I'm not trying to make some anti-concorde point, I'm just observing that no one has ever succeeded in designingv & developing a supersonic airliner as a viable commercial proposition. Plenty of airliners have been designed and developed and have recovered their investment from sales, and military aircraft are commercial proposition almost by definoition (because it's almost universally true that the intended customer pays up-front for the development).

But the original question was looking for tgings which have been developed and then discovered to have no commercial application. I would suggest that the inability to recover development costs from sales (historic and future, IMHO) puts the concept of supersonic airliners firmly in this category.

PDR

The Tarrant Tabor..............

How about Prop fans -got trialed on DC9s/MD80 test beds but went no further.

Offset nose gear, OK they did fly commercially on Tridents but no-one else adopted them. Giant aerodynamic shock bodies a la CV 990 come into this category too.

Nuclear power -I think there was nuclear powered B36 but only one and the idea was never revived.

Composite -not in the carbon fibre sense-aircraft .ie one carrying another. Short Mayo flying boat/seaplane combo and B36 (again) carrying a couple of miniature jet fighters along with it

Many weird Brit innovations from the 1950s as already alluded to in earlier posts

Going right back, the Wright Flyer..warping wings.

The Heathrow/Gatwick helilink was a highly successful operation that ran for many years.

Personal rocket backpacks fit the OP's criteria pretty well.

The Fairey Rotodyne, Saunders Roe Princess and the TSR2 were the stuff of dreams and endless fascination when I was young. They were about the most exiting things around and "The Future" according to "Look and Learn", "Ranger" and other publications. Later Concorde entered my consciousness, then became reality, unlike the Rotodyne and Princess. Those three did fly.

The Tarrant Tabor most certainly did not, and is thus a fine contender if you literally follow the title of this thread.

Another fine contender is the Piasecki Helistat, though it did just manage to crawl briefly into the air before disintegrating!

Any aircraft that billed itself as "the DC-3 replacement", although to be fair, the F-27 did quite well.

WHBM
Apologies for repeating the composite concept -I didn't see your mention of the Short Mayo on first reading.

I dont think 'verti planes 'took off' either other than as military prototype . A convair somethign i thing with immense contra rotating props and a very short fuselarge it sat on its tail for a vetical take off-that worked but reversing the process to land...... well apparently thatwas even more difficult than it sounds
PB

AMK anti-misting Kerosene.

I was going to mention prop fans and also Allen Poulson's idea of adding a fan behind the Spey engined Gulfstream. Noise was the biggest killer of the prop-fan closely followed by weight and extra maintenance.

Percival P.74

"anything built by Saunders Roe after WW2 that was meant to go more than a few inches above the surface."

A touch unfair.
They were asked to build various aircraft by the Government. They did, and they all fulfilled the specification. It's not their fault if the specification was bonkers or out of date.

You've also forgotten the Black Knight research rocket and the Black Arrow satellite launcher. Both very successful All got more than an inch off the ground.,

Read the "Sporty Game" by John Newhouse PD. Even those we might consider successful never recovered development costs. Among others he quotes the DC-9, DC-8 and L-1011 ($2.5 billion in the hole). So the Concorde is no different, except in the former it was shareholders who paid, and taxpayers in the latter.

@megan, I'm sure you're reporting Newhouse accurately, but I find this astonishing. Is it really the case that Douglas's two most successful jet airliners were loss makers? Is this by the real books, or is it Hollywood accounting? And if this was the real case, why on earth did they go on with airliners?

If I am remembering correctly a lot of Lockheed's troubles with the 1011 arose when the RB-211 did not work with the composite materials that were planned for the fan blades.

I believe that problem cost RR a bundle, (and perhaps the UK taxpayers ??) and gave Lockheed a big problem.

I spent some time on the L-1011, primarily the -500 and I thought it was probably the aircraft I enjoyed the most in my time. Not just for the flight crew but the cabin layout we had was something I have not seen since. F/C at least.

Edgley Optica - could it ever have been better than a heli for observation?

Large turboprop civil transports - The order books for the Britannia, Vanguard and Electra did not justify their development, albeit of course the Britannia and Electra were splendid airliners. The planform has not emerged again. On the other side of the wall, I accept the Il-18 was built in good numbers, but only 32 Tu-114's emerged from the shed.

To take a slight left turn from PDR1's Concorde line, maybe we can add "fast civil transports", the original failed attempt to establish this brand being the CV880 and CV990. Post SSC, Boeings subsequent paper Sonic Cruiser ended up in the waste paper basket

There's a few here, in the video below, that didn't quite make it to "commercial success". :)

At Marshalls we were making bits for the carbon fan RB211 - there was huge disappointment it did not work, and many were so keen to see RR get out of the hole we bought shares - which ended up worthless, but RR rose from the ashes...

The rotodyne my late father remembers this landing either at Westminster embankment on the old land where the festival hall is or the large platform at Westland heliport battersea there is a photo of this I have seen and I beleive it was at the heliport can any one help

Re Post 23, the B-36 in question was not nuclear powered; it carried an operative reactor for research purposes, with very heavy shielding for the crew, but the aircraft was powered by its conventional engines.

However, an eventual nuclear powered iteration of the B-70 was envisaged as opposed to its 'chemically powered' predecessor (XB-70 and eventual B-70). Alternative History can be fascinating. But it was all killed off by the XB's problems, costs, and ICBM technology.

Also, the command and control network of which the B-70 would be part was the forerunner of the Internet. But I guess you could add the beautiful but flawed XB-70 to the list engendered by this thread.

What was wrong with the Vanguard then? It was BEA's most economical airliner throughout the 60's and early 70's.