PAPER-COVERED BALSA FINS

[Luzwingnut]

First week as a TRF member... wanted to jump-in and OFFER a basic technique in the art of covering BALSA rocket fins. Gotta start somewhere, right? I didn't want to just TROLL the forums and NOT actively participate in them. So? Let's get started...

 

[Steven]

I just use typing, printing or stationary paper. Works like a charm. Don't see why more people don't use this technique.

 

[Luzwingnut]

The purpose of covering BALSA with paper provides a VERY LIGHTWEIGHT technique in strengthening the balsa itself (which is important with a less than stellar landing after a rocket launch). Additionally, the paper works as a GREAT medium to cover-up the balsa grain which is down-right unsightly in a finished model.

My project is an Estes 1/10 Scale Patriot... these Low Power Rockets (LPR) offer each one of us the opportunity to gain better and smarter building techniques which enhances our experience once Mid-Power (MPR) and High Power Rocketry (HPR) becomes more desired and accessible... if these areas of our model-craft is in one's interests. If not? Hey, who doesn't like a sharp and impressive rocket at the flying field...or sitting in a place of prominence in our shops and homes?

 

[Luzwingnut]

TOOLS and SUPPLIES:

1.) PAPER... any 8.5 X 11 paper such as typing/ print machine paper works FANTASTIC

2.) A sharp pair of scissors and/or modeling knife... (and a PENCIL)

3.) A ruler or straight edge

4.) Wax-paper

5.) Wood glue (white or yellow). I'm using "Elmers Carpenter's Woodglue" which is water-based and EASY to clean up.

6.) Sanding block and 180 grit or as I use in the project 220 grit. (400 grit to LIGHTLY sand any finished product blemishes... VERY VERY LIGHTLY sand)

7.) A sheet of wetted paper towel... or pants (the old fashion way) to remove glue from one's fingertips. LOL.

8.) A MODEL ROCKET! (this is important!!)

The whole process takes about an hour to complete, using the model rocket (four fins on this one) that I'm using.

*Thanks for the thumbs-up Steven... I see ya!* PERFECT!

 

[Luzwingnut]

Model rocket fins cause a LOT of drag if the leading edge is not shaped. This is where the sandpaper comes into play. Just a slight rounding-off of the LEADING edge of the fin is needed; however, I also rounded the FAR edge of the fin...leaving the BASE and ROOT of the fin completely square. (The ROOT of the fin ATTACHES later to the body tube of the rocket, itself.

NOTE: DO NOT PAPER THE ROOT EDGE OF THE FIN. (Glueing clean balsa structure to the rocket's body provides a more secure glue joint.

(A dressed or rounded FIN ROOT inhibits drag, as well; however, I am not rounding-off the edges of the FIN ROOT in this build.)

A quick sanding and smoothing of both the fin's FACE (both sides of the fin)... allows a better surface for the paper to adhere and the finished product will enhance a better painted surface.

 

[Luzwingnut]

With a sheet of paper, mark with a pencil the LENGHT of the rocket fin while ALIGNING the fin to the SQUARE corner of the paper, itself. With this MARK (A) on the paper thus completed, ROLL the fin over so the OBVERSE of the fin is laying flat then MARK (B) where the POINT of the LEADING EDGE and the FIN's ROOT are... on the paper. With a sharpened pencil (ALWAYS forget ONE item to INCLUDE on the LIST of TOOLS...), Lay the pencil at an angle to the FIN ROOT and the paper and draw a line from BASE (at the bottom of the fin) to the point you just marked on the paper at the point of the LEADING EDGE and BASE of the fin, itself.

Now, Connect the TWO previous MARKS... (MARKS A and B from the directions above), and draw a straight light. You "should" have an almost PERFECT square once these lines are cut-out from your sheet of paper.

 

[Luzwingnut]

Laying this freshly cut square of paper on a sheet of wax-paper, begin to wipe ONE face of the FIN surface with glue. (A little dab will do ya!) We just want the fin surface, WETTED. Wipe off ANY excess glue on a wet piece of towel, (OR on your pants... IF they are a pair of pants that are DEEMED appropriate for this technique). What IS important, is to THOROUGHLY clean away ANY glue from one's fingers and fingertips.

DO NOT ALLOW any glue to come into contact with the "show-side" of the paper. (It's gonna happen, though).

 

[rharshberger]

Thank you for sharing your method. My preference is using self adhesive label paper which works and is quite quick without the issue of weighting fins to prevent warpage from the use of water based glues. Lots of methods and its good to have options.

