SB-Helo X-Stream, a new service from Cobham with Inmarsat to improve helicopter satcom connectivity, is now live. Rotorcraft, especially the larger types, can often experience problems in airborne satellite connectivity due to a phenomenon called “rotor shadowing.” In most cases, the installation of the satellite antenna is below the rotor disc and its in-motion blades can cause interference with data transmission, leading to data packet loss.
While some degradation is acceptable, as the packet loss approaches 40 percent the connection becomes unusable. The wider the chord on the blade, and the more of them there are, the higher the degradation becomes.
“The mistake that was made in the past is the Inmarsat network catered only for fixed-wing aircraft, and we tried to install satcom on rotary-wing and we always had a much-reduced service,” said Shaun Schaper, a sales and support engineer with Cobham Satcom (Booth 8318). “The main changes we made on the network side and on our radio module."
Based on software upgrades to the Cobham connectivity hardware, the Inmarsat system can now differentiate the aircraft as a rotorcraft and will treat it differently than a fixed-wing aircraft in terms of data transmission.
“When we transmit the packets, we actually divide it into four sections and we repeat the data we send in four slots, so if we lose the two, we still have another two to make up the data,” Schaper told AIN. “So we sacrifice a bit of bandwidth, but we add a bit of resilience.”
Using SB-Helo X-Stream rotorcraft operators experience a 94 percent reduction in packet loss, a 67 percent reduction in jitter (from 18 ms to 6 ms), and a 58 percent increase in throughput, boosting it from 272 Kbps to 430 Kbps on a single SB channel—performance one would associate on fixed-wing applications. It is now standard on all new Cobham Aviator SP satcom installations and available for rotorcraft already equipped through a free upgrade.