Horizontal stabilizer

“ I will now, by means of the following illustration, try to explain how the longitudinal dihedral secures stability:
First, imagine the aeroplane travelling in the direction of motion, which coincides with the direction of thrust T. The weight is, of course, balanced about a C.P., the resultant of the C.P. of the main surface and the C.P. of the stabilizing surface. For the sake of illustration, the stabilizing surface has been given an angle of incidence, and therefore has a lift and C.P. In practice the stabilizer is often set at no angle of incidence. ”

“ The vertical stabilizer should not be too large, however, as then any side pressure due to deviation from a rectilinear course will cause the machine to swerve violently; the wing which is outermost in the turn will have preponderance of lift due to its higher speed; that is, the airplane will get into a turn where there is too much bank and a spiral dive may result. ”

“ This pawl is designed to stop stabilizer movement in the aircraft nose up direction. In this position the pawl was beyond the designed limit of its travel and could not function as a brake or stop device. The stabilizer trim brake system is actuated by operation of either pilot's control column to stop stabilizer out-of-trim motion. Should a runaway stabilizer cause a pitch in an unwanted direction, moving either pilot's control column in the opposite direction will stop the stabilizer from further movement in the out-of-trim direction, but will permit movement in the opposite direction. ”

“ The stick is a vertical column in front of the pilot which, when pushed forward or back, depresses or raises the elevator and makes the machine dive or climb. Thrown to either side it operates the ailerons or wing tips, which cause the plane to roll about its fore and aft axis. The stabilizer control is usually a wheel at the side of the cockpit, whose turning varies the angle of incidence of the small stabilizing plane in front of the elevator, to correct the balance of the plane under different conditions of loading. ”

“ You will notice on this drawing that strong piano-wires connect the instruments with all the necessary controlling planes of the machine."
"Instruments?" interrogated Mr. Giddings. "I thought there was but one."
"No; there are two stabilizers, as you will see,—here, and here," was Paul's response, pointing his finger to the parts. "But, as each one is exactly like the other in its construction, only the one has been drawn in detail. The other stabilizer runs lengthwise of the cockpit and takes care of the elevator. ”

“ Sleepy pulled back the throttle until the tachometer showed fifteen hundred revolutions a minute, and wheeled the stabilizer forward a trifle until the ship rode level. By means of the stabilizer a ship can be made nose or tail heavy by changing the angle of the two flat surfaces on the tail. ”

“ Both motors provide power through differential gearing to a drive shaft on which a dual sprocket assembly is mounted. The sprockets are connected to the common drive shaft by shear rivets, and each transmits rotation of the drive unit through roller chains to an irreversible jackscrew. Failure of either set of shear rivets freezes the stabilizer in the last selected position, and further operation is impossible. ”

“ If the direction of the force is vertical, and the beam is inclined, then the strain is increased by as much as the diagonal of inclination exceeds the vertical; for example, let one thousand pounds be suspended from the lower end of a beam ten feet long, inclined at an angle of 45°. The diagonal being ten, the vertical will be 7.07 feet, and the strain is increased as follows:—
7.07 to 10 as 1,000 to 1,414 lbs. As the angle of inclination, from the horizontal, increases, the strain from a given load decreases, until the beam is vertical, when a weight acts with its least power. ”

“ On the other hand, the adhesion of the horizontal wheels is, within its maximum limit, completely under control, and is given by a powerful screw motion, acting upon springs, which keep them always pressed against the rail with a force practically uniform. Notwithstanding any small inequalities of dimensions, all therefore that is requisite in ascending a heavy incline, is to set up the screws till the adhesion of the horizontal wheels makes up with that of the vertical ones, the total amount required for utilising the traction power of the engine. ”

“ To operate this stabilizer of ours all the pilot will have to do is to guide the rudder with his feet. The automatic pilot works the elevator and the ailerons. It takes care of 'bumps' and 'holes' and sees that the machine banks at just the right angle on the turns. This makes the operation of an airplane containing the stabilizer even more simple than running a motor-car, because you do not have to worry about going into different speed gears when climbing or descending. ”

“ The stabilisator is a mechanism which controls the rudder and elevating planes by means of sliding weights and plates of metal, and all by itself brings the machine back to an even keel if she tips too much. ”

“ The gradient is the same whether the pilot hold the aircraft in trim against an unwanted AND stabilizer position by applying a stick pull force, or the control forces are in balance through the medium of using AND stabilizer to counteract unprogrammed PTC, or extension of the PTC by use of the "test" position to balance out unwanted AND stabilizer settings. Of course, if it becomes necessary for the pilot to hold a pull force against AND stabilizer, the magnitude of the force necessary does become a factor insofar as physical quality and pilot fatigue are concerned. ”

“ I realized that as soon as I began making airships, and so I devised what I call a gyroscope equilibrizer or stabilizer. A gyroscope, you know, is a heavy wheel, spinning at enormous speed, on an anti-friction axle. Its great speed tends to keep it in stable equilibrium, and, if displaced by outside forces, it will return to its original position. ”

“ A stabilizer should automatically keep an airplane on a fairly level keel no matter how air conditions are, even so steady that it will travel along on its course for a considerable distance with the pilot paying no attention to his controls, perhaps eating his lunch or reading his orders. ”

“ The relative displacement of the two pieces which abut against each other at a joint may take place either by turning or by sliding. Safety against displacement by turning is called stability of position; safety against displacement by sliding, stability of friction.
§ 13. Condition of Stability of Position.—If the materials of a structure were infinitely stiff and strong, stability of position at any joint would be insured simply by making the centre of resistance fall within the joint under all possible variations of load. ”

