Heaters
Danny et al,
The heater on the Harvard is actually a highly technical device that has a secondary effect. The original short exhaust outlet pipe is replaced by a much longer unit. This extended pipe is then shrouded by a jacket made of stainless steel or a similar heat resistant metal. The front of the shroud has a small diameter ram inlet pipe, and the outlet(s) are fed into the cabin. Very simple and generally very effective. The secondary effect? Due to the increased length of the exhaust pipe, the noise signature is considerably reduced and the sound is of a deeper note.
The Dakota / DC3 / C47 utilises the same principle on each exhaust. The heated air is then routed through the top of each undercarriage bay and under the floor of the fuselage. The choice of hot air routing is controlled by half a dozen plunger controls behind the co-pilots seat. Oh, and most of the ducting is (was) wrapped in asbestos in order to prevent heat damage to surrounding structure.
Post-war light civil single-engined aircraft still employ the same system, which is known as heat-exchanger cabin heating. The Piper PA22 of the early 1950's even had the option of separately controllable rear cabin heating. Sheer luxury.
The air-cooled Volkswagen range of vehicles including the Beetle, and also the Citroen 2 CV employ the same technology. I suspect the air-cooled Porsche range of high performance cars were similarly equipped.
Carbon monoxide poisoning is a very real threat, and in the civil world in the UK, there is a mandated Annual inspection requirement to pressure test the exhaust mufflers, hopefully identifying any suspect sources of the silent killer. Many aircraft owners and operators fit CO detectors similar to those used in caravans etc.
Civil twin-engined aircraft generally don't use the engine exhaust method. Instead, it has been decided and agreed by various manufacturers that far more entertainment can be gained by setting fire to the aircraft fuel supply while flying. Seriously, most of this type of aircraft employ heaters that burn fuel from the aircraft supply, and have shrouded heat-exchangers that work in the same way as mentioned above. The Shackleton amongst others also employed the on-board fire method, the Dragonair heater units being capable of producing 100000 BTU per hour each. And just to make sure, the MR2 had four installed. The later AEW II had the forward number one heater removed due to the installation of the AN/APS 20 radar under the nose.
Camlobe