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herbgh(at)nctc.com
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 Posted: Wed Apr 08, 2009 6:59 pm Post subject: Mixture control... |
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Jack
See your post and am reminded...how is the mixture control
coming...? IMHO...not only does it promise a bit better fuel burn
through better mixture control...but also may allow us to dial out
the egt peak as we drop below 5k rpms? Perhaps make the engine less
susceptible to seizures...? Herb
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jbhart(at)onlyinternet.ne
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| Posted: Thu Apr 09, 2009 5:42 am Post subject: Mixture control... |
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At 09:57 PM 4/8/09 -0500, you wrote:
| Quote: |
Jack
See your post and am reminded...how is the mixture control
coming...? IMHO...not only does it promise a bit better fuel burn
through better mixture control...but also may allow us to dial out
the egt peak as we drop below 5k rpms? Perhaps make the engine less
susceptible to seizures...?
|
Herb,
For flying this winter and spring, so far, have been mean weather wise.
Most of the time my cold weather gear was used to blow snow. Spent most of
the winter in my basement shop working on stuff to try this spring. Most of
it is weight reduction stuff.
I flew for the first time in March with the new filter cover (ram scoop)
positioned at about sixty degrees up from horizontal. But I took no
pressure measurements. I was not able influence EGT with the cover in this
position. This got me to thinking about what to do to increase the positive
pressure over the float bowl. I realized that it would be better to
reference this pressure off something in the carburetor. I removed the
carburetor and put a static pressure tap plus a positive dynamic pressure
tap into the carburetor inlet. If the static tap does not do the job, I
will move to the positive dynamic tap. Since this will produce much more
pressure than needed, I will run the line to simple liquid bubble pressure
regulator to obtain constant but ground adjustable pressure. By adding the
filter air scoop to recover filter pressure loss, I have complicated things,
and so I will have to run quite a few flight tests to record air filter
pressure drops at various engine speeds and scoop positions. Then I will be
able to get back to working with the mixture control.
I remain very excited about the mixture control. The ability to adjust EGT
in flight lets one dial in the same burn rate for a given engine rpm. One
does not have sweat "should I have added fuel" thoughts. I have wondered
how it would work on a Rotax 447, but for me it is too late for that. I am
running this engine at much higher EGT than I did the Rotax.
The Victor had the same problem as you described for below 5,000 rpm. At
first I thought it was a leaky exhaust coupler. I modified the system and
changed clamps. Still the same problem. Out of frustration, I started
looking at the Bing. I noticed how the slide was polishing and concluded
the throttle return spring was too weak, and the slide needle assembly was
bouncing. Went to a heavier spring and things looked better. Then I
decided to modify the carb needle. It was an eye opener. I was able get a
flat EGT across the whole cruise rpm range. This proves to me that no
engine manufacturer can tell you what needle jet combination is correct for
every given application and it is unfair expectation. What they recommend
may work on the test bench, but one must consider this is just a starting
point.
Rambling. The snow blower is off and the mower is ready to go.
Jack B. Hart FF004
Winchester, IN
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herbgh(at)nctc.com
Guest
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| Posted: Thu Apr 09, 2009 6:17 am Post subject: Mixture control... |
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Good info Jack...much appreciated...
you may be the only engineer in the world working to improve 2
strokes... 
I haven't experimented but I suspect that the egt peak in the
high 4k range occurs when the needle/needle jet drops in influence
and we begin to go fully onto the main ... a transition point at
abt 3/4 throttle..
I think I have also noticed that some props tend to load/unload
at certain rpm ranges and effect egts...Herb
| Quote: | >
Herb,
For flying this winter and spring, so far, have been mean weather wise.
Most of the time my cold weather gear was used to blow snow. Spent most of
the winter in my basement shop working on stuff to try this spring. Most of
it is weight reduction stuff.
I flew for the first time in March with the new filter cover (ram scoop)
positioned at about sixty degrees up from horizontal. But I took no
pressure measurements. I was not able influence EGT with the cover in this
position. This got me to thinking about what to do to increase the positive
pressure over the float bowl. I realized that it would be better to
reference this pressure off something in the carburetor. I removed the
carburetor and put a static pressure tap plus a positive dynamic pressure
tap into the carburetor inlet. If the static tap does not do the job, I
will move to the positive dynamic tap. Since this will produce much more
pressure than needed, I will run the line to simple liquid bubble pressure
regulator to obtain constant but ground adjustable pressure. By adding the
filter air scoop to recover filter pressure loss, I have complicated things,
and so I will have to run quite a few flight tests to record air filter
pressure drops at various engine speeds and scoop positions. Then I will be
able to get back to working with the mixture control.
