Well-known photo (see Merrick) of Ju 88 G-1 WNr.714053 burnt out on an airfield near Braunschweig. Click on the B&W thumbnail below to go to a full-size black and white photo of this machine on footnote.com. Visible under the wing separated by about 150 cm are the transmitting and receiving antennae of the FuG101a Feinhöhenmesser radio altimeter.
These pictures - and more specifically the apertures visible on the wing upper surfaces - were the subject of an interesting discussion on Flugzeugforum.de. Thanks to Peter Achs, Christoph Vernaleken and Friedarr for assistance with the following on the work of Dr. Alfred Kärcher. The name is more usually associated with high-pressure cleaning hoses, but during WWII Kärcher build and designed cockpit heating and wing de-icing systems mounted internally as well as much larger mobile hot-air blowers for de-icing aircraft.
The Ju 88 G-1 was equipped in many instances with at least three Kärcher-Heizgeräte. These were essentially petrol heaters, more colloquially known as Kärcher "ovens" and could be mounted in the rear fuselage or more likely one in each wing close to the wing leading edge between the engines and fuselage. A supply of air via the intakes located close to the wing root was heated and then re-distributed around the airframe for heating and de-icing (see schematic drawing below). Not every G-1 had Kärcher fittings in both wings - some G-1s have only one wing-root intake or even none where there were no wing heaters present. A good indicator that the 'ovens' could be fitted in a Ju 88 G wing was the presence or otherwise of the rounded 'exit' in the top of the wing in the vicinity of the engine as clearly seen in the colour image above. The Kärcher heater was powered by the aircraft's own fuel supply. A certain number of earlier 'G' machines did not feature the Kärcher heaters, for example the well-known 2Z+EH assigned to the Gkr. I./NJG 6 Hptm. Gerhard Friedrich and illustrated on Pages 79-82 of Stipdonk/Meyer 'die Deutsche Luftwaffe' Teil 3. Aircraft such as these - with no provision for fitting Kärcher heaters - would necessarily have featured BMW 801 engines with Lufterhitzer or air heaters - along with their characteristic cowl bulges- since these would be the only source of heated air for de-icing on the aircraft. G-1s with Kärcher wing heaters are likely to have the 'smooth'-cowled BMW 801s not fitted with engine air heaters.
Below; Kärcher heaters of the type mounted inside the wings of the Ju 88 G-1 and a schematic view of the associated plumbing.
Reference is made to the Kärcher heater in the Air Intelligence report of the 7./NJG 2 G-1 that landed at Woodbridge, Suffolk on 13 July 1944.
"...De-icing of the main and tailplanes is by hot air. This is normally supplied through a muff fitted around the exhaust stubs, but in this aircraft it could not be traced. There was, however, provision for a petrol-fired heater (Kärcher Ofen) and a switch in the cockpit indicated that air could be supplied from this heater to either wings or fuselage. In this particular case the heater was not installed but there was an air intake in the leading-edge of the port mainplane between the engine nacelle and fuselage, with an exit slightly further outboard on the wing upper surface. The piping has not yet been traced out, but presumably it will lead to the heater position.."