R-4360 - an absolutely extraordinary engineering achievement by P&W turned out to be a very expensive engine to operate and its development was difficult, due to its complexity it did not make it in time for the war.Therefore I propose an unorthodox minimal alternative to the historical Wasp Major - a 22-cylinder radial engine with a standard P&W piston diameter of 5.75", but with a stroke increased from 6 to 7.5".
This gives an engine with a capacity of 4285 cubic inches with the final designation R-4290.Assuming the same height of heads as in the R-2800, its diameter should be practically round 150 cm (59"), assuming the same arrangement of manifolds as in the case of the R-4090.Assuming the same corrected mean piston speed as in the R-2800C and R-4360 (for 2800 rpm), its RPM would be 2500 rpm. On the other hand, reaching the level represented by the late Wright engines, R-2600 and R-3350 and R-4090 and Bristol would allow for the RPM of 2650, giving then the required power by the engine program at the level of 3000 hp, taking 2000 hp for the R-2800B as a reference point.
The weight should be less than the R-4090. The best estimate is a proportion using the number of cylinders for engines of the same family with the same size pistons, which works great in the Wright series for 14, 18 and 22 cylinders. In the case in question, there is also an increase in stroke. Since the crankcase dimensions are limited by the number of cylinders on its circumference, increasing the stroke only requires enlarging the crankshaft and slightly lengthening the cylinders and connecting rods compared to the version with the preserved stroke. A good model for the upper limit should be the difference in mass between the Bristol Mercury and Pegasus engines (504 vs. 483 kg). Ultimately, taking the R-2800 as a base and taking into account all these proportions, it comes out to almost a round 3000 pounds, which with a designed power of 3000 hp gives a power to weight ratio of 1 hp/lb. Of course, one can express doubts as to why the engine weight is smaller than the R-4090 in the face of greater capacity - the answer is smaller heads, smaller pistons and above all - a smaller crankcase. Increasing capacity by increasing the stroke and longer cylinders is quite cheap when the crankcase is of sufficient size.
The development cost should be minimal - it can use ready-made solutions created for the R-2800: identical heads, pistons, timing and dual-mass flywheel.The increase in stroke and engine diameter compensates for the increase in the main connecting rod diameter: sin(pi/9)/sin(pi/11) = 1.21... < 1.25 = 7.5/6, which should not cause a new source of vibration problems due to the increase in the number of connecting rods, the situation is even improved compared to the previous engine.
It is worth comparing it to a potential would-be competitor - the R-4090. Purely geometric performance (assuming identical corrected mean piston speed) gives it 99% of its efficiency, and the estimated parameters are 7.1% lower weight at the cost of 3.5% larger frontal area. It is very difficult to achieve more even performance.
There are many advantages to such a scenario of events. First of all, the R-4290 should be developed very quickly compared to the R-4360, and the shared use of more resources and reduced staff workload would allow for faster development of all P&W engines under wartime conditions.Earlier availability and greater size similarity to the R-3350 could see it adopted in designs instead, even as an alternative to the turbo-compound version in the B-29.Since the R-4290 has a 10% better power to frontal area ratio than the R-2800 (not counting the additional RPM increase), it would be quite suitable for fighters.My favorite is the Hellcat with a single-stage supercharger, where the weight increase was partially compensated for by the removal of the intercoolers. This would be an interceptor version for destroying kamikaze.
After the war, the 22-cylinder engine should have a much higher level of development and reliability than the quad radial, and could be a much greater commercial success! It is also worth noting that the price of this engine should be practically in proportion to the number of cylinders (22/28), which makes it have a better power to price ratio than the R-4360.Similar weight could make it a better competitor to the Bristol Centaurus engine.The final turbo-compound versions of the R-4290 can reach 4000 hp, which at the same time increases the requirements for the successor but also reduces the need for completing such a project.The Quad Wasp should be planned as a follow-up of this design, with an increased stroke to 7", as a model called the R-5090 - representing the last large piston engine - and perhaps be canceled in the face of the appearance of turbine engines.
It is also worth noting that sleeve valves make it virtually impossible to create 22-cylinder twin-row radials, as there is no space between the cylinders for manifolds. In engines with a classic valve train, the manifold can be placed above the head without increasing the engine diameter, whereas in a sleeve valve, the "diameter" occupied by the valvetrain inside the crankcase is wasted for other applications. It is the 22-cylinder engine that maximizes the power to drag ratio for twin-row radials and it is this that would give the best competitive advantage over Bristol products, while maintaining simplicity and reliability.
The proposed increase in stroke length to 7.5" is a conservative value, tested on many engine models with the same bore diameter. The crankcase enlarged for 11 cylinders in a row allows us to think about even 8 inches of stroke, which would result in a 60-inch engine (keeping the previous crankcase diameter). 3.27% more power (sqrt(8/7.5)) for 3.42% more frontal area (60/59)^2 is still a good tradeoff, and extends the 22-cylinder radial engine concept to its geometric maximum: R-4570. The only unknown is avoiding the collision of the connecting rods with the cylinder walls.
