Rotor bearing question

[Not Yet]

A couple of stupid newbie questions. :confused:
I have never seen what type bearing is used or how it is installed for the main rotor bearing. Is it an angular contact single rob ball? A double row ball? I know it isn't a Timken because there isn't enough room for the required 2 bearings.
In one picture I saw a large screw (25mm?) that was going through the bearing. Didn’t see a nut so don’t know if it was a bolt.
I assume that either the bolt going through the teeter or the one going through the bearing is the one I saw referred to as the Jesus bolt. But which one?

David McComber

[Doug Riley]

It's a double-roll ball bearing. The thing through the center of the bearing is a 1/2" dia. AN-8 hex bolt. Formally referred to as the spindle bolt, this is the one most commonly called the Jesus bolt -- although actually there is a series of four single-bolt load paths in the standard Bensen-style gimbal rotor head. The other three in the series are usually 3/8" AN-6 hex bolts. Each of these acts as as a pivot and is therefore loaded in shear, while the spindle bolt is loaded in tension.

IOW, each of us flies about hanging off a 1/2" castle nut.

[gyropilot]

I have never seen what type bearing is used or how it is installed for the main rotor bearing. Is it an angular contact single rob ball? A double row ball? I know it isn't a Timken because there isn't enough room for the required 2 bearings.David,

Check out this post (and the thread) on rotor head bearings:

http://www.rotaryforum.com/forum/showthread.php?p=33260#post33260

Regards,

John L.

[Not Yet]

Thanks Doug & John
I have read most of this forum, but not the Piloting Technique / Accident Discussions, maybe I should check it out. I’m particularly interested in rotor hub designs. A 3 blade would be nice? Eliminate some of the vibration?

[Victor Duarte]

David, if you want , there is a thread about the rotor design, the 3 blades thing has been discussed.. if you want to talk about that , wellcome

[gyropilot]

A 3 blade would be nice? Eliminate some of the vibration?Possibly... but with a 3-blade rotor you gain a whole lot of other problems. A 2-blade teetering rotor system is cheapest and most beautifully simple way to get a rotorcraft in the air. Any vibration issues can be dealt with through rotor head isolation from the airframe

Regards,

John L..

[Doug Riley]

Cost, weight, multiple failure modes and ground resonance are some of the issues that crop up with a 3-blade system. For small gyros, the cure is likely worse than the complaint.

[quadrirotor]

A double teetering rotor is better! (four blades)

[skyguynca]

My thoughts exactly Andre'........oh and I worked out the scissor effect on the rotor system, no lead/lag hinges at all..........oh what a work of art, but that is a entirely different thread!!!!!!!!!!!!!

[quadrirotor]

Yes David, it could be a good idea...The Pitbull enterprise has worked this idea yet...

[Victor Duarte]

Hi david >>> you post your progresses ??? ;) :D
thanks

[Not Yet]

Thanks one and all for your comments. :)
My thoughts on the 3 bladed rotors are that it would not be susceptible to blade flapping. With the teeter 2 blades the center of gravity of the blades and the pivot point are very close to each other. In a rotor that has flapping blades instead of teeter blades there is at least 5’ between these centers. This is a very strong dampening effect on any disturbances at lower RRPM.
The ability to fold a 30’ rotor to les then 17’ for transport and storage would be a big plus.
My hub would have lead lag and flapping hinges, but no pitch control.
I don’t know anything about Ground resonance, other then from what I read; it is a landing gear problem?
I’m working 60 hours a week so have very little time for CAD. When I get something worth showing I will post it.

David McComber

[MichaelBurton]

Not just a landing gear problem. The resonance is setup by having the blades out of ballance. This can also happen as the rotor is brought to flying speed when the blades have not been distributed evenly, or if there is contamination, or damage or...

[skyguynca]

New Thread for the 4 blade rotor........it is so sweet and yes it is going to work

[birdy]

Doug said,

" each of us flies about hanging off a 1/2" castle nut."

That may scare some of the ignorant Doug,but if you tell them that the "nut" on the other end of the control systm is supposed to be in control of the machine it'll realy scare 'm off. :p :D
People worry bout the jesus bolt fail'n,it's more likely the "jesus nut" will fail first. ;)

[Brian Jackson]

...it's more likely the "jesus nut" will fail first. ;)
Is that anything like a "Jesus Freak?" :D I will admit, though, I pray before every chopper flight we do, for the same reason I get nervous on amusement park rides... I'm more paranoid about the bolt inspector with a hangover than I am of the thrill of the ride!

[Chopper Reid]

Nothing wrong with praying Roto.

[Not Yet]

All right already, so ground resonance is more of a problem then I thought. ;)
So which is more likely to happen, ground resonance, of a 3-blade, or blade banging from a 2-blade teeter? As I see it they will both destroy your machine. Which is easer to control?
My main reason for choosing a 3-blade over a 4-blade dabble teeter rooter was the ability to make it folding. I now have an idea to fold the 4-blade.
So I guess I will skip the 3-blade for now.

[skyguynca]

David the dynamics of a 4 blade while being safer in resonance still have a lot of problems to work out. There is another thread for that in the builders threads were we have been hashing it out.