Is there any classic aviation/space engineering moment where the engineers had been working on a concept for months and then realised that their approach to the problem wasn't quite right and so had to discard all their hard work and re-start from scratch? Please could you give some examples?
Supermarine Type 300
There are plenty of examples, but if you want a classic then perhaps the Supermarine Type 300 fits the bill. It began as a cleaned-up Type 224 but, as first presented to the Air Ministry, retained the Rolls-Royce engine with evaporative steam cooling and a straight, tapered wing with room for around four machine guns.
While it was still on the drawing-board the PV12 engine moved to glycol cooling and "Merlin" monicker, the Ministry requirement to eight guns and the wing to thinner profile and elliptical planform. Yeah, the Spitfire.
That famous D-section main wing box is in fact the legacy of the evaporative cooling system.
De Havilland DH 106
The world's first jetliner is pretty classic too. When de Havilland started work on a revolutionary idea of a jet-powered airliner, they turned to the German secrets being brought back from the aftermath of war. The airliner was to have a tailless swept wing. They built a quarter-scale aerodynamic test plane, the DH 108. It was fast all right, but it came at a time when nobody understood the sound barrier and all three examples shook to bits, killing their pilots. In part that gave the shape an undeserved bad name, but mainly DH realised that it did not have sufficient trim tolerance of varying CG position during commercial operations, and a tail would fix that. Enter the DH 106 Comet, the world's first commercial jetliner.
Here's another almost as classic. When Convair first flew the prototype delta-winged jet interceptor the YF-102, it sucked. It handled like a pig on the approach and couldn't even go supersonic in level flight. Two new discoveries at that moment included area-ruling and conical leading-edge camber. Both were applied in somewhat ad hoc and hurried fashion to the YF-102A and it made Mach 1.25 in level flight, while also being a lot tamer on the landing flight path. Time for a breather and a proper job with 50% more thrust to boot, and the F-102B, renamed as the F-106A, happily hit M 2.3.
And one more for luck. In the 1950s Fairey Aviation developed the Rotodyne, a VTOL feederliner with conventional wing and propellers but also a tipjet-driven rotor. Complicated and expensive yes, but what ended the project was the noise made by the prototype - its tipjets sounded like a thousand banshees coming in for the kill.
The original design for the 747 had a full double deck all the way down the fuselage (similar to the A380), but discovered that evacuating from the upper deck would have been difficult and dangerous. That design was scrapped, paving the way for the widebody 747 we know today.
The first failed attempt by Rolls-Royce at using composite materials for jet engine fan blades, in the original RB211 engine design for the Lockheed L1011 TriStar, not only led to "discarding all the work" but bankruptcy and nationalization of the company in 1971.
There was no way that the contracts with Lockheed could be made profitable after changing to a conventional (metal) blade design, and the bankruptcy forced the cancellation of the original contract and re-negotiation of a new one.
The long term outcome was that the RB211 family of engine designs is still going strong (and is profitable) 50 years later - and the latest members of the family now have composite fan blades.
The Republic XF-84H "Thunderscreech" was an attempt to improve power responsiveness by using a turboprop to replace the turbojet in a transsonic upgrade to the subsonic F-84.
The supersonic tips of the propeller, however, made so much noise that ground crews became physically ill. There were other problems, as well -- engine reliability issues and aerodynamic problems. The airplane flew, but it never flew well, never set the propeller-powered speed records that had been expected of it, and never went into even limited production -- and further, supersonic tip propellers were abandoned industry-wide for three decades or so until "prop-fan" designs with highly swept blades were proposed and tested (but never adopted) for transport aircraft.
Another example would be large passenger airships. Lighter than air or heated gasses were the only means of providing enough vertical lift for reliable human flight until the first powered winged aircraft struggled into the air at the turn of the 20th century.
Airships benefitted from these new engines too, developing into skyscraper sized trans oceanic giants.
However as further improvements in propulsion made ever greater thrust available, the drag equation shifted more towards forward speed as well as lifting requirements (around 100 knots and beyond) in the 1930s. The large airships, with their draggy gasbags, became obsolete and were progressively replaced with flying boats, piston airliners, and jet airliners.
Issues with weather, similar to the Ever Given in the Suez canal (huge surface area becoming uncontrollable in high winds), also contributed to the end of their days.
The famous B-52
When Boeing engineers designed the B-52, it was to have straight wings and propeller engines, just like its predecessors. When on one faithful Friday the time came for Chief engineer Ed Wells and and two of his fellow senior engineers to present the design to the Air Force, the USAF rejected the design and demanded a swept wing and jet engines instead. Ed and his team returned to Ed's hotel room, but not before having bought a block of balsa wood. Over the weekend they then proceeded to redesign the B-52 with swept wings and jet engines, inside Ed's hotel room, preparing a full report and a balsa scale model. They then returned the following Monday to the Air Force brass who, impressed by the effort, approved an initial order of 13 B-52 bombers.
Depending on your criteria, this might qualify:
Airbus scrapped a concept, and redesigned it to make the A350. The original idea was to use A330 fuselage sections to create a competitor to Boeing 787, but after a number of bigger clients expressed their dissatisfaction with the original approach, Airbus had no other choice than going back to the drawing board.
This may actually have been more of a management level mistake, rather than just the engineers getting sidetracked, but I bet engineers had their say when choosing the ill fated "lets whip up another 330" path was at hand.
