Reciprocating engines are very big engines. Instead of a motor just spinning the propeller, electric arms would move up and down circling around the propeller line spinning it. These kind of engines were used on the titanic.
Your question isn't clear. Are you asking WHY reciprocating engines for aircraft are called heat engines, or are you asking whether or not they are considered heat engines? Or are you asking...
the total volume of displacement of gas by the pistons moving in the cylinders usually measured in cubic centimetres (cm³ or cc) or litres (l) or (L) (US:liter). Is called displacement volume.
aircraft engines are normally reciprocating engine or pistan engine, the Aircraft instruments in a reciprocating engine are
cylinder
piston
and so...................