Welcome Guest
HeliTorque
  
User Control Panel

Security Code: : Security Code
Type Security Code Here: :
 
Register Here
Lost Password?

Online Stats:
Visitors: 23
Members: 0
Total: 23

Membership:
New Today: 0
New Yesterday: 0
Registering: 0
Members: 6662
Latest: chrisw

Most Ever Online
Visitors: 447
Members: 10
Total: 457


HeliTorque :: View topic - Tail Rotor Control Failure
Forum FAQ
Forum FAQ
Search
Search
Memberlist
Memberlist
Usergroups
Usergroups
Profile
Profile
Contact Manager
Contact Manager
Log in
Log in
Log in to check your private messages
Log in to check your private messages
HeliTorque Forum Index » Flight Dynamics

Post new topic   Reply to topic All times are GMT
Tail Rotor Control Failure
View previous topic :: View next topic  
Author Message
WhirlyGirl
Administrator
Administrator


Offline
Joined: Jul 20, 2004
Posts: 3702
Location: Birmingham, UK


uk.gif

PostPosted: Thu Jul 06, 2006 9:08 am    Post subject: Tail Rotor Control Failure Reply with quote

Is there a difference in which way a helicopter will yaw if it has, for exaple, a tail rotor control failure at a high pitch setting during the cruise, as opposed to a tail rotor drive failure?

My CPL notes seem to suggest so, but Wagtendonk only mentions a yaw in the opposite direction to the main rotor. The CPL notes have been known to be wrong mind you, which makes things a little frustrating to say the least. Evil or Very Mad

WhirlyGirl Cool
_________________
CPL(H) / FI(H) - Cabri G2, R22, S300, R44, B206
Flight Examiner (H), Ground Examiner (H)
Back to top
View user's profile Send private message Visit poster's website Skype Name
Intentionally Blank
H Addict
H Addict


Offline
Joined: May 01, 2005
Posts: 331


uk.gif

PostPosted: Thu Jul 06, 2006 11:20 am    Post subject: Reply with quote

Drive failure = suddenly no T.R. thrust (cos it stops spinning) and subsequently with an anticlockwise rotating rotor (when viewed from above) a yaw to the right will be induced.

Control failure = if stuck in correct position (i.e. stuck pedal but still spinning) still T.R thrust so no yaw until you change power setting - more power = yaws right & less power = yaws left. If suddenly flat pitch (perhaps the control wire snaps, dunno, but it is still spinning) same as a drive failure - no T.R. thrust so yaws right.

These are my neophyte understandings and am happy to be corrected by someone more knowledgable.
Back to top
View user's profile Send private message
WhirlyGirl
Administrator
Administrator


Offline
Joined: Jul 20, 2004
Posts: 3702
Location: Birmingham, UK


uk.gif

PostPosted: Thu Jul 06, 2006 11:25 am    Post subject: Reply with quote

So a tail rotor control failure at a high pitch setting - what do you interpret that as, that the tail rotor is stuck with a high pitch setting, i.e. left pedal stuck on (assuming anti-clockwise rotor)?

If this is the correct interpretation then the answer should be that it will yaw right. Right?

WhirlyGirl Cool
_________________
CPL(H) / FI(H) - Cabri G2, R22, S300, R44, B206
Flight Examiner (H), Ground Examiner (H)
Back to top
View user's profile Send private message Visit poster's website Skype Name
Intentionally Blank
H Addict
H Addict


Offline
Joined: May 01, 2005
Posts: 331


uk.gif

PostPosted: Thu Jul 06, 2006 12:19 pm    Post subject: Reply with quote

Oh dear we are in the murky world of interpretation: this phrase "tail rotor control failure" is ambiguous and the examiner who wrote it should be poked in the eye!

In my mind "tail rotor control" mean the pedals and everything associated with them to "control" the pitch of the blades. But it seems they are getting at what happens if you have a tail rotor drive failure i.e. it no longer spins to produce thrust .

I reckon the question means you have a high main rotor pitch setting (i.e. lots of power and so subsequntly lots of tail rotor thrust to overcome the torque) and if your tail rotor suddenly stops producing thrust ("control failure") what will happen.

Answer - it will yaw right (assuming anti-clockwise main rotor).
Back to top
View user's profile Send private message
WhirlyGirl
Administrator
Administrator


Offline
Joined: Jul 20, 2004
Posts: 3702
Location: Birmingham, UK


uk.gif

PostPosted: Thu Jul 06, 2006 2:09 pm    Post subject: Reply with quote

Intentionally Blank wrote:
Answer - it will yaw right (assuming anti-clockwise main rotor).


Right, so this is the "opposite direction to the main rotor". Well this was apparently the correct answer, however, in my CPL notes, the ones you are meant to refer to as the bible throughout the course it explains as follows (I have highlighted in bold the part that is contradictory and in my opinion dodgy):

My CPL POF Book wrote:
A tail rotor drive failure presents the pilot with an immediate problem of controlling the helicopter that although it may be severe it is a known quantity. A tail rotor control failure may occur at any power setting dictating how the helicopter will handle and what sort of approach to land will be required. A control failure can be caused by a pedal locking, a control cable snapping, or a control rod becoming jammed. The pedals could be either free moving without effect, stiff to move or completely locked.

