In the James Bond film, Spectre, the British spy performs a 360° stunt in a helicopter. The scene had a lot of people wondering if a helicopter could actually fly upside down. A number of experts have weighed in and the verdict seems to be that it is possible, somewhat.
Pilot Mike Buckley from the British Airline Pilots Association says that a helicopter can be flown upside down for a short period of time.
“Helicopter pilots are highly trained and this footage appears to be a BO105 undertaking a very skilled maneuver with an expert pilot at the controls,” Buckley says.
Buckley explains the BO105, which has a rigid rotor head, is able to perform these types of maneuvers.
“The Westland Lynx, as flown by the UK Army Air Corps and the Royal Navy, also has a rigid head and is often seen in air shows around the UK doing rolls and occasionally loops,” he says.
The pilot recognizes that the filmmakers may have used CGI in postproduction to enhance the stunts.
“There are strict rules about low flying, so if it is real footage, the backdrop [of the city] may have been added later,” he says.
According to Emilio Frazzoli, associate professor of aeronautics and astronautics at MIT, to gain altitude and stay airborne, helicopters depend on rotor blades that generate vertical thrust. If a helicopter turns upside down, it could stay aloft by tilting its nose somewhat upwards and using its wings to generate lift while it’s upturned. In theory, an upturned helicopter could use its rotors to produce thrust toward the bottom of the helicopter, thereby keeping it aloft when upturned.
“Imagine you’re attached to a rotor blade,” Frazzoli says. “In order to generate lift upwards, you have to tilt the blade a little bit upwards. To generate lift toward the bottom of the helicopter, you have to tilt the blade a little bit downwards.”
However, for commercial helicopters to fly upside down, their rotor blades would need to be rigid enough in order to not flex too close to the main body of the helicopter. If not, the blades could rip off the fuselage or other critical components. The joint that connects the rotor blades with the rest of the vehicle would also have to be redesigned to bear the load of an upturned helicopter. Finally, new controls would need to be developed to enable the rotor blades to tilt downwards, and the engine would have to be reconfigured in order for the fuel and lubricants to be properly distributed while the helicopter is inverted.
Without these changes, however, many helicopters can still fly upside down for seconds at a time.
“Military and acrobatic helicopter pilots often perform loops and barrel rolls in which their vehicle momentarily flies upside down,” he says. “During that time, the rotor still generates thrust toward the top of the helicopter, so the pilot must maintain sufficient momentum and altitude to remain airborne,” Frazzoli says.