Via: The brilliant Self Site
"In 1926 or 27, after his torpedo, monorail and helicopter ventures, Brennan, then 73, wrote to the Secretary of State for War (Sir Laming Worthington Evans) suggesting that a gyrocar should be developed for military use- just like the intended use of the Schilovsky gyrocar. The War Office refused to finance it, but funding of £12,000 (plus a £2000 per year salary for Brennan) was found from John Cortauld.
The Brennan gyrocar worked on the same basic principle as the gyro-monorail. Two contra-rotating gyros were housed under the front seats, spun in a horizontal plane at 3500rpm by 24V electric motors powered from standard car batteries. This was the greatest speed obtainable with the electric motors available, and meant that each rotor had to weigh 200lb to generate sufficient forces. Precession was in the vertical fore-aft plane.
The car had a Morris Oxford engine, engine mountings, and gearbox. Two sidewheels (light aircraft tailwheels were used) were manually lowered on stopping; if the driver forgot and switched off the gyros and walked away, the car would continue to balance itself using the gyro momentum for a few minutes, and then the wheels would automatically be dropped to stop tipping.
The Brennan gyrocar at Farnborough in 1929
The car was completed in 1929 and proved to work well and bank correctly on turns. It was demonstrated to the leading British car manufacturers- Austin, Morris and Rover- at Farnborough aerodrome, but after consideration they said they could sell all the conventional cars they could make, so why should they take the risk of a radical new technology? Other firms said the same thing, and the project was abandoned.
Brennan died in 1932 at the age of 79, from the effects of being knocked down by a car while visiting Montreux in Switzerland."