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Anyone who knows of the Golden Age of Model Aircraft has worked with balsa wood. This excellent article was printed in several of the Megow Company catalogs during the 1930s and 1940s. Fred Megow got his start selling balsa and wood stock from the famous ‘Green Cabinet’ in local Philadelphia, PA hobby shops. The kits that followed were all made of balsa as well, so Megow took the material very seriously, color coding their stock by the grade of wood; yellow (dead soft), orange (soft), red (medium), green (hard) and black (extra hard). When World War II interfered with supplies, balsa was hoarded for production as it as at Hawk and other manufactures. Sadly, Fred Megow chose to close down his international hobby empire in the late 1940s. I hope you enjoy this article, transcribed here with all of the original photos. (Alan Bussie) Google+ profile
By OTTO EGER
Editor’s Introduction: Thousands of model airplane builders have for years used balsa wood with infinite skill and cleverness! Yet few know any more about it, other than it comes from South America. Therefore, we have asked Mr. Eger, our tropical wood expert to write the article which follow:
Well, to start with, up to this date, as far as I know, there is no literature on the Balsa Tree. The few descriptions that have appeared in this country regarding it are short and in many instances contradictory. It has been my privilege to observe and study the flora of the tropics for a quarter of a century, and the balsa tree, due to its peculiarities, has attracted my attention especially. Thanks to these special studies, I have been called upon to manage a balsa plantation, the only plantation of this kind of tree in the world, where I had the opportunity of planting, cultivating and logging the balsa tree for a number of years.
In the following I give to our readers a condensed description of this wonderful tree, which I know will be of great interest to builders of Megow models.
The Balsa Tree belongs to the Bomacaceae (Linné), and its Latin name is Ochroma. There exist many species of Ochroma, of which the following are known to me:
- Ochroma limonensis, found in Costa Rica and Panama.
- Ochroma lagopus, found in Cuba, Jamaica and the other Antilles.
- Ochroma concolor, found in Guatemala and Honduras.
- Ochroma velutina, found on the Pacific coast of Central America.
- Ochroma tomentosa, found on the upper Magdalena River, Colombia.
- Ochroma obtusa, found on the lower Magdalena River, Colombia, and finally
- Ochroma grandifolia, found in the Republic of Ecuador.
This last mentioned species interests us most, as almost 100 percent of all balsa shipped to the United States is exported from Ecuador. The reason for the predilection of Ecuadorian balsa is found in its finer texture, white color and extreme lightness of weight.
Ochroma grandifolia, or Ecuadorian balsa, is a tree reaching a height of about a hundred feet with a period of 10 short years. From this fact it is obvious, that the balsa tree grows very rapidly. Balsa is of spontaneous origin, which means, that it is a second growth tree, appearing in places where there has been already some kind of cultivation before, or where there has been a break of other vegetation in the virgin forest. Due to the rapid growth, the young balsa tree soon leaves the surrounding vegetation behind and reaches in the first year a height of about 15 feet. It develops into a tall and slim tree with leaves of tremendous size.
The surrounding vegetation drives the balsa tree higher and higher, until, at last, he has reached a height leaving all other trees behind, and now the crown of the tree develops with the natural consequence that it increases in thickness.
The Balsa tree develops flowers in its fifth year of growth, around the middle of the dry season, the sexes being separate, but on the same tree. The staminate or male flower forms a long calix, of six to eight inches in length, of a pinkish-brown color, which turns later into dark brown, and pollen is developed within 45 days. The pistillate or female flower opens around the time the pollen is ready to be disseminated, its color is green, therefore almost invisible. This latter fact has lead the natives and many foreigners to believe that the reddish flower, well to be distinguished from the ground, is the only flower of the tree, which is erroneous.
After fertilization has taken place, which occurs through wind, insects and small birds, the male flower withers and drops to the ground, whilst the female flower now develops the seed. The seed is enclosed in a long pod of about 8 to 10 inches in length and with a diameter of about an inch and a half. After a period of about two months, the seed has ripened, and the pod, splitting into six equal sections, breaks open and reveals a golden-brown fibre like cotton, light and fluffy, used by the natives to stuff mattresses and pillows. Exposed now to the hot tropical sun, this cotton dries within a few hours, and the wind carries it in small flakes, to which the seed is lightly fastened, over the countryside to find a suitable place for germination. The seed is very small, not unlike mustard seed, about 24,000 of them making a pound.
The balsa tree grows only in the lowlands of the American Tropics up to an altitude of 800 to 1000 meters. It is found in all the countries South of the Rio Grande, from Mexico to Bolivia. For a proper development, the tree needs a light and sandy soil. In clay soil the growth is retarded, and the tree develops a red heart, making it useless for commercial purposes. Although the balsa tree is extremely light, there is an abundance of difference in the grade of hardness and weight. This peculiarity is known to the natives, of course, also, and so they have classified balsa in two groups, macho and hembra, which means male and female. This classification has nothing to do with the sex of the flowers, as might be supposed. The hard and heavy trees are called the males and the soft ones the female. The machos are rejected in many local markets, whilst the hembras are sold often at a premium.
Ochrorna grandifolia or Ecuadorian Balsa is known by the following special marks: The tree is taller than usually found in other countries, with a mottled gray bark; also the wood is lighter than ordinarily. The leaves on the mature trees are nearly entire orbicular, about 10 to 15 inches in diameter. On young trees the leaves are lobed and very large, up to 40 inches. The leaves are glabrous above and rufescent beneath. The male flowers, as already mentioned above, are very large, the calix tube up to 7 inches in length, spreading at the end up to four inches in width, hairy inside, and the stamens are large and showy. Ecuadorian balsa also is whiter than the wood from other territories, the best grade coming from the provinces of Esmeraldas and Manabi, both of them in the Northwestern part of Ecuador.
Balsawood is extensively used by the natives, especially for making rafts to bring the produce of the interior parts of the country to the ports. In the olden days, and still today in a few places, where balsa is not exported up to now, after making use of the rafts, they were abandoned and left to float into the sea, people not knowing that the raft had many times more commercial value than the other agricultural products brought down on them. But in most parts of Ecuador people are now wide awake as to the value of this tree. In many places, due to cutting the trees before maturity, the natural stands of balsa are on the decline. However, now on all lands that have been used for the so-called three months’ crops, and where balsa springs forth abundantly after the harvest, the young trees are cultivated for future logging. The wood is also used for making canoes, which, of course do not last very long, especially if left unpainted. All kinds of toys are made by the natives from balsa and offered for sale in all ports to the tourists.
The best export market for balsa is the United States, where more than 90% of all balsa is sold. Other countries that have found use for it are England, France, Germany and Japan.
Balsawood, properly dried, weighs about 6 lbs. per cubic foot; the strength is approximately one-half of that of spruce.
For those of our readers, who are more interested in the properties and particularities of balsawood, I give the following data and information:
- Modulus of Rupture (strength in bending) 2100 lbs. per sq. inch
- Crushing strength (load parallel to grain) 2150 lbs. per sq. inch
- Compressive strength (load perpendicular) 110 yield point
- Shearing strength—300 lbs. per sq. inch
- Tensile strength—3500 lbs. per sq. inch
- The Thermal Conductivity, in comparison with corkboard, is – Balsawood—.31 B.T.U., Corkboard—.32 B.T.U.
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