Chadwick

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Chadwick

Postby vpcjn » Wed Dec 03, 2008 9:43 am

Hello all,
Does anyone have experience using a Chadwick along with the strobe to track the MR and TR blades on a C model?
I have access to one and would like to try and use it to track my blades....I have no experience in using the Chadwick and am wondering if it would be worth it not only to use it to track my blades but learn how to use the Chadwick.
BTW its a vibrotex (?) 2000 with the strobe.

Please do not feel you are getting too basic as I will be starting from scratch....

Thanks
vpcjn
 
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Re: Chadwick

Postby Carl.M » Thu Dec 04, 2008 3:14 pm

Hi vpcjn and welcome,

I tracked and balanced 2 Hillers with my Microvib system so far. I also recently did a Bell 206L. I have to say that there is more to do on the Hillers then the Bell even though they are both 2 bladed. Blade track is only part of the picture. The goal is to minimize vibration. With the main rotor there are 2 types of vibration, vertical and lateral. The Hillers I've done had the worst of their vibration in the lateral. Lateral vibes can be corrected with both weights and sweep. The other vibration is vertical and that is corrected with pitch links and tab angle. And then there are the paddles, they need to have their chordwise angle the same.

I haven't actually used the Vibrex but I've heard from other A&P's that there is a pretty long learning curve to figure out all that the tool can do. However strobe tracking shouldn't be that hard to do especially if you are only looking at the track picture and not trying to correlate vertical vibes.

For tracking you should have less than 1/2" of spread on the ground and in hover. If the blades fly apart gradually with airspeed then a pitch link adjustment is needed. It the blades don't fly apart until high speed then a tab adjustment will fix that. Adjusting a tab to correct for pitch causes parasitic drag.

The equipment I have tracks blades to the thousandth of an inch. It also measures blade passage rate in tenths of degrees. The computer gives vibration solutions in grams of weight for lateral, pitch link "flats" and tab degrees for vertical. My tab and paddle tools measure to the tenth of a degree. And I travel (hint, hint).

The vibrex is far superior than flagging and the microvib takes it to the next level. If anyone has comments on the vibrex then please comment. I know at least one person on the board has something to say.

Carl Mauro
Look for me on www.barnstormers.com
Carl.M
 
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Re: Chadwick

Postby vpcjn » Thu Dec 04, 2008 5:23 pm

Carl,
It's a vibrex 2000 with the strobe. I thought it would not be easy and there would be a learning curve.
Although I am an A&P, my helicopter experience is very limited. To be quite honest, I have no idea where to start on this project but intend to keep playing with the unit until I get a handle on it.
There are other tools with the unit and like I said, I have a lot to learn. I have spent hours googling blade tracking and dampening and there is little information on the internet.

Once I figure out how to use it on my Hiller, I plan on helping out a few helicopter buddies (only charging beer) to get their helicopters "tuned" as the only way we have to track the blades is flagging. Getting rid of unwanted vibrations is a big plus.

I have also considered contacting Chadwick and ask if there is a traning corse available...if not, I might take you up on your hint.

Any and ALL information, possible pitfalls, and "don't waste your time doing this" would be great.

Emmett (north of Tampa Fl.)
vpcjn
 
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Re: Chadwick

Postby Carl.M » Sat Dec 06, 2008 8:57 pm

Hi Emmet,

This is a big subject. A lot of information on balancing can be found on the ACES web site (http://www.acessystems.com/manuals.htm) and (http://www.acessystems.com/appnotes.htm). I think the ACES system is similar to the Chadwick. The tasks are all the same but the way they are performed is different.

All I know about the Chadwick is how to balance props. I not sure the modle I'm talking about but I'm sure yours would balance props. Take your typical trainer and park it in a spot where it can be run up. Remove the cowlings and attach an accelerometer to a forward engine bolt as close to the prop as possible but perpendicular to the cylinders. Secure the cable to the (left) wing out near the tip. Use wide blue painters tape to be safe. Next put a piece of refective tape on the outer third of one of the prop blades so that it is visible from the front of the aircraft. Connect up the cables and position yourself in front of the wing and to the side of the propeller disc a safe distance away like about 20'. Run up the warm engine to cruise RPM with the prop flat (take off position). Then key the strobe. You will see the reflective tape somewhere in the disc, say at the 2:00 position and the vibrex will register an acceleration of say 1.2 IPS. Now you have a start. The strobe flashes as the accelerometer reaches it's peak which was where the blade was at 2:00. You would want to counter that peak with a weght on the opposite side. After shutdown, you would move the blade to the position it was in when the strobe flashed which was with the tape at 2:00. Now the weight would be attached opposite the accelerometer. You would use a polar plot and vectors with weight and balance calculations to hone in on the correct weight and location. Each run would get you closer to a balanced condition which is under 0.20 IPS. Remember that you should only use washers for weights on the spinner screws until you are sure about location and then move them to a permanent location.

That was a propeller which is also what a helicopter rotor is. I would hazard to guess that performing a lateral balance on a Hiller with the vibrex would be much the same. Only differences would be to place one piece of tape on one blade and two on the other. I would try to attach the accelerometer facing the rear so that opposite would be at the pilot's 12:00. If you ran up the A/C and you saw two tapes at 12:00 then you would be golden. All you would have to do is add or subtract a weght to a blade tip to get your lateral. Your goal is under 0.20 IPS. However if the tape strobed at say 3:00 at 8.0 IPS then you would have some head scratching to do because more stuff comes into play. Things like weather or not to sweep a blade or add/remove weight from a paddle. (Only sweep a blade back, never forward.)

Anyway, read up and practice on a livingroom fan.

