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

General Aviation News - Press Release

Home → News → Aircraft → Accurate fuel gauges for aftermarket Cirrus

Accurate fuel gauges for aftermarket Cirrus

February 12, 2013 by Ben Sclair Leave a Comment

REDMOND, Ore. – Pilots are taught from an early age to not trust their fuel gauges. Cies Inc. wants to change that with its TSO’d fuel senders. The Digital Fuel Level System is now available as a retrofit on the Cirrus-line of aircraft (SR20, SR22, SR22TN and SR22T).

The system will measure fuel volume within 3% at all levels, within 1% when fuel volume is less than 50% and display the data on an Aerospace Logic or J.P. Instruments gauge.

“I love having the fuel flow quantity on the MFD like the new 2013 Cirrus Aircraft,” said David McGregor, Cirrus SR22 owner. “But the icing on the cake is the redundancy with the new Aerospace Logic fuel gauge that sits next to the fuel selector.”

Cies is working to expand the number of aircraft models, both certified and experiment, the Digital Fuel Level System will work with. The system costs $3,000 plus 16-18 hours of installation labor.

More information from Cies at 541-977-1043.

More news coming soon 

CIES Has New European Installation Centre

CiES Inc is proud to have RGV Aviation 
join our list of Installation Centers.  They are excited to be able to offer their Cirrus customers the new CiES  Fuel Level retrofit for SR22T, SR22TN, SR22 & SR20 Aircraft.

This modification brings legacy Cirrus Aircraft the benefit of the new factory Gen 5 digital fuel level sensor solution.  

RGV - A Cirrus Platinum Service Center -  Based at Gloucestershire Airport (EGBJ), is a family run Aircraft and Avionics maintenance business established in 1973.  As an established EASA Part 145, FAA Repair Station with EASA Subpart G and Irish Aviation Authority Subpart G approval, they have the ability and capability to support you and your aircraft, regardless of your requirements.

CiES  - A design and manufacturing business to incorporated to redefine the measurement of fuel.   CiES patented technology for measuring fuel is intrinsically safe - Non contact,  highly accurate and has proven itself reliable under the harshest conditions.   We brought accurate fuel level to aviation 

What can we do for you 

The Excitement of Initiating Change or I Double Down on Dark Horses

Imagine coming up with a new and revolutionary idea.

The challenge and the excitement.  You feel your pulse quicken

The moment you first look at the prototype and realize that you might really be on to something.

You want to share it -

You have a unique vision of the way the world should be in the future.  

You develop it and refine it and when it's ready - you bring it to market 

The world is just waiting to embrace your vision............

.....well frankly no it's not 

The reality goes something like this 

"You're selling what,  you're with who, you say its on new model aircraft.  No I haven't heard about it.   What is it again, aviation fuel gauges that work  - Say again...... how accurate really  - so why didn't the factory talk about it.......something that good you'd think.

Hold on let me put you on the speakerphone......guys listen up - this salesman on the phone here tells me he's got working aircraft fuel gauges for sale ......... Hold on - Dominic here wants to know if they are capacitive ....... yeah......... they are what........ give that to me again.   AN ISO MAGNETO DOO HICKEY - no never heard of it. Lord Kelvin really.

Boy the sales pitch just runs off your tongue doesn't it - Wait Bill in the back wants to know if it comes with a set of free steak knives -   no no send me a brochure - We'll be sure to take a look.

Functioning, Accurate Aviation Fuel Gauges 

• You now have an accurate fuel level sensor. 

• It detects how much fuel is in the tanks at any moment.

• It displays the fuel tank contents on your aircraft MFD screen but is not connected with the fuel management system on the aircraft.

• You must still enter the fuel level you observed in the tanks as you have always done on the MFD.

• The aircraft will use fuel flow data to calculate what the fuel level should be.  It will present that estimate of the fuel tank contents on the MFD.

• The level sensors give a calibrated fuel level - Not just accurate at the top and bottom accurate throughout.  These sensors also output the fuel tank contents to the MFD and then display them side by side with the calculated fuel level.

• These fuel level systems ARE SEPARATE. 

• Both indicate to you the pilot,  the amount of fuel in the tanks.  SEPARATE - But they match

• Got it?    Good. 

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.

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.