Blackhawk moving tailplane
Joined: Jul 2004
Posts: 376
Likes: 4
From: Durham, NC USA
Blackhawk Stabilator
The stabilator on the S-70 series receives inputs from:
1. Airspeed - To keep the fuselage level in cruise and to reduce the pitch attitude during deceleration to a hover.
2. Lateral Acceleration – To keep the pitch attitude level during sideslips (counteract the canted tail)
3. Pitch Rate – To enhance maneuver stability
4. Collective position – To reduce the tendency for pitch attitude changes with collective changes
I think I hit them all. It works really hard in turbulance.
1. Airspeed - To keep the fuselage level in cruise and to reduce the pitch attitude during deceleration to a hover.
2. Lateral Acceleration – To keep the pitch attitude level during sideslips (counteract the canted tail)
3. Pitch Rate – To enhance maneuver stability
4. Collective position – To reduce the tendency for pitch attitude changes with collective changes
I think I hit them all. It works really hard in turbulance.
Joined: Jul 2004
Posts: 376
Likes: 4
From: Durham, NC USA
The Blackhawk tail rotor is canted 20 degrees. At 20 degrees, a full 34% of the thrust go to lift while only a 6% reduction in anti torque thrust is realized. The Blackhawk literally holds up its own butt. This provides for an increase in longitudinal CG range. The H-53E Tail rotor is also canted 20 degrees. On a negative note, canting the tail increases the complexity of the flight control system as revealed by a quick peek at the Blackhawks flight control mixer unit.
Joined: Oct 2003
Posts: 346
Likes: 0
From: Europe/US
JC, You sure it's not 2.5% of all overall lift generated? Also it has two actuators ( typical Sikorsky redundantcy) to drive the stabilator which in turn generate dynamic stability in cruise or more level platform at the hover...key speed being 40KIAS!
Joined: Jul 2004
Posts: 376
Likes: 4
From: Durham, NC USA
You are correct! 2.5 of total lift, but 34% of Tail Rotor thrust. The stab has a dual actuator but only one air data input. That is why it defaults to an off/manual condition with any failure. Its been a while for me, do you remember if the stab also has a yaw rate input?
Joined: Oct 2003
Posts: 346
Likes: 0
From: Europe/US
I believe so, although it was a combined input ie yaw to pitch value + airspeed data transducer input. Of course the mixing unit was designed for 16850lbs or thereabouts. I'm sure you can remember the demonstration of the Heading Hold micro switches on the pedals,, and how at 16850 GWT you could lift vertical without the need for any compensation of Translating Tendency, Heading or pitch. Great Mixing!! But the Stabilator is a seperate dynamic function than the Mixing unit but addsto it's performance! When they worked the bugs out, it worked great! A few of my buddies became the statistical dead test pilots may they RIP. Price of technology is very severe sometimes, and the UH-60 extracted it's toll on life in it's advancement. A terrific Helicopter with very few competitors, if any!!
Joined: Jul 2001
Posts: 1,084
Likes: 1
From: the cockpit
That Black Hawk mixing unit is a work of genius.
Yes, I think that was part of the lateral accelerometer input you mentioned earlier. From memory, the lateral input to the stab was one of the most significant, although I dont remember the reason being the one Jack C gives above (cantered tail rotor). I recall the need for all that authority was that the stabilator itself changed relative airflows with sideslip. In forward flight, pushing left pedal caused the stab to move out from the downwash influence and would cause more lift, therefore a significant pitching moment unless the stabilator moved. Right pedal caused the opposite by moving the stab further into the downwash influence and losing lift, also causing a significant pitch moment if not countered by automatic stab movement.
Its been a while for me, do you remember if the stab also has a yaw rate input?