“ Vertical wheel shafts make the elevation of the main or generator floor of a station independent of that of the wheels, and thus give the highest degree of security against high water. After the vertical wheel shaft reaches the generator room, it may be geared to a horizontal shaft that has one or more dynamos directly mounted on it, or drives dynamos through belts or ropes. Belt-driving in this way, from horizontal shafts connected by bevel gears with vertical wheel shafts, is not uncommon in the older class of water-power stations. ”

“ The electrical stabilizer trim actuator was tested to stall torque specifications of 600-650 inch pounds in clockwise and counter clockwise directions. The unit stalled at 480 inch pounds clockwise and 456 inch pounds counter clockwise. Both the main stabilizer and autopilot cruise trim switches were found in the "on" position. ”

“ In practice, however, it has been found that lateral stability can be maintained more easily by the use of the vertical rudder than by warping. This is because the machine naturally tips inward on a turn, and, consequently, a tip can be corrected by a partial turn in the other direction. ”

“ A Model With Adjustable Stabilizer. The pull of the motors when wound is thus well distributed and, as has been pointed out, permits of a larger propeller being used without danger of their striking in turning. Still another advantage is that it keeps the strands of the motor from interfering with the planes. When the motors are strung above the planes, they have a tendency to force the machine downward. ”

“ The horizontal wheel, on the other hand, occupying a horizontal zone and attached to a shaft that is vertical, like the usual small water turbine, in position (but not in the fluid impact) receives the wind impact upon only some of the vanes at a time—not the whole circumference—with less proportional power and greater complexity of construction. ”

“ The vertical stabilizer was broken at its base and bent approximately 90 degrees to the right and was generally wrinkled; a leading edge dent appeared 18 inches below the tip. The major portion of the left side of the fin had scratches running up and slightly aft. ”

“ Furthermore, it was ascertained that the design strength of the stabilizer was such as to require more than a normal force by the pilot to cause failure in a pull-up, provided that the air-load conditions during the pull-up were as anticipated in the design requirements. In view of the above it is concluded that during the subject pull-up unusual and abnormally high air loads prevailed, but the knowledge of their origin and exact nature is limited at the present time. ”

“ The governor proper depends upon centrifugal force for its action, and generally consists of two weights which are pivoted at one end to a rotating shaft driven by the engine. When these weights are rotated rapidly the bottoms are thrown outwardly by the centrifugal force and tend to assume a horizontal position. The faster the weights are rotated, the greater will be the tendency for the bottoms of the weights to come into the horizontal, and the greater will be the pressure exerted by them on the controlling levers connected to the throttle. ”

“ Directional stability is its stability about its vertical axis, and without which it would have no tendency to keep its course.
Whenever an airplane does not fly properly, aside from conditions arising from engine or propeller trouble, either its longitudinal, lateral, or directional stability is affected. ”

“ Projectile stability in a flyer, as in an arrow, may be attained by playing the centroid in or near the line of forward resistance, and well ahead of the side resistance. The reasons for this are manifest. If, however, this arrangement be neglected, a special damping, or controlling, device is required to preserve headlong and steady motion. In particular, the objections to placing the centroid too low were emphasized in the above quoted paper as follows:
“I have mentioned the advantage of placing the center of mass below the center of surface ”

“ On a horizontal plane the only resistance which the power has to overcome is the friction of the load with the plane, and the consideration of this being for the present omitted, a weight once put in motion would continue moving for ever, without any further action of the power. But if the plane be inclined, the power will be expended in raising the weight through the perpendicular height of the plane. Thus, in a road which rises one foot in ten, the power is expended in raising the weight through one perpendicular foot for every ten feet of the road over which it is moved. ”

“ When the speed reaches a predetermined limit, the plunger A, having its center of gravity slightly displaced from the center of rotation of the shaft, is thrown radially outward and strikes the lever B. It will easily be understood that when the plunger starts outward, the resistance of spring C is rapidly overcome, since the centrifugal force increases as the square of the radius, or in this case the eccentricity of the center of gravity relative to the center of rotation. ”

“ The larger size of the stabilizer makes it approximately three times as powerful as the elevator, and therefore, about six degrees of up elevator is required to counteract the effect of an unwanted 2-degree AND stabilizer position. This amount of elevator deflection is lost insofar as recovery is concerned. Also, as speed increases, the ability to get any recovery action from the elevator diminishes, and disappears completely at about 470 knots. Other factors could also prolong the dive. ”

“ In order that no balancing feats shall be required of the person in charge, there is, on the supporting standard, a quadrant, in the notches of which a lever on the engine frame engages, thus allowing the rigid framework, and therefore the propeller shaft, to be maintained at any angle to the vertical without trouble. ”

“ As a method of controlling and changing the rate of rotation of the wheel, the rivers of water had already proven themselves; and as a method of static balancing to compensate for off-center weights, masses of it could be stopped and held in counterbalance tanks around the rim, thus assuring that the observatory, in its stationary position on the hub, would not suddenly take up an oscillatory pattern of motion as the balance within the wheel was shifted either by moving equipment or personnel. ”

“ The criteria give us minimum values from the perspective for safety. In a design for stability process, high values of GZ at small angles of heel result in an excessively stiff vessel with sharp motions, and high values at very large angles of heel (above 90 degrees) result in a violent righting action. The combined requirements of safety and comfort suggest that it should be possible to define an ideal GZ curve, or more realistically an acceptable stability envelope, with minimum values defined by the safety criteria, and maximum values by reference to acceptable motions. ”