Aircraft Fuel Level Video - Cirrus Perspective

The video promised showing the fuel level senders reporting to the Garmin Perspective panels has been completed - Thanks to Neil Hershman for his excellent efforts

http://youtu.be/DRwwEUeLiQk

Vibration Testing a Float Based Sender

Float based Fuel Level senders are not expected to see any vibration as the internal fluid is supposed to dampen the motion.

There are several critical applications where this is not  the experience in the field and people have turned to alternative technologies like - Capacitive or Ultrasonic fuel level sensors to get better performance

However -   Each one of these systems also struggles with agitated fluid  -

A float still rides on the surface giving the potential for an accurate reading no matter what is going on - The real issue with float sensors is not the float,  it is the method for recording the float position.    Resistance based senders wear as the contact rubs vigorously over the resistance trace.  Fluids attack the resistance grid and wiper

What if we kept the good part of this level sensor - the float and replaced it with a clever bit of electronics

Best of both worlds - Simple and Effective

Aerospace Logic - Cirrus Design Retrofit

In creating a new fuel level system for Cirrus Aircraft we kept in the back of our mind  the opportunity to provide this technology to legacy Cirrus Aircraft as well as other aviation applications.

Aerospace Logic was the obvious choice - 

We chose their 200 series unit over other 2 1/4 instruments as Aerospace Logic has created a quality and sunlight readable  display with a clear and concise level indication.

More importantly, Aerospace Logic like CIES saw accurate and reliable fuel level indication as a valuable instrument in the cockpit.  Aerospace Logic was hampered in achieving it's goals for fuel level indication by fuel level senders that were previously available to the aviation market.  CIES Level senders with our new and patented technology completely changed the fuel sender game.

You will note that a digital value of fuel is displayed below each quantity gauge.  This gives an unmatched accurate calculation of quantity in each tank.

Aerospace Logic has worked with us to incorporate appropriate warnings that a quality fuel level indication system can provide.

Note:  The upper display is indicating a fuel "Imbalance Condition"
and the flashing Amber bar is indicating you have exceeded the POH recommendations for fuel level imbalance. Switch to the flashing AMBER tank.

One of the most important characteristics of the Aerospace Logic Display is the trend graph featured on the second page.  This provides graphical information of fuel level over time.  The use of the displayed trend data makes it easier to manage fuel in a single engine aircraft.

Most importantly,  Aerospace Logic was willing to work with CIES in developing a display unit that would allow a digital interface between the display and fuel level sender.

Aerospace Logic and CiES Inc. look forward to pilot response for this system.

http://www.aerospacelogic.com

Digital Fuel Sender Now Certified

Digital fuel sender now certified

The AOPA Press Release came out today
It seems to be difficult to find, but it is on the web

The basic concept is ....


When we have specific aircraft (or aircraft type) information
and we demonstrate that the system is compatible to Transport Canada ... Flight Test
or operation under 337 Field Approval

We can add those aircraft onto the blanket AML STC owned by Aerospace Logic.

We believe after we demonstrate on several aircraft types that this is simple modification and installations are straight forward  additional aircraft models will fall into place.

Press Release - TSO Granted - AOPA Summit

NEWS RELEASE                                    FOR IMMEDIATE RELEASE

CIES Corporation receives FAA TSO approval for new digital fuel level senders

October 10, 2012, CIES Corporation of Redmond, Oregon has received FAA TSO C55a approval for its line of digital fuel level senders. The float based fuel level senders are designed to replace the majority of the existing fuel level sending systems in general aviation aircraft. The proprietary and patented system provides a new level of accuracy, reliability, and stability to fuel level indication in the cockpit. CIES meets a TSO standard of 2% variance in tank volume, a standard normally reserved for corporate and commercial aircraft with corrected capacitive solutions. No other float based system meets this stringent TSO standard while achieving the intrinsically safe (i.e. “no wires in the tank”) requirement.

Richard Kirkness, Vice President of CIES said, "As a manufacturer of aircraft systems, we see FAA certification as critical to our success and the foundation for everything we do. FAA approval is the result of months of hard work on the part of our team here in Redmond and could not have come at a better time for CIES as the company continues to grow and strives to achieve the goal of becoming a world class supplier of advanced systems and technologies.”

