For the 509.03 AAB, the purpose is really to provide an option for a 7200 PharaohOasis only AAB design. The main difference is that it drops passive clearance (Chirp) by about 1.2 nm, so it should be very similar to the 509.02L, but it uses a few mask alterations (very small changes) to tweak the performance to match the take off performance. The reason for the clearance drop is to optimize for 7200 RPM performance instead of making the AAB work for both 7200 and 5900 RPM. The concern around higher clearance is reader temperature for stability performance. The thinking on needing to go to a 7200 RPM only design is that we might have reader temp that is to high to allow for good stability performance. The reason to use a different mask instead of just the 509.02L is that the "further" from the nominal design point we get the more potential we have for other issues, like CSS or environmental sensivities. Really, what that means is that the "L" or "H" are close to the "N" so no real issue, but if we needed an "LL" for example we might not get as good a performance as we want and we can allow for a redesign due to if we need a 7200 RPM only AAB we are going to break commonality and there's no reason not to do a dedicated design. Please note that because the commonality break with 509.03 it is a backup plan only and not a primary path.
For the 509.03 AAB, the purpose is really to provide an option for a 7200 PharaohOasis only AAB design. The main difference is that it drops passive clearance (Chirp) by about 1.2 nm, so it should be very similar to the 509.02L, but it uses a few mask alterations (very small changes) to tweak the performance to match the take off performance. The reason for the clearance drop is to optimize for 7200 RPM performance instead of making the AAB work for both 7200 and 5900 RPM. The concern around higher clearance is reader temperature for stability performance. The thinking on needing to go to a 7200 RPM only design is that we might have reader temp that is to high to allow for good stability performance. The reason to use a different mask instead of just the 509.02L is that the "further" from the nominal design point we get the more potential we have for other issues, like CSS or environmental sensivities. Really, what that means is that the "L" or "H" are close to the "N" so no real issue, but if we needed an "LL" for example we might not get as good a performance as we want and we can allow for a redesign due to if we need a 7200 RPM only AAB we are going to break commonality and there's no reason not to do a dedicated design. Please note that because the commonality break with 509.03 it is a backup plan only and not a primary path.
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