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Picking The Right Fin Material For Your Rocket

Article by Paul Nortness

OK, you are ready to build your first scratch built rocket. You have designed it and ordered all the parts, but it's time for a crucial decision. What to use for fin material? There are several options all with their own benefits and problems. In this article, I will discuss the pros and cons of each to hopefully make that decision a no brainer.

Balsa Wood

Our first option is balsa wood. Balsa is the most common wood used for fin material. Balsa comes from a tree called "Ochroma Pyramidale", though most people call it a "balsa tree". The tree is found natively in Southern Brazil and Mexico, and is now found in Papua New Guinea, Solomon Islands and Thailand. Balsa wood is a light weight, soft wood. Due to its light weight properties, it is perfect for smaller rockets where weight is a factor. It is very easy to sand. Balsa can be cut to size with a hobby knife and straight edge. Balsa is a very coarse wood with an open grain, so using wood filler is important. For this, you can use standard wood filler or a specially made "dope".

balsa wood for model rockets

Another thing you can do to fill the grain and strengthen the fin at the same time is called "laminating". Some people use standard printer paper with a thin layer of glue, but I find it easier to use self adhesive label paper. Once you get the fin sanded, peel the backing paper off the label paper and stick the fin onto the adhesive. Then, with a sharp hobby knife, trim the fin out of the paper along the edges. Go nice and slow to avoid cutting into the fin itself. Once the fin has been removed from the paper, flip it over and repeat on the other side. Now the fin is laminated, providing a nice smooth surface and providing extra strength as well! Being a soft wood, balsa is prone to being fragile. It can break easily; the most common break is along the grain pattern. It is also prone to warpage. Balsa wood also soaks up paint if untreated, so use a good primer first.

Basswood

After balsa, we have basswood. Basswood comes from the Tilia family of trees and is native through most of the northern hemisphere. It is a light but very tough wood with a much smoother grain pattern than balsa. Aside from its hobby uses, basswood is also used in making acoustic guitars. Basswood is an excellent choice for larger rockets or fins with a large surface area. Basswood is a little harder to cut than balsa, but is done in the same manner. Run a sharp hobby knife along a straight edge until the piece is cut through.

basswood for model rockets

Do not score and snap the wood as it will not break cleanly on the other side. Because it is a tougher wood, sanding requires a little more patience. Just use a rougher grit and you will be fine. Its nice smooth grain pattern makes finishing easier. Lightly sand the surface to remove any blemishes in the wood. Spray primer onto the fin and allow it to dry. Once dry, sand it down and reapply primer. Simply repeat this process until the surface is smooth and you have no grain showing. Basswood does not have the same problem balsa does with paint. You can easily paint parts made with basswood without it soaking up the paint. A fin made of 3/32 inch basswood will be much stronger than a fin made with 1/8 inch thick balsa. The biggest trouble with basswood is the weight. It is significantly heavier than balsa, so if you choose basswood be prepared to add nose weight to balance out your model.

Birch Plywood

Finally, we have birch plywood. Birch trees are commonly found throughout the northern hemisphere. Birch is a lightly colored, fine grained wood. Birch was the primary building material used in the Hughes H-4 Hercules, how it came to be named the "Spruce Goose" is a mystery. Birch plywood is more for larger mid range powered rockets. It must be cut using a band saw. Birch can be sanded much like basswood.

birch plywood for model rockets

Start with a rougher grit and work to a smoother grit to buff out any scratches. As with basswood, birch is a heavy wood so it is important to properly balance a model using birch prior to launch. It has a very fine grain pattern, making filling a breeze. The same primer trick will work nicely with birch.

Have fun and happy flying!

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