Merlin Weight Query

This goes back to a thread I posted here a while back asking about the Merlin variants. If the engine was a 502, was it based on the 25 and was a civil-rated single stage Merlin variant (the 600 series were based on a civil rated 100 series engine and had a two speed/two stage supercharger)?

The 500 series is the civilian version of the T24/2.

This goes back to a thread I posted here a while back asking about the Merlin variants. If the engine was a 502, was it based on the 25 and was a civil-rated single stage Merlin variant (the 600 series were based on a civil rated 100 series engine and had a two speed/two stage supercharger)?

…And as far as RR299, the accident report stated that one engine was a 25 and the other was a 225.

The stbd engine was a -502, engine No: 305607.

DAI

The story about the Packard V-1650/Merlin 266 seems to have been perpetuated into the Spitfire lore, since various sources have stated that the repositioned intercooler caused the bulge. Since the Mk XVI was the first to have them and they had the Packard 266 in them, that’s probably where the legend started, as opposed to a production method change at Castle Bromwich you mentioned, as that’s where most Mk IXs were made, as well as it seems the XVI.

To pick up on one aside: the bulged upper cowling was not unique to Mk.XVIs, but also seen on late Mk.IXs. Although generally “blamed” on the Packard, apparently there is no change in the upper lines between RR and Packard Merlins and the change was due to a change in manufacturing methods at the Castle Bromwich factory.

My source for this is Edgar Brooks’ recent research into Supermarine records. If I’m distorting it perhaps he can put me right.

Just a couple of points. First the Merlin two stage supercharger deal.

All Merlins from the 60 series onward did use two stage superchargers, but there were sub-variants within the 60 series that were set up to give their best performance at various altitudes. Hence Spitfire VIIIs and IXs were often given the HF, LF and F designations (high alt fighter, low alt fighter and general purpose fighter respectively). The Merlin 61 was a general purpose engine, the Merlin 63 and 70 were high alt engines, and the 66 was a low alt engine. There was no such distinction with the Griffon, as the Griffon were given superchargers with a broader band of optimum performance. What the differences were I don’t know (this is from a Wikipedia article about Spitfire specs that does mention this and why there were no LF, F, or HF Griffon Spitfires).

And as far as RR299, the accident report stated that one engine was a 25 and the other was a 225. I don’t know where a link to the report is, but it was published and hopefully someone could advise us on where to find it. For the record, KA114 does have British built 25s in both nacelles that were installed during it’s restoration (FB26s–DHC built FB VIs–like KA114 did have 225s as stock).

And for the differences between the 266 and 66, it seems that on the Packard version, the intercooler was mounted differently compared to the R-R version (mounted up higher on the engine assembly), and that caused that bulged cowling–most late production Spitfire IXs had them, too, so that shouldn’t be used as an ID feature between an IX and a XVI.

And I’m quite surprised at how similar the Packard V-1650 and the Rolls-Royce Merlin are, since I heard that there were some fairly significant differences–major assemblies were similar or if not identical, but detail specs and parts were different. Instead, it seems that there’s just a few minor ones, mostly prop shaft types and minor fittings to suit various items. Like the prop drive shaft, the V-1650 was set up to use Curtiss Electric (P-40 F/L) or Hamilton Standard propellers (Merlin powered Mustangs), while the 266 had to be set up to use a Rolls-Bristol (Rotol) prop, and it seemed to be a simple change of drive shaft.

Chernkstewfan:
You are on the right track, but some of that information isn`t.
1:The V-1650-1 and Merlin 28 are two different engines, both made by Packard, and similar specification, the main difference being the 28 had a British SBAC splined prop shaft.

2: Quote: (only late in the Merlin’s life, as far as at least the British built versions, did they receive two stage superchargers that gave excellent performance throughout a very wide alt. regime–though all two-stage Griffon’s had them. I don’t know of the two-stage V-1650s had them).
Surely all two stage engines had two stage superchargers?!

3:The Merlin 266 was built by Packard, again with a British SBAC shaft, and the Merlin 69, also a Packard, had the US SAE shaft for the P-51.

4: I agree that the engine weights are very similar. All were made to UK thread sizes, with minor variations in components, good interchangeability and a few more major differences such as the supercharger drive on two stage engines.

5: There isn`t any difference in accessory drives between Rolls-Royce and Packard Merlins, the intercooler isn`t really an accessory. There is a difference somewhere on the Spitfire XVI, and I can`t remember what it was, even though I used to work on one! If I had to guess, it is probably only the addition of an integral header tank into the intercooler casting, which made it wider, which would mean as you say, you could retro-fit a Rolls-Royce engine into a P-51 without interference.

6: Where does it say RR299 had a Merlin 225 on one wing? I always thought it had Merlin 500s fitted, I`m sure that both engines had SU carburettors, in which case, if one was indeed a Packard 225, then it was one with a Rolls-Royce back end, which is quite possible, as this is occasionally done still today.

Pete

The only real equivalent between the R-R and Packard build Merlins is role and structure. Hence, the single stage and two stage SC engines should be of comparable weight within a certain tolerance-perhaps about 20 pounds or so at most based on my readings of Jane’s All The World’s Aircraft 1946 (sold in NA as Jane’s Aircraft of World War II–as Bill Gunston points out in the forward he authored in the present day edition, the latter title is a bit misleading).

