Air Conditioning in a Cozy IV

[John Slade]

Quite a few builders have expressed interest in my plans for AC, so lets have a thread on the subject. Let me say at the beginning that I'm very open to any input on the practical issues involved. Of course there will be those who think I'm crazy, but that's always been the case. Have at it.

 

Rational

Why put AC in a small aircraft? Once you get to 10,000 ft you dont need it, there's a significant weight penalty and much added complexity. Well, I'll begin by saying that I consider AC a safety issue. Anyone who's flown light aircraft in South Florida or Texas will know that descent, low level operations, pattern work, approaches etc. can be VERY uncomfortable. Sweat stinging you're eyes and cabin temps of 120F are not, IMHO, condusive to good piloting and have led to at least one fatal accident. Another good reason is that the wife wants it, and so do I. Yet another reason is that it's an interesting challenge (as if I didnt have enough of them building a Cozy and installing a turbo 13B engine). Finally, I'm installing a water cooled engine, and I'm going to need some form of cabin heat. The best answer to that is an automotive heater core, a heater box and a blower fan. Building the heater gets me half way to building the AC.

 

It looks as if the controls, pipes, cores etc. will fit nicely in "spare" space without impacting or interfering with anything. C of G wise, the weight will be fairly evenly distributed between front and back. If I loose 50lbs from available gross I gain it back by only weighing 160lbs, and I don't think the turbo 13B (250+ HP) will have any trouble getting it all off the ground. I don't know my gross weight yet.

 

Components

I obtained all the AC components from a low milage '91 Mazda 323. Total weight is 33lbs not including the pipes, blower motor and heater box. Cost was $75 for everything. Last week I built a fiberglass heater box which fits in the nose just in front of the Wilhelmson gear. The AC evaporator core sits on one side in front of the passenger rudder pedals. The glass box forms a 3 inch "cup" under the evaporator to collect condesation which is fed through a 1/4 tygon hose to the nose gear well. (This should get some interesting comments when people see me leaking fluid on the ramp). The glass box spans the gap across the center, curves around the nose gear and then encloses the heater core and the squirrel fan on the port side in front of the pilots rudder pedals. I had to move the brake master cylinders to make room for the center duct between the cores. 2 inch ducts will lead the hot or cold air to the panel air vents, cabin floor or screen defrost outlets based on a push pull control which will operate a mechanical valve (yet to be made). (in - vents, 1/2 out = floor, all the way out = defrost).

 

The plans fuselage side NACA air inlets are modified so that they can be closed and receive air from the AC unit instead of outside air. The hinge is simply a 1/2 inch of uncut fuselage side glass. Vents are from a Jaguar XJS (why not?) and allow variable air flow and direction.

 

Plumbing

I plan to use 3003 soft aluminum pipe (3/8 for the feed and 5/8 for return) running down the fuselage next to the electrical conduit. (one above, one below). The return will be shrouded with foam insulation of some sort. Automotive heater hose will run down the other side of the cabin leading to a mechanical variable on/off valve control behind the firewall. The condensor with attached dehumidifier fits vertically under the cowl on the port (plugs) side. It will be fed NACA intake air through a 4 inch duct off the plenum.

 

There are pictures and further discussion at http://kgarden.com/cozy/chap23g.htm I'll be adding to this as I go along.

 

Questions, comments and suggestions welcome.

Regards,

John Slade

[Dan Tomlinson]

I've already made a couple of minor mods that should help with the installation of liquid heat and A/C. My nose is wider at the front for a couple other reasons also, so there is about 50% more space than plans for heater box, fan etc.

 

John: Are you planning an A/C cut-off for full-power take-off? I know some cars use this under heavy acceleration to give full power to the wheels, then re-engage once the throttle is backed off a bit. Or a manual disengage (checklist item) for take-off and initial climb?

 

/dan

[John Slade]

Dan,

Right now I'm just trying to figure out how to make the sucker work. e.g. today I put the evaporator probe in the freezer and tested the solenoid. Sure enough it goes off when cold and comes on when warm (that's as accurate as I got). OK. This baby will connect in series with my switch and send power to the compressor clutch. I can easily wire this circuit in series with a full power microswitch, but I think I'll set it up manually via a check list for now. Obviously the first few flights will be done with AC off. Later, one of the flight tests will be to see how much power I loose with the AC on and how that impacts take off. I should have at least a 50 HP edge over an IO-360 powered Cozy. If I give up 5 or 10 HP to the AC I should still be well ahead of the game. Maybe "AC off for take-off" will only be required on a short field, or a very hot day at high elevation. We'll see.

Regards,

John