Tail rotor drive failure video
Thread Starter
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From: Abu Dhabi
Joined: Apr 2003
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From: USA
That horrendous tape is a lesson in many ways.
The tail rotor is probably hit (collision?) off camera. This leads to the loss of the tail section just ahead of the vertical pylon, most likely caused by the imbalance of the loss of a tail blade, and the ensuning structural loads at the "weak point".
This antitorque failure results in spinning about the mast, and then wild cyclic excursions as the pilot is unable to maintian orientation. One can speculate that if the collective had been dumped then, fast, the spinning might have stopped and some kind of controlled low-power (zero power) descent could have been arranged. But that is asking alot.
Note that the bucking of the fuselage as the spinning occurs leads to blade-fuselage contact. The bucking is because the rotation of the fuselage exposes different sections of the rotor to the relative wind, so that the "back flap" affects the rotor sequentially as the fuselage turns. If the crew is not able to know where the wind is coming from, they cannot keep the fuselage level. This pitching and rolling eventually leads to large flapping events and blade to fuselage contact. The broken blades are uneven in length, so there are large cyclic imbalances that help tear the helo apart.
I believe the helos are Mi-2's which are 1st gen machines with relatively weak structures (or very light structures, depending on viewpoint.)
The tearing apart ruptures the fuel cells, which spray avgas everywhere, especially onto the running engine, which ignites same.
Not at all a pretty picture.
The tail rotor is probably hit (collision?) off camera. This leads to the loss of the tail section just ahead of the vertical pylon, most likely caused by the imbalance of the loss of a tail blade, and the ensuning structural loads at the "weak point".
This antitorque failure results in spinning about the mast, and then wild cyclic excursions as the pilot is unable to maintian orientation. One can speculate that if the collective had been dumped then, fast, the spinning might have stopped and some kind of controlled low-power (zero power) descent could have been arranged. But that is asking alot.
Note that the bucking of the fuselage as the spinning occurs leads to blade-fuselage contact. The bucking is because the rotation of the fuselage exposes different sections of the rotor to the relative wind, so that the "back flap" affects the rotor sequentially as the fuselage turns. If the crew is not able to know where the wind is coming from, they cannot keep the fuselage level. This pitching and rolling eventually leads to large flapping events and blade to fuselage contact. The broken blades are uneven in length, so there are large cyclic imbalances that help tear the helo apart.
I believe the helos are Mi-2's which are 1st gen machines with relatively weak structures (or very light structures, depending on viewpoint.)
The tearing apart ruptures the fuel cells, which spray avgas everywhere, especially onto the running engine, which ignites same.
Not at all a pretty picture.
Joined: Feb 2006
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From: On the big blue planet
NickL wrote
I believe the helos are Mi-2's which are 1st gen machines with relatively weak structures (or very light structures, depending on viewpoint.)
I believe the helos are Mi-2's which are 1st gen machines with relatively weak structures (or very light structures, depending on viewpoint.)
Skadi
Joined: Dec 2001
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From: Philadelphia PA
I think they were all Mi-2, but difficult to tell. Does anybody have any idea where this was filmed? that might give a clue.
Mi-2 had / has a very weak tail rotor attachment fixture- The Poles told they tried to get the Russians to let them (the Poles) re-design it as it was causing problems. In typical Socialist fashion, they were told - if you re-design it, that means that the original designers didn't know what they were doing, and we can't accept that. Leave it as it is....
That's why the Kania (the Allison engined version of the Mi-2) is so different - the Poles did re-design it. Sadly, they seem to lack any management or sales capability, and have faded out of the market.
Mi-2 had / has a very weak tail rotor attachment fixture- The Poles told they tried to get the Russians to let them (the Poles) re-design it as it was causing problems. In typical Socialist fashion, they were told - if you re-design it, that means that the original designers didn't know what they were doing, and we can't accept that. Leave it as it is....
That's why the Kania (the Allison engined version of the Mi-2) is so different - the Poles did re-design it. Sadly, they seem to lack any management or sales capability, and have faded out of the market.
Joined: Feb 2007
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From: Cambridge
Yes, those mi-2's are horrendous helicopters. The Russians used to turn up to the World Championships in them, didn't stop them totally wiping the floor for all the trophies though!
