AC and heater placement

[John Slade]

By the way, a couple of thoughts for those people planning to install Mazda rotary engines, or any automotive engine for that matter. One of the nice things about a water cooled engine is the ability to feed a proper heater, or even a stock AC unit.

 

Think about you're pipework early if you plan to install an automotive heater and/or air conditioner. The ideal place is down the heat duct - before you close it off. Once you get the pipes in the "hell hole" they can be fed through the firewall with bulkhead fittings. I used 6061 5/8 al pipe for heater feed, heater return, vacuum and ac return, and 5/16 for AC feed. That's a lot of pipe. It doesnt weigh much, but it sure is hard to manipulate after the fuselage is all buttoned up.

 

{I was the culprit who started a new thread in the middle of an old one. Sorry. I've split them up. The cabin width discussion continues elsewhere...}

[marbleturtle]

Have you heard of anyone running pvc conduit pipes down each side of the floor for extra plumbing space? Someone just sent me that idea but I haven't seen it implemented anywhere.

 

Also John, in the picture I've got my left shoulder against the seatback and my right shoulder forward at an angle. When I tried my shoulders square against the back is when I estimated 3". I can fit as is... but I'd be a little squozen. Its the same thing I would have to put up with if I bought a Mooney. But I figure, If I'm gonna build the thing from scratch, why not have it fit comfortably if the changes are minor. (I know, there are exponential forces involved with frontal area and aerodynamics...) I'll just blame it on my wife... yeah... she wants the extra space. And to steal the immortal words of John, "what the lady wants, the lady gets."

 

My wife wants air conditioning too! Should have never let her read John's web site.

[John Slade]

PVC pipe down the side is a good idea for wiring, but it won't help much with plumbing. It would certainly be possible to run the 5/8 al pipes down the side, but its a continuous curve so this would have to be done fairly early on. When you get to the area under tha back seat you probably need to come inboard. Otherwise it might be possible to extend the electrical conduit.

 

>My wife wants air conditioning too!

Funny you should mention that. We were talking about cooling last night, and I mentioned that one advantage of having an automotive heater is that you can run it to get additional engine cooling. She wasn't impressed.

[marbleturtle]

My wife always has that "eyes glazed over" look when I talk about the plane. I guess she'll get more excited when she sits in the fuselage with me and makes airplane noises.

[LargePrime]

This is supposed to ba about cabin width, but i dont really think anyone will mind.

 

Not sure I would use solid pipes with all the vibration. I would use the stainless steel/nylon/teflon braid and fittings. Dont know about the weight, but i do know they wonk leak.

 

Having looked at dust's tub here is my humble suggestion.

 

1 Use an automotive blower on the cabin side of the firewall with a automotive heater core. Air is easy to pump, much lighter than water, and leaks dont matter. This will work with AC too as you may be able to use a standard automotive blower box, or fab something simular.

 

2 Square the heat duct down the center. Airflow is more dependant on cross section than square inches. You may even enlarge it to taste. Enlarge the tube feeding the duct to as large ot larger than the crossection of the heat duct. The plans one cuts the airflow in half.

 

I have some pics of the extention to the stock heater that we took last weekend. I'll post when i can.

[John Slade]

You may be right. Putting the blower & rads up front was a pain. My reasoning was:

1. I couldnt find a way to install a blower, heater coil and evaporator in the back without loosing or moving the back seats.

2. I'll probably need the extra weight up front for w & b

3. The wife likes the air "in her face".

 

As for vibration of the solid al pipes - I dont think there will be a problem here. The pipes are firmly attached to structure for the entire route. Most of the trip down the heat duct they're encapsulated in pour foam. That's a nother good reason for running them down the heat duct - if they leak the leaked fluid isnt going to flood the plane. The bad side of that would be getting to the leak to fix it.

[Jim Sower]

Having looked at John's firewall and rear cabin area, I'm a bit baffled as to where one would be able to locate heater cores, blowers, plenums, etc. back there. John's firewall is already about as busy as any I've ever seen. Now we propose to deny access to all that equipment by covering it up with heater plenums and ducting?

 

Afraid I'll have to stick to the forward heater system .... Jim S.

[LargePrime]

I have just read your ac install page. Then I went and got some Tylenol and 3 fingers of vodka. The questions I ask below are for my edification. I don’t intend to question your design.

 

If I read that right you have the heat and the freon lines running in the heat duct. Don’t you think that will limit the effectiveness of the AC?

 

You have a NACA feeding your heater box, right? NACA scoops are only an advantage when there is a low pressure point behind the scoop. routing into the blower will create high pressure behind the NACA. This causes a pressure wave in front of the NACA.

 

Especially for the ac I would think you would rather recirculate the inside air. Perhaps you do that. There is no way the ac will dehumidify and cool constant fresh air.

 

As a note most modern cars run the heater and the ac at the same time when you press the defrost button. The air is AC'ed then heated to make it really dry and defrost well.

 

Pretty ingenious wraparound in the front. Have you run the blower yet to check airflow? I would be very curious as to how much air it moves. I bet it is a ton.

 

I have no good idea where one would put this set up in the back. Perhaps with a smaller, flatter, blower/evaporator/heater core under the rear seat? It just seemed less complicated and lighter in the back somewhere.

 

Re: "in her face"

I had thought about putting "eye ball" vents on the short panel between the two leg holes. The plans already have supports at the sides. All one would need to do is a layer over the back side and top to make an air duct out of this panel. You would have directional air on the panel front. A more complicated version would be flaps over the plans heat duct exit points and eye ball vents with an off to make a sort of floor and/or panel automotive'ish arrangement.

