[Lang]

Mike,

Aircraft don't have "breathing air" they carry pure oxygen which is distributed either by a demand system or constant flow. The demand system allows oxygen to enter the mask at a predetermined rate (according to altitude) when the crewman breathes in. This system has a lot of similarities to a scuba regulator.

As you would know from your SCUBA it is the partial pressure of oxygen in the lungs that matters. Unlike under the sea when oxygen becomes toxic if the partial pressure of O2 increases too much (frogmen with pure oxygen rebreathers will die if they go too deep) - airmen have the opposite problem - not enough.

Over 40,000' in an unpressurised aircraft the pilot must use a pressure mask to keep his lungs pressurised enough to pass O2 through the lung walls into the blood. Breathing is very difficult as you relax to breathe in (forced by the pressure system) and force to breathe out - the opposite to what you do on the ground. Thats why you often hear fighter pilots on the radio labouring to talk.

Your reference to mixed gasses has to do with replacing slow dissipating nitrogen with more human friendly gasses such as helium at depth - pilots don't have enough not too much like divers.

Constant flow is a cheap wasteful system for emergency use (drop down masks in airlines) normally found in small general aviation aircraft and not military. Usually a flimsy, ill-fitting, mask or a couple of tubes (cannula) stuffed up your nose with oxygen flowing direct from the bottle.

Got off the track. Yes the flexible tube is either an exhaust with a spark arrester (used around aircraft) or an intake with an air cleaner. Either way, as you said, it is to use the wind to stop carbon monoxide getting in the system.

I think after all this erudite discussion someone will come up with absolute proof that the trailer is an Italian Army Mark IIIa Pasta Maker.

Lang