The Aeroplane Speaks [49]
the blades.
If the gap is too small, then the following blade will engage air which the preceding blade has put into motion, with the result that the following blade will not secure as good a reaction as would otherwise be the case. It is very much the same as in the case of the aeroplane gap.
For a given pitch, the gap of a four-bladed propeller is only half that of a two-bladed one. Therefore the four- bladed propeller is only suitable for large pitch, as such pitch produces spirals with a large gap, thus offsetting the decrease in gap caused by the numerous blades.
The greater the speed of rotation, the less the pitch for a given aeroplane speed. Then, in order to secure a large pitch and consequently a good gap, the four-bladed propeller is usually geared to rotate at a lower speed than would be the case if directly attached to the engine crank-shaft.
CHAPTER V
MAINTENANCE
CLEANLINESS.--The fabric must be kept clean and free from oil, as that will rot it. To take out dirt or oily patches, try acetone. If that will not remedy matters, then try petrol, but use it sparingly, as otherwise it will take off an unnecessary amount of dope. If that will not remove the dirt, then hot water and soap will do so, but, in that case, be sure to use soap having no alkali in it, as otherwise it may injure the fabric. Use the water sparingly, or it may get inside the planes and rust the internal bracing wires, or cause some of the wooden framework to swell.
The wheels of the undercarriage have a way of throwing up mud on to the lower surface. This should, if possible, be taken off while wet. It should never be scraped off when dry, as that may injure the fabric. If dry, then it should be moistened before being removed.
Measures should be taken to prevent dirt from collecting upon any part of the aeroplane, as, otherwise, excessive skin- friction will be produced with resultant loss of flight speed. The wires, being greasy, collect dirt very easily.
CONTROL CABLES.--After every flight the rigger should pass his hand over the control cables and carefully examine them near pulleys. Removal of grease may be necessary to make a close inspection possible. If only one strand is broken the wire should be replaced. Do not forget the aileron balance wire on the top surface.
Once a day try the tension of the control cables by smartly moving the control levers about as explained elsewhere.
WIRES.--All the wires should be kept well greased or oiled, and in the correct tension. When examining the wires, it is necessary to place the aeroplane on level ground, as otherwise it may be twisted, thus throwing some wires into undue tension and slackening others. The best way, if there is time, is to pack the machine up into its ``flying position.''
If you see a slack wire, do not jump to the conclusion that it must be tensioned. Perhaps its opposition wire is too tight, in which case slacken it, and possibly you will find that will tighten the slack wire.
Carefully examine all wires and their connections near the propeller, and be sure that they are snaked round with safety wire, so that the latter may keep them out of the way of the propeller if they come adrift.
The wires inside the fuselage should be cleaned and regreased about once a fortnight.
STRUTS AND SOCKETS.--These should be carefully examined to see if any splitting has occurred.
DISTORTION.--Carefully examine all surfaces, including the controlling surfaces, to see whether any distortion has occurred. If distortion can be corrected by the adjustment of wires, well and good; but if not, then some of the internal framework probably requires replacement.
ADJUSTMENTS.--Verify the angles of incidence; dihedral, and stagger, and the rigging position of the controlling- surfaces, as often as possible.
UNDERCARRIAGE.--Constantly examine the alignment and fittings of the undercarriage, and the condition of tyres and shock absorbers. The latter, when made of rubber, wear quickest underneath. Inspect axles and skids to see if there are
If the gap is too small, then the following blade will engage air which the preceding blade has put into motion, with the result that the following blade will not secure as good a reaction as would otherwise be the case. It is very much the same as in the case of the aeroplane gap.
For a given pitch, the gap of a four-bladed propeller is only half that of a two-bladed one. Therefore the four- bladed propeller is only suitable for large pitch, as such pitch produces spirals with a large gap, thus offsetting the decrease in gap caused by the numerous blades.
The greater the speed of rotation, the less the pitch for a given aeroplane speed. Then, in order to secure a large pitch and consequently a good gap, the four-bladed propeller is usually geared to rotate at a lower speed than would be the case if directly attached to the engine crank-shaft.
CHAPTER V
MAINTENANCE
CLEANLINESS.--The fabric must be kept clean and free from oil, as that will rot it. To take out dirt or oily patches, try acetone. If that will not remedy matters, then try petrol, but use it sparingly, as otherwise it will take off an unnecessary amount of dope. If that will not remove the dirt, then hot water and soap will do so, but, in that case, be sure to use soap having no alkali in it, as otherwise it may injure the fabric. Use the water sparingly, or it may get inside the planes and rust the internal bracing wires, or cause some of the wooden framework to swell.
The wheels of the undercarriage have a way of throwing up mud on to the lower surface. This should, if possible, be taken off while wet. It should never be scraped off when dry, as that may injure the fabric. If dry, then it should be moistened before being removed.
Measures should be taken to prevent dirt from collecting upon any part of the aeroplane, as, otherwise, excessive skin- friction will be produced with resultant loss of flight speed. The wires, being greasy, collect dirt very easily.
CONTROL CABLES.--After every flight the rigger should pass his hand over the control cables and carefully examine them near pulleys. Removal of grease may be necessary to make a close inspection possible. If only one strand is broken the wire should be replaced. Do not forget the aileron balance wire on the top surface.
Once a day try the tension of the control cables by smartly moving the control levers about as explained elsewhere.
WIRES.--All the wires should be kept well greased or oiled, and in the correct tension. When examining the wires, it is necessary to place the aeroplane on level ground, as otherwise it may be twisted, thus throwing some wires into undue tension and slackening others. The best way, if there is time, is to pack the machine up into its ``flying position.''
If you see a slack wire, do not jump to the conclusion that it must be tensioned. Perhaps its opposition wire is too tight, in which case slacken it, and possibly you will find that will tighten the slack wire.
Carefully examine all wires and their connections near the propeller, and be sure that they are snaked round with safety wire, so that the latter may keep them out of the way of the propeller if they come adrift.
The wires inside the fuselage should be cleaned and regreased about once a fortnight.
STRUTS AND SOCKETS.--These should be carefully examined to see if any splitting has occurred.
DISTORTION.--Carefully examine all surfaces, including the controlling surfaces, to see whether any distortion has occurred. If distortion can be corrected by the adjustment of wires, well and good; but if not, then some of the internal framework probably requires replacement.
ADJUSTMENTS.--Verify the angles of incidence; dihedral, and stagger, and the rigging position of the controlling- surfaces, as often as possible.
UNDERCARRIAGE.--Constantly examine the alignment and fittings of the undercarriage, and the condition of tyres and shock absorbers. The latter, when made of rubber, wear quickest underneath. Inspect axles and skids to see if there are