Steam turbine powered turboprops and turbojets 1931-1972

mvdmitri · May 13, 2019

There are several interesting steam turbines powered aircraft projects from 1930-1970s.

Campini and Rafaelli in Italy 1931 both proposed design of the ducted fan motorjet engine with IC engine replaced by steam turbine. Steam condenser was partially in wings and also inside ducted fan before jet nozzle:

Caproni-Campini C.C.2 – das zweite Strahlflugzeug der Welt | FliegerRevue X

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930094756.pdf

https://www.flightglobal.com/Flight...PDF#navpanes=0&scrollbar=0&page=1&view=FitH,0

''News has now reached us that the Breguet Aircraft works at Toulouse is building an experimental jet-propelled machine to the designs of R.Leduc.This French engineer is well known for his work in connection with the problem of jet propulsion.As reported in the fourth article on the subject appearing in the October 9th, 1941, issue of Flight, Leduc patented a thermal jet system in the year 1933.' According to Inter Avia, the new experimental type is basically similar in principle to the Caproni-Campini machine, but with one important exception.Whereas the Italian craft uses a standard type of air-cooled radial engine to drive the air compressor unit, Leduc employs a steam turbine for this purpose.Of the VUIA type running at 3,000 r.p.m.under a steam pressure of 1,910 lb.per sq.in., the turbine is estimated to develop 1,200 h.p. Experiments, presumably on the test bed, are claimed to have given satisfactory results.No details are yet available, however, of either the boiler or the necessary condenser plant.Obviously, the steam system would have to operate on a closed cycle.Condensing raises further problems which are not easy of solution in an aircraft instal-lation.The condenser would, most likely be placed in the main air stream so that heat transferred from the steam would be usefully absorbed for the propulsive jet.The development of a jet-propelled aircraft employing such a system will be watched with intense interest by designers throughout the world.''

In 1944-1972 supercritical steam cycle was under consideration for aircrafts, hovercrafts and air cushion vehicles.

Calculated condenser performance for a steam turbine propeller power plant for aircraft ( 5000 hp steam turbines, 500 mph at 30,000 ft, total cycle efficiency 10-15%):

https://digital.library.unt.edu/ark:/67531/metadc58164/m2/1/high_res_d/19930085809.pdf

Supercritical-water Cycle for Aircraft Propulsion (design of steam turbine driven turbojet aircrafts flying at 30,000-50,000 ft at speed 0.9 Mach -600 mph with total efficiency 20-25%):

https://digital.library.unt.edu/ark:/67531/metadc52887/m2/1/high_res_d/19630003317.pdf

Parametric steam cycle analysis for nuclear powered bypass turbofan engine ( steam turbine driven turbofan engine designed for flight speed 0.8 Mach and altitude 35,000 ft, with cycle efficiency 20-30%):

http://hdl.handle.net/2060/19690030675

Pratt and Whitney in 1951-1953 designed large ducted blower jet engine aircraft with two 49100 hp main steam turbines and 7930 hp condensate pump steam turbine. Supercritical boiler absorbed 410 MW of thermal power. Maximum sea level speed was Mach 0.9!

wuzak · May 13, 2019

Jumo had a steam turbine design proposal of 3,000hp in the early war years. Not sure how much was actually built, but development was cancelled early in the war (~1940/41).

A couple of steam turbine designs were proposed for the Me 264. They were to use a mixture of 70% coal dust/30% petrol until the supply of petrol was improved.

One design was for 4,000hp and the other was for 6,000hp.

The latter had two proposed variations - one with a reduction gear and large diameter propeller turning at around 1,500rpm, and one without a reduction gear, small diameter propeller turning at 6,000rpm.

Components for the 6,000hp turbine had been constructed by the end of the war, but most parts had not.

KiwiBiggles · May 13, 2019

A little earlier, in 1919, Bristol had a steam-powered aircraft in development. The Tramp was a development of their existing Pullman, with two 1500 hp steam turbines in the fuselage driving the propellors through extension shafts.

