Bamboo Sailplane
Background
I was returning to East Africa and planned to construct a vintage scale sailplane. I chose the Fafnir, an early German glider with a colorful history. Its unpainted plywood skin reminded me of the shiny side of bamboo bark—the outer layer of the plant that peels off and falls to the ground. I had used this material ten years earlier to make model sailboats, and decided to use it for the glider.
I was motivated to use bamboo for reasons other than just its appearance. Balsa wood is almost nonexistent in Nairobi. One shop imports it from Europe and sells it at a very high price. Bamboo bark would provide a plentiful supply of very light building material—at no cost.
Advantages and disadvantages of bamboo
- Advantages:
- Readily available in the area.
- Very light.
- Free if gathered locally.
- Disadvantages:
- Curved and variable in thickness.
- Breaks easily.
- Does not sand or glue very well.
But that was the challenge—I wanted to see how much of a sailplane I could build from the stuff.
Materials collection
My first step was to hike out into the coffee plantation to a stream where a bamboo grove grows. The stalks grow up to a foot in diameter. Only these stalks would provide bark that would be sufficiently large and thick enough.
A brush and water were used to remove the tiny brown hairs from the bark—these can make work very uncomfortable. With a good supply of building material ready, I began drawing plans. I had brought a photocopy of a three-view from Martin Simons' The World of Vintage Sailplanes and scaled it up so that the wingspan was almost nine feet.
Wing construction
Ribs were cut from the bamboo using the "sandwich" method. This is a good building technique for tapered wings. Templates of key ribs are cut out. Then the ribs between the key ribs are cut to the larger rib's size. The ribs are bolted together between the templates. Using a knife and sandpaper, all of the intermediate ribs are formed automatically as you cut from the large template to the small template.
I completed the wing, conceding to balsa for the leading and trailing edges. Cypress, the local equivalent of pine, was used for the spars. Everything else—the shear webbing, the cap strips, and the sheeting—was made from bamboo bark.
Fuselage and structure
The fuselage was constructed from local plywood and cypress, fully sheeted with bamboo.
Controls and assembly
Having had difficulties in the past with linkages, I decided to build the wing as one piece. A single servo mounted in the center operates the ailerons through nyrods. The wing is mounted on the fuselage using the familiar pin-and-bolt method. The rudder functions well using a pull-pull setup with catgut cables. The all-moving stab is fixed on brass slide-in pins through an L-shaped horn.
With the Fafnir framed up it was time to consider the covering materials.
Covering and finishing
Continuing with the challenge to stay with local materials, I went to downtown Nairobi in search of suitable covering. The Indian shopkeepers informed me that they no longer carry silk; instead they had a synthetic version called China silk that's used for saris. The material is certainly light and strong, if a bit shiny. I bought two meters of a light tan color.
I found that the China silk adhered well to the framework using white glue. I pulled it as tight as possible, realizing that it wouldn't shrink with water. Fortunately I discovered that it will shrink with a higher-than-normal iron setting.
Having covered the model, I turned my attention to sealing the fabric. I couldn't find dope in town, so I inquired about something similar. A hardware store referred me to a furniture shop, where I encountered a very welcome smell—they were using clear nitrocellulose auto lacquer! I bought a liter, and found that the China silk reacted well, and once again all the framework details were visible.
Flight testing
As of this writing the Fafnir is still in the testing stages. It is using human power for launches. The towline is anchored to a stake about halfway between the aircraft and the runner. The line runs from the stake up through a ring in the towman's hand and back to the glider. This pulley system doubles the speed, so the runner can relax and have more control over the ascent. Also, the towman is closer and can hear vocal instructions in case of an emergency.
The Fafnir flies well and looks great in the African sky. Taking something that falls to the ground and making it fly has been a most satisfying project.
Author
Wayne R. Lehman Rosslyn Academy Box 14146 Nairobi, Kenya
Transcribed from original scans by AI. Minor OCR errors may remain.
