USN MH-60S Down San Diego
Blade fold is driven by electric motors in the spindles, not hydraulically by the dampers..
The BH has independent dampers. The NH has all 4 connected to a common reservoir under the beanie. Not familiar with the system, don't know if a broken line can pump all 4 dampers dry.
The BH has independent dampers. The NH has all 4 connected to a common reservoir under the beanie. Not familiar with the system, don't know if a broken line can pump all 4 dampers dry.
Blade fold is driven by electric motors in the spindles, not hydraulically by the dampers..
The BH has independent dampers. The NH has all 4 connected to a common reservoir under the beanie. Not familiar with the system, don't know if a broken line can pump all 4 dampers dry.
The BH has independent dampers. The NH has all 4 connected to a common reservoir under the beanie. Not familiar with the system, don't know if a broken line can pump all 4 dampers dry.
I know it is true for some hydraulic blade fold systems.
Someone is bound to chime in with the definitive facts!
This photo nicely shows the damper, with unequal areas on either side of the piston, pushing the blade forward to the lead stop under hydraulic pressure so that a pitch lock can engage the pitch horn (visible on the left hand side of the image). There is no visible accumulator to compensate for changes in fluid volume with temperature, etc. but there is a hose leading off the damper, presumably to a central accumulator. May not be practical to design internal valving that would stop the system from draining from a damaged hose for every leak rate.
Blade fold is a necessary, but absolutely horrible thing for a rotor design.
Blade fold is a necessary, but absolutely horrible thing for a rotor design.
Avoid imitations
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Originally Posted by [email protected]
Sultan - I disagree, I have encountered full on ground resonance in a Wessex and the early stages in Sea King - there is enough time to do something about it but you need to have been trained to recognise and deal with it.
As soon as they landed and experienced the 'padding' that precedes GR, they should have lifted to the hover - if the oscillations stop, that is when you consider a running landing or a low hover throttle chop.
How much GR awareness is there amongst the Blackhawk users? If it is a very unusual occurrence on that aircraft then it is understandable why they didn't recognise it and act quicker.
As soon as they landed and experienced the 'padding' that precedes GR, they should have lifted to the hover - if the oscillations stop, that is when you consider a running landing or a low hover throttle chop.
How much GR awareness is there amongst the Blackhawk users? If it is a very unusual occurrence on that aircraft then it is understandable why they didn't recognise it and act quicker.
I flew the Blackhawk S-70 for four years. Unlike with the Wessex, I have no recollection of the type having a ground resonance tendency. I think Sikorsky had already learned their lesson.
FWIW, in 2005 it was known "the MH-60S rotor dampener lines are relatively soft and easily penetrated, which increases the risk of severe ground resonance problems on landing."
This photo nicely shows the damper, with unequal areas on either side of the piston, pushing the blade forward to the lead stop under hydraulic pressure so that a pitch lock can engage the pitch horn (visible on the left hand side of the image). There is no visible accumulator to compensate for changes in fluid volume with temperature, etc. but there is a hose leading off the damper, presumably to a central accumulator. May not be practical to design internal valving that would stop the system from draining from a damaged hose for every leak rate.
Blade fold is a necessary, but absolutely horrible thing for a rotor design.
Blade fold is a necessary, but absolutely horrible thing for a rotor design.
I stand corrected. it sounds like the damper positioning system is a passive function, I haven't found any reference to valves. The accumulator is inside the shaft extension.
As you know, the USCG eliminated the blade fold hardware some time ago.
According to the investigation report, the damper hose was crushed at some point, then suffered a progressive failure of the braid wires prior to rupture and catastrophic leak.. So it is possible it could have been found during maintenance, but it would have been improbable.
Originally Posted by [email protected]
Sultan - I disagree, I have encountered full on ground resonance in a Wessex and the early stages in Sea King - there is enough time to do something about it but you need to have been trained to recognise and deal with it.
As soon as they landed and experienced the 'padding' that precedes GR, they should have lifted to the hover - if the oscillations stop, that is when you consider a running landing or a low hover throttle chop.
How much GR awareness is there amongst the Blackhawk users? If it is a very unusual occurrence on that aircraft then it is understandable why they didn't recognise it and act quicker.
