VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.






VAF on Twitter:
@VansAirForceNet


Go Back   VAF Forums > Model Specific > RV-12/RV-12iS
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #21  
Old 11-06-2022, 09:17 AM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,818
Default

So, if the stabilator counterbalance falls off during flight... what will happen? I think that is the BIG question here, probably followed by... what will it take to prevent failure?

Will stabilator flutter wildly? Will airplane become uncontrollable? How heavy will pitch forces be? Etc., etc....
__________________
-
Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 830

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father - CFI) - USAAF 1st Lt. Captain B-17H
Reply With Quote
  #22  
Old 11-07-2022, 09:56 AM
fr0gpil0t fr0gpil0t is offline
 
Join Date: Apr 2013
Location: Colorado Springs
Posts: 101
Default

The comment on the RV-12 Facebook page was "Counter weight broke off the stab rod. Pitch got a little heavy."

Another image - taken from the Facebook post
Attached Thumbnails
Click image for larger version

Name:	311181252_10229714201658526_2567683513196846795_n-2.jpg
Views:	250
Size:	62.2 KB
ID:	33423  
Reply With Quote
  #23  
Old 11-07-2022, 11:13 AM
Marc Bourget Marc Bourget is offline
 
Join Date: Apr 2009
Location: Stockton, California
Posts: 384
Default

What happens if it falls off in flight?

This topic has shown up on several forums recently.

The counterweight is dynamic - meant to reduce control surface deflection in case of gust loads.

In a separate, related context, it improves flutter risk by lessening load and avoiding development of "aeroelastic" conditions which is a definition of flutter when you add "positive divergence." (i.e. displacement of the control surface increases - to failure)

Just slow her down soft turns, etc., and hope it isn't turbulent - till you get to the ground.
Reply With Quote
  #24  
Old 11-08-2022, 07:31 AM
gossend gossend is offline
 
Join Date: Dec 2011
Location: Georgetown, Texas
Posts: 208
Unhappy Little doubt in my mind

Quote:
Originally Posted by PaulvS View Post
My guess is that the plane was parked outside without a control lock on the stabilator and it banged up and down in the wind until the weight attach bracket fractured.
I always cringe when I see an Rv-12 parked downwind. The sound it makes when that stab slams against the up-stop is deafening. Even while taxiing, a strong tailwind gust can rip the stick right out of your hand. This is probably why the stab spar was cracking and the corrective SB was published.
My guess is that these "tail slam" events probably load the counterweight shaft beyond the limit loads. Frankly, I expected we'd be seeing them failing at the root, where it's attached to the spar itself, but I can believe this failure mode as well.

I "fixed" mine by installing a rubber cushion on the shank of the up-stop bolt. I simply slit a piece of 3/8" fuel hose length-wise and snapped it onto that bolt. It does limit my up-travel a bit, but it turns the "tail slam" into a silent, soft landing. I'd guess the shock loads are reduced fifty-fold at least.
__________________
Dick Gossen
gossend@gmail.com
Flying: EAB RV-12 with 130 HP UL Power 350is engine. Call me so I can brag about it!
408 499 8587
Reply With Quote
  #25  
Old 11-21-2022, 08:24 AM
joedallas's Avatar
joedallas joedallas is offline
 
Join Date: May 2010
Location: Spring Hill Fl
Posts: 766
Default Random Vibration Fatigue Analysis

I am still waiting for van's analysis of this problem and solution.

This video shows what I think is the cause of the metal fatigue.

This helps explain what random vibration fatigue is.

Fast froward to 8:50 in the video if you are not interested in all the engineering.

Rember the counterweight inertia (a body at rest tens to stay at rest)

https://www.youtube.com/watch?v=Jt-9KOBbIdY

From my previous posts

Quote:
Originally Posted by joedallas View Post
This problem has been on my mind since my pervious my post.

I believe this failure is caused from a frequency-based metal fatigue from harmonic vibration. (Over the maximum number of cycles allowed)

Also, the kip frequency caused by the engine balance and the prop balance when in alinement? (caused by the gear box ratio)

The engine Ballance and the prop balance and the gear box move the force in changing degrees from a horizonal plane.

