Note describing the variation in the number of revolutions per minute and provides simple formulas that allow for advanced calculation to be made of the variation of propeller speed with variation of one or more dimensions of the propeller and allow the necessary corrections to be applied.

From Introduction: "The Bureau of Mines since its establishment has always taken an active interest in the utilization of lignite and in the development of the lignite deposits of the United States. Extensive lignite fields occur in the west central States, notably in North Dakota, Montana, Wyoming, Colorado, and Texas; there are smaller areas in several other Sates, some of which are widely separated."

"The airflow about a model while being tested is often sufficiently affected by the model support to lead to erroneous conclusions unless appropriate corrections are used. In this paper some new material on the subject is presented, together with a review of the airfoil support corrections used in several other laboratories" (p. 1).

The physical resistance of passengers in establishing an upper limit to the strength of airplane cells is examined and arguments and experiments are discussed.

Report presenting an investigation of problems related to helicopters. Also included are the history of the evolution of the helicopter and a series of propeller experiments.

In soaring flight, ascending air currents are utilized and the interesting question is raised whether there are such currents which extend to any considerable distance and which can be utilized practically.

Note presenting an investigation to determine what effect joints connected with brackets, nails, and glue has on the strength of aircraft wing spars. Equations used to determine the results of loading tests are provided.

The principal result obtained in this report is a generalization of Taylor's formula for a simple eddy. The discussion of the properties of the eddy indicates that there is a slight analogy between the theory of eddies in a viscous fluid and the quantum theory of radiation. Another exact solution of the equations of motion of viscous fluid yields a result which reminds one of the well-known condition for instability in the case of a horizontally stratified atmosphere.

Note presenting an investigation of the value of wood for structural parts subject to stress. An exploration of several different types of wood is provided, including the coefficeint of elongation in bending, tensile strength, compression strength, and energy required for fracture is provided.

Note presenting a number of instruments that can assist pilots with observing the position of the airplane. Some of the instruments include an inclinometer with stationary system of reference and an inclinometer with moving axes.

"The vertical distribution of the pressure, temperature, and density of the atmosphere varies from day to day. Thus, rates of climb on different days cannot be compared directly, but must be corrected with reference to a standard rate of diminution of air density with increasing altitude. The following problem, therefore, has to be solved" (p. 1).

A formula for calculating the safety of airplanes is given and the stresses on airplane components are calculated. Some questions regarding the information obtained from the formula and its application to safe airplane design for pilots are provided.

From Introduction: "In the following pages the writer has endeavored to give an account of the many methods, advantages, and disadvantages of preparing and burning powdered coal."

Report presenting an example of a heavily staggered biplane with a single rigid outer strut in order to help determine the influence of the initial tensions in the wing bracing on the stressing of airplane parts.

Note giving an overview of five distinct methods shown for timing an airplane over a given distance and measuring the wind velocity, which provides the true speed of the airplane.

This report describes the theory of calculating the principal stresses in the envelope of a nonrigid airship used by the Bureau of Aeronautics, United States Navy. The principal stresses are due to the gas pressure and the unequal distribution of weight and buoyancy, and the concentrated loads from the car suspension cables. The second part of the report deals with the variations of tensions in the car suspension cables of any type of airship, with special reference to the rigid type, due to the propeller thrust or the inclination of the airship longitudinally.

From Introduction: "This bulletin is the sixth in the series of petroleum bibliographies published by the Bureau of Mines, Bulletins 149, 165, 180, 189, and 216 being compilations for the years 1915, 1916, 1917, 1918, and 1919-20 respectively. In this bulletin the same general plan has been followed in arranging the references, but one or two additions have been made in the classification."

Report issued by the Bureau of Mines consisting of bibliographies for petroleum bulletins. The bibliographies for bulletins published between 1919 and 1920 are presented.

"This report covers the results of an investigation carried on at the Langley Memorial Aeronautical Laboratory of the National Advisory Committee for Aeronautics for the purpose of discussing the various methods of effecting the take-off and the landing of an airplane, and to make a direct analysis of the control movements, the accelerations, and air speeds during these the maneuvers. The recording instruments developed at the laboratory were used in this test and the records obtained by them were made the basis for a comparative study of the two extreme methods of taking off (the tail-high and tail-low methods) and of various types of landings. The records should be of considerable value to a student pilot in enabling him to visualize the movements of the controls and the consequent effect upon the air speed and acceleration" (p. 555)

"The object of the investigation described in this report was to compare the damping coefficients of an airfoil as calculated from a knowledge of the static characteristics of the section with those obtained experimentally with an oscillation. The damping coefficients as obtained, according to the conventional notation, can be considered either as due to pitching or as due to yawing, the oscillation in these experiments being so arranged that the surfaces oscillate about a vertical axis. This is in reality the case when the influence is yawing about the standard Z-axis, but it can also be considered as a pitching motion when the model is so rigged that its standard Y-axis becomes vertical" (p. 118).

Memorandum presenting a method of calculating the dead reckoning in aerial navigation.

Two methods to replace the weight of gas lost on long airship flights are discussed: condensing the water of combustion and thermic sustentation. In the present article we will discuss the first method, leaving the second to be examined in a subsequent article.

The equilibrium, in still air, of a "stationary" helicopter (i.e., of one having neither vertical nor translational velocity, but a tendency to remain practically motionless within restricted limits of space) presents some difficulty in practice and justifies a theoretical investigation of its "inherent stability," i.e., independent of the pilot.

Economic and safety factors are discussed in relation to a switch from hydrogen to helium in airships.