blackhawk question

Brent Drake

Gyroplane Instructor
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Jun 15, 2004
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Shelbyville, Indiana
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I just watched a blackhawk I think take off at the local National Guard.
My question is. If the copter I saw was a Blackhawk. then it had what I believe to be an elevator back by the tail rotor like an airplane. does anyone know the purpose of this elevator. I've not seen one on a copter before.
 
Blackhawk Stabilator

Blackhawk Stabilator

I think what you saw is called a stabilator. It helps keep the cabin angle at a managable level. On aproach the stab deflects trailing edge down to help lower the nose for visibility.
During high speed the leading edge is down pulling the tail down so the acft flys about level.
I know that there are several other reasons for it and most helicopters have some form of stabilator/elevator on the back.

Hope It Helps
Brian G. Douglas
CIV TI
AH-64D, UH-60A/L/M, UH-1H and serveral other Army Acft
Killeen Texas
 
Brent,

Many helicopters have a, for lack of a better term, "horizontal stabilizer". The one on a Blackhawk is proportionally very large. This is probably why you noticed it.
 
Here is part of a post about BlackHawk stabilators by Nick Lappos, former chief testpilot for Sikorsky, from the pprune.org forum:

"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."

 
Brent, I could name a lot of helicopters that have either fixed stabilizers or active stabilators. The Jet Ranger series are fixed. The UH-1, AH-1, AH-64 and UH-60 all have active stabilators. The "why" question came up in class at Ft. Eustis when I was In Cobra Repair school. The biggest reason the AH-1 has an active stabilator is to prevent the nose tucking under during forward acceleration. Even the lowly 269 has a fixed stab, as does my Schleuter Moskito r/c copter. I tried flying the Moskito once with out the stab because I thought it looked better with out it. Turns out the stab is functional. I didn't crash, but the grass was little shorter in my take-off path.
 
Thanks guys for your answers. I knew some helicopters had fixed stab. But I thought I saw the Blackhawk move. That's why I questioned it. And since it moved I figured It would be called and elevatorand not a stab.
You gys always answer my questions. Many thanks and God Bless.
 
Brent,
The Stab or Sync Elevator on the UH-1 Huey and the AH-1 Cobra doesn't move so much that it is notices from a distance. The Blackhawk has a massive Stab and like the others have mentioned helps maintain the cabin in a position for visibility and stability of the aircraft.
 
The Blackhawk's general shape and external dimensions were dictated by the Army's requirement that one complete UTTAS helicopter be air transportable within the cargo bay of a single C-130 Hercules (with the additional requirement that two helicopters fit within a single C-141 Starlifter, and six within each C-5 Galaxy). The UH-60 is thus a long and low-set craft with a streamlined pod-and-boom layout, and is characterized by a downward-sloping tail boom fitted with a moving stabilator, a sharply-swept vertical tail, and a four-bladed anti-torque rotor canted twenty degrees off the vertical to produce added lift and thus allow a reduction in the main rotor diameter. The tips o1 each of the Blackhawk's four fully-articulated, high-lift main rotor blades are swept twenty degrees to reduce control loads and the effects of high Mach numbers, and all four blades can be manually folded. The UH-60A can be fitted with an External Stores Support System (ESSS) consisting of two stub wings, one fixed to either side of the central fuselage above and just forward of the main cabin doors. These stub wings can carry auxiliary fuel tanks, electronic countermeasures (ECM) equip-ments, machine gun, cannon or rocket pods, up to sixteen Hellfire anti-tank missiles, or four M-56 landmine dispensers.
 
Brent,

It's called a "stabilator," as in "stabilizer and elevator" together, and it sweeps through a pretty big arc, depending mostly on airspeed and collective input.

Your eyes did not deceive you !!! It moves pretty quickly, too (full up (6-9 degrees up) to full down (34-42 degrees down) in about 7 seconds)

The stabilator is 40 square feet (for Army models - Navy models fold, and are smaller).

