Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
May 29, 2020, 01:00:49 PM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
 
Home Help Search Login Register
Pages: [1]   Go Down
Print
Author Topic: Carbon tube spar dihedral?  (Read 217 times)
0 Members and 1 Guest are viewing this topic.
Jetsrforkids
Bronze Member
***

Kudos: 1
Offline Offline

United States United States

Posts: 18

Topic starter


Ignore
« on: January 29, 2020, 07:11:43 PM »

Starting on a cool little Bob White Pixy 20. It is my first build with a carbon spar. So I give up, what is the best way to do the dihedral breaks? It’s a polyhedral wing, do you cut and then sand the angle on the breaks before glueing on the ribs? Also what is the best glue for a carbon/balsa joint? Last question, it has a nice rolled balsa fuselage all finished. Should I cover it with tissue, and then dope it,?or just floor it?

Thanks,
Attached files Thumbnail(s):
Carbon tube spar dihedral?
Logged
OZPAF
Palladium Member
********

Kudos: 184
Offline Offline

Australia Australia

Posts: 5,562



Ignore
« Reply #1 on: January 29, 2020, 07:28:27 PM »

I haven't tried a wing with a carbon tube spar, however as the ribs slide on I would approach it by joining the spars at the polybreaks first. I would have the bevels done for the centre dihedral done but would slide all the centre ribs on first before completing the centre joint.

Line the wing up on the plan and glue the centre ribs in place, glue the centre dihedral joint and then glue the tip panel ribs over the plan packing up the rest of the wing to keep the tip flat on the plan. Use a combination of thin and medium CA to glue the ribs and dihedral/poly joints.

How are the dihedral and poly joints at the tube spar, reinforced? Internal braces in the tubes?

Hope this helps - I think there would be many here that have solved this problem - the above is just a possible approach.

Doping tissue onto the outside of the tube would be a nice light way to finish it. Use 3-4 coats of thinned dope - 50/50?, rather than thick.

Good luck and happy flying - it looks a nice model. definitely consider a DT.

John
Logged
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Offline Offline

Finland Finland

Posts: 1,222



Ignore
« Reply #2 on: January 30, 2020, 12:20:38 AM »


I build my wings utilizing tubular spars (P-30, E-36, used to do F1B that way in 1980's) in panels, with the spars slightly too long. When finished, use a dremel to cut the tube end to roughly the right length and angle (maybe finish with sanding block). then it is two options. The stronger is to apply light carbon or glass cloth with laminating epoxy over the tube, thus extending the tubular material over the DH joint. Use some tape to pull the cloth tight. The other way to to cut a braze into the tube from carbon sheet and glue with epoxy, In this case I also wrap some kevlar rowing around the tube ends to avoid the braze splitting the tube (while flight or landing  loads bend the wing). In both cases, DH break rib is only added once the tube joint is finished.

 
Logged
gman
Bronze Member
***

Kudos: 2
Offline Offline

United Kingdom United Kingdom

Posts: 61



Ignore
« Reply #3 on: January 30, 2020, 09:18:12 AM »

Hi, I've built several small, as in P30 & coupe, models using cheap model shop pultruded carbon tube sanded to the appropriate weight. For each of these I used the same method for the dihedral joint. The panels are built with the end ribs angled as required by the dihedral (i.e. at half the included angle). Everything sanded nice and flush with the rib, as if you were going to simply butt joint the panels. Then make a ply brace to the correct angle (1mm for a coupe and P30 centre, 0.5mm for a P30 tip) and the same depth as the inside diameter of the tube. It needs to project maybe 15mm into the tube in each panel. Laminate soft balsa either side and then sand the whole thing until it fits the tube nicely. So you now have a balsa/ply/balsa circular section dihedral brace and you should be able to dry assemble the joint to check everything is right. When you're dead sure it's all as you wish ('cos you're going to get one chance at this) use thick cyano and make the joint. It sounds terribly risky and heart stopping but, in truth, with a well fitted brace you can repeat dry assembly until you know it's going to be ok. I've never bothered to wrap the tube locally on these small models, and I've not had any failures. For glue on my tube spar wings I've always used cyano, thin for the rib to tube joint, medium/thick elsewhere. Cheap model shop tubes (and rod for trailing edges) are made with Polyester resin and cyano seems to be very compatible. In general building I almost never use the stuff -smelly and heavy!
Gavin
Logged
Jetsrforkids
Bronze Member
***

Kudos: 1
Offline Offline

United States United States

Posts: 18

Topic starter


Ignore
« Reply #4 on: January 30, 2020, 05:44:09 PM »

Thanks, some good ideas. I think I’ll give the ply doubler a try.
Logged
Pages: [1]   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!