The only reliable way to tell the difference is to take samples from the burn patterns and test them in a laboratory for the presence of flammable or combustible liquids.

NEWYORKER: Trial by Fire

But in 1999, Aviation Partners showed in test flights that its devices cut fuel burn, and the companies formed their joint venture.

WSJ: Air War: 'Winglet' vs. 'Sharklet'

The X-43A, or "Hyper-X" was built specifically to test scramjets, or supersonic ramjets, which burn fuel in air travelling at supersonic speeds.

BBC: Mach 10 scramjet prepares for launch