Charlie Babb, General Manager of CIES added, “After the successful introduction at the beginning of this year of our senders on all new Cirrus production aircraft, we began working with other manufacturers and owners groups to provide specific fuel level sending solutions for production and legacy aircraft. The next logical step was to acquire FAA certification to validate our quality control system and lean manufacturing processes while making aircraft integration and approval significantly easier to obtain.”

The CIES fuel level senders require a dedicated digital fuel level display to ensure that the 2% accuracy achieved in the fuel tank is provided in the cockpit as well. As a result, CIES partnered with Aerospace Logic in Hamilton, Ontario to utilize their digital fuel level cockpit display. Aerospace Logic updated their fuel level gauging system to accept the digital communication link from the CIES digital senders.

CIES Corporation of Redmond, Oregon USA provides a range of high-technology products and support services to aviation, aerospace, and the broader transportation marketplaces.

For additional information on CIES and its products please visit the CIES Inc Website

For additional information on Aerospace Logic and its products please visit the Aerospace Logic Website

Cirrus Engineering: Integrated Fuel Level Display

Cirrus Engineering: Integrated Fuel Level Display: The last analog gage in the cockpit has been the fuel level gage. All the other gages had been integrated into the Garmin Perspective system...

TSO C55a Approved Fuel Float Level Sensor

CIES Inc has obtained FAA TSO Approval - C55a - at the most rigorous standard for it's line of float based digital fuel level senders.

Its official we now are producing a line of TSO'd Fuel Level senders applicable to most aircraft below 12,500 lb gross weight. 

This effort provides a real alternative to the old Stewart Warner  senders long out of production for current General Aviation Aircraft fleet.

We are working with every major manufacturer to incorporate our senders as original equipment.

Sensors Expo - Aircraft Fuel Level

Sensors Expo 

Cirrus Aircraft and CIES Inc made a joint presentation at the Sensors Expo Conference in Chicago the first week in June.

Topic of discussion was

- Applying our AMR Fuel Level Technology to an Application

• Fuel Level and Ice Protection Fluid Sender in an Aircraft Application
• Integration to Aircraft Avionics / Instrumentation 
• Implications for reliable redundant fuel level - Fuel Qty and Fuel Flow     
• Better Annunciation 
• Fuel Imbalance Annunciation - proper left to right trim single engine aircraft
• Low Fuel or IFR Reserve Warning 
• Automatic fuel management - switching between tanks 

Discussed why a float based sensor is ideal for this application 

• Shallow Tank 
• Lots of fluid motion - constant motion 
• Solid State Technology 
• Intrinsically Safe - Explosion Proof 

Illustrated the advantages of AMR for this application - with a video 

• We hold the patent - so no licensing 
• Tolerant of angular and displacement alignment - position immune 
• No appreciable temperature effect - critical for aircraft 
• No hysteresis effect  
• Issues with existing systems 

Illustrated the studies on the aircraft to achieve an accurate level for each aircraft produced 

• Number of calibration points to reduce tank indication errors  
• 5 was chosen - 
• 0 Gallons - FAA regulations 
• 5 Gallons - provide excellent accuracy at the bottom of the tank
• 30 Gallons - At the aircraft TABS - Internal tank visual  reference 
• 40 Gallons - reduce error at transition between inbd and outbd sensors 
• 46 Gallons - Full 
• The fuel quantity indication less than 1/2 gallon or 1% in potential error throughout the fuel level range.

In looking at this fuel level indication performance and evaluating the system in its application over time

• Improved annunciation 
• Low Fuel Annunciation 
• Low Fuel Caution 
• Low Fuel Warning 
• Fuel Imbalance Caution 
• Fuel Level Sensor - Failure 
• The fuel quantity indication can be compared to the fuel totalizer and if in agreement 
• Automatic switching of fuel from left to right tank 
• If not - revert to manual actuation . 

Fuel Management

Fuel Management

“From an accident prevention perspective, fuel mismanagement is one of the most frustrating problems. The accidents are easy to avoid. The hardpart is reaching the pilots who are most at risk, because they’re not the ones attending safety seminars or taking online courses. A new approach is needed to get pilots to stop and think about the issue. Airing some ‘dirty laundry’? Perhaps, but we think it’s more than justified by the lives, aircraft, and dollars we lose to this problem every year. 

ACCIDENTS do far more damage to GA’s reputation than educational efforts to rectify the situation.

It shows that, the pilot community,  is making a good faith effort to address the problem.”

