Materials engineering expert is calling for more collaboration and research regarding supersonic passenger planes to help deliver safer, environmentally friendlier and more economical aircraft.
Supersonic passenger planes are back on the radar more than 20 years after the last ultra-fast aircraft was withdrawn from service.
US aerospace company Boom Supersonic recently broke the sound barrier in a test flight, opens in a new window of its XB-1 jet, while NASA and Lockheed Martin hope to put its X-59 research plane, opens in a new window in the sky later this year.
Commercial supersonic air travel has been off the schedules since 2003 when Air France and British Airways ended operation of their Concorde planes, which flew at a maximum height of 60,000 feet or 18,288 m, and at more than twice the speed of sound, approximately 2,336km/hour.
But a UNSW materials expert says much more research and development is needed across the aeronautical industry to ensure supersonic aircraft of the future can cope with the strains of flying at such high speeds.
Adjunct Professor Dr. George N. Melhem, from the School of Materials Science & Engineering, highlights issues with cracks discovered in the Concorde’s wings while it was still in service as one of several reasons to be rigorous when it comes to safe design of such planes.
“I think there's two things we want in the industry. The first is to have that fast supersonic travel again, definitely. But number two, we’ve got to make sure it's safe, and we need to make sure we have enough information about the materials being used, particularly with the micromechanical processes inherent within materials” he says.
“These high-speed aircraft are exposed to high temperatures and also higher strains in terms of the materials expanding and contracting, and that’s where I have some reservations. The overall structure of the Concorde’s fuselage expanded by 200mm during flight causing sustained creep strain in certain materials.
“When you want to fly an aircraft, especially at those speeds, you have got to be really confident that every bit of the plane can handle the pressure and the temperature at the heights being flown, and the increased friction that is created.”
Prof. Melhem is calling for increased access to top-level wind tunnels to rigorously test the kind of materials – such as titanium and carbon fibre – needed for future supersonic planes.
He is wary that lessons from problems previously discovered in the wings of the Concorde may not have been fully learnt.
In July 2000, British Airways revealed that cracks had been discovered, opens in a new window in all seven of the Concorde supersonic planes (in spars and crossbeams of the wings) in their fleet.
One aircraft was taken out of service, but the other six were deemed safe to fly. The largest cracks were found in the rear wing spar, reaching up to 76mm on the grounded plane.
Air France also confirmed four of their six Concordes also had cracks in the wing, but did not take any of them out of service.
The issue was completely overshadowed just a day later, however, when one of the planes operated by Air France crashed shortly after take-off from Paris Charles de Gaulle resulting in the deaths of all 109 people on board, plus four on the ground.
However, the crash was completely unrelated to the cracks in the wing and was instead caused by a strip of metal on the runway – which had fallen from a preceding aircraft – puncturing one of Concorde’s tires and sending debris into the fuel tank which subsequently ignited and resulted in a catastrophic engine failure.
Modifications were made to protect the fuel tank to ensure the remaining Concordes could fly safely, but within three years they were all removed from service by both Air France and British Airways – and the wing crack issue was largely forgotten about.
When you want to fly an aircraft, especially at those speeds, you have got to be really confident that every bit of the plane can handle the pressure and the temperature at the heights being flown, and the increased friction that is created.
"Because of the crash, which had nothing to do with the cracks, I feel no-one addressed that issue at the time, and they haven’t done since. Those cracks haven’t been talked about at all,” says Prof. Melhem.
“During my research I have found there may have been a problem with the materials they were using, in terms of a mismatch with materials at certain temperatures and certain stress-loads.
“The only place we can come anywhere close to simulating the conditions of real supersonic flight is in a wind tunnel, but those are very rare.
“As materials researchers it would be amazing to have access to facilities like that where we could test for two or three hours, but it’s really only organisations like NASA that can do that.
“So that is a limitation we have to test these materials proposed for supersonic aircraft.”
Prof. Melhem has been in discussions with NASA about conducting tests in a wind tunnel at their Glenn Research Center in Cleveland, Ohio which can simulate airspeeds up to Mach 6.0 (around 7,400km/h).
“The plan is for NASA to dedicate one of their scientists to work fully with us on our testing and research. NASA are the only body that can perform the tests that we require to address the next level of research.”
Prof. Melhem says supersonic passenger planes are likely to come back into service at some point in the future – driven by the desire to significantly reduce flight times, even if it’s a service that only the rich and famous could afford.
But he is not convinced such aircraft will be flying by the end of the decade, as promised by Boom Supersonic with a 65-seat version of their XB-1.
“I am confident supersonic commercial flights will happen again, but no time soon,” said the UNSW academic, who has written a book on the supersonic effect on rivets, opens in a new window on aircraft.
“I think it is more likely to take 10 or 15 years to get to that stage, so maybe around 2040. But the whole industry needs to be working hard right now, with more research and more students coming through and more knowledge exchange.
“And I don’t think there’s enough of that right now, and there’s also not enough facilities available to test the materials.”
