Thanks Kevin. In reference to; “Why would it even delaminate? The spar cap on the compression side is actually pushed against the balsa.” Although somewhat counterintuitive, in every case (except one) that I have seen or experienced myself, the spar cap has broken through the Kevlar wrap and delaminated from the balsa. It’s not clear if the Kevlar fails first or the lamination. The fix has been to increase the ‘pitch’ of the wraps or add layers. I’m obviously not up-to-speed on co-curing prepreg & balsa and was not aware that a bond powerful enough to eliminate spar wrapping was possible. This discussion is, no doubt, of little interest to indoor flyers so could you contact me off line? I would love to learn more about it and see whatever engineering analysis you might have. Thanks.
- Chuck
From: Indoor_Construction_at_yahoogroups.com [mailto:Indoor_Construction_at_yahoogroups.com]
Sent: Friday, January 16, 2015 1:04 AM
To: Indoor_Construction_at_yahoogroups.com
Subject: RE: [Indoor_Construction] Carbon capped spars
No, also in F1A me and many of my friends fly without any wrapping (even with LDA models) and delamination of spar caps never happened. Again, we do wrap around the wing joiners. Why would it even delaminate? The spar cap on the compression side is actually pushed against the balsa. All this stuff doesn't really depend on the loads. Of course, dimensioning does, but the basic mechanics remain the same.
Kevin
Op 15 jan. 2015 18:20 schreef "Chuck Etherington chuck.etherington_at_jeppesen.com<mailto:chuck.etherington_at_jeppesen.com> [Indoor_Construction]" <Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com>>:
You’re right Kevin. I should have prefaced my comments by saying that it depends on the loads that the wing will see. If the F1B and F1G loads are within the capability of the spar without the thread, it would certainly be wasted weight that could otherwise be used elsewhere. In the case of events like F1A and F1C, an unwrapped spar will suffer catastrophic failure.
- Chuck
From: Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com> [mailto:Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com>]
Sent: Wednesday, January 14, 2015 4:19 AM
To: Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com>
Subject: Re: [Indoor_Construction] Carbon capped spars
I disagree. When doing it properly, the carbon will not pop off and wrapping with kevlar thread only adds weight. In F1B, the spars I make never use wrapping and they have never come loose. Only around the wing joiner wrapping is necessary since the wing joiner introduces a peeling force inside the spar. For the rest of the spar, wrapping does not add anything but weight.
Co-curing 19 gsm UD prepreg with balsa might be an option for indoor spars as well. Although I think boron is much stronger on the compression side due to the higher buckling strength compared to the 20 micro meter thick UD prepreg.
Best wishes,
Kevin
2015-01-12 18:38 GMT+01:00 Chuck Etherington chuck.etherington_at_jeppesen.com<mailto:chuck.etherington_at_jeppesen.com> [Indoor_Construction] <Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com>>:
The carbon spar cap that is in compression will pop off the balsa regardless of adhesive or technique. Wrapping the spar with Kevlar thread, however, will increase its strength exponentially.
- Chuck
From: Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com> [mailto:Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com>]
Sent: Monday, January 12, 2015 10:09 AM
To: Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com>
Subject: RE: [Indoor_Construction] Carbon capped spars
Vladimir,
I dabbled a little in making laminated spars for Coupe d’Hiver so it may not be in your league. I think it was probably in the early 1990s that some carbon sheet, 0.003/0.004 thick became available on the English market. The carbon appeared to be very thin strips joined side by side and mounted on a brown paper backing. I cut a strip of carbon about 0.5” wide, leaving the paper backing in place, cleaned the other side and then glued it, with contact adhesive (‘Evostick’), to the balsa sheet, which was about 0.1” thick. This was stripped with a normal, home-made, balsa stripper and the backing paper was then removed.
The big trouble was that if the spars flexed the carbon would ‘pop off’ the balsa and the popped off pimples would need reattaching with cyano. The problem could have been wrong glue or poor technique but I realised that it was good for the wing spars to flex upwards under load and the spruce spars that I was already using were better than carbon capped balsa for a Coupe. I hope this is of some help if only in a negative way.
John Barker - England
From: Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com> [mailto:Indoor_Construction_at_yahoogroups.com]
Sent: 11 January 2015 23:11
To: Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com>
Subject: [Indoor_Construction] Carbon capped spars
Dear All
Has anyoneaminated unidirectional carbon on sheet and then sliced wing spars producing capped spars top and bottom with carbon? If so please share details.
Vladimir Linardic
Received on Sat Jan 17 2015 - 10:55:14 CET
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:48 CET