Who Knows About The UH-60 Blackhawk ??

[billt460]

I always wondered about the tail. It appears to have a movable vertical stabilizer back by the tail rotor. Much like the elevator on an airplane. Or a type of, "Flying Stabilizer" like a DC-9. (Remember when the jack screw broke on the Alaska Airlines DC-9 / MD-80, jamming it in the down position)? This is obviously movable also, because I've seen photos of it in different positions on the Blackhawk. It's not something that is very common with helicopters. My question is, if anyone knows how this control surface is moved and controlled? Along with it's purpose? Wouldn't moving the cyclic full up to full down give the bird enough vertical pitch like most other copters?

Is it operated by computer, in relationship to the cyclic? Or is it controlled by the pilot utilizing some other type of format? I would think that when the bird was in hover, it would be catching a lot of downdraft from the main rotor in the flat, level position. Which could force the tail down / nose up. But when flying forward at speed, it would act more like an elevator. Or am I wrong?

 

[billt460]

Here it shows it in flight with the stabilizer flat and level. And on the ground with it pitched fully down. It has a great deal of surface area.

 

[y_p_w]

It should be automatic. There was a Coast Guard Jay Hawk in season 1 of Jack Ryan, and the "stabilator" is pointing down in all scenes near the ground.

This Sea Hawk is landing and it's never horizontal. I think that's only when it moving forward at a high speed.

 

[wpod]

Helos are complicated. They are not connected to the cyclic operation [mechanically]and are speed input [ computer] controlled.

 

[ripcord]

Just guessing, but looks like it would help reduce or induce forward or backward pitch of the bird under high power?

 

[ripcord]

Outrageous! The guy on that roof has no safety gear. Somebody call OSHA!

 

[billt460]

It should be automatic. There was a Coast Guard Jay Hawk in season 1 of Jack Ryan, and the "stabilator" is pointing down in all scenes near the ground.

This Sea Hawk is landing and it's never horizontal. I think that's only when it moving forward at a high speed.

Here is a photo of it hovering close to the ground, and the stabilizer is level.

 

[wwillson]

https://www.rotaryforum.com/threads/blackhawk-question.11375/post-254080

"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."

 

[y_p_w]

Here is a photo of it hovering close to the ground, and the stabilizer is level.

It's not level.

 

[zeky]

I would look at it as more of a trim tab while in straigh ahead flight. Look at it as a flap for landing or hovering close to ground.

 

[billt460]

It's not level.

Sure looks level to me. The rear of that stabilizer is v shaped. You can by looking at it, it's straight across.

 

[SatinSilver]

Maybe because it's not landing and only pitches when landing or decending. Funny I was just watching a landing video of these and wondering about the tail design. Then come on here and see this thread.

 

[Killer223]

what happened to @AH64ID? he might know.

 

[y_p_w]

Sure looks level to me. The rear of that stabilizer is v shaped. You can by looking at it, it's straight across.

You mean the big honking thing at the end that's typically at a downward angle when landing and parallel tp the ground in level flight? The photo you linked isn't great and doesn't show a lot of context compared to video, but it's still at an angle.

This is what they look like hovering.

 

[Dodgetracker]

Been working on Hawks for 34 years now, it is much as Wwillson explained more or less, up a few posts. When the stab is in the down position its roughly 37-39 degrees trailing edge down. In full up its appx 3-4 degrees trailing edge up. It is speed dependent and starts to move at appx 40 knots. It can be manually slewed as well via a stab switch in center console or a pinky switch's on each cyclic. The older alpha models and Lima models have 2 stab amplifiers where as Mike models only have 1. It slews down to help dissipate the rotor wash downforce from raising the nose at hover or slow speeds. At speeds close to 100 knots it will be at zero angle. Above 120 knots it slews to full up. Pinky switches were installed due to 2 major crashes in 1984 or 5. 1 at FT Campbell and 1 at FT Bragg, both low Low level flight and stab failed for whatever reason. When stab fails it defaults to full down position and at high airspeeds low altitude you crash from nose over. The one at Campbell crashed into back of school bus parked alongside road with driver asleep inside 4 people killed. Bragg doing grunt insertion and had pax on board all killed.

 

[wwillson]

Been working on Hawks for 34 years now

I'm always amazed at this community, there is always someone who knows the answer!

 

[Dodgetracker]

Ah the stories I could tell lol

 

[cbear]

I've always wondered why the tail rotor is tilted, ie not perpendicular to the main rotor?

 

[Dodgetracker]

That tilt provides 400 lbs of lift, and with the 3degree bias input in PC links just a tad more.