Aviation Fuel Level

Traditional Aircraft Fuel Sender 

Why don't my fuel gauges work?

Let us cover a few basics  

• Aviation industry has utilized level senders from other applications
• Aviation is not the largest market or the most financially rewarding for a dedicated fuel level sensing solution.

• Aircraft fuel tanks are larger than those for most other applications. 
• An aircraft carries more fuel.

• An aircraft has three degrees of motion freedom 
• The liquid fuel is free to move about.

There are other factors.

• Why not design a new system 
• Fuel Level Intellectual Property is hotly contested territory (a patent minefield) 
• A new aviation design must avoid other patents 
• The market share is small
• The perceived liability - Top 5 aircraft incident issue

• Fuel Level in Aircraft needs to be "Intrisically Safe".
• Explosion Proof 
• Limited Spark or Heat Energy in the fuel tank. 
• Non - Contact "The best solution" for Intrinsic safety is the hottest IP in Fuel Level
• Required for multi fuel and hybrid vehicles
• Required for vehicles with long term fuel storage - i.e. Boats
• Required in LNG / LPG

------------------------------------------------------------------------------------------------------------Fuel sending works in my car.

• Automotive fuel tanks are smaller
• What would be adequate for a resolving 16 gallons of fuel has difficulty with 3 times the volume.   
• If you have a boat - this is also an issue as you are well aware
• The variable resistor technology used in automotive applications doesn't scale well
• The variable resistor cards used,  allow 60 degrees of travel  - a good resistive card for aircraft or boats would require minimum. 180 degrees or more.

• Relatively stable fluid motion 
• The automotive sensor is exposed to some fluid motion but overall less. 
• Aircraft fuel can remain quite stable - however turbulence will creates concentrated fluid motion.
• This motion wears the resistive trace - so inadequate resolution of the variable resistor is now faced with increased wear.  From bad to worse.

• The basic requirements 
• Standard aircraft fuel gauges are calibrated only for the full and empty position.
• Caveat - new automotive systems are calibrated to the tank - great improvement
• Caveat - new aircraft MFD's allow tank calibration - Aerospace Logic, JPI, Garmin

• Almost daily use  
• The automotive sensor is continually washed with new solvent at every filling and fuel fills are more frequent. 
• Aircraft fuel can remain in the tank for long periods - it is designed to do so - however impurity buildup on the variable resistor are common at a fraction of usage time of the automotive application.
•  it is quite common to have your aircraft senders ultrasonically cleaned

---------------------------------------------------------------------------------------------

Propane Level Gauge

New requirements for intrinsic safety for all aviation fuel level systems 

• The general aircraft industry found that they could utilize a commercial off the shelf, patented float sending unit from the propane industry
• This met the new safety requirements and directly replace a float level legacy system.

• A Non- Contact solution - the resistance card was removed from the tank environment.
• Shock inputs from turbulent air can however de-couple the matched magnetic drive and the the gauge will take a set but in-accurate reading or drift back to the correct reading.
• Suffice to say - Propane Tanks were not meant to fly

----------------------------------------------------------------------------------------------------------------------------------

Aircraft Capacitive Sender Ad - 1948

Alternatives  - 

Capacitive Senders -

Conceived in the Late 1940's this aircraft fuel sending system set about to address the two most common issues presented above - fluid motion and resolution of the larger fuel quantity.   

These are the most widely used in aircraft above 12,500 lb 

Capacitive Sensor Benefits 

• Immunity from fluid motion 
• Greater resolution of the large fuel volume 
• Shapable to the fluid volume - tailored to the tank volume.

Capacitive Sensor Issues

• Difficult to Prove Intrinsic Safety
• The definition of the sensor is to utilize two metallic or conductive elements in the tank 
• The intrinsic safety requirement must be met with increasing the complexity of the system.
• It is a spark in the capacitive sensor that initiated the explosion in TWA 800 fuel tank. 

• Moisture Rejection
• An aircraft fuel tank breathes on ascending and descending - moisture in the air is constantly brought in contact with the fuel.  Sealing the tank is not an option.
• As the capacitive utilizes the fuel contents as an integral element of the level reading - this variable is very difficult to manage.

