Why was the Seafire Mk.III so slow?

[Admiral Beez]

According to Wikipedia, the Seafire Mk.III had a top speed of 359 mph, and that at a very high 36,000 feet. Presumably at lower altitudes where carrier fighters would often operate the Seafire was slower. For an aircraft entering service in late 1942 into 1943 this has to be slower than Merlin-powered Spitfires of the time. Presumably the weight of folding wings, arrestor hook, undercarriage and airframe strengthening would have contributed to its slow speed. But anything else, was the Seafire Mk.III tuned for slower top speed?

 

[EwenS]

The Seafire III, like the Seafire I & II was based on the Spitfire Mk.V with a two speed single stage supercharger Merlin. The Mark III was a Mark II with folding wings. Production only began around Sept 1943 IIRC.

By mid-1943 the Spitfire models in production were the two speed, two stage Merlin 60 series Marks VII/VIII/IX.

The Seafire III was intended to be superseded by the Griffon engined Mk.XV from about mid-1944. A decision that dated back to 1942. But there were development problems and it didn't enter low rate production until Sept 1944 with the first squadron receiving them in May 1945 in Britain intended for service on the second batch of light carriers then due to complete by the end of 1945. They began to arrive in Australia a couple of months later to re-equip the Seafire III squadrons in the BPF. Ultimately however only 801 in Implacable got them in Sept 1945.

 

[ThomasP]

Seafire Mk I/II/III all had single-stage/single-speed superchargers. The Mk III used either the Merlin 45, 46, 50, 55, or 55M.

If Wiki says the Mk III was doing 359 mph at 36,000 ft they got it wrong. The power curve for the Merlin 55 was similar to the Merlin 45 at the same rpm & boost, so maybe 358 mph TAS at 16,000 ft? The Merlin 55M was a low altitude engine with a reduced impeller diameter and IIRC its Vmax was at around 9,000 ft. The Seafire Mk III with a Merlin 46 would have had a critical altitude about 1,500-2,000 ft higher, so maybe 358 mph at 17,000-18,000 ft?

 

[Geoffrey Sinclair]

Agreed the Seafire III quoted altitude is way too high, top speed about right but around 20,000 feet lower for the Seafire F.III with Merlin 55 and about 10,000 feet lower again and slower for the LF.III with Merlin 55M, the engines were about the same as the 45 and 45M fitted to mark V so maybe search for their performance and round down. The 1945 Janes quote the 45 as 1,470 HP at 3,000 RPM at 9,250 feet, the 45M as 1,585 HP at 3,000 RPM at 2,750 feet.

Westland started F.III production in April 1943, but only 8 built to end August, after 85 were built it switched to LF.III in December 1943 and continued LF production until July 1945, plus another 103 F.II June to September 1944. Cunliffe Owen started LF.III production in November 1943, also finishing in July 1945 with 350 built. Westland continued to build Spitfire Vc until October 1943, Vickers stopped Vc production in August.

When it comes to the Seafire XV Supermarine built 6 prototypes February 1944 to March 1945, Westland built 1 in August 1944, another 8 in October and November 1944, then production from January 1945, Cunliffe Owen started XV production in March 1945, Westland mark XVII in April, meantime Vickers started F.45 production in February. So from April to July 1945 there were two lines of mark III, 2 of XV, 1 of XVII and 1 of F.45.

 

[Admiral Beez]

So maybe 358 mph at 17,000-18,000 ft?

For a carrier or landbased fighter in 1944 this isn't great, but still faster than the A6M5 then entering service. Wikipedia has this later Zero topping out at 351 mph.

Mitsubishi A6M Zero - Wikipedia

en.wikipedia.org

 

[Clayton Magnet]

For a carrier or landbased fighter in 1944 this isn't great, but still faster than the A6M5 then entering service. Wikipedia has this later Zero topping out at 351 mph.

Mitsubishi A6M Zero - Wikipedia

en.wikipedia.org

Seafire III was no slouch, even though it was based on the "old" Spitfire Mk.V. Below about 15000Ft, it was probably the highest performing fighter available to ANY navy in 1944.
This is from Armoured Aircraft Carriers

"...The Merlin 55 was very similar to the 45, but had automatic boost control and barometric governing to reduce the load on the pilot. These refinements, along with the aerodynamically "cleaned-up" wing and four-bladed propeller, boosted the IIIs top speed by some 20mph at all heights over the IIC

The F III was designed to fight between 8000ft and 15,000ft and proved to be 20mph faster than the IIC at all heights. In operational service it proved to be faster than the F6F-3 Hellcat between 3000ft and 14,000ft, and was evenly paced with the F4U-1A Corsair between 6000ft and 10,000ft..."

