DETERMINATION OF CORRECT SENSITIVITY

TM 55-4920-201-14

7-16. DETERMINATION

CORRECT

established, add to the assembly a measured

SENSITIVITY.

am amount of unbalance (w x d) equal to the balance

tolerance. Addition of this amount of unbalance

7-17. The listed arbor sensitivity setting for a given

should cause the centralized balance indication to

assembly may be verified in the following manner:

shift until the black indicator disc circle becomes

a. Mount propeller or blade on the arbor in

tangent with the indicator bushing circle. If this

accordance with the instructions applying to the

occurs, sensitivity setting is satisfactory.

individual assembly.

b. Position piloting adapters on arbor at the

NOTE

listed sensitivity setting in accordance with ap-

Static balance tolerance for the specific

plicable instructions.

assembly being balanced is usually

c. Install quick-disconnect coupling; hoist

specified in the applicable maintenance or

arbor and balancing assembly approximately 1/4

overhaul instructions for the assembly.

inch off work stand or other support. Check to

(Refer to appendix A).

insure that suspended assembly if free from in-

terference with stand or other objects.

f. If the indicator deflection from the cen-

tralized position, caused by addition of the balance

d. Observe stabilized balance indication and

tolerance, w x d, is less than the tangency point of

add temporary weights, as required, to centralize

the two circles, insufficient sensitivity is indicated;

balance indication. If balance indication cannot be

repeat the procedures above with assembly

centralized, too high a CG position on the arbor

mounted higher on the arbor. Conversely, if the

(instability) is indicated. Try lower positions of the

introduction of the balance tolerance, w x d, causes

assembly on the arbor until the balance indication

displacement of the balance indication beyond the

can be centralized by addition of temporary

tangency point of the two circles, sensitivity is too

weights.

great and the assembly should be repositioned

e. Once the centralized indication is

lower on the arbor.

7-5