Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
Here are some calculations showing why steam turbine aircraft was cancelled before 1945 and restarted after 1945.
One of the many proposed projects was 1940s German design of 3000 hp propeller steam aircraft powerplant.
It was designed to deliver 3000 hp to propeller. Steam turbine inlet pressure and temperature were 1470psi and 1022 F, steam turbine outlet 2.2 psi and 219F. Powerplant efficiency is 25%, not counting efficiency of the boiler with auxiliaries about 85%.
At cruising altitude 30,000 and 400mph ram air temperature is approximately -18F. Condenser cooling efficiency is 80%. That rises temperature of cooling air after condenser to approximately 172F. 141 lbs of cooling air per second is required. That is comparable to airflow of a turbofan business jet engine at the same conditions.
At takeoff the turbine exhaust parameters are 14.7psi and 249F. Efficiency is slightly lower- 23%.
Ambient temperature influence the cooling air requirements very much. At winter temperatures cooling fan power is very low. At 86F it will reach up to 50% of turbine power or significant water loss has to be managed.
The biggest problem was large size of the steam condenser required. This was due to low volumetric density of exhaust steam and low temperature difference between condensing steam and cooling air.
In 1948 two solutions were studied: one with the backpressure steam turbine with exhaust temperature and pressure up to 340F and 100 psi and the other was mercury vapor turbine with higher efficiency and much higher condensing temperature of at least 600F.
First design could not work efficiently at high speed of 500 mph. Out of 5000hp turbine power only 2140 hp were transformed in propulsive power and net efficiency was just 6-8%.
Mercury turbine was better with net efficiency exceeding 20% and radiator with 3 times less cross section but with the same weight (due to use of steel radiator instead of aluminum one). Total weight per hp was practically identical in both cases.
Part of the radiator air resistance was partially or completely offset by the Meredith effect. Mercury turbine Meredith effect was very significant at high speed due to much higher air temperature after radiator.