Teeter bolt sheer strength

Donnier

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Do any of you people know what the sheer strength is for the 3/8" AN teeter bolt? Seems like an awful thin bolt to hang my big behind on.
 

fara

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Roughly 20000 pounds in double sheer to break
 

eddie

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Donnier if the teeter bolt should break you are already having bigger problems than the teeter bolt shearing off.

I looked at your profile happy birthday Thursday the 22th,we are same age.
 

eddie

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JMS I have never heard of a teeter bolt breaking,but that doesn't mean they haven't ,perhaps someone else knows of a breakage ?
 

Uncle Willie

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20,000lbs means you may need to pull over 20Gs to shear the bolt.
It is difficult to pull even 2Gs in a hard turn.
The Rotor Blades tend to catastrophically fold up long before the teeter bolt even starts to yield.

It would be unusual for a Teeter bolt to shear even in a crash.
They are way, Way! over engineered. As they should be!
 

fara

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Teeter bolt should not completely sheer. If its an AN6 bolt, it will bend (yield) much before that and that is what you want.
The only way it may sheer is due to fatigue and incorrect installation and even that will take a very long time. But if you have its threads in one of the sheer spots (only one thread is allowed to be inside in sheer), then the fatigue that will set in over hundreds of hours of rotor head vibration may act as a knife and cut the threads. That would take may be 800 hours ... So if you simply change it say every 400 hours, you will be just fine even if you don't know what you are doing. We used AN6 bolts in trikes (Jesus bolt, basically same application as teeter bolt) and I simulated its sheer strength in double sheer ... We still asked people to change it every 300 hours because we did not have bearings there and because the bolt was the bearing surface, also we were doing a bit of CYA in a SLSA maintenance manual otherwise it could technically last the life of the aircraft.
To this day I do not know of any trike even crashed one ever having AN6 bolt there completely sheer off. Things around it made of Aluminum generally come apart but not the bolt. The SAE bolts are a little different and slightly more brittle. Many Euro model rotors will use a M12 usually Class 10.9 bolts. Those are harder but also close to 1/2 inch diameter so their sheer strength is a level above. Incorrect Hydrogen De-embrittlement on plated bolts would be one reason a plated bolt of any kind can sheer off much before its time. This would be a concern when buying a SAE bolt. That is why its important to use either Black Oxide bolt with lithium grease or plated M12 bolt from a reputable manufacturer.
 
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Gyro28866

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20,000lbs means you may need to pull over 20Gs to shear the bolt.
It is difficult to pull even 2Gs in a hard turn.

It is my understanding that a rotorcraft will only pull about 2 1/2 G's and then it just mushes through.
 

Doug Riley

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I've been hanging around gyros since 1969. I've never heard of a teeter bolt shearing off. Ditto the two pivot bolts in the gimbal head which, of course, are the same diameter and each carry the same load as the teeter.

Once or twice, someone has OMITTED the teeter bolt when setting up a gyro, resulting in the rotor flying away as soon as it built some RPM on takeoff. Of course, the gyro never gets off the ground in these situations.

FW planes, incidentally, have lots of "Jesus bolts," they just are generally better hidden than those on rotorcraft. Think of what happens if one or other of the bolts at each end of a Cessna 172 wing strut sheared. But they don't.
 

Alan_Cheatham

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Recall that Christine had a pitch pivot bolt fatigue and break in half on her Butterfly.

https://www.rotaryforum.com/forum/kit-makers-manufacturers/the-butterfly/38525-safety-alert/page2
 

JohnyWalter

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Would appreciate it if you can inform me of the breaking load of a grade 8 – 3/8 teeter by 10″ bolt. This bolt will be inserted horizontally one on top of each another spaced 8″ apart. load will be in the center of bolt with 4″ of downward vertical pressure supported by 3″ on each end. Basically bolt is going thru 2- 2 by twelves on each end that equals 3″ on each end. A 2 by 4 -3-1/2″ is in between the 4- 2 by 12s. Sorry for my long question. I guess im asking what would it take to snap the bolt in half. Respectfully Jon
 
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Vance

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Based on a quick search of the internet it appears to me a 3/8 inch grade eight bolt has a single shear strength of around 9,900 pounds.

In my opinion a grade eight bolt is not the best choice for a teeter bolt.

I use an AN-6 bolt on the teeter that appears to me based on my limited information to have a single shear strength of a little over 10,000 pounds.

In my opinion teeter bolt is in double shear.

If you are building a gyroplane from plans I feel it is best to use the hardware called out in the plans.

If you are designing a gyroplane I feel there is a lot to be learned about hardware before making a selection.
 

JohnyWalter

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Vance;n1134070 said:
Based on a quick search of the internet it appears to me a 3/8 inch grade eight bolt has a single shear strength of around 9,900 pounds.

In my opinion a grade eight bolt is not the best choice for a teeter bolt.

I use an AN-6 bolt on the teeter that appears to me based on my limited information to have a single shear strength of a little over 10,000 pounds.

In my opinion teeter bolt is in double shear.

If you are building a gyroplane from plans I feel it is best to use the hardware called out in the plans.

If you are designing a gyroplane I feel there is a lot to be learned about hardware before making a selection.

Many thanks,useful respond.Very appreciated!
 

Jazzenjohn

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Christine Toev's pitch pivot bolt on her Aurora is the only one of the 4 "Jesus" bolts I know to have failed. I know of at least 2 crashes because the rotor pivot bolt came loose due to a too large washer contacting the rotor bearing housing. I believe Christines breakage was because of the powerful Metro launch prerotator and a defective pully putting huge loads on the bolt, eventually breaking it. .
 

Doug Riley

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The strength we've been discussing is shear ("sheer" refers to women's stockings, a different topic entirely). For a part to be loaded in shear, the load and the (opposing) reaction to the load must be right next to each other -- just as the two blades of a pair of scissors (or shears) come together, with no space between them.

The problem with the Butterfly Metro-launch system on Chris's gyro (and others with the same design) is that there's a tendency for the loads NOT to be pure shear. The load and the reaction to it are separated by a measurable distance. This puts the pivot bolt in bending, instead of shear. It's much, much weaker in bending than in shear. We don't want ANY of the three 3/8" horizontal Jesus bolts (two pivots plus teeter) to end up loaded in bending to any significant extent.

IIR, the Butterfly head can be adjusted to avoid this unhealthy situation. I don't have one handy to be more specific, though.
 
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