Dihedral setting

[Kyle_Guo]

I have been using Dave Ziegler's 2017 freedom flight kits and I have had some difficulty with the dihedrals. I planned to adjust these later so I used model cement. ("Testors cement for wood and metal" to be exact with a green tube color). In one of the earlier steps, it said to angle the outer 2 wing supports outwards so the dihedrals can be glued onto them. When I aligned the dihedrals with the outer supports, they had negative angle ( went down instead of up) so I had to glue onto the side (flat) and tilt it a little up. I followed instructions, laying 2 thin lines of cement on both surfaces, letting sit for 3-4 minutes, then adding another layer and holding the pieces together. ( I rested the dihedrals on a 1 1/2" blocks to angle them the same for both and to get maximum wing length (45 cm this year). I held the pieces together for about 5 minutes, then I let them dry for 1-2 hours. When I came back, I thought it was done so I took the blocks the dihedrals had been left on off and they sagged almost 3 cm. I don't understand how they don't stay up. The joints appear well glued together, just very flexible and not at all study and hard like a CA bond. Is it because my cement isin't right? I asked several of my peers and they said I could use the cement.
Drawing generalizing the situation
https://sketch.io/render/sk-4bf5575741c ... 89eef.jpeg

[bjt4888]

Kyle_Guo,

My compliments on the detailed description o f your dihedral issue. I am sure that I can help, but I think it would be best to post some close-up pictures from several angles.

Testors cement takes overnight to cure and joints using this glue need to be braced or supported this entire time. It is easy to unbond testers with acetone So that you can reposition and reglue.

Brian T.
AMA member since 1972

[Kyle_Guo]

Is a wooden block holding the dihedral up not enough support? Should I cut out a triangular support that conforms to the entire dihedral so that it can lay on it? Should I use little clamps to hold the dihedral to the wing tightly? Also, if Testors cement takes overnight to cure, is there any cement that only requires several hours to cure? Does any accelerant work on Testors? I think I saw an "Aliphatic based cement accelerant" before. Testors cement seemed like the only adhesive the Local Hobby Lobby had that looked right. (The glue they used in the instructions was clear and it a metal tube like Testors.) Another glue Hobby Lobby has was a model airplane glue that came in a cylindrical bottle with an applicator tip. It looks opaque and yellowish, similar to wood glue) It also came with an accelerant.If that can be used, ill get one to compare results. Is the bond not being very "solid" because the glue hasn't cured completely? I was referring to a previous build and I can't get the pictures from that time now. I was asking just so I can learn from what I did wrong and do it right this time. (making an second plane)

[bjt4888]

Kyle,

A wooden block support for dihedral is the typical method. I also put a light weight on the wing tip (maybe a 2" piece of the fuselage wood) to prevent any movement while the glue dries as Testors wood glue (and Duco, etc.) shrinks as it dries. Accelerant doesn't work on Testors. Testors or Duco Cement are good glues for the dihedral joint. The fact that these glues take time to dry allows you to reposition the angle and the joint a little, unlike CA (cyanoacrate, or super glue) which bonds instantly and doesn't allow you to adjust joint or dihedral alignment as you glue.

My teams use CA glues for joint that are easy to align or are aligned by jigs (ex. wing post to wing spar joints, tailboom to motor stick joint, stabilizer attaché to tailboom joint, rudder/fin attach to tailboom, nosebearing and rearhook attach to motor stick) and that we want to bond instantly and Duco Cement (thinned with acetone about 30%) for all other joints. The primary reasons to use Duco or Testors for most other joints is to save weight and to allow a few seconds of repositioning.

On your original build, it does sound like you may have a basic issue with your construction. Pictures would be helpful if you want feedback on this.

Good luck with your next build.

Brian T.

[Kyle_Guo]

So, all I needed to do was leave the joint alone for a day and It would have properly glued? The only reason it appeared to be flimsy was because I didn;t let it fully cure?

[bjt4888]

Kyle,

Possibly. A tight fitting joint with minimal gap will be pretty strong after an hour when glued with Testors and will completely hardened and cured after drying overnight. The best formula of testors to use is the tube with the green label. Also, i believe that Duco Cement is better than Testors. Duco is in the same family of glues as Testors, but i think it dries a little quicker. Duco can be purchased at any good hardware store.

Brian T.

[Kyle_Guo]

I have heard of Duco cement and something called Sigment. I went to the local hobby stores to find them, and the only model cement for wood that looked right was Testors. Could you find Duco in some of the Major Hardware stores like Lowe's, Ace, or Home Depot?

[bjt4888]

Yes, Duco is a household cement of the same type of formula as Sigment and Testors and is a favorite of the indoor modeling community. Thinned with acetone about 30% to 50% is ideal. Small fine tipped applicator squeeze bottles for this thinned glue can be Purchased from gun dealers. Gun owners use these bottles to hold light oil.

Brian T

[calgoddard]

You can typically purchase Duco cement at ACE hardware stores and at Walmart. This cement is relatively inexpensive when purchased at Walmart

Duco cement is an excellent adhesive for gluing balsa wood parts together. It should be thinned with acetone when building lightweight indoor model airplanes. I usually thin it so that the mixture is about 30% - 50% acetone and the remainder Duco cement when building indoor models. As Brian noted, you need a fine tip dispenser to accurately apply small amounts of thinned adhesive to the parts you are joining. Thinned Duco cement dries sufficiently in about five minutes to allow joined parts to remain fixed together. Let it dry over night to achieve a full strength joint.

Brian is also correct in suggesting that you need to post some pictures so we can understand your dihedral problem. We can then advise you how to best solve that problem.

Dihedral is important to help free flight models achieve lateral stability. In general, it should be symmetrical. Sometimes vertical tip plates are used on the ends of the wing instead of upwardly angling outer sections of the wing. Tip plates effectively produce dihedral and make the wing much easier to construct. Neither configuration results in any advantage over the other on indoor duration models in terms of flight duration.

[Kyle_Guo]

Calgoddard,

Don't tip plates weigh more than dihedrals? Isn't that a advantage for using dihedrals?