Breaking the ice
The third-generation Cirrus SR22 GTS is blazing a trail for enhanced capabilities in high-end general aviation aircraft
Flight into known icing (FIKI) and enhanced vision for the third-generation Cirrus SR22 GTS, aka "turbo", are two options that, taken together, will boost the utility and safety of this high-end, piston-powered, turbo-charged single -an aircraft that was already an extremely capable cross-country machine.
These enhanced capabilities, combined with the synthetic vision already offered in the Garmin-based Cirrus Perspective avionics suite, offer a preview of features that will, increasingly, become available to general aviation aircraft as sales of such equipment go up and prices come down.
Flight International sampled these relatively new offerings on a night demonstration flight in the Washington DC area with Cirrus mid-Atlantic region sales director Boni Caldeira on 8 July.
Our flight, in N569PG, took us from Lee Airport (ANP) in Edgewater, Maryland, eastward to the relatively unlit sections of the state's eastern reach, a perfect location to demonstrate the company's new dual-wavelength (infrared and visual) enhanced vision system (EVS) option for the SR22 while observing in flight the workings, though not the need for, the ice protection system.
During our evening pre-flight, Caldeira pointed out various changes to the top-of-the-line $650,000 SR22 turbo that were required to support FIKI and, to a lesser extent, EVS.
© John Croft
The SR22's enhanced vision system includes a sensor unit mounted beneath the left wing
The basic ice protection already offered for the SR22 includes a 15-litre (4USgal) tank of TKS fluid in the aircraft's right wing, with electrically powered pumping and piping systems to carry the glycol-based anti-icing liquid to the leading edge of the wings and horizontal stabiliser, where it seeps through laser-drilled holes in the titanium leading-edge cuffs, coating the aerodynamic surfaces.
For the propeller, the TKS fluid is metered out through a "slinger" ring that allows a coating of fluid to be pulled by centrifuge action along each of the three blades.
The $24,500 FIKI version of icing protection system for the Cirrus, developed in conjunction with CAV Aerospace, maker of TKS systems for a wide variety of GA aircraft including the Cessna Caravan and Beechcraft Bonanza, is significantly different.
In addition to a second 15-litre TKS reservoir and a new maximum flow rate option, the system has longer leading-edge cuffs chord-wise, with more holes, a cuff for the vertical stabiliser, two nozzles for keeping the windshield clean, a backup pump and a stall detection system.
To help pilots assess whether they are picking up ice in flight, Cirrus has added LED lights on both sides of the fuselage ahead of the wings.
A prism in the lights splits the beam to illuminate both the horizontal stabiliser leading edges of each wing, each of which has a "witness" plate about the size of a razor blade to which ice will attach first.
Icing equipment for the horizontal stabiliser has changed as well. Cirrus found protection was needed on the outboard section of the elevator, which extends forward at the edges of the horizontal stabiliser, to stop ice building up in the gap. The resulting system required the company to route TKS tubing into the elevator itself.
Perhaps most intriguing is a new stall speed indication system incorporated by Cirrus.
The stall speed of a wing can vary because of ice's ability to change the shape of an aerofoil and add weight when accumulating on unprotected areas, so airframers seeking FIKI certification will generally develop and install an alerting system that acknowledges the actual aerodynamic condition of the aircraft, whether due to ice accumulation or g loads of other factors affecting stall speed.
In this case, Cirrus chose to create a dynamic stall speed overlay for the pilot's primary flight display on Perspective, computed by using output from a pressure transducer on the right wing. A separate approach-to-stall alerting system is also fitted, as required by Part 23 regulations.
The pressure transducer measures the force of the airflow on the leading edge, and by association measures the angle of attack of the wing, and sends the information to a stall warning computer, which creates an overlay for the airspeed tape.
In this way, the computer maintains and displays a dynamic measure of the aircraft's stall speed in its present configuration of weight, drag, density altitude and load factor.