The engine is the on the front end of a teeter totter (so to speak) inertia stable.

The center mass is at the spar, balance point (so to speak), The spar the fuel tank and the occupants. Note full fuel tanks in the wings would help dampen the vibration.

The counterbalance is on the longer arm of the teeter totter (so to speak)

Note my background is in engineering (I am not a wordsmith)


A good prop balance and pitch match would mitigate this problem.

My view



From my pervious post
__________________
Joe Dallas
Kit-#12400
www.joesrv12.com
www.EAA1298.com

Last edited by joedallas : 11-21-2022 at 09:09 AM. Reason: Typing
Reply With Quote
  #26  
Old 11-22-2022, 10:05 AM
LettersFromFlyoverCountry's Avatar
LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
Join Date: Jan 2005
Location: St. Paul, MN.
Posts: 4,857
Default

Quote:
Originally Posted by BobTurner View Post
I think itís red RTV, used to hold the abrasion protection in place. Or a lot of blood!
I'm sure I'm misremembering things but I very vaguely recall a warning not to use Red RTV on aluminum. I think it was when I was building my RV-7A rudder or elevators and the instructions called for a dab of RV inside the stiffeners at the trailing edge. Now I don't remember if it was in the instructions where the caution was made or if it was in an issue of the RVator (which is how we got our RV news from the factory way back when).

Am I dreaming this? Because I've made sure to always use blue RTV where it's called for on the airframe since.
__________________
Bob Collins
Working on RV-12iS avionics
N612EF Builder log (EAA Builder log)
Professional Grandfather
St. Paul, MN.
Reply With Quote
  #27  
Old 11-22-2022, 12:22 PM
rv6n6r's Avatar
rv6n6r rv6n6r is online now
 
Join Date: May 2007
Location: Gearhart Oregon
Posts: 541
Red face

Quote:
Originally Posted by LettersFromFlyoverCountry View Post
I'm sure I'm misremembering things but I very vaguely recall a warning not to use Red RTV on aluminum. I think it was when I was building my RV-7A rudder or elevators and the instructions called for a dab of RV inside the stiffeners at the trailing edge. Now I don't remember if it was in the instructions where the caution was made or if it was in an issue of the RVator (which is how we got our RV news from the factory way back when).

Am I dreaming this? Because I've made sure to always use blue RTV where it's called for on the airframe since.
I'll jump in on this one even though it's serious thread drift...
That was a long-running debate way back in the day that was eventually debunked with some testing. I'm going by memory but as I recall the results were published in the RVator and showed no increased corrosion from RTV versus other materials. The theory is that the acetic acid (which is there to etch and help make it stick) outgasses off leaving no ongoing corrosive effect.
That said, RTV also breaks down over time and so shouldn't be used anywhere that could cause a problem, like between the carb and sump for example. For that and other reasons, I prefer proseal for most things other than baffle seals etc.
__________________
Randall Henderson
RV-6 / O-360 / CS, 1600+ hrs, 1st flight Sept. 1999
Outstanding Workmanship OSH 2000, Craftsmanship award AWO 2000
Airport committee chair & AOPA ASNV for Seaside, OR Municipal (56S), www.seasideairport.org
Last Donated August 2022
Reply With Quote
  #28  
Old 11-26-2022, 09:49 PM
gossend gossend is offline
 
Join Date: Dec 2011
Location: Georgetown, Texas
Posts: 208
Default counterweight failure

I took a close look at mine - maybe found the failure signature? A square notch in the flat plate welded to the CW arm was cut to fit the CW arm and then welded. However, the corner radius of that notch - at least on mine- was not radiused properly and creates a stress riser in the corners. if the speculation voiced here about resonant horizontal vibration is correct, then I wouldn't be surprised to see the failure mode we're seeing here.
Just my impression, but I'll wait for the VANS engineering team to opine!
__________________
Dick Gossen
gossend@gmail.com
Flying: EAB RV-12 with 130 HP UL Power 350is engine. Call me so I can brag about it!
408 499 8587
Reply With Quote
Reply


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 10:18 PM.


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.