This snippet will allow you to use a radio button field to submit the form without using the submit button.

radio-button-submit

<script>
 jQuery(document).ready(function($) {
 $('input[type=radio]').on('change', function() {
 $(this).closest("form").submit();
     });
   });
</script>

Full tutorial here: https://wpmantis.com/gravity-forms-submit-form-when-radio-button-selected/