Starting my Homemade Hackman

60 posts in this topic

Posted

When I did my hacman it was a total home built effort. Made a distribution manifold (looks nice but was not needed) Made the nipple that threads into the carb to supply vacuum. Quicker and cheaper to make one on a lathe than to order one. Modded a run of the mill brass needle valve to do what I needed (more lathe work) My avid is a C model so opted not to static source from the air cleaner. Felt I was already fighting a problem with lean running at cruise due to the air filter being directly exposed to outside air pressurization. Gave the reference port its own filtered air source underneath the cowl. You will be happy with it once it is all sorted out.   :BC:

Saskavid, how did you make your carb nipple? I’ve been having a hard time finding one. I have a friend who can make anything on a lathe. 

I just took out the screw where the nipple will go and measured the thread pitch with a metric pitch gauge. My lathe will cut metric threads. the coolant bypass nipple may be the required thread pitch as well. just made the nipple end to the same look and dimensions as the vent nipples for the carb float chamber.

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Posted (edited)

Chris, I have two questions. What did you use for the orifice restriction and where did you source the filling for the carb with the 6M-1 thread?

I went to several auto parts stores and bought various 1/8 inch tubing couplers. I ultimately chose the one with the size which gave me the desired range of adjustment. It ended up being the 1/8 inch plastic coupler with the smallest thru hole that worked best for me.

You don't want the reference orifice to be too small or you will be able to pull enough vacuum to kill the engine. The larger the orifice the less effect the control has. Start big and go smaller. You might not even need an orifice actually just the resistance to flow in the 1/8 inch tubing may be sufficient.

When I first built my in flight mixture control I started with a very small orifice. (Not one of the 18 inch tubing couplers I mentioned above but a random super tiny jet I had laying around.) I started with the valve closed and took off. EGT's were too high so I put in a larger main jet and it flew normally. I then went up to several thousand feet and started opening the valve there was some delay from opening the valve and when the engine died. That was a surprise! I shut the valve and managed to get it started again before what would have been a forced landing. That made me break a sweat! I think it pulled fuel from the carb bowls into the lines. I finally got it started again and realized I only needed to open the valve a bit to go from full rich to engine quit. I landed and made the orifice much larger and it worked way better. I ended up using an orifice that only changed the EGT's a couple hundred degrees over the full range of operation. 

I would still change main jets between summer and winter even though if I used a smaller orifice I would not have needed to. For me a couple hundred degree range allowed me to optimize EGT's at any altitude during any particular season but did not allow enough range to cover seasonal change. For me the benefit was I could not accidently kill the engine! I felt safest with this and it proved out in reverse several times when I took off in a leaned setting by accident and didn't nuke my engine :-) 

I flew with my mixture control for probably close to 1000 hours and did not have an engine problem related to it once I got it ironed out. I would start with big to no orifice. It will still work. You can restrict it to get as much "control" as you are comfortable with! :-)

Edited by Chris Bolkan
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Posted

I think Lockwood has the fitting.

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Posted

I think Lockwood has the fitting.

 

Thank you Chris for the the great explanation. Was it a head nipple you ordered or some other part?

:BC: 

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Posted

What needle valve did you get?  I have been looking a bit this morning for a panel mount needle valve.

:BC:

 

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Posted

I will try and find the receipt or get you the model and part number off the control valve. I think I got it off Ebay and I ordered two before getting the right one. $25 range. I will let you know. 

 

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Posted

I think Lockwood has the fitting.

 

Thank you Chris for the the great explanation. Was it a head nipple you ordered or some other part?

:BC: 

If my memory is accurate the throttle cable adjuster fitting has the same threads as the nipple requires. I would have used the jam nut as a dimensional gauge to cut the threads to the proper depth on the fitting I made. Also put a ball valve plumbed into the system so I could have a secondary venting source separate from the restriction orifice. It was a piece of mind redundancy at the time I put it all together. Might be useful in an inflight jam. Also help to gravity feed fuel into the carbs quicker when the plane is not running or just getting running. 

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Posted

https://www.ebay.com/i/163206690047?chn=ps

 

The M6x1 fittings.  They have them on amazon too.  Have that and some 3/16" tygon tubing in my cart.  Gonna make Bob add this to the 670 before I fly his mod 4 again so I can start off on the rich side and dial it down as needed to help the EGT's

:BC:

 

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Posted

Here you go. 

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Posted

I would have went with the in-line brass one had I found it when I was looking. I have poly 90 fittings if you need them. I had to buy 10 to get 1. 

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Posted

Valves are hard to find that work well for this purpose. I do not thing you want a valve with too many turns. From my experience a single turn would be perfect. Don't even mess with those 10 turn precision valves. Way too much hassle when you need to change it fast when you accidentally take off with it lean. I could never find a single turn valve. I wanted to try a quarter turn ball valve but never did. I think that might work. 3-4 turn valves are available and what I ended up using even tho I think that is more turns than you will need.

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Posted

Well Damn!! This valve I have is about 15 turns from open to close. Guess I better look at something else. 

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Posted

Don't panic yet Vance,my setup needed multiple turns initially.the restricter orifice to the air cleaner has a huge impact on sensitivity,as already stated ,start big and work back to a smaller reference orifice.now up to 10.000 ft is covered in just less than one turn.

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Posted

I’ve already decided to use the control valve I have until I come up with something different. It mounts well and is plumbed already. Not a lot of thee turn options out there that work for this application and where it is mounted. 

