How hard is it to build a flying car

There are some wonderful home videos of Hong Kong in the 1970s. I remember one which showed the harbour and all the ships in and out. the Western ships were modern and the Chinese were cruising around in those junk ships. In those days the Chinese were very traditional and did things as they had always done. All of that has gone now. Back in 1860 the British warships blew them out of the water. It was no match. The scenes were very ugly as we were using our military power to bully then into submission.

So one looks at China today and what CPC professors often say is China is going through their industrial revolution now. They are doing what we did in the mid 19c but without all the nasty hostility. In China everywhere you look there is this excitement about technology. If you go back to the time in Britain when they were building those railways, like the London to Manchester line, they built them mostly with their own hands, like very labour intensive, but they built them much faster than we build things today. The public were 100% behind all this new tech. Railway became fashionable. We went on to build railways all over India and many other places around the world. Some are still running today. However now China is turning up and replacing this 100 year old tech with high speed rail. So what we see is the Chinese do what we once did and we are now doing what the Chinese once did with our olde worlde museum pubs with their authentic medieval looks and benches carved from mighty oak trees, fit for your Knights Templar.

I used to fly just such a craft, a Piper Cherokee with a 180hp Lycoming engine, probably the most ubiquitous general aviation aircraft along with the Cessna 172..

There is no way a PA-28 would give you 30 mpg. Even at economy cruise (65% power) you would be lucky to see even half that. If you go to performance cruise, consumption would rise accordingly.

You really ought to do a little fact-checking before making such outrageous claims. Piper and Cessna pilot handbooks are easily accessible online.

As for travelling in a straight line 'as the crow flies' that also needs to taken with a pinch of salt. If you are in the aforementioned wilds of Wyoming or Inner Mongolia that might conceivably be the the case, but in most areas there are all kinds of controlled airspace that as a private pilot you would be wise to steer clear of. When, for instance, I needed to fly from the South Bay to Mendocino County it wasn't a simple matter of flying across the San Francisco TCA. I would have to either give it a wide berth or fly so low close-in (200 ft) that it became a dangerous exercise.

It would be just the same driving your flying car from say Oxfordshire to the Lake District.

You simply don't know what you are talking about.