What is it?

Thermawing is an ice protection system developed by Kelly Aerospace. Flight Test Pilots flying the NASA Twin Otter Research Aircraft were looking for a better de-ice system. They worked in conjunction with a company called EGC Enterprises to form Northcoast Technologies and begin development. Original funding was provided by a NASA small business grant.

The launch customer for the first Thermawing install was ... Columbia Aircraft which released it under the marketing name of Evade. In this install, it has 6 heating elements, 3 heat control modules (HCM), one controller and one 7500W alternator.

Conceptually, it's a thermoelectric deice/antiice system. The heating elements are graphite foils (good thermal properties but soft material), coated with a layer of Tedlar (PVF - polyvinyl fluoride) for protection. The strips are heated just enough to break the ice bond with the surface after which aerodynamic forces do the rest.

How does it work?


Thermawing uses a pulsed power technique which activated each heating strip in sequence over a 60s cycle. The heaters are activated in the following order:
evade_zones.JPG
Heater strips


  1. Right Inboard (RI)
  2. Left Inboard (LI)
  3. Right Tail (RT)
  4. Left Tail (LT)
  5. Right Outboard (RO)
  6. Left Outboard (LO)


Once armed, the system will activate at 41°F starting the de-ice cycle. The impingement area, or leading edge, is kept warm, continually melting impinging ice, or simply, "runs wet.” The area just aft of this impingement area, or shedding zone, is kept below freezing, causing the run-back to freeze and collect as ice.

During a de-ice cycle, the voltage is increased and the heaters are pulsed to temperatures above freezing. Raising the temperature of this aft shedding zone breaks the bond between the ice and the heater surface, thereby allowing the ice to be aerodynamically shed from the protected surface.
evade_strip.JPG
Strip layout


Once power is removed from the heater, the shedding zones immediately freeze and continue to collect ice until the next deice cycle. The unique heater characteristic — virtually instantaneous cooling of the heater — precludes the creation of liquid water and minimal run-back onto unprotected areas of the wing.

Test performance

evade_runback.JPG
The ThermaWing De-ice System Minimizes Runback
evade_faa.JPG
FAA Icing test flight photo


System power


Evade system is powered by a dedicated alternator used exclusively to power the deice system. The aircraft bus is used to power the Evade controller. The heaters are supplied a nominal 70VDC @ 130Amps.

The Evade prop deice system (if installed) uses the main aircraft bus for its power source and has its own Prop Timer.

Components


  • 6 Heaters Mats
  • 6 Temperature Sensors
    Under each mat near the wing root
  • 3 Dual Zone Heater Control Modules (HCM’s)
    One inside each wing access panel, one in the tail access panel
  • 1 De-Ice Controller (contains software and alternator regulation components)
    Located in the avionics bay.
  • 1 Ground Fault Sensor (GFS, detects power returning through paths other than through the heater mats)
    Forward side of deice controller.
  • 1 De-Ice Alternator ES13070 or NC71200-1
    Right-rear of the engine on 350/400 installs, front-mount driven off main prop shaft on 300.
    Alternator tensioning bracket designed to handle: Kelly M-Drive, Iskra or TCM Energizer starters.
  • 1 Outside Air Temperature Sensor
    Using the standard system OAT sensor (under right wing access panel)
  • 1 Airframe De-Ice Switch
    Left side of instrument panel, under Prop Heat/Pitot Heat switches

Pilot interface


Initial Turn On
  • Battery and avionics master on
  • System is now monitoring heater temps, OAT and alternator output
  • To turn system on, press Airframe De-ice switch

