VansAirForceForums  
Home > VansAirForceForums

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

- Today's Posts | Insert Pics

  #1  
Old 12-10-2008, 04:28 PM
ArVeeNiner's Avatar
ArVeeNiner ArVeeNiner is offline
 
Join Date: Jun 2006
Location: San Jose, CA
Posts: 1,125
Default Van's demonstrators and cracked canopies

I'm at the point where I'm re-examining how I'm going to secure my slider canopy. I had decided long ago that I would Sikaflex it. However, I just got back from the airport and looked at a friend's who, despite Sikaflex, still developed cracks at the rear of the slider. I still have to talk to him more about what happened. I think he's thinking that he just didn't have enough bond line back there. So naturally, I'm now looking at perhaps going the conventional route using screws.

My question is, does anybody know how the canopys on Van's demonstrators are holding up? I'm sure they are screwed on and they probably have been flown more than a lot of other RVs.
__________________
Kelly Johnson
San Jose, CA
RV-9A

Pink slip issued: 5/7/12

First flight: 5/28/12, Memorial Day.

Phase I Complete: 8/18/12!

2020 donation: complete
Reply With Quote
  #2  
Old 12-10-2008, 07:41 PM
Mel's Avatar
Mel Mel is online now
 
Join Date: Mar 2005
Location: Dallas area
Posts: 10,769
Default

My -6, completed in '93, is done completely with aluminum pulled rivets. No cracks to date.
__________________
Mel Asberry, DAR since the last century.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
Recipient of Tony Bingelis Award and Wright Brothers Master Pilot Award
USAF Vet, High School E-LSA Project Mentor.
RV-6 Flying since 1993 (sold)
<rvmel(at)icloud.com>
Reply With Quote
  #3  
Old 12-10-2008, 08:53 PM
Ironflight's Avatar
Ironflight Ironflight is offline
VAF Moderator / Line Boy
 
Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,256
Default

Louise's -6 (Mikey), kit number 20004, has been flying for about 19 years - original canopy, no cracks.

Paul
__________________
Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
http://Ironflight.com
Reply With Quote
  #4  
Old 12-10-2008, 08:59 PM
N131RV N131RV is offline
 
Join Date: Jun 2007
Location: Elmendorf,TX
Posts: 358
Default Where exactly did it crack?

Quote:
Originally Posted by ArVeeNiner View Post
I'm at the point where I'm re-examining how I'm going to secure my slider canopy. I had decided long ago that I would Sikaflex it. However, I just got back from the airport and looked at a friend's who, despite Sikaflex, still developed cracks at the rear of the slider. I still have to talk to him more about what happened. I think he's thinking that he just didn't have enough bond line back there. So naturally, I'm now looking at perhaps going the conventional route using screws.

My question is, does anybody know how the canopys on Van's demonstrators are holding up? I'm sure they are screwed on and they probably have been flown more than a lot of other RVs.
Can you describe exactly where the exemplar canopy cracked? On the rear at the side rails? Was there any penetration of the canopy near the crack?

I just finished the sika treatment on my canopy/windscreen. I ended up doing the screws on the side skirts, but no other holes in canopy or windscreen. It's very, very strong stuff. In addtion, I laid up fiberglass skirts at the rear of the canopy. My previous canopy was done per plans, and had no cracks in 298 hours of operation (until asked to support the weight of the aircraft,that is).
__________________
---------------------------------------------------------
Hangared since 11/23/2011, working on getting airborne again!
Joe Portman
N131RV - RV-7A, IO360A1B6, CS
Rebuilt as TD
Added dual MGL EFIS.
Airborne again at last! 2/21/2009

Elmendorf, TX (28TE)

baron (AT) baron (dot) com
Reply With Quote
  #5  
Old 12-10-2008, 09:55 PM
Skytrash's Avatar
Skytrash Skytrash is offline
 
Join Date: Jan 2005
Location: Cameron Park, CA
Posts: 73
Default Aft Canopy Cracks

Here are a couple of pictures of the cracks on my aft canopy. One looks to be originating from where the canopy frame has a slight kink from bending during fitting to the fuselage. The bond line should have been thicker between the frame and the plexi. The bond line should vary in thickness with the shape of the frame to allow for the as bent shape of the frame while allowing the plexi to be as stress free as possible.

