Would i need a palate expander if i have a cross bite?

Maybe.: It depends on whether or not your mandible (lower jaw) is in the right position as it relates to the skull. If you have mandibular prognathism, you may need orthognathic surgery to reposition the mandible and that may correct the crossbite.

Yes: Posterior crossbites can be treated with a palatal expander, especially at the young age (up to 25 years old) when the result are predictable. As an adult, it is better treated with crown or briges.

Depends: At age 40 if your upper jaw is too narrow you will need sarp surgically assisted palatal expansion followed by corrective orthodontic treatment. If it's a dental crossbite with no skeletal component you will need corrective orthodontic treatment. Crossbites are best treated before puberty, so take your child with you when you go for an orthodontic examination. Don't put this off.

Not at 41: a palate expander is not going to work on someone your age.

Engineering...: Indeed, a palatial expander (possibly)may NOT expand the palate significantly, BUT it can expand the arch of your teeth to possibly correct a cross bite.! several orthodontic-engineering principles need to be evaluated. Good luck !-)