This sure is one area where you want to get it right! There are many stories of a prop coming off in flight.
Maybe that 4-6 is a metric value?
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This sure is one area where you want to get it right! There are many stories of a prop coming off in flight.
Maybe that 4-6 is a metric value?
Here's what Culver Propellers says (using a backer plate) :
Torque Specifications for Propeller Bolts:
1/4” bolts . . . . . . . . . . . 132 inch pounds (+ or – 10 inch pounds)
5/16” bolts . . . . . . . . . . . 144 inch pounds (+ or – 15 inch pounds)
3/8” bolts . . . . . . . . . . . 200 inch pounds (+ or – 20 inch pounds)
7/16” bolts . . . . . . . . . . . 250 inch pounds (+ or – 25 inch pounds)
1/2” bolts . . . . . . . . . . . 300 inch pounds (+ or – 25 inch pounds)
Does anyone lockwire the prop bolts together ?
I thought everybody did.
The Whirlwind props don't use lockwire. They use Nordlock washers.
Typically props are secured using safety wire. Some use the self-locking nuts, which should be replaced every time.
Reason I asked the question about lock wiring of prop bolts was a friend of mine used to work with the Australian ATSB (equivalent to USA NTSB). He was investigating an accident where the aircraft lost a prop and the resulting landing involved a serious injury. Turned out the prop bolts were not positively locked in any way. They merely relied on torquing of the bolts, not even lock washers, and it was a wooden prop. Whether it had a crush plate I can't recall, but for me, it's a no brainer - some form of positive bolt retention is critical.
Whirlwind allows multiple tightening cycles for their Nordlock washers, I believe it was up to 12 cycles. They are quite impressive as a locking device. There is no way they can gradually back off; it takes full torque reverse "pop" to cam up over the ridges before they will turn in reverse. As long as they have that definite "pop" they are still good to go. I have nothing against traditional lockwiring, but my whirlwind prop bolts did not come with drilled heads.
Interesting. First I Googled Nordlock washer. wow, expensive by washer standards. Then I thought, "why replace inexpensive safety wire that has worked for everyone so far with such expensive washers?". I then watched www.youtube.com/watch?v=cDlmbMV9ICU. I learned why.
Eddie
Nordlock washers are on the Sensenich ground adjustable prop I have , they hold tight and "snap " when undoing. A great lock washer.