V-1710 supercharger development potential

Nothing with a service ceiling of 41,000+ feet was really a low-alitude engine in WWII. Perhaps with respect to a later development, but was it a low-altitude engine with respect to earlier developments?

In the development scheme of things, the -7 was after the -1 and -3. It was supposed to be better, and I'd expect a -9 to be better than a -7, too, assuming the new dash isn't / wasn't a special-purpose engine, such as a sped record one-off or other special project. That's what I meant anyway.

When the -7 came out, it wasn't a low-altitude engine. You might consider it so when compared against the -9 but remember the -9 was not an engine that saw combat in WWII as the P-51H didn't see combat in WWII. It barely made the war, but wasn't a factor in combat at all.

I was thinking of WWII comparisons and will grant it seems to be "low-altitude" compared with the -9 of post-war fame.

GregP said:

Nothing with a service ceiling of 41,000+ feet was really a low-alitude engine in WWII. Perhaps with respect to a later development, but was it a low-altitude engine with respect to earlier developments?

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The -7 had lower Full Throttle Height/Critical Altitude in both Full Supercharge (FS) and Medium Supercharge (MS) gears (HI and LO in US parlance).

GregP said:

In the development scheme of things, the -7 was after the -1 and -3. It was supposed to be better, and I'd expect a -9 to be better than a -7, too, assuming the new dash isn't / wasn't a special-purpose engine, such as a sped record one-off or other special project. That's what I meant anyway.

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The -1 was a single stage 20-series Merlin.

The -3 was equivalent to a Merlin 63.

The -7 was equivalent to a Merlin 66.

The -9 was equivalent to a 100-series Merlin (not sure whjich one exactly - I will have to check).

The -3 and -9 had the same supercharger gear rations, while the -7 had different ratios.

The 66 was strengthened compared to the -3, and the -9 was further strengthened. The -9 also featured further refinements, such as end-to-end lubrication of the crankshaft, compared with the earlier engines.

GregP said:

When the -7 came out, it wasn't a low-altitude engine. You might consider it so when compared against the -9 but remember the -9 was not an engine that saw combat in WWII as the P-51H didn't see combat in WWII. It barely made the war, but wasn't a factor in combat at all.

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It was a low altitude engine compared to the Merlin 70 series engines, which did see service in Spitfires and Mosquitoes.

Spitfire IXs were fitted, initially, with Merlin 61s or Merlin 63s. Around 1943/1944 they started putting in Merlin 66s and Merlin 70s. The Merlin 66 versions were named LF.IX, the Merlin 70 versions named the HF.IX.

The LF.IX had better low altitude performance and climb rates than the HF.IX, which took over the performance advantage at mid altitudes and held it at high altitudes.

I believe that the Mustang received the V-1650-7 was to bolster its low altitude performance, particularly climb.

Wayne,

The USA didn't USE UK-built Merlins (in US-built aircraft anyway) and you specifically said a -7 and -9. or so I thought. Those were specific-use engines for the most part.

I made an assumption here that you were talking Packard Merlins in WWII. If you weren't, OK ... I understand. I thought this was a WWII forum and the US and UK-built Merlins weren't interchangeable in a LOT of respects. Today they are not considered interchangeable ... at least by the 20 or so owners I know. Some of them have Rolls Royce Merlins and some have V-1650-X, and ALL like what they have ... but they don't interchange parts very without rework of said parts. That's from the owners, not me. I know ALlisons pretty well but have only helped a bit on Merlins. More lack of opportunity than anything. The owners that HAVE issues with them tend to send them to Mike Nixon instead of trying to work it our with local guys.

If you are opening it up to ALL Merlins, then go for it. I'd stop at WWII since this is a WWII forum, but they STILL make parts for Merlins today if you want to get technical about it. They race every year at Reno and can stomp the crap out of any WWII or slightly post-war stock Merlins ... for about 8 laps or so anyway ... at about 5,000 feet. Nobody knows their higher altitude characteristics.

I was assuming a sort of logical limit but, hey, go for it.

When you compare P-51's, you don't usually hold up the P-51D or H to a P-51A and say how far the design progressed. But you CAN if you lean that way.

About the 3200 rpm, you are right, they DID make four V-1710-121 (F-26R) engines that could be operated at 3200 rpm. They needed some test mules for the G-series rods. Forgot about those 4 engines. The original engine in the XP-40Q-2 was a -101 and only was run to 3,000 rpm. It was later when the engine was changed to the -121 that they tried that rpm. Helped a bit ... but not much.

