- DARPA has initiated an effort to construct a brand new, stealthy spy plane.
- Unlike other aircraft, this X-plane will feature a hybrid electric propulsion system.
- The XRQ-73 will likely be much quieter than traditional aircraft, making it harder to detect over enemy territory.
The Pentagon’s advanced research and development arm is launching a brand new effort to fly a quiet spy plane. The XRQ-73 SHEPARD will use a hybrid electrical propulsion system that can eliminate engine noise over enemy territory. Combined with a radar-evading design and a reduced infrared signature, SHEPARD could remain undetected over enemy territory and scoop up intelligence without an adversary knowing it was there.
Hybrid Spy Plane
The Defense Advanced Research Projects Agency, or DARPA, announced the brand new plane earlier this week via its website. The plane is designated XRQ-73: X for experimental plane, R for reconnaissance, and Q for unmanned. It might be the 73rd official X-plane developed by the Department of Defense—a protracted line of famed aircraft that began in 1946, with the Bell X-1 supersonic jet plane.
The plane’s designation gives away its purpose: an unmanned spy plane. The SHEPHARD name is an acronym—Series Hybrid Electric Propulsion AiRcraft Demonstration—and explains what is going to make the machine special. It is going to be the primary known military aircraft to will get rid of jet engines entirely, counting on electricity for propulsion.
In keeping with DARPA, the XRQ-73 will likely be an unmanned aircraft designed to gather intelligence. Concept art depicts a flying wing design (just like the B-21 Raider stealth bomber), the dearth of a fuselage, vertical stabilizers, and a cockpit. The drone will likely be several orders of magnitude smaller than a bomber, nevertheless—DARPA says it’s a Group 3 drone, a size class that tops out of 1,320 kilos. XRQ-73 will weight 1,250 kilos. Just like the B-21 Raider, the XRQ-73 can be being built by Northrop Gruman. First flight is scheduled for sometime this yr.
Electric Flight
On an everyday jet aircraft, gas turbine engines suck in and pressurize air, then burn oxygen and jet fuel in a combustion chamber. The engine then pushes the gasses created by the method through the rear of the engine, creating the thrust that propels the aircraft forward.
In a hybrid electric propulsion aircraft, engines burn jet fuel to create electrical power. The ability is then used to show fans that create thrust. A hybrid propulsion aircraft can briefly depend on batteries, leading to a quieter aircraft—a serious quality of life improvement for people living near airports. It might probably use each direct electric power and battery power to temporarily increase power, akin to during takeoffs. Engineers have been working on business hybrid electric aircraft for years, but a useful, fully operational craft has been elusive so far.
Avoiding the “Flying Lawnmower”
Smaller, short range flying drones like quadcopters and hexacopters are typically powered by batteries. As drones grow larger, they’re expected to have longer ranges and greater payloads, and an internal combustion engine like a prop-driven engine or gas turbine is taken into account mandatory.
All of that additional power from burning fuel has a price: internal combustion engines are loud. The Shahed-136—a prop-driven kamikaze drone designed by Iran and utilized by Russia in its war in Ukraine—makes a lot noise that it’s often called the “flying washer.” Ukrainian air defenders can often hear the Shahed before they’ll see it, giving them time to man their anti-air defenses and scan the skies.
American drones aren’t any exception. The U.S. Army’s RQ-7B Shadow is similarly noisy, producing a sound that resembles one continuous, unending fart. Just like the XRQ-73, the RQ-7B is classed by the Pentagon as a Group 3 class drone—a category of drones that typically fly at a maximum altitude of 18,000 feet. A RQ-7B engine produces as much as 99 decibels of sound, which at 18,000 feet could be reduced to 13 decibels. That’s the noise equivalent of a human being respiration, meaning that hearing a RQ-7 at three miles up is actually possible.
Unlike civilian hybrid electric aircraft, military aircraft would use electric power in a different way. A plane just like the XQR-73 would take off and land with the engine providing electrical power to the fans. Because it nears enemy territory, the aircraft would switch off the gas turbine and power the fans from batteries. The drone’s engine noise disappears, and the plane is suddenly flying silent.
Son of Great Horned Owl
XQR-73 is a direct descendant of Great Horned Owl (GHO)—one other project to develop a quiet unmanned aerial vehicle. GHO was a project of the Intelligence Advanced Research Projects Activity (IARPA), DARPA’s equivalent within the intelligence community. The name is a reference to the power of owls to fly silently, undetected by their prey.
It’s not clear whatever happened to Great Horned Owl. A 2011 PowerPoint presentation outlines the identical key objectives of the XQR-73 program, so it’s possible that GHO was eventually deemed technically unachiveable on the time. The 2 aircraft programs depend on battery technology to succeed—a field that has seen remarkable progress within the last 13 years. So, perhaps DARPA thinks the tech has advanced to some extent where silently flying a 1,250 pound drone is feasible.
Great Horned Owl was also a Northrop Grumman Project, so a number of the design will likely carry over to the XQR-73. One area where the 2 planes differ is the location of the fans—GHO features 4 fans mounted above the aircraft, while the XQR-73 buries them contained in the body of the aircraft. Burying the fans eliminates their radar signature, making the aircraft harder to detect.
Hybrid electric aircraft have the potential to revolutionize the aviation industry. A successful XQR-73 will likely be a groundbreaking aircraft, ushering in an era of quieter flight. Excellent news for people living within the flight path of airports, and bad news for America’s adversaries.
Kyle Mizokami is a author on defense and security issues and has been at Popular Mechanics since 2015. If it involves explosions or projectiles, he’s generally in favor of it. Kyle’s articles have appeared at The Day by day Beast, U.S. Naval Institute News, The Diplomat, Foreign Policy, Combat Aircraft Monthly, VICE News, and others. He lives in San Francisco.