• What's in the tank - matters a great deal 
• Fuel must be:
• uniform 
• moisture-free
• stable and uniform temperature
• contaminant free
•  to give a consistent and accurate fuel level indication 

When you review the system above - the capacitive sender solved several issues with fuel level indication, however it brought a few of it's own limitations along for the ride.

--------------------------------------------------------------------------------------------

Ideal Aircraft Solution Characteristics

• Non Contact - New FAA Requirement
• Intrinsically Safe - 
• The alternative is proven safe electronics in the fuel
• Immune to fuel contamination

• Unaffected by Fluid motion 
• No wear items related to fuel level reporting

• High Resolution 
• Address the larger quantity of fuel in aviation systems.

• Simplicity 
• The best aviation solutions eschew complexity where a simple system provides equivalent benefit.

----------------------------------------------------------------------------------------------------------------------------------

CIES Inc AMR Fuel Level 

Float Based Level Sensing - Retrofits or directly replaces most units in the field

• Non Contact 
• No - Safety Issues 
• No - Fluid Contamination
• No - No moisture or fuel quality issues

• Immune to Fluid motion
• No wear of fuel level reporting system

• Resolution 
• Digital output
• More fuel level information 
• Integrity of the level signal
• Interfaces to modern avionic solutions
• Ability to output fuel temperature - Lbs fuel. 

• Simplicity




• No complexity required
• On the platforms we have been applied - exceed it's requirements

CIES Inc AMR  A sensor that was designed for and patented with the aviation industry in mind, but suitable for all high value applications.

What Accuracy in Fuel Level Means for General Aviation

Why would I want accurate fuel gauges in my aircraft. 

Predicting and shaping the future are the providence of engineers.  

If accurate and reliable fuel level sensing for aircraft became a common reality 

What are the effects on the aircraft/pilot interface.

Warnings and Annunciation 

With cross checkable and reliable information between the Fuel Totalizer and Fuel Quantity 

• Low Fuel  
• It is already exists - 
• What if it was reliable and predictable

• Fuel Imbalance - 
• Let you know when you exceeded tank imbalance limits
• Warns you of a rapidly depleting tank - safety  

• Fuel Leakage or Venting  
• Matched information fuel totalizer and tank volume
• If rate of flow d not match - a leakage or venting warning 
• With a residual power or memory input
• Internal leaks annunciated 
• Fuel Theft 

• Errors - 
• As a reliable cross check between fuel flow and fuel tank volume 
• Provides a reliable diagnostic to errors or faulty components in each system
• Failure to follow a predictable path can be flagged as an sensor or tank system requiring maintenance. 

• Secondary Fuel Totalizer - Cross check to the fuel we can derive rate to give a simple totalizer function.

Automation 

With cross checkable and reliable information - Fuel Totalizer and Fuel Quantity we can use this information to relieve pilot workload 

Fuel  Management Computer - 

• Tank Switching -
• The aircraft system would handle switching between tanks for single engine aircraft.
• This could be overridden manually in the cockpit.

• Fuel Management. 

Allow a pilot to mange total fuel volume on the aircraft with an interconnected pump system 

• Minimizes human refueling errors 
• Cross-check quantity of fuel added and correct
• Manage the fuel added or remaining to balance tank volumes.
• Use fuselage wing tanks for weight and balance corrections or trim

Customer Feedback - Cirrus Retrofit

Folks I just picked up the plane this evening from Advanced Aviation in Lancaster PA.

Joel Glover and his team did an outstanding job installing the new CIES digital fuel sensors despite a steep learning curve on this first ever install.

The next one (an SR 20 was already in the shop) should go a lot faster as the first is always the hardest.

I had a chance to run the system through its paces on the short hop from KNLS to KMMU this evening.  I must say my first impression is WOW !  A huge improvement.

I love having the fuel flow quantity on the MFD now, but the icing on the cake is the redundancy with the new digital fuel guage that replaces the former analog version.

Really cool looking, but more important is the functionality.  I really like how you can flip between fuel quantity and the fuel burn graph, really helpful for fuel balance. 

