How Many Fresh Overhead Air Vents Do You Have?

[Tom Sullivan]

OK, I guess I need to describe my heating, ventilation and A/C systems. Being pressured, bleed air mixes with outside air, and is then either cooled (in the summer) by routing through the "Flow Pack" or kept warm with routing directly into the cabin (by passing the Flow Pack). My heat is delivered through vents under the instrument panel and at the feet of the rear seat passengers. (Well, the heat duct to the right back seat has a selectable valve to direct air to Beth's window to de-fog in the FL's in the winter when she desires to see outside).

My ventilation system, used only when NOT Pressurized (below 12K), is air routed from the NACA vent in the vertical tail, through a formed fiberglass tube (no flexible hose with the inherent drag and resistance) to a purpose built "VALVE" at the aft side of the upper seat close out panel. This valve will 100% close off ventilation air from the NACA Vent, which is absolutely necessary to allow pressurization. On the interior cab side of that "Vent System" is a gravity door that is top hinged to open with air flow from the NACA Vent, but close once my special purpose vent system "VALVE" is closed. This allows pressurization in spite of an outside air vent system.

The interior portion of A/C (Evaporator, & fan) is in the same "box" as the above stated Gravity door. On the ground, whether the engine is running or the plane is moving, I have the ability for all fan speeds including "high" when the Master Switch is on. The air flow I see from this fan is virtually identical in every phases of operation of my plane! That said, until I have started the engine, I have no actual A/C. My A/C system has an engine drive compressor. But, once running, with a turbine my A/C compressor speed is very high due to turbine idle being 70% of actual full power.

My system is likely much more complex than most, especially non-pressurized planes. But the point of my original submission was, if you have sufficient "fan volume", your vent size "COULD" be limiting the VOLUME of air you are getting out of your system.

A final note on "MY A/C". I was hearing a lot of complaints on the effectiveness of the typical IVP A/C in truly cooling the cabin down in hot weather, especially on the ground. The common system being used was 10k BTU. I spent my life working on commercial heavy vehicle A/C systems and decided I would build my own. I bought a commercial (Red Dot, a big supplier of Heavy Truck HVAC Systems) 16K BTU roof mount A/C unit. I removed all the critical components, built all the essential enclosures, mounts, attachments, etc. to install it in an efficient manner in my IVPT. I had an aeronautical engineer review and approve my inlet scoop to cool my condenser (for size, wind drag, flow, and structural integrity) which opens into the airstream for ground and climb out operations, and then can be closed during cruise for zero drag. I have no exit scoop because, after hearing Lance speak at a Lancair Banquette back in early 2000's, it was clear everything not tied down in the aft area's of the plane will find it's way out the tail surface gaps. I had many pilots, including Chris Rust, comment my A/C was the most effective they have seen in a IVP or IVPT. Chris would routinely ask me to turn it down because he was getting cold.

Tom

[Dan O'Brien]

FWIW, I have four of the aluminum eyeball top events on the overhead console, two pointing forward (adjustable direction and openings) and two of the same pointing backward. I find that I get lots of air out of the front two on the ground with the old squirrel cage blower, though it's warm air on a hot day. I get tons of air in flight. Those naca scoops really funnel in air.

Happy & safe flying,
Dan

[George Wehrung]

The only thing that I wish I could do would be to run some ducting from that overhead Naka vent down to behind the instrument panel to cool off the avionics in the summer. Have you ever touched the top of your glass shield that’s black? It’s smoking hot. And also even the sun beating in from the side windows onto the front panel of your instrument. Panel causes a lot of heat as well. Thus, it would be neat to funnel some of that air out of the overhead duct down into the instrument panel.


Sent from my iPhone using Tapatalk