Broken T/R Shaft
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Broken T/R Shaft
R44 Tail Rotor Shaft.
10/07/2003
The tail rotor shaft on a R44 severed in half, just behind the hanging bearing, located about half way up the tail. Fortunately the Engineer/Pilot managed to get it on the ground. The flight was after the owner had complained of poor handling and took the ship in for an inspection.
The obvious “Tail Rotor Seizure” was initially suspected, but that was found to be okay (so far).
The AAIB representative was with the ship yesterday, and is taking the parts to Farnborough for further investigation.
Not an obvious fault, which could have been spotted on the Check A.
Anyone have any thoughts as to why this may have happened?
10/07/2003
The tail rotor shaft on a R44 severed in half, just behind the hanging bearing, located about half way up the tail. Fortunately the Engineer/Pilot managed to get it on the ground. The flight was after the owner had complained of poor handling and took the ship in for an inspection.
The obvious “Tail Rotor Seizure” was initially suspected, but that was found to be okay (so far).
The AAIB representative was with the ship yesterday, and is taking the parts to Farnborough for further investigation.
Not an obvious fault, which could have been spotted on the Check A.
Anyone have any thoughts as to why this may have happened?
Iconoclast
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First response most likely wrong.
If the fracture is of a torsional nature or if it stress related then I couldn’t offer much. However if the crack was circumfrential in nature and very narrow it could have been some dangling lock wire or some FOD in the tail cone.
We had a Bell AH1-J on a test flight and the pilot had it in a low hover. Suddenly the helicopter started to spin and the pilot lowered collective and when the helicopter hit the ground it rolled.
The pilot suffered a broken back and the Iranian student pilot was pretty well banged up.
The problem was traced to a small piece of rubber that kept faying surfaces from abrading on each other. The helicopter had about six hours on the clock. The tail rotor drive shaft had been cut in two just due to the abrasion of this small piece of rubber on the shaft. Stranger things have happened.
We had a Bell AH1-J on a test flight and the pilot had it in a low hover. Suddenly the helicopter started to spin and the pilot lowered collective and when the helicopter hit the ground it rolled.
The pilot suffered a broken back and the Iranian student pilot was pretty well banged up.
The problem was traced to a small piece of rubber that kept faying surfaces from abrading on each other. The helicopter had about six hours on the clock. The tail rotor drive shaft had been cut in two just due to the abrasion of this small piece of rubber on the shaft. Stranger things have happened.
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Broken tailrotor shaft
Just a thought,but,as the hanging bearings supporting the tailrotor shaft have built in damping and considering it is by the movement upwards of the shaft whilst it is rotating that pushes the hanging bearing into its final running position. it must mean that during this period (cluth engage/disengage) the shaft must be bending to some digree. mmmmmmmm
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Hi all,
remember that on the Robinson this bearing does not hold any loads. It is there only to raise the resonant frequency of the T/R shaft to a point where it never gets (hopefully). This bearing hangers are very lightly loaded frictionwise. If this friction is adjusted wrong, it may impose some side load into the shaft it is not designed to take on for a long time. There is a regular inspection to check T/R shaft runout and damper bearing friction - actually not the friction of the bearing but its hangerarms that are connected to the tailboom.
It is rather a chore to do these inspections. To a nontrained person it may also appear that the damper is "loose" and it gets tied up to hard.....
As the clutch engagement is a regular procedure, I believe that Robinson very much designed the bending forces so it will not affect shaft integrity if assembled correctly. The angular movement from disengaged to fully engaged is a minimum at the damper bearing.
The only shafts I ever saw broken where in severe situations: crash, sudden T/R stopage, MR-blades going through the tailboom (wind gust and the rotorbrake not available because actuator chaing broke...), and most of them refuse to brake, they twist 2-4 times before cracking!!
Happy Landing!:
It would be very interesting if you could keep us posted on the final findings on this one!
3top
remember that on the Robinson this bearing does not hold any loads. It is there only to raise the resonant frequency of the T/R shaft to a point where it never gets (hopefully). This bearing hangers are very lightly loaded frictionwise. If this friction is adjusted wrong, it may impose some side load into the shaft it is not designed to take on for a long time. There is a regular inspection to check T/R shaft runout and damper bearing friction - actually not the friction of the bearing but its hangerarms that are connected to the tailboom.
