Short Shaft Balancing

[mawddawg]

####: I would love to know what the limit is! Maybe it is in the manual but I can't seem to find it . Could you advise the chapter and para? I would like to maintain the helicopter to some printed standard if its out there.Can the couplings be changed on the early shafts? Why so little info in the books or am I looking in the wrong area? any help would be great

Thanks

[highbladedown]

Try Eurocopter Product Support - Terry Kozar 905.871.7772

[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.

[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