I stand corrected there.

It was only the G-series for production planes ... but they DID do it in the very pretty but short-lived the rebuilt XP-40Q-2 in 1944, about the time the G-series was being tested and turned into a shippable engine.

I think the big pistons would have dome some amazing things power-wise had development continued instead of dying in 1945 - 1946. I can see Allisons and Merlins (as well as some others) getting another 300 - 500 HP with continued development, and I think a LOT of it would have come from RPM increases and improved boost systems. The Merlin would have needed new rods and pistons, but they were not out of reach, certainly, and it was a very smotth-running and reliable engine in most of its forms. A winner for sure.

GregP said:

Wayne,

The USA didn't USE UK-built Merlins (in US-built aircraft anyway) and you specifically said a -7 and -9. or so I thought. Those were specific-use engines for the most part.

I made an assumption here that you were talking Packard Merlins in WWII. If you weren't, OK ... I understand. I thought this was a WWII forum and the US and UK-built Merlins weren't interchangeable in a LOT of respects. Today they are not considered interchangeable ... at least by the 20 or so owners I know. Some of them have Rolls Royce Merlins and some have V-1650-X, and ALL like what they have ... but they don't interchange parts very without rework of said parts.

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Packard Merlins were almost entirely interchangeable with British built Merlins. There were a few items that differed, such as the supercharger drive gear train (on 2 stage engines) and the output shaft for US use and the carby IIRC.

Remember that the bulk of Merlins produced by Packard went to thr UK. They were used in the Lancaster, Spitfire and Mosquito. The Spitfire XVI was a Spitfire IX with a Packard built Merlin - the Merlin 266. Merlin 225s were supplied by Packard for Mosquito production (Canadian production mainly?). Merlin 224s and 228s were for Lancasters.

British bound Packard Merlins had SBAC standard output shafts, American bound Merlins had SAE standard shafts.

The screws, nuts and bolts used on Packard Merlins were BA (the small ones, on the supercharger housing for example) and Whitworth (standard or fine).

Each Packard model was equivalent to a Rolls-Royce model, or family of models. Except the experimental version with the fluid coupling drive for the supercharger. They used the same ratings as were used for Rolls-Royce. These ratings are denoted by RM.XSM - this means Rolls-Royce (R), Merlin (M), rating number (X), supercharger specification (S = supercharged = fully supercharged, M = medium supercharged, L = low supercharged).

The Merlin 66 was rated RM.10SM. The V-1650-7 was rated RM.10SM.

The V-1650-3 was the Packard equivalent of the Merlin 63. The supercharger used gear ratios of 6:39:1 (MS/Lo) and 8.095:1 (FS/Hi).

The V-1650-7 was the Packard equivelent of the Merlin 66. The supercharger used gear ratios of 5.8:1 (MS/Lo) and 7.34:1(MS/Hi) .

The V-1650-9 was rated RM.16SM (or was it 14SM?), as were the Merlin 113 and 114.. The supercharger used gear ratios of 6:39:1 (MS/Lo) and 8.095:1 (FS/Hi).

So, the V-1650-7 ran the supercharger slower than either the -3 or -9, which means that the pressure ratio is lower. The lower speed means that the supercharger uses less power to drive, but runs out of capacity at a lower altitude. That is why it is called a "low altitude" engine.

If you like to believe they were interchangeable, go ahead; no argument here. From the owners I know, it isn't the case. It could ALSO be that these late-day Merlins have been modified over the years so they are not very interchangeable, but ... maybe they started out that way. Could be so.

The old crew chiefs say no, but that could be just wanting to run US engines in US planes. If they never installed a British Merlin, maybe they just don't know. Also could be. I have NOT gotten into Merlins the way I have Allisons.

One of the few things I can say for SURE about the Merlin is that when Joe Yancey got the Dago Red engine, he had to do custom machining to get the supplied spare parts to fit within specified tolerances. We didn't know if the parts were Packard or RR ... we ujsed what was supplied. You can make of that whatever you want. Without guessing, I KNOW the Merlin 224 was a basically stock Packard-built Merlin 24. Ditto the other 220-series post-war engines.

Some owners of the -3s and -7s say it isn't so (intercahngeability). I don't know all that many ... maybe 8 or so. I am not an owner but will usually believe an owner over a book, especially when I ride with him in the plane and note he is flying it EXACTLY to book numbers and is getting book speeds exactly as expected ± a few knots at the book manifold pressure and rpm.

