I have always understood "soar" to mean 'rise quickly'. But I have just consulted quite a few dictionaries and found, to my surprise, that "soar" also means 'fly high in the sky with little effort'. If that is the case, when you hear or see "soaring eagle", which image do you have: an eagle flying in the sky (maintaining height) or an eagle rising up in the sky (changing height)?
And "soaring airplane"?
Flying high, eagle or airplane alike. Possibly rising, though not necessarily. Certainly not losing altitude.