Thread Tools
May 11, 2019, 08:22 AM
Registered User
Thread OP
Discussion

XPS foam core shear web


How have people done shearwebs in XPS foam wings in the past and maintained the accuracy of the foil shape, particularly in longer wings. Clearly the thickness of the cut through the core needs to match the shear web plus adhesive, but what system of making the cut is accurate over a long span and then how have people been rejoining the two halves with the web in place?
I will be making wings 3-4m in span and this is currently one of the bigger challenges.
Sign up now
to remove ads between posts
May 11, 2019, 10:45 AM
The Junk Man
Hot wire cutting long spans is problematic no matter how you do it. The problem being wire drag. you end up with scalloped panels.

It is MUCH better to cut shorter panels and just join then, since joining is so easy. I never cut panels longer then 20 inches yet have cut wings for 3 meter gliders, no problem.

If i were including a spar in a wing panel, I would use the "laser method". It doesn't involve an actual laser and was invented LONG before hobby lasers came into being. Works fine, shapes the ribs along with any spars perfectly with the wire cut.

Here are some links:

https://www.rcgroups.com/forums/show...WS-1-7th-scale Start with post #3

https://www.rcgroups.com/forums/show...5#post41170633

https://www.rcgroups.com/forums/show...0&postcount=11

Video:
(1 min 35 sec)


Tom
May 11, 2019, 02:31 PM
supreme being of leisure
ZAGNUT's Avatar
vertical cut the whole length of the panel? table saw works great for that, just need to attach the core and shucks to a flat board. with a euro style panel saw just need to clamp the core and shucks down to the carriage.
May 11, 2019, 10:14 PM
Registered User
Thread OP
I built a cnc hot wire cutter, so making the cores is taken care of. I can accurately cut 1000mm or so.
The shearweb needs to be accurately slotted . I'll look at adaptations of a table saw. Most blades I have seen are far too wide. Perhaps I can find some diamond tooling fine enough.
May 12, 2019, 02:13 AM
Auzzie built planks
timbuck's Avatar
Just Ruler and a fresh razor blade , XPS cuts like butter and then 3m77 everything back together.
On a 3 or 4m wing do it in sections..... Iím guessing your 1m core length and then join.

Also...You want to sand the spar cap grove before you cut foam for shear webs.

Cheers

Tim
Latest blog entry: More colours
May 12, 2019, 05:19 AM
Registered User
Thread OP
Thanks Tim. Yes generally 1m core length maximum, even if made from 2-3 sections. Given F5J application the shearwebs and spars may not have to be that substantial.
May 12, 2019, 06:18 AM
Registered User
Thread OP
Interesting idea here:
Core foam milling(Ninja1.8T build) (1 min 47 sec)


Not sure if vac-bagging one side of the wing is a good idea or not - adds another process and more risk.
May 12, 2019, 04:56 PM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by ZAGNUT
vertical cut the whole length of the panel? table saw works great for that, just need to attach the core and shucks to a flat board. with a euro style panel saw just need to clamp the core and shucks down to the carriage.
That seems to be a good way to do it.
It might require a tapered packing piece alongside the cores to allow for the taper, so that the fence on the saw could be utilised. Not difficult to arrange.
May 12, 2019, 07:31 PM
Registered User
Thread OP
I spent some time refining my vacuum pump setup last night. Perhaps this can be used to hold the core in place?
May 13, 2019, 12:00 AM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by RaceMag
I spent some time refining my vacuum pump setup last night. Perhaps this can be used to hold the core in place?
???
May 13, 2019, 02:23 AM
Registered User
Thread OP
CNC machines often use vacuum to hold pieces in place during machining.
May 13, 2019, 03:50 AM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by RaceMag
CNC machines often use vacuum to hold pieces in place during machining.
Ok. Understood.
May 13, 2019, 06:15 AM
Registered User
Thread OP
I assume this bloke is using a hard half mould?
Bagging a DLG wing (0 min 58 sec)
May 14, 2019, 09:37 AM
Barney Fife, Vigilante
tom43004's Avatar
I generally use a sharp knife and straight edge. I built vacuum tooling for my CNC machine to hold them down and CNC the slots in place, but it's a HUGE amount of work for results that are sadly no better than just a sharp knife.

If you do choose to do vacuum hold down, just take your shucks from hotwiring and drill "breather" holes for the vacuum table with a sharpened brass tube. Super easy.
May 15, 2019, 06:33 AM
Registered User
Thread OP
Thanks for your input Tom. You and Timbuck have done a lot of this before. I will try a knife n a test piece first and will see how I go and will compare it to another form of cutting.


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion BOT shear webs Kirwin Sailplane Talk 3 Apr 28, 2017 01:19 PM
Discussion Shear webbing kenh3497 Modeling Science 31 Apr 07, 2017 07:11 PM
Discussion Wing Spar ideas - CF Tube or Shear web ? SoarMe Electric Sailplanes 67 Jan 08, 2017 11:37 PM
Help! Using foam for shear webbing Stan_in_AR Sailplane Talk 3 Apr 17, 2007 11:36 AM