Here are useful links to allow people to decide for themselves what the helicopters really are:
mi-2: http://www.scramble.nl/mil/2/kop/gfx/mi2-orbat.jpg
mi-8: http://www.pidocchio.net/turboland/l...i%208%2002.jpg
mi-17: http://perso.orange.fr/aeromil-yf/MI...0CK%200201.jpg
I think JAB may be correct on the TR failure with the mi-17. To me (a rather untrained eye on russian aircraft) it looks like mi-8 and mi-17 are relatively similar. Any thoughts on this?
nick
Here are useful links to allow people to decide for themselves what the helicopters really are:
mi-2: http://www.scramble.nl/mil/2/kop/gfx/mi2-orbat.jpg
mi-8: http://www.pidocchio.net/turboland/l...i%208%2002.jpg
mi-17: http://perso.orange.fr/aeromil-yf/MI...0CK%200201.jpg
I think JAB may be correct on the TR failure with the mi-17. To me (a rather untrained eye on russian aircraft) it looks like mi-8 and mi-17 are relatively similar. Any thoughts on this?
nick
Joined: Nov 2005
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From: Variable
Hi Shawn
Definitely Mi-17's with hard points. I have flown the civil version quite a bit and although the tail looks too long and thin, its quite strong. Did have some problems with skin cracks during logging but thats hard on any machine. I have never heard of a tail breaking off for no reason. Friend had a tail rotor blade delaminate in flight and the entire tail rotor transmission broke off as they touched down, lucky.
Definitely Mi-17's with hard points. I have flown the civil version quite a bit and although the tail looks too long and thin, its quite strong. Did have some problems with skin cracks during logging but thats hard on any machine. I have never heard of a tail breaking off for no reason. Friend had a tail rotor blade delaminate in flight and the entire tail rotor transmission broke off as they touched down, lucky.
Joined: Jun 2001
Posts: 506
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From: Europe
Definitely all Mi-17! I couldn't understand how some of you guys could confuse it. The Mi-2 is a much smaller helicopter with nothing in common with Mi-8/17.
Have flown and tested both types in civil and military outfit and equipment for more than 500h and we have never found any weak structural designs. Astonishing Shawn, you as a real expert believe it? They have problems in flight performance and some other problems, but this kind of russian helicopters are real "iron pigs".
For the Mi-8/17 as a more than 12to MTOW helicopter exist limits. But's the same as on other big ships.
I don't know the reason for this tail rotor separation. But i would bet, it was a main rotor strike into the tail boom. This and only this is a weak point on Mi-8/17 with several accidents. This big and hinged rotor with very flexible blades don't like aerobatics. The distance between rotor and tail boom isn't large enough. And it is no problem to strike the blades into the tailboom. And if the blades strikes the boom, than they will do it in the vicinity of the intermediate gearbox. And that's exactly the first breaking point in the vid.
Have flown and tested both types in civil and military outfit and equipment for more than 500h and we have never found any weak structural designs. Astonishing Shawn, you as a real expert believe it? They have problems in flight performance and some other problems, but this kind of russian helicopters are real "iron pigs".
For the Mi-8/17 as a more than 12to MTOW helicopter exist limits. But's the same as on other big ships.
I don't know the reason for this tail rotor separation. But i would bet, it was a main rotor strike into the tail boom. This and only this is a weak point on Mi-8/17 with several accidents. This big and hinged rotor with very flexible blades don't like aerobatics. The distance between rotor and tail boom isn't large enough. And it is no problem to strike the blades into the tailboom. And if the blades strikes the boom, than they will do it in the vicinity of the intermediate gearbox. And that's exactly the first breaking point in the vid.
Joined: Feb 2007
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From: Cambridge
Test pilot,
I wasnt debating that the mi-2 is a smaller helicopter! i was merely saying that i thought that the helicopters going from right to left were mi-2s because of their stubby look.
Maybe its just the camera angle, and its a fairly poor quality vid anyway.
still dont know the difference between mi-17 and mi-8?
nick
I wasnt debating that the mi-2 is a smaller helicopter! i was merely saying that i thought that the helicopters going from right to left were mi-2s because of their stubby look.