As soon as they landed and experienced the 'padding' that precedes GR, they should have lifted to the hover - if the oscillations stop, that is when you consider a running landing or a low hover throttle chop.
How much GR awareness is there amongst the Blackhawk users? If it is a very unusual occurrence on that aircraft then it is understandable why they didn't recognise it and act quicker.
13. The pilots were attempting to follow the NATOPS emergency procedure by pulling the PCLs for .. Unusual Vibrations on Deck", but were unable to do so based on the violent shaking of the aircraft and the centrifugal forces resulting from the yawing motion of LT 616. The PCLs were most likely not secured prior to the aircraft rolling off the flight deck. [Findings of Fact 63, 93]
Bottom line there should not have been a single unenunciated failure mode that could lead to ground resonance. The question now is why did NAVAIR allow this design to proceed?
Apparently pulling pitch is not an option per the NATOPS. As stated the procedure could not be accomplished due to excessive vibration. This does highlight the benefits of collective mounted throttles like on Bells.
The NATOPs procedure may have been written for experiencing vibrations on start up rather than on landing.
Originally Posted by [email protected]
Yes, sometimes blindly following the rules isn't the best option - airmanship always trumps rulebooks in such scenarios. I also wonder if they were trying to follow the checklist rather than doing it from memory - that might explain the delay.
The NATOPs procedure may have been written for experiencing vibrations on start up rather than on landing.
The NATOPs procedure may have been written for experiencing vibrations on start up rather than on landing.
The NATOPS procedure for Unusual Vibrations On Deck is singular in its response:
1. Collective — Lower.
2. PCLs — OFF.
3. Rotor brake — Apply as required.
The procedure is a Critical Memory Item (CMI), and the steps are expected to be performed immediately, without reference to the checklist.
It probably considers the complicated nature of shipboard operations and the severe safety implications of a helicopter suddenly becoming airborne on a busy deck.
However, a NATOPS FM copy I reviewed includes the option of going airborne in a previous section referencing ground resonance (possibly in an unstated reference to non-shipboard operations):
“If ground resonance should occur, primary consideration should be given to getting the helicopter airborne. If this is impossible, immediately reduce collective pitch, place the PCLs to OFF, and apply the rotor and wheel brakes.”
Since the Navy’s Command Investigation only addresses a potential equipment modification, I assume becoming airborne is not an option:
“Helicopter PCL location in the upper center console is not ideally located for quick securing of the engine in an emergency. Recommend NA VAIR direct a review of emergency procedures and equipment to determine whether it is possible to enable a quicker and easier PCL response during a ground resonance event.”
Thanks Jim - seems like there might be mixed messaging in the books
The braided hose has redundancy, but the fittings do not.
The Navy Command Report has some interesting items that reflect on the assessment of the design…
· Hose is an “on condition” part.
· Hose is inspected at various intervals.
· Hose replacement rate is about 1 per aircraft per year.
· The mishap aircraft had 2 hose changes in the month prior to the event.
· “Mechanical damage (flattening) of steel braid strands on a damper hose would not be evident during any external inspections.” The braid is covered by a chafing guard, and it therefore not visible.
· A one time replacement of all fleet hoses was recommended.
· Fleet inspections apparently have not been changed.
Sultan noted the Accident Report did not discuss the Engine PCL's being on the Overhead Panel being a detriment as compared to the Collective mounted Throttles on Bell Helicopters.
Many aircraft have "Levers", "Buttons", "Knobs" instead of the Bell Collective Throttles.
With the advent of electronic digital control systems we see new and different methods of controlling the Engine(s) as compared to legacy systems using electro-mechanical means.
I have flown several different aircraft with various approaches to Engine Control....and have seen advantages and disadvantages in all of them.
So what should be the determining factor in which design method is employed?
One look at a V-22 Thrust Lever and I shudder to think what engineering issues and human factor issues would have to be confronted to move the PCL's from the overhead Panel to the Thrust Lever.
As it is now....they are moved to the Fllght position not touched until Shutdown of an Engine or Engines.
This does highlight the benefits of collective mounted throttles like on Bells.
