Quote:
Originally Posted by Graham Boak
Thanks for the additional detail on the cabin pressurisation of the G-5. I'm a little surprised, therefore, that the G-5 canopy is not clearly distinguishable from the standard.
It would not surprise me to find that the V49 was not pressurised. Its role would be entirely to get engine hours up on the new engine, with the high altitude regime studied later. Presumably the head armour could easily be restored, although perhaps this depends upon just why they took it off in the first place?
It shouldn't have surprised anyone that the high-altitude engines require a larger cooler. Or is the timing just in advance of the appearance of AS/D engiines?
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The reason that the pressurized and unpressurized three-piece G canopies are very similar is because of standardization: a new heavy steel canopy framing was designed for the G, to be used one both pressurized and unpressurized variants. In unpressurized variants, this heavy framing mounted single-layer transparencies, and the typical sloped head armor. In the pressurized variants, double transparencies were mounted in the same basic canopy frame, and a vertical combined pressure bulkhead/armor plate with small triangular transparencies and pressure valves was installed at the back of the central canopy part, forming the upper rear wall of the pressure cabin. Silica gel cartridges and pressure valves for the barrier were incorporated into the lower right corners of the outer transparencies. The canopy framing was not the only part that was standardized: the basic cockpit tub of unpressurized early G versions is also similar to that of pressurized variants, using the same pressure-sealed connections for cabling and connecting rods; these were dispensed with on later versions, when development and construction of pressurized 109 variants was discontinued.
It is indeed possible that the V49 (W.Nr. 16281, converted from G-3) lost its pressurization: only ten rather short flights are documented for this machine between 23 April 1943 and 14 May 1943, and the majority of them is concerned with evaluating the effects of the longer and heavier engine on stability around the axes and general handling (Vogt 2018). It is also known that the aircraft started flying without the first compressor stage of the DB 628 installed due to continued metallurgical problems with the bearings of this stage. The machine was then transferred to DB at Echterdingen, where the second compressor stage was finally installed and tested in flight on 18 August 1943. In total, there seems to be a record for at least six flights at DB between 21 June 1943 and 30 October 1943 (Mermet & Ehrengardt 2015). All these flights seem to have focused on general performance of the engine, lubrication and cooling systems (which proved insufficient). So, for this type of work, the aircraft indeed would not have needed pressurization. The machine was reportedly destroyed on 14 August 1944 in a raid on Echterdingen (Vogt 2018). One, or possibly two more Bf 109s were equipped with the DB 628 – this may have involved the V50 (W.Nr. 15338, converted from G-5/U2) of which very little is known, but Mermet & Ehrengardt (2015) report that W.Nr. 15708 (converted from G-5/U2) was also used as a DB 628 test bed prior to being converted into the V54 as a full H-prototype with extended wings. The only (partial) photograph I know of that shows a DB 628-engined Bf 109 undergoing maintenance shows it had the pressurized windscreen; however, the canopy is removed, and the rear part of the cockpit is outside the frame of the photograph, so it is impossible to know if it had a pressurized canopy or not.
And while indeed it seems fairly obvious that flying at high altitude would have required increased cooling capacity, the V54, which was tested with the DB 605 A and B, and a significant part of AS-engined machines were equipped with the standard smaller Fo 870 oil cooler, before switching over to the larger Fo 987 during G-14/AS production.
References:
Mermet, J.C. & Ehrengardt, C.J. (2015)
Messerschmitt Bf 109. Caraktère Presse & Editions, Aix-en-Provence, France. 192 p.
Vogt, H.H. 2018.
Messerschmitt Bf 109. Versuchs und Erprobungsträger und der Weg zur Serienproduktion. VDM Heinz Nickel, Zweibrücken, Germany. 496 p.