Short Shaft Balancing

[Uncommanded LoadRelease]

A good thing to remember is only go up a part number of washer at a time. If the chart calles for 5g of weight still only add one dash number up. If you have to start trimming cotter pins to get it to balance them something is wrong. Make sure your driveshaft rubbers are in good shape. Sometimes a good fix is to swap the 5 bearing with one farther down the shaft. The 5 gets all the heat and tends to harden the rubber bushings faster than the rest. I had a B2 with a shaft I couldn't balance. After using all the tricks mentioned by other forum members it still was .5ips. Turned out the MO5 output bearing was shot. The fact that we changed 3 mag seals in the last 200 hours should have been an indication .

 

[skullcap]

ULR; In regards to the trimming of cotter pins, would love to say, "been there done that" but can only say"been there, SEEN that" and more a one or two times. Seemed like when the AME was around .15 and going for .1 that the difference was how much cotter pin was taken off. Maybe was wrong but worked.

sc

 

[Uncommanded LoadRelease]

Skull: I'm saying that if one has to trim cotter pins to balance the shaft then it's an indication that something is worn. On a healthy shaft assembly trimming a cotter pin will make almost zero difference. Having said that; ya gotta do what ya gotta do at the time. I've spent my fair share of time grinding washers to tune a sensitive short shaft.

 

[MagSeal]

Ok, I finally got off my butt and dug around.

The MET chapter 65 doesn't say much but does tell you about the liquid solder. If it's there it means it was dynamically balanced, and do not disassemble those bolts.
The MRR does give you some limits to check also in chapter 65.10.00.726.
Our MRV for overhaul goes into a bit more detail, but on the field level those limits don't apply to you.
The runout with V-blocks on either end is 0.6mm and the flange run-out is 0.1mm according to the MRR. As well there is a torsion check to do.
Since there isn't much more listed, as long as you can balance below 0.8 IPS, there's nothing stopping you from running them as long as you can. Or until you hit a tree.... :wacko:

 

[mrwhirlwind]

one thing not mentioned is if the splines are worn on your adapter then it is a real bear to strobe.
Along with others I highly recomend the triangulation form of stobing as preached by the Reverend Mooney @ Northern lights college. It is a very effective way to strobe any rotating mass in 4 runs ( no wieght, weight @ 120, weight @ 240, plot on a random clock and see which angle will give you the best shot to the centre from your original run) as proved by a 4 cyl car that I saw strobed at the clutch plate with washers under the bolts @ 3000 rpm to under .1 ips, now the car happily revs to 7000 with no vibration! all this from an engineer with too much time on his hands.

 

[Uncommanded LoadRelease]

One can statically balance and run-out the shortshaft as mentioned by Mag; don't waste the company's money by sending it out for "overhaul". Man....all this talk about shortshafts is bringing back nightmares of a certain D-model in the Arctic.................ahhhhhhhhhhhhhhhhhh!!!!!!!!!!!!!!!!

 

[chopperdr]

all those interested, have attached a trouble shooting guide from dave dunstan, he is the american eurocopter as-350 tech rep. he asked me to pass this information on, if you have any questions contact dave directly through the american eurocopter website, look under tech reps.
thanks
dr