James IRVING // Pietro Di CESARE

Offset Propellers

Provides better balance, reduces vibration & stress, increases efficiency


Scientific American (July 6, 1918), p. 14

"An Air Screw That Ridicules Propeller Theories"

Were it not for the stern theories regulating the design of air screws, we would not be using propellers today which differ but little from those of the pioneer panes. Indeed, while airplanes and engines have been constantly improved during the past 10 years, the air screw --- the most important member of any aircraft --- has remained practically at  a standstill, due to the adherences of propeller makers to those orthodox theories which no one dared violate.

It has, therefore, remained for James A. Irving of New York City to disregard most air screw theories and strike forth along new lines. As a result, he has invented a new propeller or tractor screw of radical design which, according to the testimony of several well-known aviators who have tried it on their machines, presents a definite advance in air screws.

Essentially, Mr Irving's device is two propellers in one, as will be noted in the accompanying illustrations. In the working model shown, one set of blades is 8 feet 6 inches in diameter, while the other is about 20% shorter. The longer blades may be termed the leading blades, while the shorter ones may be termed the auxiliary blades.

The blades are built up of 3-ply ash and mahogany, the latter being laminated crosswise of the grain of the two outside strips of ash; this arrangement, the inventor holds, is positive insurance against splitting. The blades are mounted upon Monel metal arms the shanks of which are taper-fitted to a two part hub of the same metal, provided with sockets for the purpose. The tapered shanks are drawn home and securely held by means of specially designed llock-nuts, to any desired pitch which may be graduated upon the shanks and hub sockets.

In the side view of the new propeller it will be noted that the arms and blades have a dihedral arrangement, which calls for an explanation. There are four reasons for this design, according to the inventor: First, in effecting centripetal action, drawing and forcing air to the center, thus eliminating radial slip; second, applied to the auxiliary blades for the purpose of gripping and concentrating the air, effecting a powerful center thrust at the pint where the conventional propeller is absolutely void of impelling force; third, the effect upon the long, leading blades where centrifugal force against great air pressure, is to relieve the blades of practically all except lateral and torque strains; fourth, owing to the fact that the tips of the blades are kept under a rigid, constant tension between centrifugal force and air pressure, vibration or fluttering is reduced to a minimum or entirely eliminated, and this leads to a considerable correction of the very objectionable whir or hum of the conventional type of propeller. In fact, the proof of the latter is indisputably brought out in an electric-fan blade of similar design invented by Mr Irving, which is now being offered as the regular equipment of a well-known electric desk-type fan, and which is practically silent.

Structurally, the new propeller has distinct advantages. The hub of the new air screw becomes part of the engine, and any changes in blades for any reason can be easily made. Extra leading blades can be carried in the airplane for emergency use. In cases of ordinary propeller breakage were but one or even both of the leading blades would be damaged, the cost of repairs would not exceed one-third of the net cost of the complete propeller; in short, fully 50% of the new propeller would be practically indestructible, outliving several motors.

An ingenious arrangement is provided for the ready balancing of the companion blades. Small lead washers are placed in holes in both blades, and by transferring washers from one hole to another balance is soon established. The washers are held in place by a screw in each hole.

One of his objects in making the auxiliary blades shorter than the leaders, explains Mr Irving, is for the purpose of obtaining an advanced, differential pitch with which to create impelling force from the inner, slow-speed circle or "dead" space; and results from numerous practical flying tests quite justify the claim that the propeller is fully one-third more efficient than the usual design, and at no extra cost of power. When used as a tractor, the concentrating action of the auxiliary blades results in enveloping the fuselage for its entire length within a cylinder of air wash of somewhat less diameter than the short blades. It is also apparent that these auxiliary blades serve still another and valuable purpose, namely, that of forcing or assisting the leading blades into undisturbed air. But Mr Irving is not given to theories: he merely states that he has a propeller that does the work, and that it is more or less inconsequential to the practical aviator just how it does the work.

Considerable success has attended the use of Mr Irving's marine propeller, designed along the same general lines as his present air screw. Some years ago captain Baldwin, a well-known figure in American aviation, tested one of Irving's propellers on his "Red Devil" biplane. Crude as that propeller was, the results were most gratifying. Captain Baldwin was astonished with the climbing power and speed of his machine so equipped. Other aviators have also been impressed in the same way, after a trial of the propeller which ridicules propeller theories.

US Patent # 1,022,846

James A. Irving
(April 9, 1912)

My invention relates to propellers, and more particularly to aeroplane propellers.

Experiments have shown that there is distortion when cutting a thread in a solid substance of great resistability. When a thread is cut in such an elastic medium as air, which has little normal resistibility, this distortion is greatly increased. This distortion is analogous to the disturbing of the air by a rotating propeller. Investigators of aerial propellers arrive at the conclusion that the less a propeller disturbs the air the greater its efficiency, and that a theoretical propeller of infinitely minute thickness and weight would travel through the air without disturbing it its exact pitch distance when rotated one revolution, if we disregard the frictional surfaces of the blades; but as it is impossible to construct such a propeller or avoid frictional surfaces, the problem must be resolves with a propeller constructed for practical work, which must necessarily have thickness, weight, area and frictional surfaces. Such a propeller will set up disturbances in the air which practically preclude its being considered as a screw, because these disturbances influence or distort the air, and it does not offer the necessary resistibility for cutting a screw thread. In constructing propellers for aeroplanes, great care must be taken to see that the design is such that the propeller will not throw the air laterally. This is so for the efficiency of a propeller is due to its ability to grip the air, form it into a cone and give to it volume, weight and velocity, the sum of these being a mechanically created cyclonic force which, projected against substantially inert air, propels the aeroplane at the necessary speed to exert elevating and sustaining power. Smoke and vapor experiments tend to prove that a propeller draws or absorbs air from the space around it. This air is condensed and takes the form of a truncated cone, with a slightly rotating movement, and is really a modified cyclone as the action and effect are almost identical.