I still think that bonding is the way to go and will do it again if I build again.


__________________
Jim Bray
RV-9A Commuter
4000+Hours
Loving Cameron Park, California
Reply With Quote
  #6  
Old 12-10-2008, 10:02 PM
N131RV N131RV is offline
 
Join Date: Jun 2007
Location: Elmendorf,TX
Posts: 358
Default Youch!

Quote:
Originally Posted by Skytrash View Post
Here are a couple of pictures of the cracks on my aft canopy. One looks to be originating from where the canopy frame has a slight kink from bending during fitting to the fuselage. The bond line should have been thicker between the frame and the plexi. The bond line should vary in thickness with the shape of the frame to allow for the as bent shape of the frame while allowing the plexi to be as stress free as possible.

I still think that bonding is the way to go and will do it again if I build again.
Is the rear skirt riveted on? I can't really tell from the images.
__________________
---------------------------------------------------------
Hangared since 11/23/2011, working on getting airborne again!
Joe Portman
N131RV - RV-7A, IO360A1B6, CS
Rebuilt as TD
Added dual MGL EFIS.
Airborne again at last! 2/21/2009

Elmendorf, TX (28TE)

baron (AT) baron (dot) com
Reply With Quote
  #7  
Old 12-11-2008, 01:08 AM
Captain Avgas Captain Avgas is offline
 
Join Date: Oct 2005
Location: Melbourne, Australia
Posts: 1,868
Default

Quote:
Originally Posted by Scott Chastain View Post
In either case, cracks begin like any other fracture in an airframe---from what metallurgists and engineers refer to as stress risers. In this case, a stress riser at the edge of the plexi, originating from pehaps a tiny chip or an unburnished edge, gave birth to a crack that migrated to the extent that it did.
Maybe, but maybe not.

Acrylic as used in RV canopies is very prone to solvent attack leading to microscopic crazing and the subsequent forming of larger cracks therefrom as a result of work-of-fracture theory.

The Sika 209 adhesion promoter actually contains approx 25% MEK and approx 20% Ethyl Acetate. Both of these solvents are in the worst category for damage to acrylic.

Sikaflex is mainly used in marine applications where generally the small acrylic windows are not thermoformed. Severe double curvature thermoforming (such as in RV canopies) may give rise to instrinsic stresses remaining in the canopy after it cools which might make the canopy more prone to cracking from solvent attack.

This is not the first case of cracks being reported in a Sikaflex canopy. It is possible that these cracks are not formed by edge imperfections but by microscopic solvent breakdown of the acrylic polymer.
__________________
You’re only as good as your last landing
Bob Barrow
RV7A

Last edited by Captain Avgas : 12-11-2008 at 03:38 AM.
Reply With Quote
  #8  
Old 12-13-2008, 09:28 PM
rv7charlie rv7charlie is offline
 
Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884
Default

Interesting. If you study the Sika literature, it says that it's specifically designed for bonding acrylic to other materials. I would think that the boating people would have serious problems since most boats are out in the weather 24/7 & the stresses are likely to make a/c loads look pretty tame. Has anyone heard of cracking problems from the boating crowd?

Charlie
(almost to the point of applying the Sika...)
Reply With Quote
  #9  
Old 12-14-2008, 12:34 AM
Mark Castle-Smith's Avatar
Mark Castle-Smith Mark Castle-Smith is offline
 
Join Date: Apr 2005
Location: Dorset, England
Posts: 42
Default

I have a small (22ft) mini tonner in which I bonded new windows about 10 years ago with Sikaflex, no problems at all.

I followed all the rules with my canopy, very hot when it was cut and drilled, used the recommended plexiglass drills etc. All looked good with the naked eye, no sign of cracks. I then decided to make doubly sure and used a magnifying glass all around the canopy with a strong light. All the cut edges were fine but I found two micro cracks emanating from 2 holes in the sliding section of the canopy which I would never have found by just examining by eye and would have definitely led to in flight cracks. I dressed out the micro-cracks with fine emery cloth on a small dowel. Checked the whole canopy again with a magnifying glass!

No problems with cracking so far.
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 06:54 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.