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A vertical vibration developed on one of my blades that was caused by bad thrust bearings that had less than 50 hours on them. As it turned out, they were not getting any lubrication as the lube fitting was blocked.

Steve Chenoweth

Hello Steve and other Brantly operators and maintainers,
When thrust bearings are first installed, they shoud be pre-packed with grease (most everyone knows this). However, once installed in the blade and after the system is put back on the helicopter, each blade should be greased (about 10 shots each blade, listen and feel if they are accepting the grease) and then ground run and greased again until all three blades are slinging (from the inboard area of the yoke) about the same amount of grease.
Always add the same amount of grease to each blade to keep the balance the same. You cannot over grease the system when first installing/greasing the same, and ground runs (with or without the outboard blades) will force all of the air pockets out of the bearings and help ensure that adequate grease is present. This method can be done at any time if one is doubting how much grease is getting to the bearings. If this is not done, odds are good that one or more bearings will wear out prematurely due to lack of lubrication.
General note on Brantly's, when "hops" or vertical vibrations occur, a minimal amount of tracking should fix the situation, if NOT, then bearings are the only problem, and you can follow the maintenance manual guidelines for rotating the bearings/blades to get more life out of the bearings before replacement (P.S. DO NOT try to tab a blade to fix a "hop"). If all is done properly, things should last a long time. My set of bearings have over 450 hours, and I haven't ever changed the track of any blade, and I don't get carried away with greasing at the 25/50/100 time periods (this cuts down on dirt accumulation). Have fun, talk back with questions or comments. Kevin

Hi Kevin,

When I bought my machine it had 215 hours on it since 1200 hour in 1997 with all bearings replaced with new. It was balanced with a Chadwick 2000 down to .01 and was very smooth. I have put about 70 hours on it since buying it 10 months ago and it has developed a vertical hop (not too bad) with a 3-per cycle. Visually, you can see the track is off on one of the blades. It has just recently developed this hop in the last 20 hours. I have greased it per the manual every 25 hours. The collective is very smooth throughout the full range; although, it does tend to "seek" a little when friction is let off. Overall, it is still pretty darn smooth, I just like it perfect so I want to take action. A previous Brantly employee recommends tabbing a blade, but I see you don't think that is a good idea. Of course, I wouldn't do it myself, but either way I don't see a reason to tab one when the change can be made in a PC link. Does your experience support a slight track change on one of the blades will cure the problem? Everything else is in such good order that I hate to change anything. Autorotation RPM's are perfect and the vibration is acceptable; however, this vertical hop can be seen and felt. What is the best way to determine the low blade? In other helicopters I have used the stick method. I seem to remember Cy Russum telling me to use reflective tape on the blades and a flashlight. Thanks for your contributions in this forum.

Todd

Hello Tod,
You are right in my being against tabbing. The best way to look at it is that if everything was tracked and balanced at one point in time, what has ocurred over the last 100 or 500 hours to change the aero-dynamic shape of the blade and change its track? Basically, nothing. Tabbing is used when the blade is first made, and to provide all of the blades with a similar aero-dynamic pitching moment, which should provide a pre-load on the collective (slight downward movement with no friction). With this preloading, tight linkages & swashplate, and some friction, feedback from the blades should be non-existent. Changes in the flight characteristics means bearings are wearing or something is preventing the blade from moving to where it is being asked to go.
The Chadwick systems are great, but remember to keep the problem solving to the simpliest. In 1959, Mr. Brantly did not have a chadwick. The system was designed to need very little adjustment. The inboard and outboard systems were dynamically balanced, bearings "packed with slinging grease", linkages set to nominal settings, and then checked and fine tuned with the tracking tips and flag. This results in minimal maintenance and lubrication of the system. My ship here has 450 hours with no changes in track being made. Let me know your thoughts or comments. Kevin

I just got N888CF back from being worked on by Harold Jenkins who did a great job in getting my vertical hop out. He indicated that the Aeroshell 14 is not the best choice for thrust bearings, even though this is what is recommended in the service manual. He recommends Mystik JT-6. He said the Aeroshell 14 gets too thin, especially in the summer months. He also indicated that the two can be mixed if you want to add the JT-6.