It never flew, unfortunately.

mvdmitri · May 13, 2019

The most complicated part of closed steam cycle aircraft power plant is steam condenser. Almost all waste heat has to be absorbed by the cooling air. Because temperature difference between condensing steam and cooling air is relatively small, the air volume will be large, comparable to airflow of the modern turbofan engine of similar thrust. The cooling fan of steam turboprop will demand 20-50 percent of turbine power, depending of its pressure and ambient temperature.
The only way to design and build such powerplant with exceptable weight and volume is to use hybrid turboprop-turbojet cycle with high pressure and temperature steam condenser and supercritical pressure steam turbine. Propeller is used for takeoff and low speed. At high speed and altitude propeller is feathered and disconnected, and all power is transfered to the ducted fan.
Pratt and Whitney's design had turbine inlet pressure and temperature 5000psi, 1000F and condenser at 430 psi-450F. Exhaust air was heated to 390F. Weight to thrust ratio was close to 0.5 , not including weight of the boiler-reactor.
The other steam turbojets designs were with steam condensers working at 100-1200 psi.
Waste heat was added to air stream compressed by ram effect and ducted fan and significantly improved thrust and efficiency, reaching net 20-25 percent.

mvdmitri · May 13, 2019

Steam powerplant for Me-264 could not provide advertised specifications because of the enormous size of the condenser required for 6000 hp turbine with only 2 psi exhaust. The only way to make it work was to raise steam pressure and temperature in condenser to at least 400 F and to use powerful cooling fan absorbing possibly up to 50 percent of power. But efficiency would be much lower unless motorjet cycle could be implemented.

The other option was to use mercury or sodium or potassium metal vapor turbine and condenser with much higher condensing temperature:

Mercury vapor 2x5000 hp turbine propeller aircraft:
https://digital.library.unt.edu/ark:/67531/metadc64188/m2/1/high_res_d/20050019308.pdf

Supersonic 1000 mph sodium vapor turbine compressor jet aircraft:

https://digital.library.unt.edu/ark:/67531/metadc929305/m2/1/high_res_d/966690.pdf

mvdmitri · May 13, 2019

https://shareok.org/bitstream/handle/11244/45264/Hays_okstate_0664D_14182.pdf?sequence=1&isAllowed=y

"CLOSED CYCLE PROPULSION FOR SMALL UNMANNED AIRCRAFT"

Closed Rankine cycle powerplant for a small low noise RC aircraft.

mvdmitri · May 13, 2019

Calculated condenser performance for a steam turbine power plant for aircraft

By Leroy V. Humble, and Ronald B. Doyle

''A rough estimate of the total power-plant weight Including propeller but excluding reactor is Included along with values of the ratio of usable load (load-carrying capacity) to airplane gross weight for a steam-turbine-powered aircraft at one set of turbine operating conditions and two flight conditions.
At a turbine-inlet pressure of 1400 pounds per square inch absolute and a turbine-inlet trmperature af 866F, the minimum specific condenser weight was 257 pounds per 1000 net thrust horsepower and the mInimum specific condenser frontal area was 16.7 square feet per 1000 net thrust horsepower.These values occurred at a turbine-outlet pressure of 100 pounds per square inch absolute, a flight speed of 500 miles per hour, and an altitude of about 15,000 feet.''