It is rather a chore to do these inspections. To a nontrained person it may also appear that the damper is "loose" and it gets tied up to hard.....
As the clutch engagement is a regular procedure, I believe that Robinson very much designed the bending forces so it will not affect shaft integrity if assembled correctly. The angular movement from disengaged to fully engaged is a minimum at the damper bearing.
The only shafts I ever saw broken where in severe situations: crash, sudden T/R stopage, MR-blades going through the tailboom (wind gust and the rotorbrake not available because actuator chaing broke...), and most of them refuse to brake, they twist 2-4 times before cracking!!
Happy Landing!:
It would be very interesting if you could keep us posted on the final findings on this one!
3top
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Did a vibration investigation a few years back on an R-44, T/R drive shaft. Found bad shaft misalignment, to the point that the bearing next to the drive belt assembly had let go, if memory serves me correctly it was an oil filled bearing / viscous damper, the assembly was damaged to the point that all the oil had escaped. Anyway, to cut a long story short, the bearing assy was replaced, with the clutch assy re-adjusted. I only did the vibe work, didn't do the rectification, but again from memory, I belive the guys had to make an adjustment to the clutch extension distance.
Hope this helps. If you need more I can dig through my archive and see what else I can find on the subject, I think I have photos of the damage.
The aircraft had hydraulic controls, and I had only just done an RTB on it, so the Main and Tail rotors, and the engine fan were all smooth, we picked up the TRDS vibe during a vibration survey, previously the M/R & T/R vibration had kept it masked from the pilot.
Hope this helps. If you need more I can dig through my archive and see what else I can find on the subject, I think I have photos of the damage.
The aircraft had hydraulic controls, and I had only just done an RTB on it, so the Main and Tail rotors, and the engine fan were all smooth, we picked up the TRDS vibe during a vibration survey, previously the M/R & T/R vibration had kept it masked from the pilot.
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Further to my last..
Dug out my report to the owner / maintenance organisation re: R44 TRDS Vibe.
Fault was with linear actuator over- extending. Contact me privately for full report, I think it will interest you.
Dug out my report to the owner / maintenance organisation re: R44 TRDS Vibe.
Fault was with linear actuator over- extending. Contact me privately for full report, I think it will interest you.
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Interesting to note that the shaft was completely severed, akin to twisting a liquorice stick and breaking it off. It was obvious that the shaft twisted first, as the break on both ends spiralled to a taper.
The ship is hydraulic, with only 260 odd hours flown. The pilot was able to dump the lever and run it on making for a safe landing.
I wonder if Frank will provide for an inspection hole in the tail ?
The ship is hydraulic, with only 260 odd hours flown. The pilot was able to dump the lever and run it on making for a safe landing.
I wonder if Frank will provide for an inspection hole in the tail ?
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I remember once at HC-4 mechs replaced a T/R driveshaft on one of our CH-53E's.
But it seems one of the bolts used on the flex couplings was incorrect, and stuck out a bit along the same axis as the shaft.
With the 53, typically all 3 engines are started, then the rotor brake is released..
Well, Nr spun up, and hydraulics on one system went to 0.
The stuck out bolt hit an adel clamp in the right spot and tore it out, with it's associated hydraulic line running parallel tot he shaft, it was strange, and you should have seen the hyd line after the shaft was "unthreaded" thru it's middle, as it looked like a warped pretzel wrapped around the shaft.
But it seems one of the bolts used on the flex couplings was incorrect, and stuck out a bit along the same axis as the shaft.
With the 53, typically all 3 engines are started, then the rotor brake is released..
Well, Nr spun up, and hydraulics on one system went to 0.
The stuck out bolt hit an adel clamp in the right spot and tore it out, with it's associated hydraulic line running parallel tot he shaft, it was strange, and you should have seen the hyd line after the shaft was "unthreaded" thru it's middle, as it looked like a warped pretzel wrapped around the shaft.