The first action should be to control the aircraft. The amount of yaw will vary with collective pitch, so the pilot should establish a flight condition that will provide a stable power, speed and yaw combination. If tail rotor pitch control cannot be regained then the pilot must ascertain whether the failure occurred at a high pitch setting or a low pitch setting as the results and actions to recover can be significantly different.

A tail rotor control failure with a high fixed pitch setting will cause the helicopter to yaw in the same direction of the main rotor during the cruise. Lowering the collective lever will increase the rate of yaw and raising the lever will reduce it. Obviously, this condition is not safe to conduct an engine off landing and even small power reductions should be made with caution.

Before attempting to land the helicopter, the pilot must establish the minimum speed and power combination at which the rate of yaw is acceptable. This should be done at height in small increments to enable recovery should the yaw become excessive. Ideally, the airspeed should be reduced to as low as possible

_________________
CPL(H) / FI(H) - Cabri G2, R22, S300, R44, B206
Flight Examiner (H), Ground Examiner (H)


Last edited by WhirlyGirl on Sat Oct 20, 2007 9:52 pm; edited 1 time in total
Back to top
View user's profile Send private message Visit poster's website Skype Name
Intentionally Blank
H Addict
H Addict


Offline
Joined: May 01, 2005
Posts: 331


uk.gif

PostPosted: Thu Jul 06, 2006 4:22 pm    Post subject: Reply with quote

Quote:
A tail rotor control failure with a high fixed pitch setting will cause the helicopter to yaw in the same direction of the main rotor during the cruise. Lowering the collective lever will increase the rate of yaw and raising the lever will reduce it.


The above seems a clumsy (dodgy!) thing to say to me. It gives the impression that if you have a stuck pedal, for example, the first indication will be a yaw in the same direction as the main rotor.

If the pedals became stuck at the correct setting for the cruise -in the cruise- you would have a "high fixed pitch setting", but only when you started to lift or lower the collective would the helicopter yaw and which way it did yaw would depend on whether you lifted or lowered the lever!

If you lift the collective you do not have enough pitch on the tail rotor blades for the power you are now pulling = not enough T.R. thrust = it will yaw the opposite way to the main rotor, like putting in not enough left pedal. Lower the lever and you have too much pitch on the tail rotor for the power you are now pulling = too much T.R. thrust = yaw in the same direction of the main rotor, like putting in too much left pedal.

Another control failure could be If the pitch suddenly washed off - e.g. the control cable suddenly snapped , you would immediately have no tail rotor thrust (like a drive failure) and the helicopter would yaw in the opposite direction to the main rotor, again like not having enough left pedal. Lowering the lever (entering autorotation) would reduce this yaw rate.

Again my neophyte understandings.... Any experienced and constructive correction welcomed!
Back to top
View user's profile Send private message
paco
'Torquing Regularly
'Torquing Regularly


Offline
Joined: May 14, 2005
Posts: 90
Location: Wycombe Air Park, Calgary, Dubai


canada.gif

PostPosted: Fri Jul 07, 2006 5:05 pm    Post subject: Reply with quote

Whose notes are these?

The highest pedal deflection you would get is in the hover - which way does the nose go then? In the cruise it would be no different, and the tailboom/fin would only serve to hack it round faster.

The only time the fuselage would go the same way as the main rotor would be if the engine fails.

"Obviously, this condition is not safe to conduct an engine off landing...."

I haven't got my 206 flight manual in front of me, but I'm sure it says something about going into autorotation if the tail rotor becomes inoperative.

"Before attempting to land the helicopter, the pilot must establish the minimum speed and power combination at which the rate of yaw is acceptable."

You can actually fly along without yawing.

"The engine should be shut down prior to lowering the collective lever to prevent yaw on the ground."

Have you got three pairs of hands? "Reduce the throttle setting" would have been a better turn of phrase.

"A control failure at a high pitch setting in the hover will not be as severe as at height because the power setting is already high."

Yes, and the fuselage will be like a coiled spring. At height, in the cruise, the tailboom does most of the work anyway, so you likely won't notice.


This is from my own CPL(H) course (coming soon folks!):

When the tail rotor fails, it will be in varying degrees of positive, neutral or negative pitch, depending on what you were doing at the time, so if you can remember what it was, you will have an idea of the state of the pedals. Unless it's a drive failure, or you lose some of the components, the chances are that you won't discover the problem until you change your power setting, as it's very unlikely you'll be flying along in the cruise, for instance, and find a pedal forcing itself completely over to one side, as simulated by instructors on test flights, unless you have a motoring servo or similar, in which case your problem has something to do with hydraulics as well. More typically, you will be in a descent, climb, cruise or hover, with the pedals where they should be and won't move when you want to do something else. When descending, for example, in the AS 350, you will have more left pedal (more right in the Bell 206), both of which will aid the natural movement of the fuselage against the main rotors. The pedals would be in a neutral position if you were flying at medium to high speeds, and the power pedal would be forward in high-power situations, like hovering. In any case, the spread between the pedals is not likely to be more than a couple of inches either way, certainly in a 206 - try an autorotation properly trimmed out to see what I mean. You will notice the same in the hover.