I'd bet Rod Lewis and Tom Friedkin own both US and British Merlins at the same time. They should know but I only see them at airshow time.

So no argument here other than there are some guys with pretty good credentials who say otherwise. They certainly could be wrong.

I know one guy who had a crank made, but I don't know the specs and would not care to guess whether it was made stock or not. Runs good, but we haven't discussed specs at all.

Most of the -7s I see these days have transport heads on them (... not stock for a -7), modern mags coupled with the stock Merlin carbs, stock superchargers, gearing and accessories, but some are running different reduction gears from different model Merlins or even custom reduction gears for the racers.

The most stock V-1650-7 I have seen in years is at the Museum now and has transport heads with almost everything else as stock as possible ... except for more modern mags and a modern new spark plug wiring harness. I can get pics Saturday and also of a single-stage, 2-speed Merlin 224 ... but the pics likely won't tell you anything you didn't probably already know.

All the other -7s I've seen in the last 5 - 6 years won't tell you much about -7s because they aren't stock in several areas ... depends on parts available. So this really COULD be a case of modern -3 and -7 engines simply not having the parts to BE interchangeable. I can't say and don;t wish to guess. I know we are running out of Merlin parts and they are flying parts now they'd have thrown away 25 years ago.

We fly two -7 engines at this time and Ken Wagner flies a Rolls Royce Merlin ... but I have never looked at the data plate for the exact engine model (the cowling has always been on it ... except when they pulled the engine and sent it to Mike Nixon). I will ask next time I see Ken. His plane is Lady Alice and is as bone-stock as it can be except for the panel, which has some modern consessions. BEAUTIFUL P-51.

Here is Ken's P-5D:



and here is Dr. Ken Wagner, as happy as every other time I've ever seen him:



If I flew a P-51D, I'd probably be happy all the time, too!

Cheers.

Update:

Hey Wayne,

Found some info that says the Merin 266 was a Packard-built Merlin 66 and the V-1650-7 was similar to a Merlin 66, but modified for the P-51D. The Mods are not specified in the only place I found these data.

Know anything about the differences between a Merlin 266 and V-1650-7? Or was it simply renamed and they were the same engine otherwise? I know they went to American accessories, such as vacuum pumps, etc. Know of any OTHER modifications?

Merlin 266 had SBAC (Society of British Aircraft Constructors) output shaft splines.
V-1650-7 had SAE (Society of Automotive Enginners) output shaft splines.

These pictures show the differences.
http://upload.wikimedia.org/wikipedia/commons/e/e5/RR_Merlin_labeled.jpg
http://usautoindustryworldwartwo.com/images/Normandy/allison-v-1710-107w-1.jpg

I think, but am not certain, that they used different carburettors. Other than that, I cannot think of any major changes.

US built 2 stage engines had a different drive system for the supercharger (epicyclic) than did British built Merlins (Farman).

I knew the Merlin 66 was used in LF Spits, but never considered the V-1650-7 to be a low-altitude engine since it typically fought in Europe at 20 - 30+ thousand feet. Would be nice to find out for sure, but I see te V-1650-3 was similar to a Merlin 63 high-altitude version.

Why the hell would they go from a high-altitude to a lower-altitude engine for a fighter supposed to escort bombers?

Makes no sense to me, but I don't really have the time right now to look at it.

Cheers.

Climb and mid-altitude (c. 20,000ft) performance. I'm sure that is the reason.

GregP said:

If you like to believe they were interchangeable, go ahead; no argument here. From the owners I know, it isn't the case. It could ALSO be that these late-day Merlins have been modified over the years so they are not very interchangeable, but ... maybe they started out that way. Could be so.

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When I say interchangeable, I mean between equivalent series. There will be some components in a V-1650-3 that can't or shouldn't be used in a V-1650-7 or -9, simply because the part has been strengthened and may be bigger and thus will not fit on the earlier engine.

btw, the 220-series Merlins were not post war - they were very definitely war era engines, serving in Mosquitoes and Lancasters.

The "transport" Merlins were the 600 and 700-series.

The V-1650-9 is a 100 series engine, so most parts should be a direct swap for those in a Merlin 130/131 (from a Hornet). But with end-to-end lubrication teh crankshaft would be unsuitable for early marks, and -3 and -7 crankshafts wouldn't work in a -9 becuase the bearings would not be properly lubricated, if at all.