I remain very excited about the mixture control. The ability to adjust EGT
in flight lets one dial in the same burn rate for a given engine rpm. One
does not have sweat "should I have added fuel" thoughts. I have wondered
how it would work on a Rotax 447, but for me it is too late for that. I am
running this engine at much higher EGT than I did the Rotax.
The Victor had the same problem as you described for below 5,000 rpm. At
first I thought it was a leaky exhaust coupler. I modified the system and
changed clamps. Still the same problem. Out of frustration, I started
looking at the Bing. I noticed how the slide was polishing and concluded
the throttle return spring was too weak, and the slide needle assembly was
bouncing. Went to a heavier spring and things looked better. Then I
decided to modify the carb needle. It was an eye opener. I was able get a
flat EGT across the whole cruise rpm range. This proves to me that no
engine manufacturer can tell you what needle jet combination is correct for
every given application and it is unfair expectation. What they recommend
may work on the test bench, but one must consider this is just a starting
point.
Rambling. The snow blower is off and the mower is ready to go.
Jack B. Hart FF004
Winchester, IN
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jbhart(at)onlyinternet.ne
Guest
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| Posted: Thu Apr 09, 2009 1:21 pm Post subject: Mixture control... |
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At 09:15 AM 4/9/09 -0500, you wrote:
| Quote: |
Good info Jack...much appreciated...
you may be the only engineer in the world working to improve 2
strokes...
I haven't experimented but I suspect that the egt peak in the
high 4k range occurs when the needle/needle jet drops in influence
and we begin to go fully onto the main ... a transition point at
abt 3/4 throttle..
I think I have also noticed that some props tend to load/unload
at certain rpm ranges and effect egts...
|
Herb,
If I had not been forced into using a two stroke, I would be flying a four
stroke. In the past I was influenced by what has been written about two
strokes. I have found that there is a lot of misinformation out there. A
lot of it came directly from the EAA by picking an expert that was not a
flyer but was a two cycle motorcycle man. When the two cycle engine is
placed on an airframe, one does not have to worry about quick throttle
response time. Most of the time the engine is run at constant speed with
short bursts of max output for take off and climb out.
As for 4k rpm EGT peaking, I do not believe it has anything to do with the
main jet. After mounting throttle slide position indicator, I found that
both the Rotax 447 and the Victor will develop max engine speed at around
40% of the throttle opening. This is just where the main jet starts to pick
up. Checking my flight notes I had recorded 5,000 rpm at 25% and 4,500 rpm
at 20% carb opening. In this range the Bing is under the influence of the
pilot(idle) jet, slide cutaway and the needle position. This gives a couple
of things that can be done to adjust the carburetor. One cannot adjust the
cutaway but you can lean and richen the mixture about 50 degrees EGT with
the idle mixture control. The other and I consider the best choice was to
modify the needle between the 20% to 40% region. This has worked out very
well. All of this indicates the carb size is much too large, but one just use
what is available and fit or refit the needle to your specific application.
My disappointment is that I had to figure this out. But it has made me much
more excited about flying a two stroke engine. It has moved me from a
piston port to reed valve engine. I have discovered I can run this engine
at higher EGT than the Rotax 447. The reason for this is advanced
technology and design. With ceramic cylinder coating lets you run a tighter
fitting piston due to both being made of aluminum alloys with a common
temperature expansion ratio. Liquid cooling is a pain, but it helps get more
heat away from the cylinder as apposed to a steel liner in aluminum
interfacing directly with air. Running a tuned exhaust helps with engine
breathing and the reduction of unburnt fuel in the exhaust. This type of
engine design is supposed to be less prone to cold seizure. Before I added
the fuel mixture control, I had problems of the engine quitting on final
after a long low throttle decent. Idle jet adjustments did not seem to
help. After adding the mixture control, I can fly the FireFly down at
cruise speed, close the throttle and land without the engine quitting. This
technique keeps the carburetor throat warmer and less prone to icing.
Best of all, the Victor is running at half the fuel flow rate of my Rotax
447. Could I have gotten to this point with the Rotax 447? I don't know.
The next question is why doesn't Bing added this mechanism in or to the
carburetor and make it a true aircraft carburetor?
Not flying enough - Rambling #2
Jack B. Hart FF004
Winchester, IN
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