—Bruce Landsberg, President, AOPA Foundation

Fuel Management Accidents

Fuel management accidents are among the most preventable types of GA mishaps, and yet pilots still manage to turn perfectly good airplanes into impromptu gliders at an alarming rate well over two per week in the US.

The primary way GA pilots manage fuel on board is to do arithmetic.



 You look at the length of your trip, the winds, read some performance charts, then bust out your calculator or whiz wheel  to figure out how long it will take you to get to your destination at what fuel burn. I might get anywhere from 10 to 18 miles per gallon on a flight. And if the headwind is stronger than I expected or I'm routed the long way, it might take more than that. The 30 minute required reserve  is really not enough. 

FAR Part 91-151

Fuel Level Sender Video

Video Overview of Fuel Level History and Retrofit

We will start getting videos together of units in test and evaluation

Aerospace Logic Instrument Panel Interface

Here is the interface for the digital fuel level sender 

History of AMR Fuel Level

Charles Beck, a Navy Veteran, Lawyer, NASA Alumni and Engineer has looked closely at the issue of fuel level reporting and annunciation in aircraft.

Charles had designed and produced, through his company International Avionics,  master caution and annunciation panels and other electrical systems for great number of popular general aviation aircraft.

Charles had a particular interest in the number of aviation accidents regarding fuel in aviation or the lack thereof.  His insight and skills as a pilot and engineer allowed him to look at the problem to see if he could apply his considerable technological skills and spacecraft experiance to mitigating the hazard.

Charles initiated this work at an accurate low fuel warning system - known to most as the annunciation system on the Mooney M20 series aircraft.  This system  has been copied and emulated in software by a majority of the GA industry.  It was not an FAA requirement at that time to have a separate annunciated low fuel warning - It was just a good idea.

Charles ran into a problem however in that the information from the fuel level senders available to the GA fleet did not lend themselves to accurate and reliable output.

At first Charles addressed this with signal conditioning and looked at methods for getting the sensor out of the fuel.   Patents followed these efforts and Charles turned his attention to Hall Effect sensors as a possible opportunity to remotely and accurately measure fuel level.   His experiments with Hall effect did not produce a reliable aviation sensor.   Temperature, magnetic fields and drift over time rendered these Hall Effect efforts to be unsuitable to the aviation application.

About this time an old technology, in a new and compact form became commercially available  -  We may remember the Suunto wristwatch compass as the first consumer application of Anisotropic Magneto Resistive (AMR) technology - an electrical sensor discovered by Lord Kelvin to measure the direction of a magnetic flux.

Combining the remote moving magnet connected to mechanical float or other means and measuring the position  of that magnetic field  remotely and accurately with AMR technology  lead to Charles fuel level patent.

AMR technology allowed an angular measurement potential down to 0.02 degrees -and  provided a  remote, safe and accurate fuel measurement immune from temperature, other magnetic fields, drift or wear.

Charles Beck's relationship with Mooney Aircraft allowed him opportunity to test this system and improve it's output and interface.   As Mooney Aircraft struggled to find firm footing,  first with economic and then competitive issues this system and its advantages was literally left waiting in the wings.

I was encouraged by two Mooney Alumni to take a close look at the system and it's advantages.   Issues with fuel level systems were on the  top ten customer complaints for every major air and rotorcraft OEM  -  there was a clear opportunity for something new, and CIES has captured  that opportunity. 

Float Based Sensors - Accuracy Quality Reliability

Float Based Sensors 

These sensors have been in use for a long period of time.  They have a few advantages that are difficult to overcome.   If they have a less than stellar reputation it is more about the electronics used, than the method  of finding a fluid level.    We will assume that quality and good practice

• The float will find the surface 

• Provides a reliable value for full and empty
• Provides a stable output, even under fluid agitation.

• Simple mechanism and controlled motion about a pivot.

• Used everyday in the most critical applications 

• Independent of fluid type or composition

• The singular most popular method for measuring liquid level 

• A float and pivot arm can be maintained for millions of operational cycles 

The typical methodology for finding level is resistance - either in a wound wire or a resistance grid.  The output is simply a distinct resistance value.  However this mechanical method for obtaining an electrical value for fluid level has a few problems.

• This practice introduces a mechanical wear item into the system.  It is this wear on the resistance surface that draws the most criticism.

• The CIES Inc float sensor design has only a pivot to wear - and we can utilize a lighter float as there is limited friction to overcome.

