Saturday, June 19, 2010

Thinking Small

To All:

Some days ago I posted a short message to this blog to which a number of you responded. Alas, in most cases the response was not a good match for the topic, in that most of the responses dealt with other subjects. Indeed, the majority dealt with the use of wood from the lumber yard as opposed to Spruce from an aircraft materials supplier, and the general theme was that I should not encourage people to build their airplanes out of scrap lumber.

Which is good advice.

But the use of scrap lumber is justified when you are trying to learn how to set up your saw, or fit pieces into a jig, or nailing those pieces together to form a side of the fuselage. Indeed, it is important for you to consider scrap lumber as a valuable tool.

As a point of interest this method of fabrication is known as the de Havilland Method. That is, side-frames are fabricated in a jig to ensure their accuracy. The side-frames are then plated with plywood to provide shear strength, then a left & right side-frame is assembled to form the 'box' of the fuselage.

You can expect the typical fuselage to be from twelve to 20 feet in length and one of the trickier bits is to ensure the side-frames are perfectly parallel to each other. That is, that they form a perfect square or other figure the designer may have called out. And to hold the sides square you are going to need lots of scrap sticks and pneumatically-driven pins.

This is also a good time to check the alignment of your gluing, in that once it is stapled or pinned it's not going anywhere.

The product of your labor is a copy of the real fuselage. Add some utility wheels to give the thing mobility and use it as your test module for the other fabrication steps. Of course, the copy is fabricated from materials obtained at the local lumber yard. Which brings us back to the question of Sitka Spruce versus just about anything else.

What we keep running into here is the ASSUMPTION that 'aviation-grade' lumber automatically means Sitka Spruce. It doesn't. Indeed, more than two dozen woods have been identified as suitable for aircraft construction.

-Bob Hoover
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