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
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