Talk to Nowlan about Australia's plans to spend billions of dollars on a fleet of F-35 Joint Strike Fighters, he is equally scathing.

"I took one look at the F-35," Nowlan says. "Jaw. Hit. Ground."

Nowlan doesn't work in the military. He doesn't fly jets. But he has always loved things that go fast. Really fast. He put his aeronautical skills to work on race cars, designing some clever computer software to simulate what happens after a tweak of the springs, a change to the gear ratio, or a slight adjustment to the wind spoilers - all to tune the car for as much speed as possible.

He's written a book, The Dynamics of the Racecar, and travelled from Sydney to Indianapolis, Bathurst and  Monaco to apply his tests with pit crews working  on Nascar and Le Mans prototypes.

But while he spends his days at the track, and his weekends swooping radio-controlled planes near his home on the NSW central coast, Nowlan can often be found of a night scouring the internet, watching YouTube videos of jet fighters as they roll and thrust at airshows around the world.

His is more than idle curiosity. Nowlan downloaded complex technical reports about military aircraft from the website of the Pentagon, headquarters of the US military, then with his engineer's eye, made a few mathematical calculations of his own, sharing views with friends and colleagues.

His research has left him convinced - utterly and unwaveringly - that Australia is making a catastrophic and costly mistake, a $24 billion error that puts the very future of the country at risk.

"We're in for a world of hurt," he says

The F-35 is the sleek, futuristic stealth plane  to which a grinning Tony Abbott gave a cockpit thumbs up as prime minister last year, committing Australia to a multi-billion dollar purchase of a fleet of 72 to replace the existing F/A-18 Hornets.

But Nowlan is among an informal collection of doubting private citizens, not only in Australia but across the world, in countries that have formed a partnership with the United States in the F-35 project who worry the replacement plane will turn out an expensive lemon.

Not enough missiles, too slow, too visible on radar, easy prey for an enemy - the list of complaints is many and various. The F-35 is years behind schedule from when it was originally supposed to be ready, and has been plagued by technical difficulties; the latest, a concern the force of the aircraft's ejector seat could snap a pilot's neck.

What is striking is how much Nowlan and others like him have amplified  the public view of  these problems in the usually staid and elite-driven field of military acquisitions.

This garage band of backyard critics - some who have previously worked in defence or the sprawling support industry, or others who are simply informed lay-persons - have proved a public relations nightmare for the military in several countries, as well as the giant defence company, Lockheed Martin, builder of the aircraft.

"Narratives have emerged in the news media stating the aircraft is too expensive, consistently behind schedule and is not able to achieve its stated missions," reads an somewhat anxious set of official talking points leaked in September from the US Air Force.

The advice to military officers dealing with journalists was to stress the F-35 was indeed "lethal, survivable, and adaptive". Meanwhile, Lockheed Martin spruiks the merits of the fighter and benefits to local industry in ads on websites and in Twitter feeds.

But critics like Nowlan don't see a false "narrative", just more spin. He has panned the F-35 in written submissions to parliamentary inquiries on defence purchases, while others have sought to pick apart technical claims about the aircraft's capabilities and drawn mostly unfavourable comparisons with the modern fighters from China or Russia.

The critics are connected online, bouncing emails back and forth, and eager readers of the new breed of blogs focused on the military. They seized on reports in June after another leak to the website War is Boring indicated the new-age jet had failed to better the much older F-16 in a trial dogfight.

Any snippet of evidence that suggest design flaws in the F-35 is quickly shared, and invariably passed to those politicians yet to be convinced of the merits of the purchase. It has helped foster a sense of    crisis about the nearly 20 years the fighter jet has been in development.

"If a bunch of part timers using open source material can raise serious questions about a program with billions invested in it by the military and Lockheed Martin, then you know something is seriously wrong," says Nowlan.

Last month, the doubters appeared to win their first major scalp. Canada, one of the original nine partners to share the costs of developing the fighter, elected a new government on a promise to abandon plans to purchase the aircraft and instead select a new fighter from a competitive tender. Canada's withdrawal could add an extra $100 million to the price tag for Australia's F-35 order.

Doug Allen runs a Canadian online blog, bestfighter4canda and is another F-35 critic. His father was a flight engineer in the Royal Canadian Air Force, but despite briefly flirting with the becoming an aerospace engineer, he instead became a paramedic.

"I would describe myself as a well-informed layman," Allen tells Fairfax Media. "I can cut through obvious 'PR-speak' and I know enough about aircraft to (hopefully) not embarrass myself."

Allen was initially a fan of the F-35 program, he says, but as delays mounted and cost overruns struck, he thought it less impressive.

"More to the point, it was looking to become more of a bomber than a fighter," he says. "This seemed to me as contradictory to Canada's reputation, as I feared the F-35 was more geared towards aggressive 'shock and awe' type invasions, like that seen in Iraq.  It also seemed too delicate to handle use in Canada's winter climate and Arctic bases."

Allen's blog has been running several years and he boasts 3000 hits a day, one of the ever burgeoning number of online forums that allow people to share perspectives, tidbits, specialist insights, or just voice an opinion. The website Air Power Australia is a favourite for F-35 critics, where the jet is  critically contrasted against its likely competitors.

This phenomenon of online sharing has put more scrutiny from diverse points of view on military developments.

Sam Roggeveen, editor of the Lowy Institute blog, The Interpreter, says online forums are quick to spot new advances on topics such as China's military technology, often earlier than the traditional gatekeepers, the formal experts.

"There are a vast number of subject matter experts dotted all around the world, and what the internet does it is brings this geographically isolated expertise together," Roggeveen says.

Discussion of such issues used to be confined to a very small elite, but the internet has "democratised" some of these highly technical and specialised areas.

"Enthusiasts and experts who never would have heard of each other before they find each other online," Roggeveen says.

But he also points to the danger of indulging in nationalist "horse races" when assessing military hardware, to run a simple a mathematical comparison of stacking one country's forces against another, only to ignore crucial context, intent, and overall strategy.

The Defence establishment certainly has little time for the F-35 doubters.

"We have been very patient over the years, because the majority of commentators who make comment on this aircraft have never flown a fighter in their lives," then RAAF chief Air Marshal Geoff Brown shot back in during a testy exchange in a parliamentary hearing last year when quizzed by Greens senator Scott Ludlam about the F-35 performance.

"I will quote again the number of air forces around the world that have ordered this aircraft," Brown went on, after Ludlam questioned the wisdom of Australia's intended purchase. "What you are fundamentally saying is that the US Air Force, US Navy, US Marines, the Israeli Air Force, ourselves, the Turkish Air Force, the Dutch and the Italians have got it wrong. Frankly I find that insulting."

Nowlan is steadfast in his faith the F-35 is a dud. "If concerned citizens, like my good self, can use data that is on the public record, not classified, and working from engineering first principles, to figure out something is very, very seriously wrong - what's the real story here? Why are we persevering with this?"