Power Up Test
  • Occurs first time, after Airframe De-ice switch is pressed after avionics master is ON
  • Will occur again if Avionics switch or circuit breaker is cycled
  • Test takes 30-45s and should be done during a normal 1700RPM run-up
  • A small amount of power is applied to each heater to check resistance, temp rise and alternator power output
  • Green and Red lights will alternate back and forth during test
evade_button_test.GIF
System Armed
  • Once system passes Power Up Test and as long as OAT is above 41dF, system will be armed but not operating
evade_button_1.JPG
System Operating
  • If system is armed and OAT falls below 41dF, the system will begin to de-ice
  • No other interaction is required from the pilot.
  • The power output and required heater temperatures are automatically adjusted by de-ice controller
  • A De-Ice Cycle will occur every 60 seconds
evade_button_2.JPG
Soft Fault
  • A Soft Fault may occur if a portion of the system is not operating correctly
  • If one heater zone has failed, but the other zones are working a soft fault will be indicated
  • If the system is Armed and On while taxing at low RPM, it is possible to have a soft fault due to low alternator power output. It will clear once RPM is brought up for takeoff
evade_button_3.JPG
Hard Fault
  • A Hard Fault may occur if something in the system has failed and the system is not operating at all
  • You can cycle the circuit breaker once to reset the system. If Hard Fault remains, service is required
evade_button_4.JPG
Ground Fault
  • A Ground Fault may occur if the system is sensing electrical current returning through a path other than the heater mats
  • The system is automatically shut down and power is cut to the alternator
  • You can cycle the circuit breaker once to reset the system. If fault remains, service is required
evade_button_5.JPG

System Operation Notes:

  • Once the Power Up test has been completed turn the system off until ready for takeoff
  • To increase longevity of all components only operate the system when visible moisture is present and temperatures are low enough to produce ice
  • Operate the system like you would a Pitot Heat or Prop De-Ice System
  • If prolonged periods of non usage are to occur (greater than 20 hours, such as the summer months) continue to conduct Power Up tests on the ground to allow some power to be put through the alternator. This will increase the life of the alternator

Diagnostics


Evade/Thermawing system allows streaming of data from the various sensors and systems while in service. This allows the very large majority of problems to be diagnosed locally (even by the pilot) and without much need for trial and error at the shop.

Setup


The data port is located on the side of the deice controller in the avionics bay. It's a serial RS232 port while the connector is a rather non-standard mini-DIN plug. As a result, to connect to a laptop, you need a special DIN-to-RS232 cable that Kelly can provide at no charge. You can plug this cable into the plane and simply leave it there permanently to be used as needed. This will allow you to diagnose problems in real time, during flight, which will allow you to catch even rare, and otherwise hard to reproduce problems.

Data can be read through any serial terminal. Basic requirements are the ability to accept RS-232 serial ASCII text at 19,200 BPS and display it in a 132-column format. Due to the large volume of rapidly generated data, capabilities for back scroll and capture to a textfile are highly desirable.

A standard laptop computer running Windows HyperTerminal and having a standard DE-9 (sometimes erroneously called out as DB-9) RS-232 serial port fulfills this requirement. Laptop computers manufactured after approximately 2002 often do not have such a serial port, but adapter cables to provide such a serial port via USB are readily available.

Configure the terminal for 19,200 BPS data rate, 1 stop bit, no parity, no handshake, and 132-column display.

For HyperTerminal, these settings are made under the <File><Properties><Connect To><Configure> menu. You must “disconnect” using the Call menu before changing settings, and reconnect again using the Call menu after establishing the settings. Then use the <File><Properties><Settings> menu to select VT100 emulation, and select 132-column mode under <Terminal Setup>.Hyperterminal doc.

Note there is no special dependency on Windows for this. Any computer-like device (including iPads) that either have a serial port themselves or support an adapter with a serial port (eg. USB-to-serial or serial-to-wifi, etc.) will do the trick. If you plan to use this in flight, it's best if the device uses a solid state drive though simply so you can continue to use it at all altitudes. Regular harddisk are likely to crash above about 10000ft.

Data


Note: the explanations here are a short summary of what is going and should be sufficient for the casual user. More details about what's really going on are available in the Thermawing installation manual.

Position the laptop in a convenient location and connect it to the serial cable. Standard straight-through PC serial cables may be used as required to extend the cable to any length up to 100’. Enable data capture to a text file if desired, and then apply power to the Avionics Bus to power the Controller. Several pages of internal power-up diagnostics will be generated, and then the system will begin streaming data in columns. Either turn off the Avionics Bus when this columnar data starts, and scroll back to find the configuration table, or use a text editor to locate the final configuration table via the captured data file.

