Advanced French Fighters vs 1942/1943 contemporaries (16 Viewers)

[Bretoal2]

Regarding the second chart, first column is of course altitude in m, 2nd column is rate of climb in m/s over the given 1000m altitude range, 3rd column is climb time to a given altitude in minutes (') and seconds ("), and finally rpm and manifold pressure.

What makes you think that there is room for extra power with better cooling? I'm curious about the factor you saw?

The 12Y-45 and 49 themselves improved performance over the 12Y-31 essentially through the supercharger which reduced losses and increased efficiency so you could increase power a little bit on similar fuel without changing the rest of the engine, while the 12Y-51 achieved that through increased rpm (enabled by the Sarrazin devices increasing crankshaft strength) and improving combustion (larger valves while the fuel now goes to 92/100 octane to prevent knock).
I would infer from this that the 12Y-31 basis that the 12Y-45/49 used was limited at this stage by mechanical durability and breathing rather than cooling, though this is partially accounted for by the larger valves and increased octane rating.

The swirl throttle supercharger meant that the power loss when going from the critical altitude to sea level was lower (the power curve is flatter below critical altitude), such that it was possible to keep a given sea level/low altitude power while increasing critical altitude (shifting the curve to the right on a power/altitude diagram), thus increasing available power at altitudes above the critical altitude. The 12Y-51 engine with the original H-S supercharger is a straight up more powerful raw engine with a worse supercharger, so low altitude power is better but not as much as it could be while the critical altitude is lower.

In theory at least, the 12Y-51 with the swirl throttle supercharger would at least enable the same curve shifting that happened with the -45/49 and thus actually exploit the more powerful base engine at high altitude; depending on the selected critical altitude, it should also generally increase low altitude power a bit to make it closer to the peak power which is achieved at critical altitude. Possibly, if mechanical durability or breathing aren't the limiting factors, it may be possible to repeat the trick of the -45/49 compared to -31 and actually achieve a little extra maximum power over the base engine with H-S supercharger, but public information on that engine/supercharger combination is basically nonexistent AFAIK.

Assuming that the maximum output couldn't exceed 1000 hp and that 1100 hp remained reserved to take-off however, we can know that the minimum low altitude power even with S-P supercharger can only be somewhere between 900 and 1000 hp (so 0 to 100 hp gain over H-S supercharger). So, compared with a hypothetical D520 with 12Y-51 with H-S supercharger, the low altitude speed could only ever be increased by what an extra 100 hp gets you.

Indeed, the early models of the Hispano-Suiza 12Y-51 were equipped with the original H-S supercharger, which was significantly inferior to the Turboméca (Planiol-Szydlowski) unit.

At low altitudes, the P/S supercharger's main advantage was its ability to significantly lower intake temperatures; this feature simultaneously reduced the risk of detonation and improved efficiency by increasing the charge density.

There remained, of course, the question of the engine's structural integrity—its ability to withstand these conditions. While Hispano's finish and manufacture quality was universally praised, its lightweight design meant it lacked the robustness needed to handle the increased stresses associated with higher performance.

It is also worth noting that, in Émile Dewoitine's view, the arrival of the D551 rendered the D520 obsolete. Had the collapse of June 1940 not occurred, the D551—which offered superior performance and, crucially, was far easier to manufacture—would likely have quickly replaced its predecessor.

 

[Elan Vital]

It is also worth noting that, in Émile Dewoitine's view, the arrival of the D551 rendered the D520 obsolete. Had the collapse of June 1940 not occurred, the D551—which offered superior performance and, crucially, was far easier to manufacture—would likely have quickly replaced its predecessor.

Indeed. There was no question of keeping both types in production concurrently aside from what was necessary to wait until D55X tooling was completed.