rgmwa Posted June 11, 2015 Posted June 11, 2015 A worthwhile read. http://www.casa.gov.au/wcmswr/_assets/main/airworth/awb/55/010.pdf rgmwa 1
K-man Posted June 17, 2015 Posted June 17, 2015 We had the threaded rod on our horizontal stabiliser trim tab fail in flight. Fortunately, I was in the circuit at the time and could land without further damage. Cause of the incident was fatigue in the threaded rod. Using threaded rod means that the thickness of the rod is reduced by nearly 50%. To compound the problem the rod has two 90 degree bends putting further strain on the rod at those points. That has to be an accident waiting to happen. The rod was replaced by rod with thread at each end. 1
dazza 38 Posted June 17, 2015 Posted June 17, 2015 We had the threaded rod on our horizontal stabiliser trim tab fail in flight. Fortunately, I was in the circuit at the time and could land without further damage. Cause of the incident was fatigue in the threaded rod. Using threaded rod means that the thickness of the rod is reduced by nearly 50%. To compound the problem the rod has two 90 degree bends putting further strain on the rod at those points. That has to be an accident waiting to happen.The rod was replaced by rod with thread at each end. Jesus, we're glad you're OK.
dutchroll Posted June 17, 2015 Posted June 17, 2015 When I was in the RAAF we had an incident on a C130 where a miscommunication resulted in a crew member mistakenly thinking he was authorised to disconnect a malfunctioning aileron trim tab to get the aircraft home on a ferry flight (thus allowing the aileron tab to "drift" in the airflow). Severe vibration started throughout the whole airframe as the aircraft accelerated after takeoff. They slowed down, reducing the vibration enough for them to return to the departure field. Could easily have resulted in the loss of the aircraft. The engineering staff had thought he was going to simply disconnect the electrical side, leaving it locked inoperative in the neutral position. He thought they meant disconnect the tab physically from its trim motor. Safety briefings on flutter, as well as clear communication between crews and engineering, were the order of the day for a while after that! 1 1
fly_tornado Posted June 17, 2015 Posted June 17, 2015 P51s are famous for losing trim tabs http://www.warbird.com/voodoo.html
dutchroll Posted June 17, 2015 Posted June 17, 2015 Racing modified P-51s.........such a waste of a beautiful warbird. 1 1
fly_tornado Posted June 17, 2015 Posted June 17, 2015 as opposed to being buried away in a hangar flown once a decade like the rest? 1
K-man Posted June 17, 2015 Posted June 17, 2015 Jesus, we're glad you're OK. Thank you. Owning your own plane means that you know everything that goes wrong. I'm not sure if that is a good thing or a bad thing but it certainly is character building.
facthunter Posted June 18, 2015 Posted June 18, 2015 Putting bends in a threaded rod is a bit "OFF" in a critical part. A crack probably started at the time of bending. Nev 2
Downunder Posted June 18, 2015 Posted June 18, 2015 I've bent plenty of threaded rod (none for a/c) and they all crack on the bends immediately or eventually to some degree. Even larger radiuses will crack. The bottom of any thread is a high stress point primed for cracking. 1
Guest Andys@coffs Posted June 18, 2015 Posted June 18, 2015 So, not a mech eng at all but.....can you buy or make on a mill real quick, a small metal cube with threads cut 90degrees apart to take the now broken in two rod (after you cut the bent portion away) ....I doubt the weight gain would be heaps and add a locking nut, or loctite probably end up with something that achieves the same outcome but wont crack....that said if its at the very end of the aircraft each gram added has a multiplier effect to offset up the front Andy
facthunter Posted June 18, 2015 Posted June 18, 2015 Never put a bending load on a threaded piece. (If you can avoid it) Nev
Ultralights Posted June 18, 2015 Posted June 18, 2015 The elevator trim tab linkage bolt after 1000Hrs. showing considerable signs of wear. dont forget, the test aircraft in the story above was flying above VNE, deliberately to test for flutter. its a good reason to respect that red on the ASI. 1
facthunter Posted June 18, 2015 Posted June 18, 2015 Check free play in your controls before flight. Nev 1
K-man Posted June 18, 2015 Posted June 18, 2015 So, not a mech eng at all but.....can you buy or make on a mill real quick, a small metal cube with threads cut 90degrees apart to take the now broken in two rod (after you cut the bent portion away) ....I doubt the weight gain would be heaps and add a locking nut, or loctite probably end up with something that achieves the same outcome but wont crack....that said if its at the very end of the aircraft each gram added has a multiplier effect to offset up the frontAndy Nah. We got home by a bit of judicious welding but the next day it was consigned to land fill, replaced with a solid rod threaded at each end.
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