Was the Hispano-Suiza 12Y the worst ≥25L V-12 of WW2? (1 Viewer)

[Engineman]

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.

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

 

[ThomasP]

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.

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.

Make sense?

 

[Reluctant Poster]

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?

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

The three smaller gears of this set each drive an outer shaft. In low gear the inner shaft is locked to the outer shaft by by a roller clutch like you see on a bicycle. If you apply torque the shafts are locked if the torque is released the shafts can turn at different speeds
In high gear a friction clutch engages which stops the inner shaft from turning. The roller clutch is now in overrun and the inner and outer shafts can rotate at different speeds. The sun gear is mounted on the inner shaft so it too is now stationary. The planetary gear set can now function.
An interesting mechanism to say the least.

 

[Reluctant Poster]

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

Single stage Packards used the Farman drive.

 

[ThomasP]

re

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

Fixed it.

 

[Engineman]

Single stage Packards used the Farman drive.

So, I have had a bit of correspondence with "Mr Merlin" Peter Grieve and it is correct that the single stage Packard Merlin and V-1650 engines had the Farman 2-speed supercharger drive. This is quite a turn-up for the books, literally, and something that is missing from many books that feature the Merlin.
By the generosity of Peter Grieve, I enclose two photo's of, a Packard Merlin Mk29 and also a V-1650-1. Both photo's show the distinctive Farman type two-speed drive with clutch packs.

Eng

 

[ThomasP]

Yay!

 

[Engineman]

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 804187

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?

Hi, these illustrations are also in the RCAF Merlin V-1650-3/-7 Description and Maintenance documents dated 2 Dec 1949. The description is, IMO, somewhat vague and the illustrations are not that good. There are other illustrations in there that show the pressure oil feeds that operate the bronze/steel lock-up plates that act on the "planet gears". Unfortunately, the vagueness continues to not fully describe the way the "lock-up" rollers are activated, although this is apparently similar to a sprag-clutch action.
Nonetheless, I find the description as shown as being weak.
The baseline seems to be that the three supercharger drive layshafts each have a similar geared drive to the single supercharger driveshaft and each of those three layshafts has its own 4 x planet gears that can be locked to give Low ratio, or unlocked to allow the planets to revolve in the geartrain and give High ratio.
I think that you can see the planet gears in the illustrated drivetrains and understand that there is a different drive ratio if the planets are free to revolve, compared to if they are locked. It is just the precise illustration of the locking clutch-plates and their pressure oil operation that is lacking.
I enclose a couple of illustrations. The first should be the general drives and ratio's, the second the layout of the supercharger drive.
Cheers

Eng

 

[Engineman]

Hi,

The same RCAF document has some detail about the propeller reduction ratio.
It describes the Merlin 68 and 69 as having a .42 prop ratio with gears of 21/50.
It goes on to state that the V-1650-3 / -7 has a .479 reduction ratio BUT, then says that the gears are 21/44 (.477) and shows a photograph of the reduction gears
that count as 21/44 which is .477! The .479 ratio requires a gearset of 23/48!
Was someone numerically challenged at Packard?

Eng

 

[SaparotRob]

...
Was someone numerically challenged at Packard?

Eng

It doesn't make us bad people.

 

[Simon Thomas]

A difference of < 0.4% is way less than a tad, and almost a smidgen. I'd give them a pass.

 

[Engineman]

Because gear ratio's are often very long numbers when quoted as decimals and there are multiple tooth number possibilities to give the same ratio, it is usual to quote 3 Decimal places for ratios but also to include the tooth count to prevent mistakes. For instance, a .500 ratio could be 25/50 or, 24/48 or, 23/46 or 22/44 and A LOT of other number combinations.
As far as quoting to say, 3 decimal places, the .420 is simple as 21/50 is .420. However, other decimals can be long, the .477 (21/44) ratio is .477272727 repeating. Reducing this to 4 decimal places would be .4773 or, 5 decimal places to .47727, but this ratio is never normally quoted as a 2 decimal place because that would be .48 (21/44).
Likewise, 3 decimal places for .479 (23/48) is 0.479166666 repeating or, 4 decimal places to .4792 or, 5 decimal places to .47917. However, to 2 decimal places, .48 (23/48) !!!
So, you can see the logic of firstly, using 3 decimal places and secondly, quoting the tooth count.

