Helicopter Gear Lubricating Problems

Since the gearing in question is high speed, reference to a previous section, which deals with problems in lubricating high speed gears, may indicate similar problems. Also an investigation by peck et al.^39 is an aid in this regard. Under high speed conditions, good results were obtained by lubricating with a “jet hitting the center of the gear tooth on the outgoing side of the tooth mesh”. Also baffles were used to prevent swirling of the oil with resulting heating. Likewise, baffles were necessary to direct oil to the suction lines “without being picked up by high velocity airflow's and whirled around”. The characteristics of suitable oil for lubrication of highly loaded helicopter transmission, turbo-prop reduction gears, variable pitch propeller gearing etc., are similar to those required in aircraft turbine oils. Therefore, if lubricating problems occur, they will be similar in both instances.

Air-Oil Devices for Lubricating Gears

By injecting or pumping oil drop-by drop into an air stream the air will carry the lubricant to the points of application, such as gears. A similar mixture can be obtained by the aspiratory action of compressed air. With such systems, provision can be made to start the oil flow with the start of the machine and stop it when the gears stop. The delivery is positive and there is little chance for contamination because the gear box is under some pressure which prevents entry of dust. Also,rate of oil feed can be regulated.

On the negative side, it is necessary to provide compressed air and a considerable flow of air escapes through the vent of the gear case. While this air will have some cooling value, it may carry some oil mist. The oil is used on a once through basis and provision has to be made to drain the sump of the gear case at times.

Adhesion of gear and transmission lubricants

Adhesion is a comparative term, and what is in mind in this case is stickiness which will insure that the lubricant will resist the action of centrifugal force and thus remain on the gear teeth. This quality is most important in the case of open gears. Desirable adhesion is obtained by the use of high molecular weight and high softening point compounds. That is, asphaltic residua, resins, and polymers are largely used for the purpose. Which this type of product is desirable for open gears, it is not suitable for most gear sets because of its high fluid friction and poor cooling effect.