This gives an engine with a capacity of 4285 cubic inches with the final designation R-4290.Assuming the same height of heads as in the R-2800, its diameter should be practically round 150 cm (59"), assuming the same arrangement of manifolds as in the case of the R-4090.Assuming the same corrected mean piston speed as in the R-2800C and R-4360 (for 2800 rpm), its RPM would be 2500 rpm. On the other hand, reaching the level represented by the late Wright engines, R-2600 and R-3350 and R-4090 and Bristol would allow for the RPM of 2650, giving then the required power by the engine program at the level of 3000 hp, taking 2000 hp for the R-2800B as a reference point.
The weight should be less than the R-4090. The best estimate is a proportion using the number of cylinders for engines of the same family with the same size pistons, which works great in the Wright series for 14, 18 and 22 cylinders. In the case in question, there is also an increase in stroke. Since the crankcase dimensions are limited by the number of cylinders on its circumference, increasing the stroke only requires enlarging the crankshaft and slightly lengthening the cylinders and connecting rods compared to the version with the preserved stroke. A good model for the upper limit should be the difference in mass between the Bristol Mercury and Pegasus engines (504 vs. 483 kg). Ultimately, taking the R-2800 as a base and taking into account all these proportions, it comes out to almost a round 3000 pounds, which with a designed power of 3000 hp gives a power to weight ratio of 1 hp/lb. Of course, one can express doubts as to why the engine weight is smaller than the R-4090 in the face of greater capacity - the answer is smaller heads, smaller pistons and above all - a smaller crankcase. Increasing capacity by increasing the stroke and longer cylinders is quite cheap when the crankcase is of sufficient size.
The development cost should be minimal - it can use ready-made solutions created for the R-2800: identical heads, pistons, timing and dual-mass flywheel.The increase in stroke and engine diameter compensates for the increase in the main connecting rod diameter: sin(pi/9)/sin(pi/11) = 1.21... < 1.25 = 7.5/6, which should not cause a new source of vibration problems due to the increase in the number of connecting rods, the situation is even improved compared to the previous engine.
It is worth comparing it to a potential would-be competitor - the R-4090. Purely geometric performance (assuming identical corrected mean piston speed) gives it 99% of its efficiency, and the estimated parameters are 7.1% lower weight at the cost of 3.5% larger frontal area. It is very difficult to achieve more even performance.
There are many advantages to such a scenario of events. First of all, the R-4290 should be developed very quickly compared to the R-4360, and the shared use of more resources and reduced staff workload would allow for faster development of all P&W engines under wartime conditions.Earlier availability and greater size similarity to the R-3350 could see it adopted in designs instead, even as an alternative to the turbo-compound version in the B-29.Since the R-4290 has a 10% better power to frontal area ratio than the R-2800 (not counting the additional RPM increase), it would be quite suitable for fighters.My favorite is the Hellcat with a single-stage supercharger, where the weight increase was partially compensated for by the removal of the intercoolers. This would be an interceptor version for destroying kamikaze.
After the war, the 22-cylinder engine should have a much higher level of development and reliability than the quad radial, and could be a much greater commercial success! It is also worth noting that the price of this engine should be practically in proportion to the number of cylinders (22/28), which makes it have a better power to price ratio than the R-4360.Similar weight could make it a better competitor to the Bristol Centaurus engine.The final turbo-compound versions of the R-4290 can reach 4000 hp, which at the same time increases the requirements for the successor but also reduces the need for completing such a project.The Quad Wasp should be planned as a follow-up of this design, with an increased stroke to 7", as a model called the R-5090 - representing the last large piston engine - and perhaps be canceled in the face of the appearance of turbine engines.
It is also worth noting that sleeve valves make it virtually impossible to create 22-cylinder twin-row radials, as there is no space between the cylinders for manifolds. In engines with a classic valve train, the manifold can be placed above the head without increasing the engine diameter, whereas in a sleeve valve, the "diameter" occupied by the valvetrain inside the crankcase is wasted for other applications. It is the 22-cylinder engine that maximizes the power to drag ratio for twin-row radials and it is this that would give the best competitive advantage over Bristol products, while maintaining simplicity and reliability.
The proposed increase in stroke length to 7.5" is a conservative value, tested on many engine models with the same bore diameter. The crankcase enlarged for 11 cylinders in a row allows us to think about even 8 inches of stroke, which would result in a 60-inch engine (keeping the previous crankcase diameter). 3.27% more power (sqrt(8/7.5)) for 3.42% more frontal area (60/59)^2 is still a good tradeoff, and extends the 22-cylinder radial engine concept to its geometric maximum: R-4570. The only unknown is avoiding the collision of the connecting rods with the cylinder walls.