• Resistance needs electrical modification to correlate with volume 

• The CIES Inc. float sensor design is digital output and can be programmed to tank volume 

• Resistance circuits immersed in fluids are susceptible to corrosion from alcohol in gasoline or de sulfered diesel or potentially to the 100LL replacement.

• The CIES Inc. float sensor design sensing element is outside of the fuel compartment no chance for corrosion 

CIES Inc answered the quest  - What if we could combine the simple and effective elements of a pivoted float and replaced the resistance element and its problems from the fuel tank sending system

Only CIES Inc has a patent to combine a sophisticated, reliable and stable sensor technology to a simple float mechanism.

CIES FUELRITE Level Sensor 

Utilizing the patented Anisotropic Magneto Resistive technology allows CIES Inc in an intrinsically safe non contact system.

CIES Inc  effectively married the simplicity and effectiveness of the float based system with a non contact level sensing technology with the following characteristics:

• Effective 
• Accurate
• Sensitive - Measures down to 0.02 Degrees 
• Immune to nearby magnetic fields
• No hysterisis -
• No drift over time or temperature - stable 
• Intrinsically Safe 

A proven system backed by exhaustive testing. 

Let us know your unique application

Contact Us

How Do You Inspire Pilot Confidence

- The Answer is Simple -

You Provide Them with Information They Can Trust 

It seems uncomplicated, ... accurate, reliable and trusted information is key to instilling a conviction that everything is going well.

Imagine a Synthetic Vision System that throws a few imaginary mountains at you, just for fun.   This would not be a system that inspires confidence.    Random false information would make a routine IFR flight more stressful and  stomach clenching even if you knew without a doubt that no mountainous terrain exists at any time in the State of Illinois.

  Conflicting information no matter how outrageous or unbelievable adds to pilot workload.

Cross checking normally reliable sources and getting similar results are the hallmarks of a good pilot.  Minor anomolies in calculation or display can be noted and corrected before a situation occurs.  To make this effective, any display in the cockpit should match what the pilot believes to be true most of the time.

In aircraft fuel level systems - reliable trusted information is hard to come by.

Pilots Trust in Fuel Sight Gauges 

Ignoring the issues of having a flammable substance with clamped connections on transparent and UV susceptible tubing or a fragile glass tube in the cockpit  - pilots trust seeing fuel as the most confidence inspiring  vs. any other method of level gauging.   If I can see it,  I have fuel and I know how much.   If I can't see it,  I don't have fuel in that tank.   I trust it, universally most pilots do.   But the limitations (high wing mostly)  revolve around the visibility of fuel  - Cessna uses a ball on the 162 Skycatcher.  But really these systems are best left in the dark.

Pilots have Faith in Capacitive Fuel Gauges

Professional pilots use them, they are the system of commercial aviation.  I hear from pilots that capacitive systems have no moving parts and are exact and reliable,  these pilots have not taken a careful look at commercial systems or the problems and solutions contained in a commercial or business aircraft system.   Good capacitive systems are expensive - the have extensive compensation for the fuel characteristics,  like temperature, water, entrained air, component corrosion These are all part of the capacitive equation for fuel level.   Good commercial Capacitance level systems compensate for this,  systems that rely on the capacitive reputation and fail to compensate or address these issues leave quite a bit to be desired.

Pilots will Believe in Anisotropic Magneto Resistive 

While more difficult technology to grasp,  digital output for fuel level from a float based system truly represents a real breakthrough in fuel level sensing.  

• It is safe, reliable - no wear parts
• There are no electronics in the fluid
• It is compatible with modern cockpit displays
• The fuel flow totalizers will match fuel quantity - giving you a truly redundant system in the cockpit.
• Provides a level output under extreme conditions

Youtube Video of the Sender under Test

How Can a Float Based Sender be so Accurate

Accuracy in Fuel Level Sensing 

Absent the aircraft substantiation that is protected intellectual property at the present time,  it is hard to demonstrate what this system does for the average pilot.  

This fuel system component will generate considerable interest, but fuel level senders of the past have been, an ineffective tool for pilots to utilize.

We can all point to or tell stories of classic flying films where the lead has - tapped the fuel gauge to see if it was reporting correctly.

A technological advancement in this field may not just improve an existing fuel quantity indication system  - but may become a new component with the potential to be disruptive to aviation safety. 

Why? 

In earlier dialogs we discussed the digital aspect of the fuel level sensor output - but what does that mean.