 

[Luzwingnut]

It is at THIS point, the glue-wetted side of the fin is CAREFULLY aligned with the paper square that was made earlier. TRY to align the BASE of the fin with the edge of the paper that was cut. (SEE PHOTO ATTACHMENT).

 

[Luzwingnut]

I agree with you, rharshberger. GREAT point!

On the Estes Patriot and "trying" for a scale appearance as in the product image using paint, just painting over balsa is not a good idea for TWO reasons: (A) Balsa LOVES to suck up paint... which ADDS additional weight; and (B), without a "specialized technique" to prepared the surface, balsa grain is almost impossible to "hide" using normal painting methods. Unlike cardboard rocket body tubes and plastic nose cones.

BRING ON THE SUGGESTIONS and HELPFUL hints, everyone!! GOOD STUFF!

 

[Luzwingnut]

Once the fin is in contact with the paper, apply glue to the balsa on the surface of the balsa that is now FACING you. Once this side has been PROPERLY "wetted" and holding BOTH fin and paper at the FIN BASE edge, ROLL the fin over. This technique automatically "covers" the FAR EDGE of the FIN. PRESTO!! (More pics in FRAME #12 of this thread).

 

[Luzwingnut]

 

[Rex R]

for me, a 1" foam paint brush works a treat to spread glue and keep the pinkies clean and dry. a baker's cooling rack lets both sides of the fin to dry evenly w/o needing vast weights to prevent warpage .
Rex

 

[Luzwingnut]

And THIS is where the FUN, begins.

The FINS LEADING EDGE, in flight, is RIPPING through the air immediately AFTER a SUCCESSFUL launch. What we DO NOT want, is for this extremely fast flowing air GRABBING an ill-applied glued paper surface of our FIN structure. THAT WOULD BE BAD!

So? We HAVE TO DRESS the LEADING EDGE of our FIN with a technique that is GUARANTEED not to allow for this to happen. Think of an "envelope" and this pretty well explains MY method of applying this technique. It's QUICK, FAST, and EASY!!

In the NEXT FRAME (Frame #14), you'll see how I use scissors to CUT the paper, both sides-one cut, LEAVING roughly an 1/8th of an inch of the paper from the BALSA that can be manipulated.

 

[Luzwingnut]

Just an 1/8th of an inch...

 

[Luzwingnut]

More pics....

 

[Luzwingnut]

DO NOT CUT this side of the paper EVEN with the BALSA at the FIN's LEADING EDGE. (We WANT to have some paper excess, here, at this point.

Once we have TRIMMED our paper at the FIN's LEADING EDGE, apply a small bead of glue on the BALSA structure of the FIN's LEADING EDGE. Using a thumbnail, press ONE EDGE of the paper onto the balsa of the FIN's LEADING EDGE. NOW CAREFULLY "squeegee" any excess glue, KEEPING your fingers and hands CLEAN!! (Wetted paper towel... pant leg... just KEEP THEM FINGERS CLEAN!)

Now, roll the OTHER paper edge over the first that was just applied.

 

[Luzwingnut]

See what HAPPENS with just a SMALL amount of glue on one's fingers?? UGLY, aint it!!

(Sorry about the first picture... camera wouldn't focus enough for this one).

I SINCERELY hope that the "idea" of this technique is being communicated well enough...

 

[Luzwingnut]

WET PAPER DISTORTS and gets a wavy surface.

THIS is why I was SO CAREFUL to advise that "Just a little dab of glue will do ya!" The balsa surface (in the aforementioned step), JUST needs to be "glue-wetted" and NOT "inundated with glue" and "squishy".

Using a block of wood, (I'm using my home-made sanding block), lay it on the near finished PAPERED FIN and press VERY HARD for an instant, relieve, re-station the block of wood, PRESS DOWN HARD AGAIN. REPEAT this technique ON BOTH SIDES... while keeping the FIN on the wax-paper.

NOTE: PLEASE ensure that you are placing the FIN on the surface of the wax-paper that is GLUE-FREE in EVERY step of this technique!!

 

[Luzwingnut]

CAREFULLY cut the edge of the paper at the FIN's ROOT... EVEN with the ROOT, NO OVERHANG or EXCESS is acceptable. Trim it CLEANLY!

Once the FIN is glued to the rocket body tube, a filet of glue between the FIN and the Body Tube serves THREE purposes: (A) To secure the FIN to the rocket's body tube (B) To provide an AERODYNAMIC surface at this junction (C) Anchors ANY loose paper NOT correctly glued AT the FIN's ROOT to be made secure.

 

[Luzwingnut]

All finished and ALMOST ready to apply PRIMER and PAINT.

The FINS in these photos were done just tonight... so I NEED to allow them to FULLY cure. (Let the glue dry).

