Regarding having to check the balance of a rotor system due to say an overnight change or change from one flight to another it would require some investigation to determine the cause before hooking up the Chadwick system. Depending on the weather in your area the blades can pick up water during a rainstorm and if it freezes during the night the blades depending on their position relative to the rain direction can pick up varying amounts of weight. Blades in most cases are mass balanced to ¼” ounce and any additional weight no matter how much, can effect the balance of the rotor system. If you go directly to the electronic balance you can compensate for the weight change but the next day when it warms up the water will be expelled and then you have to go back to the balance procedures. That is why I would recommend the use of blade sleeves in rainy or freezing weather or at the least, tie down tip boots. If the Hughes rotorhead is that sensitive to mass balance then the same problems with freezing water can manifest itself causing a mass imbalance.
Dampers can at times cause a shuffle due to the imbalance of the rotor disc. They can as described above cause a memorable ride when they seize. In the described case on the S 61 it would require a dual failure to result in the described effect. On a 300C, a damper was improperly assembled and it caused the helicopter to crash killing the pilot. There is another problem lurking in the wings for the operators/pilots of the later Hughes / MD helicopters that have elastomeric dampers. This also includes the AH-64.
When the elastomeric dampers are selected to go onto a rotorhead they must test to within 5% total deviation between the damper that tests highest in resistance to stretch and compression to the one that tests lowest to the same tests. If one or more of the dampers exceed this 5% limit then you can get into (are you ready for this) air resonance.
Air resonance like ground resonance will have the same effect. It can tear you apart. Herein lies the lie about elastomeric elements. If you find that there is sufficient deterioration in an elastomeric element requiring change you should check the new one against the ones already installed on the rotorhead. That means that each operator must have the machine to perform the tests. I do not know if this is the case because I left the Apache program many years ago.
In order to properly perform the test the elements must be removed from the rotorhead and installed in the machine. So much for an improvement of Maintainability when using elastomerics as opposed to metal bearings and viscous dampers. If in the performance of the test, you find that you can’t match the new one to the old ones removed from the head you will have to, either place the old ones on the shelf and start with all new ones, and when you accumulate sufficient dampers on the shelf you can run the test and select those dampers that comply with the stretch/compression limits and the next time a damper goes bad you install the newly selected set on the rotorhead and start over again. This will have limits as some of the dampers will reach mandatory retirement before others in the same set and you must start over again. I don’t know if this is covered in the maintenance manual. I got this straight from Lord over fifteen years ago.
On a fully articulated rotorhead you can test for a bad damper by bringing the helicopter to a hover and rapidly move the cyclic in a circular motion in the same direction as blade rotation. The introduction of cyclic in this manner will cause the disc to tip all around the tip path and cause the blades to continuously lead and lag. This will give an indication of bad damper, as it will cause the disc to shuffle. The rest is up to the mechanics to determine which damper is bad.
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The Cat
[This message has been edited by Lu Zuckerman (edited 04 February 2001).]
[This message has been edited by Lu Zuckerman (edited 04 February 2001).]
[This message has been edited by Lu Zuckerman (edited 04 February 2001).]
[This message has been edited by Lu Zuckerman (edited 04 February 2001).]