In the diagram above illustrates a distinct position output of the float arm as represented as a ray on the hemisphere.

The middle point being represented by the binary 10000000  - the next ray above is 01111111 the next ray above by the binary 01111110.   Each of these is different.

What this provides is a positive address for the float position for every ray shown on the diagram.

By combining a digital address to a non contact level system.  We allow free motion of the float - no discernible wear - no wear that would affect this digital output.

A measuring system with many discrete addresses over the rise and fall of the float makes it is easier to carefully describe the tank volume into usable information for the pilot.

More information allows complex tank shapes and configurations commonly found in aircraft to be described in more controlled and accurate manner.

The non-contact part of the sensor takes the fuel contents of the tank and it's varying electrical and physical properties out of the equation.  

The controlled float finds the fuel / air boundary in all flight conditions.

Legacy Systems 

Resistive Systems 

So lets compare to a resistive based float system with the resistance trace in the tank  - most general aviation aircraft in the field use this or some variation.

So the manufacturer of the fuel sender will talk about how this resistor card is laser trimmed and it has 50 or 60 precision resistive steps from empty to full when the unit is brand new.  

So that appears to be similar to the example above - yes the digital example has more steps but it is more expensive - yes.  

What is not revealed  is that the resistive steps in output are not distinct or different  - but rather a subtle step increase or decrease in the electrical property when new - after use or wear the subtleties are easily blurred or worn away.  So we in actual practice have a system that now may incur discontinuities in the stepwise output - and provide a less than adequate reading or even deceptive reading for fuel level .   

When we talk about modern general aviation aircraft and the resistance traces become much smaller as shown on the right.   The need for intrinsic safety - explosion proof requirement brought about some subtle changes in aviation fuel systems.  It was no longer acceptable to have wires or traces in the fuel tank proper.  The general aviation industry turned to propane gauges that had the wiper driven by a magnetic couple to an external wiper system enclosed in plastic.


Capacitive Systems

Capacitive Systems - this is the domain of larger aircraft and some small aircraft.  It is the defacto system for aviation.  The designs have no moving parts and are reliable in principle.

Again we are not dealing with distinct positions but an electrical subtlety between one level and another.  So while the fluid provides a good dielectric - the qualities of the fuel become a critical component in how the system works.  Therefore what you add to the tank is a measurable component for the fuel gauge system and is known as the k factor in a capacitance equation.

So what you add - Fuel -  Quality, Temperature, Composition, Entrained Air, Water and Temperature  have a direct bearing on the output of the gauge.

Components of a good Capacitive level systems contain the following:

• Probe Compensators - measure permittivity of the fuel  - ability to carry a charge
• Densitometers  to determine the specific gravity of the fuel
• Temperature compensation - direct though linear effect on k 
• Compensation of tube diameters to provide a linearized output

If your capacitive level system does not have compensation,  it has limited value in aircraft applications. 

Capacitance probes while highly developed and may utilize segregated DC or AC power, can meet requirements for intrinsic safety.   Capacitive systems however will never overcome the fact that we have separated metal tubes connected to external wiring in the aircraft.

Capacitive systems have difficulty with

• Fuel Stratfication - hot fuel added over cold soaked fuel 
• Contamination
• Corrosion 
• Indifferent fuel quality or in non aviation applications alcohol percentages

Capacitance systems in transport aircraft are redundent in that there are two systems for each tank to insure dispatch reliability for transport aircraft.  

Why Don't They Just Fix It

What is the Aviation Market for Fuel Level Sensing Technology

• Fuel Level Sensing is a very large market for other vehicle types or stationary fuel storage, aviation is a minuscule percentage of sales.

• The following companies are big players in these markets and are protective of their market share:

• Textron Kautex      -TI Group
• Wallbro                  - Robert Bosch
• Hyundai Mobis      - Delphi
• VDO                      - Toyota
• Bourns                    - Methode  
• Rochester Gauge    - Wema, Isspro, S-W

• Most of these companies are not interested in or will actively avoid the aviation market 
• Business interest to license is minimal and no interest in government controlled production
• Exposure to litigation  

• Fuel Level Sensor industry is protective of its Intellectual Property. 

• Hotly Contested Territory (It has been termed a patent minefield) 
• A thorough  patent search is required, prior to initiating a design process.
• Interest in sharing and licensing intellectual property is limited at best.

• Fuel Level Sensing in aircraft needs to be "Intrisically Safe".

