Merlin Question

[GregP]

At the Planes of Fame Museum, one of the guys told me that he had seen a Merlin (don't know if it was Rolls-Royce or Packard) that had a continuously-variable supercharger drive. I said that as far as I knew, all Merlins were either single-stage, single speed; single-stage, 2-speed; or two-stage, 2-speed with intercooler, but that the 2-stage units were all mechanically geared S/C wheels, some with a hydraulic clutch to help shift gears.

Does anybody know of a Merlin with a consinuously-variable supercharger drive? If so, was it available during the war?

If it exists, I can't find any mention of it in the usual places, and that includes early Merlins, the 20, 30. 40, 50, 60, 70, and 130 series engines. Other than this guy saying we has seen one at the Planes of Fame, I haven't heard of it, but that doesn't mean it doesn't exist.

 

[wuzak]

I don't think RR ever used a variable speed drive for the Merlin. Like you, my understanding is that they are all fixed ratios - 1 or 2 speeds. The Griffon had a 3 speed variant, but not the Merlin.

 

[GregP]

Thanks Wayne, that's what I thought.

However since we also have a hand in modern racing, you never know what someone came up with at some time.

While I was at Joe Yancey's shop, we had a guy come by with pictures of an Allison that had the internal supercharger removed and two turbochargers added, one along each cylinder bank. It was never available from Allison, but it seems to have been created and seems to run ... he had videos!

 

[tomo pauk]

There was a prototype of Packard Merlin with hydraulycally driven S/C. The article should be at the AEHS site.

 

[GregP]

Thanks, Tomo, I'll go look into that there.

Turns out to be the experimental V-1650-19. Apparently theye made two of them using a variable Sundstrang supercharger in 1945.

So, perhaps this friend at the Planes of Fame was correct, and I think at least one survived since he claimed to have seen one coming through the Planes of Fame. I'll ask Steve Hinton and see if he recalls this beast.

 

[Koopernic]

I don't think RR ever used a variable speed drive for the Merlin. Like you, my understanding is that they are all fixed ratios - 1 or 2 speeds. The Griffon had a 3 speed variant, but not the Merlin.

The V1650-7 of the P-51H and the 100 series Merlins of the DeHaviland Hornet used 3 speed drives. I believe the V-1710-121 used on the P-63 and P-40Q used a hydraulic drive but still with two speeds. The Hydraulic variable speed drive was of course a trick of the Daimler Benz 601/605/603 series. The final version of the 603, the DB603N would have had two mechanical speeds with hydraulic variable speed on top.

Some method needs to be employed to regulate the manifold boost pressure: either a valve (corlis valve etc) or the supercharger speed needs to be regulated via an infinitely variable speed drive. There is a slight loss in mechanical power of the variable speed drive but only that portion going to the supercharger. Superchargers with a valve of course suffer from inefficiencies from the pressure loss at the valve.

Turbo superchargers can regulate RPM via a waste gate to bypass the turbine. Some Soviet engines used a variable pitch stator/diffuser on the supercharger.

Engines with turbo compounding don't usually need a waste gate, they drive all of the turbo's power into the engines main drive shaft. Supercharging is then achieved with conventional methods.

Some proposed engines used 4 speeds, I think usually configured as 2 x 2 independent drives for the two stages. One was the BMW 801R, abandoned after Bombing of the BMW factory in June 1944.

 

[wuzak]

The V-1650-7 and Merlin 130/131 did not have 3 speed supercharger drives.

The 2 stage Allisons used a variable speed drive for the auxiliary supercharger (the 1st stage), while the engine stage supercharger remained single speed.

Boost pressure in the Merlin was regulated by the throttle plate.

 

[Milosh]

The P-51H was powered by a V-1650-9 engine.

 

[wuzak]

The P-51H was powered by a V-1650-9 engine.

Which also had the 2 speed supercharger drive.

 

[rinkol]

A three speed supercharger drive was considered for a postwar civilian version to be used in the Canadian version of the DC-4.