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I think it was better than that, the two stage superchargers would also be blasting their air into a low pressure ambient, which also improves thrust. Higher pressure should lead to both higher mass flow and higher exhaust gas velicity. The thrust is given by F =dm/dt x v. Jet thrust is also of greater value at higher speeds where mach effects reduce airscrew efficiency
though turbo is conspicuously absent on the R-4360 of the B-36B
There is no doubt that the bulk of the turbo system is a major design issue, especially with a very trim design like the Ta-152. If it could have been made to work it would probably been impressive. The P-47 seems to have solved the mass problem with massive, and bulky, hp, kind of like using a sledge hammer to get a square peg into a round hole. It worked, though.FW did try to develop the FW 190C "Kanguruh' with turbo charger: the result shows how difficult it could be to integrate a turbo-supercharger:
Shortround6 said:....
The B-36's R-4360s didn't have one turbo - they had two. They used two C-series turbochargers, similar to the ones used by the P-47.
The B-29 used 2 B-series (also used on P-38, B-17 and B-24).
The choice of turbocharger was based on engine size and/or power output.
And the wastegate which needs to be controlled and its own ducting and exhaust. Diesels don't need one.
Please note that the combined power at 25,000ft is 1067.2hp which is quite a bit shy of what a turbo-supercharged engine would have capable of delivering. A Turboed MK XX would have been capable of 1280hp if not more at 25,000ft to the propeller. Wither the extra 20% in power is worth the extra 400-500lbs and the extra bulk and drag of the installation is the question.
two stage Merlin would probably need in excess of 400hp to run it's supercharger set up.
Are you sure? The B-36A and B-36B seem to have had only mechanical superchargers: the R-4360-51VDT never entered service.
Are you sure? The B-36A and B-36B seem to have had only mechanical superchargers: the R-4360-51VDT never entered service.
It is my recollection (from things I have read) that the B-36 had two conventional turbochargers. I also recall that for high altitude cruise, all the exhaust would be routed through one turbo. Of course the 4360s still had their mechanical supercharger too.
The VDT 4360 did not enter service just as stated by Siegfried. I believe in its final form the VDT engine did not have a supercharger, and the throttle was basically controlled by restricting the output of the "turbo"; hence the name VDT - Variable Discharge Turbine.
Yes, I'm sure.
I was looking at a schematic of the B-36 engine installation, with its two turbos hanging beneath one end of the R-4360, when I typed that.
Each engine was also provided with two General Electric Model B-1 (or BH-1 on later models) exhaust driven turbosuperchargers arranged in parallel. The Primary purpose of the turbos was not to increase the power rating of the engine. Instead, they allowed the sea-level power rating to be maintained up to 35,000 feet, with a gradual degradation at altitudes above that.
The right-hand turbosupercharger on each engine also provided air for cabin pressurization. The flight engineer had teh ability to select dual or single opertaion of the turbosuperchargers for each engine. When single mode was selected, all exhausts gases were passed through the right hand turbo - there was no option to select using the left turbo only.
I think there were several variations on the VDT theme. Some certainly did not have an engine stage supercharger, but some may have. Some also had compounding - that is, the turbine in the supercharger also fed power back to the crank.
My limited understanding of the supercharger v turbocharger in aircraft was that whilst the supercharger provided sterling service and was stretched (thanks to multi-stage/speed inter-cooling) to meet just about everything asked of it in allied service, the turbocharger was the superior unit for larger aircraft and very high altitudes.
Germany in fact I think illustrates the limitations of the supercharger better than most, whilst they had a beautifully elegant design (the infinitely variable fluid coupled supecharger) - according to a Robbie Coltrane TV show on the DB engines - they simply didn't have large supplies of the fuels required to max out the supercharger, unlike the allies, in general service.
Hence the permanent high altitude issues almost all German planes had.
Of course jets rendered this moot it is quite obvious Germany was prepared to sacrifice 'otto' engine R&D resources for the jets.....and had things not collapsed so quickly who knows maybe their choice could have paid off, tactically at least even if the strategic picture would change little.
Even turbo's only had a short period in the sun as turbo-prop engines rendered the piston engine obsolete and offered much better outputs altitude.