With the advent of electronic digital control systems we see new and different methods of controlling the Engine(s) as compared to legacy systems using electro-mechanical means.
I have flown several different aircraft with various approaches to Engine Control....and have seen advantages and disadvantages in all of them.
So what should be the determining factor in which design method is employed?
One look at a V-22 Thrust Lever and I shudder to think what engineering issues and human factor issues would have to be confronted to move the PCL's from the overhead Panel to the Thrust Lever.
As it is now....they are moved to the Fllght position not touched until Shutdown of an Engine or Engines.
I've flown twist grip throttles on TH-57 and Hueys, the center console mounted ECL's in SH-2F's (which can be inadvertently bumped out of the "fly" position, don't ask me how I know that), and the Sikorsky overhead PCL (also used on the CH-53E, can't speak from memory as regards the S-61 / Sea King but I suspect they do also) .
They are fit for purpose.
Also, as you noted:
As it is now....they are moved to the Flight position not touched until Shutdown of an Engine or Engines.
If you have an inflight engine malfunction, you often move the malfunctioning engine's PCL out of fly and either take it to idle, shut it off, or retard it so that it's about 10% below the good one. (Depends on the problem, see your local NATOPS manual for details).
The ECU Lockout feature allows the crew to bypass the electrical control of the engine governor while retaining the load demand spindle / HMU based governing to keep the Nr in pretty close limits (though you will usually see a little bit of lag in getting back to 100% Nr if you make a lot of power changes).
Bad Vibes from Sultan.....please say it ain't so.
As the V-22 is a Bell-Boeing Design....can he actually say Bell products have Collective mounted Throttles?
Boeing calls the "Collective" a "Thrust Lever" owing to its aircraft being Tandem Rotor designs for the most part.
In the Tilt Rotor it is also called the "Thrust Condition Lever".
Engine controls are called "Engine Condition Levers" as they were called on the Chinook.
From an Osprey Test Pilot.....when told of this thread.
As the V-22 is a Bell-Boeing Design....can he actually say Bell products have Collective mounted Throttles?
Boeing calls the "Collective" a "Thrust Lever" owing to its aircraft being Tandem Rotor designs for the most part.
In the Tilt Rotor it is also called the "Thrust Condition Lever".
Engine controls are called "Engine Condition Levers" as they were called on the Chinook.
From an Osprey Test Pilot.....when told of this thread.
Ground resonance is not a problem. Very rigid inplane rotor system coupled with rigid fixed wing type gear. No oleos nor dampners, hydraulic spring absorbers on gear. Throttles are Engine Condition Levers (ECL'S) on center forward overhead panel. Totally electronic. Full forward to fly and forget. TCL (thrust condition lever) controlled by left hand with forward for increasing power, after for decreasing. Acts like a collective in helo mode and throttle in airplane mode. All controlled through triple redundant flight controlled computers. Pilot has NO mechanical linkage to engine or flight controls. All fly by wire. Pilot is one of 4 voting members and is subject to being out voted on routine basis.
No idea what this has to do with the incident in question - are you suggesting the PM/PNF should hold the ECLs during T/O and Landing just in case there is ground resonance (or TR failure)?
A slightly mixed up statement I think. FO and Capt can both be either PF or PM, however, many/most airlines state that only the Capt can decide whether to abort the take off. So, if the FO is the PF it is SOP that the Capt also guards the throttles until V1, so that he can abort the T/O without the delay of instructing the PF to do so.
No idea what this has to do with the incident in question - are you suggesting the PM/PNF should hold the ECLs during T/O and Landing just in case there is ground resonance (or TR failure)?
No idea what this has to do with the incident in question - are you suggesting the PM/PNF should hold the ECLs during T/O and Landing just in case there is ground resonance (or TR failure)?
Just food for thought.
Before mocking, contemplate if it may have saved this aircraft and crew. I doubt the Navy's investigation reccomending changing the location of the H-60 PCLs would ever happen.
I wouldn’t suggest it without it being SOP and prior training. I don't expect the thought to be well accepted either, the industry as a whole has a hard enough time getting a PF to give the NFP a proper takeoff or pre-landing brief.
