Speed Spitfire Question

Could this rib on the aileron be the position where the later shorter (Mk.VIII etc) aileron ended?

Because of this thread, I’ve realised that my (thankfully unfinished) Mk.III model actually has a HSS wingtip. Plus Mk.VIII ailerons… I must have had a real rush of blood to the head when doing that. The Mk.III wing appears to be simply the clipped standard wing (but the Universal one, not the earlier). Yes, the overall span of the HSS wing is greater than that of the clipped.

Yes, the SS span is conceivably greater, as the tip has a curve to it 🙂 That could even be true if the ‘tip section’ began a little further inboard.

The quoted web article has a number of doubtful points to it, such as the PRU Wingco not realising that reduced tankage meant reduced range until after he’d taken delivery of the aircraft..

The wing span was quoted as 33.76ft, removable wing tips are a nominal 3ft each, and the clipped wing tips are about 6″ so the span of the SS is greater than the later clipped wing marks?

There does seem to be some inconsistencies between the above quoted article, and the specifications in the M&S book, where the engine power is quoted as 2100 hp , also the section on fuel capacity seems to suggest that the top tank (removed to fit the header tank for the total loss cooling) wasn’t replaced, this on an A/C in a PRU flight!

Interestingly, doing that dubious thing of scaling and overlaying 3-views surprised me by showing a wing tip ‘break’ line – a panel line – along with the outboard end of the aileron a couple of inches further inboard on the SS than on the Mk 1

This tallies with the 3 1/4 Square inch reduced aileron area.

It would not be such a major structural mod to put a ‘terminal’ rib here, a couple of inches further in along the spar. I agree there might not be too much speed advantage, but it may just be that this was the biggest change that was indeed possible with the resources necessary – ie without major structural redesign?

I’ll not annoy with my clumsy graphics here – but it’s worth a look if anyone can be bothered.

As for the cooling system – there was a lot of work done on this but it is all within the envelope said to be the same wing, as bounded by the limits of the undercarriage housing.

The comments about workload ring true: there may well have been meetings not covered by the published data, where the earlier plans for changes were discarded in favour of minimum change, and that is what we are seeing in the final shape. However the less the surface area, the higher speed the aircraft is capable of, so further reduction would have brought the record nearer. Whether it could have got anywhere near the Me209 is another matter.

Perhaps much of the wing redesign was for the new internal cooling system ?

To answer my own post – looks like they abandoned the cooling system mod so I would imagine that much of the wing mods were deletion of armament and access panels !

Given the immense pressure that the Supermarine design team were under in the immediate pre-war years, not least because of Mitchell’s death, I doubt that they were I any position to undertake much more than minimal redesign for the Speed Spitfire. Good photos are few and far between but I came to the conclusion that it was just the wingtips that were reshaped. Modifying the spar and leading edge box would have been a really major undertaking so I think that any change would have to be restricted to the ribs, false rear spar and trailing edge, and I really cannot see any evidence for that. The ailerons give every impression of being standard size and I doubt that fiddling with the odd inch here and there would make that much difference to performance.

Perhaps much of the wing redesign was for the new internal cooling system ?

The M&S text states that the wing was the same from the fuselage out to the wheel housing, and that a new tip was to be designed. This does imply that the wing outboard of the undercarriage and inboard of the tip would have to be redesigned, which I think is where the initial poster came in? The change in aileron area from 18.9 Sq ft (both) to 9.18 sq ft (single) suggests that this change was small, and probably restricted to a slightly greater trailing edge curve forward to match the new tip shape. I agree that scanning different plans, and rescaleing them to be the same, is probably the best way to detect whatever changes there were, but the usual warning against placing too much reliance on industry General Arrangement drawings has to be made. They are often only indications, and existed in different issues which may or may not accurately reflect the actual state of build. It is only the detail parts drawings that will provide the true shape.

It is interesting to note what is said later in the book about the Mk.III, where there’s a quote about the reduced wing area as “already incorporated and flown on the High Speed Spitfire” But the two were not the same shape.

Whilst we now see the removal of the wing tips as perfectly normal, the early MKI’s didn’t have removable tips, so a “redesign” isn’t completely inaccurate; with regards to the ailerons, the figures for the SS of 9 sq ft, and the MKI of 18 sq ft (approx.) could conceivably be for one aileron, and for both respectively, given that the figures quoted weren’t for direct comparison.
I can’t actually see what improvement in straight line speed that would give, even if were the case.

The link would have done 🙂 As above, Morgan and Shackady pages 63-67 are more authoritative, and include a GA that may be useful. (All the M&S GA’s are from primary sources). It does seem to indicate that it was only really the tips, manufactured as a separate unit, that were different about the wing in terms of profile. Also ref. the Alf Price chapter, also mentioned before.

