Bearing Number and Size, Twinstarr Rotor Head

[okikuma]

I'm curious. What is the bearing number and size that is used within the original Twinstarr Rotor Head?

Thank you,

Wayne

 

[MikeBoyette]

I'm curious. What is the bearing number and size that is used within the original Twinstarr Rotor Head>

Thank you,

Wayne

Since it was a bolt for bolt copy of my Dad’s rotor head I imagine it’s two 5206 main bearings. Don Farrington bought a double bearing head from Dad. Dad gave him a deal with hope that he would be supplying them in the future. A month later Don called him up said he was unhappy with it and would like his money back. Dad told him to ship it back and he would return his money. We got it back in a box. The head was completely take apart. The next fly-in we went to they had a duplicate claiming it was their own design.

 

[okikuma]

Wow Mike. Never read that story before. Not surprised though.

Somewhere within the dura matter between my ears, I seem to recall the Twinstarr Rotor Head bearing was larger than the typical MRC 5206 bearing, and a single bearing was used. I just cannot recall where I obtained that information.

Jerry Barnett used a larger, single MRC 5304 bearing in his spindle rotor head.

Wayne

The following Twinstarr Rotor Head photos are from Ed Newbold.

 

[okikuma]

Wow Mike. Never read that story before. Not surprised though.

Somewhere within the dura matter between my ears, I seem to recall the Twinstarr Rotor Head bearing was larger than the typical MRC 5206 bearing, and a single bearing was used. I just cannot recall where I obtained that information.

Jerry Barnett used a larger, single MRC 5304 bearing in his spindle rotor head.

Wayne

The following Twinstarr Rotor Head photos are from Ed Newbold.

Mike,

In retrospect, the bearing block does look tall enough to hold two stacked bearings.

Wayne

 

[MikeBoyette]

Mike,

In retrospect, the bearing block does look tall enough to hold two stacked bearings.

Wayne

Yeah that’s not the one they copied of Dad’s. The bearing block on dad’s is sealed. You can’t see the bearings as they are loaded from the bottom up.

 

[Brent Drake]

I'll get the number off my bearing when I get back to the hangar.

 

[okikuma]

I'll get the number off my bearing when I get back to the hangar.

No rush Brent.

I was pondering over why the majority of the rotor heads for heavier gyroplanes were designed with two MRC 5206 bearings and not designed with one larger, heavier duty bearing? I know the bearings used are off-the-self bearings for industrial applications. No harm in using what already has been engineered, proven with hundreds of thousands of hours of fail free operation, and is readily available for purchase.

Wayne

 

[Mayfield]

No rush Brent.

I was pondering over why the majority of the rotor heads for heavier gyroplanes were designed with two MRC 5206 bearings and not designed with one larger, heavier duty bearing?

Wayne

Hopefully Abid, or Roger or another engineer will chime in, but I suspect the stacked bearings help with the overturning loads at a lighter weight and cost than one larger bearing.

Jim

 

[Brent Drake]

No rush Brent.

I was pondering over why the majority of the rotor heads for heavier gyroplanes were designed with two MRC 5206 bearings and not designed with one larger, heavier duty bearing? I know the bearings used are off-the-self bearings for industrial applications. No harm in using what already has been engineered, proven with hundreds of thousands of hours of fail free operation, and is readily available for purchase.

Wayne

Mine has one larger one.

 

[okikuma]

During the history of gyroplane development here in the USA, we know that many other designers started by copying the Bensen off-set gimbal rotor head including the use of the MRC 5206 bearing. So granted, this is why the 5206 is the most common bearing used.

There are few that deviated following the crowd. As mentioned previously, Jerry Barnett used a single, larger bearing in his rotor head. Certainly Wing Commander Wallis would have chosen a different bearing used than the 5206 in his rotor heads. After first copying the RFD double bearing rotor head, Don Farrington came up with a different version of the rotor head using one singular and larger bearing.

It certainly would be very informative to have a complete, comparative list of the types and model numbers of bearings used in all of the manufactures of gyroplane rotor heads worldwide.

Wayne

 

[MikeBoyette]

Jim is correct. The double bearing was used to account for the over turning loads that higher undersling causes. Chuck Beaty calculated that most single bearing heads on heavy too places were inadequate and would eventually fail. We took a few of these heads apart at various fly-ins and they all had severe wear and one was only minutes from a catastrophic failure. Stacking the bearings is a very inexpensive and affective way to deal with the added load. It also makes the life virtually unlimited.

 

[Abid]

Hopefully Abid, or Roger or another engineer will chime in, but I suspect the stacked bearings help with the overturning loads at a lighter weight and cost than one larger bearing.

Jim

We use double row SKF bearing. We stack two of them (4 rows total). We do not use 5206 bearings.

Bearing Life is calculated by

L10 = (C/P)^e x 10^6 / 60 x N
where:

• C = Dynamic Capacity (dN or Lbs)
• P = Equivalent Bearing Load (N or Lbs)
• N = Rotating speed in RPM
• e = 3.0 for ball bearings, 10/3 for roller bearings
  
  
  All ball bearings, tapered roller bearings, and spherical roller bearings are capable of taking a significant axial thrust load. The “equivalent bearing load”, P, used in the rating life formula, needs to be calculated when combined radial and axial loads occur. This calculation can be somewhat complicated as it depends on the relative magnitudes of the radial and thrust loads to each other and the contact angle developed by the bearing.

 

[okikuma]

Hopefully Abid, or Roger or another engineer will chime in, but I suspect the stacked bearings help with the overturning loads at a lighter weight and cost than one larger bearing.

Jim

Jim is correct. The double bearing was used to account for the over turning loads that higher undersling causes. Chuck Beaty calculated that most single bearing heads on heavy too places were inadequate and would eventually fail. We took a few of these heads apart at various fly-ins and they all had severe wear and one was only minutes from a catastrophic failure. Stacking the bearings is a very inexpensive and affective way to deal with the added load. It also makes the life virtually unlimited.

We use double row SKF bearing. We stack two of them (4 rows total). We do not use 5206 bearings.

Bearing Life is calculated by

L10 = (C/P)^e x 10^6 / 60 x N
where:

• C = Dynamic Capacity (dN or Lbs)
• P = Equivalent Bearing Load (N or Lbs)
• N = Rotating speed in RPM
• e = 3.0 for ball bearings, 10/3 for roller bearings
  
  
  All ball bearings, tapered roller bearings, and spherical roller bearings are capable of taking a significant axial thrust load. The “equivalent bearing load”, P, used in the rating life formula, needs to be calculated when combined radial and axial loads occur. This calculation can be somewhat complicated as it depends on the relative magnitudes of the radial and thrust loads to each other and the contact angle developed by the bearing.

Jim, Mike, and Abid,

Once I visualized in my mind's eye the increased radial and axial loads upon a bearing as a result of taller teeter towers to accommodate greater undersling of larger rotors it now makes sense to me

Thank you guys.

Wayne.