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  • Hi, Steve: There have been a few gyro designs (mostly welded-tube frames but some others as well) that use rigid masts. Bensen warned about excessively stiff masts over and over.

    The rigid mast violates a a design rule that goes all the way back to the development of the very first successful 2-blade rotor, by Arthur Young for Bell Helicopter (mid-1940's). Young found that underslinging the teeter hinge helps, but that the real secret to preventing excessive vibes is to make the mast "soft." Young did it by making the engine-transmission unit one rigid assembly, but mounting the whole assembly on soft rubber engine mounts. Bell 2-blade helos are built this way, as are Robinsons.

    The Barnett and Twinstarr just ignore the issue. People put up with the vibes and just watch for cracks.

    A "slider" head helps, though in my experience it's not a complete solution. Chuck Beaty came up with the slider concept, and Ernie Boyette modified it and put it into production. Some others have copied the idea.

    I wouldn't put up with the vibes, and the possibility of cracking of the frame, blades, or whatever else gives out first!

    Doug
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    GyroCraft
    Doug,

    Thank-you for the quick response. This info you provided was about what I thought. At the same time, I thought surely Don Farrington knew enough to not have a rigid mast. That's what led to some confusion. I do recall my days of flying a Bell 206L3 that part of the pre-flight was to grab the mast and give it a shake to make sure it would move laterally. It makes sense. Is there any rule of thumb as to mast dimensions, wall thickness. length from mounting point, etc to best ensure proper "softness" ?

    Thanks again....

    Steve
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