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Posted

So has anybody looked at how Cowlove set up his manual leaning system?  It's way simpler than this hacman system, with no drilling or other mods to the carburetors or air cleaner.  It just uses a small, cheap 12 VDC vacuum pump hooked up to a rheostat, with the suction side plumbed into the float-bowl vents.  A small orifice lessens the effect of the vacuum pump.  With the rheostat I can run the vacuum pump at any speed and pressure ratio I want.  I crank it up to kill the engine at idle, instead of stressing my fuel pump by shutting the fuel off then waiting for the lines and float bowl to empty and the engine to stop..  BTW, no change is needed to any of the jets.  Is there any disadvantage to this set-up?. I have not had a chance to use it at altitude yet.  

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Posted

One of the reasons we shut down airplanes with fuel starvation rather than ignition is to make sure there isn't a fuel/air charge sitting in a cylinder ready to 'go' if someone moves the prop and the mag P-Lead is busted, or a nice hot lead ball isn't still there to give them a really bad day.  Even after cool down, the lack of fuel in the float bowl/fuel lines reduces the chance of an inadvertent start on prop movement.

In our 2 stroke, gear reduction engines, I'm not sure if that is a big concern or not.

Mark

 

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Posted

Old school, you never ran the carbs dry to shut down. The float being dry for awhile could cause an in-flight situation where the float could stick. You stayed clear of the prop at all times. Turbo, do you have a picture of the vacuum pump set up?

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Posted

Here is a picture Turbo mentioned of the vacuum pump system cowlove posted on the other thread.

Here is a picture of my system. It’s pretty much to the plans Chris put out. I tried some poly reducers and fuel line but the poly reducers are weak and smash easily. The fuel hose is harder to work with and harder to get off the barbs if you need to take it apart. 

Turbo, I am interested in the vacuum pump set up but have already made an investment into this system. I can easily be swayed into changing gears in a project but have learned it cost time and flying. If this does not work for whatever reason I might take another look. 

More to come. 

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Posted

I got the carb drilled today. I have to say it was a little nerve racking drilling the last hole from inside the carb slide areas but if you take your time and measure carefully it’s pretty easy. The measurement from the larger opening surface is 1.90”. I hit the side holes exactly. I used a 582 head vent (which I had in my stuff) with an oring and a little permatex aviation sealer. It’s all installed on the plane and looks great. All I need is my jets and I can test the system. 

Thanks to Chris B.  for the great documentation. If you follow his lead you will not go wrong. 

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Posted

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Posted

Nice job, Vance!  My craftmanship is so underdeveloped I was afraid to try to drill my venturis.   I like your carb-leveling plate.

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Posted

I may be wrong but try a 582 vent nipple from the head? It was awhile ago.

Yes, exactly the same part.

 

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Posted

So bringing this one back up because I'm getting ready to do something on my 582.  I want to make sure my thinking is correct before proceeding. In this and the other associated thread there are basically 2 systems presented and I would like to discuss the merits of both. So the 2 systems I'm talking about are Chris Bolkan DIY Hacman type system and the vacuum pump system by Cowlove. Here are the links to the posts with the descriptions/plans

DIY Hacman - http://www.avidfoxflyers.com/index.php?/topic/5717-leaning-the-carbs-for-altitude-on-the-cheap/&do=findComment&comment=53166

Vacuum pump - http://www.avidfoxflyers.com/index.php?/topic/5717-leaning-the-carbs-for-altitude-on-the-cheap/&do=findComment&comment=53084

Both systems work by applying a small amount of vacuum to the carb bowl vents with the difference being the source of the vacuum. I am interested in putting something on my airplane not for high altitude operation but primarily for ambient temperature changes. I don't mind changing needles or jets a couple times a year but around my area, and I'm sure others, the temp can vary wildly from one day to the next. I plan to fly year round and in bitter cold to hot temps. Changing jetting a coulpe times a year is fine but in the winter months it could be every other week.

With the DIY Hacman system, or for that matter the "real" Hacman system, the vacuum source is the carburetor venturi, so the amount of vacuum you get varies depending on throttle position. This means that changes of throttle require adjusting the valve to again achieve the proper mixture. The instructions for the "real" system state that the valve should be closed any time a throttle adjustment is made. 

With the vacuum pump setup the pump supplies the vacuum. With a well regulated electrical supply the vacuum should be constant. So with a constant vacuum source the float bowl pressure should be constant just like it is with no leaning system. As far as I can tell, with this sytem, even with the pump on, the mixture should behave normally with throttle changes.

Getting a little more into it, the Hacman system uses manifold vacuum which is inversely proportional to throttle position. IE: low throttle - high vacuum, high throttle - low vacuum. So lets say you have the Hacman adjusted to provide good EGT at a cruise power setting. If you open the throttle the vacuum drops and the mixture gets richer. Conversely if you retard the throttle the vacuum increases and the mixture leans. The system works, but seems like it would be a pain to use for something like touch and go landing practice.

Now the vacuum pump system has constant vacuum which would not change for any throttle position. It seems that if you were doing that T&G landing practice that you could set it and pretty much forget it for that flight. Then it could also be used for leaning at altitude.

It seems to me that the vacuum pump system  would be less cumbersome to use, simpler to install, and not require any potential carb drilling. I'm wondering why this isn't the more chosen route compared to the Hacman type system.  

Am I thinking about this right? Is there something I'm missing?

 

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Posted

Not exactly. Yes, the vacuum pump holds a constant vacuum, but the thing you want to control is difference between the carb throat pressure and the bowl pressure, not just the vacuum to the bowl. As you reduce throttle, the throat pressure rises (the throat velocity drops with less airflow velocity. I have found with my Hacman that the EGT stays reasonable steady with normal throttle changes, since the balance of throat-bowl pressures is held somewhat constant. 

If the vacuum pump holds low enough pressure, as you reduce throttle is might be possible for the bowl pressure to be lower than the throat pressure, so gas won't flow at all. Then it gets pretty quiet.

 

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