Initial Powerup Check


Data will look like this:

N,Loc,Bus,Couplr, Int, Ext,Sq,Of,Model,Manuf Date,Watts, Ohms ,Ratio, Wet ,Shed
0, LO,Lft,021618,777F,FFFF, 0,DE, 80,2005-04-01, 7500, 0.44, 4.20, 2.00, 5.20
1, RT,Fus,021773,8192,FFFF, 1,E9, 80,2005-03-23, 7500, 0.61, 4.20, 2.00, 5.20
2, LT,Fus,020A25,7336,FFFF, 2,DD, 80,2005-06-02, 7500, 0.61, 4.20, 2.00, 5.20
3, RI,Rgt,020C17,7A2B,FFFF, 3,EB, 80,2005-06-02, 7500, 0.70, 4.20, 2.00, 5.20
4, LI,Lft,020AD1,759B,FFFF, 4,E2, 80,2005-06-02, 7500, 0.62, 4.20, 2.00, 5.20
5, RO,Rgt,021115,8253,FFFF, 5,E1, 80,2005-04-01, 7500, 0.44, 4.20, 2.00, 5.20
6, OA,OAT, , ,81B9, ,F6, 81,2005-04-15
6 htrs
0 Cpl CRC?
0 Int CRC?
6 Ext CRC?
Start PwrUp Test
Stack 4749 bytes HCM temps: 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,

The 0-5 lines correspond to the 6 heating elements (Left Outboard, Right Tail, Left Tail, Right Inboard, Left Inboard, Right outboard) and is the same order the heating elements will cycle. Line 6 is for the Outside Air temp sensor.

Main things of interest here are the version numbers of the software used on each heating element and the ohm column. Any short will show as a high resistance value on the affected element.

Normal operation


Data will look like this:

XSM, Time,DT,C, OAT,Vbus,Powr,Adj,PWM,Vfld,Ifl,Vdeic,Ideic, Ohms,Watt,Intgr,Prqst,Targt, RI, LI, RT, LT, RO, LO
YD,2040.4,36,2, -4.9,27.2,7500, 83, 39,26.1,3.5, 68.9,105.8, 0.65,7289, 112,12035, 50.0, 52.1, 53.5, 67.5, 77.1, 95.2,119.6
YD,2040.5,36,2, -4.9,27.2,7500, 83, 39,25.9,3.5, 69.2,106.3, 0.65,7355, 112,12035, 50.0, 52.7, 53.7, 67.8, 76.9, 94.9,118.8
YD,2040.6,36,2, -4.7,27.7,7500, 83, 39,25.6,3.5, 68.7,105.2, 0.65,7227, 112,12035, 50.0, 53.1, 54.1, 68.2, 76.5, 94.5,118.0
YD,2040.7,36,3, -4.5,27.7,7500, 83, 39,25.6,3.5, 68.4,105.2, 0.65,7195, 118,22951, 50.0, 53.4, 54.5, 69.0, 76.0, 93.9,117.4
YD,2040.9,36,3, -4.6,27.2,7500, 83, 39,26.3,3.5, 70.6,105.0, 0.67,7413, 118,22951, 50.0, 53.8, 54.7, 69.9, 75.8, 93.5,116.5
YD,2041.0,36,3, -4.6,27.2,7500, 83, 39,26.1,3.5, 70.1,104.5, 0.67,7325, 118,22951, 50.0, 54.0, 55.0, 70.9, 75.6, 92.9,115.7

Most fields should be self-explanatory. The ones of most interest are:
panel_temps.png
Panel Temps during operation

  • Vbus - check for fluctuations. If you see any, something is likely wrong with either the alternator or the voltage regs.
  • Powr - target power setting.
  • Watt - power actually drawn (ie. as measured)
  • Ohms - measured resistance of the system
  • Targt - temperature target for each heating element
  • RI/LI/RT/LT/RO/LO - actual temperature of each heating element

Real use example

For the curious, a full data run is available here. Same data in spreadsheet format.

If you watch closely, you can see the various HCMs cycling in/out at various power levels and the strip temperatures converging to the targets. The system log messages are mixed in there also (look for lines like "Temp Sens OK" and alike) and are intended for human readers. The system only uses the raw data.

Heater repairs


The heater panels are covered with a layer of Tedlar (DuPont brand name for PVF - Poly-Vinyl Fluoride) for protection. So how strong is it? Well, as per DuPont, tensile strength at ambient temps is about 5000 psi (which is about 34.5MPa). For comparison, HDPE (polyethylene) is at 33MPa, aluminum alloy is at 400 and steel starts at 520 (for the record, Kevlar is at 3620). HDPE is what is commonly used for various food containers like milk or soft drink bottles so this Tedlar is about as strong as that. In other words, this is more or less regular recipient grade plastic as far as damage resistance goes.
evade_patch.JPG
While resilient, this material is not bulletproof though so it's possible to eventually get cut or punctured. If so and assuming the cut is not all the way through, the system will continue to work as electricity and heat will continue to flow around the damage area.