Carl Mauro
Look for me on www.barnstormers.com
Carl.M
 
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Re: Chadwick

Postby Rotormatic1 » Fri Dec 12, 2008 10:58 am

The Chadwick used on the Hiller works a little different on the main rotor than balancing a propeller. Balancing the tail rotor is very similar to balancing a propeller.

You need to get balance charts and brackets from Chadwick for the main rotor and tail rotor. The charts have instructions for balancing, and how to install pickups and targets on the rotors. I seem to remember they also had an instruction book that went into greater detail on using the Chadwick on helicopters. The kit they sell is for the D/E version of the Hiller, so you may have to modify the mounting brackets a little for the C model. I only used the Chadwick on E model Hillers.

Main Rotor Balancing:

Three pick ups need to be installed on the helicopter to balance the main rotor. You also install two reflector targets on the main rotor blades

A magnetic pick up is installed on the wobble plate support bracket (the V shaped brace on the back of the transmission the keeps the wobble plate from spinning). Then you install interrupters on the main rotor mast. The interrupter has a single and double interrupter. You adjust the interrupter so the double interrupter passes the magnetic pick up when the blue main rotor blade is at 11:00 looking down on the main rotor (left of center looking forward).

Then you install the accelerometer on the main transmission, at 9:00 on one of the split line bolts of the transmission. The cable from the accelerometer points out to 9:00. After that, you go in the cabin and install the vertical accelerometer on the instrument panel pedestal (where the circuit breakers are) on one of the inspection cover screws with the electrical connector pointing down.

Then secure the cables from the accelerometer and magnetic pick up, routing the cables into the cabin. Hook up the power wire, and strobe to the Chadwick box. You also hook up the accelerometers to the box, attaching the wire from the transmission to the A channel, and hook up the wire from the pedestal accelerometer to B channel for vertical measurements.

The track of the main blades needs to be close before attempting to balance. There is a switch on the Chadwick to select “track” or A or B.

There are two ways you can check the track. Use the track setting on the Chadwick, or manually tune the strobe with the knob on the light. Later versions have a counter that you can set the RPM easer for the strobe to pick up the blade track from the reflectors. This is handy if you main blades “cross over” around the rotor disc (you can have the blades tracked together in the front, with the blue blade high at 9:00, and the yellow blade high at 3:00. This was on E models, so I don’t know if the wood blades do this. To fix it, you adjust on trim tab down, and one up. If you have a counter, set it to double the RPM of the main rotor. You need to move the switch on the Chadwick to B to get the vertical IPS.

To use the Chadwick box to check track, you select “track” and pull the trigger on the strobe with it pointed at 11:00. Adjust pitch change links until you get a good track.

After you get the track, pick the ship up in a hover, and get your balance readings. You select A on the switch, and tune the ring of lights on the Chadwick box.

To tune, you watch a ring of lights on the Chadwick that is arranged as a clock. There is also a knob, push button, and counter on the Chadwick. You set the counter at 370 for the main rotor rpm for flight RPM (this was on the E, C may be different). You push the button, and watch where the light is on the clock of lights. You turn the knob until the light is at the same clock angle with the button pushed or released.

You record the clock angle from the ring of lights, and also record the IPS reading from the dial on the Chadwick. Then you go to the main rotor chart and put a dot where the clock angle and IPS line up. The chart tells you how many grams to add to the blades, paddles, or blade sweep. Add weight only to one spot the first time. Make adjustments until you get .2 IPS or lower.

For in flight tracking, you can either just use the strobe, and adjust the tabs using the instruction in the Hiller maintenance manual, or you can select track and record the clock angle and IPS to use a chart to figure how much to bend the tabs.

Tail Rotor Balancing

You hook up an accelerometer on the T/R gearbox output shaft seal cap top rear bolt, with the electrical connector pointing aft. The accelerometer is installed parallel to the top of the bearing cap. You also install reflective targets on one of the blade roots so you can see it from the left side of the helicopter, and on the end of the blades for track. The reflectors on the blade end are installed with one vertical and one horizontal, so you see and x when they are in track. The blades on the C’s don’t have as much area on the tip, so you may have to trim the reflective targets.

You need to run a power cord out to the tail rotor, and make sure you have enough slack in the power cable to reach the rear of the helicopter to view the track. You need to run and secure the cable from the accelerometer so it does not get caught in the tail rotor, or drive train, and route it also to the left side of the helicopter. There are some tooling holes on the tail rotor cable fairlead brackets that you can use to tie wrap the cable to. Hook up the accelerometer to the A channel.

Get the helicopter up to take off RPM, and shine the strobe at the tail rotor, so you can see the one reflector on the blade root. Adjust the strobe until you get 4 targets, and move to the rear of the tail rotor, and look at the track reflectors on the ends of the blades. Adjust until you get them in track.


Set the switch to the A channel, and point the strobe at the side of the tail rotor with the reflector on the blade root. Then tune the Chadwick with the button pushed and released until the target on the blade root does not move when the button is pushed or released. Record the clock angle of the reflector from the tail rotor, and IPS reading from the Chadwick on the tail rotor balance chart. Add weight as indicated. You only add weight to one location of the first run. This is to check that your moves are going the right way. They have a clock correction tool if it does not go the right way. You should only adjust one weight on the main rotor from the first reading also for the same reason.

That is a quick overview on how the Chadwick works on a helicopter. It has been 10 years since I used the equipment. Making this rant from my memory, a few details may be missing, or a little off... Getting the instructions and charts from Chadwick is a good investment.

Good luck….
Rotormatic1
 
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Re: Chadwick

Postby vpcjn » Thu Dec 25, 2008 11:02 am

Thanks for all the replys.
I have printed everything and hopefully I will figure it out. If I cant, I hope to at least get my celieng fan balanced! :lol:
vpcjn
 
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