Spitfire and the Merlin 100 Series

[BarnOwlLover]

I wonder why this wasn't considered, aside from the fact that the first Griffon powered Spitfires came before the Merlin 100 was fully developed. The Merlin 100 series of course powered the de Havilland Hornet (130 series) most notably, and I believe formed the basis of the Packard V-1650-9/11/23/25 that powered the P-51H Mustang and the XP-82/F-82B Twin Mustangs. I think that if it was workable, a Merlin 100 powered Spitfire would've been an interesting proposition.

Only thing is that, like the Griffon versions, fuel capacity would've had to have been increased, since the Merlin 100s were capable of making about 300+hp more than the Merlin 60 series engines. Not to mention that more power does also usually mean more strengthening, which generally means that the resulting aircraft will be somewhat heavier, though the power should hopefully offset that.
But I do wonder why this wasn't seriously pursued in war time (I'm betting that some Spitfires flying today are using later engines based on the 100 series that were sold commercially), aside from the fact that the Griffon Spits took the lead in development terms after the Mk IX and Mk VIII were developed.

 

[tomo pauk]

I agree with the idea. The Merlin 100 on the Spiteful is also attractive IMO.

 

[Shortround6]

A deeper dive into the power levels is warranted.
As is the availability of 100/150 fuel instead of 100/130.

I think you will find that the two stage Griffon offered 100-200hp over the 100 Series Merlins if both were running on the same fuel.
The Griffon also offered higher altitude

Like:
engine...............................................high gear 100/130...................................high gear 100/150
Merlin 130.......................................1690hp/18,000ft.........................................1845hp/14,250ft
Griffin 60 series..............................1810hp/21,000ft.........................................2060hp/15,750ft

 

[BarnOwlLover]

As for altitude, the XP-51G (a lightweight experimental P-51 Mustang powered by a Merlin 100 series engine) did apparently reach 45-46,000 feet in testing, though the Merlin 130s in the DH Hornet were rated for about 37-38,000 ft service ceiling (though a Hornet in testing achieved almost 42K ft if I remember correctly).

The big thing that I'm kind of looking at is redesign of the Spitfire airframe. Even though the Griffon engine Spits were evolutions of the later Merlin powered Spitfires, they did have heavy redsigns to accept the heavier Griffon engines, such as the lengthened noses and fuselages, different thrust centerlines, etc.

Interestingly, the Spiteful was initially planned to have a Merlin powered variant. This seemed to be a contingency plan for if the Griffon 60 series engines ran into technical or supply issues. Of course, seeing that the Spitfire XIV and such were Griffon 60 powered, the Merlin-powered Spiteful became redundant.

 

[yulzari]

A neglected comparative issue is the comparative torque of the two. The larger capacity of the Griffon should give it a greater torque than the Merlin. I have no figures to make the actual comparison.

 

[Shortround6]

A neglected comparative issue is the comparative torque of the two. The larger capacity of the Griffon should give it a greater torque than the Merlin. I have no figures to make the actual comparison.

It can be computed fairly easily.
torque = horsepower x 5252 divided by the rpm.

However in the figures posted above on 100/130 fuel the Griffon makes about 7% more power about 3,000ft higher. The Merlin will be losing about 2.6-2.7% of power per 1000ft of altitude. or the Merlin will be down to about 1560hp at 21,000ft if I have done the math right.

Is the Merlin 130 going to be enough lighter and lower drag than the Griffon installation to make up for having 230-250hp less?
Power to weight of the whole plane, not the power to weight of the engine installation.

IF the Merlin powered late model Spitfire or Spiteful can make do with 86-87% of the power after the smaller engine is taken into account then it may be a good deal.

And lets not forget that for speed the Griffon is going to give more exhaust thrust. It will more than the Merlin in climb but exhaust thrust varies with speed and at climbing speeds it is less that at high speed for the same amount (mass) of exhaust.

 

[BarnOwlLover]

It probably depends on power-weight ratio and such. The Spitfire IX with the Merlin 60 series engines did have (I've read) a climb rate of 4900 ft/min. Though, that also varies with height as well. But the Spitfire IX had a normal takeoff weight of 7500 lbs, while later Griffon engined Spits had TO weights of above 9000 lbs.

