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Thread: Spitfire Mk 1 Performance - Propellers - Hornchurch June 1940

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    Spitfire Mk 1 Performance - Propellers - Hornchurch June 1940

    Anyone ever noticed how difficult it is to pin down the performance figures for the Spitfire Mk 1? Obviously, in the main this is because by the end of 1940 the Mk 1 was such a very different aeroplane to what it was when it entered service in 1938. But why is it so difficult to nail the performance figures for it in its typical Battle of Britain configuration? Having done some research, here is the story, as I have pieced it together from various sources. I think it highlights one of the most impressive, critical, but unsung endeavours of the whole Battle of Britain. But, can anyone shed any more light on it? In particular I would like to know more about what was being said and what was happening at RAF Hornchurch during the first half of June 1940.

    On the morning of 23rd May 1940 Al Deere, flying his Spitfire Mk 1, KIWI 1, N3180 from RAF Hornchurch over northern France became the first Spitfire pilot to have an officially confirmed victory over the Messerschmitt 109. This in itself makes N3180 a historic aircraft and the story has been told many times. But the plot thickens. N3180, the 416th production Spitfire was not entirely standard. First flown on 13th November 1939, it was one of a small batch of the RAF's second order for 200 Spitfire Mk 1s to be trial fitted with a Rotol constant speed propeller. At that time the 3 bladed de Havilland variable pitch propellers with just two settings - fully fine or fully coarse – were still standard. Although they were a big improvement on the original two bladed, fixed pitch wooden propellers, they still lacked performance flexibility. The first of the Rotol batch, production no 413, N3171 was retained at Boscombe Down for flight trials, recording some impressive figures. The others were tested operationally by 54 Squadron, probably N3172, N3173, N3174, N3176, N3180, N3183, N3184, N3185, N3187 and N3188. Although, apparently initially assigned to 74 Squadron, also based at RAF Hornchurch, N3180 was taken on charge by 54 Squadron and had become Al Deere's KIWI 1, KL-B in early 1940.

    Interestingly and possibly very significantly on his return on 23rd May Deere lunched with Robert Stanford-Tuck, who had just arrived at Hornchurch with 92 Squadron to start patrols over the French coast. Tuck was well known at Hornchurch, having been there with 65 Squadron from August 1936 until just a few weeks earlier in early May, when he had received his posting. Their conversation must have at least touched on the morning's engagement and the relative performance of the Spitfire and Messerschmitt 109. This matter was now exercising many minds and was to be of particular interest to Tuck just over a week later.

    Deere subsequently wrote,

    "In my written report on the combat I stated that in my opinion the Spitfire was superior overall to the Me 109, except in the initial climb and dive; however this was an opinion contrary to the belief of the so-called experts. Their judgement was of course based on intelligence assessments and the performance of the 109 in combat with the Hurricane in France. In fact, the Hurricane, though vastly more manoeuvrable than either the Spitfire or the Me 109, was so sadly lacking in speed and rate of climb, that its too-short combat experience against the 109 was not a valid yardstick for comparison. The Spitfire, however, possessed these two attributes to such a degree that, coupled with a better rate of turn than the Me 109, it had the edge overall in combat. There may have been scepticism by some about my claim for the Spitfire, but I had no doubts on the score; nor did my fellow pilots in 54 Squadron. Later events, particularly in the Battle of Britain, were to prove me right."

    It may well be that some of the scepticism of the 'experts' was based on their knowledge of the performance figures of the standard production Spitfire Mk 1, as equipped with the de Havilland variable pitch propeller. It had a time to 20,000ft of, at best 9.4 minutes. Many of the performance figures available at this time would also have been gleaned from Spitfires fuelled with 87 octane fuel, rather than the 100 octane becoming increasingly available. However, tests on N3171 at Boscombe Down showed that the time to climb to 20,000ft could be reduced by almost 20% to 7.7 minutes with the constant speed Rotol propeller and 100 octane fuel. This would mean that a bomber force at 20,000 feet travelling at 250-280 mph could be intercepted a potentially critical 8-10 miles further out. The official comments on these tests on 19th March 1940 were limited to suggesting that the flying characteristics were not greatly changed by the Rotol propeller.

