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  #1  
Old 12-02-2015, 08:35 AM
kritsher kritsher is offline
 
Join Date: Feb 2007
Location: Stow MA
Posts: 174
Default smoky residue at cowling hinge

Hi guys,

I could use some advice on this. This is a picture of the right side of my RV-12 where the lower fiberglass cowling (on the right) meets the aluminum fuselage structure (on the left). The lower of the two hinge pins on the lower cowling runs down the center of the photo.



A while ago, I started noticing some "smoky" residue streaming rearwards from the hinge line. You can clearly see some of this residue at the top of the photo, above the black paint stripe, but it extends along much of the length of the hinge pin. Originally, I thought this was caused by the pin vibrating against the hinges and I didn't worry too much about it.

More recently, the paint on top of the flush squeezed rivets securing the hinge to the fiberglass has started cracking around the rivet heads. You can see this in the lower right side of the photo. This makes me think the rivets are loose and they may in fact be the cause of the residue. I likely under-sqeezed them during assembly in fear of damaging the fiberglass.

I haven't taken the cowling off yet to investigate, but I'm wondering what the best remedy might be...?
1. Re-squeeze the existing rivets and hope that tightens everything up?
2. Drill the rivets out and replace them with the same rivet?
3. Drill them out and replace with a larger, round-head rivet? (I figure a round head rivet would provide better compression)
4. Drill them out and replace with LP4-3? This is what I'm leaning towards. Any reason not to use a pulled rivet here?

My tentative plan is to drill out each rivet, open the hole to #30, and cleco before moving to the next rivet. Then remove the hinge, deburr, and clean up/scuff the mating fiberglass. Then smear some epoxy on the fiberglass and hinge, cleco the assembly together, and re-mount the cowling while the epoxy cures. Finally chase the holes with a drill and rivet with LP4-3.

Comments? Other suggestions?

Thanks!
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Ken
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  #2  
Old 12-02-2015, 09:04 AM
Harvey rv12 Harvey rv12 is offline
 
Join Date: Apr 2015
Location: Olympia WA
Posts: 198
Default

I have the same residue on my -12. I did not build the airplane, so I don't know exactly what the structure is behind there. I am watching closely, and hoping someone from Vans will comment.


Tom O.
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  #3  
Old 12-02-2015, 09:13 AM
DHeal DHeal is offline
 
Join Date: Sep 2006
Location: Windsor, California
Posts: 1,005
Default

I suspect that your "smoking" residue is a combination of cowl hinge pin wear and exhaust pipe connector joint blowby -- with the emphasis on the exhaust blowby. I suggest that you remove your lower cowling and look for evidence of exhaust leakage around your exhaust pipe connector joints. If you find any leakage, fix it*, and see if your "smoking" residue goes away. How many Hobbs hours on your plane?

* Reset exhaust pipes/muffler and add fresh coat of anti-seize to joints per plans.

ps -- Be sure to clean the cowl hinge pins occasionally and use some lubricant on them upon their reinstallation.
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EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B 2020) - N124DH flying since March 2014 - 1,080+ hours (as of Oct 2021)!
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  #4  
Old 12-02-2015, 11:04 AM
JBPILOT JBPILOT is offline
 
Join Date: Nov 2007
Location: Jesup, Iowa
Posts: 1,678
Default Since I have maybe the most hours - -

on a customer plane ( 800 + ), I have put Vasoline on the hinges, and it seems to help. I think it is mostly Alum from the vibrating hinges. A little of all mentioned is contributing also I'd say. Try putting some on these hinges. Can always wipe it off if you don't like it. Vasoline spreads on its own and covers all neighboring surfaces.
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Flying RV-12 - Serial #120036
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  #5  
Old 12-02-2015, 11:25 AM
DHeal DHeal is offline
 
Join Date: Sep 2006
Location: Windsor, California
Posts: 1,005
Default

That's one of the "problems" with our ROTAX 912 ULS engines, they don't leak any oil! How is a pilot supposed to keep the engine compartment and airframe properly lubricated without oil leaking out of every engine orifice!
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David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B 2020) - N124DH flying since March 2014 - 1,080+ hours (as of Oct 2021)!
VAF donation through June 2022.
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  #6  
Old 12-02-2015, 11:51 AM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,662
Default

Quote:
Originally Posted by JBPILOT View Post
on a customer plane ( 800 + ), I have put Vasoline on the hinges, and it seems to help. I think it is mostly Alum from the vibrating hinges. A little of all mentioned is contributing also I'd say. Try putting some on these hinges. Can always wipe it off if you don't like it. Vasoline spreads on its own and covers all neighboring surfaces.
Any wet type lube (oil, grease, etc.) tends to attract and hold dirt and the metal particles that are being worn from the hinges. This makes the lube more abrasive, accelerating the wear.

A better choice is a dry type lube. We rub Boelube on the pins along with occasional polishing on the pins with fine Scotchbrite. I think the RV-12 Maint. Manual mentions using Boelube.

As for paint cracking on rivets... That is usually in indicator of excess vibration (might be solved by a dynamic prop balance), or excessive built in strain cause while initially fitting/ installing the cowl.... or a combination of both.

The worst thing a builder can do for cowl longevity is to force it to a position that it doesn't naturally take, while drilling the rivet holes to mount it..
I.E., if you ever trim slightly in an area but don't want there to be an excessive gap, so you force the cowl to a position that has the gap you want and puts a pre-load on the cowl.
Do that a couple of times and then add some vibration, and it will have an influence on the longevity.
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  #7  
Old 12-02-2015, 02:25 PM
rdoerr01 rdoerr01 is offline
 
Join Date: Jan 2005
Posts: 117
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I've had this on my RV-10 and it is the hinges wearing because the hinges is made out of aluminum while the pin is steel, so the eyelets on the hinge is what is wearing and you will see the eyelets which are the shape of a 9 will wear at the top of the 9 part until the eyelet completely breaks off. After I seen this dusk for many month, I pull the hinge pin out one time and about 5 of the eyelet half dropped on the floor. I had to then install a new hinge on the side that is mount to the firewall.


Thanks

Ray
RV-10 (N519RV)
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  #8  
Old 12-02-2015, 03:21 PM
sblack sblack is offline
 
Join Date: Dec 2009
Location: Montreal
Posts: 1,520
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The black stuff is aluminum dust for sure.
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  #9  
Old 12-02-2015, 03:35 PM
algrajek algrajek is offline
 
Join Date: Jun 2006
Location: Boca Raton, Florida
Posts: 441
Default

Totally normal. Not to worry.
Nordo
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  #10  
Old 12-03-2015, 06:59 AM
blythet blythet is offline
 
Join Date: Sep 2011
Location: selma, NC
Posts: 16
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During my latest condition inspection on my RV12 @255 Hr, I had to replace that same hinge half in the cowling. Several of the eyes were worn thru and broke off. That side of the cowling assembly has less support than the left side that is supported by the fiberglass tunnel. Push on the horizontal hinge line on the left and right sides. You can see and feel the difference. I replaced the hinge half in the lower right cowl. I also added an aluminum brace between the oil tank bracket and the lower cowl. It's riveted to the oil tank brace and is secured to the lower cowling via a 6-32 screw. It noticeably reduces the flexing of the right cowl assembly in the area just ahead of the lower cowl right hinge pin area. One extra screw to remove when the lower cowl is removed.
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