US2098877A - Stabilizing device for aerial navigation machines - Google Patents

Description

Nov.'9, 1937. E. E. OEHMICHEN 2,098,877

STABILIZING DEVICE FOR AERIAL NAVIGATION MACHINES Filed on. 28, 1935 4 Sheets-Sheet 1 Nov. 9, 1937. QEHMICHEN 2,098,877

STABILIZING DEVICE FOR AERIAL NAVIGATION MACHINES Filed 001:. 28, 1935 4 Sheets-Sheet 2 Nov. 9, 1937. g QEHMICHEN 2,098,877

STABILIZING DEVICE FOR AERIAL NAVIGATION MACHINES Filed Oct. 28, 1935 4 Sheets- Sheet :s

Fig-.3" Fi .7

Nov. 9, 1937.

5. E. OEHMICHEN 2,098,877

STABILIZING DEVICE FOR AERIAL NAVIGATION MACHINES Filed Oct. 28, 19:55 4 Sfieeis-Shget 4 Patented Nov. 9, 1937 UNITED STATES PATENT OFFICE Etienne Edmond Oehmichen, Valentigney, France Application October 28, 1935, Serial No. 47,173 In France October 31, 1934 4 Claims.

This invention relates to aircraft, and more particularly to devices for stabilizing aircraft.

Devices of the kind referred to comprise a closed volume such as an envelope filled with a gas, e. g. atmospheric air, the general center of gravity of the entire machine being determined by all masses forming part of the machine, including the gas contained in said envelope.

It is an object of the present invention to establish in machines of the type aforesaid distinct positions for the general center of gravity and for the center of static pressure, and to simultaneously provide for as close as possible or even identical positions for both the general center of gravity and the center of the aerodynamic pressures resulting in the propulsion of the aircraft.

This is to say that when the craft starts moving horizontally in any direction, the principle of this invention is realized by the resulting aerodynamic resistance being applied as near as p0...- sible to the general center of gravity of the craft and by the center of volume being simultaneously spaced as far as possible from and above the 5 general center of gravity.

The reasons for this arrangement will be explained hereafter. They are based on a general theory, established by the inventor, of the equilibrium of a body heavier-than-air, which is sustained by mechanical means and may remain floating in the air in the absence of any horizontal velocity.

This theory, which will be explained below at least in its outlines, leads to the arrangements 3 according to the invention, which have been completely supported by experience. The invention has been tested by means of reduced models wherein the said conditions have been realized.

In the drawings affixed to this specification and forming part thereof several embodiments of my invention are shown diagrammatically by way of example.

In the drawings Figs. 1, 2 and 3 are diagrammatical elevations i of three models of helicopter devices adapted to demonstrate the invention.

Figs. 4, 5 and 6 are diagrams illustrating the theory underlying the invention.

Figs. 7, 9 and 11 are and elevations, and

Figs. 8, and 12 are the corresponding side elevations of various stages of development of the invention.

Fig. 13 is an end elevation, and

Fig. 14 is a side elevation of one embodiment of the invention.

Fig. 15 is an end elevation of a modification of the embodiment shown in Figs. 13 and 14.

Fig. 16 is a side elevation, and

Fig. 17 is an end elevation of another embodiment of the invention.

Referring now to the drawings, and first to Figs. 1, 2 and 3, a rectangular frame I, 2, 3, 4 supports two helicopter screws 5 and S, placed on both-the sides of the bar 2, 3 and rotatable in inverse directions under the action of a mechanical motor, which is mounted in a vertical cylinder 1.

Small ballonets 8 and 9, inflated with air, may be adjusted to the frame and displaced along the frame struts I, 2 and 3, 4 respectively, with the aid of collars l0 and H. They may occupy any desired position along the struts l, 2 and 3, 4 as shown in dotted lines in Fig. 1. Resistance planes in the form of the so-called auxiliary planes l2 and I3 may be fixed on different points of the struts I, 2 and 3, 4.

When the device is centered, i. e. when the air resistance to the lateral displacementsis applied to the general centre of gravity i5 and when at the same time, the static pressure, the centre of which is indicated at M (Fig. 2), lies above the said general centre of gravity, the equilibrium is quite perfect, whatever may be the angle, under which the aircraft is left off. The latter may even. be left to itself in overturned position; it will get upright again every time.

If the aircraft is not aerodynamically centered, the equilibrium is far from being correct and it is necessary to make use of a much more power- -ful static couple in order to bring the machine out of the bank. I

Moreover, the completely closed chambers, such as the ballonets, may be replaced by cylindrical chambers l6 and I1 (Fig. 3) open at their bottoms and insuring only a partial solidarization between the air contained in the chamber and the aircraft itself. The equilibrium is nearly as good as in the case of a completely closed chamber.

