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jbhart(at)onlyinternet.ne
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 Posted: Mon Aug 08, 2011 1:56 pm Post subject: FireFly & MZ 34 Progress |
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Kolbers,
The new belt sheave and modified propeller hub have been mounted. Several
attempts to run the engine at speed with the tail tied to the pickup were
terminated when the belt became slack. When I torqued up the clamping bolt
to spec. the problem went away. With the 2.6 ratio, there is no problem of
getting the engine up to speed. Flew for 27 minutes with the engine running
flat out, with the EGT at 1,250 and CHT at 400 degrees F. Calculated fuel
burn was 2.2 gph. Very hot and humid day. Engine quit on taxi in due to
carburetor ice. Did not get good air speeds as my old GPS did not find
enough satellites during the flight to register.
Took the carburetor off and brought it home to modify. Added a static air
pressure port to the carburetor bore just behind the air filter attachment
ring. Since I am running low hp, I want to test to see which air filter
provides the lowest air pressure drop when the engine is at speed. Loss of
air pressure at the point of the carburetor is due to the air accelerating
through the propeller. This may not be much of a problem with a larger
engine, but with a smaller engine it is important to recover as much of the
pressure as possible.
With the FireFly tied to the pickup, I will test the round cylindrical foam
air filter that came with the engine, and the K&N under three conditions.
Since I have encased the filter in a scoop, I will run it with the scoop
opening plane parallel to the air flow followed by rotating the scoop 90
degrees into the air flow while on the ground. Then I will again take data
with the scoop forward while in flight. I expect to pick up several inches
of water increased pressure.
In an attempt to counter the ice build up at low engine speeds during high
humidity conditions, I have drilled and tapped a hole to 8-1.25 mm thd in
the boss on the bottom of the carburetor next to the mounting flange. I
will be inserting a 20 watt heater that I obtained from KTMtwins.com.
Should get the carburetor back on tomorrow or the next day.
To be sure the engine is pointing in the right direction at cruise, I
designed a little adjustable level that is attached to the left longeron,
just back of the throttle. It will let me discover when I am in level
flight by being able to center the bubble. Then once on the ground the tail
of the FireFly can be elevated so that bubble can be returned to level
flight position. Then with a digital level, the aoa and the propeller
vertical plane of rotation can be measured. If the latter is off, one can
washer the mounts until the propeller in dead on. If you would like to see
the device, it can be found at:
http://jackbhart.com/firefly/firefly163.html
Still lots to do. When I get time, I will put up the new carburetor and
belt reducer mods.
Jack B. Hart FF004
Winchester, IN
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Mon Aug 08, 2011 2:49 pm Post subject: FireFly & MZ 34 Progress |
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Jack,
Following your continuing efforts to get better efficiency from your
Firfly is always a treat. I like the guitar string gearbox.... great
idea!
Thom
On Aug 8, 2011, at 5:57 PM, "Jack B. Hart" <jbhart(at)onlyinternet.net> wrote:
| Quote: |
Kolbers,
The new belt sheave and modified propeller hub have been mounted. Several
attempts to run the engine at speed with the tail tied to the pickup were
terminated when the belt became slack. When I torqued up the clamping bolt
to spec. the problem went away. With the 2.6 ratio, there is no problem of
getting the engine up to speed. Flew for 27 minutes with the engine running
flat out, with the EGT at 1,250 and CHT at 400 degrees F. Calculated fuel
burn was 2.2 gph. Very hot and humid day. Engine quit on taxi in due to
carburetor ice. Did not get good air speeds as my old GPS did not find
enough satellites during the flight to register.
Took the carburetor off and brought it home to modify. Added a static air
pressure port to the carburetor bore just behind the air filter attachment
ring. Since I am running low hp, I want to test to see which air filter
provides the lowest air pressure drop when the engine is at speed. Loss of
air pressure at the point of the carburetor is due to the air accelerating
through the propeller. This may not be much of a problem with a larger
engine, but with a smaller engine it is important to recover as much of the
pressure as possible.
With the FireFly tied to the pickup, I will test the round cylindrical foam
air filter that came with the engine, and the K&N under three conditions.
Since I have encased the filter in a scoop, I will run it with the scoop
opening plane parallel to the air flow followed by rotating the scoop 90
degrees into the air flow while on the ground. Then I will again take data
with the scoop forward while in flight. I expect to pick up several inches
of water increased pressure.