In summer 1937, the Rolls-Royce engineers began to work on a new “Merlin II” powerplant which was able to produce 1536 hp. This was almost one third more than the initial engine. The K9834 airframe was fitted with this new motor but this was not the only modification. The military equipment was deleted, the numerous access panels were removed and the surface of the plane was smoothed with the use of flush rivets. To reduce drag, the wing tips were rounded and the total wingspan was reduced to 10,26 m. A new high pitch four blade wooden propeller was designed with a smaller diameter to reduce the circumferential speed and eliminate the supersonic flow around the blades. The windshield and the canopy were streamlined and finally, the tailwheel was replaced by a fixed tail skid. The modified plane weighed 2470 kg, 135 kg more than the standard version!

In November 1937, Rolls Royce hoped to obtain 1995 hp out of the special version of the Merlin, which would have been enough power for the Speed Spitfire to reach 603 km/h (375 mph) at low altitude. But at the same time, the Messerschmitt Bf 109 V13 was already able to fly 608 km/h (378 mph)! From now on, the type 323 had to reach 616 km/h (383 mph), 1% more than the german plane, for the record to be approved. With further modifications and even more power (2122 hp) the engineers still hoped they could break the record. The first flight of the Speed Spitfire took place in November 11th with Mutt Summers as test pilot. After that, all the panel lines of the aircraft were filled (except around the engine), the surface was painted in Royal Blue and Silver color and finally everything was polished.

In February 1939, Harry “Bruin” Purvis managed to reach 656 km/h (407 mph) with the Speed Spitfire at the altitude of 990 m. At ground level the speed would have been slower, but still enough to beat the Germans. However, the British knew that Heinkel was about to enter the competition so it was imperative to gain a few km/h (mph) more. It was decided to delete the big radiator under the right wing to improve aerodynamics. With this modification, a top speed of 684 km/h (425 mp/h) at low level was anticipated. To replace the external radiator, a new internal cooling system was designed which allowed the plane to fly the few minutes necessary to break the record. Work on the new cooling system only began when suddenly any effort was made useless: the Heinkel He 100 set the absolute World Speed Record to 753 km/h (468 mph) and less than a month after, the Messerschmitt 209 flew even faster! So fast that the record of 755 km/h (469 mph) was only broken on August 16, 1969 by a highly modified 3100 hp F8F-2 Bearcat, at an average speed of 483.041 mph!

Of course this meant the end of the Speed Spitfire project. The plane was crated and later used as a static demonstration plane for the “Salon aéronautique” of Bruxelles in summer 1939. This could have been the end of the Speed Spitfire but in 1940, the RAF desperately needed combat planes. The type 323 was summarily reequiped and fitted with a Merlin XII engine and a three blade propeller with variable pitch. However, the modifications didn’t allowed any armament to be fitted inside the wings and the fuel capacity was also much lower than on a standard Spitfire. The only squadron that could have made good use of this hybrid plane was the Photographic Reconnaissance Unit (PRU) based at Heston. The Speed Spitfire, with it’s smooth finish, still was one of the fastest aircraft in the world and Wing Commander Geoffrey Tuttle expected to be able to safely fly reconnaissance missions over France with it. Alas, he soon realized that he would have ran out of fuel 35 km before reaching the British coast on it’s return flight!

The Speed Spitfire finished it’s career as a liaison aircraft and became the personnal plane of the Commander of the 106 Photo Reconnaissance Wing, Air Commodore John Boothmann. Some said he flew over Normandy on June 6th 1944 to shoot pictures of the D-Day beaches, but this could well be a legend. Finally, K9834, the 48th Spitfire ever made, was scrapped in June 1946… without to have beaten only one record.
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I would have to find my copy, but I think Alfred Price’s “Spitfire Story” has a good chapter, or at least a section, on the Speed Spit.

From a simple eyeballing of the aircraft in photos, the ailerons do not look any different to a standard aircraft, however I’d have to read through the text to be certain!

Page 63 of the Morgan & Shacklady book describes in reasonable detail the modifications to a STD mkI wing which include a redesign outboard of the wheel wells, reduced in span, but still the NACA 2200 sections; it gives all of the important dimensions, I haven’t got the time to compare them like for like with a STD wing, but either they weren’t that much different from STD or else the wings were changed, because the A/C saw service, not being struck off charge until ’46

Having looked at the dimensions of both the MKI and the Speed Spitfire, I think the “redesign” was limited to wing tips, certainly the SS span is given as 33.67ft, and whilst the figures quoted tor the ailerons, seem to suggest they are half the square area of a MKI, I think that unlikely.

Interesting question Olympus, but as for in depth reading material on the speed Spitfire can’t say I’ve found anything, most just skates lightly over it. Pity Mark 12 isn’t on here now, he’s sure to know .