wcfung

For the third time the socket collar screw (M2 x 12 mm) locking the main rotor housing and the main shaft has broken, leaving only a short length of threaded screw inside the hole. The third time it broke, there was virtually only a brief period of test fly (1 to 2 minutes), and the screw broke.

Can anyone tell what has gone wrong ? Is it a design problem ?

ahamay

I've seen this before and it can be very dangerous. Make sure your using a high quality bolt. If the hole through your mainshaft is slightly oversize it can cause the head block to twist a little and this will be putting extra pressure on the bolt and may cause it to sheer off. Hold the mainshaft and twist the headblock once you have it all done up, it should not rotate or have any play in it.

Hope that helps.

Jonesy

wcfung

Jonesy,

Thank you for your reply. I am aware of the size of the hole in relation to the bolt size. There is no play. Everything is original from Align..........the bolt, the main shaft and the rotor head. There is no wear nor tear on the hole of the rotor head. The hole through the main shaft is not worn as the metal of the main shaft is harder than the bolt.

I want to buy some high quality bolts, but it is not easy to come by as they are too small. Local hardware shops sell larger bolts. I doubt if hobby shops carry different grades than those supplied by Align.

pawraith

your talking about the jesus bolt right? i would say your probably torquing it down too much to start with. if your using any thread lock on it, you shouldnt have to crank down the torque on this bolt. just get it snug after applying the thread lock and it will last you for a very long time. good luck

Rafael23cc

My Feedback: (6)

I agree with the overtorque-ing of the bolt. Make sure you are using the correct type of bolt for the application. Not all bolts are made the same. If you continue having trouble, maybe a shouldered bolt with just a few threads at the tip will do the trick.

The bigger birds all use shouldered bolts for Jesus bolts. I don't recall what the 450 uses.

[link=http://www.google.com/images?hl=en&q=shouldered+bolt&gbv=2&gs_l=heirloom-hp.3.0.0l7j0i10l2j0.857.5250.0.6544.11.8.0.3.3.0.2 34.1340.0j7j1.8.0...0.0...1c.1.goupHNBxx9k&sa=X&oi=image_result_group&ei=XLs4UY-kOK290QGlvoHAAQ&ved=0CB4QsAQ]Google Image search for Shouldered Bolt[/link]

Rafael

wcfung

You are right. I replaced with another shoulder jesus bolt, and it works alright, cos I remember I did not torque it too tight.

Thank you.

wcfung

The 450 also uses shoulder jesus bolt as standard. May be over torquing is the culprit.