The prototype T-10 was designed in the early 1970s as a direct response to F-15 (which was being finalised then). By the mid-70s it turned out that T-10 was underperforming and would lose to F-15 overall.
Mikhail Simonov, its chief designer, insisted on a new design (against a substantial government pressure). The new design, coded T-10C and which would become Su-27, had amost nothing to do with T-10 except for general principles: integral aerodynamic design, fly-by-wire with reduced/negative static stability, etc. As Simonov put it, only the main wheels and the ejection seat remained from T-10.
As a result, Su-27 will probably forever remain a pinnacle of aerodynamic design for agile piloted fighters.
In commercial aviation it's definitely the BD-5. Jim Bede sold thousands of kits for this small sport plane, before he had a working engine. There is a lot of history recorded about trying various small engines that would fail after a few hours. Meanwhile he was selling more kits to fund his day to day operations, and eventually went bankrupt, leaving all the kit owners hanging. Incomplete kits with no engine. One to my dad in the mid 70's.
Some were completed, but the bulk of kits sold and contracted for never saw the light of day. Bede didn't now how to say no to a customer's money, even though he never had a viable engine.
A couple more candidates : the Avro Manchester deserves a mention. The (arguable) mistake was to make a heavy bomber as a twin engine aircraft, using bleeding edge 24 cylinder engines without the luxury of time to work out their reliability problems.
A relatively simple re-design with 4 reliable Merlin engines, readily available in mass production, gave us the Lancaster (saying anything more would be redundant). As such, the airframe engineers didn't lose much of their work, though the engine design didn't go any further.
Another candidate might not deserve to be on the list : the BAC TSR-2 of which Sir Sydney Camm said : "All modern aircraft have four dimensions: span, length, height and politics. TSR-2 simply got the first three right."
I would not agree that Concorde should be on the list because it entered production and served for decades; further sales simply didn't materialise. However you might consider the Boeing SST which started out as variable geometry, was re-designed as a Concorde-like delta wing, and then cancelled when two things became clear : like the TSR-2 and Concorde, it got the politics wrong, and the 747 was about to be a big winner.
When Theodore von Kármán was visiting, along with US Army officers, the German seized Aerodynamic research sites, German engineers were deported to the US, USSR, France,...he made an urgent call to his company headquarters in USA, indicating to discontinue all designs made for what later became the B-47, after watching results of sweptback wing, a concept spread in a High Speed Aerodynamics congress held in Italy in 1937. Blessings +
The one I know is the B-49 series .... to the XB 35 flying wing :
As far as I know were the control systems outdated and the machine became an elephant to steer , in critical situations . Though many , many improvements and with the ONLY technical systems they had , that time , even when it did reasonably well in the end :
EACH AND EVERY ONE of the XB 35 flying wing got scrapped , literally .
They built from their experience on , on the B2 spirit , though , so scrapping a plan does not mean that the experience , made upon it , is also lost . By the way , that happens all the time : from steam engines to diesel to electric , ... nobody wants to heat up a locomotive in the morning for 5! hours anymore ... , just to start it up .
The final decision for the XB 35 flying wing seems the weight and complexity of the control systems : nowadays make electronics the things much lighter and those airplanes were designed for tomorrow but had the technology of the 40's . Think about it for a moment : even the Liberty ships , that freed Europe at the end of WW2 had TRIPLE EXPANSION STEAM engines . Diesel ? - Existed , Double - Action Steam Engines ? - Existed .... so what I mean : sometimes they are bold enough to do the opposite : taking a step back for several good reasons .
Here 's a video on the development of the B 49 / YB 49 and XB35 flying wing
LATER EDIT : some " numbers " for this extraordinary bomber , taken out of the book
" VLIEGTUIGEN " by Enzo Agelucci :
first , the text about the NORTHROP XB-35 FLYING WING ( 1947 , USA ) translated from dutch into english :
On the 25th of june , 1946 , the first flight was made with the " flying wing " , as Northrop calls this type of airplane without fuselage or tail . That was the N9M , which was just a third in size , compared to the later XB-35 . The test flights were satisfying and 3 prototypes of the bigger B-35 bomber got built . Already in 1941 , they began with the design . As a result of technical difficulties , the XB-35 , which could carry 20 machine guns and a capacity of 41200 pounds of bombs , was not built in series production . Two of the prototypes got equiped later on , with jet engines but also these tests were not successfully .
Technical data ( the " green " pages out of the end of the book ) name : Northrop XB-35 Flying Wing . built by : Northrop Corp. , USA . type : bomber . year of introduction : 1947 or later . engines : 4 x Pratt and Whittney R-4360 jet turbines , each 3000 SAE HP . wingspan : 172 Ft or 52.43 meters . length : 53 Ft or 16.15 meters . high : 20.0 Ft or 6.10meters . empty mass : 89560 pounds or 40.624 Kgs . maximum takeoff - mass : 209000 pounds or 94802 Kgs . maximum speed : 391 miles/h or 629 kms/h . cruising speed : 183 miles/h or 294 kms/h . range : 10000 miles or 16100 kms . crew : 9 brave guys .
The rather small cruising speed confirms : it steered like an elephant , maybe they got redundancy in some kind of way but with all the heavy equipment and updates that added to this , the design specs were NOT met .
To be honest , if you drop 40000 ponds of bombs , you GOTTA get away FAST ;-)