Loss of tail rotor

MikeD said:
appears to have come after the initial spin.

if the tail gearbox separated,
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What would cause this? The tail gear box just separates from the helicopter?

In the video it looks like the tail came off and the helicopter was already spinning out of control, before the main rotor struck the tail boom.

the pilot has to autorotate and get the engine shut off to avoid a spin or minimize any spin that has already occurred. And while doing that, keep the bird as level as possible with only controller turns and no gyrations….sometimes easier said than done.
That would already be a challenge because with the loss of the tail rotor and/or gearbox, there’d be a marked forward CG shift to overcome. If the helo isn’t kept somewhat level/upright in an autorotative descent, and especially with a helo equipped with a 2-blade semi-rigid rotor system, any max deflection of the rotor disc by the pilot with the cyclic stick, makes blade flex a high possibility along with the movement of the rotor system itself, resulting in a high probability of chopping the tailboom off the bird. At that point, the bird and anyone in it, is done, as the rest of the helicopter disintegrates on its way down to earth like a rock. At the end of the day, physics always wins.
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I’m the dummy on helicopters, why can’t they be designed so even rapid full movement on the stick while climbing won’t hit the tail boom ? Isn’t it just a matter of placing the main rotor swash high enough?

What’s a controller turn?


If it loses the tail rotor (which it looks like they did here), won’t it immediately enter a spin? Which is what it looks like here. How do you prevent that in this case?
 
Cherokee_Cruiser said:
What would cause this? The tail gear box just separates from the helicopter?

In the video it looks like the tail came off and the helicopter was already spinning out of control, before the main rotor struck the tail boom.
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A tail rotor or gearbox failure could be Mx related, fatigue related, pilot technique related. Though, in cruise this would be lesser issue because the tail rotor is doing less anti-torque work than it would be in a hover, which is where most gearbox failures occur. It does appear that some TR issue occurred before the tailboom got chopped off.

I’m the dummy on helicopters, why can’t they be designed so even rapid full movement on the stick while climbing won’t hit the tail boom ? Isn’t it just a matter of placing the main rotor swash high enough?

What’s a controller turn?


If it loses the tail rotor (which it looks like they did here), won’t it immediately enter a spin? Which is what it looks like here. How do you prevent that in this case?
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my comment should have said “controlled turn”, just misspelled.

blades still flex. It’s not really possible to design a main mast height that will preclude rapid cyclic movement from flexing the blades near the tips.

As explained in the previous post what the pilot actions need to be for loss of full anti-torque in cruise flight. Those actions need to be undertaken with the least bit of delay.
 
MikeD said:
A tail rotor or gearbox failure could be Mx related, fatigue related, pilot technique related. Though, in cruise this would be lesser issue because the tail rotor is doing less anti-torque work than it would be in a hover, which is where most gearbox failures occur. It does appear that some TR issue occurred before the tailboom got chopped off.



my comment should have said “controlled turn”, just misspelled.

blades still flex. It’s not really possible to design a main mast height that will preclude rapid cyclic movement from flexing the blades near the tips.

As explained in the previous post what the pilot actions need to be for loss of full anti-torque in cruise flight. Those actions need to be undertaken with the least bit of delay.
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So push the collective handle bar all the way to the floor to disengage (?) immediately ?

Watching some YouTube videos of Robinson, I’m still confused by the bicycle handle bar. I picture a yoke-like handle in between the legs.
 
Cherokee_Cruiser said:
So push the collective handle bar all the way to the floor to disengage (?) immediately ?

Watching some YouTube videos of Robinson, I’m still confused by the bicycle handle bar. I picture a yoke-like handle in between the legs.
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With complete loss of tail rotor thrust…..or the whole assembly, need to go collective full down initially to flatten the pitch of the main rotor blades, and thus remove as much torque as possible. Otherwise the equal and opposite reaction will quickly occur of the fuselage spinning in the opposite direction of the main rotor blade direction, basically Newtons 3rd law, will occur, and there will be nothing to counter it with,. Doing this will help negate a spin, but you will now be heading down to earth. You’ll be under control, just with a very high vertical descent rate.
 
