prop bolt torque

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taildrags
Posts: 637
Joined: Tue Mar 07, 2017 10:39 pm

prop bolt torque

Post by taildrags »

In a recent post and discussion on another list, a pilot reported having broken several prop bolts after experiencing vibration after takeoff and returning to the field under reduced power. Inspection upon landing revealed that the prop bolts apparently weren't properly torqued and there had been burning or fretting between the prop hub and the back face of the prop. A discussion of the proper prop bolt re-torquing interval followed, and it is essentially the information contained in the Sensenich propeller installation instructions here:

http://www.sensenich.com/files/document ... 800693.pdf

Obviously, other wood prop makers can provide similar information, and sometimes it is very specific to their products. Prop bolt torque values in particular should be as recommended by the manufacturer, since it may be related to the wood species used in the prop. I thought about this yesterday when I pulled my airplane out of the hangar on a sunny but cold afternoon, started the engine, and taxied around for a bit to get the oil warmed up. Static ground runup-rundown sequences were made till the oil was reasonably warm, mag check and carb heat check was run, then I shut the engine down and put the airplane away. The last time I ran a prop torque service on it was late last spring when I was thinking about flying down to the West Coast Piet fly-in but ended up not going. That was a warmer and wetter time... a good 40 degrees warmer and quite a bit different humidity. In the intervening 6 months, we went through a very hot and dry summer, and now here we are in winter. Before I ran my engine I should have cut the safety wire, loosened the prop bolts to let the wood relax a bit, then re-torqued and safetied the bolts for the winter. The swings in temperature and humidity are just too wide up here where I live, and just watching the heads loosen and tighten on any of my tools that have wooden handles and steel heads easily convinces me of the large seasonal changes in fit between them. Anyone else have prop bolt torque experiences to relate? Dan Helsper and others who have whittled your own, what do you use for bolt torque?
gcardinal
Posts: 12
Joined: Wed Feb 22, 2017 5:02 am

Re: prop bolt torque

Post by gcardinal »

Good subject, Oscar.

Marc Zeitlin has developed an installation system using Belleville washers.
Information here:
http://cozybuilders.org/Prop_Bolt_Bellville_Washer/


I've used this method on several props in Minnesota with extreme temperature / humidity swings.
Here is a picture of one of the installations:
(Yes, I know it isn't safety wired...)

Image
Attachments
Belleville Installation.jpg
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