Friday, May 16, 2008

Propellers Forever!

In a May 13th story titled "Single engine turboprops prosper", Kate Sarsfield of Flight International makes the point "The single-engined turboprop sector is riding high. Continued hikes in the price of oil worldwide, coupled with their unrivalled operational flexibility, are pushing up demand for these versatile, efficient propeller-driven aircraft.". In another story on May 15th, also from Flight International, writer Mary Kirby, says in her piece called "Embraer resumes analysis of turboprops" "Developing a new commercial turboprop is under renewed analysis at Embraer, and could provide an eventual substitution for the Brazilian manufacturer’s small regional jets."

Why is it that propellers are more efficient than straight jet engines?

1. Props move a larger volume of air more slowly that jets. An illustration is that the 40 foot rotor of the helicopter can lift more with less horse power than can smaller props.

2. Turbo props have larger diameters than jets, and move more air more slowly and more efficiently.

It conveniently happens our Arc Wing VTOL airplane not only uses a large propeller, but it is a dual rotating propeller, which is even more efficient than a single propeller, by a factor of 8%. Dual rotating props have a straight slip stream, but single rotation props leave a twisting slipstream that loses force by the angle of the twist.

With aviation gasoline prices very high, and likely to remain well above past averages, more efficient airplanes will have a big advantage over less efficient ones. We've discussed before how our Arc Wing airplane has vertical take off and landing, which is the most ideal method of operation. Now we can say that with its dual rotating propeller - and we believe its arc wing as well - it is the most efficient flying machine.

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