Jobs at small Wichita companies nobody posts about - first time posting

A friend who works at a local manufacturer says there are openings not advertised online. They like a brief email with a résumé. Should I visit in person?

A short email with two sentences about what you can do and your résumé attached worked for me. I followed up after a week.

Visiting in person worked for a trades job. For office jobs, email was better.