Solid modelling

 19 November 2021

I think the main difficulty with solid expanded foam modelling is the sanding required for proper shape and texture. However, if gloss over this seemingly inherent difficulty, expanded foam is about the lightest modelling material easily available for flying models.

The least work is profile planes. Where the wing and tails are to the planform without regard to the cross-sections and the fuselage is to side profile. In the case of light RC models, a profile fuselage is sufficiently strong and 'stiff', especially if wrapped with tissue or paper which takes care of the tensile and torsional strengths.

Next 'level-up' in aesthetic is to make the wings and tails airfoiled and to make the fuselage conform to the planform as well. The performance of the wings and tails are almost maxed out and the fuselage has lesser drag. 

The ultimate is to have the wings and tails tapered from root to tip in thickness and to have the fuselage conforming to cross-section.

Carving the wings with HWC is relatively easy but compound curved fuselage is difficult. Not all aeroplanes' fuselages have compound curves and some are easier to achieve by building up the fuselage cross-sections.

Instead of cutting fuselage to side profiles, some can be cut to the planform. In these cases, the planform fuselages can be stacked together to the depth required and cut to the side profile. Turtledecks and front deckings can be curled paper with some formers.

I wonder if it is easier to sand expanded foam (polystryene) in water. 

Don't forget that XPS can be sanded. However, if used in slab construction, it is probably twice as heavy as EPS. Depends on the density of EPS comparison.