MikeD said:
With complete loss of tail rotor thrust…..or the whole assembly, need to go collective full down initially to flatten the pitch of the main rotor blades, and thus remove as much torque as possible. Otherwise the equal and opposite reaction will quickly occur of the fuselage spinning in the opposite direction of the main rotor blade direction, basically Newtons 3rd law, will occur, and there will be nothing to counter it with,. Doing this will help negate a spin, but you will now be heading down to earth. You’ll be under control, just with a very high vertical descent rate.
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How much time would you say one has before all is lost?

Once the spinning in a circular fashion is developed, is it too late? Say in the video above while it’s spinning if they went full collective down, does that make any dent in their problem?
 
Cherokee_Cruiser said:
How much time would you say one has before all is lost?

Once the spinning in a circular fashion is developed, is it too late? Say in the video above while it’s spinning if they went full collective down, does that make any dent in their problem?
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It all depends on a number of factors. The objective is to keep a spin from starting if at all possible, or to keep one from getting any worse than it is. If there is forward speed, and the torque is then taken out of a spin, it’s possible that the tail boom and tail fin(s) can streamline with the relative wind, and the helo can at least be descending straight once again. Whereas if you’re in a hover when this occurs, you’re stuck with whatever rate of spin developed before you removed the torque. There’s no set time limit.

In the video of this accident, there’s a quickly developed spin which unfortunately appears to turn into a tumble around at least two axes, where at least some negative G was likely encountered that flexed the rotor system enough to chop off most of the entire tailboom. I haven’t seen any video taken of what the helicopter was doing immediately prior to the loss of the aft tail boom portion, so it’s difficult to answer whether there was either any time for the pilot to take action, or whether the pilot didn’t take action in a timely manner.
 
Cherokee_Cruiser said:
What would cause this? The tail gear box just separates from the helicopter?

In the video it looks like the tail came off and the helicopter was already spinning out of control, before the main rotor struck the tail boom.
………
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The gear box did NOT separate from the assembly. The T/R with gearbox are still attached to the aft section of the boom.

The video picks up AFTER the main rotor chopped off the tail rotor section. As the cabin/structure descends and rotates, the main rotor strikes the tail boom again.
 
dustoff17 said:
The gear box did NOT separate from the assembly. The T/R with gearbox are still attached to the aft section of the boom.

The video picks up AFTER the main rotor chopped off the tail rotor section. As the cabin/structure descends and rotates, the main rotor strikes the tail boom again.
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yes, the initial loss of the tail assembly and resultant tail assembly on the ground, can both be seen. My question is whether there’s any video preceding the first tailboom strike and what was going on at that time.

I think CC was asking about generic full loss of tail rotor control, including the TR itself or the gearbox assembly, and what pilot actions would be were that to occur. His being fixed wing only, the question comes off as incomplete, but I know what he’s asking.
 
melax said:
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I was about to post this, his analysis is pretty good for an airplane guy.

It's been pretty firmly established that the main rotor blade cut the boom off. Practicing settling with power and a bad reaction by the SP with late/inappropriate reaction by a new CFI is a good theory as any for now.
 
USMCmech said:
I was about to post this, his analysis is pretty good for an airplane guy.

It's been pretty firmly established that the main rotor blade cut the boom off. Practicing settling with power and a bad reaction by the SP with late/inappropriate reaction by a new CFI is a good theory as any for now.
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he talks about coning of the rotor system if the Nr begins to decay. Unless they lose engine power, at the MSL altitude they were at, there should be no issue with Nr loss in a power settling demo. And even if the rotor system was coned somewhat, somehow, the blades would be further distant the tailboom. It would take a rapid full aft cyclic pull to make a tailboom strike happen, and likely with a rapid collective down input, which would flatten the rotor disc, not cone it. But if done rapidly enough and with deep aft cyclic (which there shouldn’t be, as fuselage would be slightly nose up during the PS demo), that could result in a tailboom strike from downward blade flex, even without a mast bump.

Homeboy needs to stick to airplanes.
 
I have no idea how a "mast bumping" video came up on my youtube feed, but I blame this thread. Cue the cheesy 70s music

 
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