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Teeter bolt sheer strength

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  • Teeter bolt sheer strength

    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.

  • #2
    Roughly 20000 pounds in double sheer to break

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    • #3
      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.
      Best Regards,
      Eddie Sigman,Polvadera,nm
      (575) 835-4921

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      • #4
        Thanks for the info. 20,000 lbs, WOW! And best regards to you too Eddie.

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        • #5
          I've wondered about the teeter bolt, too. What might cause it to break? How often has that occurred?

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          • #6
            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 ?
            Best Regards,
            Eddie Sigman,Polvadera,nm
            (575) 835-4921

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            • #7
              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!

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              • #8
                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.
                Last edited by fara; 02-18-2018, 08:41 PM.

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                • #9
                  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.
                  David McCutchen
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                  • #10
                    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.

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                    • #11
                      Recall that Christine had a pitch pivot bolt fatigue and break in half on her Butterfly.

                      https://www.rotaryforum.com/forum/ki...ty-alert/page2

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                      • #12
                        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
                        Last edited by JohnyWalter; 05-31-2018, 01:29 AM.

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                        • #13
                          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.
                          Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

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                          • #14
                            Originally posted by Vance View Post
                            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!

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                            • #15
                              Technically a 1/4 inch bolt would be plenty, so feel good about the 3/8!!!

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