four tube pylon mast?

WHY

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Hello to all with the Twin star.

As I intend to use a pylon type mast on my tractor design, I was wondering what and how the rotor shake is with a pylon type support structure, since this would seem to be very strong and "ridgid".

Do you use a "slider" head or just how do you compensate for the 2 per rev pulsing of the blades?

Tony
 

mcbirdman

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On one of the first designs (Little Wing) Ron used a rubber dougnut at each of the four ends I believe. He then went to 2 donuts at the bottom of the rear support and most recently having 2 doughnuts sandwiched together with a metal washer seperating the two, but mounted in a short tube. I remember him saying he actually liked the pylon better than the mast but since most people are familiar with the alluminum tube he incorporated it into subsequent designs. Hope that helps, jtm
 

C. Beaty

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A 4-tube pylon is a tetrahedron. It is stiff only for loads applied at the apex (or projected apex) in which case all tubes are in compression or tension.

If the load is applied at any place but the apex, we simply have the stiffness of 4 tubes in bending.
 

Doug Riley

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...Assuming it isn't also triangulated. Designs such as the Barnett and Bandit are.

A gyro pilot from New York related a very hair-raising in-flight failure that likely resulted from this "pulsing" applied to a rigid pylon. Two of the four top tubes broke away from the rotor head while he was flying his Barnett. Obviously he got down, but he was lucky.
 

WHY

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Hi Doug

This is exactally the kind of concern that I am having, actually my system will have two tubes in front with a short longitudinal tube going back to a single 2x2 vertical in back, so I am really in new territory. The two tubes in front will be 4130 and form a triangle rising to a single short 2x2 aluminum longitudinal tube of about 1 foot in length going back to a single 2x2 aluminum vertical at the back of the cockpit with the cheek plates fastening to the longitudinal tube.

Tony
 

EI-GYRO

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I believe the McCandless design had this problem.
I think the PFA removed it from the list for this reason.

The Twinstarr with the Averso head and rotors, which I believe is
a slider head, has almost no perceptible vibration.
 

WHY

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Hi Fergus

Is the Averso head and rotor mainly a European design and manufacture ?

Tony
 

Doug Riley

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Tony, the assembly you're describing doesn't sound rigid to me -- at least it isn't if there is no diagonal running from the bases of the forward "down tubes" to the rear end of the short longitudinal piece up top.

I don't see any down side to using a slider or other isolating mechanism, though, except a trivial amount of weight.
 

barnstorm2

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I believe the McCandless design had this problem.
I think the PFA removed it from the list for this reason.

The Twinstarr with the Averso head and rotors, which I believe is
a slider head, has almost no perceptible vibration.

Ahh, that reminds me I need to add Averso Info to the Twinstarr web page.

Do you have any close photos of this head on a Twinstarr?
 
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