I can't figure out how to have the woocommerce long product description hidden by default when a product page is loaded. It looks much better, when the visitor has to click on "D
You can hide the 'Description' tab simply by leaving the product description empty. WooCommerce will not output the tab. Many sites don't use anything but the 'Short Description'.
But if you want to have the long description and still hide the tab you'll have to add or modify some code, in this case the PHP and/or the jQuery.