In fact, landing with a power pedal jammed forward is relatively easy, since the tail rotor is already in a position to accept high power settings, so you may be able to come in very slowly and even hover. If the pedals jam the other way (right in a 206), look for more speed, as there will not be enough antitorque thrust.

A drive failure, on the other hand, or loss of a component, will cause an uncontrollable yaw, and maybe an engine overspeed, so the immediate reaction should be to enter autorotation, keeping up forward speed to maintain some directional control (which is difficult in the hover, so try to get one skid on the ground at least), if you have time. If you lose a component, the C of G may shift as well. Pilots who have been there report there is a significant increase in noise with a drive shaft failure, and that the centrifugal force in the spin is quite severe. Anyhow, an autorotation is certainly part of the game plan, and as speed is reduced towards touchdown, you will yaw progressively with less control available in proportion, so it may be worth trying to strike the ground with the tailwheel or skid first (if you've got one), which will help you to keep straight - according to the JetRanger flight manual, you should touchdown with the throttle fully closed, as you would if the failure occurs in the hover, to stop further yaw when pitch is pulled to cushion.

However, in some circumstances, such as the cruise, sudden movements like this may not be the best solution. If you can reduce the throttle and increase the collective pitch, this would reduce the effect of the tail rotor at the same time as keeping the lift from the main rotors, as does beeping down to the bottom of the governor range (difficult in most AS 350s or Gazelles, where the throttle is not on the collective). The tail rotor is there to counteract torque, so if you give it less work to do, you will be more successful.

Otherwise, you might find a power and speed combination that will maintain height until you find a suitable landing area, then you've got as much time as your fuel lasts to solve the problem - you don
Back to top
View user's profile Send private message Visit poster's website Skype Name
Ascend_Charlie
H Addict
H Addict


Offline
Joined: Aug 23, 2005
Posts: 266
Location: On a course.... golf course


australia.gif

PostPosted: Tue Jul 11, 2006 7:11 pm    Post subject: Reply with quote

Don't make the mistake that "high speed =high power = lots of left pedal".

The most left pedal you will use is on moving from the hover to take off. After that, you are taking the left pedal out. The fin is unloading the pedals.

Almost any mode of t/r jam or t/r loss of control is landable from either the hover or a running landing with power, but "loss of thrust" which comes from a driveshaft failure will usually require autorotation.

(I just stepped out of the simulator from practicing these for 90 minutes! Only crashed once, during a driveshaft failure when I pulled the throttles back before lowering the lever - revs bleed off pretty fast...)
Back to top
View user's profile Send private message
trekker7622
Shy 'Torquer
Shy 'Torquer


Offline
Joined: Oct 24, 2007
Posts: 5



PostPosted: Wed Oct 24, 2007 8:32 am    Post subject: Reply with quote

i don t know much about civilian aircraft but in mh-53's we had a yaw shear pin so that if pedals got stuck in either a high or low t/r pitch position you stand on one pedal against the binding the pin shears and flight controls center you can maintain forward flight andexecute a run on landing the only answer for tail rotor drive falure is auto rotation
Back to top
View user's profile Send private message
afterburner
H Addict
H Addict


Offline
Joined: Feb 20, 2008
Posts: 1059
Location: New York


usa.gif

PostPosted: Fri Feb 22, 2008 4:48 pm    Post subject: Reply with quote

Hi folks,
I love this topic! There are so many interpretations that I ponder the confusion. Keep things simple. In a counter rotating system, when under power, at TR loss, ship will rotate opposite the blades or to the right. How much rotation depends on the amount of thrust the TR was producing at the moment of failure. Forward speed tends to reduce the yaw as the ship will tend to align itself with the wind direction, which may or may not be the flight path.

However, as speed is reduced, torque is reduced, and yaw may reverse.
If an autorotation is entered, the ship will tend to follow the rotor blades due on the drag of transmission and rotor system.

Therefore, you will go from right yaw to left yaw (or less right yaw).
I experienced complete TR failure in an old Sirkorsy S58. Thing started to spin like a top until we entered autoration. Then is was like a gentle spiral. Prior to ground contact in the flair, the nose came up and started to come over to the other side. Thats the key to these failures. Slow it, flare it, and get it on the ground in short order.

Hope this helps a bit. Clockwise system do just the opposite. hahahaha
_________________
"A Copter Pilot's Life has it's... ups and downs"
Bell 47-206, Schweizer 300/500, Citation 525
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    HeliTorque Forum Index » Flight Dynamics All times are GMT

 
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Sponsors


Billund Air Center

Visit HeliTorque!