Of course, the mechanism of calculation will not be indicated, for it is known to anyone acquainted with the ordinary mathematical analysis applied to the systems of differential equations. This mechanism or sequence may be easily reconstituted by the application of the current methods and will not be mentioned in the following explanation.

Under these conditions, I give the following summary of the outlines of this fundamental theory:

Referring to Figs. 4, 5 and 6, let us examine a helicopter of the weight P (or mg), lifted by means of a propeller which furnishes a. stress F which is equal to P. Consequently, the machine keeps the air in a fixed point, neither rising nor sinking and without any side slip, if F is vertical.

The helicopter is given an initial inclination so that the force F, which is supposed to act always in a constant direction relative to the machine, forms a very small angle one with the vertical line OY.

The result is a horizontal traction component equal to F sinao or my 5111410 or simplier mg m); the angle and the sine may be interverted.

'I'hishorizontal component causes the machine to slide and it is supposed that this slip takes place in horizontal plane so that the centre of gravity .of the machine originally situated at O (origin of abscissas) movesalways along the line OX-without rising or sinking beyond this line.

I designs the moment of inertia of the machine, and it will be endeavoured to find out in different cases the law of the variation of the angle a in dependency upon the time. In order to have a stable equilibrium, the angle a must have the tendency to become zero, when the time t in-, creases indefinitely. Otherwise, the equilibrium is unstable and the machine has the tendency to deviate more and more from its position of equilibrium.

Fig. 4 illustrates the case of the pure helicopter,

- i. e. a machine which is limited to a frame provided with an engine which drives a sustaining system capable of balancing the weight P.

It is known that when a sustaining system is submitted to a substantially perpendicular dis- This displacement 8, which gives rise to an upright moment of forces, is' proportional to the velocity 4 i dt at which the helicopter progresses along the line ox. Thus will be obtained the following system of equations:

wherein S isa constant relative to the trail of the machine during its displacement along the line OX; with slight velocities of displacement,

the trail is substantially proportional to the ve' locity, its form being:

dz Trail equal to kwherein R: is a constant. In the Formula (II), F0 is a constant relative to the displacement of the centre of pressure. Eliminating between these two equations, we obtain the resulting equation:

mIcfa slaw F, dt F dt (m) the general integral thereof having the form:

a=Ae 1+Bem+ce a wherein X1, X2, X; are the roots of the characteristic Equation (V):

X',= .+,ii

X =)\-p1' The expression a: may then be set under the form I a=Ae +e (B cos pt-I-C sin pt) (VI) By forming the sequence or curve of forces of Rolle'and substituting in the form (V) in the ordinary manner, one can demonstrate with the aid of the ordinary mathematical methods that A is always positive. or increases therefore in definitely with the time, and there is no equilibrium possible.

Another case is shown in Fig. 5. It is supposed that the displacement in the forward direction of the centre of pressure of the propellers may be neglected on. account of the use of very rapidly rotating propellers, which are therefore scarcely sensitive to the lateral displacements. On the other hand, the machine is surmounted by a plane 2 and has the tendency to be brought out of bank owing to the reaction R, which the displacement produces on'the plane 2. p is the distance of the application point of this resistance R to the centre of gravity 0.

The fundamental equations are therefore wherein S is the constant of the trail of the helicopter itself and S is the constant of trail of the plane 2.

The elimination of a; n between these two equations leads to the fundamental Equation (III) ml'd'a (s+s')r S pdt S'p d d P rf+p g+ l I (111') under the condition that S be very small, which is the whenever use is made of small propellets rotating at a very high speed. It will be found further, that the general integral of the form presents always positive values for i. For this reason, the equilibrium is rendered as impossible as in the preceding case and the adjunction of an aerodynamic resistance above the general centre of gravity has no other effect than that to cause resonant oscillations of the machine and to hasten its fall instead of stabilizing it.

In a third case, illustrated in Fig. 6, the machine is surmounted by a chamber 8 with any suitable gas filling, such as air or a light gas.

A designates the static pressure exerting its action on the envelope, the volume of this envelope being very important relative to the other elements of the helicopter.

The trail of the air screws may be neglected in comparison with that of the envelope. When the propellers furnish T, we obtain T+A=mg The motor component of the yaw is:

The resistance of the whole to displacement, parallel to OX and of the velocity V, is:

S being a constant.