    The aircrew and ground crew at RAF Hornchurch, however were extremely impressed with the performance of the Rotol constant speed propellers and were not prepared to let the matter drop. As the Dunkirk evacuation was being completed and after a brief rest at RAF Catterick in Northern England, 54 Squadron, with its combat experience of the Rotol constant speed prop returned to Hornchurch on the 4th of June. There followed a quiet spell operationally, but a time, which could not but
    prove uniquely fertile for innovation. Between the 9th and the 18th, 92 Squadron was again posted briefly to Hornchurch with Robert Stanford-Tuck as commander of B Flight. Tuck had just flown comparative trials with Spitfire test pilot, Wing Commander George Stainforth of a captured Messerschmitt 109 with the Air Fighting Development Unit at the Royal Aircraft Establishment, Farnborough during the first week of June. 'Sailor' Malan, then with 74 squadron at Hornchurch had also participated in these trials and to cap it all, Supermarine's chief test pilot, Jeffrey Quill started a temporary attachment to 65 Squadron at Hornchurch at around that time. Out of such a cauldron it is hardly surprising that on 9th June, F/Lt McGrath, an engineering officer from Hornchurch contacted de Havilland's propeller division at Hatfield directly, enquiring if it would be possible to convert their standard issue variable pitch propeller to a constant speed one, "without a lot of paperwork and fuss." Somewhat surprisingly the answer was "Yes, easily," and 4 days later an expert engineering team was sent to Hornchurch by de Havilland with newly manufactured conversion parts, along with their test pilot, Mr E. Lane-Burslam. The work started at the end of an operational day and took all of the night of 14th June. The converted aircraft of 65 Squadron was tested by several pilots and the performance found to be much superior to that of the variable pitch version of the propeller, with a shortened take off run, the service ceiling increased by up to 7,000 ft, and an improved rate of climb and manoeuvrability at height, comparable to that of 54 Squadron's remaining Rotol fitted aircraft (probably N3173, N3174, N3183 and N3184.)

    So successful did the conversion prove that on 17th June Air Marshall Hugh Dowding received permission from the Air Ministry for the in-service retro-fitting of all RAF Spitfires, Hurricanes and Defiants to upgrade them to constant speed propellers. Receiving only verbal instructions on Saturday 22nd June, production of conversion sets was commenced, and from Monday 24th June teams were sent out from de Havilland to every fighter airfield. The procedure was demonstrated by the team to ground crew on one aircraft, who subsequently undertook the modifications, initially under supervision and then by themselves, throughout the hours of darkness on other squadron machines, as the early stages of the Battle of Britain raged.

    So, in addition to maintaining and undertaking repairs of combat damaged aircraft each night, RAF ground crew were carrying out delicate modification work, critical to aircraft performance. By 16th August, every single RAF Spitfire and Hurricane had been converted. However, to the best of my knowledge no formal performance figures exist, or were ever established for the Spitfire Mk 1 in what had thus became its typical Battle of Britain configuration – it worked, so presumably it just wasn’t a priority. Incidentally, by 1943, the Air Ministry in Whitehall were still wrangling over the paperwork – no change there, then!

    As a postscript to the story, when it left RAF Hornchurch on the 18th of June, 92 Squadron moved to the relatively quiet and remote station of Pembrey in South Wales. So concerned was Tuck that this might delay the conversion of their Spitfires to the constant speed prop, that a regular, but unofficial ferry flight was set up, whereby one or two of the squadron's Spitfires were flown to Hornchurch each evening to have the conversion performed overnight by a special detachment of its own ground crew: the aircraft returned the following morning. The fact that this also allowed the pilots access to London's night life was, of course, entirely incidental, but rather typical of the characteristically unorthodox approach to matters often taken by 92 Squadron!
    Keith

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    Thumbs up

    Very interesting read.

    I don't know if you've come across the WWII Aircraft Performance Testing site before, but the Spitfire I page makes for interesting reading.

    I agree that it's been difficult to find the performance figures for a MKI at the time of the BoB, but I think
    the RAE figures at +12lbs Boost should give a good indication of what they would have been.

    Cheers

    Paul
    Last edited by Bradburger; 27th August 2008 at 20:42.
    The most usless commodity in aerobatics is the amount of sky above you!