The CIES team even made sure it dims with the instrument dimmer.

I will get some more time this weekend (during the daylight) to run it through its paces, but 

I would HIGHLY recommend this a must have upgrade to your Cirrus.

Get in line now and place your orders, I am convinced you will not regret it.

If you want to eliminate all your fuel level issues, this is the only way to go.

Like you I highly recommend Advanced Aviation in Lancaster PA as the place to get it done.  Joel and his team are the defacto experts now for this upgrade.

In Memoriam - Charles W Beck

Charles Wesley Beck II.,Born in Fort Worth, Texas on June 26, 1933, and passed away on December 19, 2012. 

In 1975 he founded International Avionics, a position he held until his death. The company is a supplier of annunciator systems and control electronics to the general aviation industry, both original equipment manufacturers and aftermarket completion centers.

Charles was dedicated to the design and manufacture of products that improved the safety and operation of aircraft.

The Mooney Aircraft Master Annunciator was one of those projects.

Charles designed and patented the AMR fuel sensor concept owned and utilized by CIES Inc.

We are proud to carry on his legacy in providing accurate and reliable fuel senders to the aviation market.

Why Anisotropic Magneto Resistive

Why use Anisotropic Magneto Resistive Sensors 

Anisotropic Magnetoresistive (AMR) Sensors Technology used by CIES Inc  for our fuel level solutions   These sensors use the basic premise that the electrical resistance of certain ferromagnetic alloys, such as permalloy, are influenced by external magnetic fields.

Like a compass that always points North no matter how you move - our sensor always points to the float.

For larger fuel tanks like those in aviation or marine applications  - we need more information or position information to correctly depict the amount of fuel in the tank.  Our sensor technology does this we can measure tiny fractions of a degree. So not only pointing North but also with a high degree of precision.  In fact we have thousands of discrete data points to measure fuel level.

Automotive resistance sensors re-configured for these critical applications - are just not adequate.   60 discrete points might be good enough for 18 gallons - but it falls short  handing 5 times that volume - plain and simple.  The 60 or so discrete points found on thick film resistance cards just don't cut it.  Fuel movement found in aviation and marine applications adds additional problems to resistive senders - float motion out of of the pivot plane tends to make the resistance wiper act as a make and break switch.

These compromised systems attempting to scale current automotive ceramic resistive elements by adding a longer float arm or other measures - simply provides poor performance.  

CIES Inc Patented Method

Utilize a solid state magnetoresistive effect or anisotropic magnetoresistance can be fabricated in thin film technology, allowing the production of a very precise yet cost-effective angular measurement sensors.  Replace the coarse variable resistor with a solid state device.

From Wikipedia: 

Anisotropic Magneto Resistive - (AMR) is the property of a material in which a dependence of electrical resistance on the angle between the direction of electric current and orientation of magnetic field is observed. 

Why is this a better way to measure fuel 

It works under all conditions, temperatures and with moving fluid volumes - PROVEN IN AVIATION 

And there is a combination of influences but for an AMR sensor the built in 

strong magnetic external field attached to the float arm locally saturates the sensor, the actual magnitude of the local field strength has no impact on the measurements. - Remember temperature effects on both the magnetic strength and the efficiency of the sensor.

Only the direction of the field is evaluated.

Only the local magnetic field on the rotor has influence - the presence of other nearby magnetic fields such as motors will have no effect on the sensor as long as the rotor magnetic field strength is dominant. 

While other magneto resistive sensors are available - AMR has the capability to work under all conditions and give proven repeatable results. 

Non-contact fuel level sensing is a good idea.  It was a good idea to remove the electronics from the fluid measured.

Other fuel level reporting systems don't measure up


SUMMARY OF AMR ADVANTAGES

• Voltage in the case of our AMR sensor is converted to a bit stream digital output.
• More information for every degree of float travel
• Independence of magnetic drift during lifetime
  
• Independence of magnetic drift with temperature
  
• Independence of mechanical assembly tolerances
  
• Independence of mechanical shifts caused by thermal stress