''Power-plant-weight estimates. Weight estimates indicate that for a turbine operating at an inlet pressure of 1400 pounds per square inch absolute, an outlet pressure of 100 pounds per square inch absolute, an inlet temperature of 866F, and a power output of 5000 horsepower the total powerplant weight including propeller but excluding reactor and working fluid would be 5460 pounds at a flight speed of 500 miles per hour and an altitude of 30,000 feet. This weight would correspond to specific weights of 1.09 pounds per turbine horeepower, 1.59 pounds per net thrust horsepower with the condermer submerged in the wings (no external nacelle drag), and 2.55 pounds per net thrust horsepower with the condenser in a necelle at a flight speed of 300 miles per hour and an altitude of 15,000 feet, the powerplant weight would be 5870 pounds (owing to a heavier propeller) and the corresponding specific weights would be 1.17, 1.74, and 1.97 pounds per horsepower, respectively.
For the condenser enclosed in a nacelle, the ratio of disposable load to gross weight of the airplane would be 0.41 for a flight speed of 500 miles per hour and an altitude of 30,000 feet. If the condenser could be installed in the wings as to eliminate external drag, this value could be raised to 0.48. In other words, a weight-carrying capacity equal to 41 to 48 percent of the gross weight of the airplane would be available for a nuclear reactor, working fluid, and cargo; or conversely, the gross weight of airplane with a nuclear energy steam turbine power plant would be about 2 to 4 times the weight of the reactor, working fluid, and cargo.
For the same condenser and operating conditions but at a flight speed of 300 miles per hour and an altitude of 15,000 feet, the values of the ratio of disposable load to gross weight for the cases of the condenser in a nacelle and the condenser submerged would be 0.51 and 0.52, respectively.''

Calculations in above mentioned studies clearly show that the best results can be obtained for a high altitude, high subsonic speed steam compressor jet propulsion. Best speed is 500-600mph at 30000-40000ft and total net efficiency could be higher than 20 percent, better than for ic propeller powerplant.

When propeller and compressor-jet engines have identical steam turbine and condenser the compressor-jet aircraft at high altitude and speed has almost two times higher efficiency than propeller aircraft. This is due to loss of efficiency due to propeller 80-85 percent efficency and large radiator air drag. In compressor-jet radiator is cooled by large volume of pressurized air and waste heat is accelerating jet exhaust, improving thrust to weight ratio and net efficiency. Also it is much easier to sustain constant boiler power at high altitude because air is already being pressurized by inlet and ducted fan.
But propeller provides much higher takeoff thrust with the same turbine power. Therefore hybrid design is the best solution for steam aircraft.

mvdmitri · May 14, 2019

Significant work on steam turbine powerplants for heavy aircrafts was done in USSR in 1932-1939.
First design was 2x1800 hp PT-1 steam propeller power plant. Weight of complete installation including auxiliary IC engine was 3000 kg. During tests in 1937 two engines together reached only 1600 hp, less than 2200hp necessary for takeoff. Large share of the turbine's power was absorbed by steam condenser cooling fan.
The other more powerfull powerplant PT-6 had two 3600 hp steam turbines and two turbocharged boilers with 90 percent capacity each. Total powerplant weight was 9000 kg and it was planned to install it on Tupolev TB-4 heavy aircraft. Fuel was heavy oil or crude oil. Water loss was low and sufficient for 15 hours flight.
It was also uncessful experiment.

Smaller 180hp 6 cylinder radial steam engine was designed for a biplane U-2.

mvdmitri · May 14, 2019

Besler 1954 work on 4x200 hp steam engines STOL airplane:
https://apps.dtic.mil/dtic/tr/fulltext/u2/051752.pdf

mvdmitri · May 14, 2019

Possible design of MIG-13( I-250) motorjet aircraft with steam turboprop powerplant.

mvdmitri · May 14, 2019

mvdmitri · Oct 20, 2019

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.

mvdmitri · Oct 20, 2019

Another problem with high efficiency steam aircraft turbine was large size of the exhaust outlet.
For comparison, attached are dimensions of 8000 hp steam turbine condensing locomotive.

mvdmitri said:
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.

PFVA63 · Oct 20, 2019

Hi,
Thanks for posting all this info. It's really fascinating stuff.
Pat

mvdmitri · Oct 20, 2019

The other design that was studied in Italy, France and Germany, and later in US was motorjet(thermojet) aircraft engine. Steam turbine was driving air fan with pressure ratio 1.3-1.4 through reduction gearbox or directly in case of centrifugal blower. Compresser air was going through air-steam condenser where it was heated and after that was accelerated in jet nozzle to a speed of 500-800 feet per second.

"No sooner had aviation engines become efficient and reliable in aviation after the First World War, then some inventors began to deal with jet propulsion. At the same time unusual suggestions were made to say the least. For example, in 1930, Italian engineer Ing. Secondo Campini actually suggested putting a heatable steam boiler into a fuselage whose steam was supposed to propel a propeller through a turbine. Campini was serious about his proposal. A good year later, he founded his own company, VENAR, to develop steam turbine-based drives for aircraft.

