Seawolves or a helicopter crash question

There is a clutch in the transmission that operates automatically to disconnect the main shaft from the gear section of the transmssion.  This is true of all helicopters that I know of.  If the engine fails, or is simply throttled back, this clutch will disengage and then rotor rpm is determined by airflow up through the rotor system.  When you autorotate, you manage rotor rpm by maintaining the right combination of forward speed and rate of descent, forward speed with the cyclic stick primarily, and rotor speed with the collective.  RPM of the engine is controlled with the grip of the collective, rotating the grip will add or reduce power, in combination with the governor on turbine engines or a correlation box on piston powered helicopters.  To start an intentional autorotation the pilot rolls the power off and applies the proper cyclic and collective controls.  If the collective is dropped all the way the rotor blades reach a pitch stop that limits the top rpm the rotor system can reach.  If too much pitch is pulled, rotor rpm falls off and that can be a very bad thing because the only way you can get it back is to increase the rate of descent.  The blades don't have to come to a complete stop for the helicopter to fall like a rock.  Just how a transmission might fail surely depends on where the damage occurs, but I would suspect that gear and bearing damage and oil loss would be as big a factor as actual system lockup from the initial impact.

   Not sure why I'm so intent on trying to solve the question.....sorry thinking out loud....

     Yes it could be one of the skids, most likely explanation, it truly is a pile of parts. 

You may be correct.

midnightprowler

Can't be the drive shaft its facing forward. Very strang

It appears to be one of the huey's skid landing gear.  You can see the other one at the bottom of the pile if you follow the skid cross member down to the ground.  The crash really scrambled up the pieces.

Can't be the drive shaft its facing forward. Very strange.

Yep, my bad took a second better look, yes a Heuy. Can anyone identify the long straight thing coming out of what is left of the engine deck? My first thought was the tail rotor drive shaft but given the angle the fuselage is laying??? Could it have been a collision with a high raised object? Radio antenna, cell tower?

midnightprowler

 

 

armornut

 The last pic looks like a BELL 206 or Kiowa, the rotorblades on the mast are fully articulated. By that I mean there are many more pitch links involved in operating the rotors, it is possible those were damaged in the crash and the "lead" blade simply turned over on impact.

    I also agree with the other posts about the transmission seperating from the aircraft in the event of a siezure, most definitely. The cause of the rotor stoppage and blade siezure could be a combination of a broken main driveshaft from the engines to tranny and a defective OR improperly applied rotor brake.

 

 

 

 

No, it is clearly a Huey.

 

I was gonna say that the 206/OH-58 does not have that cross bar across the  top of the main rotor....

keavdog

During my 1/2 helicopter flight instruction we did a short auto rotation.   In involved pulling down a lever that disconnected the rotor from the engine.  The instructor pointed out the difference in rotor rpm and engine rpm.  Based on this interesting thread I assume the transmission is still involved, yes?

 

That lever is called the collective, it changes the pitch of the main rotor. When autorotating the pitch is lowered and the rotor freewheels, by the air rushing thru the underside of the rotor and the helicopter acts like a quickly falling autogyro.So in a way the transmission is involved. If it seized the rotors would still stop.

armornut

 The last pic looks like a BELL 206 or Kiowa, the rotorblades on the mast are fully articulated. By that I mean there are many more pitch links involved in operating the rotors, it is possible those were damaged in the crash and the "lead" blade simply turned over on impact.

    I also agree with the other posts about the transmission seperating from the aircraft in the event of a siezure, most definitely. The cause of the rotor stoppage and blade siezure could be a combination of a broken main driveshaft from the engines to tranny and a defective OR improperly applied rotor brake.

 

No, it is clearly a Huey.

Rob Gronovius

 

 

midnightprowler

Yeah the ground would pop smoke and the aircraft would confirm color. Ground never said what color because Charlie would pop the same color.

and yeah, if the rotor seized, the chopper would fall like a anvil.

 

 

 

 

Exactly, ground announces pop smoke. Aircraft confirms the color of smoke they see.

 

Yep.

Only saw one go down thankfully about a hundred feet away. They were coming in for a medevac and not very high fortunately, maybe a couple hundred feet, when there was an explosion and it knocked out the tail rotor.

No, the reports where the rotors slowed to a stop gibes better than just stopped suddenly.

UH-1 blades were still made of steel back then.  There was a pilot demo where , with the a/c on the ground, the engine would be shut down, and you could get a 3' hop by just putting in pitch on the still spinning rotor

But, that's just my 2¢, take it for what it's worth.

