Small retractable jet engines are available on some types of glider (sailplane) such as this HPH Shark. It is mounted behind the pilot
<a href="//commons.wikimedia.org/wiki/User:Jmcc150" title="User:Jmcc150">Jmcc150</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>