Hi guys,

Came across this video of a tail rotor tracking job. Can you shed some light on what this does?



Thanks,
Razorback

TR Tracking is  the process of "Balancing AND Tracking the TR blades as it's installed on the Heli.....

Balancing = Important because of Centrifugal rotation.... Out of balance means Imbalance in the system & Creates Vibration.... NOT  good in any Aircraft Fixed wing or Rotary wing
Tracking = Important because of  the Blades "in line" or Flying in the same  plane (rotational)

Both come together as the TR is installed per Each installation of a TR Assembly.


The same process is required for the Main Rotor system and ALL Heli's have a similiar requirement


1) He's "Feeling"  the Fuselage/Tail boom/Horizontal Stab/Stinger for vibrations.... & yes you can feeeeeel  the "buzzing" if it's  quite  a bit out of Balance (not  the tracking part)
2) he's pointing/dialing  the Frequency (RPM) of the TR Rotating on his Hand held tracking/balancing equipment.
2a) he couldn't get a  good reading--- possibly because the "Pick up's" (Small reflective tape/ (or possibly small brackets mounted on the TR Blades) aren't set correctly  OR because it's Very Bright out...   most Equipment will pick up the signal's but I did this a few times and the BRIGHTNESS of the day interfered with my balancing.....  so I waited about  1/2 hr (+/-) so the sunshine didn't "bounce off"  the reflective tape/brackets

3) lastly -- he's checking the TS drive shaft bearings (temp's) for "enough" grease and proper/improper operation.




Looks  like the Huey was in for Major maintenance, hence all the little checks they are  accomplishing....

Very interesting read guys. Although huey as all other choppers can take a lot of punishment, seems they`re quite delicate piece of machinery with very precise mechanics .

Thanks Hawkeye.

But how can one tell which blade is out of balance? The stroboscope should give a reading while the tail rotor/main rotor is turning, which will be translated into a mechanical adjustment, right? Once the tail rotor has stopped turning, how does one know which blade to adjust?

Thanks Hawkeye, great explanation.

(B/229) Razorback wrote:
...But how can one tell which blade is out of balance? The stroboscope should give a reading while the tail rotor/main rotor is turning, which will be translated into a mechanical adjustment, right? Once the tail rotor has stopped turning, how does one know which blade to adjust?

I'm trying to remember how we used to perform the Track/Balancing procedure (over 25 years ago for me)  so I may be slightly off on the Exact procedure but I'm close.


Lets back up  just a bit...
That "stroboscope" is generally a dual purpose Vibration analyzer (Chadwick/Helmuth is one Manufacturer (Mfg), there are others).


A) The Tracking Portion  can be done in a bunch of ways..... basically  we're looking for the blades to be in the same "plane of  rotation"(Having the same blade pitch..)  *** Tracking is done BEFORE  the balancing---  if the tracking isn't correct... then the Balancing can NEVER be corrected...
--------------- ***Best way I can explain it  ::: If one blade is Working harder (pitch of blade is "Greater" than the opposite blade...) then   that blade is doing Most of the work...... not "sharing the load"  as each blade SHOULD share the loads together ---  So if Tracking is "off"  then Balancing won't help.....

A₂)When I was performing the "Track" portion....  there were / Brackets and \ Brackets that attached to the Blades(Tip)      ie.. / went on the "Master blade" &  \ went on the other blade (or vise/versa). Using the Strobe portion..... When all was correct  BOTH  the  / & \ to  form a X to show you the Tracking of the blades was/is 0K. (** Much the same as a timing light for your car engine).
For a 4 bladed rotor  | and\ and ^__ and /  were used.


Another way of Tracking was to "Paint"  the (Rotor)tips with different colored Chaulk/Grease pencil or similiar.  Then SOMEONE would hold a flag (on a pole) & see what color "hit"       high...low....etc....



For tail rotors it was a stick with a grease pencil taped to it....and slowly poked into the tail rotor from the side.

Adjusting was done by changing/adjusting the Linkage to that particular blade...Called Pitch Change Links (PCL).



B)Balancing--It  senses (takes input) from the Vibration sensors located on the Helicopter. Technicians install them and  remove them  when the Tracking/Balancing is needed.
  Now -a-days most Modern heli's have the sensors/equipment installed  during the Manufacturing of the Heli.... as in Permanently installed... then all  the Technician has to do is "plug in" to a cannon plug (receptacle) with his new digital equipment and go from there.
B₂  Once the rotors have stopped (Obviously... )Taking  the "Master blade"  ie:..  /blade  & put it at 12 o'clock or Straight up (if you're looking at the TR from the side of the Heli) and for Main rotor--- 12 o'clock is front of the Heli.  remember...  everything is referenced off the master blade. Then you add weights as necessary to that Lower (6 o'clock blade) or Main rotor Blade that is at Tail  of Aircraft..

But WAIT... what if  the Master blade is the Heavy blade....  We don't want to ADD more weights to the lower (Lightest blade....)  So  -REMOVE-  a weight from the Heavy blade & try again.....Run up the rotors......... adjust....run again.

(dial #6,shows the amount of imbalance in IPS  (inches per Second)) and  Dial # 13  will show the imbalance & where to put the weight--Nearest blade.

Thanks for making it clear to me Hawkeye. Awesome description.
It sounds like a very costly procedure since every time a weight adjustment is done, the aircraft has to be start up again. Do you go throught the complete start up checklist with every restart or are certain items being skipped?

