"The possible methods for overcoming the ice hazard ..." ¹

From NACA-ACR-A-53, 1941. ²

Summary

Numerous methods were tested to find effective aircraft ice protection in the NACA-era.

Introduction

During the war, more than a hundred cargo planes of the Air Transport Command, flying from bases in India over the Hump to battlefronts in China, crashed in the Himalayas. Most of them were brought down by ice. In a single day in 1944, nine of these big Army transports, loaded with sorely needed supplies for the Allies’ fighting forces, were lost.
Many of the fatal crashes of commercial aviation have been traced to this same cause. For years commercial transports have been equipped with anti-icing devices, but the apparatus in common use was designed to assist in meeting an emergency when it arises, not to prepare the plane for deliberate flight into ice clouds. If dangerous icing conditions are inadvertently encountered, transport pilots are instructed to turn back or land at a safe alternate airport.
“The greatest advance that can be made in air transport from its present level,” said Edward P. Warner in 1946, “is not in speed, or even in economy, important as that is, but in regularity. When cancellations on account of weather are eliminated, or even reduced to a fifth or a tenth of their present number, air transport’s whole status will be changed.” It is difficult to see how aviation can come into its full destiny as an every-day competitor of steamships and railroads unless airplanes are made capable of flying in any weather.

Excerpts from George W. Gray, Chapter 14, “Heat Against Ice,” in Frontiers of Flight: The Story of NACA Research, reprinted in "The Wind and Beyond: Journey into the History of Aerodynamics in America, Volume 2, Reinventing the Airplane.", NASA-SP-4409, 2007. http://history.nasa.gov/sp4409-vol2.pdf

Discussion

In addition to developing components and systems, test and analysis methods were developed. Airplane flight tests in natural icing conditions proved out complete designs.

Several of the publication, while from NACA, are not listed in the 132 publications of the "Selected Bibilography of NACA-NASA Aircraft Icing Publications".

A few selected publications are from the NACA-era, but not from NACA.

Deicing boots and ice adhesion

"The removal of ice from a De-Icer surface depends on the true adhesion of ice to rubber..."

• Pneumatic boot deicers were the first widely used form of aircraft ice protection, and are still used today.

Carburetor and Induction Systems

"A demon was operating the throttle."

• Carburetor icing has been a known hazard for over 100 years, and many protection strategies were studied in the NACA-era.

Engine exhaust heat

"an airplane that will be immune from the dangers of ice accumulation is ... only a matter of technical development."

• A robust heat source provided robust ice protection.

Combustion heated air and heat transfer coefficients

"an effective system for ... wing surfaces to prevent the formation of ice requires knowledge"

• Combustion heated air, independent of the engines, was used on some aircraft.

Compressed air heat

"the most economical icing protection ... consists of a system utilizing hot gas from a convenient heat source, namely, the turbojet-engine compressor"

• Hot engine compressor "bleed" air is used in the jet-era.

Electric heat

"... the power required for ice prevention may be excessive for certain applications, although sufficient power for some degree of ice removal may be provided readily."

• Electric heating is applied to propellers and wings.

Freezing point depressant fluids

"Alcohol as a means of protection against ice formation on propeller blades is widely used by commercial air lines on transport airplanes."

• Freezing point depressant fluids were used widely in the NACA-era.

Windshield Protection

"ice on the airplane windshield ... is known to be a problem in urgent need of solution."

Component Tests

"I am surprised to find that there are so many details which have not been anticipated before the de-icing tests were started." (1942)

• The effects of icing on small components must be addressed.

Thermal Analysis and Surface Wettedness

"ice formation can be redefined in more general terms as a thermodynamic problem"

• The thermal analysis of icing conditions has unique challenges, including the determination of heat transfer coefficients and fraction of the surface wetted.

Ice Protection Design Manuals

"An aircraft engineer can use this report to design adequate ice protection systems for any type aircraft for any flight mission profile."

• The knowledge of aircraft icing reached enough maturity to produce engineering design manuals.

Conclusions of the Ice Protection Thread

"The optimum icing protection system for ... any particular aircraft cannot be generally specified; the choice of the optimum system is dependent upon the specific characteristics of the airplane and engine, the flight plan, the probable icing conditions, and the performance requirements of the aircraft."

• There are many, viable ice protection technologies and strategies to choose from.

Related

The next thread in the NACA review series is the Icing Cloud Meteorology Thread.

Notes