Module 17 (Propeller) Sub Module17.7 (Propeller Storage and Preservation)

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Module 17 - PROPELLER

Category – Aerospace

Sub Module 17.7 - Propeller Storage and Preservation

MODULE 17 Sub Module 17.7 17.7

PROPELLER STORAGE AND PRESERVATION

For Training Purpose Only

ISO 9001:2008 Certified

17.7

CAA Approval No: HQCAA/2231/44/AW Dated: 11 th Sept, 09

Rev. 00 Nov 2009

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Contents

STORAGE PROCEDURES ----------------------------------------------------------- 1 INSTALLED PROPELLERS----------------------------------------------------------- 1 UNINSTALLED PROPELLERS ------------------------------------------------------ 1 PROPELLER BRAKE------------------------------------------------------------------ 2



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STORAGE PROCEDURES

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

Propellers and their accessories contain various parts made from different materials. If they are inappropriately stored they can deteriorate to a stage where they are incapable to perform their function efficiently, or can cause untimely failure due to the erosion or corrosion of the component parts. The existing state of the propeller will dictate the method of storage required, for example a propeller installed on a stored aircraft and a propeller disassembled and stored in its component parts in a crate, will require for different treatment. INSTALLED PROPELLERS

While 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 is exercised to ensure a circulation of oil. If the engine cannot be run the propeller should be feathered and followed by unfeathered by feathering pump, this exercise should be carried out weekly (if possible). 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 approved inhibiting oil and refitted. The following procedures \ should be adopted in over 3 months storage:- Coat the surface of the blades with lanolin, - Coat the spinner with lanolin, - Spread exposed oil seals with silicone grease,

- Treat all detachable or exposed parts, i.e., screw threads etc., with rust preventative compound, - Frequently inspect all the components for corrosion and deterioration, paying specific attention to the blades and spinner. 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 air circulation. Three or more bladed propellers can be stored vertically on stands 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. Under three months term storage of an uninstalled propeller, the pitch change mechanism should be carried out 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. Disassembled propellers, prior to packing, should be prepared for long term storage installed with following safety measures:For Training Purpose Only


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- Dip the pitch change cylinder in inhibiting oil, allow draining then wrapping in waxed paper. - All exposed surfaces such as eye bolts, bolt heads, should be smeared with rust preventative. - Rust preventative should be applied to the exposed bore and hub splines. - Dip the pitch change piston complete with oil seals, oil tubes, hub retaining nut, cones and all other loose parts in mineral jelly, and wrap individually in waxed paper or moisture vapor proof bags. - Electrical connections should be thoroughly cleaned and coated with petroleum jelly. - Fit all blanking caps and covers. - Blades should be coated with lanolin then wrapped in grease proof paper. - All exposed surfaces of the blade root bearings should be coated with mineral jelly and wrapped in waxed paper. The packing crate should be labeled with:1. 2. 3. 4.

Part number Date put into store Exercise date of bearings Modification standard

PROPELLER BRAKE

When parked, the propeller can revolve at some speed even in Moderate wind. It happens because of the free wheeling characteristics of turbine engines (free turbine type), Due to inertia stored in a propeller at engine shut down it will continue to rotate for a while. The propellers on the passenger access side of the aircraft can be a risk to disembark passengers. A propeller brake is fitted to drop the free wheel run of the engine. The brake (Figure 17.115) is hydraulic and is fed from the aircraft's hydraulic system. When the brake is applied, the friction pads ' held in the caliper by pistons, are squeezed against the disc which is bolted to the drive shaft of the engine. The friction produced slows down the rotation of the drive shaft and consequently causing the propeller to a halt. The propeller brake lever is generally fitted into the centre console of the flight deck. It is usually interconnected with the propeller brake lever with the high pressure fuel cock, so that to ensure the fuel cock is selected OFF before the brake lever can be selected ON. It means that the brake cannot be applied while the engine is running. RH engine of some aircraft such as the ATR allow 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. Fusible plugs are incorporated in the body of the brake unit, because of the heat produced by friction of the pads contacting For Training Purpose Only


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Module 17 -


PROPELLER


the rotating disc. These plugs melt in case of extreme, releasing the hydraulic pressure and turn brake into ineffective. To prevent overheating condition of the brake, manufacturers lay down maximum engine speeds at which the brake can be applied. Brakes should never be applied at higher speeds than mentioned.

Fig 17.115



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Module 17 (Propeller) Sub Module17.7 (Propeller Storage and Preservation)

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