Imagine you have a propeller with an efficiency of 50% at a particular differential pressure. What happens to that lost 50%? It turns into heat. Now imagine you

Imagine you have a propeller with an efficiency of 50% at a particular differential pressure. What happens to that lost 50%? It turns into heat. Now imagine you have a fancy new propeller with an efficiency of 99% at that particular differential pressure. All that energy that you were using making heat before is not turning into thrust. Your overall engine-propeller system is now twice as powerful at that same differential pressure.