Blackhawk Stabilator
Avoid imitations
Joined: Nov 2000
Aviation Qualifications: ATPL
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From: Wandering the FIR and cyberspace often at highly unsociable times
Its an integral part of the AFCS and is constantly adjusting in flight. It motors even when you might think it wouldn't need to, such as in turns, as the offset tail rotor has effects on pitch.
There is a manual reversion system in case of a malfunction.
There is a manual reversion system in case of a malfunction.
Joined: Aug 2000
Posts: 35
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From: 13 Mad Street, Reasons Edge, Colonia
Spotter's Answer:
The Stabilator;
1) Streamlines with rotor downwash below 30kts;
2) Moves with collective to counter changes in downwash 30-60kts;
3) Trailing edge up on increasing airspeed to maintain speed stable attitude 30-150kts;
4) Motors up or down in turns to counter effect of the 'area of reduced downwash' moving over or off the stabilator. Cued from lateral accelerometers. Moves to as much as full down in a 1.25g turn to left;and
5) Pitch stability augmentation +/- 6 deg.
Stabilator is dual channel and takes inputs from Air speed sensors, Pitch rate gyros, lateral accelerometers and collective stick position sensors. But then again, no one really needs to know this; it just moves when you're flying and no one gives a cr*p unless it breaks. Of course that never happens
Shytorque was entirely correct; just that he's not as sad as I am.
The Stabilator;
1) Streamlines with rotor downwash below 30kts;
2) Moves with collective to counter changes in downwash 30-60kts;
3) Trailing edge up on increasing airspeed to maintain speed stable attitude 30-150kts;
4) Motors up or down in turns to counter effect of the 'area of reduced downwash' moving over or off the stabilator. Cued from lateral accelerometers. Moves to as much as full down in a 1.25g turn to left;and
5) Pitch stability augmentation +/- 6 deg.
Stabilator is dual channel and takes inputs from Air speed sensors, Pitch rate gyros, lateral accelerometers and collective stick position sensors. But then again, no one really needs to know this; it just moves when you're flying and no one gives a cr*p unless it breaks. Of course that never happens
Shytorque was entirely correct; just that he's not as sad as I am.
Joined: Apr 2003
Posts: 3,012
Likes: 1
From: USA
Shy and Empire have it mostly right (and certainly quite right enough to fly the aircraft for a career, as Empire says). Here is a functional way to look at the stab's duties (I flew the first flight of the stabilator on the Hawk, back in about 1975):
1) It keeps the nose down when slowing at low speeds - by aligning with the downwash. This lets the pilot see more on approach, allows a greater aft CG, and keeps the main rotor shaft bending loads down. It is the main reason why the stabilator moves at all.
2) It makes the nose rise up a bit when speed is increased, thus requiring the pilot to push a little forward stick. this gives an utterly useless, but quite measurable characteristic known as "longitudinal static stick stability" which is easy to measure, and so becomes a required characteristic.
3) It keeps the nose attitude level when the ball is pushed out either left or right - the lateral accelerometers (electronic trim balls) feed the stabilator info so it moves up or down to quell the natural tendency for the nose to pop up in left pedal/right sideslip maneuvers, or pop down in right pedal/left sideslip events. This is a natural single rotor helicopter tendency.
4) It makes the nose drop in steep banked turns in either direction, so that the pilot must pull the stick back to keep trimmed in the turn. This creates a positive maneuvering stability, where the back stick builds the load factor, making it easier to trim to a given G level.
The stabilator has its own controller boxes (the stabilator amplifiers) and they compare their outputs to shut it down if they disagree.
Contrary to popular mythology, there has never been a failure of the stabilator that caused an accident.
1) It keeps the nose down when slowing at low speeds - by aligning with the downwash. This lets the pilot see more on approach, allows a greater aft CG, and keeps the main rotor shaft bending loads down. It is the main reason why the stabilator moves at all.
2) It makes the nose rise up a bit when speed is increased, thus requiring the pilot to push a little forward stick. this gives an utterly useless, but quite measurable characteristic known as "longitudinal static stick stability" which is easy to measure, and so becomes a required characteristic.
3) It keeps the nose attitude level when the ball is pushed out either left or right - the lateral accelerometers (electronic trim balls) feed the stabilator info so it moves up or down to quell the natural tendency for the nose to pop up in left pedal/right sideslip maneuvers, or pop down in right pedal/left sideslip events. This is a natural single rotor helicopter tendency.
4) It makes the nose drop in steep banked turns in either direction, so that the pilot must pull the stick back to keep trimmed in the turn. This creates a positive maneuvering stability, where the back stick builds the load factor, making it easier to trim to a given G level.
The stabilator has its own controller boxes (the stabilator amplifiers) and they compare their outputs to shut it down if they disagree.
Contrary to popular mythology, there has never been a failure of the stabilator that caused an accident.
Joined: May 2002
Aviation Qualifications: ATP+Mil
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From: Downeast
Nick,
What was all the hub-bub about shielding of the boxes or whatever? After the Fort Bragg crash, was it not a concern that some microwave radiation or something like that had caused a runaway stabilator? There was some history there about those kinds of issues/concerns.....was it just some much speculation and found not to be an issue?
