Originally Posted by
TheFrenchConnection
On the ground "run ups", the prototypes could reportedly be heard 25 miles (40 km) away.
Bit like the Vanguard then ... 
Unlike standard propellers that turn at subsonic speeds, the outer 24–30 inches (61–76 cm) of the blades on the XF-84H's propeller travelled faster than the speed of sound even at idle thrust, producing a continuous visible sonic that radiated laterally from the propellers for hundreds of yards.
I believe the Viscount's Darts, at 15,000rpm, were supersonic at the tips as well.