From steam drive to thermojet
According to his ideas would be installed in the rear part of the machine, a tube boiler, which is heated by a burner. The steam generated with it was supposed to drive a compressor via a steam turbine, which presses air with injected fuel into the tail of the aircraft for combustion. In addition, his design on the compressor shaft is a reduction gear that is to propel a propeller. The hot combustion air emanating from the end of the fuselage should strengthen the propeller drive by pushing power. As absurd as it sounds, the idea was heard at the Italian Aviation Authority. There was only doubt as to whether the great weight of the water in the aircraft would have allowed passable flight performance and a usable range when driven by steam. Thus, the project Campinis already seemed to fail in the design phase."

"''News has now reached us that the Breguet Aircraft works at Toulouse is building an experimental jet-propelled machine to the designs of R.Leduc.This French engineer is well known for his work in connection with the problem of jet propulsion.As reported in the fourth article on the subject appearing in the October 9th, 1941, issue of Flight, Leduc patented a thermal jet system in the year 1933.' According to Inter Avia, the new experimental type is basically similar in principle to the Caproni-Campini machine, but with one important exception.Whereas the Italian craft uses a standard type of air-cooled radial engine to drive the air compressor unit, Leduc employs a steam turbine for this purpose.Of the VUIA type running at 3,000 r.p.m.under a steam pressure of 1,910 lb.per sq.in., the turbine is estimated to develop 1,200 h.p. Experiments, presumably on the test bed, are claimed to have given satisfactory results.No details are yet available, however, of either the boiler or the necessary condenser plant.Obviously, the steam system would have to operate on a closed cycle.Condensing raises further problems which are not easy of solution in an aircraft installation.The condenser would, most likely be placed in the main air stream so that heat transferred from the steam would be usefully absorbed for the propulsive jet.The development of a jet-propelled aircraft employing such a system will be watched with intense interest by designers throughout the world.''

Main disadvantages of the steam turbine motorjet design were
1) lower thrust-to-power ratio 1-1.5 lbs per 1hp v
2) steam generator has to be rated for the cruise flight, not for takeoff power(3-4 times more ) to minimize powerplant weight.
To solve this issue it was suggested to build variable cycle steam turbine turboprop.
During takeoff and low speed flight 60-80% of turbine power was used to drive the propeller and the rest to drive the cooling fan.
At high altitude and speed propeller was feathered and almost all turbine's power was used to drive the fan, effectively converting powerplant in a motorjet. That allowed to use the same size steam generator for takeoff and high speed cruise flight.

mvdmitri · Oct 20, 2019

https://warwick.ac.uk/fac/soc/economics/staff/mharrison/public/jeh03postprint.pdf

Review of unsuccessful attempts to build high power steam turbine power plant for a heavy TB-4 and TB-7 Tupolev aircrafts in 1932-1939.
Lightweight high speed steam turbines and high capacity steam generators were build but all attempts to design the steam condenser of acceptable weight and volume had failed.
There were several designs, two of which were close to experimental phase: PT-1 (2x1500/1800 hp at 15000 rpm) and PT-6 (2x3000/3600 hp, 15000 rpm). Weight of complete powerplant with water and auxiliaries was 3000 kg and 9000 kg.
Official test results in 1937 were not good. 1500 hp unit delivered only 800 hp which was not enough for aircraft takeoff. Large share of the turbine's power were used to drive the steam condenser fan.

mvdmitri · Oct 20, 2019

The condenser cooling fan design of these steam projects was used later in motorjet aircrafts radiator cooling projects in 1941-1945.
Those aircraft could be using steam turbine powerplant if turbojets were not developed successfully.

mvdmitri · Nov 7, 2019

Project of the 80,400,500 and 1200 hp steam turbine propeller aircraft powerplants with flash boiler designed in late 1930s by Romanian inventor Traian Vuia. 55 pages with drawings and calculations in French language.

