JPH0752892A - Ground resonance preventing device for helicopter - Google Patents

Abstract

PURPOSE:To positively prevent helicopter's ground resonance without ground tests and even if a variation in pay load is observed. CONSTITUTION:The fuselage 1 of a helicopter is connected to a skid 2 with springs 3 having adjustable spring constant. The spring constant is increased when the rotating speed of a main rotor blade 10 is low. Switching is made to decrease the spring constant when the rotating speed of the main rotor blade 10 has reached to the set value to positively prevent ground resonance of the rotation of the main rotor blade 10 and the rigidity of an air frame.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground resonance preventing device applied to a body support portion of a helicopter.

[0002]

2. Description of the Related Art A ground resonance of a helicopter is an unstable vibration generated on the ground by a combination of a rotation of a main rotor blade of the helicopter and a rigid body mode (a whirling mode) of an airframe. This ground resonance is usually generated by coupling with the rigid body mode of the airframe while increasing the rotation speed of the main rotor blade from the stationary state to the operating rotation speed. That is, ground resonance occurs in a region indicated by A where the rotation of the main rotor blade indicated by the line a and the frequency of the rigid body mode indicated by the dotted line b in FIG.

In the conventional device for preventing the ground resonance of the helicopter, the coupled vibration level is reduced by adding damping when the rotation of the main rotor blade and the rigid body mode of the machine body are coupled. Actually, FIG.
As shown in FIG. 1, a lead lug damper 1 for attaching a damper 11 to the mounting portion of the skid 2 on the body 1 or for adding damping to the main rotor blade 10 in the in-plane direction of the blade is provided.
2 is attached to prevent ground resonance.

[0004]

In the above-mentioned conventional ground resonance preventing device for a helicopter, a damper 11 is provided at the mounting portion of the skid 2 and a lead lug damper 12 is provided to add damping in the in-plane direction of the main rotor blade. However, due to the addition of damping, resonance at a certain response level will remain, so ground resonance cannot be sufficiently prevented, and if the helicopter payload changes, ground resonance will occur. It was also difficult to prevent. Furthermore, to set the damping constant of the damper,
There was also a problem that a helicopter ground test was required.

The present invention is intended to provide a ground resonance preventing device for a helicopter capable of solving the above problems.

[0006]

In the ground resonance preventing device for a helicopter of the present invention, the body of the helicopter and the skid are connected by a spring whose spring constant can be changed.

[0007]

According to the present invention, from the stationary state of the main rotor blade of the helicopter on the ground to the set number of rotations, the spring constant of the spring that connects the helicopter body and the skid is large, so that the rigidity of the body is considered to be high. The frequency of the rigid body mode is increased to prevent the rotation of the main rotor blade at low frequency and the resonance of the rigid body mode of the airframe.
When the number of rotations of the main rotor blade becomes equal to or higher than the set number of rotations, the spring constant of the spring is small, so that the rigidity is kept small and the frequency of the rigid body mode of the machine body is reduced, and the main rotor blade at high frequency is reduced. Prevents resonance between rotation and the rigid body mode of the airframe.

In this way, it is possible to prevent ground resonance between the rotation of the main rotor blade and the rigid body mode of the machine body, which changes from the stationary state to the steady rotation state. Further, as described above, since the spring constant of the spring that connects the body and the skid of the helicopter is changed at the set rotational speed of the main rotor blade to prevent ground resonance, the payload of the helicopter changes. Also, ground resonance is reliably prevented.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. Reference numeral 1 denotes a helicopter fuselage having a main rotor blade 10, which is provided at the front and rear of each of two skids 2 provided in the front-rear direction below the fuselage 1 at a slight distance in the lateral direction. The mounting portion 2'is connected to the body 1 via a variable spring 3 whose spring constant can be changed. The variable spring 3 includes a sliding member 7 including a piston-shaped member 7a slidable in the cylinder 6, a rod 7c attached to the piston-shaped member 7a, and extending upward, and the sliding member 7.
The coil spring 5 is provided between the piston-shaped member 7a and the bottom of the cylinder 6. 4 is a stopper provided in the cylinder 7, and the stopper 4 is shown in FIG.
As shown in FIG. 3, the cylinder 6 is penetrated from the outside to the outside, engages with the notch 7b in the lower portion of the piston-shaped member 7a, and
A rotary shaft 4a extending upward along the outer circumference of the cylinder 6 is provided. The rotary shaft 4a is rotated by a signal from a tachometer of a main rotor blade 10 (not shown), and the stopper 4 is provided with a notch 4b of a piston-shaped member. The variable spring 3 forms a semi-active type spring. The rod 7c of the sliding member 7 is fixed to the body 1, and the cylinder 6 is a mounting portion 2'of the skid 2.
It is fixed to.

