Cirrus Aircraft Factory Fuel Level

We have been supplying Cirrus Aircraft fuel level senders for over a year.  There have been no issues or in-field replacements.  Now that the senders have proven themselves day in and day out and showing excellent reliability and repeatability.  We can now start to exploit the advantages accurate fuel level can provide.   

In the Cirrus Aircraft Facebook post yesterday - one of these new features came to light.  

Cirrus wrote the following:

Since spring of last year, our aircraft have come equipped with fuel level sensors that read accurately at all levels. In fact, they are so accurate that we were able to integrate a fuel imbalance message on the PFD in Generation 5 aircraft. The fuel level sensors in most of our competitors’ planes only read accurately when the fuel tank is empty or full. For more on the astonishing innovations that make Cirrus an industry leader: 
http://bit.ly/YZO6rT

Better information =  "informed"  decisions

As always when you forget,  a careful reminder will get things back to normal

Resistance is Futile

When you are talking about Fuel Level.  

When we designed our new digital fuel level sender we gave a lot  of thought on how to interface with older aircraft systems.

The question was:

Could we produce an resistance output to mimic an existing resistance fuel level reporting system.  

There would be a few clear benefits:

• We could interface with many more legacy aircraft 
• Incorporation of our system in aircraft already using resistance based sending would be easier.

However some of the issues of legacy aircraft were directly related to relaying resistance through the aircraft wiring as issues with resistance can provide false or error prone signals.   Resistance measurement on an aircraft was identified by us early on in the design process as not the most favorable method for accurate fuel measurement:

• Aircraft have long wiring runs
• There are multiple sensors and connections
• The connections needed to be ordered to produce a series for multiple sensors
• There were other connections in the aircraft - bad connections produced resistance 
• There were multitudes of different resistance values even for the same aircraft
• There were amplifiers in some aircraft to address the issues above
• The wire run was subject to aircraft vibration 
• The gauge quality and accuracy in legacy aircraft was - not ideal

The favorable aspect of resistive gauging was that it was easy for the average mechanic to diagnose.

• All they needed was an Ohmmeter.

• We had heard stories of Cessna 210 Centurion and Cessna Twin Aircraft with the dreaded Cessna breakout box to tune and diagnose the capacitive system.

So what we needed was a simple digital signal that could be read with the modern equivalent of a ohmmeter  - the Digital MultiMeter (DMM).  We can now get a digital frequency output of any connected sender.

We found that Digital Frequency gave us clarity for fuel level information over all the known wiring challenges - corroded contacts, poor splices and induced signals.  More importantly it gave us a good signal or nothing - induced errors did not conspire to give bad fuel level.

What seemed more natural is that the signal was similar to that used by the fuel flow transducer.  It seemed a natural  - and we could read the read and diagnose the signal on a DMM.

When we sat down after months of delivering a fuel level sending product that had zero issues and was easy to diagnose.  ---

We had come to  realized that we had found the best method for reporting fuel level on the aircraft and a communication standard for any application we applied our product to

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

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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

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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.

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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.

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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.

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.

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

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.