Medication to induce labor (oxytocin) may be used, tocolytics may begin or halt labor, steroids may help the fetus' lungs mature, antibiotics fight infections.
A model aeroplane is used for presentations and testing. Model planes are also used for fun. They are used model-plane clubs, aeroplane company headquarters and studios. (Bedroom, in my house)
The only answer that comes to mind is "Airships". Hydrogen, the lightest element, was used in airships, where excess weight was undesirable. However, accidents like the Hindenburg disaster showed...