My propeller has been so designed not only to disturb the air as little as possible, but the blades are adjustable relatively to each other and to the hub, to permit of a ready adjustment of the blades with reference to the weight, the resisting surface, and the frictional surfaces of the aeroplane, and the normal speed of the engine.

Additional objects of the invention will appear in the following complete specification, in which the preferred form of my invention is disclosed,

In the drawings, similar characters of reference indicate corresponding parts in all the views, in which: ---

Figure 1 is a rear view of my propeller;

Figure 2 is a plan view of Figure 1, partially in section;

Figure 3 is a transverse sectional view showing the two propellers mounted on one of the shanks;

Figure 4 is a view of a propeller blade with one of its side members and the manner of securing it to the shank;

Figure 5 is a side elevation showing one of the hub members;

Figure 6 is a face view showing a hub member;

Figure 7 is a plan view similar to that shown in Figure 2, but showing another adjustment of the propeller blades;

Figure 8 is a fragmentary view, showing each shank divided with one of its members disposed in an opening in the other to permit of the rotation of one blade on the shank relating to the other; and

Figure 9 is a sectional view on line 9-9 of Figure 8.




By referring to the drawings, it will be seen that a hub is provided, consisting of members 10 an 11, there being two roughened concave bearing surfaces 12 on the inner face of each of the hub members 10 and 11. As shown in Figures 5 and 6 of the drawings, I prefer to cut channels 13 in the hub and insert in these channels 13 bearing members 14, having the roughened concave bearing surfaces 12 referred to. The bearing members 14 are held in place by means of screws 27, and I prefer to have them project beyond the sides of the hub members. The bearing members 14 on one of the hub members co-act with the bearing members 14 on the other hub members, to grip the shanks 15 on which the propeller blades 16 and 17 are mounted. As will be understood by referring to the drawings, the bearing members are so disposed relatively to the axis of the hub, that the shanks 15 will be disposed at an angle to each other, and obliquely relatively to the hub axis. With this construction two of the propeller blades are normally disposed in advance of the hub, the other two propeller blades extending rearwardly of the hub. There are threaded orifices 18 in the hub members, which register with each other, and in these threaded orifices mesh screw members 19, having angular heads 20. Nuts 21 are provided for locking the screw members in place, and a face plate 22 with angular openings 23 is provided, the angular heads 20 being normally disposed in the angular openings 23, the face plate 22 being secured to the hub member 11 by means of screws 24. Two of the propeller blades are constructed by providing side members 25, which are bolted to opposite sides of the shank 15, as shown in Figures 3 and 4 of the drawings, the peripheries of these side members 25 being secured together at 26 by any preferred means.

As will be seen in referring to Figures 2 and 7 of the drawings, the propeller blades 16 are considerably larger than the propeller blades 17, and these blades 16 are preferably the leading blades; that is, I prefer to have them extend in a direction in advance of the hub, the shorter blades 17 extending rearwardly of the hub. It will readily be understood that by removing the face plate 22, and unscrewing the screw members 19, the shanks 15 may be rotated as my be desired to secure the desired pitch for the propeller blades, and that the shanks 15 may also be shifted longitudinally to position the propeller blades at predetermined distances from the hub. Each of the shanks 15 is divided by marks 15a, which may be referred to in obtaining the desired adjustment. The arrangement of one forwardly extending set of propeller blades in combination with one rearwardly extending set of similar blades tends to prevent a vacuum forming around the hub of the propeller, and thereby removes undesirable suction.

In Figures 8 and 9 I have shown a divided shank consisting of a tubular member 15b having longitudinal slots 15c, the shank member 15d being disposed in the tubular member 15b. When the tubular member 15b is gripped by the bearing member 14 it will press against the shank member 15d and hold the tubular member 15b relatively to the shank member 15d. With this construction the blades 17 may be disposed at any predetermined angle with relation to the blades 16.

It will be understood that the smaller or inner blades 17 may be set to a much greater pitch than the larger leading blades 17 and that the diameter of the larger blades 16 may be expanded as desired. When the positions of the blades 16 are not changed relatively to the positions of the blades 17, any increase in the pitch of one set of blades will reduce the pitch of the other set of blades. The adjustability of the propeller permits of the balancing and the setting of the blades of the propeller at the desired pitch forced to produce the best results.

Pierino Di CESARE

Aviation magazine, March, 1937, p 45.

Arc-bladed Props – Introduced at show by Maynard-di Cesare

First introduced at the New York National Aviation Show, four aircraft propellers bearing Department of Commerce Certificates are now offered to the industry by the Maynard-di Cesare Propeller Corporation, Milwaukee. The blades of all of these propellers feature a decided arc, and three of the four types – the automatic, the constant speed, and the adjustable pitch – have the blades offset at the hub. The fourth propeller, known as the turbine type, has its blades set in the customary manner but is otherwise unconventional.

It is claimed that the unique arc of the blades acts to bring the point of fatigue four inches closer to the hub, and that the offset blade arrangement provides better balance and reduces propeller vibration transmitted to the engine. Improved engine cooling is also claimed as a feature of the design. A further claim is that these propellers are considerably lighter in weight than present types.

All of these propellers have been developed under the direction of Lieut. Pierino di Cesare.







Variable pitch propeller hub construction



Propeller blade

Variable pitch propeller



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