VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #1  
Old 06-04-2018, 05:44 PM
vic syracuse vic syracuse is offline
Super Moderator
 
Join Date: May 2005
Location: Locust Grove, GA
Posts: 2,313
Default Jam nuts :(

I am about ready to start a movement like Nancy Reagan's "just say No to drugs", only mine is going to say "Just say NO to loose jamnuts!"

I thought I had started a thread on this some time ago, but I can't find it right now, so you get to hear me again.

I performed a prebuy on an RV-10 today that has been flying for 8 years. So that's an Airworthiness inspection, and at least 7 Condition Inspections, and amongst the 800 hours, hopefully some preflights.

I found 7 loose jamnuts on the tail surfaces! They had never been tightened, as there was no scoring on the mating surfaces. I just reached in with my fingers and turned them.

So, please go check your jamnuts on your next preflights. This is a high stress area to begin with, with a SB even being issued across most of the models for cracking around the nutplate rivets. Perhaps someone on this forum can set up a poll that says "I have checked my aircraft jamnuts." It would be interesting to see if we could achieve 100% in the next year.



Vic
__________________
Vic Syracuse

Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, Just Superstol, DAR, A&P/IA, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES
EAA Homebuilt Council Chair/member EAA BOD
Van's East Coast Representative
www.Baselegaviation.com

Last edited by vic syracuse : 06-04-2018 at 07:59 PM. Reason: added text
  #2  
Old 06-04-2018, 06:10 PM
Bob Kuykendall's Avatar
Bob Kuykendall Bob Kuykendall is offline
 
Join Date: Sep 2006
Location: Douglas Flat, CA
Posts: 569
Default

The temptation might be to look at this as an issue of the jam nuts preventing the rod ends from unthreading themselves. You'd see that the angle brackets on the stabilizer prevent the rod end from turning very far, decide that the jam nuts have no particular purpose, and carry on.

However, what the jam nuts actually do is apply clamping pressure that helps transfer bending loads from the shank of the rod end into the control surface of the spar. In the absence of this clamping pressure, all that's resisting the bending loads are a couple of wimpy AN427AD3 rivets, and these rivets react the bending loads in tension. And rivets, especially when there's only one or two of them, are not all that good at reacting tension.

Once those tiny rivets break, the control surface has a lot of play to move out of plane. And that's very bad from a flutter perspective.

__________________
Bob Kuykendall
HP-24 kit sailplane
EAA Technical Counselor
  #3  
Old 06-04-2018, 06:33 PM
plehrke's Avatar
plehrke plehrke is offline
 
Join Date: Sep 2006
Location: Defiance, MO
Posts: 1,413
Default

Quote:
Originally Posted by Bob Kuykendall View Post
The temptation might be to look at this as an issue of the jam nuts preventing the rod ends from unthreading themselves. You'd see that the angle brackets on the stabilizer prevent the rod end from turning very far, decide that the jam nuts have no particular purpose, and carry on.

However, what the jam nuts actually do is apply clamping pressure that helps transfer bending loads from the shank of the rod end into the control surface of the spar. In the absence of this clamping pressure, all that's resisting the bending loads are a couple of wimpy AN427AD3 rivets, and these rivets react the bending loads in tension. And rivets, especially when there's only one or two of them, are not all that good at reacting tension.

Once those tiny rivets break, the control surface has a lot of play to move out of plane. And that's very bad from a flutter perspective.

Most excellent drawing to go with explanation. I have sketched many such drawings on my whiteboard to visualize what is really happening.
__________________
Philip
RV-6A - 12 years over 850 hours
Cessna 140 - 68 years over 3400 hours
Based at 1H0 (Creve Coeur)
Paid dues yearly since 2007

Last edited by plehrke : 06-04-2018 at 06:37 PM.
  #4  
Old 06-04-2018, 06:51 PM
Steve Melton's Avatar
Steve Melton Steve Melton is offline
 
Join Date: Apr 2011
Location: Cincinnati, OH
Posts: 1,745
Default

reminds me of a jammin song. think of this when you check your nuts.

