|
-
POSTING RULES

-
Donate yearly (please).
-
Advertise in here!
-
Today's Posts
|
Insert Pics
|

04-26-2017, 12:32 PM
|
 |
|
|
Join Date: Nov 2011
Location: Aurora, OR
Posts: 843
|
|
Quote:
Originally Posted by ChiefPilot
Certainly that's true. But that doesn't mean that you need to accept cracking or delamination - I chose to accept neither after seeing enough damaged fairings and talking to multiple builders who wished they had done something differently. So I learned from their experience and used CF + sikalfex. Almost 5 years and 700 hours later, no issues to date and it's been kicked (accidentally, of course) multiple times. The sika is still holding strong and no cracks on the paint.
|
Any photos of your process and result? Sounds interesting.
__________________
Greg Hughes - Van's Aircraft - Community, Media, Marketing
Van's web site | Instagram | Facebook
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Building RV-8A since Sept 2014 (N88VX reserved)
Dual AFS 5600, Avidyne IFD 440, Whirlwind 74RV, Superior XP IO-360
VAF build thread - Flickr photo album - Project Facebook page
Aurora, OR (EAA Chapter 105)
|

04-26-2017, 12:54 PM
|
 |
|
|
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
|
|
Quote:
Originally Posted by ChiefPilot
Certainly that's true. But that doesn't mean that you need to accept cracking or delamination - I chose to accept neither after seeing enough damaged fairings and talking to multiple builders who wished they had done something differently. So I learned from their experience and used CF + sikalfex. Almost 5 years and 700 hours later, no issues to date and it's been kicked (accidentally, of course) multiple times. The sika is still holding strong and no cracks on the paint.
|
Coming back full circle to my primary point.....
There is little if any structural benefit in using carbon fiber cloth and the extra stiffness (along with higher cost, higher difficulty to work with, etc.) can be a detriment......
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
|

04-26-2017, 12:57 PM
|
 |
|
|
Join Date: Jan 2005
Location: Twin Cities, MN
Posts: 1,565
|
|
Quote:
Originally Posted by rvbuilder2002
Coming back full circle to my primary point.....
There is little if any structural benefit in using carbon fiber cloth and the extra stiffness (along with higher cost, higher difficulty to work with, etc.) can be a detriment......
|
Sigh.
And coming back to my primary point - the CF wasn't there for structural benefit, but rather finish benefit: no paint cracking due to flexing of the underlying structure. Was it extra work? Hard to tell, but it was nothing compared to the rest of the canopy work.
ETA: I don't think the two points are incompatible - it comes down to what the builder wants.
__________________
Brad Benson, Maplewood MN.
RV-6A N164BL, Flying since Nov 2012!
If you're not making mistakes, you're probably not making anything
Last edited by ChiefPilot : 04-26-2017 at 01:01 PM.
|

04-26-2017, 01:00 PM
|
 |
|
|
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
|
|
Quote:
Originally Posted by ChiefPilot
Sigh.
And coming back to my primary point - the CF wasn't there for structural benefit, but rather finish benefit: no paint cracking due to flexing of the underlying structure. Was it extra work? Hard to tell, but it was nothing compared to the rest of the canopy work.
|
No problem..... The aft targa strip on my personal airplane has 1 layer of carbon for cosmetic purposes on the portion that is not painted.
One layer has very minimal impact on overall stiffness.
I should have been more specific to say that I would recommend not using carbon for the entire thing.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
|

04-26-2017, 07:13 PM
|
|
|
|
Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 774
|
|
So I think I have this thing worked out, at least I hope I have because I'm about to go and lay some composites down. If the coefficient of thermal expansion of perspex is 0.000075mm/mm per degree kelvin, and assuming the canopy side is 1000mm long (round figures here) then for a 40 degree celsius maximum desired temperature and assuming I bond at 20 degrees celsius, the canopy will expand by 1.5mm. Sikaflex has a 500% elongation to break per the data sheets, and IIRC a working elongation up to 300%, thus of this canopy can shear expand up to 1.5mm compared to the skirt, then basic trig suggests that a 0.5mm spacer should be adequate to allow the bond to shear this amount (ok, the hypotenuse of a 1.5mmx0.5mm triangle is 1.58mm, but close enough).
Thus, in summary, I intend to lay up some electrical tape first to a 0.5mm thickness to fill the void where the sikaflex will be in the future (this step may not even be necessary as you should get enough flex in the skirt even with carbon in the mix), then cover the tape and the void between the canopy and the fuselage with packing tape tape, lay up the glass/fiber skirt, pop it off when cured, tear off the electrical tape spacer (if I decide to use it), replace this with some 0.5mm small spacers (fishing line perhaps) then finally bond the canopy in place with sikaflex. At least in theory. The only downside I can see to this is the fact that you will have a 0.5mm thicker layup than you would otherwise., but there's no reason why you can't put a nice slope on the sikaflex bead. Time to put this into practice.
Tom.
|

04-26-2017, 08:45 PM
|
|
|
|
Join Date: Dec 2009
Location: Boulder, CO
Posts: 4,436
|
|
I'd put a large factor of safety on that elongation. That 300% isn't a "working" number, it's elongation to failure. You don't want it to fail. Do search in VAF for the thickness that other people are using even without the carbon, and I think that you'll find that the gap really ought to be considerably larger.
Dave
|

04-26-2017, 09:42 PM
|
|
|
|
Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 774
|
|
Hi Dave. The elongation to failure for 295 UV is definitely 500%. I checked VAF threads and it appears that many are using no spacers at all for joining the skirt to the canopy.
http://www.vansairforce.com/communit...ad.php?t=98485
Thus I fail to see why 0.5mm won't be better than nothing. I just don't want an unnecessarily high step up to my already thick skirt and targa strip. Although there is little linear elongation in the carbon/fiberglass skirt, it does have the ability to flex outward to some degree. The spacing specs issued by Sika are assuming mounting to a far more rigid marine structure.
The world has 10 minutes to convince me otherwise, as I'm about to lay down the last layer of tape.
Tom.
|

04-26-2017, 09:44 PM
|
|
|
|
Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 774
|
|
But thanks for your feedback anyway Dave. That's the whole reason I'm hashing this out on the forum and not making the decision in complete isolation.
Tom.
|

04-26-2017, 09:54 PM
|
|
|
|
Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 774
|
|
I increased the thickness by 50% to 0.75mm. Don't say I'm not good to you Dave.
|

04-27-2017, 06:56 AM
|
|
|
|
Join Date: Jun 2005
Posts: 846
|
|
Glue
Put a few screws in and it will be alright.
Bob
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
All times are GMT -6. The time now is 09:07 AM.
|