(B/229) Razorback wrote:..... Do you go through the complete start up checklist with every restart or are certain items being skipped?

Correct answer-----If the helicopter was ready to be started....then it was ready for flight.. and all the Checklist (C/L) items  were accomplished.

Real life Answer.....  Certain  C/L items were "bypassed" or acknowledged to be "Not needed for this start/flight".

Ask Six...or Flyer...or Samri (or any one of the Pilots who flew helicopters/Aircraft in real life)-- about "Thru flights".
--------------------------------
Normally we did this procedure with a Minimum of 2 people....Pilot and Technician. But a 3rd person  was always around for "Spotting" purposes (Safety concerns).

Pilot always ran the heli & flew it (If needed) when there was an "in flight Vibration" that needed more attention to narrowing the Vibration down (not all vibrations were Rotor related.....)

Technician did the Physical testing & addition/removal of weights.

Then  the fun began..... Paperwork/logbook entries.    

(B/229) Nage wrote:.... Although huey as all other choppers can take a lot of punishment, seems they`re quite delicate piece of machinery with very precise mechanics .

I know you've heard this before but here it is again:

Each Helicopter=  10,ooo Parts.... all flying in (precise) formation at the same time !

We use a magnetic pick-up to measure the rpm and tell the computer where blade 1 is. And accelerometers for the vibrations.
We run flat pitch ground, hover and from 60 to 140 kts.
You can adjust weights for balancing and trim tabs and pitch links for track (vertical vibrations). Still pitch links will affect lateral vibrations aswell.
Blades are statically balanced before installation and a maintanance test pilot does the dynamic balancing. Also measuring lead lag values may tell you something might be wrong with the rotor head itself (dampers or phasing). All in all we have around 40 something accelerometers measuring vibrations on almost every rotating component. From generators to pumps and driveshafts. After so many hours all the data will be evaluated and is used for condition based maintanance. So you dont have to replace some parts after a given set of hoyrs anymore. You just track the increase in vibrations to monitor the wear and tear

Depending on what type of flight, we need to check certain systems at startup. Some items always require checking.
If we remain running on the APU after the engines are shutdown, we dont need to do a thru flight.
If components are replaced, you might be required to perform additional checks during start-up and flight. The maintenance pilot has a maintenance test flight checklist with all the extra checks and is the one performing these tests.
Still its aircraft type and service dependend on who is allowed to perform test flights and how are they performed.

Brings back memories of countless hours of ground runs and test flights, hunting down nuisance vibrations and post maintenance test flights.

From a (Huey - 2 bladed helo) pilot perspective - my basic recollection:

Fact - the huey vibrates alot and is normal.....but there are limits.
The types of vibes we feel are:
High Frequency Vibrations - Tail rotor related. (usually a balance issue.)
We feel it as a "buzz" through the pedals and even the airframe.
Normally - you should not feel any high freg vibes, so if you did you would shut down, write it up and go get another jet.

"1 to 1" and "2 to 1" vibrations - associated with the Main Rotor:
These are usually a result of main rotor blade tracking.  These vibes usually get worse with an increase in airspeed.
You would normally notice them when you pick up into the hover - again, if it felt excessive, you would put it back down and go get another one.
(But not always - and may only become evident as airspeed increased)

1:1 vertical - One blade not tracking correctly which causes a vertical "jump" each rotation.
ie 1 vertical vibe - 354 times a minute (or about 6 times a second) at full throttle.

2:1 vertical - both blades out of whack - 2 vibes  - 354 times a minute - about 12  a second.

You can also get lateral vibrations as well - these have more of a wobble feel and are main blade balance or lateral issues (blades not laterally aligned).

(DCS Huey does a good vertical vibe if you approach / exceed Vne - is it a 2:1 or a 1:1 ?)

From a post maintenance perspective, say after a major servicing where blades are replaced etc,
it would require several ground runs for both the tail and main rotors (as well as other checks) and quite often would be an all day (sometimes several days) affair.

After constant starts and shutdowns so the techies could add/remove a washer to the tailrotor assembly to adjust its balance, or tweak a trim tab on the main rotor to correct its tracking, you would take to the skies with the techie in the other seat with his strobex to check the blade tracking at various airspeeds up to Vne.
Invariably - further tracking adjustments were required requiring further test flights after each tweak.
Once everything was good - the final Vne run was usually done "lower" than normal past the hanger      - letting the boys know it was all good and to get the beers out. (usually by then it was way past knock-off).

The thru checks (the ones with the asterisks next to them in the checklist) are used after the first start of the day.
Also, another consideration with short interval shutdown / starting is high residual EGT, which could lead to a hot start.
You would sometimes need to "motor" the eng before introducing fuel (ie compressor air, cooling the combustion chamber - Throttle closed), as well as "modulating" the start - using the throttle to control the amount of fuel introduction during light off in order to control EGT rise.

That's the great thing about DCS huey - the virtual techies always provide us with a fully serviceable - well maintained aircraft ready for us to abuse!!

I should also add - with respect to High freq vibes:
worn drive shaft bearings were also a main culprit of high freq vibes.

As mentioned above - touching the bearing housings to feel if any were excessively hot, was helpful in sourcing the bad bearing.

+99/100 - you only mentioned beer once ! - great explanation, i keep forgetting about the amount of maintenance and testing on weps and equipment we always did, very time consuming.

And some people wonder why a helicopter flight hour is so expensive...

Thanks alot for the feedback guys. Very interesting read.