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    Quote Originally Posted by Bradburger View Post
    Very interesting read.

    I don't know if you've come across the WWII Aircraft Performance Testing site before, but the Spitfire I page makes for interesting reading.

    I agree that it's been difficult to find the performance figures for a MKI at the time of the BoB, but I think
    the RAE figures at +12lbs Boost should give a good indication of what they would have been.

    Cheers

    Paul

    Thanks, Paul. Yes I have been on the site, but not for a while and I confess I hadn't seen those RAE figures before - that's probably the closest we will ever get. Isn't it interesting that these tests weren't done until August 1941! I'd still love to know more about the conversations going on at Hornchurch in June 1940.

    Cheers
    Keith

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    Hi Keith:

    >Anyone ever noticed how difficult it is to pin down the performance figures for the Spitfire Mk 1?

    Yes

    Nice job of weaving various loose threads together to form a clearer picture of developments to the Spitfire leading up to its Battle of Britain configuration. I can share a few more strands to weave into the story.

    In December 1939 54 Squadron recorded the delivery of the following “Rotol Spitfires”: N.3097, N.3103, N.3104, N.3110, N.3111, N.3122, N.3124, N.3130, N.3160, N.3172, N.3174, N.3176, N.3183, N.3185, N.3187, N.3188. In January 1940 N.3180 and N.3184 were taken on charge, presumably Rotol equipped, while 152 Squadron collected 15 Spitfires from 54 squadron, all these aircraft being in the K.9xxx serial range. As of 14 June the aircraft remaining from the initial re-equipment with Rotol Spitfires, still flying operations with 54 Squadron, were as follows: N.3097, N.3111, N.3173, N.3160, N.3183 & N.3184.

    The experience in France should not be overlooked as an influence in Spitfire development. Gleed & Richey both make note of Hurricanes based in France in May 1940 equipped with Rotol constant speed props. France based RAF Hurricane squadrons were also retro-fitting armour to their aircraft. Similarly, Spitfire squadrons quickly retrofitted armour before going into combat over Dunkirk.

    The first Spitfire II's were delivered during the latter part of June equipped with Rotol props. Also during June 40 all Hurricanes were delivered from the manufacturers with the Rotol CSP while Morgan & Shacklady note that de Havilland was to supply Supermarine CSP conversion sets for new production Spitfire Is. (See: also http://www.wwiiaircraftperformance.o...ane-csprop.jpg )

    In late July A & AEE reported on trials it had conducted of R.6774 fitted with a de Havilland constant speed aircrew and found performance to be similar to that of N.3171 fitted with a Rotol CSP.

    Regarding Spitfire I performance, the RAE chart that Paul linked is better than the usual figures generally presented since it shows level speed performance using +12 lbs/sq.in. boost which had been approved in March 1940 and used by Spitfires over Dunkirk and during the Battle of Britain. Climb performance is more of a problem since the figures generally given are based on the early ½ hour climb limit of 6.25 lbs/sq.in./2600 RPM. There must have been a very significant increase in climb rate when using the 5 minute emergency setting of +12 lbs/sq.in./3,000 RPM.

    >I'd still love to know more about the conversations going on at Hornchurch in June 1940.

    Yes, that would me interesting. 74 Squadron’s ORB, which is generally quite sparse in detail, simply remarks on 29 June for K.9871 – “Constant speed airscrew test”. I wonder if 65 Squadron’s ORB could shed any further light on this subject.

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    Thanks for that, Mike.

    Climb performance is more of a problem since the figures generally given are based on the early ½ hour climb limit of 6.25 lbs/sq.in./2600 RPM. There must have been a very significant increase in climb rate when using the 5 minute emergency setting of +12 lbs/sq.in./3,000 RPM.
    Up to 10,000 feet that would probably have been the case, although most of the time spent in a climb to 20,000 feet would be taken above 10,000 feet. Reading between the lines of the permission of +12 lb emergency boost in March 1940 A.P.1590B/J.P-W http://www.spitfireperformance.com/ap1590b.jpg would indicate that its use was intended to be pretty limited. Fuel use, already at a premium would have been increased by a further 40% and there would probably have been a significant increase in engine wear, not to mention the disincentive to pilots of having to report it and enter it into the engine log. Pilots' accounts I have read seem to record that they would engage emergency boost either just before, or during combat - indeed, didn't it involve breaking through a restraining wire to do so? I suspect that +12 lb boost was hardly ever used in climbing to altitude and the chart http://www.spitfireperformance.com/s...-rae-12lbs.jpg would suggest that it also had less effect on performance at common combat altitudes of 15,000 to 25,000 feet than we might hope to think.

