Air Conditioning

Why?

Air conditioning in not very common in smaller General Aviation aircraft and a majority lack such a typical convenience.  Why is that you ask?  Well it add's weight, complications and costs to the product.  At altitude it could be argued that it's really not needed since you can suck in cool air which is essentially AC without the hassle.  However if you live in a warm climate and you want to fly in the middle of the day you could spend a good 10 mins on the ground, 5 mins climbing to altitude which is about 15 minutes in sauna like conditions and very unpleasant. Case in point- you pack the plane with your family, get a late start and find yourself sitting on a central Texas tarmac during the afternoon heat (107F) in the middle of the summer.  This is not a good time.. especially if you're waiting on a clearance, rushing through items just to get into the air.   To me it's a matter of comfort and safety, if I'm not comfortable I'm liable to skip things trying to rush to the sky. Being that I live in Oklahoma and want to be able to fly in the middle of the day in the summer I knew the next airplane I owned was going to have AC in it.

Fortunately you have some options in the kit community for cooling an airplane.  Available are some small plug in type electrical AC options but that's just recirculating air around the cabin, not really dissipating the heat.  You have these cooler deals you fill with ice and they have a fan/blower on them.  Not definitive but they may also increase the humidity in the plane and moisture isn't great for electronics. That leaves two main players in the permanently mounted AC systems and they're fairly different. One is an all electrical system and the other is driven by an engine mounted compressor (Much like your car).  Nothing against that and I've been in a few planes that utilize that but probably work best on a 28V system, which further ups the complexity when most experimentals run off 14V systems.

On my searches I came across a system that is not unlike what everyone has in their cars. It's a compression system from Airflow Systems  and makes the most sense to me.  It consists of three major components; compressor, condenser & evaporator. The weight of the system gets spread out with an compressor on the engine, a condenser on the belly and the evaporator on a shelve in your tail. Having the condenser mounted externally seems more efficient as well.  So this is what I'm going with.

Installation Planning

There is no single way to install anything in the plane and an AC system is no different.  I have been talking with Bill at Airflow Systems on this subject. I'm weighting through some options that may work with the most challenging component being how to route the Freon lines between all three major system components.  Bill has a method to route them on the belly of the aircraft, some have put them through the sides and others have gone down the middle either over spars and covering them or straight through the spar drilling extra holes.

For me everything on this build needs to be serviceable once flying. I don't want to have a problem, say a Freon hose leak and have to drill out the back seats to check to see if that's what it is.  I thought about running them down the sides but I would have to come back through the tunnel and then down the side and have still have to drill through some pieces and modify a few things.  Aesthetically I don't like the thought of putting them on the bottom either so I kept getting pulled back to running them down the middle.  It seems I was trying to create a solution for something that's not a problem, ie drilling through the rear spar and bulkhead piece.

Down the tunnel seems to be the easiest way with the biggest heartache on drilling through the above mentioned parts.  If I asked the interwebs about this I would get 100 different answers.  To avoid this I looked into routing the hoses over the spars and do some type of modification to the tunnel cover pieces.  Problem being that you wouldn't have a flat area between the rear seats and the carpet would stick up a bit ect.  I wanted to get a more definitive answer before looking too much into that.. decided to shoot an email off to Vans on the ill effects of drilling through the spar and bulkhead webbing. I sent an email with some pictures to the Engineers over at Vans and promptly received this reply-

"Over the years we have seen many builders add additional holes for wire routing, air conditioning, oxygen and the list goes on. We however have not done structural testing beyond what is show in the plans pages for the RV-10. The best advice I have to offer on this would be to keep the holes as small as possible (if a ¾” will work don’t drill 1”) and maintain 2D edge distance. In the end the risk is very low but this is still a do at your own risk. Following what builders before you have done and proven is usually a pretty safe bet."

So what is the take away from that?  It's not that I'm going to crash and die if I do it, it's not even we advise against it.  It's them pushing the liability of changing up the plans and making sure you as the builder consider the risk.  The last line is really what drove my decision.  Greg Hale who I've mentioned a few times in the build log did a fantastic job documenting his installation. So while my build log won't be in such great details anyone interested should check out his install and write ups and work from there. I will tell you that the kit has changed since he did the install and will probably continue to change as Bill refines and improves things.

My Install

Here are some specifics about my install.  I went with an upgraded version of the Airflow System called the 'Aussie' Version.  It has a larger evaporator and will push out more air.  I'm using the Aerosport overhead to distribute the air along with a large cabin flood vent on the back bulkhead. I'm working with Bill on the details of that so won't have pictures of that till much later, same with the compressor.  I need my engine first and I know I'll have to mod the cowling a bit to accommodate a small bump.  But my goal was to set everything in place, get the scoop and condenser on and get the lines routed.

I talked about getting the scoop in on another post.  Goes on with rivnuts and is pretty straight forward.  I've been told that some people decide to use nutplates because rivnuts can loosen ect. Not a bad idea but you need to do that before you put your floor boards down.  In the end if some rivnuts start slipping I can just drill them out and replace them, not overly worried about it. Outside of painting there's really no reason to take this thing off once it's installed.

Specific to the freon lines I essentially followed Greg's .pdf.  He did a fabulous job showing how he did it and I mimicked it almost exactly.  I replaced the cable eyelets with 1048G rudder guides, I used 3/4 aluminium standoffs and #10 screws to hold the Adels.  I did a few of these with countersunk screws and the rest with low profile pan head types.  It gets tricky when countersinking a #10 in such a thin piece that in two cases I had to countersink a few washers to get them tight.  My suggestion is to do one hole, adel at a time and work your way back.  That will let you measure clearances and such while you're moving along.

On the holes through the rear spar I did two different size holes. I found the two larger hoses (H-03, H-04) worked with a 7/8" hole and caterpillar grommet.  The smaller hose going out the back (H-05) worked with a 3/4" hole and a SB-750 plastic snap bushing. When it comes to the 2D rule (hole center 2x the diameter from the edges) I was able to easily meet that but on the rear bulkhead piece I wasn't able to keep it 2d from the pushrod hole.  Given the concern is more on the edges and the angles I decided to center it as best as possible. Here are some pictures-

Rear Spar - Centered on spar. 2D from edge, cable holes and pushrod hole.

Rear Bulkhead - Min 2D from angle edge, centered a bit between throttle and pushrod hole.

With the holes cut I ran the lines, drilled, debured and attached adels.  I found that 3/4" and 1.5" #10 screw lengths worked best.  Combination of CS and pan type heads, I put CS on the front tunnel and the attachment directly over the rear spar.  I used low profile pan heads on the rest, all cad plated.  Here's the end result.

Right behind firewall.  Used standoffs on right side to clear access panel screws.

Forward of wing spar

Aft of wing spar

Looking aft, used cable-tie bases

Close up of standoffs

Here's a picture of my previously mentioned countersunk washer.  The helps nests the CS screw tight against the standoff.  This is especially important right here because the clearance above the throttle cable is only 1/8".

That's where I'm at right now, I should have my engine in the next few weeks so I'll be able to do the compressor install.  I'm going to continue working with Bill on the evaporator placement and final connections. Then it's just a matter of routing the lines to the overhead and working through the cabin flood and air return.