Ralf B wrote:

 

I assume that the air intake in the tail is originally designed to be used for the ac unit and that the previous owner cut a hole in the bottom of the fuselage to force more air through the heat exchanger of ac unit. I want to close the hole in my tail now since I am not using this air intake.

 

Would you recommend my plan or does the air intake in the tail serve another purpose?

 

 

Ralf,

The “original” Lancair IV did not have air conditioning, and was not pressurized. The air intake in the tail was used to collect high pressure air in this area and duct it forward for cabin ventilation/cooling. It worked extremely well. When later models of the IV were pressurized, a flapper valve was added where this ventilation air passed into the cockpit at the rear pressure bulkhead so ventilation air could move forward into the cockpit, but cockpit pressurization air could not “leak” backward through the ventilation ducting. This system also works well, but you can either have a “ventilated” or a pressurized cockpit; but not both at the same time. As a result, some builders, especially those who installed air conditioners, just eliminated the cockpit ventilation feature completely and used the A/C for cooling. From your description, that’s the configuration you have…the air intake in the tail has not been connected to the cockpit through ducting—typically along the fuselage top.

 

Before closing off the tail inlet, I’d check carefully on the air flow through the A/C heat exchanger. It’s possible the heat exchanger uses air from both sources, although either should be adequate in most conditions. You didn’t say where the air exited the fuselage after it passed across the heat exchanger…this is a consideration as well, as the total A/C effectiveness/efficiency depends on the condenser working properly. If you’re satisfied with the outflow, I’d suggest plugging the tail opening with Styrofoam to test the effect, and if the A/C and aircraft ventilation systems still work to your satisfaction, glass over the plug and paint…

 

Hope this helps; glad to exchange information with you off-line if desired.

 

Bob Pastusek