Hacman Kit install

[ChrisBolkan 130]

I designed and flew my in flight mixture control before green sky adventures started selling theirs. I had heard of an automatic "HAC" module for snow machines and bought one to try on my plane. It worked but didn't provide ideal mixture all the time. I got the idea from the diaphragm controlled module that I could "replace" the needle valve and air chamber in the HAC module with a manual valve.  I flew mine for years with awesome results.

My ego believes green sky was watching design progress which I documented on the "other" avid site and got the idea to produce theirs. Here is some documentation I produced as I thought through how it might work and how I set mine up originally. It may be of some help to anyone interested in building one of these or who has the Hacman and is setting it up.

Chris Diagram.pdf

Manual mixture.PDF

[ChrisBolkan 130]

I also had to modify one of my carbs to produce the low pressure port for the system to work. Here are the pics of how I modified the carb.

Carb mod.pdf

[ChrisBolkan 130]

At the very bottom of the carb mod pics is a PDF document that describes the operations. You will miss it if you don't know it is there.

I ended up using 180 and 190 jets in my system. 180's summer 190's winter. I set my reference orifice to only allow a couple hundred degrees total change with the valve. That felt safest to me. When I originally designed the system I used a super tiny reference orifice and managed to kill the engine in flight. Got it re started but decided that wasn't the best idea so I limited total delta T to a reasonable amount and changed mains seasonally.  I found and used a three turn needle valve and found it to be too many turns. I don't see how anyone can use a 10 turn valve and have no idea why the hacman has so many turns. You do not need that level of resolution and there were times I had forgotten to enrich the mixture prior to takeoff that I would have appreciated less than three turns! I always idled and did all ground operations at full lean because the engine ran so smooth. the trick was remembering to enrich prior to takeoff. If I could have found on 1 turn valve, it would have been plenty of resolution while being able to change mixture quickly when necessary (like forgetting to enrich at takeoff)

On time while testing my setup I took it to 14,500 feet. The engine ran great but it was producing very little power and was eerily super smooth.

[Emory Bored 61]

Beautiful job Chris.  I need to copy all that and archive it in a file on the 'puter for future reference.  I'm not smart enough about carburetor theory of operation to understand how applying a reference vacuum to the float bowl drains changes the mixture.  But I suppose if I spent some time on the two hand drawn documents with a carburetor in front of me I might begin to "get" it.  Thanks for posting that.

[Dusty 126]

The hollow treaded rod is the vacuum source ,this the basis for the unit,best tap off both carbs.If your carbs don't have the tapping already done I would suggest finding a set of later body's (seems to be all late silver top and all blues have them)

the fitting you refer to in the picture is for priming, I thinkI posted a schematic a short while ago of how I set up my mixture control, 

well worth the effort once sorted

[nlappos 413]

Let me try to answer the big picture question - what exactly is all that tubing and the cockpit valve doing? 

Short answer: providing a mixture leaning system.

Long answer: Using the venturi pressure as a fine low pressure reference, the Hacman mixes this low pressure into both carb bowls, so the bowl pressures drop a bit, and the difference between the bowl pressure and the venturi becomes less (when you are leaned). , The less the pressure, the less fuel flows up from the bowl, and the leaner the mixture.The venturi is the place where the air pressure is lowest, due to all the air rushing past the hole. That is the screw fitting you put into the side of the forward carb with the single tube.It becomes one of the two pressures that the tubes carry to the cockpit valve. Why only one tube? because there is plenty of venturi suction from either carb, and this tube won't change it, so only one is necessary.

The other tubes around the carb all connect the carb bowls and the filter volumes together to be sure whatever mixing you do is balanced between the two carb bowls (woe be the guy who leans one and not the other!) When the valve is opened (leaned) in the cockpit, it mixes low pressure venturi air with the bowl pressure, so the bowl air pressure drops. When the carb operates, the pressure in the bowl pushes the fuel up into the lower pressure venturi. Less bowl pressure, less push, and less fuel flow. Less bowl pressure acts the same way as if you had put a smaller orifice into the carb jet line. Less pressure difference between the bowl and the venturi, less fuel flows up, so the mixture is leaner.

[Emory Bored 61]

When the carb operates, the pressure in the bowl pushes the fuel up into the lower pressure venturi. Less bowl pressure, less push, and less fuel flow. Less bowl pressure acts the same way as if you had put a smaller orifice into the carb jet line. Less pressure difference between the bowl and the venturi, less fuel flows up, so the mixture is leaner.

Thanks man.  Good post.  Gotcha.

[Knuckledragger 135]

The collective wisdom on this forum is great!  Thanks to all who posted

[Fly-n-Low 181]

Emory,

I must be having a airhead day, as I seem to have more questions than ideas.  Why am I tapping into the venturi vacuum? why only one carb? what connects to the outward facing threaded portion of the hollow threaded rod that screws into the venturi vacuum?  in the pic below,what is the hose coming off the right carb and leaving the picture connected to?    

  I don't mind guessing on a car where I can call AAA when I guess wrong, but when it comes to my plane if I don't have the facts, it stays in the box.

 

One tube goes to the air cleaner... The other pics for reference have one filter instead of two.

Edited 26 Nov 2015 by Fly-n-Low

[Fly-n-Low 181]

That is what I was thinking about how this works. I think it is way simpler than the extra cables and parts in the mixture system I have uses. I think you guys have converted me!!!

[ChrisBolkan 130]

At the top of the post with all the carb tubing pictures are two PDF files. One I sketched up when I thinking about how I might build a manual mixture control it is a PDF labeled Chris Diagram. The other is a 2 page PDF that describes my actual implementation. I don't know if those two files are obvious because of all the pictures, but one describes my reasoning and the other is a "how to make your own" drawing.