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Blackhawk tail rotor


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#1 Brianmech72

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Posted 28 March 2007 - 19:57

I have a question about the tail rotor on a Blackhawk. Why is it tilted the way it is? I have wondered this for a while and I got a look at the Delaware ANG's machine today. I saw it during my lesson today at EVY (Summit, DE). I also thought the tail rotor was on the left side but this one was on the right. I need to go and check photos to see if I am wrong about that one though.

#2 Corbec

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Posted 28 March 2007 - 22:49

The tail rotor is on the right. It's canted 20 deg to provide more vertical lift. The design was originally used on the H-53, and Sikorsky carried it over to the H-60.

#3 Gunner

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Posted 28 March 2007 - 22:58

additional lift and maybe to cut down on transalting tendency??? Just a guess...

#4 JDHelicopterPilot

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Posted 28 March 2007 - 23:06

I don't remember, I think someone had said due to the excessive aft CG tilting the rotor was a way to help keep the tail up higher. Have you ever seen them do autos? When they flare I have seen some really tail low. Any blackhawk drivers around who can help??????
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#5 Corbec

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Posted 29 March 2007 - 09:22

I flew the Seahawk for 3 1/2 years at Mayport, FL. The Seahawk and the Blackhawk have the same tailrotor.
The cant may cut down on translating tendency and also limit the effects of various tailrotor effects, like tailrotor vortex ring, etc. I haven't look in the NATOPS (operating manual) in a while, but I think it only talks about the added vertical lift, most likely to correct the CG issue you talked about.

The flare in autos is excessive, but I don't think the CG plays into it. It's a 20,000lb helo and there's a lot of momentum. The flare starts at about 200ft and it's not too bad there, maybe 10 deg. At about 100 ft it starts to get big, maybe up to 35 or 40 deg. You can't really see out the front anymore.

I've heard that the 53 autos similarly. I've also heard autoing the 53 compared to autoing an apartment building. :lol:

#6 lowflyer169

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Posted 06 April 2007 - 11:28

Tail rotor assembly.

(1) Tail rotor is to provide directional and anti-torque control for the aircraft plus a measurable lift of 400 lb.. The assembly incorporates two cross beam tail rotor blades with flexible spars that provide flapping and pitch change. Securing of the tail rotor blades to the tail gear box is accomplished by an inboard and outboard retention plate. Lateral inputs of the tail rotor servo is transmitted to the pitch shaft, pitch beam, pitch links and then to the blades. The 20 degrees cant of the tail rotor assembly provides the following advantages: Low profile, 400 lb.. Lift, greater hover and low speed flight stability, increased rate of climb, allows the nose of the aircraft to be short.



Tail rotor assembly.

(1) Tail rotor is to provide directional and anti-torque control for the aircraft plus a measurable lift of 400 lb.. The assembly incorporates two cross beam tail rotor blades with flexible spars that provide flapping and pitch change. Securing of the tail rotor blades to the tail gear box is accomplished by an inboard and outboard retention plate. Lateral inputs of the tail rotor servo is transmitted to the pitch shaft, pitch beam, pitch links and then to the blades. The 20 degrees cant of the tail rotor assembly provides the following advantages: Low profile, 400 lb.. Lift, greater hover and low speed flight stability, increased rate of climb, allows the nose of the aircraft to be short.

#7 ECD

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Posted 26 May 2007 - 20:02

Number one positive effect would be lift..
Canting the tail rotor could "never" impact drifting. The tail rotor counters moment of main rotor. The amount of force needed is given by moment from main rotor and the distance to its axis. This amount of thrust must be delivered to keep the helicopter steady in yaw direction and will also be the amount of thrust creating the drift. To counter drift the main rotor should be tilted.
Tilting the tail rotor upwards will reduce the amount of counteracting thrust but ad lift. Most likely the tail rotor assembly is a bit too heavy and delivers abundant thrust, thus it makes sense to tilt it.
It’s a question of proportion. The main rotor is so big that the tail must be quite long, therefore heavy, to provide for distance between main and tail rotor. It then makes more sense to ad lift aft than to ad weight in front. A redesign, with all costs involved, to make the whole tail lighter, move the COG or even cant the main rotor is most likely a more expensive option than canting the tail rotor..

Edited by ECD, 31 May 2007 - 01:24.


#8 Dumb60pilot

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Posted 14 June 2007 - 23:24

The tail rotor is Canted 20 degress to provide lift (2.5% of total lift). This in turn improves CG. As far as the Flare at the bottom of an Auto, the Army recommends it at 50 to 75 ft AGL and no more that 25 degrees to prevent stabilator/ground contact.

#9 snoogan6

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Posted 10 December 2007 - 10:27

The tail rotor is Canted 20 degress to provide lift (2.5% of total lift). This in turn improves CG. As far as the Flare at the bottom of an Auto, the Army recommends it at 50 to 75 ft AGL and no more that 25 degrees to prevent stabilator/ground contact.





