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  #21  
Old 03-29-2017, 10:42 AM
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Snowflake Snowflake is offline
 
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Originally Posted by jimgreen View Post
...
I'm out of ideas.
The red cube is deadly accurate but I want functioning fuel gauges.
Should I put new senders?
With two Red Cubes, and a fuel gauge that works by subtraction of fuel flowing through them, you would have accurate gauges.
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  #22  
Old 03-29-2017, 10:53 AM
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RV7A Flyer RV7A Flyer is offline
 
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Originally Posted by Snowflake View Post
With two Red Cubes, and a fuel gauge that works by subtraction of fuel flowing through them, you would have accurate gauges.
Unless you had a leak in the system (stuck quick-drain, failed connection, etc.) between the tank and Red Cube.
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  #23  
Old 03-29-2017, 11:07 AM
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Originally Posted by RV7A Flyer View Post
Unless you had a leak in the system (stuck quick-drain, failed connection, etc.) between the tank and Red Cube.
And then there's that pesky 14 CFR part 25.1337 to consider...
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Built an off-plan 9A with too much fuel and too much HP. Should drop dead any minute now.
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  #24  
Old 03-29-2017, 01:07 PM
larosta larosta is offline
 
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Default Perhaps Consider a different sender technology

Part of my business and career has involved the application of a variety of sensor technologies. The sensing of liquid levels would seem to be pretty straightforward and often is, unfortunately that is not always the case in vehicles like aircraft. The consequences of having an unreliable fuel level indication can be easily offset through other means but sometimes we humans overlook the obvious and get into trouble, in an aircraft that can be pretty serious.

The small aircraft industry has relied on restive float sending units like the ones in our automobiles since the early days and that has mostly worked because no one trusted them and the analog displays were small and difficult to read. Enter modern glass panels and digital displays. Now we expect resolution down to the 0.1 gal and linearity and accuracy to the fraction of a percent. This is probably not possible with a restive or capacitance sensor within the confines of most budgets.

A technology that I have been looking at for another application is a magnetoresistive sensor. Magneto Resistive - This is another one of those technologies that was described by the one of the giants of physics back in the 1800's, Lord Kelvin.

https://en.wikipedia.org/wiki/Magnetoresistance

Up until the advent of advanced semiconductor technology it has mostly remained practical for use in the laboratory and expensive, complicated instrumentation applications. Today, Honeywell and Allegro Semiconductor have reduced the technology to sensing that are available off the shelf these can be integrated into float type sending units that may be useful in general aircraft.

One company that I have found that has products that use this technology and has TSO'd devices available for several aircraft is CIES in Bend, OR. The last time I talked to them they were trying to gauge interest in a sending unit that would be appropriate to the experimental aircraft market.

https://www.ciescorp.net/

https://www.ciescorp.net/vans-rv-fuel-level.html

- Phil
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  #25  
Old 03-29-2017, 01:27 PM
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Neat concept, but the only real advantage this will have in our planes over the resistive floats is the size of the float, giving 80 degrees of travel over 70 degrees. We can do that now with a different float. Unless the CIES device amplifies the number of degrees of travel somehow for the B field on the sensor, it's not a major improvement. The resistive sensors currently have plenty of resolution, that's not the problem.

EDIT - I thought perhaps I had an "Ah-HA!" moment looking at the drawings for the Vans-supplied Stewart Warner float senders, because when the sender float arm is bent as shown and installed as shown on the drawing, you get only about 60-65 degrees of movement across the rheostat. I thought it would be simple enough to change the way the float arm is bent and increase that to 90 degrees or better, and sure enough that's fairly simple to do. Then I thought about the rheostat itself... so I called Stewart Warner technical support and asked the question, sure enough the rheostat itself is limited to 70 degrees rotation. Vans design actually does a fairly good job of using all that without encountering the deadband on the ends, so no realistic improvement is available with that sender.
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Built an off-plan 9A with too much fuel and too much HP. Should drop dead any minute now.

Last edited by airguy : 03-29-2017 at 01:57 PM.
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  #26  
Old 03-29-2017, 08:52 PM
jimgreen jimgreen is offline
 
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RV7A Flyer, I did of course mean the converters. They are the Dynon supplied converters. Doesn't seem like there is much to go wrong with them, but I'm not an electronics guy.
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  #27  
Old 03-29-2017, 09:54 PM
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Quote:
Originally Posted by jimgreen View Post
RV7A Flyer, I did of course mean the converters. They are the Dynon supplied converters. Doesn't seem like there is much to go wrong with them, but I'm not an electronics guy.
As noted earlier, since you can't set the endpoints, you can (like on an RV) end up with the empty-to-full range using a very, very small range of voltages, rather than the whole 0-5V. On mine, I think almost 3/4 of the calibration points showed NO difference on the display (which shows 2 decimal places). Granted, the actual data (which you can see via other menus) did have some slight differences in the 3rd and 4th digits, it still seems less than optimal to use such a tiny fraction of the available data range. And, indeed, they were inaccurate in the mid-range.

So, I recommend using the Princeton 2-setpoint converters.
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  #28  
Old 03-29-2017, 10:57 PM
jimgreen jimgreen is offline
 
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Quote:
Originally Posted by RV7A Flyer View Post
As noted earlier, since you can't set the endpoints, you can (like on an RV) end up with the empty-to-full range using a very, very small range of voltages, rather than the whole 0-5V. On mine, I think almost 3/4 of the calibration points showed NO difference on the display (which shows 2 decimal places). Granted, the actual data (which you can see via other menus) did have some slight differences in the 3rd and 4th digits, it still seems less than optimal to use such a tiny fraction of the available data range. And, indeed, they were inaccurate in the mid-range.

So, I recommend using the Princeton 2-setpoint converters.
Thanks, I think I will.
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  #29  
Old 03-29-2017, 11:03 PM
woxofswa woxofswa is offline
 
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The holy grail for me would be self calibrating gauges. They say it can't be done, but I don't understand why.
It seems to me that you would just need a simple sensor to determine which tank is selected. It could be very similar to the magnetic door sensors and added to the selector valve.
With tank selection known, fuel added is a known quantity, fuel burned is a known quantity(from red cube), leaving simple math of fuel remaining. The computer should be able to calculate what the reading should be versus what the current reading actually is, and automatically make the requisite voltage change corrections itself. Even fuel tank temperature could be added to the mix to really refine. It could then store averages over myriad flights and constantly compare and refine itself from its stored history, presenting its own performance grade similar to how the magnetometer is calibrated.
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Last edited by woxofswa : 03-29-2017 at 11:05 PM.
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  #30  
Old 03-29-2017, 11:31 PM
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RV7A Flyer RV7A Flyer is offline
 
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Quote:
Originally Posted by woxofswa View Post
The holy grail for me would be self calibrating gauges. They say it can't be done, but I don't understand why.
It seems to me that you would just need a simple sensor to determine which tank is selected. It could be very similar to the magnetic door sensors and added to the selector valve.
With tank selection known, fuel added is a known quantity, fuel burned is a known quantity(from red cube), leaving simple math of fuel remaining. The computer should be able to calculate what the reading should be versus what the current reading actually is, and automatically make the requisite voltage change corrections itself. Even fuel tank temperature could be added to the mix to really refine. It could then store averages over myriad flights and constantly compare and refine itself from its stored history, presenting its own performance grade similar to how the magnetometer is calibrated.
And then you could add a Kalman filter to it...
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