• Explosion Proof 
• Limited Spark or Heat energy in the fuel tank
• TWA 800 Disaster brought about changes in FAA policy / regs.
• SFAR 88 - Wire separation from fuel system.
• Electronic Wiring Inspection System - EWIS.  

• Fuel Level Sensing in aircraft is complex. 
• Fuel can contain dissolved air - ie. Jet A 14% by volume 
• This will outgas like soda at altitude.
• This will influence simple capacitive level systems
• Aviation fuel will contain water
• The changes in altitude due to descent will suck ambient air into the fuel tank, that air will contain water vapor that will condense and mix with the fuel. 
• This will  influence simple capacitive level systems
• Aviation fuel will support biological growth and water in fuel will initiate corrosion
• Metallic or resistive components in the tank will be adversely effected and fuel level output in turn will be adversely effected.
• Fuel in aircraft is more dynamic.
• A vehicle with three dimensions of motion allows for a very dynamic fuel environment. 
• This movement will wear away resistance senders of all types and require mechanical complexities to capacitive sensors to stabilize the local fuel level.
• Replacements to 100 LL Avgas may not be so friendly to existing resistance senders in the fuel tank.

• Non-Contact Fuel Level Sensing, which meets the requirement for "Intrinsically Safe" is actively pursued and "IP" accumulated in the Fuel Sender Industry for functional and business reasons.

• Current best sensor system for Multi-Fuel vehicles
• Best sensor system for 100% alcohol fueled vehicles 
• Solves issues with partial alcohol content - corrosion
• Solves issues with de-sulfered diesel 
• Required for LNG -  LPG
• Future vehicle systems with long term fuel storage i.e.. Chevrolet Volt

• Aviation specific fuel system suppliers are not actively interested in the Non-Commercial, Non-Business aircraft application of their products or product lines.

So designing, building and certifying an aviation specific fuel level sender for aircraft under 12,500 lb is like most things in aviation. difficult, challenging and more involved than a cursory examination suggests.   It was however, not impossible.

Intrinsic Safety for Aircraft Fuel Tanks

INTRODUCTION    
A flammable mixture of fuel vapor and air can exist at times in a partially filled aircraft fuel tank containing jet fuel or much less so Avgas.  Research has been done to develop methods to eliminate or reduce the risk of having an explosive condition in the fuel tank. There are a few different approaches to preventing fuel tank explosions. Explosions need three conditions to occur simultaneously: a flammable fuel source, sufficient oxygen to react with fuel molecules, and an ignition source to start the chemical chain reactions. Eliminating any one of these conditions will prevent a fuel tank explosion. 

REDUCING OXYGEN CONCENTRATION

Recently, attention has been focused on developing a low-cost, low weight, high-efficiency fuel tank inerting system for use in large transport airplanes. This system uses high temperature bleed air from the engines to create nitrogen-enriched air (NEA) with as high as 98% nitrogen concentration. The NEA is plumbed into the ullage space above the liquid fuel in the fuel tank, forcing air out the vents and creating an atmosphere with a maximum oxygen concentration of 12%. This value has been shown to be the lowest oxygen concentration that will support ignition of  fuel vapors. This approach eliminates one of the key ingredients required to have a fuel tank explosion (sufficient oxygen). 

So now we have added a component to the aircraft to address what can't be addressed with a capacitive system in the fuel tank.

REDUCING IGNITION PROBABILITY
Ignition of fuel vapors can occur as a result of several different mechanisms. Voltage sparks, thermal sparks, and hot surfaces are the most probable ignition sources present in or around a fuel tank. Any of these ignition sources could occur due to lightning strikes, electrical faults in fuel tank electronics, or short circuits caused by cleaning debris, such as steel wool or other small conductive filaments that may have been inadvertently left within a fuel tank. Combined with fuel tank inerting, reduction or elimination of the likelihood of ignition sources could provide an additional safety factor to preclude virtually any fuel tank mishaps during the life of an aircraft.

Electrical spark has been the standard method of determining ignition energy required to ignite a flammable mixture. The generally accepted minimum ignition energy for a hydrocarbon/air mixture is around 200 micro Joules (μJ) for a specific mixture of fuel and air, usually at a stoichiometric mixture or slightly richer. The 200-μJ energy in most experiments is the energy stored in a capacitor and discharged across an electrode gap as a voltage spark. It should be noted that the stored capacitor energy is not the exact amount of energy deposited into the spark, as there are always losses between the capacitor and the electrodes. Nevertheless, the capacitor energy is a very good approximation of the minimum ignition energy of a mixture and the relative ignition strength of a voltage spark.