Once this is done, I am going to TRY using some 400 grit sandpaper to LIGHTLY smooth ANY small imperfections that ARE at the FIN's corners, and surface.

NOTE: LIGHTLY sand is KEY! NO SANDING at all would be better advantageous as this would preserve the most STRENGTH that the paper-covering is allowing us to have on the FINS.

GOTTA KEEP them fingers clean while performing this technique!

I'll provide further UPDATE on the "400 grit sanding idea" whether it is a LAUNCH or a CATO.

(CATO... this means "bad", yes?") Catastrophic "something something".

 

[Luzwingnut]

GREAT POINT, Rex R!

The balsa FINS on this model are pretty smallish and the balsa that came with the kit is pretty dense and heavy. I'd be more concerned with warpage IF these were constructed with competition grade balsa... and? I'm being VERY careful with the amount of glue that is being applied, i.e. NOT soaking the balsa with glue.

I fully concur with the "baking-rack for drying technique" that you've described.

It was my desire to construct a "How-To" for those who are just experiencing this fine hobby for the first time
... and I am HOPING our younger rocketeers understand that wiping gluey fingers on brand new pants will impart the wrath of God upon their heads by said parents! (At least MINE did!!) But "play-pants"?... now that's a whole different story.

Just having FUN and trying to enhance a hobby that we have all grown to love and appreciate.

 

[Rex R]

the foam brush also does a better job at spreading glue evenly than my fingers do(don't know how well your fingers do the job ). you'll no doubt have noticed that I have not mentioned using a Delrin rod as a 'rolling pin' to roll the paper flat...or the fact that paper has a grain...
Rex

 

[BDB]

I let mine dry under pressure from a stack of books. I always assumed warping could be an issue. Is that really not necessary?

Great method. I particularly like the envelope technique for the leading edge.

 

[dhbarr]

I had thought most folks folded over the leading edge and sanded the tip flat.

 

[K'Tesh]

It's always good to see other's ideas on doing things. You never know what you'll learn. Here's a link to my tutorial... https://www.rocketryforum.com/threads/papering-balsa-ply-fins-a-foolproof-method.65628/

 

[les]

I don't fold over the leading edge like you suggest. It would appear that you are left with a ridge where the paper ends.
If the fin has a straight leading edge I apply the paper to one side and then fold the paper over the leading edge and glue to the other side of the fine. Then there is no edge to catch the air.
If the fin has a curved or compound leading edge, then I paper each side up to the leading edge. Once the glue has cured I will then apply a thin coat of CA to the leading edge to help seal the edge. So far I've yet to loose and paper....

Also, maybe I'm doing it backwards, but I apply glue to the paper, squeegee it to a thin layer, and then apply the fin to the paper.....

 

[neil_w]

I don't fold over the leading edge when using label paper, but then again many of my leading edges aren't straight so it wouldn't work anyway.

I just paper each side and make darn sure the edges (all the edges, but especially the leading edge) are sealed down with glue. Nowhere for air to get in.

Label paper seems much easier to me than gluing, but gluing probably ends up a bit stronger.

 

[afadeev]

I let mine dry under pressure from a stack of books. I always assumed warping could be an issue. Is that really not necessary?

Absolutely essential, IMHO, if you desire straight fins (unless you are purposely making curved ones). I put mine under the center of the large self-healing cutting mat. This way I can easily add new ones while the earlier ones are still drying.
Also helps to quickly apply glue and paper skins to both sides of balsa fin, to minimize warping in the first place!

I don't fold over the leading edge when using label paper, but then again many of my leading edges aren't straight so it wouldn't work anyway.

I just paper each side and make darn sure the edges (all the edges, but especially the leading edge) are sealed down with glue. Nowhere for air to get in.

+1 on sealing all exposed edges with think CA.

Label paper seems much easier to me than gluing, but gluing probably ends up a bit stronger.

I like gluing smaller & medium sized fins for strength.
On longer and more complex fin-shapes it's exponentially harder to avoid warping from uneven glue absorption into balsa. Especially when you had glued multiple smaller balsa segments into a larger shape (each segment may have different glue absorption rates => warping). That's when self-adhesive labels come out.

YMMV,
a

 

[Rex R]

warping/ curling occurs when the two flat sides have different levels of moisture(wood fibres swell as they absorb moisture and shrink as they dry), providing that both sides swell and shrink at the same rate, the fin will stay flat. granted I have on occasion encouraged the redistribution of moisture with a clothing iron(dry set to linen about 10 - 15 seconds per side 2x) for the most part the fins stay flat, and since there isn't glue to begin with, they dry fast.
Rex