In the air, Caldeira demonstrated the variable stall speed readings by slowing the aircraft, pulling gs and pointing out that the indicated stall speed increased correspondingly on the speed tape. Conversely, the indicated stall speed decreased when he unloaded the wing.
With the ice lighting turned on, Caldeira "primed" the TKS with several 3s bursts of TKS fluid on the windshield, a practice that accelerates start-up time for the system, before he demonstrated overall TKS operations at various flow rates.
If icing is expected on a flight, pilots are instructed to prime the system on the ground to minimise delay between system activation and fluid delivery.
In addition to the "normal" and "high" flow rate rocker switch in the cockpit for the standard ice protection system, the FIKI system includes a pushbutton for a "maximum" setting that provides double the flow rate of the "high" setting for 120s, then returns to the previously selected flow rate.
Although safety is paramount, pilots are likely to consider the cost of TKS fluid when selecting flow rate because the liquid costs between $4 and £6.60/litre ($15-$25/USgal), depending on where it is purchased and whether it is bought in bulk.
The icing protection system display in Perspective shows how much fluid remains in each of the two tanks, plus the time and distance remaining at the selected flow rate.
If the primary pump fails, pilots can select the backup pump by rocker switch, although flow rate is automatically set to "maximum" in that case.
There is also an option to select which TKS reservoir the system draws from, as opposed to the automatic setting, which keeps the levels fairly well balanced. An annunciator alerts when the fluid level goes below a pre-set threshold.
Less extensive changes to the SR22 GTS were required for the enhanced vision system (EVS), a $15,000 upgrade Cirrus had planned to include with the unveiling of Perspective in May 2008.
Because of the US military's purchase demands, EVS vendor Max-Viz was unable to supply Cirrus enough units for it to launch the product comfortably.
However, Cirrus began building Perspective aircraft with all the wiring and software needed to accommodate the EVS unit once it was available in quantity - about four months later.
The sensor in question is a 0.5kg (1.2lb) hermetically sealed package carrying an 8-14 micron, 320 x 240 pixel long-wave infrared (LWIR) sensor fused with a visible light sensor that provides a 40° horizontal by 30° vertical field of view forward.
Mounted beneath the left wing, the unit is aligned so that the horizon line is continuous between the synthetic vision view on the 12in (305mm) primary flight display (PFD) and the EVS view on the 12in multi-function display (MFD), both of which mimic the visual field of view from the pilot's seat.
On this flight, Caldeira selected the EVS for the MFD upon turning onto Runway 30 at Lee Airport, which gave him a view of the runway during our take-off at dusk. Living objects, such as deer or people, would have shown up brighter than the surroundings had there been any such obstacles in our path.
During take-off, having the synthetic view of the runway on the left and the EVS view on the right provided ample situational awareness as daylight faded.
While climbing out to the east, Caldeira showed how the vertical position of the flight path director - the circular target on the PFD that shows the actual direction the aircraft is travelling - can be superimposed visually over the EVS display to find out whether the aircraft will fly into or below clouds that are readily observable on the EVS but not out of the window.
He also pointed out how a portion of the propeller arc is ever present on a small portion of the right side of the EVS view.
Caldeira said the system would not see through dense clouds, for instance a solid cloud bank extending down to 200ft above the ground, but was likely begin to pick up hints of the airport when descending through 400ft, rather than 200ft with the naked eye - a tactical advantage when flying an approach to minimums.
He said the EVS-600 camera inthe system would pick out incandescent and the newer LED runway and taxiway lights, which can cause problems for higher-end cooled IR systems that are not tuned to pick up LEDs.
On this night, Caldeira followed his standard procedure of bringing up the EVS display at about 500ft above ground level when turning onto final approach to get a clear look at the runway environment.
Despite the moonless night, we had a day-like, albeit monochrome, view of the otherwise cloaked runway in the 20:00 darkness, both on landing and during taxi back to the ramp.
Thanks to the EVS, there was no doubt there were no obstacles in the way.
Source: Flight International