According to the indications of the Fig. 6, the system of equations is:

In these equations, p is the distance of the centre 0 from the centre of air resistance for a general displacement in the direction OX and A is the distance of the centre 0 from the centre of static pressure- It is demonstrated, that in the expression of the general integral:

a=Pe l+e (Q cos pt+R sin pt) is negative under the condition that:

which may be written (paying attention that T+A=mg):

1 Apm Thus, we have simply: I=mr".

The inequality is then:

of T is:

T=mg

(the whole ascension realized by means of the air screws without any static ascensional effect) i. e. the equilibrium is always realized, since it is in the limit case.

It will be seen that when the machine is stabilized by the propeller thrust and centered, the

, the most favorable one.

sible to increase systematically the resistance toequilibrium is always stable and that it is only so under this sole condition.

Starting from these outlines, it is possible to put the invention into practice in different manners, various stages thereof being shown diagrammatically in Figs. 7 to 12, where for the sake of greater simplicity, the sustaining means have been omitted.

Use may be made for example of a fuselage, which is not a revolution body, such as illustrated in Figs. 7 and 8.

It is evident that such a fuselage may have a volumetric centre C different from the centre of air resistance R, as the said fuselage moves horizontally ina perpendicular direction relative to its greatest dimension, that is to say laterally along the line 1111'.

A fuselage of this type may be provided by way of adjunction of a revolution shaped envelope with a keel Q (Figs. 9 and 10).

The conditions to be realized in this case require that the general centre of gravity of the whole machine (including always the air mass contained in the fuselage) be as near as possible to the point R, which is not to be confounded with the point C, for the condition of stabilization of the static couple requires in the contrary to part the point C as far as possible from R and place it above the latter.

It is to be noted that the arrangement as shown in Figs. 7, 8, 9 and 10, does not entirelyv realize the aims of the principle according to the invention. These are only realized as to the transversal displacement, the longitudinal.

displacement in the direction :rz' must still be considered. (The air resistance to a displacement along Cy or Cy'is indicated by the arrows.)

It will be seen that as the fuselage moves in the direction 311:, the centre of volume and the centre of air resistance are both situated on the line 0:1 itself. The air resistance is therefore placed too high with respect to the general centre of gravity and the conditions called for are not fulfilled. It is therefore necessary to lower the application point of the aerodynamic resistance in order to obtain a displacement in the direction mm.

For this purpose, all the elements offering resistance relative to the direction :cz may be placed as low as possible in points, such as rirz (Figs. 11 and 12).

This arrangement does not substantially modify the location of the resistance to the transversal displacements, viz in the direction yy, and it results in the lowering of the centre of air resistance for the displacements in the direction xx.

This arrangement, however, is far from being Indeed, it is not posthe displacement in the direction are with the single aim to attain a good centering. There is no means but to place the unavoidable air resistances of the machine at the most convenient and lowest possible points and to try, in the contrary, to diminish the said resistances to a minimum.

Moreover, it is not to be forgotten that these resistant elements (engine fuselage, passengers nacelle) have each their volume which are to be centre of volume are also lowered, although about a lesser distance, so that one cannot expect too much from this particular arrangement.

Fortunately, the centering oi the machine, that is the coincidence between the application point of the air resistance and the centre of gravity of this machine, does not need to be perfect any more when the velocity of the machine proceeding in the direction :rz' increases.

Indeed, it must be remembered that the theory applies to a flying machine, which keeps the air in a fixed point, i. e. to velocities of horizontal displacement which may be neglected completely or almost completely and which do not exceed in any case the few yards per second which rep- .esent the velocity of a yaw.

Consequently, the centering of the direction xx is required only in the case where the machine keeps the air in a fixed point or at least has a horizontal velocity of too slight a value to permit the tail fins of the machine to stabilize this machine in a sufllcient manner.

For this purpose,.there may be imagined a "provisional" centering system, which would produce the lowering of the aerodynamic resistance only in the case of slight velocities of translation in the direction at.

When the velocity becomes sufilcient to insure the stabilization of the machine by means of the said tail flns, it should be possible to retract this system so as not to impair the progress of the machine.

If all the above requirements are taken into consideration, structures adapted for use in practicing my invention will result.

Figs. 13 and 14 illustrate one embodiment of the invention. In Figs. 13 and 14, C is the volumetric centre of the envelope or more exactly of the whole machine. Q is a keel, G the general centre of gravity, Pi and P2 are panels which may pivot about respective axes min and cab: so as to occupy for example the position, shown in dotted lines in Fig. 13. These panels do not substantially modify the application point of resistance to the displacement in the direction 1/, whatever may be their position on their axes aibi and (12172, owing to the presence of the keel. They modify however considerably the place of the application point of the air resistance for displacements in the parallel direction of at, when disposed perpendicularly to this axis :rz'.

