Velomobiles are marvels of light weight structures. The design of practical velomobiles touch a lot of contrary aspects:
These pages try to give an answer in short reviews. Most abstracts are from Werner Stiffel.
Here, the design criteria of tricycles are discussed.
If there is an elch on the road, tilting may be a striking design criterium
The steering of tricycles is a subject that is often discussed. This is an extensive abstract so this subject.
And what about velomobile tandems? This page gives the answer.