Also a note is that the DH Hornet (2X Merlin 130 series) was described as having an excess of power by Eric Brown. But that was a twin engine aircraft with engines that made nearly 2100bhp and had a normal TO weight of under 16,000 lbs, and a max TO weight of less than 19,000 lbs. So that's also a possible reference for power to weight ratio.

But then again, the Spitfire XIV weighed less than 8500 lbs with a Griffon.

 

[pbehn]

You need a different war, the Griffon just made it into service before the first jets were in service, the P-51D actually came into service in Europe after Germany and UK had their first jets operational.

 

[Shortround6]

twin engine aircraft with engines that made nearly 2100bhp and had a normal TO weight of under 16,000 lbs

Great, what altitude are you flying at?

The engines may have been good for 2070hp (close enough) at just under 2,000ft. using 25lbs of boost.
That is in low gear, the question is what power does it make in high gear and at what height?

Aircraft data card says 1890hp at 14,750ft using 25lbs boost. Does not include RAM I believe. Now as you climb above 15,000ft you will loose about 2.5% of power for every 1000ft


(just about all non-turbo engines hit zero power at around 55,000ft)
The Griffon makes 2060hp at 15,750ft at 25lbs of boost. from a different source.

Now at low altitude (like 500ft) the Griffon makes 2300hp using 25lbs of boost.

 

[thunderbird]

Mk XIV empty weight is nearly 1600 pounds heavier than a Mk IX, gross weight is 1100 pounds for the Mk XIV heavier than the Mk IX. The Merlin 130 has essentially the same power as the griffon 65. To me its obvious which plane would be better. Except i strongly suspect there was untapped capability in the 2240 cubic inch griffon versus the 1650 cubic inch merlin, like perhaps a 3000 hp griffon.

 

[Shortround6]

The Merlin 130 has essentially the same power as the griffon 65

The 60 Series Griffons had over 10% more power than the Merlin 130, see earlier posts.

10% is not "essentially" the same power.

Now, can you install a Merlin 130 for the same weight as the engines used in Spit MK IX?
The Merlin 130 seems to be around 50-80lbs heavier than Merlin 60-70 series engines.
Can you cool the Merlin 130 making 2000hp using the same size radiators as the 60-70 series engines?
Can you use the same propeller on the Merlin 130 that you used on the 60-70 series engines?
Or do you need a around a 12ft four blade prop or a smaller 5 blade prop compared to the 60-70 series engines?

 

[tomo pauk]

It should be far easier to install the Merlin 100 on a Spitfire vs. installing the Griffon.

 

[Shortround6]

It should be far easier to install the Merlin 100 on a Spitfire vs. installing the Griffon.

It is easier, Just don't expect the same results with over 10% less power and with more weight than the engine, radiator, prop from the base line MK IX.

 

[pbehn]

Wasnt the Griffon fitted because it was available long before the 100 series Merlin?

 

[Shortround6]

Wasnt the Griffon fitted because it was available long before the 100 series Merlin?

yes and yes.
They were flying the single stage Griffon in Nov 1941. (DP845)
The 2nd prototype showed up in August of 1942.
No 41 squadron became operational in April of 1943.


The MK XIV with the two stage engines showed up for test (six of them) in the Spring/summer of 1943,
First production aircraft showed up October of 1943.
Spitfires with Merlin 66 engines (or any other kind) don't get 150 octane fuel until April of 1944.

100 series Merlins, of any kind, show up when?

 

[wuzak]

As for altitude, the XP-51G (a lightweight experimental P-51 Mustang powered by a Merlin 100 series engine) did apparently reach 45-46,000 feet in testing, though the Merlin 130s in the DH Hornet were rated for about 37-38,000 ft service ceiling (though a Hornet in testing achieved almost 42K ft if I remember correctly).

A Griffon powered Spitfire PR.XIX would reach 50,000ft post war.

