Author Topic: Belleville washers to hold props on?  (Read 4852 times)

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Offline DWilliford

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Belleville washers to hold props on?
« on: December 27, 2011, 11:39:48 AM »
I'm curious as to how many carnard drivers are out there that are using Belleville washers to secure their propellers?  I for one have converted after discovering that my prop is no longer air worthy.  I just no longer believe that bolt torque is a good (safe) measurement of the force needed to keep the propeller on my plane.  Do you feel the same way?   Have you ever come close to loosing a propeller in the air? 

   

Offline flyingwaldo

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Re: Belleville washers to hold props on?
« Reply #1 on: December 27, 2011, 04:47:43 PM »
"I just no longer believe that bolt torque is a good (safe) measurement of the force needed to keep the propeller on my plane."

 ???  How many millions and millions of hours have been flown and continue to be flown safely without bellville washers.......   ???

KISS still works, but then I'm not an Engineer.....  :-\
« Last Edit: December 28, 2011, 11:14:14 AM by flyingwaldo »

Offline Joe Dubner

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Re: Belleville washers to hold props on?
« Reply #2 on: December 28, 2011, 10:37:48 AM »
I'm curious as to how many carnard drivers are out there that are using Belleville washers to secure their propellers?

I have been using them (in accordance with instructions from Marc Zeitlin and Gary Hertzler) for the past 2-1/2 years.

Quote
I for one have converted after discovering that my prop is no longer air worthy.  I just no longer believe that bolt torque is a good (safe) measurement of the force needed to keep the propeller on my plane.  Do you feel the same way?

No.  I have total confidence that bolt torque is a "good (safe) measurement of the force needed to keep the propeller on my plane".  And note the words "good/safe" -- it's good enough if done right.  But I don't have total confidence in my ability to maintain that bolt torque without frequent checking and adjustment, which is more work than I'm willing to do.

Quote
Have you ever come close to loosing (sic) a propeller in the air?

No, never.  But then, I would check bolt torque 3-4 times a year (in my pre-Belleville days).

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Joe
« Last Edit: December 28, 2011, 06:10:48 PM by jdubner »
Joe Dubner
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Offline DWilliford

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Re: Belleville washers to hold props on?
« Reply #3 on: December 30, 2011, 06:29:11 PM »
And note the words "good/safe" -- it's good enough if done right.  But I don't have total confidence in my ability to maintain that bolt torque without frequent checking and adjustment, which is more work than I'm willing to do.

I agree with you. Regular bolt tighting can be safe.  One just has to be very diligent. It's my hope that the Belleville washers will simply add a measure of safety, and as Sam with Saber manufactureing said, "they can't hurt".  The bolt torque on my prop went from a heathy 45 lbs to a dangerous 20lbs in less than 30 hours of actual flying.  That's scary.  I account for the change to a large temperature decline.  So, with the right amount of dilligence, bolt torgue does suffice.  The difference is that in using the washers, do I increase or add a margen of safety in making sure my prop stays on safely? I think I do.  Hopefully, I won't have to rely on the " it's good enough if done right" method.

Thank you,
Anyone else?

David
 

Offline admin

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Re: Belleville washers to hold props on?
« Reply #4 on: January 04, 2012, 01:21:53 PM »
Marc Zeitlin has a good writeup on his site: http://cozybuilders.org/Prop_Bolt_Bellville_Washer/index.html

I think if Marc endorses it it's a safe thing to do as he seems to be anti-eyeball engineering for most things. And if
the prop god Gary H. does it then then it's got to be ok  ;D


Offline dorr

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Re: Belleville washers to hold props on?
« Reply #5 on: January 11, 2012, 03:05:58 PM »
I'd have to say that there are many thousands of hours on properly built props with simple bolt torque - maybe there is something wrong with the prop if the thing losses torque that fast!  One of my friends failed prop bolts when his metal spinner fractured and vibrated for about 7 minutes to landing... a vibrating prop might do similar damage.  I'm at 3200+ canard hours and have never found the torque drop at 25 hour checks so now I do 50 hour checks on the latest prop designs.  I live in dry country...

But a Long EZ owner/engineer suggested to me that the belville washer thing is fine, but a simple pair of bellvilles is more effective than more pairs in stack.  He says the more you use, the less effective...I think Hertzler uses only one pair per bolt...I'm too simple to understand why, but the engineer was adamant.

Beagle
David A.C.Orr
"Beagle"
www.canardfinder.com