I couldn't agree more and, a side note the 2.5% lift is at a hover only.
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#10 as350b3

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Posted 11 December 2007 - 22:22

It's been a a while for me, but if I remember correctly, here's the deal.
Technically, 2.5% lift out of the -10 is only applicable when gross weight is exactly 18,625 lbs. and Nr is exactly 100%.
Multiple replies to the OP are correct in stating that the t/r provides approx. 400-500 lbs of vertical lift. Along with the speed-dependent stabilator, it allows for a a significant enlargement of the safe CG envelope.
The canted t/r increases the complexity of flight control cross coupling considerably. There are dedicated mechanical flight control mixing units for four different aerodynamic coupling effects, which minimize inherent control negative coupling: collective to pitch, collective to yaw, collective to roll, yaw to pitch. The pilot never sees his flight controls move, but inputs to both the m/r and t/r are interdependent and are coordinated mechanically between the trim/SAS motors and the hydraulic servos.
There is an additional electronic coupling that takes place on top of the 4 mentioned above: collective/airspeed to yaw. It helps to compensate for the torque effect caused by changes in collective position. It has the ability to decrease t/r pitch as airspeed increases and the t/r and cambered vertical fin become more efficient. As airspeed decreases the opposite occurs.
Overall, this is a very amazing albeit complex flight control system. And all of this primarily because the t/r is canted 20 degrees....

#11 snoogan6

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Posted 12 December 2007 - 10:35

Technically, 2.5% lift out of the -10 is only applicable when gross weight is exactly 18,625 lbs. and Nr is exactly 100%.


Well the -10 is based on the design weight of 16,825 lbs. The -10 dated 17 April 2006 states on page 72 under paragraph 2.51 "The tail rotor head and blades are installed on the right side of the tail pylon, canted 20° upward. In addition to providing directional control and anti-torque reaction, the tail rotor provides 2.5% of the total lifting force in a hover." After looking through some maintenance manuals and speaking with some MTP's (Maintenance Test Pilots) it provides 400 lbs. of lift and spins at 1,190 RPM's. While 2.5% at design wight is equal to 420.6 lbs. of lift. However, even at heavier gross weights your RPM's are still the same and it will still provide you 2.5% of lift. There may be a thresh hold to this but no definitive answer that I could find. I guess the only way to truly find the thresh hold is to ask Sikorsky.
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#12 CharyouTree

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Posted 16 December 2007 - 12:23

It's been a a while for me, but if I remember correctly, here's the deal.
Technically, 2.5% lift out of the -10 is only applicable when gross weight is exactly 18,625 lbs. and Nr is exactly 100%.
Multiple replies to the OP are correct in stating that the t/r provides approx. 400-500 lbs of vertical lift. Along with the speed-dependent stabilator, it allows for a a significant enlargement of the safe CG envelope.
The canted t/r increases the complexity of flight control cross coupling considerably. There are dedicated mechanical flight control mixing units for four different aerodynamic coupling effects, which minimize inherent control negative coupling: collective to pitch, collective to yaw, collective to roll, yaw to pitch. The pilot never sees his flight controls move, but inputs to both the m/r and t/r are interdependent and are coordinated mechanically between the trim/SAS motors and the hydraulic servos.
There is an additional electronic coupling that takes place on top of the 4 mentioned above: collective/airspeed to yaw. It helps to compensate for the torque effect caused by changes in collective position. It has the ability to decrease t/r pitch as airspeed increases and the t/r and cambered vertical fin become more efficient. As airspeed decreases the opposite occurs.
Overall, this is a very amazing albeit complex flight control system. And all of this primarily because the t/r is canted 20 degrees....


I thought all of those couplings (collective to pitch, yaw, roll) were for stability in a hover?

#13 snoogan6

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Posted 17 December 2007 - 22:51

I thought all of those couplings (collective to pitch, yaw, roll) were for stability in a hover?


Well what as350b3 stated is correct about the inputs. If you look in TM 11-1520-237-23 (AFCS) on pages 12-5 and 12-6 it will state what he did almost verbatim.
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#14 chamerican

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Posted 20 December 2007 - 06:42

I thought all of those couplings (collective to pitch, yaw, roll) were for stability in a hover?


Yes they primarily provide stability in a hover but it is a mechanical linkage that is still present in flight. In flight, stability is primarily maintained by the pilot (obviously), and the Automatic Flight Control System. As AS350b said it is a complicated flight control system (a proverbial can-of-worms). Even at a hover AFCS is providing assistance to the pilot whether it be heading hold or short term rate dampening (e.g. the effects of wind gusts). To sum it up, stability is a combination of mechanical linkage, pilot input, and electro-mechanical input from the AFCS.

Edited by chamerican, 20 December 2007 - 06:43.


