I have been adjusting the pitch of my DUC prop and have noticed that the bolts are no longer holding their torque and the washers stay flat when loosened.

Does anyone know where to order replacement washers and how many times you can loosen/tighten them before you should replace them?

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What type washers are you using, but wonder if you've looked at using Nord-Lock washers?  We use them for our Warp Drive prop and brake assembly.   While even Nord-Lock says we may reuse them a few times, we don't because of the critical application.  They come in different material.


I saw Nord Lock washers in the Aircraft Spruce catalog.  They are not Nord Lock but similar.  They are conical shaped and compress as you torque the bolts. 

Unfortunalty they stay flat now and I have to retorque my prop bolts often.  In the washer's defence, I have been testing out prop pitches and loostening/tightening these bolts a lot. 

I'll take a closer look at the Nord Lock washers.  Thanks!

We used less expensive Nord-Locks (galvanized) during test flights to adjust the prop pitch, and then once set replaced with pricey SS Nord-Locks.  I special ordered ours through a local Fastenal store, but others such as Grainger likely carry as well.   Again, we chose to never reuse Nord-Locks at any time, we just used cheaper ones during test phase.

Thanks, I'll give those a try!

You might first ask Duc if there's a reason not to?

Be careful not to stretch your bolts by over torquing. Also, if the washers are what I am thinking they are only designed to be used one way, they are not reversible. 

   McMasterCarr has Nordlocks.  I purchased them for my WhirlWind prop bolts.  Viking 130 engine has 2 prop spacers so I needed longer bolts and washers.  Good Luck!

I think I found them on McMaster under Lock washers.  I'm going to measure and make sure the size is accurate and order a bag and check them out.

Belleville Spring Lock Washer, Black-Phosphate Steel, for M8 Screw Size, 8.4mm ID, 18mm OD   

a pack of 50 is $14

Thanks to all that responded!

We have those and from the same place.  

I would not use any more torque than 180-200 inlb.  

Looking for clarification.  200 inch - pound is for prop angle clamping bolts.  What is the prop hub attachment torque value.  And can we place wedge style locking washers on the hub attaching bolts.

The DUC Manual in English can be found here for the FLASH version of the prop..  http://www.duc-helices.com/client/document/dh_fsh_be_02_129.pdf

Pg 11 shows 2.5 KG/M for both the main bolts and the outer bolts that hold the pitch.  By my conversion, thats about 18 Ft/LB or 216 Ft / LB.  It does feel just a bit excessive.  

My DUC prop came with the wedge shaped "Bellville washers" under every bolt on the prop hub. I was able to buy replacement Bellville washers on McMaster Carr.

Thanks for the manual.  You're right on about torque values for M8 (all of them).  I was a little nervous about prop bolts not having safety wire or nord lock.  But it's also a carbon fiber hub and no were near the vibrations of a tradition aircraft engine.  Can't wait to get this thing in the air.


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