Re. 'low' vs. 'hi' Merlins - when compared with other similar engines, the Merlin is almost always a high altitude engine. However, once we compare one 2-stage Merlin with another 2-stage Merlin, we will always call the one with rated height of ~20000 ft a low-alt version, the one with rated height of ~25000 will be called mid-alt version, the one with rated height of ~30000 ft would be the hi-alt version.
Hope it makes sense

The Merlin 226 (Packard production) was used on the Spitfire Mk.16?

tomo pauk said:

The Merlin 226 (Packard production) was used on the Spitfire Mk.16?

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No, it was the 266, which actually started life as the Packard-built 69, but became surplus to requirements due to them no longer being needed on the Canadian-built Mosquito. First conversions were done here, then taken over by Packard, and, because the mods essentially produced an engine identical to the Merlin 66, it was given the number 266.

Ah, I see - not 226, but 266. Thanks.

Hi Wayne,

I DO belive they were very equivalent and, yes, I was talking about interchangeable. Maybe we're saying essentially the same thing.

Again, I donlt condsider anything thath has a service ceiling of over 41,000 feet to be low altitude ... but maybe it starts losing speed versus the other engines at ... say ... 26,000 feet on up. I was talking baout the PLANE it was used in.

I'll ask tomorrow if the guys at Planes of Fame think the -7 was a "US-modified" Merlin 66. Perhaps it really was and, if so, they'll likely know the exact differences since they have operated virtually all Merlin marks over the years.

I'm leaning toward believing you are right, but will ask and report back, probably Sunday ... assuming the Hintons are there. Maybe not since our F-86F was just flown east for a show yesterday ... Steve usually flies it with the Horsemen. If not, I'll STILL get pics of the -7 and 224 ... assuming the -7 hasn't been installed this weel, that is.

Best regards, - Greg

According to Rolls-Royce the -7 was the same as the -3, but with different supercharger gear ratios (5.80 7.35 against 6.39 8.095.)
Both were the equivalent of the Merlin 61.
Years ago, I read, but was never able to verify, that Packard used larger, and fewer, bolts to attach the supercharger to the crankcase, which wouldn't have helped interchangeability, never mind the different intercooler header tank layout.

A Merlin -61 makes WAY more sense to me for a V-1650-7 since the P-51D, it's primary mount, usually operated at 20,000 to 35,000 feet, at least in Europe.

Lumsden notes the V-1650-3 as equivalent of Merlin 63, the V-1650-7 as 'similar' to the Merlin 65, 66, 68, 69. FWIW.

stan reid said:

Sorry to go off topic for a minute but does anyone know why these engines weren't dohc? Was it cost or that the increase in power didn't significantly make up for the extra weight or, being bulkier, the loss in aerodynamics?

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I see that the Napier Lion was dohc.

Both the Allison and the Merlin were 4-valve per cylinder SOHC and didn't need to be DOHC. The SOHC design was and IS quite good in both engines. Nothing wrong with either DOHC or SOHC as long as it does the job equally as well as the other would, and these DID.

A lot of things change over time. Valve springs are one of them. They look simple but changes in alloys, heat treatment, and finishing techniques (shot peening/bead blasting) and other things mean that the rpm limits of different types of valve trains change enormously over the years. Push rod engines with cam/s in the block now routinely operate at speeds that DOHC only reached in racing applications in WW I or the 1920s. And they last hundreds of thousands of cycles longer. If an engine in the late 1920s managed to go 500 hrs without breaking a valve spring the Maker took out full page ads in magazines celebrating/advertising the event. As valve springs got better the need for complicated valve mechanisms that kept reciprocating (as opposed to rotating) valve train parts as few and as light as possible.

Not even a rocker arm or cam follower. It doesn't get much simpler for the valve spring.
The gears and shafts needed to operate 6 cams for a 12 cylinder engine are another story.
As valve springs got better they could simplify the cam drives at the expense of using cam followers or rocker arms.

Please note that after a change of designers and over 10 years Napiers next engine used long pushrods.
napier rapier | 1935 | 0548 | Flight Archive


despite running at 3900rpm at full throttle.
Granted it was only a 539 cu in engine and had small cylinders and valves. 16 cylinders to do what a Lycoming IGSO-540 will to today ( or would do in the 1960s)

Shortround,
Why were there 6 cams vice 4 (2 per bank) in a V-12?
Cheers,
Biff