 

[BarnOwlLover]

IMO, biggest issue with the Merlin vs Griffon for the Spitfire and Spiteful (design-wise) is weight. On just the broad figures, a Merlin installation vs the Griffon installation would have a 400-500lb advantage to the Merlin. But the Merlin would be operating with about 10% less max power. However, I do expect that other considerations that were Griffon related lead to the Spiteful having a gross weight (Wikipedia doesn't indicated max take off or normal take off) of 9950lbs, with the last Spitfires having essentially the same weight. The heaviest Merlin Spitfire I saw as far as normal take off weight was the PR XI that had a normal TOW of over 8000 lbs. The Spitfire IX had a max TOW of 9200-9300 lbs.

You do have to remember that the Spitfire had to be redesigned fairly extensively to take advantage of the Griffon, as the Griffon offered several hundred more HP, but was also 400-500lbs heavier. Not to mention that other parts had to be beefed up (radiators, oil coolers, intercooler, etc).

Of course, the fact that the later Spitfires (Mks 21, 22, and 24) weighed as much as a loaded Spiteful (using similar engines) is sort of academic, given that the F/FR 14 was the most common of the Griffon powered Spitfires (only one at least to see major service in World War II; Mk 18 just missed the war, Mk 21 saw some use, but not much in 1945, and the Mk 22 and 24 were basically post war). That version of the Spitfire had a normal take off weight of 8400lbs.

Thus, from a pure performance and engine availability standpoint, the switch and redesign to accommodate the Griffon was probably worth it. A Spitfire with the Merlin 100 might have pushed the speeds and climb-rate of the Mk 14, given the weight and speed of the PR 11 (430mph), and the normal take of weight of the Spitfire 9 series normal loaded weight of 7400 lbs.

However, that's basically conjecture, since, one, an official Merlin 100 powered Spitfire never happened, two, I'm speaking purely from power to weight ratio (the Yak-3 had to top speed of quite a bit over 400 mph with 1300 bhp, but weighed less than 6000 lbs loaded), which leads to three, there's probably other factors that could sway things to favor one camp over the other.

 

[BarnOwlLover]

yes and yes.
They were flying the single stage Griffon in Nov 1941. (DP845)
The 2nd prototype showed up in August of 1942.
No 41 squadron became operational in April of 1943.


The MK XIV with the two stage engines showed up for test (six of them) in the Spring/summer of 1943,
First production aircraft showed up October of 1943.
Spitfires with Merlin 66 engines (or any other kind) don't get 150 octane fuel until April of 1944.

100 series Merlins, of any kind, show up when?

I don't think the Merlin 100 was even much of a thought until the de Havilland Hornet was designed and DH decided they wanted 2000+bhp Merlins to power it. de Havilland probably favored the Merlin over the Griffon for weight considerations (see post above and given the Hornet's role as a light weight twin engine fighter). That being said, I doubt the first Merlin 100s showed up much before the Hornet prototypes were ready (summer of 1944). A Merlin 100 ended up in a XP-51G (slightly modified XP-51F with the Merlin 100 replacing the Packard V-1650-7), but I'm sort of thinking that came after the Hornet prototypes first flew.

 

[wuzak]

I don't think the Merlin 100 was even much of a thought until the de Havilland Hornet was designed and DH decided they wanted 2000+bhp Merlins to power it. de Havilland probably favored the Merlin over the Griffon for weight considerations (see post above and given the Hornet's role as a light weight twin engine fighter). That being said, I doubt the first Merlin 100s showed up much before the Hornet prototypes were ready (summer of 1944). A Merlin 100 ended up in a XP-51G (slightly modified XP-51F with the Merlin 100 replacing the Packard V-1650-7), but I'm sort of thinking that came after the Hornet prototypes first flew.

I think de Havilland designed the Hornet around 2000hp Merlins as that is what Rolls-Royce were promising.

The 100-series Merlin was under development from about 1943.

 

[Shortround6]

Merlin 100s were intended for Lancaster IVs, Windsers, Replacements for the Merlin 85,
There were a slew of proposed or development models in the teens (like 110-114) for PR Spitfires and Mosquitos.
The commercial 600 series engine were just 100 engines with 500 added to the military number.

There was a lot of fooling around with accessory drives/gear boxes and different air bleed offs for cabin pressurization for different applications.

A lot I am leaving out but the end of the war slowed down or stopped some of them and RR had a hard time breaking into the commercial airline business.