Although the true tooth count that Packard and Rolls-Royce refer to in the two decimal numbers .477 and .479 is not proven for the .479 ratio, I feel that there are three major factors that make me expect they are different tooth counts.
First, .477 and .479 are different numbers.
Second, Rolls-Royce were a very highly technical precision engineering company that routinely dealt with complicated numbers and specifications and they would not mis-quote
gear ratio's that they fully understood.
Thirdly, Packard were also a very highly technical precision engineering company that routinely dealt with complicated numbers and specifications and they would not mis-quote
gear ratio's that they fully understood.

Finally, I do expect that suitable original Packard documentation for the Merlin 266 exists that can prove the original .479 tooth count and so resolve the anomaly!

Cheers

Eng

 

[wuzak]

Surely the total tooth count between the two gears should be the same?

If 0.479:1 is 23/48, then the ratios either side would be 22/49 = 0.449:1 or 24/47 = 0.511:1.

If the total tooth count is different, the centre distance between the gears would be different.

 

[Engineman]

Surely the total tooth count between the two gears should be the same?

If 0.479:1 is 23/48, then the ratios either side would be 22/49 = 0.449:1 or 24/47 = 0.511:1.

If the total tooth count is different, the centre distance between the gears would be different.

Hi,
In highly loaded gears that transmit a lot of power for their size, the shape and size of the gears is important for their strength and lifespan. Yes, gears are designed to mesh efficiently and accurately and the number of teeth to a certain diameter and width is very important. The designers of these reduction gears will design their gears to suit the size of the housings etc. Different teeth numbers will have an effect upon the whole design, and it is usual for gearsets to be optimised for each ratio. However, on low power transmission gears, it is not unknown for the gear form to be much less optimised and even mix and matched with sub-optimal gear forms, but not usually on highly loaded gears like these.

Eng

 

[Engineman]

Surely the total tooth count between the two gears should be the same?

If 0.479:1 is 23/48, then the ratios either side would be 22/49 = 0.449:1 or 24/47 = 0.511:1.

If the total tooth count is different, the centre distance between the gears would be different.

The varying ratio of teeth numbers is all in the gear designers' box of tricks. Within the limits of reliable ratio extremes and size/power, you can use many ratio's to get the desired effect. You are correct that there are general relationships between the sizes of the gears and the teeth numbers, but as you can see from looking at reduction gears and housings, there are limits on what can be fitted in each application.
There are some general limits, like not usually having gears that have paired ratio's such that the same teeth always contact the same teeth, it is usually better that the teeth interact with different teeth through a number of rotations before meeting the same tooth again.

Eng

 

[Jugman]

The Packard V-1650does have a reduction ratio of 0.479. Per drawings 615079 and 615080. The pinion gear had 23 teeth and the propeller shaft gear had 48. Packard also had a 0.477 and 0.478 reduction gears. I believe the 0.478 was a counter clockwise version.

 

[Engineman]

The Packard V-1650does have a reduction ratio of 0.479. Per drawings 615079 and 615080. The pinion gear had 23 teeth and the propeller shaft gear had 48. Packard also had a 0.477 and 0.478 reduction gears. I believe the 0.478 was a counter clockwise version.

Hi,
Thank you for that information, 23/48 is .4791666 and that is what I expected. Is it possible to post copies of those drawings with the details please?
As an additional comment, although this information is slowly coming out, it does seem surprising that the general quotations about decimal reduction ratios is not always qualified by the actual tooth count, which is the true factor. Of course, the specific parts books and manuals should have the correct data but, there is still the anomaly of the RCAF manual that does not clear this up.

Eng

 

[Jugman]

I have a lifetime membership to Aircorps Library. I don't own copies of them myself and I think I still need to pay to download them to my computer. If one technically minded I think membership is very much worth it.

Gearing for gearheads should have some info. I'm working right now so no time to read.

 

[wuzak]

The Packard V-1650does have a reduction ratio of 0.479. Per drawings 615079 and 615080. The pinion gear had 23 teeth and the propeller shaft gear had 48. Packard also had a 0.477 and 0.478 reduction gears. I believe the 0.478 was a counter clockwise version.

It makes sense that the opposite rotation version had a different ratio, as there was an idler gear between the crank gear and the propeller gear.

I can't see how they could get 0.477 and 0.479 without an idler gear.

 

[Jugman]

It makes sense that the opposite rotation version had a different ratio, as there was an idler gear between the crank gear and the propeller gear.

I can't see how they could get 0.477 and 0.479 without an idler gear.

Easy, the 0.477 has a circular pitch of 0.8352 vs. 0.7646. The combined pitch diameters were 17.2844 and 17.2799 respectively.