Tensioning Elevator Cables

[N2520V]

The POH for my '48 170 says to tension the cables to 30lbs. What I've noticed is that when tensioning the cable at the bottom of the elevator bellcrank (rear tailcone bulkhead) to the proper tension, the upper cable is well below the prescribed tension and results in slack in the upper cable when the elevator is in the full down position. Attempting to remedy by re-tensioning the upper cable to the proper tension result in over-tension on the bottom cable. After numerous back and forth adjustments, I just can't seem to get these tensions correct. I know I'm missing something obvious here.

What is the proper procedure for setting cable tension on the elevator cables? What position should the elevator be in when tensioning? Neutral seems logical, but I'd sure like to have someone smarter than me tell me for sure.

Thanks in advance.

-Dustin

[Metal Master]

The elevator controls are a closed loop system. The cable tensions can not be different top and bottom. However the scale readings can be different. I have always noticed this same issue when tensioning elevator cables particularly with balanced control surfaces when the elevator is hanging on the cables, Your 170 has no balance weights however. I have always averaged the two tensions to equal the required tension. Just make sure the travels are correct,

Check the travels both up and down from neutral.
Set the cable tensions to the 30 Lbs. tension. Adjust it so that that the totals of the upper cable and the lower cable equal 30 lbs tension. Example
upper cable 25 + lower cable 35 = 60 / 2 = 30 lbs tension. Re-check your travels.

If your cables are old then the may be stretched and need to be replaced. If the cable is stretched it has a smaller diameter and will read a lower scale reading on the tensiometer for a given cable tension.

Hope this helps,

Jim

[GAHorn]

.... Your 170 has no balance weights however. I have always averaged the two tensions to equal the required tension. ...

Just FYI for the later 170-B owners... the B-model does indeed have counterweights (balance wts). A method to avoid mis-adjustments that might occur when tensioning all models is to support the elevator while tensioning the cables. If the elevator is supported then balance wt differences will have no effect.