Regarding the flow of CO into the R-44 cabin I have a theory. Do I hear a lot of “Oh Not Again” from the readers. Well, I never let that get in my way before. A while back someone posted a question on the rotorheads forum asking why the R44 has a tendency to waddle at high speed. Although I didn’t respond at that time I feel it is necessary to comment since it might relate to the CO problem.
I think it is the shape of the rear of the fuselage that causes a phenomenon known as vortex shedding. This vortex shedding causes a change in the pressure level on alternate sides of the fuselage at a speed directly related to the forward speed and the air density. This alternation in pressure causes the movement of the fuselage from side to side.
Now to the CO problem. How many of you drive a hatch back automobile? Have you ever noticed that when you drive in the rain a great deal of road slop will plate out on your rear window? The theory of this design is that the recirculating air will create a positive pressure on the rear of the car and add to the propulsive force imparted by the drive train. The airflow under the car picks up the crap from your tires (tyres) and it ends up on your rear window. If this is the case on the R 44, this pressure front will consist of not only recirculated air; the air will entrain exhaust gasses. The pressure front and the entrained CO will be forced into the rear of the fuselage where the gasses can be picked up in the cooling system and injected into the cockpit.
Many drivers of effected cars will install an air scoop just at the rear of the car at the hinge line of the hatch. This solves the problem of the dirty rear window. It may also solve the CO problem and the waddle problems on the R 44.
Any counter theories?
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The Cat