 

[EwenS]

From "The Seafire. The Spitfire that went to sea" level speeds in mph for Mark Ib/IIc/LIIc/FIII/LIII/15

Sea level - 295/280/316/304/331/352
5,000ft - ?/?/?/?/?/371
6,000ft - ?/?/335/?/358/?
9,500ft - ?/?/?/?/?/371
11,500ft - ?/?/?/352/?/?
13,000ft - 355/335/?/?/?/?
13,500ft - ?/?/?/?/?/383
15,000ft - ?/?/?/350/?/?
19,000ft - 341/345/328/345/331/?
23,000ft - ?/?/?/?/?/378

By way of comparison the figures I have for the F6F-3 & -5 are
Sea level - 312 (or 324 per another source)/318
20,000ft - ?/400
25,000 ft - 388/?

F4U-1 Corsair II
Sea level - 320
19,900ft - 417
24,000 ft - 392

The RN intention was that the Seafire III would be the premier shipboard interceptor for 1943, the Seafire XV for 1944 and for 1945 either the Seafang 32 or Seafire 45 series, with the latter finally being chosen due to its anticipated better handling around the flight deck. Each generation was expected to have a life of about 18 months before enemy aircraft performance overtook it. But development and production delays pushed each generation backwards.

 

[Denniss]

I have informed the Wikiproject Air to take a look at the spec changes introduced in 6/2019. Might be just a typo and 3600 was meant instead of the illogical 36k

 

[Admiral Beez]

I have informed the Wikiproject Air to take a look at the spec changes introduced in 6/2019. Might be just a typo and 3600 was meant instead of the illogical 36k

Maybe it's supposed to be 3,600 meters (36,000 cm), so ~12,000 feet.

One of my pet peeves on Wikipedia is inconsistent ordering of units of measure. Some aircraft specs are shown in metric first, followed by imperial, while other aircraft show imperial first followed by metric.

 

[Denniss]

AFAIR en wiki handles air specs by using units of the home country first so metric for most of european aircraft but imperial for UK aircraft

 

[wuzak]

With Merlin 50, 321mph @ 4,000ft, 352mph @ 10,500ft, 328mph @ 24,000ft.

Seafire Mk. III Trials

 

[Admiral Beez]

Would a folding wing, Mk.III equivalent Seafire entering service in spring 1940 but with the Fulmar Mk.l's Merlin VIII have been a slug? I have to think that even a sluggish folding wing Seafire would have been useful in the MTO in 1940-42.

List of Rolls-Royce Merlin variants - Wikipedia

en.wikipedia.org

Merlin VIII

1,080 hp (805 kW) at 3,000 rpm

1,275 hp (951 kW) at 3,000 rpm, +9 psi (62 kPa) boost, sea level with 100 octane

 

[EwenS]

Well of course it would have been useful.

But take a moment to consider how you achieve it. Remember at that point you not only need folding wings, but also a hook, catapult spools, strengthened airframe etc etc.

ADM 1/10752 Notes of a Meeting held 4 Jan 1940.

There was discussion of obtaining Spitfires and/or Hurricanes for both use as shore based fighters for defending Naval bases and for basing on carriers. For the latter role folding wings would be required. It was reported that:-

"..... The Firms concerned were already working on designs for modified wings for this purpose and they hoped to be in a position to report upon the possibilities very shortly. It was expected that it would be at least nine months before Aircraft of these types with folding wings would come into production. ...."

A 'hooked' Spitfire was actually flown in Oct 1939 and Joseph Smith was working on a folding wing design (unlike the Seafire Mk.III they would have folded like those of the Firefly to sit alongside the fuselage. By Dec 1939 various Supermarine proposals were put forward, the quickest would have seen a standard Spitfire with folding wings, with a prototype in 5 months and 50 available after 16 months. Cutting the prototype would have saved 2 months. The cost? 75 production Spitfires so it wasn't allowed to go ahead. (These timings are all from the point at which instructions to proceed were given).

In mid-1942 the Admiralty requested a scheme for the upward folding wing as a result of work done by Supermarine and General Aircraft Ltd on an old Mk.I airframe in April that year. The first production Mk.IIc MA970 was converted Oct/Nov 1942. But getting it into production was a different matter. The first folding wing production Mk.III from Westland didn't fly until May 1943 and Cunliffe-Owen until Oct 1943. 30 early aircraft got fixed wings instead. The first 50 with folding wings took until almost the end of 1943 to produce. (So nearly 20 months from Supermarine/GAL getting that old Mk.I to play with).

