Was the Hispano-Suiza 12Y the worst ≥25L V-12 of WW2?

Reluctant Poster said:

Jerry Wells article "The Packard Merlin Supercharger Drive Mechanism for Two-Stage Engines" in Torque Meter Volume 1 Number 4 Fall 2002 clearly shows that the Packard drive was NOT a true epicyclic. It starts with:
"The Packard designed supercharger drive for the two stage Merlin engines is often described as "epicyclic" but this is quite erroneous. It was in fact basically a conventional compound spur gear step up mechanism consisting of three sets of paired gears equally spaced around the impeller/crankshaft center line axis.
….For those familiar with the British built Merlin this arrangement is exactly the as that on the single stage Merlin engines."

Basically there is a layshaft within a layshaft connected by a planetary gear set. In low gear the inner layshaft is locked out and the power flow from the engine to impeller is the same as the single stage Merlin via spur gears. In high gear the planetary set is engaged with the power flowing through the planetary gear set to dive the outer layshaft at a higher rpm.

The single stage Packard used the same the Farman drive as the Rolls Royce Merlins.

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ThomasP said:

I think I found the reason for the term epicyclic being used.

Hear is a view of the V-1650-3/-7 SC gear drive that is from the opposite side to that of the views of the Merlin 60 series SC gear drive I posted up-thread.
View attachment 802197

Apparently, they are referring to the workings of the interior/back-side of what I called the 'planetary' gears on the (RR) Merlin 60 series illustration I posted up-thread.

With the (RR) Merlin 60 series, the upper 'planetary' gear drives the impellers in low gear directly when clutched in, while the lower 2 'planetary' gears drive the high gear directly when the upper 'planetary' gear is clutched out and the lower 2 gears are clutched in.

With the Packard V-1650-3/-7 all 3 'planetary' gears are either clutched in - or not - at the same time. When not clutched in the main drive shaft from the engine drives the impellers in low speed directly. When all 3 of the 'planetary' gears are clutched in the impellers are driven in high gear via the epicyclic gearing inside of the 'planetary' gears.

Here is the description from the Packard V-1650-3/-7 Descriptive and Maintenance manual.
View attachment 802198

Make sense?

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Engineman said:

Interesting comments that deserve some further action. Unfortunately, I do not have the Jerry Wells article to consider, it would be good if you could post it please?

As far as the term used for the Packard "Epicyclic Drive", that term seems to have been used by all references that I see, principally in all descriptions that I find in Rolls-Royce books that mention it. It might be that it was the term used by Packard, or possibly interpreted by Rolls-Royce? Here, I would not wish to arbitrate or claim information that is conclusive, other than to repeat the term from RRHT books. Maybe this is another point to resolve from original data?

Beyond this, it may be worth pointing out the obvious. The single stage Merlin was built in early versions that were single speed single stage, later versions that were 2-speed single stage. later again, the 2-speed two stage engines were developed. Unsurprisingly, these different supercharger types needed different supercharger drives and the 2-speed drives needed a system to change between the speeds. The gear change method on 2-speed drives is the point in question, it was a Farman design licence by Rolls-Royce. The question seems to be what was used on the early Packard 2-speed single stage engines?

Eng

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Reluctant Poster said:

What you have labeled as sun gear is incorrect. It is a part of constant mesh gear set.

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Reluctant Poster said:

Single stage Packards used the Farman drive.

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