So how much to fix? The repair kit for minor repairs is $25 and takes less than 1h to install (as per Kelly). See side photo for how such a repair looks like. If the entire panel is damaged beyond repair, removal and reinstallation of a new panel runs between $900 and $1200. The panels themselves are between $500 and $800 (depending on which panel) and labor budget is 6h.

HCMs cost $1000 each and require about 2h labor to replace. Alternator, belt and associated hardware cost $1900 and require 3h labor to remove, install, run the aircraft and retension the belt.

Bubbling paint


As per a post from Erik Pederson:

There have been no bubbling paint issues on any of the Lancair experimental aircraft, the Cirrus SR-22 we have been flight testing or other similar surfaces that we use the de-ice system on. The bubbling paint issues only appear on a select few Columbia’s. The total known at this time is 3 out of all the installations and this includes Steve Master’s original bubbling paint issue.

The aircraft that we have been able to examine here in the Kelly hangar seems to point to a static discharge issue involving the paint. The aircraft with the bubbling paint have had nearly 30 or more very small static discharge holes along the leading edge of the wing in the paint. The aircraft in question had either bad static wicks or bad electrical connection between the static wicks and the rest of the aircraft. This causes the static buildup to discharge through the leading edge of the wing and possibly under the heater. Upon examination of the heaters we have found that the bubbles have never been in the heater itself. They have always been between the layer of paint and primer. We suspect this is due to the static discharge and/or improper curing of the paint. We believe Cessna is remedying the paint issues at the factory and this issue will no longer exist.

Magnetic interference


The Evade system is basically a big electric circuit running at high enough power to shed the ice. A side-effect of this is that it also generates a substantial magnetic field too and an alternating one at that. As each panel is energized in turn, the magnetic field source moves around. The magnetic compass is affected the most with fluctuations of up to 15 degrees (which effectively makes it useless). The PFD copes better and has only mild +/- 1 deg fluctuations while operating the deicing system at full power.

Weight


  • 48 Volt Electric AC to 28 Volt Electric AC Upgrade Only: -25lbs (weight reduction)
  • Thermawing only install (no A/C): 46lbs
  • Thermawing and 48 Volt Electric AC to 28 Volt Electric AC Upgrade: 21lbs
  • Thermawing Installation and Mechanical AC to 28 Volt Electric AC Upgrade: 40lbs

Availability


STC approved for 300/350/400, 14V and 28V planes (entire Thermawing is on a fully independent electrical bus). The only problem is for planes with mechanical A/C because the mechanical compressor is sitting in the same spot where Evade alternator needs to go (which is the last space left under the cowl. Not much room in there).

For 28V planes, Kelly got a separate STC to convert their mechanical A/C to an electric one which frees up room under the cowl to install the Evade alternator. There is no such conversion STC for the 14V planes though (market is tiny) so ... if you have a 14V plane and have A/C installed, you can't have both. You'll need to choose which one you want more.

Where and how much?


As of Jan 2010, the Thermawing install is $24500 ($27500 if you have mechanical A/C. See details here). There are 73 Evade/Thermawing systems installed on Columbia-s so far. Installations are available at the following locations:

  • RDD Enterprises in Redmond, OR
    15 installs so far (no Columbia-s yet but multiple Lancair-s, C421, and Evolution)
  • Tom's Aircraft, Long Beach, CA
  • Goodrich Aviation in Binghamton, NY
  • Kelly Thermal Systems in Willoughby, OH and Kelly Power Systems, Montgomery, AL
    Factory shops. Most Columbia installs. Ferry option offered for $1000 each way, pilots insured by Kelly.
  • MAS Air Service, Leutkirch, Germany / Europe

Warranty coverage is provided by Kelly (regardless of install location) for 2 years or 500h HOBBS whichever comes first (parts and labor).

References


  1. Kelly technical manuals
  2. Thermawing STC approval
  3. Thermawing prop deice STC
  4. Mechanical to electric A/C conversion STC
  5. Evade/Thermawing AMOC for AD 2006-25-08
  6. Belt tensioning procedure
  7. Evade data sample