Little Wing
Active Member
Thinking about making an automatic alternate air door, one like Mooney uses. Anyone know what pressure differential would be suitable for actuation?
Rod
Rod
Van's Air Force
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Automatic alternate air door
- Thread starter Little Wing
- Start date
Norman CYYJ
Well Known Member
Van's use to have them and they were held shut with a magnet. Can't remember why they dropped them.
Carl Froehlich
Well Known Member
Just be cautious on how you make it. Very easy for hardware and such to get sucked into the engine, and vibration of hardware on fiberglass tends to loosen bits.
I recommend staying with the standard cable operated door.
Carl
I recommend staying with the standard cable operated door.
Carl
Jpm757
Well Known Member
The cable operated door is simple, and with a little redesign you can get it to open AND close smoothly from the cockpit control.
blaplante
Well Known Member
I recall because the magnets would sometimes come loose and vanish. Where... through the engine... maybe.
Read up on all service difficulty reports about automatic air doors in certified aircraft beforehand!
Also spring loaded auto air doors cause a substantial drop in MP (and hence power) which is maybe not what you want as you (unintentionally of course) load up with ice.
Rod, this is one of those areas, like fuel system design, where you will hear lots of people encouraging you to take care. Quite a few engines have stopped due to very non-obvious design issues. I believe that DanH has a pretty solid design - see details here: https://vansairforce.net/community/showthread.php?t=162845
Design embeds the heavy music wire into the glass door, in flox between surface plies. There is no hardware in the air path, or even in the alternate air path.
Starts opening at 3" H2O. Complete blockage of the primary intake richens mixture by 7%, with a manifold pressure loss of less than 0.5" Hg. I can live with that...literally.
Starts opening at 3" H2O. Complete blockage of the primary intake richens mixture by 7%, with a manifold pressure loss of less than 0.5" Hg. I can live with that...literally.
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Little Wing
Active Member
Thanks all!
Since I am using the Vans snorkel I'm going to go with the stock alternate air. Don't want to worry about loose parts in the induction.
Since I am using the Vans snorkel I'm going to go with the stock alternate air. Don't want to worry about loose parts in the induction.