The problem with determining the precise details is Rolls-Royce’s own numbering system. R-R initially gave the Packard V-1650 family numbers that were unused within the single- and two stage Merlin families. Hence, the V-1650-1 was the Merlin 28 to Rolls-Royce, and the V-1650-7 was the Merlin 69. All The World’s Aircraft, IIRC, did say that the “69” was based on the Merlin 66 as a general purpose engine for the P-51D/K Mustang (Mustang IV in RAF service). However, the Merlin 66 was a medium altitude engine used in low altitude/medium altitude versions of the Spitfire VIII and IX, and this the V-1650-7 and the Merlin 66 might have run differing settings for the supercharger (only late in the Merlin’s life, as far as at least the British built versions, did they receive two stage superchargers that gave excellent performance throughout a very wide alt. regime–though all two-stage Griffon’s had them. I don’t know of the two-stage V-1650s had them).

Then, very late in the war, did Rolls-Royce give the Packard V-1650s their own number range, with the “200” series. Problem with that is that the Merlin 69 and 266 were based off the Merlin 66 per most lists that I’ve read. So either they’re the same engine, with late examples given the 266 number, or the 266 was build to R-R/RAF specs as far as supercharging and other items.

However, that doesn’t make sense, because though all versions of the Merlin–whether or not built by Packard or Rolls-Royce–weigh the same basically and are built to the same dimensions, not all parts would interchange due to differing material specs and manufacturing practices. For an infrantry weapon, think of it as being like the “inch pattern” and “metric pattern” FN FAL rifles, where whole sub-assemblies would interchange, but detail parts often won’t.

The Packard engines had a different arrangement for the engine accessories at the rear of the engine, and that caused difficulties for placing the Packard built engines into Spitfire airframes without modifying the Spitfire’s engine mounts (I believe that the issue was the intercooler’s mounting, which is why Spitfire XVI’s had a unique upper engine cowling). It caused an issue with installing engines into airframes on occasion, as mentioned with the Spitfire XVI. However, many Mustangs use R-R built Merlins, apparently without modification to the engine mountings. And the DH Mosquito RR299 was reported to have had installed in it a Merlin 25 (R-R built) in one nacelle, and a Merlin 225 (Packard built) in the other when it crashed.

The biggest difference between the US and British Merlins seems to be accessory arrangement, though this also happened with the R-R built Merlins (the 100 series, especially the 130 series built primarily for the DH Hornet), which caused some issues for some British aircraft adapted to take the Packard V-1650 engines.

However, the engines all weighed the same basically, at least within a tolerance, provided that they’re at least within the same single stage or two stage families. However, the key phrase is “within tolerance”, because of minor manufacturing and material differences, especially with the accessories for the engines.

Equivalent marks between RR and Packard Merlins are not easy –

The Packard V-1650-1 / Merlin 28 seems to have no real RR counterpart though horse power-wise the RR Merlin 30 (used on Barracuda I and Fulmar II) has the same 1,300hp rating. The Merlin 28 was however built for Canadian Lancaster Mk I and III which in Britain used the RR Merlin 24 of 1,620hp!
The Merlin 29 was the V-1650-1 / Merlin 28 fitted with a splined airscrew shaft and was used on Canadian Hurricanes.
The Merlin 31 was again the same engine but for Canadian Mosquito XX and Australian Mosquito 40.

The Packard Merlin 33 was the direct equivalent of the RR Merlin 23 and used on Canadian and Australian Mosquitoes.

The Packard Merlin 38 was the direct equivalent of the RR Merlin 22 and used on Canadian Lancasters.

The Packard V-1650-3 / Merlin 68 was used on Mustang III (P-51B / C) – no RR equivalent hp-wise

The Packard V-1650-7 / Merlin 69 was used on Mustang III and IV (P-51C / D / F / K) – no RR equivalent hp-wise

The Merlin 224 was the direct equivalent of the RR Merlin 24 and used on Canadian Lancasters.

The Merlin 225 was the direct equivalent of the RR Merlin 25 and used on Canadian Mosquitoes.

The Merlin 266 was the direct equivalent of the Merlin 66 and used on Spitfire LF XVI

It probably is that easy, providing you are dealing with the directly equivalent versions of the engine. So for the V-1650-3, look at a Merlin 61 or 63, and for a V-1650 -7 look at the Merlin 66. They may not differ significantly in weight between these versions (as opposed to P vs RR)

I suspect (but don’t know for sure) that the closest equivalent of the Merlin 28 is the Merlin 22, but it may be the 20.

I don’t think that there is a Packard equivalent of the Merlin 85.

Thanks, folks! Should’ve realised it wouldn’t be that easy!
The reason for the question was that I read an article about Maurice Hammond some time ago in which he said that the Packard engine had half the number of bolts around the supercharger casing and I just wondered if they did some other things that may (or may not!) have saved weight
Regards
Dave

The dry weight of the RR Merlin (with 2.5 % tolerance) varied from 1,385lb for the Merlin 1 to 1,650lb for the Merlin 85.

The Packard V-1650-1 (Merlin 28) was produced for the Canadian-built Mosquito and Lancaster, the V-1650-3 (Merlin 68) and V-1650-7 (Merlin 69) were essentially the same as the Merlin 61 with two-speed two-stage supercharger and used in the P-51B/C and D Mustang respectively. Packard also built the Merlin 266 (1,640lb) for the Spitfire Mk XVI.

There are so many different versions of each that there isn’t a definitive answer. The difference between, for example, single-stage Rolls-Royce and Packard Merlins would be primarily in the carburettor, which would be negligible. The castings are the same weight.

Pete

Does anyone know the difference in weight between the Rolls Royce and Packard Merlin?

The answer will depend on precise versions, but I believe they were very close.
(Could be around 50lb difference).
Further info in “British Piston Aero Engines and their Aircraft”

(Just to be pedantic, I suppose the answer is “yes”). 🙂