[John Slade]

>Then I went and got some Tylenol and 3 fingers of vodka.

Yea. I needed this treatment a few times while putting it in.

 

>If I read that right you have the heat and the freon lines running in the heat duct. Don’t you think that will limit the effectiveness of the AC?

 

Yes. Why would this be a problem? The pipes are insulated from each other by pour foam, and I don't plan to run heat and cool at the same time. The water feed has a manual valve just forward of the pilot seat.

 

>You have a NACA feeding your heater box, right?

No. The air is recirculated. My fresh air NACA'a have flaps to close them off when AC is in use. As you say, there would be little value in trying to cool incoming air. A lot of the benefit from AC is dehumidification.

 

>Have you run the blower yet to check airflow?

Yes. It's ok. I would have liked more. It suprising how much airflow you loose through 3 feet of scat hose.

 

The rear seat is about 6 inches high at the highest point. It might be possible to put something in the hell hole, but it wouldn't be easy, and blowing air through the heat ducts will reduce flow to a trickle by the time it gets to the front. Direct it all you want - I dont think it's going to be a noticable draft unless the blower is up front. There's room in the nose and the blower doesnt weigh much. I only weigh 165lbs, so extra weight up front should replace ballast on solo flights.

 

The center panel is very close to the nose wheel cover. Not much room there for pipes.

 

If I can figure out how, I'll move the AC part of this thread to another thread

[bigdaddie]

I too will be adding A/C to my Mazda powered monstrosity. I was figuring to put the heater/ac box on the firewall. My firewall is 4" wider than plans and I may move the engine back a few inches to increase propeller efficiency, thus increasing room. About airflow: I didn't realize how small the heat duct was until I constructed it! I will be increasing it's size. Anyone have any reasons why this would cause a conflict? My fues is 8" wider than plans at front seatback so I think I'll have plenty of room.

 

Regarding airflow: I understand why some have reservations in trying to push air fwd in an airplane going 200mph+. The cabin is closed in so no biggie right? If you just look at the length of these fueselages you'll realize airflow could be a problem. My solution is this, two fans. One to push the air from the firewall to the front and one to boost airflow at the front. I hope this will work. Works in my Suburban, but it has two evaporators.....

 

John, I've been following your web site, looks good. I'm looking forward to seeing the first flight photos! Did you use the stock Mazda turbo? If so, is it intercooled? I'll be VERY interested in cooling info, especially on the ground....

 

Steve

[LargePrime]

Three things can help with the long distance to the front.

 

1 smooth pipe. I would bet replacing scat with smooth pipe will increase airflow 50%

 

2 cross-sections. No matter the pipe's shape it basically sees it as a circle. Largest radius of that circle is what we want. Airflow volume is, of course (PIxR^2) exponential to that cross-section. Just squaring the plans heat duct to the largest edge should double air flow.

 

3 pressure. This will give oomph to the air at the end of the trip. Blower motors are funny though. A slightly larger blower can deliver much larger volume and pressure than a smaller version. Blowers are pretty good suckers, unlike fans. I would take a wild guess that two smaller blowers in the cozy are better than one large, but I wouldn’t put money on it. In this area johns should be perfect. Large and up front. I a very surprised the flow was disappointing.

 

Perhaps it is the blower. The Honda has a thin bladed squirrel cage instead of a full, or fuller bladed blower. I might suggest this 146 cfm at .5 inch static pressure. That should do it.

[John Slade]

>I'm looking forward to seeing the first flight photos!

Me too

 

>Did you use the stock Mazda turbo? If so, is it intercooled?

Yes and yes. (note - stock 2nd gen single stage turbo on 3rd gen engine)

 

>I'll be VERY interested in cooling info, especially on the ground....

Me too. On the ground doesnt worry me. That big Ferrari fan sounds like a turbine when I switch it on. The REALLY interesting data will be climb and cruise.

 

By the way, I took a 172 around the patch yesterday. I'd forgotten how truely BASIC those damn things are. An occasional ride in a 172 can help put into perspective all the "extra stuff" we do to our experimental airplanes.

[John Slade]

>smooth pipe. I would bet replacing scat with smooth pipe will increase airflow 50%

Good point, and a very simple change. I might try this later, if I can find something suitable. That scat tube wasnt cheap either....

 

>cross-sections.

2 inch is about all you can do when leading air from a blower in the nose to the air vent. There isnt a lot of room for big pipes, especially where they go under the F22 bulkhead. Hmmm. Maybe shaped fiberglass ducts would be a good option. I could flatten and widen them to keep the same volume where they go under the bulkhead.

 

>In this area johns should be perfect. Large and up front. I a very surprised the flow was disappointing.

Disappointing is a relative term. My wife is dissapointed if AC airflow is anything less than CAT 2. You can certainly feel the air coming at you from 2 feet away. I've seen cars with poorer air flow. Most are better. The scat tube will be costing me airflow for sure. Also, I may have built the plenum a bit too close to the fan. The other concern I have is leakage from the NACA scoops. I don't think there is much of a seal there when they're closed.

 

It'll do for now.

John

[LargePrime]

>cross-sections.

2 inch is about all you can do when leading air from a blower in the nose to the air vent. There isnt a lot of room for big pipes, especially where they go under the F22 bulkhead. Hmmm. Maybe shaped fiberglass ducts would be a good option. I could flatten and widen them to keep the same volume where they go under the bulkhead.

 

 

My point was that flattened widened tubes drasticaly reduce airflow since they have a reduced circle cross section. One larger tube that splits would be lighter and flow more air. There is a small gain in making the tubes larger than the blower outlet.