What was all the hub-bub about shielding of the boxes or whatever? After the Fort Bragg crash, was it not a concern that some microwave radiation or something like that had caused a runaway stabilator? There was some history there about those kinds of issues/concerns.....was it just some much speculation and found not to be an issue?
Gentleman Aviator
Joined: Jul 2000
Posts: 3,722
Likes: 91
From: Teetering Towers - somewhere in the Shires
Of course that never happens
... you might not notice it when it's working, but you sure miss it when it's not!
Joined: Apr 2003
Posts: 3,012
Likes: 1
From: USA
SASless,
There were BH accidents on first introduction, and somehow the redheaded step child of stabilator was the first blamee, every time. The Bragg one was propelled by "reports" that the stabilator was seen moving toward the hover position (it was in level high speed mode when the aircraft hit.) A bolt left un fastened in the upper deck pitch controls was found as the eventual cause, but that didnt stop the rumors. Similar groundings followed NVG accidents and such, with the stab getting the blame in the rumor mill.
The shielding was introduced (and very high capability shielding was demanded for all new US Army helos) when a BH in Germany had the stab move about 7 degrees and then shut down as they flew past a Radio Free Europe transmitter. No big problem, but we frown on involuntary remote control helos!
Matthew, LSS is the measure of how the speed effects the stick, on a microscopic scale. A stick that moves forward .1MM to reflect a 10 knot change is said to be "positively stable" even if the helo's arispeed wanders all over the dial when the aircraft is flown hand's off. In work I have done, pilots can't tell "stable" from "unstable" aircraft, because they release trim, and let the stick flop around.
There were BH accidents on first introduction, and somehow the redheaded step child of stabilator was the first blamee, every time. The Bragg one was propelled by "reports" that the stabilator was seen moving toward the hover position (it was in level high speed mode when the aircraft hit.) A bolt left un fastened in the upper deck pitch controls was found as the eventual cause, but that didnt stop the rumors. Similar groundings followed NVG accidents and such, with the stab getting the blame in the rumor mill.
The shielding was introduced (and very high capability shielding was demanded for all new US Army helos) when a BH in Germany had the stab move about 7 degrees and then shut down as they flew past a Radio Free Europe transmitter. No big problem, but we frown on involuntary remote control helos!
Matthew, LSS is the measure of how the speed effects the stick, on a microscopic scale. A stick that moves forward .1MM to reflect a 10 knot change is said to be "positively stable" even if the helo's arispeed wanders all over the dial when the aircraft is flown hand's off. In work I have done, pilots can't tell "stable" from "unstable" aircraft, because they release trim, and let the stick flop around.
Avoid imitations
Joined: Nov 2000
Aviation Qualifications: ATPL
Posts: 15,110
Likes: 1,083
From: Wandering the FIR and cyberspace often at highly unsociable times
Empire One, you're right, I'm not as sad or knowledgeable as you are as I gave up flying the S-70 over 7 years ago - but I still consider the Blackhawk my all-time favourite helicopter.
For those that haven't seen it, if you ever get a ride, ask to see a max transient take-off power vertical departure....
I understand the S-76 was also originally destined for a moving stabilator (and a two foot higher tail pylon) ...but it was actually found unneccessary.
'Zat True, Nick?
For those that haven't seen it, if you ever get a ride, ask to see a max transient take-off power vertical departure....
I understand the S-76 was also originally destined for a moving stabilator (and a two foot higher tail pylon) ...but it was actually found unneccessary.
'Zat True, Nick?
Joined: Aug 2000
Posts: 35
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From: 13 Mad Street, Reasons Edge, Colonia
ShyTq,
I agree, the Blackhawk is also my all-time favourite aircraft. It does almost everything you ask of it very well (within the constraints of a retarded military procurement system) and I have friends who've walked away from serious smashes. There aren't many helicopters (designed 30 years ago) that can boast the same amount of crash survivability. I particularly miss it now that I've just started flying the mighty 206. What a difference!!
Teets,
Yeah ok, my parting comment was a bit glib
I've had a couple of stab failures, not including the QHI initiated ones and it makes a hell of a difference when its not working. The extra nose high attitude in transtion to the hover is particularly noticable (especially when you're a short-ar*e who can barely see over the instrument panel in level flight!).
EO
I agree, the Blackhawk is also my all-time favourite aircraft. It does almost everything you ask of it very well (within the constraints of a retarded military procurement system) and I have friends who've walked away from serious smashes. There aren't many helicopters (designed 30 years ago) that can boast the same amount of crash survivability. I particularly miss it now that I've just started flying the mighty 206. What a difference!!
Teets,
Yeah ok, my parting comment was a bit glib
I've had a couple of stab failures, not including the QHI initiated ones and it makes a hell of a difference when its not working. The extra nose high attitude in transtion to the hover is particularly noticable (especially when you're a short-ar*e who can barely see over the instrument panel in level flight!).EO