Maybe its just the camera angle, and its a fairly poor quality vid anyway.
still dont know the difference between mi-17 and mi-8?
nick
Joined: Feb 2007
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From: New Zealand
Nick Lappos made the interesting comment that if the pilot had removed power quickly things might have ended up better; it does appear from the video that there are quite a few seconds before the situation turns really ugly. What do the experts on the panel think?
Joined: Feb 2006
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From: On the big blue planet
tecpilot wrote:
I don't know the reason for this tail rotor separation. But i would bet, it was a main rotor strike into the tail boom. This and only this is a weak point on Mi-8/17 with several accidents. This big and hinged rotor with very flexible blades don't like aerobatics. The distance between rotor and tail boom isn't large enough. And it is no problem to strike the blades into the tailboom. And if the blades strikes the boom, than they will do it in the vicinity of the intermediate gearbox. And that's exactly the first breaking point in the vid.
I don't know the reason for this tail rotor separation. But i would bet, it was a main rotor strike into the tail boom. This and only this is a weak point on Mi-8/17 with several accidents. This big and hinged rotor with very flexible blades don't like aerobatics. The distance between rotor and tail boom isn't large enough. And it is no problem to strike the blades into the tailboom. And if the blades strikes the boom, than they will do it in the vicinity of the intermediate gearbox. And that's exactly the first breaking point in the vid.
skadi
Joined: Jun 2001
Posts: 506
Likes: 1
From: Europe
Running the vid in slow motion and found my first toughts right. At first the ship lost the complete last tailboom part incl. the intermediate gearbox and not only the T/R. A few seconds later parts of rotor blades disintegrated. For me a sign of a damaged M/R. And a damaged M/R is not the result of a "simple" T/R loss.
On this scenario a power cut will do nothing. The damaged M/R blades will result in heavy vibrations, an unbalance and may be in an uncontrollable helicopter. This unlucky guys were doomed. May be they have done it and tried an AR. But an increasing M/R RPM will rapidly increase the forces on the blades and a disintegration.
The best way to decide if seeing an older Mi-8 or the newer models (names are difficult, sometimes Mi-17 variants are decribed as Mi-8 MTV) is to look at the engine cowlings. On the newer variants with the more powerful engines the engines are much shorter than the old TW117 on the Mi-8. Therefore there is more distance between the front of the helicopter and the air inlets. The next, the newer models have the T/R on the left side. At least the first helicopters in the vid seems to have a left sided T/R.
No, this armed Mi-17 variants have selfsealing and azotic pressurized fuel tanks. They couldn't have ruptures on the cells due to a few fast rotations and they have no fuel lines in the tailboom. I believe after the disintegrated M/R blades the unbalance broke out the main gearbox and engine struts, rupturing fuel or hydraulic lines in the vicinity of the engines.
On this scenario a power cut will do nothing. The damaged M/R blades will result in heavy vibrations, an unbalance and may be in an uncontrollable helicopter. This unlucky guys were doomed. May be they have done it and tried an AR. But an increasing M/R RPM will rapidly increase the forces on the blades and a disintegration.
still dont know the difference between mi-17 and mi-8?
The tearing apart ruptures the fuel cells,
Last edited by tecpilot; 28th February 2007 at 13:02.
Joined: Feb 2007
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From: New Zealand
tecpilot: if you look very carefully at the video when the stricken machine first comes into view there is some debris falling to earth and the rear tail-boom section is still attached. The falling piece is well below the ship so it could have come off a few seconds earlier. My guess was that it is a tail rotor blade but it is not at all clear. Would the vibration caused by losing a TR blade cause the boom to fail?
Joined: Jun 2001
Posts: 506
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From: Europe
Would the vibration caused by losing a TR blade cause the boom to fail?
Never heard about design problems, only limited on cross wind.
I liked these ships, this is an old Mi-8. Long engines, t/r right side.
This is a Mi-17. Short engines, m/r blades disintegrated, surely after tail boom or ground contact. Not inflight surely.
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From: Den Haag
"I remember the video ( somewhere in this forum ) of the ditched Mi, where the mainrotor struck the tail while attempting S/E Water T/O."
Er, not quite: the nose 'submarined' under whilst attempting a running take off (or taxying too fast) in a choppy sea. The MR blades hit the sea in front of the aircraft.
Er, not quite: the nose 'submarined' under whilst attempting a running take off (or taxying too fast) in a choppy sea. The MR blades hit the sea in front of the aircraft.