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I am building a LTD engine ( I am following James Senft's instuctions for his N-92 engine ) and have a question concerning the material that is used in building the displacer. I originally used Styrofoam from a hobby/craft shop. I needed a < 6 inch by 5/16 inch piece. After putting everything together I noticed the Styrofoam wrapped. So I now want to replace this hobby quality material with either balsa wood or pink construction grade Styrofoam. The balsa wood is easier to work with and seems sturdier, but I worry it is heavier than the Styrofoam. The Styrofoam is difficult to cut and size but is it a better material? I would appreciate any thoughts.

Many use balsa wood, and the weight is rarely a problem, especially if counterbalanced on the flywheel.

Adding holes in the displacer stuffed with steel wool (preferably stainless) will give you a built in regenerator as well. This will give you better performance, and put the weight somewhere between the foam and a solid piece of balsa.

aeglevski, you could make the balsa displacer hollow, build it with 1/16" sheet, two discs, a strip formed to a circle, and maybe some cross pieces to brace it. Ian S C