During my 1/2 helicopter flight instruction we did a short auto rotation.   In involved pulling down a lever that disconnected the rotor from the engine.  The instructor pointed out the difference in rotor rpm and engine rpm.  Based on this interesting thread I assume the transmission is still involved, yes?

 The last pic looks like a BELL 206 or Kiowa, the rotorblades on the mast are fully articulated. By that I mean there are many more pitch links involved in operating the rotors, it is possible those were damaged in the crash and the "lead" blade simply turned over on impact.

    I also agree with the other posts about the transmission seperating from the aircraft in the event of a siezure, most definitely. The cause of the rotor stoppage and blade siezure could be a combination of a broken main driveshaft from the engines to tranny and a defective OR improperly applied rotor brake.

Strange in the photo above both rotor blades face the same direction.

Intersting stuff.... now in the one eyewitness statement, there is the description of the helicopter entering a flat spin. Perhaps that would be cause by the energy transfer from the main rotor after the transmission has seized?

I tend to believe the people who were actually there. Its a good question.

According to JC Pennington of the 174th AHC "the transmission seized at about 1,000 feet and it dropped straight in." CW2 Tews had no chance of autorotation and the aircraft pancaked.

This is not dissimilar to the deaths of 2 Marine Corps pilots in a UH-1Y Venom Jan 2015 for a recent example, and only at 400' AGL on short final.

"Two Marine pilots killed in a January helicopter crash in California were just a few hundred yards from their destination when the transmission of their aircraft seized, stopping its main rotor and causing it to plummet, according to a lengthy investigation into the crash."

https://www.marinecorpstimes.com/news/your-marine-corps/2015/10/25/investigation-faulty-filter-cover-pilot-error-caused-fatal-marine-helicopter-crash/

Here is another case, "According to the pilot, the helicopter was about 500 ft above ground level (agl) when he saw the master caution warning light illuminate; he then saw that the low transmission oil pressure light was also illuminated. He immediately maneuvered away from power lines and set up an approach to land. While descending, the helicopter yawed left and right, and, about 10 ft agl with the airspeed almost at 0, the main rotor speed slowed and then stopped, and the helicopter subsequently fell to the ground. The pilot reported that the engine continued to operate for about 15 seconds after impact.
An on-scene examination revealed that both main rotor blades remained intact with no leading edge damage. "

https://aviation-safety.net/wikibase/wiki.php?id=139915

Another, from B Co 123rd AVN (caps per link)

"THE SLICK WAS HEADED GENERALLY NORTH, THE SAME DIRECTION AS THE 174th FLIGHT, AND AT THE SAME ALTITUDE-1500 FEET MSL. THE SLICK WAS OBSERVED IN STRAIGHT AND LEVEL FLIGHT FOR APPROXIMATELY ONE MINUTE. APPROXIMATELY TWO MINUTES HAD ELAPSED FROM THE TIME THE SLICK FIRST REPORTED THE LOSS OF TRANSMISSION OIL TO TEAM LEAD UNTIL HIS SECOND CALL OF DISTRESS, DURING WHICH HE TRANSMITTED ALMOST CONTINUOUSLY, NEARING IMPACT WITH THE GROUND. THE SLICK WAS OBSERVED TO ENTER A GRADUAL RIGHT TURN, BEGIN WITH A DESCENT, AND INCREASE BOTH THE RATE OF TURN AND THE RATE OF DESCENT. HALFWAY THROUGH THE TURN, THE SLICK ENTERED A SPIN, DURING WHICH THE MAIN ROTOR BLADES WERE OBSERVED TO SLOW DOWN. AT AN ESTIMATED ALTITUDE OF FROM 400 FEET TO 700 FEET AGL, THE ROTOR BLADES STOPPED PERPENDICULAR TO THE FUSELAGE, AND THE SLICK ENTERED A FLAT SPIN, IMPACTING SLIGHTLY NOSE LOW AND IN A SLIGHT LEFT BANK. THE IMPACT FLATTENED THE HELICOPTER AND DROVE PARTS OF IT INTO THE GROUND."

http://www.bco123rdavnbn.org/id52.html

and yet another,

On Nov. 15, 2011, Boatman was about 4 miles west of Valle, he said, when the helicopter began to experience mechanical failure. In a call to 911, Boatman indicated the helicopter’s transmission had failed and he was attempting to land the craft when it completely seized up and fell from the sky

Rotors intact again indicative as before of them not being in motion at time of impact.

https://www.williamsnews.com/news/2018/apr/17/glendale-man-awarded-241-million-2011-helicopter-c/

Hello!