The stab schedules down from almost level in forward flight to about 40 degrees down at a hover.

It has a bunch of sensors that schedule the stab up and down based on various inputs, but the basic function is to provide longitudinal stability, and basically keep the aircraft level.

It assists the SAS and FPS in keeping the airframe a stable platform.

It has a HUGE effect on longitudinal stability, as can be witnessed by the "Lawn Dart" reputation it earned when the stabilators scheduled to the full down setting uncommanded (ughhhhhh - at certain airspeed and power combos, it is unrecoverable).

It's why I'm such a big fan of H Stabs on ALL gyros.
 
Amazing Force

Amazing Force

If you want to do something that's amazingly fun....


Low pass down the airport in a UH-60 @ approx. 160knots (Vh)....

Have an uncommanded trailing edge up failure in the stabilator....

The nose up attitude created by the aerodynamic force of that 40sq/ft slab is unbelievable!!!


I've also heard tell of a ACM manuever in a 60 called and X over Y take off that could not be done were it not for the stabilator. It goes something like this:

From a standard 10ft hover pull the collective to 100% torque. Simultaneously lower the nose to 90 degress nose low. The aircraft will shoot forward at incredible accelaration, leveling out due to the stabilator moving to full up.


Walker Armstrong
UH-60 Pilot
RAF 2000 Owner
 
since it moved I figured It would be called and elevatorand not a stab.

Don't want to step on the UH-60 drivers here (I just have a lot of riding-in, jumping-from, rappelling- and fastroping-outa, and a bit of getting-medevaced-by 60 time). But I want to address terminology.

Both "Stabilator" and "Elevator" come from fixed-wing terminology.

An "Elevator" is a moving control surface attached to the trailing edge of a horizontal stabilizer. The H-stab is fixed, the elevator moves, and provides pitch control about the lateral axis. In airplanes, this direct control of pitch indirectly controls airspeed.

A "stabilator" is an all-moving control surface that combines the functions (as the word combines the names) of stabilizer and elevator. It was invented, I believe, by Fred Weick of NACA and is found on aircraft he had a hand in, and on those that John Thorp worked on (a very familiar example being the Piper Cherokee and its many derivatives). On a f/w, a stabilator lets you get away with a smaller and lighter tail surface, at the cost of a little more trim sensitivity. It's mostly used in light to medium GA aircraft; transport category machinery is more likely to have a divided elevator and stabilizer.

Since the helicopter surface is not used as a primary attitude control, it's either fixed (a stabilizer) or all-moving (a stabilator). There may be a helicopter that has a two-part (fixed stab and moving elevator) surface, but if so I am unaware of it. (Given the many hundreds of helicopter designs that have flown, I'd not be at all surprized if there is one out there somewhere).

The helicopter's stabilator is, unlike the airplane's, not directly controlled by the pilot.

The RAF Rotor Stabilator is a different animal entirely. It seems to be a truly useful sort of trim vane or artificial feedback device, but it doesn't perform all the functions of a classical tail stabilator.

cheers

-=K=-
 
Interesting thread guys, but I'll take the old reliable UH-1 Huey anytime. All I know is when the last UH-60 Blackhawk is retired, the crew will be picked up in a UH-1

Happy New Year everyone!

Wayne
 
Interesting thread guys, but I'll take the old reliable UH-1 Huey anytime. All I know is when the last UH-60 Blackhawk is retired, the crew will be picked up in a UH-1

Happy New Year everyone!

Wayne
I found this thread in a search on "stabilator" ... it's many years later now, and I just wanted to point out that Black Hawks are still picking up, moving, and putting down :)

Last Huey: https://www.army.mil/article/180593...n_retires#:~:text=The last UH-1 Huey,15, 2016.

Last Black Hawk?
https://www.reuters.com/business/ae...ract-build-black-hawk-helicopters-2022-06-27/
 
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