spiral may cause side strains on the engine bearers; a flight in bad weather may cause bending stresses on the longitudinal members of the body, besides stretching the landing and flying wires. No part of a machine can be safely overlooked, and good mechanics will always be seeking for the possible cause of accidents and bringing them to the notice of the officer in charge of the machines.
During all inspections the following matters of detail deserve particular attention:
Look out for dirt, dust, rust, mud, oil on fabric. Cleanliness is the very first consideration.
Give the control cables particular attention. These should not be too tight, otherwise they will rub stiffly in the guides. The hand should be passed over them to detect kinks and broken strands. They should be especially well examined where they run over pulley. Don’t forget the aileron balance wire on the top plane.
See that all wires are well greased and oiled, and that they are all in the same tension. When examining wires, be sure to have machine on level ground as otherwise it may get twisted, throwing some wires into undue tension and slackening others. The best way, if time is available, is to jack the airplane up into “flying position.” If a slack wire is found, do not jump to the conclusion that it must be tensioned. Perhaps its opposite wire is too tight, in which case it should be slackened.
Carefully examine all wires and their connections near the propeller, and be sure that they are snaked around with safety wire, so that the latter may keep them out of the way of the propeller if they come adrift.
Carefully examine all surfaces, including the controlling surfaces, to see whether any distortions have occurred. If distortions can be corrected by adjustment of wires, well and good, but if not, matter should be reported.
Verify the angles of incidence, the dihedral angle, the stagger, and the overall measurements as often as possible (at least once a week) and correct as outlined in notes on assembly and adjustment of airplanes.
Constantly examine the alignment and fittings of the undercarriage, the condition of tires, shock absorbers and the skids. Verify the rigging position of the ailerons and elevators.
Constantly inspect the locking arrangements of the turnbuckles, bolts, etc.
Learn to become an expert at vetting, which means the ability to judge the alignment of the airplane and its parts by eye. Whenever you have the opportunity practice sighting one strut against another to see that they are parallel. Standing in front of the machine, which in such a case should be on level ground, sight the center section plane against the tail plane and see that the latter is in line. Sight the leading edge against the main spars, the rear spars, and the trailing edges, taking into consideration the “washin” and “washout.” You will be able to see the shadow of the spars through the fabric. By practising this sort of thing you will, after a time, become quite expert, and will be able to diagnose by eye faults in efficiency, stability and control.
The following order should be observed in the daily and weekly inspections:
Daily Inspection.—All struts and their sockets, longerons, skids, etc.
All outside wires and their attachments.
All control levers or wheels, control wires and cable and their attachments.
All splices for any signs of their drawing.
Lift and landing gear cables or wires for any signs of stretching.
All fabrics, whether on wings or other parts of the machine, for holes, cuts, weak or badly doped places, or signs of being soaked with gasoline, and to see if properly fastened to wings, etc.
All outside turnbuckles, to see that they have sufficient threads engaged, and that they are properly locked.
Axles, wheels, shock absorbers, and tires, pumping the latter up to the correct pressure.
The seats, both for passenger and pilot, seeing that they are fastened correctly.
Safety belts and their fastenings.
This examination should be carried out systematically in the following order:
(a) Lower wings, landing gear complete, tail planes with all wires attached to these tail skids and all attachments and rudder.
(b) Nacelle or fuselage, bolts of lower plane, all control levers and wires.
(c) Top wings, wing flaps or ailerons and wires.
Inspection after Each Flight.—The landing gear, tail skid and attachments and lift and drag wires for tautness.
The wheels, after a rough landing, for bent spokes, uncovering them if necessary.
After flying is finished for the day, wipe all oil off the planes as far as possible with a cloth or cotton waste.
Weekly Inspection.—Check over all dimensions, span, chord, gap, stagger of wings, angles of incidence or set angle of wings and tail, dihedral angle, alignment of fuselage, rudder, elevators, and the general truth of the machine.
Examine the points of crossing of all wires to see that there are no signs of wear, and that each wire is properly bound with insulating tape to prevent rubbing.
Examine all places where wires cross the strut to see if the plates require renewal.
Examine any control wires which are bound together, and see that they are correct. (Insulating tape should be used for this in preference to wires which are bound to slip and cause slack.)
Examine the wheels for bent or loose spokes, uncovering if necessary.
Examine all nuts and bolts of cotter-pin applications, lock washers, etc.
The following directions for inspection are given to the U. S. Inspectors of Airplanes:
Inspection of Cables.
Are there any kinks in the cable?
Are loops properly made?
Are thimbles used in eyes?
Are ends wrapped properly (when wrapped splice is used, wrap must be at least fifteen times the diameter of wire).
No splicing of the cable itself is permitted.
Has acid struck cable during soldering?
Are any of the strands broken?
Are unwrapped ends stream-lined and show the result of skilled workmanship?
For Roebling Hard Wire.
Are there any file cuts or flaws to weaken it?
Is loop well made?
Is ferrule put on correctly?
Are there any sharp bends or kinks?
Are wires too loose or tight in machine?
Fittings.
Is workmanship good?
Is material good?
Are holes drilled correctly to develop proper strength?
Are there any deep file cuts or flaws to weaken it?
Is rivet or fastening wire put in properly?
Are thimbles of large enough diameter?
Turnbuckles.
Any file cuts, tool marks, or flaws in shank or barrel?
Are there too many threads exposed?
Is turnbuckle of right strength and size to develop full strength of wire?
Are shanks bent?
Are threads on shank or in barrel well made?
Is barrel cracked?
Is turnbuckle properly wired?
Inspection of Linen.
All linen used in airplane construction should be of the following specifications:
Free from all knots or kinks.
Without sizing or filling.
As near white as possible.
Weight, between 3.5 and 4.5 oz. per square yard.
Strength as per Government Specifications.
Inspection of Wood.
All wood should be inspected before varnish is applied.
Is grain satisfactory?
Are there any sap or worm holes?
Are there any knots that look as if they would weaken the member?
Any brashiness?
Any holes drilled for bolts or screws that would weaken the member?
Any splits or checks?
Are laminations glued properly?
Are there any plugged holes?
Any signs of dry rot?
Inspection of Metal Fittings.
When fittings are copper plated and japanned the inspection should take place after the copper plating.
Have fittings been bent in assembling?
Does fitting show any defects that lessen its strength?
Are holes drilled properly. Do fittings fit?
Sheet aluminum should be inspected for defects such as cracks, bad dents, etc. Where openings occur in sheet aluminum the corners should be rounded, allowing a good-sized radius.
Directions for Work.
Before you start work on rigging you are advised as follows:
1. Do not hurry about the work. No rush jobs can be done in airplane rigging.
2. You are cautioned against leaving tools of any kind in any part of the airplane.
3. The bolts and their threads must not be burred in any way; for this reason, the use of pliers or pipe wrenches on bolts is very bad form.
4. Start all turnbuckles from both ends every time they are connected up.
5. Full threads must be had in every case to develop the full strength of a bolt and nut, with turnbuckles at least turn on for a distance equal to three times the thickness of the shank.
6. Lock with safety wires all turnbuckles and pins, and cotter-pin every nut.
7. Watch for kinking of wires and their rubbing around controls and wherever they may vibrate against one another.
8. All bolts and pins must have an easy tapping fit only; do not pound them into position.