I just love the discussion here... That was my point from the start - the rotor has A LOT of energy when it's spinning. Robert Mason wrote in his book, Chickenhawk, that when you have the rotor spinning in a Huey, you can cut the engine, take off, turn the huey aroung 360 degrees and land - the rotor has enough energy for that. Now to stop the rotor in place by a frozen transmission - where would that energy go? Like Gino wrote, it would twist the rotor shaft off, ot take the whole transmission out of the fuselage - I just don't know what's stronger. Plus, there's the airflow trying to turn the rotor around, right?

At least that's my opinion here, I would like to see more comments on that.

Have a nice day

Paweł

lowfly

The only way a helo can auto rotate is if the rotor blades spin freely.  I would think that if the transmission were locked up the rotors will not spin freely and the helo will drop like a rock

Correct, I already know this.  My point is that I don't think the transmission actually seized up.  I believe that if it were to do so, the rotor would separate from the mast due to the torque involved.  I don't think it would just stop spinning.

HeavyArty

 

 

Note lack of damage to helicopter rotor blades, indicating that they were not rotating at the time of impact.

 

 

Or he auto-rotated to a hard landing and the aircraft burned up on the ground.  Just because the rotors didn't shatter doesn't mean they were stationary when it hit.

 

The only way a helo can auto rotate is if the rotor blades spin freely.  I would think that if the transmission were locked up the rotors will not spin freely and the helo will drop like a rock

Now that would make more sense if the transmission seized. There is a lot of inertia in a Huey rotor.

This is my own 'blades coming off' story.

As a young Huey crew chief at Cu Chi Vietnam in 1967, I saw a UH-1D land and come to a full stop on the metal runway.  As I was watching from above, I saw the rotor and much of the mast separate from the Huey on the ground and sail off, still spinning, into the air.  The rotor landed a couple of hundred feet forward and to the right of the runway, in the grass and still spinning.  I was later told that the helicopter was returning from a mission and had taken several hits in either the transmission or the mast, but never heard any more about it.

Note lack of damage to helicopter rotor blades, indicating that they were not rotating at the time of impact.

Or he auto-rotated to a hard landing and the aircraft burned up on the ground.  Just because the rotors didn't shatter doesn't mean they were stationary when it hit.

Man that's crazy. If those rotors stopped in flight it fell like a anvil. Very little damage to the rotors there. Would sur like to know more about that crash.

174th Assault Helicopter Company

CW2 Henry J. "Hank" Tews
11 Apr 48
29 Dec 68
Shoshone ID
35W07

CW2 Tews was a maintenance officer who had gone to recover an UH-1D that had made a precautionary landing west of Ba To at the Special Forces camp at Gia Vuc. The UH-1D's crew had landed the aircraft because of noises from the transmission area after they had taken several hits from small arms fire. CW2 Tews inspected the aircraft and, having missed noticing a bullet that entered the "hell-hole" and hit the transmission, determined the aircraft could make a one time 30 minute flight to Duc Pho. CW2 Tews flew alone in the aircraft. Enroute, the transmission seized, and the aircraft crashed. Source: Jim McDaniel after a phone conversation with Russel Doersam, Jan 90. (Below, photo of Tews' crash site taken by Dave Lovett, 30 Dec 68, and photo of Hank the day he received the Bronze Star medal. Note lack of damage to helicopter rotor blades, indicating that they were not rotating at the time of impact.)

I think if a transmission did seize up the rotor blades wouldn't stop, they would depart the general area.  I don't have any memory of a transmission seizing up, but I have heard of damage to the rotor pitch linkage that made things terminally unpleasant.

On the CH-37's I worked on there was temperature sensitive paint on the transmission housing that would change color in an overtemp situation, but in case of impact damage it wouldn't be much help.

Hello!

Thanks for bringing the topic up - I'm still not sure if it is possible for the main rotor of the helo to get "frozen in place" as a result of a serious hit to the transmission or any other component.

As for the smoke I have heard the procedure as you describe it so many times that it seemed very strange to see it described in the book the other way. Made me wonder how did the author come up with that?

Have a nice day

Paweł

midnightprowler

Yeah the ground would pop smoke and the aircraft would confirm color. Ground never said what color because Charlie would pop the same color.

and yeah, if the rotor seized, the chopper would fall like a anvil.

 

Exactly, ground announces pop smoke. Aircraft confirms the color of smoke they see.

Yeah the ground would pop smoke and the aircraft would confirm color. Ground never said what color because Charlie would pop the same color.

and yeah, if the rotor seized, the chopper would fall like a anvil.

That doesn't sound right to me either. I would think the momentum caused by either the engine or the rotor would cause the transmission to keep spinning and come apart before it would seize.