#15 Sundowner

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Posted 25 March 2008 - 19:48

Is there much difference in basic handling of S-70B, compared to standard S-70 ? I assume the tail folding modifications, and changing tail wheel position, and forward avionics compartments mixed the C.G. a bit, and the main rotor hub is also modified for blades folding. I'm also wondering if the AFCS is also modified because of the time those machines spend in hover...

Sorry for those unrelated with topic questions, but I can't find manual for that bird, maybe the NATOPS A1-H60BB-NFM-000 (and whatever JayHawk drivers got) is somewhat restricted, as I was able to find the TM 1-1520-237-10 and TM 1-1520-253-10 with no joy on the old SeaHawk.

#16 Rob Lyman

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Posted 17 April 2008 - 13:18

Is there much difference in basic handling of S-70B, compared to standard S-70 ? I assume the tail folding modifications, and changing tail wheel position, and forward avionics compartments mixed the C.G. a bit, and the main rotor hub is also modified for blades folding. I'm also wondering if the AFCS is also modified because of the time those machines spend in hover...

Sorry for those unrelated with topic questions, but I can't find manual for that bird, maybe the NATOPS A1-H60BB-NFM-000 (and whatever JayHawk drivers got) is somewhat restricted, as I was able to find the TM 1-1520-237-10 and TM 1-1520-253-10 with no joy on the old SeaHawk.

The mechanical mixing is the same in both models. The AFCS is different. They both have SAS1 and SAS2, although I believe SAS1 may be different between the two. The SH-60B has nothing in the start checklist to ensure SAS1 is off. The UH-60 has Flight Path Stabilization (FPS) while the SH-60B has Autopilot. The latter incorporates an altitude hold (RadAlt and BarAlt), an automatic approach to hover, and a coupled hover. The collective has a trigger to engage and disengage the collective trim on the SH-60B. The UH-60 has a friction lock for the collective.

There are alot of other minor differences that make the transition between the two annoying, such as no rotor brake, less sturdy landing gear, no ECS, no built in hydraulic rescue hoist, no torque limits for rotor engagement (due to the tailwheel being further back) on the UH-60, different locations for the parking brake, tailwheel lock, boost pump switches, rotor deice.

The UH-60 has a cyclic trigger switch to slew the stabilator up, the SH-60B, with shielded wiring for the stabilator control, does not. The Army also has a bunch of EPs for the UH-60 that are not in the SH-60B NATOPS which include: Lightning Strike, Uncommanded Nose Up/Nose Down, FPS failure, and Pedal Bind.

I also noticed this weekend there is no positive open lock on the pilot's door in the UH-60. The SH-60B door must be "unlocked" from the full open position by turning the door latch. The Navy knew to expect gusty winds. I guess the Army figures that you won't leave your hands, feet or anything else near the door opening while sitting in the aircraft. I nearly lost some fingers when a gust of wind pushed the UH-60 door closed with a slam on Saturday.

Oh, and who had the bright idea you need a key to unlock and start a military helicopter? The "ignition" switch in the UH-60 is actually like a car, requiring a key. If I look on the overhead console for the igntion switches (#1 and #2) one more time I am going to start banging my head against the glare shield which, as luck would have it, is padded in both models.

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#17 lelebebbel

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Posted 19 April 2008 - 01:20

The lift produced by the Blackhawks T/R should be directly proportional to the pedal input, right? Will the nose go up noticably in a right pedal turn?
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#18 CharyouTree

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Posted 20 April 2008 - 11:05

The lift produced by the Blackhawks T/R should be directly proportional to the pedal input, right? Will the nose go up noticably in a right pedal turn?



Having learned a lot since my previous post in this thread...

The mechanical mixing unit (MMU) provides yaw to pitch coupling, to compensate for the lift of the tail rotor.

So right pedal causes a decreased t/r lift vector, nose pitches up, and the helicopter drifts aft. The m/r tilts forward to compensate.

(I cheated, and used one of my books that deals specifically with left pedal inputs, but it's just the opposite for a right pedal turn)

#19 Puff Daddy

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Posted 09 November 2008 - 13:46

Oh, and who had the bright idea you need a key to unlock and start a military helicopter? The "ignition" switch in the UH-60 is actually like a car, requiring a key. If I look on the overhead console for the igntion switches (#1 and #2) one more time I am going to start banging my head against the glare shield which, as luck would have it, is padded in both models.


The idea for a key in all army aircraft came from an incident in the late 70s, or early 80s where a disgruntled student stole a UH-1 from Fort Rucker an flew it to the White House. At least that's the legend that everybody is told.

#20 heli.pilot

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Posted 09 November 2008 - 14:32

The idea for a key in all army aircraft came from an incident in the late 70s, or early 80s where a disgruntled student stole a UH-1 from Fort Rucker an flew it to the White House. At least that's the legend that everybody is told.


A 750 mile trip? And they couldn't stop the guy??

Edited by heli.pilot, 09 November 2008 - 14:33.

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