Structural Design
5OCT22
I haven’t had a lot of time to devote lately to designing the Sf-1. The next big step is something that I have been putting off lately but I need to work on the structural design. Originally, I planned a composite construction method for the Sf-1. Doing some more research and reading Dan Raymer’s Simplified Aircraft Design for Homebuilders he had an interesting quote from Garrison who designed and built two airplanes (one composite, one out of aluminum) in there about structural material:
“When I started the second airplane, I thought it would be quick because Burt Rutan seemed to be able to turn out airplanes in a few months. Instead, I found composite construction of a large, sophisticated airplane to be far more complicated and time-consuming than metal. The weights of the two airplanes are about the same. The main advantage of composites was the ability to form compound curves easily - but I’m not sure that in the 20 years I spent on the second airplane, I couldn’t have learned to use a planishing hammer and an English wheel just as well. Viewed aesthetically, even a perfect composite airplane (and mine is not perfect) is less satisfying than a metal one because its perfection is superficial and can be added later. There’s no way to fake good metalwork.”
Primarily though, in my case the structural analysis seems to be easier using aluminum. Since this is a scratch design and build I’ve got to do all my own “maths”. Raymer recommended Stress Without Tears that I am getting into now. This should be a good place to start. I’m playing with the idea of 2024t3 aluminum of varying thickness like the Van’s aircraft and a semi-monocoque fuselage. The primary concern is the structure is strong enough AND it can be manufactured easily.
On Fusion 360 I’ve been playing with a design similar to the Van’s aircraft. .032” aluminum bulkheads with flanges where the skin would be riveted to.
In this example I was just playing around with a structure design that could in theory be manufactured easily. The flanges on the bulkheads are the primary concern at the moment. They need relief and multiple segments along the flanges to be cut that would allow them to be bent.