Module 17.7_b1_rev 00.pdf

Module 17 – PROPELLER Sub Module 17.7 – PROPELLER STORAGE AND PRESERVATION

CATEGORY B1– MECHANICAL

MODULE 17 SUB MODULE 17.7 PROPELLER STORAGE AND PRESERVATION

Rev. 00 Oct 2006

17.7 For Training Purposes Only

Module 17 – PROPELLER Sub Module 17.7 – PROPELLER STORAGE AND PRESERVATION

CATEGORY B1– MECHANICAL Contents

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STORAGE PROCEDURES..................................................... 2

Rev. 00 Oct 2006

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17.7

Module 17 – PROPELLER Sub Module 17.7 – PROPELLER STORAGE AND PRESERVATION

CATEGORY B1– MECHANICAL

“The training notes and diagrams are compiled by SriLankan Technical Training and although comprehensive in detail, they are intended for use only with a Course of instruction. When compiled, they are as up to date as possible, and amendments to the training notes and diagrams will NOT be issued”.

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17.7

Module 17 – PROPELLER Sub Module 17.7 – PROPELLER STORAGE AND PRESERVATION

CATEGORY B1– MECHANICAL

INSTALLED PROPELLERS

STORAGE PROCEDURES Propellers and their associated components contain numerous parts made from different materials. If they are improperly stored they can deteriorate to a stage where they are unable to perform their function efficiently, or can cause premature failure due to the erosion or corrosion of the component parts. The existing state of the propeller will dictate the method or procedures required, for example a propeller installed on a stored aircraft and a propeller disassembled and stored in its component parts in a crate, will call for different treatment.

Rev. 00 Oct 2006

When propellers are to remain installed but out of service for more than three months, the engine should be run and the propeller and its pitch change mechanism exercised to ensure a circulation of oil. If the engine cannot be run the propeller should be feathered and then unfeathered using the feathering pump, this exercising should if possible be carried out weekly. For periods of greater than three months the pitch change mechanism and its associated parts should be removed, draining off all the oil. The assembly should be flushed with an approved inhibiting oil and refitted. The following procedures should also be adopted in long term storage (over 3 months):-

Coat the surface of the blades with lanolin,

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Coat the spinner with lanolin,

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Treat all detachable or exposed parts, i.e., screw threads etc., with rust preventative compound,

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Smear exposed oil seals with silicone grease,

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Cover the propeller hub and operating mechanisms with waxed paper and tie into position,

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Frequently inspect all the components for corrosion and deterioration, paying particular attention to the blades and spinner.

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Module 17 – PROPELLER Sub Module 17.7 – PROPELLER STORAGE AND PRESERVATION

CATEGORY B1– MECHANICAL

jelly, and wrap individually in waxed paper or moisture vapour proof bags.

UNINSTALLED PROPELLERS Propellers if stored assembled should be kept in conditions that are warm, dry and dust free. Small two bladed propellers can be stored in racks above ground level to allow for the circulation of air. Three or more bladed propellers can be stored vertically on stands with their weight supported by a mandrel passing through the centre of the hub. For better protection from the elements the propeller can be dismantled, protected and stored in a specially prepared crate. For short term storage of an uninstalled propeller (under three months) the pitch change mechanism should be exercised prior to removal from the aircraft. Longer term storage of an assembled propeller involves methods which are similar to those used for long term storage whilst installed on the aircraft, except that any attachment fittings removed are to be treated with rust preventative compound and individually wrapped in waxed paper.

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Fit all blanking caps and covers.

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All exposed surfaces of the blade root bearings should be coated with mineral jelly and wrapped in waxed paper.

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Blades should be coated with lanolin then wrapped in grease proof paper.

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Electrical connections should be thoroughly cleaned and coated with petroleum jelly.

The packing crate should be clearly labelled with:1. Part number 2. Modification standard 3. Date put into store 4. Exercise date of bearings

Disassembled propellers, prior to packing, should be prepared as for long term storage installed with these extra precautions:-

Rust preventative should be applied to the exposed bore and hub splines.

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All exposed surfaces such as eye bolts, bolt heads, should be smeared with rust preventative.

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Immerse the pitch change cylinder in inhibiting oil, allow to drain, then wrap in waxed paper.

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Dip the pitch change piston complete with oil seals, oil tubes, hub retaining nut, cones and all other loose parts in mineral

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17.7

Module 17 – PROPELLER CATEGORY B1– MECHANICAL

Sub Module 17.7 – PROPELLER STORAGE AND PRESERVATION

PROPELLER BRAKE

Due to the heat produced by friction of the pads contacting the rotating disc, fusible plugs are incorporated in the body of the brake unit. These plugs will melt if the temperature of the brake is excessive, releasing the hydraulic pressure and rendering the brake ineffective.

Due to the free wheeling characteristics of turbine engines, (especially those of the free turbine type), when parked, the propeller can revolve at some speed even in relatively light winds. Because of the inertia stored in a propeller at engine shut down, the engine, and thus the propeller, will continue to rotate for some time. The propellers on the passenger access side of the aircraft can be a risk to disembarking passengers. A propeller brake is fitted to cut down the free wheel run down time of the engine.

To prevent overheating of the brake, manufacturers usually lay down maximum engine speeds at which the brake can be applied and brakes should never be applied at higher speeds than those specified.

The brake (Figure 17.115) is hydraulic in operation and fed from the aircraft's hydraulic system. When the brake is applied, the friction pads ' held in the calliper by pistons, are squeezed against the disc which is bolted to the drive shaft of the engine. The friction produced will retard the rotation of the drive shaft and thus the propeller, eventually bringing it to a halt and holding it stationary. The propeller brake lever is usually fitted into the centre console of the flight deck. It is usual to interconnect the propeller brake lever with the high pressure fuel cock, in such a way as to ensure that the fuel cock is selected OFF before the brake lever can be selected ON. This of course means that the brake cannot be applied while the engine is running. Some aircraft such as the ATR allow the RH engine to be run as an ‘APU’ . This is called ‘Hotel Mode’ and while in this mode the propeller brake is applied to prevent the propeller and its free power turbine from rotating. Power restriction in this mode apply to prevent damage to the turbine.

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Module 17 – PROPELLER Sub Module 17.7 – PROPELLER STORAGE AND PRESERVATION

CATEGORY B1– MECHANICAL

Fig 17.115

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17.7

Module 17 – PROPELLER Sub Module 17.7 – PROPELLER STORAGE AND PRESERVATION

CATEGORY B1– MECHANICAL Student Notes:

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