https://youtu.be/EtTRAk7iQnA
__________________
Steve Melton
Cincinnati, OH
RV-9A, Tip-up, Superior O-320, roller lifters, 160HP, WW 200RV, dual impulse slick mags, oil pressure = 65 psi, EGT = 1300F, flight hours = 600+ for all

Simplicity is the art in design.

see Amanda Melton for www.rvplasticparts.com
  #5  
Old 06-04-2018, 07:33 PM
j-red j-red is offline
 
Join Date: Dec 2015
Location: Lewes, DE
Posts: 239
Default

While I’ve taken these warning to heart and check the jam nuts on every preflight, I appreciate the helpful discussion and drawings of what’s really going on. It’s always good to understand the “why.”
__________________
Rebuilt RV-6A N94CR
RV-8 In Progress
2017 Dues Paid
  #6  
Old 06-04-2018, 07:42 PM
az_gila's Avatar
az_gila az_gila is offline
 
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 9,555
Question

Quote:
Originally Posted by Bob Kuykendall View Post
The temptation might be to look at this as an issue of the jam nuts preventing the rod ends from unthreading themselves. You'd see that the angle brackets on the stabilizer prevent the rod end from turning very far, decide that the jam nuts have no particular purpose, and carry on.

However, what the jam nuts actually do is apply clamping pressure that helps transfer bending loads from the shank of the rod end into the control surface of the spar. In the absence of this clamping pressure, all that's resisting the bending loads are a couple of wimpy AN427AD3 rivets, and these rivets react the bending loads in tension. And rivets, especially when there's only one or two of them, are not all that good at reacting tension.

Once those tiny rivets break, the control surface has a lot of play to move out of plane. And that's very bad from a flutter perspective.
....
Given that explanation, wouldn't a regular washer under the jam nut be a good idea?
__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
  #7  
Old 06-04-2018, 08:53 PM
Jesse's Avatar
Jesse Jesse is offline
 
Join Date: May 2005
Location: X35 - Ocala, FL
Posts: 3,564
Default

Vic, I have found the same thing on several occasions. When I preflight I often check the jam nuts. Not every time, but regularly, and every time on a plane I havenít flown before.
__________________
Jesse Saint (Saint Aviation, Inc. - VAF Advertiser)
352-427-0285
jesse@saintaviation.com
RV Hotel (hangar, room, car) at X35 in north FL

Commercial ASEL/S A&P/IA EAA Technical Counselor

Dynamic Prop Balancing, Prebuy Inspections, Condition Inspections, Repairs and Mods, Injector Tuning, Airframe, Engine, Panel Upgrades, Ferrying, etc.
  #8  
Old 06-04-2018, 08:54 PM
coffeeguy coffeeguy is offline
 
Join Date: Jul 2015
Location: Lake in the Hills, IL
Posts: 102
Default

I do a visual on the jam nuts before every flight in my Cherokee. I don't always check them with my fingers though. It looks like it would be a good practice.
__________________
Jeff Dingbaum
RV-14A empennage, wings
Cherokee 180
2018 dues paid
  #9  
Old 06-05-2018, 05:08 AM
snopercod's Avatar
snopercod snopercod is offline
 
Join Date: Aug 2016
Location: Asheville, NC
Posts: 1,319
Default

On my inboard gear door - a high vibration area on takeoff - I found a loose jamb nut which allowed the rod end to partially unscrew. I didn't notice it but my tail-cam video showed that the door wasn't closing all the way. I'll be adding that to my preflight checklist.
__________________
(2018 dues paid)
  #10  
Old 06-05-2018, 05:34 AM
ColoCardinal's Avatar
ColoCardinal ColoCardinal is offline
 
Join Date: May 2010
Location: Morrison, CO
Posts: 298
Default Loose nuts

Isn't everyone using a torque seal after torquing their fasteners? I would think that it's an excellent way to indicate that the fastener has been torqued and whether it has moved since then. Check and retorque at annual and reseal with a new color.
__________________
Carl - - Morrison, CO
Inspection is weeks away.
Garmin fiasco is over.
paid 'til 10-18
Closed Thread


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 04:23 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.