Flammable mixtures can also be ignited by means of thermal or friction sparks. Thermal sparks are different from voltage sparks; they are very small burning particles of metal that radiate bright colors due to high temperature burning. Thermal sparks are produced either by two hard surfaces sliding against each other creating a shower of sparks or a wire or filament making or

Spontaneous ignition of flammable vapors can also occur due to heat transfer from a hot surface to fuel molecules. A standard test method has been developed to measure the autoignition temperature of a liquid fuel by dropping a small amount of fuel onto a flat, heated surface and noting the temperature at which a flame is observed. It has been accepted that the autoignition temperature of jet fuel is around 450 ̊F and Avgas is around 536 ̊F , although these are not exact figures. Many factors can affect the ignition of the fuel vapors and the propagation of a flame front from the hot spot. The design of the test apparatus will determine the type of combustion that will occur. Cool flames can develop and propagate through a flammable mixture without creating an explosion as long as the rate of heat generated is not much greater than the rate of heat lost; explosions can only occur if significantly more heat is generated than lost.

Currently, the Federal Aviation Administration (FAA), guidance for electrical systems that introduce electrical energy into fuel tanks, such as fuel quantity indication systems (FQIS), provided in draft Advisory Circular (AC) 25.981-1C, states a maximum steady-state current of 10 milliamps (mA) root mean square (rms) is considered an intrinsically safe design limit for FQIS. It also states that current levels above 10 mA rms, particularly for failures and transient conditions, could also be considered acceptable, provided that proper substantiation by test and/or analysis justifies them as intrinsically safe. As an example, the AC states that for transient conditions, it is acceptable to limit the transient current to 150 mA rms, and failures that result in steady-state currents above 10 mA rms should be improbable and not result in steady- state currents greater than 30 mA rms. These values were determined after a considerable factor of safety was applied to the lowest values found from previous tests using Jet A vapors and steel wool filaments as the ignition source. The experimentation presented in this work was performed using a calibrated gas mixture with a predetermined minimum ignition energy to solidify the confidence in the electrical current guidance in draft AC 25.981-1C. 

CIES Inc FQIS SENDERS - 
Our senders do not have any electrical components in the tank, and no generated heat energy to ignite fuel in the tank.   The system measures the position of a magnetic pair on a float arm located inside the tank from a location outside the fuel tank proper.   This method of sensing is Anisotropic Magneto Resistive technology and is exclusive to CiES Inc.   

The CIES Senders eliminate the in tank ignition sources that could occur due to lightning strikes or  electrical faults in fuel tank electronics.   As the sensor does not rely on the fuel interface for measurement,   corrosion removal is not an issue.   Cleaning materials like steel wool that are used to clean capacitive sensors are not required with the CiES sender design.

Made in the USA

One of the most clear moments of my youth was delivering newspapers - the Tribune in Chicago .   I remember one day carefully dropping the paper on the front porch at a home where the older couple were particular about their delivery.

They asked me to come in to their home and see men walking on the moon.

We were all proud of what we accomplished that day, a well delivered paper, lemonade, cookies and manned space flight.

My dad had gone to Grumman in Bethpage, NY a few weeks before and brought back a Lunar Module Model I was absorbed by the accomplishments around me.

I was immersed in aviation - I grew up in it, and I had aeroshell grease on my hands.   If I was good, I got to go flying.  My recollections of youth and aircraft pretty much trump anybody else I talk to.  From messing around in the DeHavilland Comet that sat idle for so long at O'Hare,  to a ride in the space behind the pilot in a Grumman Bearcat for teasers.

These formative experiences led me to pursue a life of working in and around aircraft.  This is (fuel level sensor) is the best accomplishment and neatest engineering work of my life in aviation...so far.

The fuel level sender program is a culmination of a career of aircraft experience, good fortune and a little of the space program all wrapped up into a convenient aviation system package.

I am waiting patiently (I am not capable)  for the time when what we have accomplished here at CiES will reach the light of day or more specifically the aviation press.