In the present embodiment constructed as described above, the stopper 4 slides while the helicopter is on the ground and the main rotor blade 10 reaches a certain rotational speed lower than the normal rotational speed from the stationary state. Piston-shaped member 7 of member 7
By engaging with a, the movement of the sliding member 7 is restricted, the coil spring 5 is fixed, and the rigidity of the variable spring 3 (spring constant)
Is maintained at a high value. When the rotation speed of the main rotor blade 10 reaches the preset rotation speed, the rotation shaft 4a of the stopper 4 rotates, the stopper 4 is disengaged from the piston-shaped member 7a of the sliding member 7, and the coil spring 5 operates. Therefore, the rigidity (spring constant) of the variable spring 3 becomes a low value.

Therefore, as shown by the line c in FIG. 5, the frequency of the rigid body mode including the variable spring 3 is the rigidity switching point which is the set rotational speed when the rotational speed of the main rotor blade increases. In the above, it changes in a stepwise manner and decreases, and the ground resonance between the rotation of the main rotor blade and the rigid body mode of the airframe is prevented.

Further, in this embodiment, as described above, the rigidity of the variable spring 3 is stepwise changed at the rigidity switching point to prevent the rotation of the main rotor blade and the ground resonance of the rigid body mode of the machine body. Therefore, it is not necessary to perform a ground test for setting a damping constant and the like unlike the conventional ground resonance preventing device for a helicopter. In addition, even if the helicopter payload changes, ground resonance can be reliably prevented.

A second embodiment of the present invention will be described with reference to FIG. In this embodiment, the variable spring of the first embodiment is modified as follows. That is, air is enclosed in the chamber of the cylinder 6 formed below the piston-shaped member 7a of the sliding member 7 of the variable spring 3, and this portion is used as the air spring 8. There is no difference from the first embodiment.

In this embodiment, the coil spring 5 of the first embodiment is replaced with an air spring 8, and the same action and effect as the first embodiment can be obtained.

In the above embodiment, the spring constant (rigidity) of the variable spring is changed by engaging / disengaging the stopper with the sliding member at the rigidity switching point. However, for example, a double spring is used. When the rotation speed of the main rotor blade is lower than the rigidity switching point, both springs are activated, and when the rotation speed of the main rotor blade is above the rigidity switching point, one of the double springs is activated to reduce the spring constant. It is also possible to change the spring constant of the variable spring stepwise at the rigidity switching point by a means such as reducing it.

[0016]

According to the present invention, by connecting the body and the skid with a spring whose spring constant can be changed, the frequency of the rigid body mode of the airframe can be changed. Therefore, by switching the spring constant from a high value to a low value during the rotation of the main rotor blade from zero to the normal rotation speed, avoiding the rigid body mode of the airframe and the resonance of the main blade rotation, Resonance can be prevented.

Further, as described above, the ground resonance of the helicopter is prevented by switching the spring constant at the set rotation speed of the main rotor blade, so that ground resonance can be reliably prevented even if the payload changes. You can

[Brief description of drawings]

FIG. 1 is an overall view of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a variable spring of the same embodiment.

FIG. 3 shows a piston-like member and a stopper portion of the sliding member of the embodiment, and FIG. 3 (a) is a longitudinal sectional view thereof, FIG.
FIG. 3B is a sectional view taken along the line AA of FIG.

FIG. 4 is an explanatory diagram of a variable spring according to a second embodiment of the present invention.

5 is a graph showing the relationship between the main rotor blade rotation frequency and the main rotor blade frequency in the rigid body mode of the above-described embodiment of the present invention and the conventional helicopter ground resonance preventing apparatus. FIG.

FIG. 6 is an explanatory diagram of a conventional ground resonance preventing device for a helicopter.

[Explanation of symbols]

 1 Helicopter body 2 Skid 2'Mounting part 3 Variable spring 4 Stopper 4a Stopper rotating shaft 5 Coil spring 6 Cylinder 7 Sliding member 7a Piston-shaped member 7b Notch 7c Rod 8 Air spring 10 Main rotor blade 11 Damper 12 Lead lug damper

Claims (1)

[Claims] 1. A ground resonance preventing device for a helicopter, wherein a body of the helicopter and a skid are connected by a spring whose spring constant can be changed.