Nord-Lock Washers with Wooden Prop

[ahramin]

Can Nord-Lock washers be used for prop bolts on a wooden prop or must the bolts be lockwired?

[Marc Zeitlin]

Can Nord-Lock washers be used for prop bolts on a wooden prop or must the bolts be lockwired?

Since wood prop hubs can shrink when they dry out, a washer that depends on compression for anti-rotation would not be useful. Now, as it turns out, safety wire on wood props isn't all that useful either, since it does nothing to maintain compression but only prevents the bolts from turning.

If you're using a wood prop, what you want (if you have a diameter bolt for which I've engineered a solution) is belleville washers. See:

http://cozybuilders.org/Prop_Bolt_Be...her/index.html

for more information. Feel free to contact me directly if you have any questions. But even with the bellevilles, safety wire is required. It might be interesting to try Nord-Locks in combination with bellevilles instead of safety wire - I'll have to think about that a bit more, but it should work as a safety wire replacement in that instance.

[ahramin]

Very interesting Marc. Thank you.

[melann]

Since wood prop hubs can shrink when they dry out, a washer that depends on compression for anti-rotation would not be useful. Now, as it turns out, safety wire on wood props isn't all that useful either, since it does nothing to maintain compression but only prevents the bolts from turning.

While I agree that safety wire will not maintain compression on the bolts, it WILL prevent them from departing the aircraft.

[Marc Zeitlin]

While I agree that safety wire will not maintain compression on the bolts, it WILL prevent them from departing the aircraft.

Nope - didn't on my plane. See:

http://cozybuilders.org/Oshkosh_Pres...ert_Center.pdf

The safety wire will prevent the bolts from turning, but that's not worth diddly squat if the hub shrinks away from the crush plate and the hub loses compression. Prop starts moving back and forth on the drive flange, the bolts fatigue, and bam - gone.

[Bill Berson]

Interesting report. I guess it glides well with no prop.....

What is "static torque"? (from report: "only checked static torque")

edit, I found from your other webpage that said loosen the prop bolts first, then retorque while rotating in motion. Is that procedure adequate in most cases?

[Marc Zeitlin]

Interesting report. I guess it glides well with no prop.....

Better than with it windmilling, yeah. And smooth, too :-).

What is "static torque"? (from report: "only checked static torque")

edit, I found from your other webpage that said loosen the prop bolts first, then retorque while rotating in motion. Is that procedure adequate in most cases?

Yes. There are always inaccuracies in torque measurements, due to friction, surface finish, lubrication, interference fits, etc., but if the bolt isn't rotating while you're measuring the torque, you're pretty much guaranteed to get a very inaccurate number unless you've lubricated the hell out of the threads first. Which you can't do if the prop's been on the plane for 6 months to a year prior to the torque measurement :-).