So, no matter how you dice & slice it, to get your folding wing Seafire in early 1940, regardless of Merlin version used, means having an outline design ready by the end of 1938 at the latest i.e. before the RN got full control of the FAA and before it realised that the RAF wouldn't be able to protect its Naval bases like Scapa Flow (that only became clear after the outbreak of WW2 and that was the initiator for the acquisition of a new single engined, single seat, high performance fighter).

Now the first production Spitfire I didn't fly until 15 May 1938 with the first squadron receiving its aircraft in Aug. By the end of 1939 there were only about 13 Spitfire squadrons. So understandably the RAF doesn't want to give up any production.

So who else can build them? Well Fairey was the obvious choice, but firstly it was already committed to developing the Fulmar. At the end of 1938 the Admiralty tried to persuade Richard Fairey to build Spitfires for them. But he wasn't interested in building someone else's aircraft designs (still peacetime - more profit in building his own designs). So you need to find a manufacturer with spare production capacity even if Supermarine have the design capacity in late 1938, which is perhaps open to question given the other projects they had in progress at the time.

 

[Admiral Beez]

With Merlin 50, 321mph @ 4,000ft, 352mph @ 10,500ft, 328mph @ 24,000ft.

Seafire Mk. III Trials

Very interesting, thanks for sharing. I see that the trials report indicated mph. Would that be knots or ground speed miles? Did WW2 aircraft have a ground speed indicator? Or do they just convert knots to ground miles?

Now the first production Spitfire I didn't fly until 15 May 1938 with the first squadron receiving its aircraft in Aug. By the end of 1939 there were only about 13 Spitfire squadrons. So understandably the RAF doesn't want to give up any production.

So who else can build them? Well Fairey was the obvious choice, but firstly it was already committed to developing the Fulmar. At the end of 1938 the Admiralty tried to persuade Richard Fairey to build Spitfires for them. But he wasn't interested in building someone else's aircraft designs (still peacetime - more profit in building his own designs).

Excellent points. If only Fairey wasn't such an obstructionist, even though a pragmatic one.

 

[PAT303]

Very interesting, thanks for sharing. I see that the trials report indicated mph. Would that be knots or ground speed miles? Did WW2 aircraft have a ground speed indicator? Or do they just convert knots to ground miles?

Excellent points. If only Fairey wasn't such an obstructionist, even though a pragmatic one.

From what I've read Sydney Camm wasn't much better. .

 

[Admiral Beez]

From what I've read Sydney Camm wasn't much better. .

I imagine Lord Beaverbrook knocked some heads.

 

[wuzak]

Very interesting, thanks for sharing. I see that the trials report indicated mph. Would that be knots or ground speed miles? Did WW2 aircraft have a ground speed indicator? Or do they just convert knots to ground miles?

Speed was measured using pitot tubes, the reading is affected by the air pressure and temperature, so it changes with altitude.

Indicated Air Speed is what the gauge says based on the pitot tube.
True Air Speed is calculated from IAS and the air temperature and pressure.

At seas level TAS and IAS are the same.

But if TAS is held constant, the IAS falls with altitude.

 

[EwenS]

I imagine Lord Beaverbrook knocked some heads.

The odd thing is that Beaverbrook gets credit for a lot of things but are they really deserved?

Minister of Aircraft Production - 14 May 1940 to 1 May 1941. He took over when aircraft production was already increasing. By sheer force of personality he resolved a number of issues but not all. He resigned from the post.

Minister of Supply - from 29 June 1941 to 4 Feb 1942.

As for Fairey, the problems went on long after Beaverbrook's departure from both the above positions. First Lord of the Admiralty to Churchill 30 April 1943:-

".... Nobody has suffered more bitterly than the Admiralty from the continued failure of Faireys to live up to their promises. ...."

Of the 10 major problems identified in the Barracuda that had led to delays, 7 were attributable to the Admiralty and / or MAP changing requirements, equipment etc. The others were placed firmly at Fairey's door and were considered to have caused the greatest delays. In addition:-

"... Also the exceptionally large number of errors in both production drawings and tool drawings, many of which would have been discovered by a more competent organisation before the drawings were issued, has materially contributed to the long delay in bringing this aircraft into production."

By Spring 1943 the Admiralty had started to put naval officers with pilot experience into factories producing naval aircraft as "overseers" in the same way the RAF was already doing. These were in addition to MAP supervision. The first appointee went to Fairey Hayes factory responsible for the Firefly, followed by Blackburn Brough responsible for the Firebrand.

So there were a lot of questions being asked about Fairey as an organisation as a whole.

 

[Admiral Beez]

So there were a lot of questions being asked about Fairey as an organisation as a whole.

Interesting. Fairey sounds like a British equal to Brewster. I wonder what the FAA thought of their USA-rejected F3F Corsairs.

 

[SaparotRob]

I initially thought that too but the Brewster had saboteurs and outright criminal activities.