On several occasions I have down loaded the charts in the AIP. When planning the trip they are in the memory. After shutting down the iPad and restarting for the trip the AIP charts have disappeared. Have I some incorrect settings?

Luciano, what you are describing is not SkyDemon behaviour. Once you have downloaded a plate it will turn green, and will remain available while offline even if you terminate and restart SkyDemon. The only time it will disappear is if it's replaced by a new version, at which point you'll need to download it again.

If you are actually downloading the plate (e.g. it is turning green) then something is causing your downloaded data to be deleted. But possibly as Mike says, you're not actually downloading them at all.