Garner's electro-fluidic autopilot - thermistor information

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piolenc

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When I first ran into this at Oshkosh '82 I was fascinated. It was my first contact with the discipline of fluidics, and it was shocking that such a simple mechanism could be used for wing leveling and heading adjustment.
Now, many years later, I want to build it, but in the meantime the most important components - thermistors made by Fenwal Electronics - are no longer available. I am trying no to find out their characteristics, so that I can replace them with something that is currently on the market. This is made even more complicated by the fact that my information is on a second- or third-generation photocopy, in which the exact component designation is not readable. Starts with 32...
I am trying to find someone with either the necessary component information, the component itself or anything else that will get me closer to my goal.
 

Vigilant1

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Now, many years later, I want to build it, but in the meantime the most important components - thermistors made by Fenwal Electronics - are no longer available. I am trying no to find out their characteristics, so that I can replace them with something that is currently on the market. This is made even more complicated by the fact that my information is on a second- or third-generation photocopy, in which the exact component designation is not readable. Starts with 32...
Wow, an esoteric subject fer sure! Fun.

Fenwal Controls is still in business, maybe contact them and see if you can find out about their old thermistors--part numbers, alternate part numbers, old spec sheets or data sheets, if that product line was sold to another company, etc. Some old coot tech rep may know all of this and you'll have a good chat. Worth a shot.
It looks like Fenwal was assigned some patents for fluidic components. You might be able to search for other components made under those patents. They've long expired, but the numbers might still be in available literature.

Fenwal Controls
400 Main St.,,
Ashland MA, 01721-2150

Phone: (508) 881-2000

My guess is that modern digital processing has gotten so cheap, easy, and good that there won't be many folks who spend a lot of time thinking about fluidics. That doesn't mean fluidics isn't a valid way of doing some things, but it has largely been overcome by technology.
 
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wsimpso1

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IIRC, these devices use thermistors to sense air flow by looking at the the difference between two thermistors. We now have air mass flow sensors of a variety of types - I suspect that you will not be restricted to the thermistors for this function...
 

Pops

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That was my first homemade autopilot and using the homemade vacumm billow servos like used on the Britten autopilots.
Worked good. The biggest down side was the life of the small electric motor making the small air flow over the thermistor.
I ditched that and went with a early solid state gyro sensor , ( also not made now) and flew it for 2 years in the SSSC using RC giant scale servos to power trim tabs. Worked good. Plan on putting it in the JMR Special after going to a late model sensor.
I also used the thermistors in the pitch part of the autopilot that locked on a pressure altitude to within 25'.
I have the part # for the thermistors if you need to try to find a replacement. They are very little, about the size of a grain of rice with 2 small wires.
Back at that time I bought the instruction booklet that Doug Garner sold .
I also built the magnetometer and it also worked good.
Short version of a long story. My youngest son built upon the magnetometer idea while in his senior year in college and designed a nav system the measured the earths magnetic lines in different vectors and made a nav system like a GPS using the earths mag field. Just needed a little more work to tighten the programing up and allowing for the iron deposits in the homemade computer. ( I designed all the PC boards for him ).
He had the company that sold the magnetmeter wire wound coil that Doug used to wound all the coils used in his system.
At that time my son was hit head on by a semi-tanker truck on the interstate and spent 2 years in hospitals with a lot of injures including a head injury.
Doing good now , dealing with the problems but married with 2 sons.
Your post brings back a lot memories, some good and some not.
Thanks.
Pictures added. the slot in the mounting for the sensor was for adjusting the sensor to detect yaw and roll.
 

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Bill-Higdon

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That was my first homemade autopilot and using the homemade vacumm billow servos like used on the Britten autopilots.
Worked good. The biggest down side was the life of the small electric motor making the small air flow over the thermistor.
I ditched that and went with a early solid state gyro sensor , ( also not made now) and flew it for 2 years in the SSSC using RC giant scale servos to power trim tabs. Worked good. Plan on putting it in the JMR Special after going to a late model sensor.
I also used the thermistors in the pitch part of the autopilot that locked on a pressure altitude to within 25'.
I have the part # for the thermistors if you need to try to find a replacement. They are very little, about the size of a grain of rice with 2 small wires.
Back at that time I bought the instruction booklet that Doug Garner sold .
I also built the magnetometer and it also worked good.
Short version of a long story. My youngest son built upon the magnetometer idea while in his senior year in college and designed a nav system the measured the earths magnetic lines in different vectors and made a nav system like a GPS using the earths mag field. Just needed a little more work to tighten the programing up and allowing for the iron deposits in the homemade computer. ( I designed all the PC boards for him ).
He had the company that sold the magnetmeter wire wound coil that Doug used to wound all the coils used in his system.
At that time my son was hit head on by a semi-tanker truck on the interstate and spent 2 years in hospitals with a lot of injures including a head injury.
Doing good now , dealing with the problems but married with 2 sons.
Your post brings back a lot memories, some good and some not.
Thanks.
Pictures added. the slot in the mounting for the sensor was for adjusting the sensor to detect yaw and roll.
I can't remember if it was Doug Garner of Don Hughes who made a later version that used speaker as the air pump
 

Pops

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I can't remember if it was Doug Garner of Don Hughes who made a later version that used speaker as the air pump
I think it was Don Hughes.

Picture of the static air source. Glass jar, have to use a container with stiff walls so engine vibration will not effect the airflow. The thermistors are in series. As air is coming out as the airplane is going up the static air will be going out cooling the leading thermistor more than the down airflow thermistor and unbalancing the circuit. Opposite for descending.

I think I built this in about 1985 or so. When I first built the pitch part of it, I would lay everything on my car seat and watch it work the servo as I went up and down the WV hills. Set the gain up and if you can see any slope in the road the servo would be correcting.
 

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Vigilant1

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Good find, really neat. I can't imagine Sport Aviation running anything like that today (updated to use Arduinos, etc). It is too bad.
Analog circuits, fluidics, etc-- you had to be really smart and try a lot of things to make something work. In retrospect these devices are easy to understand, but to get the idea and carry it to completion required imagination (first) and grit.
 

Pops

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Good find, really neat. I can't imagine Sport Aviation running anything like that today (updated to use Arduinos, etc). It is too bad.
Analog circuits, fluidics, etc-- you had to be really smart and try a lot of things to make something work. In retrospect these devices are easy to understand, but to get the idea and carry it to completion required imagination (first) and grit.
Just having fun.
I use the SA for building a fire in my wood burning stove in the hanger/shop. The slick paper doesn't even do a good job at that.
 
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