    I wonder if 65 Squadron’s ORB could shed any further light on this subject?
    So do I, anyone got access to it? I take it you have seen 54 Squadron's ORB, Mike?
    Keith

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    Hi Keith:

    The following information ties into your story of the de Haviland constant speed propeller conversions:

    609 ORB, 26/6/40: “Quite unheralded, a crew of De Haviland fitters descended on the squadron and proceeded to convert the V.P. aircrews to C.S. One aircraft was completed in the evening and flown. The improvement in performance is astounding and it was remarked that the Spitfire now "is an aeroplane." The remainder of the aircraft will be converted within a period of 8 days.”

    611 ORB, 28/6/40: “Aircraft Modification: Work was started on the alteration of the De Havilland V.P. airscrews to constant pitch. It is expected to complete one aircraft a day.”

    611 also recorded on 3/7/40 that “Air tests of the new constant speed airscrews have proved very satisfactory. One pilot reports that he can now turn inside a Rotol Hurricane. The same pilot reached 35,000 feet (indicated) on a height test.” I have my doubts about a Spitfire turning inside a Rotol Hurricane, however, this statement is interesting none the less in that it implies that a Spitfire equipped with the constant speed propeller turned better than one without.

    I think D. Ross got the Spitfire I development leading up to the Battle of Britain story pretty well right in his book on 603 Squadron. Its more than I have time to type out so See Here

    >Reading between the lines of the permission of +12 lb emergency boost in March 1940 A.P.1590B/J.P-W http://www.spitfireperformance.com/ap1590b.jpg would indicate that its use was intended to be pretty limited. Fuel use, already at a premium would have been increased by a further 40% and there would probably have been a significant increase in engine wear, not to mention the disincentive to pilots of having to report it and enter it into the engine log.

    Dowding is on record complaining that “some pilots pull the plug with little excuse on every occasion”. My research leads me to believe that use of +12 lb/sq.in. emergency power was so frequently and freely used as to justify Dowding’s complaint.

    >I suspect that +12 lb boost was hardly ever used in climbing to altitude and the chart http://www.spitfireperformance.com/s...-rae-12lbs.jpg would suggest that it also had less effect on performance at common combat altitudes of 15,000 to 25,000 feet than we might hope to think.

    For the Hornchurch squadrons you need look no further than Deere and Gray with 54 Squadron, Vigors with 222 and Quill with 65 Squadron as to why there was a need. For example from Gray: "54 Squadron, take off, take off, for Christ's sake take off", followed by section leaders ordering the Pilots to: "...press their emergency boost **** (giving double take off power)".

    Increasing boost increases climb and level speed performance up to full throttle height. Increasing RPM from the ½ climb limit of 2600 RPM to the 5 minute Emergency limit of 3000 RPM will increase climb performance up to the aircraft’s ceiling. I estimate this increase in climb rate to be somewhere in the order of 400 ft/minute from sea level to ceiling. As your initial post noted, however, it is difficult to pin down the performance figures for the Spitfire I. As I previously noted, in my opinion, this is more of an issue with climb rate than with level speed.

    Keith, yes the Rotol Spitfire serial numbers come from 54 Squadron’s ORB. It turns out I have a copy of a portion of 65 Squadrons’s ORB which I forgot about, but they recorded too little to be of any value. Where did you get your information about 65 squadron’s conversion to the DH CSP? Oh, btw, Quill didn’t report to 65 Squadron until 5 August, so I’m not sure to what extent he would have been involved directly in the discussions at Hornchurch. I expect 65 squadron had already converted to CSP’s by the time Quill arrived.

    Regards, Mike
    Last edited by Mike Williams; 22nd September 2008 at 21:47.

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