Paper fillets

[Jacktango22]

I am working on a BT 80 scratch build with TTW epoxied in place fins. The fillets come next. I papered the fins and was thinking of soaking some white glue onto some paper strips that I would then form into rounded fillets. Did a quick search and did not find any discussion of this question.

Any thoughts?

Thank you.

 

[David Schwantz]

Hi, I have used 1/64th ply, thin aluminum sheet and of course epoxy. Although your idea may work very well, my question is how to get them rounded and then peel off form after the glue dries. Might try saran wrap around a formed dowel as a form. Mold release compound. Would like to see pics of your process.

 

[SolarYellow]

Are the fillets meant to be structural, or just aerodynamic?

 

[Jacktango22]

Here are two photos. First shows where I am in the process with papered fins TTY expoxied in place. The second is same as the first but with a paper fillet cut to size where I would glue it in.

 

[neil_w]

Why not just do regular fillets? What is the purpose of the paper?

 

[kuririn]

Looks similar to the old embedded gauze fin joint strengthening technique.
But smoother.

 

[MidOH]

Not much triangulation to that. Split the difference. Make a tiny regular fillet, and then paper over it, if you want to try something different.

 

[waltr]

If the fins are TTW and glued to both the MMT and the BT then the filets are mostly cosmetic or aerodynamic.

I do paper 'angles' on many scale models to mimic the fin mounting flange.

With Fin on the Tube paper flanges do add a little strength but find that they dodn't fail nor does the glue but the top layer of the BT fails.

 

[Sandy H.]

Here are two photos. First shows where I am in the process with papered fins TTY expoxied in place. The second is same as the first but with a paper fillet cut to size where I would glue it in.View attachment 546586View attachment 546587

I've never thought about it, but that falls into the category of a composite as far as I'm concerned. Epoxy/Carbon Fiber or Glue/Paper - bo0th composites as are many other things. I know people like papering balsa to gain stiffness and I've tried that as well, but it will be interesting to see your results, as the goals are slightly different than papering balsa, but could be very valid.

Good experiment!

Sandy.

 

[Jacktango22]

Here i what i did. Used titebond to shape what might have been a titebond fillet but then papered it over. See photo. I should add this is for mid power E and F engines. I like the clean lines.

 

[techrat]

I did this on my Citation Patriot because I converted it from 18mm to 24mm motor mount and was concerned about ripping off the fins with more powerful motors. However, if you've got Through the Wall fins already, and they are epoxied to the motor mount as well as the body tube, you're now over-engineering this thing as the airframe will fail before the fins separate. What's in there, a 29mm motor mount? Best you're going to get is a large "G" or baby "H", neither of which are going to rip the fins off if everything is glued together properly.

Sounds like you're using wood glue however, so maybe going a little overboard is OK. Just make sure that after the glue has dried on the paper fillets, you do a second round of just glue and/or epoxy. This way it'll survive sanding without tearing anything up.

 

[ep29030]

I have made narrow paper strip (1 inch wide) folded them in half down the length, then glued them to the fin and body tube. After they dried I put on traditional fillets over them, then used thin CA on the outside edge of the strips to harden the paper so I could feather sand the edges. Paper strips add more surface area to the fin joint and give additional strength.

 

[neil_w]

I have made narrow paper strip (1 inch wide) folded them in half down the length, then glued them to the fin and body tube. After they dried I put on traditional fillets over them, then used thin CA on the outside edge of the strips to harden the paper so I could feather sand the edges. Paper strips add more surface area to the fin joint and give additional strength.

As an underlying strengthening technique... sure, but probably not needed here. As a surface finishing technique... I don't get it. Standard fillets will look better.

 

[BABAR]

Interesting idea. Couple things.

if you are applying these AFTER fin is already fixed in place, so paper to paper or paper to wood, I would go with white or wood glue, and avoid the expense, weight, and need for gloves for expoxy.

for thru the wall fins, from a strength standpoint it seems like it is overkill if you have descent fixation internally , an external filler with white or yellow glue followed by a thick glue (I think it’s now Titebind mold and trim glue,used to be quick and thick) should be plenty strong.

for Cosmetic appeal, it looks good although it does leave “edges” which you either accept or may be able to hide with a heavy primer.

for MINIMUM diameter this might make fin attachment aka “tack” easier If combined with a balsa fillet or “cheater.” A cheater is a balsa strip the length of the fin root (or slightly smaller) , other dimensions 1/16x1/16.
draw your fin marker lines as usual. Attach the cheater on the edge of the line with yellow glue, double glue joint is faster and because these are so light, they tack pretty quickly.

make your fins as usual, the put 1/2 of your paper filler attached to each side of fin root, leave about 1/16” of the lateral side of the root of the fin unattached to leave room for the cheater. Use the same side for each fin (see clockwise and counter below)

now use yellow glue to attach the fin and the paper to the body Tube, using the balsa fillet to get perfect alignment. Make sure the paper is completely covered with a THIN layer of glue (use a key card or laminate cardboard piece to “squeegee” off any excess. Keep a damp paper towel handy to wipe your finger off.

since the balsa fillet will “offset” the fin 1/16”, make sure each fin goes on same “side” (clockwise or counter) as all the others.

i think this will provide a mush faster tack than the fin alone, the paper hides the cheater, and it will be stronger than the fin alone, although I am not sure it will be any stronger or cosmetically better than a regular guest fillet followed (when dry) by a thick Titebind fillet.

i am betting @neil_w has some tips for concealing paper on paper ”edges”……

 

[neil_w]

i am betting @neil_w has some tips for concealing paper on paper ”edges”……

Yes, avoid them when possible.

Failing that, I guess some filler along the edge, or else bury the whole thing in a fillet (in which case the paper served no purpose).

 

[BABAR]

Yes, avoid them when possible.

Failing that, I guess some filler along the edge, or else bury the whole thing in a fillet (in which case the paper served no purpose).

There is also the “I meant to do that” approach, where the papers are all straight, identical, and you put fake rivets on them so they look like metal plates or panels, I think Neil did this with the Vent hole in one of his models, labeled it something sci-fi -ish.

 

[astronwolf]

I used a type of paper fillet to create the fairings on the root edge of a V-2. Using paper made it much easier than glue alone.