I am very proud of the group that created this a design.  From it's initiation by a former space program engineer, it's re-vision and re-creation by our customer and internal team, it's integration by the interface team that allowed display in a modern cockpit, and it's thorough evaluation and certification that allowed CIES to provide a better level of reliability and accuracy to aviation fuel level sending.  Something that may,  improve the safety of flight for general aviation aircraft.

We really feel at CIES that we are on the edge of delivering something new in aviation in an area that has really waited for a better technology to appear.

All of this effort to design, evaluate, test and manufacture can be stamped with a Made in America. (we had some Canadian assistance)

We are most proud that we initiated the American Dream here in Oregon.

We built a new company,  we put people to work,  we build a world class product.

Digital Output - Fuel Level Sensors

Digital Fuel Level 

When you enter the term above in Google you get a variety of responses most of them showing a display indicating fuel as a digit value on a screen.

What this is a numerical  manipulation of the the analog signal that most fuel level senders provide as an output:

Simple electronic analog values are the tradition for fuel level measurment.

• Resistance
• Capacitance
• In the case of Reed Switches  - Current or No Current.

But what we have is just another way of showing what analog sensors are providing digital is display only.

Digital output at the Sender is Unique - there are several aftermarket Capacitive Sensors in the Marine industry or Telematics that use a conditioned digital output.  There are conversion processes for these senders - temperature compensation signal conditioning maybe a de- bounce (smoothing) function.

Capacitive senders take an analog signal give it a binary component and communicate the signal.

What if the native language of the sensor were digital in that each fuel level was represented by a binary stream - natively   No conversion - no compensation - and if non contact

 No issues with Fuel quality or Fuel type  - NONE .

 In fact no compatibility issues with the measured liquid in question whatsoever

When Fuel is Important or Critical to Operation
Fuel level is important but what if knowing how much remained meant the difference between an inconvenience or something more significant.

The manner in which we handle the digital output signal is proven in aviation applications -

Signal integrity is paramount - in an environment where static charge and exposure to radiated fields would bring most fuel level systems to their knees.  If you couple the requirements for vibration shock and the extremes in temperature - it is surprising that any fuel level sender works at all in aviation.

So why Digital 

• The level output is provided continually -
• The Fuel Level is reported over and over again to the gauge or display
• The signal does not suffer from signal loss or interference
• Either the complete signal is transmitted or nothing at all 
• Not effected by voltage variation
• Many more data points to map the fuel tank
• 3,800 distinct points for 80 degrees of travel possible 
• No Temperature Effects 
• No compensation
• The device will output fluid temperature if required
• Failure is hard and the results predictable
• False signaling of tank volume due to wear is virtually eliminated.

Imagine a level sender that thrives in the critical  aviation environment and think what it could do for your application.

Fuel Level Sensors for Collector Vehicles

Aviation Float Fuel Sender - Historical Perspective

Dawn of Aircraft Instrumentation

The initial non-electrical float system was used on various aircraft, the most famous being the Piper J-3 "Cub." which used a cork with a wire imbedded in it that extended into the view of the pilot. Lots of wire showing, lots of gas; no wire showing, no gas.  Equally glass sight gauges are used in high wing aircraft and high wing fuel can to flow to the engine by means of gravity.

Electrical Aircraft Instrumentation Comes of Age

With the addition of electrical systems in aircraft the float was connected to the arm of a variable resistor whose electrical leads are brought through the wall of the tank and connected to the fuel quantity gauge and to the ship's electrical bus. 

Thus, the change in resistance as the float follows the level of the fuel.  This electrical value causes the needle on the fuel quantity gauge to deflect indicating the quantity of fuel in the tank.  Simple and direct.

For odd shaped tanks, particularly a flat tank in a wing with dihedral, multiple resistance floats are connected in series to correctly categorize this onger sloped tank.

This is the fuel gauging system on most, if not all, automobiles, the majority of piston engine aircraft, and some turbine aircraft. This system has been given very poor reviews over the years, some of which is deserved, but a large portion of the criticism is not.

If the resistance float is poorly designed and constructed, if the gauge is poorly designed and constructed, if the gauge is poorly marked, if the damping of the complete system is not suitable for aircraft or it's particular use,  or if the system is poorly installed and calibrated,  criticism for poor operation is rightly deserved. 

Digital Display and Interface  

In the instance of fuel level - Nothing really 

Well in the case of Commercial Aircraft the capacitance value was converted to ARINC 429 protocol and transmitted to the cockpit.

Until Now 

The First Digital Output General Aviation Fuel Level Sender