Care may be taken thatthe panels in combination with the fuselage of the centre-C may insure a position of the air resistance to the displacement along 2:1 as near to the point G as possible. Under these conditions, the machine will be centered in all horizontal directions with a position of the volumetric centre higher than the centre of gravity.

The panels, such as P1 and P2, may be replaced by propellers with variable incidence of the blades, such as hi and h: (Fig. 15).

when the machine moves in the direction :rx' so that the propellers hi and hi have their blades at zero incidence, there will be an immediate 4 increase of the resistance on the part of these propellers which attack the air with an incidence which is diiferent from the zero position. These propellers fulfil then the task .of the panels Pi and P: in their transversal position.

When on the contrary, it is desired to pass to a higher translational velocity, the pitch of these propellers may be modified in such a manner that these cease to ofler any resistance to the air, always for a displacement of the machine along :1.

They may even be placed so as to become propulsive; thus, their brake efiect ceases to have any influence and may even form a traction force.

It will be observed that the propellers hi and hz,

which must be controlled by the pilot, permit of 5 doing so with great efliciency during a yaw in the direction at, the machine keeping then the air in a fixed point.

When the machine is driven for example in Besides, it is possible to conceive automatic devices which produce the desired result. In gen- 20 eral, it is preferable that the system in itself be capable to insure the centering without any attention of the pilot.

In order to attain the desired eifect, the propellers hi and hi must be of considerable size and must be provided with. a sufllcient number of blades, for otherwise their resistance would be in general slightly inferior to that of a plane with a surface which is equal to the circle which they describe.

It is to be noted that these propellers are arranged in the normal manner to obtain the desired result, when use is made of the system with inclined propellers. complete the action of the principal propellers, such as H (Fig. 16) by providing auxiliar propellers,such as h, unfolding components of traction t capable of resisting .to the components of traction t of the principal propellers H, and it will be seen that a system of this type, moving in the direction xx, meets with an increasing resistance along the line man, so that the translational displacement takes place in the direction Ca: or in the direction Cx'.

Indeed, it is necessary to The plane of the propellers h extends in the When the machine moves in the direction 01:,

the horizontal component of traction of the principal propellers diminishes while the counter efiort t of the propellers h increases. pears thus a resistance to the displacement in the direction zixi' having the same effect as the panels Pi and P2, as mentioned above.

When on the contrary this displacement takes 1 place in the direction 01:, the thrust of the propellers h diminishes, since these propellers move in the direction of their eiIort of traction, without their velocity of rotation being changed. There appears again a resistance in the direction $1321 which is opposed to that in which the translation tends to exert its influence.

There ap- In summary, with the arrangements according to Fig. 16, if the dimensions oi H and h are judiciously chosen, that is, calculated in such a manner that the general resistance of the craft to any displacement in the direction :rz comes as close as possible to the centre of gravity G, it will be then sufiicient to provide the fuselage with a keel Q, which insures the aerodynamic centering in a perpendicular direction to 12:.

Fig. 17 shows an end view of a'machine such as described with reference to Fig. 16, comprising the keel, the auxiliary propellers and the panels as well as the inclined propellers. 7

Various changes may be made in the details disclosed in the foregoing specification without departing from theinvention or sacrificing the way its depth at the center of its longitudinal axis, the center of gravity of the aircraft being spaced downwardly from the said volumetric center, and a'liftlng screw device located'downwardly from the center of gravity whereby for each horizontal displacement the resistance opposed to such displacement by the ambient air is applied at a point situated close to the center of gravity and below the center of volume of the aircraft.

2. In an aircraft of the helicopter type, an airfilled cell elongated horizontally and having a depending longitudinally extending keel, the volumetric center of the aircraft being midway the length of the longitudinal axis of the cell and the center of gravity being between the volumetric center and the bottom of the cell, and propellers mounted at opposite sides of the keel and each angularly adjustable about a horizontal axis.

3. The structure of claim 2 wherein a pair of the propellers are located adjacent the front end of the keel with the keel between the same and the second pair of propellers are'located intermediate the length of the keel rearwardly of the longitudinal center of the keel whereby the front propellers may be set to direct air blasts rearwardly at an upward incline and the rear propellers set to create air blasts intersecting air blasts of the front propellers.

4. The structure of claim 2 wherein the propellers are provided with adjustable blades for increasing the resistance to horizontal displacement in the axial direction of the air-filled cell.

ETIENNE EDMOND OEHMICHEN.

Images