gen1

mvdmitri · Nov 23, 2019

1932 Great Lakes Aircraft Company project of a steam turbine 40 passenger flying boat.
Description of this aircraft is from Rivista Aeronautica 1932 N9.
Steam generator is under the floor of the first class passenger area.
Cruising altitude is 5,000 ft.
There are two 363 kg steam turbines 2x1150 hp each. Cruising power is 2x500 hp.
Steam temperature is 538C, pressure 70 bar.
Steam generator weight - 1070 kg, steam condensers -2x275 kg.
Powerplant weight with water- 3344 kg.
Cruising fuel efficiency - 270 g/HP (0.595 lbs/HP).

Great disadvantage of this project was large size and air resistance of the steam condenser.
Also, powerplant was about 2 times than a gasoline aircraft engine with the same power.

mvdmitri · Nov 23, 2019

Reverse engineering calculations of the steam turbines powered Me-264:

General characteristics

Crew: 8
Length: 20.8979 m (68 ft 6.75 in)
Wingspan: 43.00 m (141 ft 1 in)
Height: 4.2990 m (14 ft 1.25 in)
Wing area: 127.700 m2 (1,374.55 sq ft)
Empty weight: 21,150 kg (46,627 lb)
Max takeoff weight: 56,001 kg (123,460 lb)
Powerplant: 4 × BMW 801D (or BMW 801G) 14-cylinder air-cooled radial piston engines, 1,300 kW (1,700 hp) each for take-off

1,070 kW (1,440 hp) at 5,700 m (18,700 ft)

Propellers: 3-bladed constant-speed propellers

Performance

Maximum speed: 546 km/h (339 mph, 295 kn) at 36,000 kg (79,366 lb) at 6,101 m (20,015 ft)

470 km/h (290 mph; 250 kn) at 34,400 kg (75,840 lb) at 8,300 m (27,230 ft)565 km/h (351 mph; 305 kn) at 8,300 m (27,230 ft) with GM-1 operating

Cruise speed: 349 km/h (217 mph, 188 kn) at 8,001 m (26,250 ft)
Range: 15,000 km (9,300 mi, 8,100 nmi) 333 km/h (207 mph; 180 kn)
Service ceiling: 8,000 m (26,250 ft) at 36,000 kg (79,366 lb)
Rate of climb: 2.00 m/s (393 ft/min)

It is known than the steam powerplant was rated at 6000 hp at sea level and up to 10,000 m. Powerplant weight with water was 4,200 kg and fuel consumption was projected at 190 g/HP.

1948 NACA technical memorandum "Calculated condenser performance for a steam turbine propeller power plant for aircraft" and "Supercritical-water Cycle for Aircraft Propulsion"
are good references for this study.

https://digital.library.unt.edu/ark:/67531/metadc58164/m2/1/high_res_d/19930085809.pdf
https://digital.library.unt.edu/ark:/67531/metadc52887/m2/1/high_res_d/19630003317.pdf

Let's assume that the aircraft's top speed was 400 mph at 30,000 ft. L/D ratio is 15 and required thrust at 54,000 kg flight weight is 3,600 kg. Net propulsive power is 6315 HP.
Steam turbine parameters are:
Isentropic efficiency-85%, temperatures and pressures are 1000F, 2200psi/320F, 75psi; net cycle efficiency -19.3%, steam flow- 44,800 lbs/hr.
Powerplant has two 5000 hp steam turbines.
Each turbine drives propeller and air fan via second and first gearbox stages.
At takeoff 70% of power goes to propeller and 30% goes to steam condenser air fan.
At cruising altitude almost 100% of power is used to drive the ducted air fan and propellers are free wheeling. Compressed air is heated in radiator-steam condenser and accelerated in convergent jet nozzle, producing required thrust.
Calculations are made for the tropical atmosphere , 90F at sea level and minus 26F at 30,000 ft.
At sea level air condenser heat rejection is 59.3 mln Btu and air flow is 350 lbs/s. Air fan power is
1500 HP.

Steam turbine powered turboprops and turbojets 1931-1972

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