However, it is usually a minor gain compared to the airframe's detrimental effect on propeller efficiency.

There have been propeller aircraft which attained up to the Mach 0.8 range, but the low propeller efficiency at this speed makes such applications rare.

In it he talks about the needs for high-speed flight and the use of turbojets as the only reasonable solution to the problem of propeller efficiency.

Remarkably, German wind-tunnel tests showed that the simple rounded nose improved propeller efficiency and raised the top speed by 14 km/h (9 mph).

This reduces propeller efficiency and causes vibration inducing structural propeller fatigue and noise.

The propeller efficiency is increased by recovering energy from the tangential (rotational) flow from the leading propeller.

The MIDP increased propeller efficiency and virtually eliminated the shipyard downtime which was formerly necessary for repairing the erosion problems.

Turboprops generally have better performance than turbojets or turbofans at low speeds where propeller efficiency is high, but become increasingly noisy and inefficient at high speeds.

Usually a single engine is more efficient, but using two propellers allows a better distribution of pressure, increasing propeller efficiency more than the disadvantage of using two engines.

The propeller was driven from the nose of the camshaft in the central vee, rather than from the crankshaft, thus providing an automatic half-speed reduction, improving propeller efficiency.

Fullscale wind tunnel investigation of the canard Rutan VariEze showed a propeller efficiency of 0.75 compared to 0.85 for a tractor configuration - a loss of 12 %.

The forces associated with air moving around the tiny devices are more pronounced than with conventional aircraft in flight, causing increased drag, reduced lift under the smaller wings at low speeds and decreased propeller efficiency, engineers say.

The advantages of the engine were increased propeller efficiency through the reduction gearing effect of having the engine effectively running at 1,800 rpm for only 900 rpm of the airscrew, and excellent high-altitude performance due to the high compression ratio achieved.

While there is a loss in efficiency as the fan is drawing on a smaller area of the free stream and so using less air, this is balanced by the ducted fan retaining efficiency at higher speeds where conventional propeller efficiency would be poor.

If the reduction in pressure is too much in relation to the ambient pressure of the fluid, cavitation occurs, bubbles form in the low pressure area and are moved towards the blade's trailing edge where they collapse as the pressure increases, this reduces propeller efficiency and increases noise.

Even before the start of World War II, engineers were beginning to realize that the piston engine was self-limiting in terms of the maximum performance which could be attained; the limit was due to issues related to propeller efficiency, which declined as blade tips approached the speed of sound.