REFLECTOR:Alternate Air

[Jack Sheehan]

Scott,
You need to look at the system on the gallery. The filter is not a 
typical aircraft filter system. It is a conical K&N located under the 
engine in the heated area and is not exposed to any weather. The 
purpose of the filter is to provide filtered air for ground 
operations. Normal induction air comes through the ram air scoop in 
flight. If for some reason such as ice or a seagull stuck in the ram 
air scoop I can switch back to filtered air from with in the engine 
compartment. I made the system actually backwards from a typical 
aircraft system which always operates on filtered air unless it is 
clogged then a little door opens and it receives alternate air. The 
advantage of using unfiltered Ram air is about a .7 inch increase in 
manifold pressure at about 10,00 feet.
So The concept of alternate air is somewhat reversed. I have not yet 
experienced any reason in flight, either rain or ice, that has 
prompted me to close the Ram air and switch to filtered air but it is 
an option On runways where I am concerned about dust or dirt I take 
off on the filtered air and there is no degradation in performance. I 
usually open the ram scoop at the same time I raise the gear.

I hope that is a little clearer.

Jack
N55XL