Free Flight: Old-Timer
It also went up more slowly and came down more quickly than some of my earlier efforts. It began to dawn on me that wood selection was an important part of model building. I guess I should have suspected something when longeron sizes for a Miss America dropped from 3/8-in. sq. to 1/4-in. sq. on later plans to allow for stronger (but heavier) wood.
About this time my friends were using terms like "C" grain, quarter-sawn, and density. To me, balsa was balsa. I suspect many of us feel the same way, but a little effort expended on wood selection for the job is well worth the time.
As with most things that are grown, balsa has many variables. It has the highest strength-to-weight ratio of any wood. Generally speaking, the heavier grades are the strongest. Weight of balsa is specified in pounds per cubic foot and is referred to as density. At the risk of oversimplification, the density depends, among other things, on how fast growth took place in a given growing season. Rapid growth produces lightweight wood (approximately 6 lb. per cubic foot), whereas slow growth produces heavy wood (up to 24 lb. per cubic foot).
General categories of stock are:
- Light: 6–8 lb./cu. ft.
- Medium: 9–12 lb./cu. ft.
- Hard: 12–16 lb./cu. ft.
Some designers call out intermediate categories falling between those listed.
Based on the foregoing, one could determine the desirable grade of balsa by matching it to its importance in the structure, but there is another factor of considerable importance known as the "cut" — often improperly called "grain." This property refers to the orientation of the annular rings in relation to the edges of the stock and controls the rigidity of the wood in a particular direction. We all know how trees grow, one layer per year, around the heartwood of the tree. Each year produces one annular ring. As the log is sawed into lumber, some cuts are tangent to these rings, others are directly across them, and some randomly cross the annular rings. These cuts are called "A," "B," and "C," respectively.
To better visualize these cuts, picture a balsa plank one inch thick and three inches wide, viewed from the end:
- "A"-cut: the annular rings run the long (three-inch) dimension.
- "B"-cut (quarter-sawn): the rings run the short (one-inch) dimension.
- "C"-cut: the rings run diagonally across the board.
Now that we have some idea of wood selection for specific purposes, how do we go about procuring the needed stock? The best bet is to select it yourself at a local hobby shop. However, this may prove difficult if you do not live near large shops. I make it a practice to check the balsa rack of every hobby shop I visit. Be sure to ask permission from the proprietor first, as some don't appreciate your pawing through the entire stock and maybe purchasing only one or two sheets. This system allows you to accumulate a good selection of balsa for future projects. If you have access to sawing equipment, don't overlook the planks with the thought of resawing to usable dimensions. Often, the lighter woods are in the thicker sizes.
If self-selection is impractical, you can order contest-grade balsa (usually 5–6 lb. stock) from some mail-order firms. This practice may yield some undesirable wood, but perhaps it can be used on projects where weight or strength is not a major factor.
Sig Mfg. Co.
I had the opportunity and pleasure this past summer of touring the Sig plant in Montezuma, IA. I was given the red-carpet treatment, even though no one knew me. I was just another modeler, but I have the feeling that all modelers are special at Sig. I was particularly interested in the balsa aspect of their business, and it was almost more than I could stand to see all those lovely balsa planks stacked in the warehouse awaiting sawing, sanding, and grading operations. Planks were color-coded on their ends to indicate density. I was a little distressed to see how few planks were 5–6 lb. stock. My tour guide advised me that only a small percentage of the balsa falls into this category—another reason to always be on the lookout for desirable wood to add to your stockpile. Sig is one of the suppliers that will fill an order for contest balsa.
The tour took about three hours and involved several people as I was passed from department to department. I'm sure most of you have read their catalog, but it was overwhelming to see how all those kits are produced: die-cutting, wire-bending, plan-printing, decal production, canopy-forming, boxing and labeling, then final shipment. Sig does it all right in their own facilities. Many of the machines and fixtures were designed and produced by the late Glen Sig. Also, Sig sells many items produced by others and has a large portion of their operation devoted to this facet of their catalog. Incidentally, the catalog is also printed on the premises. If you have the opportunity to visit Sig, don't miss this memorable experience!
Rediscovering America.
I recently received the following letter from G. R. Nolin of Fairborn, OH:
"Reference your October 1983 MA column about 'sleeper' O-T designs. Prewar, Harold deBolt was a 'power' in PF in Upstate NY. He flew an Ohlsson .19/.23 combo design with a round, planked fuselage, and a wing and tail much like his later Airfoiler. I'd say that the Airfoiler was an easy copy, so to speak. This ship was published (actually two ships, I think) in one of the midwest mags in about 1941. Hal should know all about this. He used to wipe us out with these ships.
"Also, someone in central New York had a Bantam design called Blitzkrieg, a semi-pod-and-boom built-up. This design could be seen at all the contests in '40 and '41. It was noticeable because of its terrific corkscrew climb (which sometimes went wrong). This ship was also published in two different magazines, as I recall.
"Further, H. deBolt had a class C original like a somewhat-shrunken Playboy. It flew perfectly. Someone with a good magazine location should be able to find deBolt's planked Airfoiler and the Blitzkrieg. Hal might still have details on his class C job."
Phineas Pinkham department
Bob Whittier, Drawer T, Doxbury, MA 02332 has a scrapbook left over from a 1974 printing. You can obtain one for $6.50, postpaid.
Clarence Haught 3226 Honeysuckle Dr. Coeur d'Alene, ID 83814
Transcribed from original scans by AI. Minor OCR errors may remain.
