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Well, there are always these scenarios...
First, I would always close the valve if I was in IMC (actually, my airplane is VFR only, but no matter), thereby counting on the combination of fuel injection's natural resistance to icing, and the warm side air flow into the filter. If I was caught sleeping, I would still hope that the tendency would be for the ice to build on the cowl inlet, and on the valve shaft and sideways facing butterfly. My airplane suffers a 6-8 kt. reduction in airspeed due to the reduction in MP and the warmer (less dense) air being used when the valve is closed.
Likewise, for the bird strike, I am hoping that the bird is large enough to lodge in the cowl inlet, or up against the valve shaft, or if it is small enough to pass through to the servo body, small enough to allow enough airflow to make a safe landing. Sure, there is a size range that will defeat the system. I always avoid that size bird :o) The real small ones go through, and out the exhaust pipe. Then there is the guy who was cutting toilet paper, and that clogged his intake, and he landed dead stick (at the airport).
A screen would help some of these cases, but then there is the possibility of the screen getting ingested because it came loose, or got knocked loose. Some of the no-filter guys use plastic screen to mitigate this possibility.
Take your choice.
John
Matt Hapgood wrote:
John (or anyone else),
Your construction and design is beautiful. I have been facing the "alternate air" issue and haven't done anything so elegant.
I do have one concern though - If and when you need alternate air, will your system function as desired? Specifically, where would the foreign object (bird) or ice be likely to cause a problem? I would think that it would be so far into the back of the system that your alternate air would not be functional - ie. the filter would be in front of the problem.
A possible simple suggestion would be to put a basic screen at the cowl opening that would block passage of foreign objects.
Would ice accumulate on a screen? Would this be better than accumulating farther back in the fuel servo? Is that even possible?
Thanks,
Matt
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