Comac has delayed C919 natural icing trials with Canada’s International Test Pilots School (ITPS) in Ontario until autumn due to Covid-19-related travel complications, ITPS president Giorgio Clementi told AIN Thursday. Having reached a sufficiently advanced stage to conduct the trials in early spring, C919 program officials notified ITPS that it won its bid for the contract only two weeks ago.
Whether or not the delay will affect the overall schedule remains in question, however, as Clementi declined to comment on reports that Comac hopes to finish Chinese certification by the end of this year.
Also training test pilots for the program, ITPS is headquartered in a part of the world whose weather makes for ideal conditions for icing tests—one of the reasons Comac conducted the same testing for its now-certified ARJ21 with a different Ontario-based company. A flight-test pilot himself since 1987, Clementi characterized the C919’s icing system as a fairly conventional design, using a typical bleed air system found in most airliners. That doesn’t mean the program doesn’t carry some unknowns, however.
Asked about the duration of the testing, Clementi referenced the ARJ21’s eight-day campaign but could not pinpoint the expected length of the C919’s icing trials.
“It depends on the number of encounters that you have and the quality of the icing that you encounter,” said Clementi. “You basically have to demonstrate a sufficient number of encounters with sufficient ice accretion on critical areas within the appendix C envelope of FAR 25.”
That regulation essentially defines the combination of liquid water content and mean droplet diameter, he explained. “So you will have a number of icing encounters and you'll see where you are within the envelope,” noted Clementi. “And so if you've got a bunch of encounters which have got low liquid water content and small droplet diameters, you’ll be looking for something bigger. You want to populate as much of the envelope as possible. You obviously can't do it all because it depends on the weather.”
Each day of testing, a meteorologist advises the flight team of the forecast and recommends where the airplane should fly to encounter icing. “It's completely counterintuitive—you’ll be in the air talking to Toronto center and asking them to give you vectors toward an area of icing,” said Clementi. “So it's interesting work and a potentially hazardous flight test.”
Along with the pilot in command, an ITPS pilot likely will serve as a communications facilitator, working the radio and talking with air traffic control. Two flight-test engineers in the cabin will operate a multi-spectrum cloud probe that measures and displays in real-time droplet diameter and liquid water content. Meanwhile, a meteorologist, either onboard or communicating from the ground on a satellite phone, will relay vectors toward areas of high icing concentration, explained Clementi.
The testing involves validating anti-icing functionality on protected surfaces and ensuring the airplane acts as modeled when ice accretes on non-protected surfaces. The team measures the anti-icing system’s effectiveness on thermally protected surfaces, which include the leading edge of airfoils. For unprotected surfaces such as the airplane’s belly, the crew must gauge the airplane’s flying characteristics during a holding pattern, typically for 45 minutes.
Unfortunately for Comac and ITPS, all that will have to wait until sometime in early to mid-autumn, when the next window of opportunity for optimal icing conditions opens in the southern Ontario-Great Lakes region. “You’ve got to have the airborne moisture,” explained Clementi. “It can’t be so cold that all the moisture freezes out because then you’ll have no liquid water content, and it can’t be too warm, where you don’t get the freezing [you need].”