[klemchen]

Hello,

the contribution by Ferdinando D'Amico on the various DB 606 AS/D cowlings encourages me to post here what I call "my big Erla cowling problem", with a few more remarks about the background, which at the same time can be viewed as questions asking for confirmation or rejection. In advance I apologize for being somewhat lengthy.
The Regensburg Me 109 K cowling (Mermet type 100) was still pretty much based on the Me 109 F cowling. The lower cowling was basically the same, except that a deeper oil cooler was inserted and the so-called chin bumps were added. In particular, it was symmetrical. The upper cowling halves were asymmetrical because the large DB 603 supercharger did no longer fit inside the DB 605 A cowling. Therefore the port upper half had to be reshaped to accommodate it, and at that occasion the bump over the breech of the port MG 131 was made integral to the cowling half. At the same occasion also the bump over the starboard MG 131 was made integral. Behind these integral bulges two shallow elliptical blisters were attached to the fuselage sides (accompanied by a widened so-called weapons cover in front of the windshield); these extended downward only to slightly above the wing fillets. Since the rear part of the upper port cowling half was wider than a normal DB 605 A cowling but the port lower cowling was not, what some author has called "an untidy construction" was employed for the transition of the upper half to the lower part behind the exhaust stubs. The forward part of the upper cowling remained the same as for the DB 605 A; on starboard this part extended backward to the normal panel line, while on port that panel line had to be moved forward some length because of the larger bulge for the supercharger. Because of combining the normal forward part with the wider integrated bulges the shape of the upper cowling contained some concave portions.
Since these were not aerodynamically optimal, Erla redesigned the whole cowling. The new cowling (Mermet type 110) did not have any concave curvatures; that is why the gun throughs from the side appear much narrower as before. In order to avoid the "untidy construction" aft of the port exhausts, the lower cowling was made wider on port and thus became asymmetrical. As a consequence, the port blister on the fuselage side behind the engine compartment had to keep about the same distance from the original fuselage side over the entire height of the fuselage side; that is why its rear edge could no longer be elliptical but had to become vertical. This construction must have demanded also a new forward port wing fillet.
That the lower half of the forward cowling ring (immediately behind the spinner) had to be widened and deepened on its lower sides has been pointed out before by other contributors. It was probably also deepened slightly in the middle, so the lower cowling line between spinner and oil cooler would appear slightly bulgier than on other 109s. Ferdinando D'Amico has drawn it that way, and I think it can be seen weakly on some photos. Some time ago somebody showed me a Messerschmitt drawing comparing the lower cowling lines of the "Me 109 K" and of other109s. Since the lower line of the Regensburg K was essentially the same as that of the "normal" F/G, the drawing must have shown the lower line of the Erla cowling. The "K" lower line was about 1 or 2 cm lower than the other one over its entire length, until it met the underside of the forward wing fillets (which also were forming the rear part of the bottom engine cover). When I later asked that person to show me that drawing again, he could not find it among his lots of Me 109 stuff, so I cannot say more about it.
This is where "my big problem" is entering the scene: The Erla cowling also got a new oil cooler bath. Many people have claimed that the radiator underneath was shallower but wider than the Fo 987 of other G-10s and K-4s, but I doubt this. I admit that the oil cooler of the Erla cowling appeared shallower than that of a "normal" G-10/K-4, but this could as well have other reasons: Assuming that a Fo 987 type radiator was installed in exactly the same position with respect to the engine as usually and that the bottom of the Erla cowling was indeed slightly lower than on other cowlings, then the oil cooler cover would appear shallower too. Another hint, however weak, that the Erla cowling was equipped with the Fo 987 is given by the famous Messerschmitt drawing of an Erla G-10, which was published in many places, e.g. in the booklet on the various Me 109 G cowlings by Jean Claude Mermet. Although quite crude in some details, that drawing is very precise with respect to the basic outlines, and the front opening of the oil cooler on it has a width corresponding to about 46 cm. For comparison, the duct of the Fo 827/870 oil cooler of earlier Gs was 462 mm wide at the base and 448 mm at the top, and the Fo 987 must have been similar. Of course this correspondence may be due to the crudeness of the drawing. I also tried to determine the width of the oil cooler by taking measurements on a photo that is showing an Erla G-10 exactly from the front by relating it to the length of a propeller blade (1.5 m) and to the wing span (9.92 m). Because the propeller was closer to the photographer than the oil cooler it yielded a width smaller than 46 cm, and because the wings were further from the photographer they yielded a greater width. Unless the exact distance of the photographer from the aircraft is known, this method cannot be refined to give a precise answer.
My main argument is that it seems highly improbable that at that stage of a losing war the logistics situation would be aggravated by introducing yet another type of radiator. Of course this can be said about a new type of cowling as well, but Erla were making their cowlings themselves. I do not know this for sure but I imagine that this does not hold for their oil coolers as well and that they had to order these from some subcontractors. If somebody could confirm this, I would consider my problem as very probably solved; otherwise it would remain open.
There are two more questions: On photos of Erla G-10s I could not detect the small vertical strut in the front of the oil cooler that was there on other Me 109 F/G/Ks. Finally, I have come to know a number of names of Messerschmitt engineers but never heard of the creative engineers at Erla, who not only constructed the most advanced Me 109 cowling but before that had designed the Erla cockpit hood, which became common for all late 109s.

Again apologizing for being so lengthy,
klemchen