In an attempt to counter the ice build up at low engine speeds during high
humidity conditions, I have drilled and tapped a hole to 8-1.25 mm thd in
the boss on the bottom of the carburetor next to the mounting flange. I
will be inserting a 20 watt heater that I obtained from KTMtwins.com.
Should get the carburetor back on tomorrow or the next day.
To be sure the engine is pointing in the right direction at cruise, I
designed a little adjustable level that is attached to the left longeron,
just back of the throttle. It will let me discover when I am in level
flight by being able to center the bubble. Then once on the ground the tail
of the FireFly can be elevated so that bubble can be returned to level
flight position. Then with a digital level, the aoa and the propeller
vertical plane of rotation can be measured. If the latter is off, one can
washer the mounts until the propeller in dead on. If you would like to see
the device, it can be found at:
http://jackbhart.com/firefly/firefly163.html
Still lots to do. When I get time, I will put up the new carburetor and
belt reducer mods.
Jack B. Hart FF004
Winchester, IN
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_________________
Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
- Anonymous |
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Richard Pike
Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee
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| Posted: Mon Aug 08, 2011 2:55 pm Post subject: Re: FireFly & MZ 34 Progress |
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Jack, since I do not know the exact arrangement of your ram induction air into the filter, maybe I am off the mark, but it occurs to me that when you ram air into a carb with a float bowl, it changes the air pressure of the float level and fuel level within the float bowl chamber, have you taken into account that the ram effect can alter the float bowl cavity pressure affecting the fuel level/induction into the manifold?
Just asking - probably you have. Thanks for your studious and precise experiments.
Richard Pike
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jbhart(at)onlyinternet.ne
Guest
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| Posted: Wed Aug 10, 2011 10:24 am Post subject: FireFly & MZ 34 Progress |
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At 03:55 PM 8/8/11 -0700, you wrote:
| Quote: |
Jack, since I do not know the exact arrangement of your ram induction air
into the filter, maybe I am off the mark, but it occurs to me that when you
|
ram air into a carb with a float bowl, it changes the air pressure of the
float level and fuel level within the float bowl, have you taken into
account that the ram effect can alter the float bowl pressure affecting the
fuel level/induction into the manifold?
Richard,
You are correct. All one has to do is put a static tap into the ram filter
housing and then connect the float vent to it and both the carburetor throat
and the volume above the float chamber run at the same pressure at all
engine speeds.
This is why I used a dynamic pressure tap to control air/fuel mixture in the
Bing on the Victor 1+. What you do is set the Bing for the richest normal
setting. Then you bleed off air using a negative dynamic pressure air that
is supplied from the carburetor throat to reduce the pressure over the float
bowl to lean the mixture out. How this is done can be seen at:
http://jackbhart.com/firefly/firefly146.html
Then later on, I added a positive pressure dynamic tap to the carburetor
throat and instead of venting to the static air, I vented to this new tap.
This ensures that one can drive the pressure above the float bowl positive.
One can see the pressure recover found for the Victor 1+ at:
http://jackbhart.com/firefly/firefly147.html
All of these pressure readings were taken from above the wing. With the MZ
34 running inverted, the carburetor is much lower and I may be able to
modify the scoop to include a 90 degree elbow to capture higher pressure ram
air from below the wing. The scoop mounting can be seen in the second and
third photos of:
http://jackbhart.com/firefly/firefly158.html
At this time I am using mechanical method to enable me to adjust the
Tillotson low and high speed jets from the cockpit while on the ground. But
I have placed plus and minus and static taps in the carburetor for the
purpose of adjusting the air/fuel mixture while in the air. The Tillotson
carburetor will react to positive pressure air under the control diaphragm
as does the Bing with positive pressure over the float bowl. If you would
like to check it out, it can be seen here:
http://jackbhart.com/firefly/firefly153.html
The pressure controlled air/mixture control will not be mounted until I get
a few more hours on the MZ 34. I am very excited about this method as it
weigh almost nothing, and there is only one mechanical thing, which is, a
tiny mixing valve. I had very good luck with it on the Victor 1+, in that,
I could run constant and stable EGT numbers and I did not have to guess what
the fuel burn rate was going to be today or over any time of day. Once this
system is installed the mechanical needle controls will be removed.
Jack B. Hart FF004
Winchester, IN
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