A compensating linkage for the rotor control system on rotary wing aircraft is described. The main rotor and transmission are isolated from the airframe structure by clastic suspension. The compensating linkage prevents unwanted signal inputs to the rotor control system caused by relative motion of the airframe structure and the main rotor and transmission

Huber, R. F.

Jeffery, P. A. E.

English

NASA Technical Reports Server

[54] COMPENSATING LINKAGE FOR MAIN 
ROTORCONTROL 
[76] Inventors: Robert A. Frosch, Administrator of 
the National Aeronautics and Space 
Administration, with. respect to an 
invention of Philip A. E. Seffeery, 
Trumbull; Rudolf P. Huber, Shelton, 
both of Conn. 
[21] Appl. No.: 969,755 
[22] Filed: Dec. 15, 1978 
[51] h a .  C1.3 .............................................. BQQC 27/72 
416/500; 74/519 
74/469, 519; 244/17.25, 17.27, 17.13, 83 J 
1521 U.S. a, ................................. 4 ~ ~ 1 4 ;  2 ~ 1 7 . 2 5 ;  
[ S S ]  Field ~f Search ............... 416/114, 115, 162, 500; 
1561 References Cited 
U.S. PATENT DOCUMENTS 
2,385,881 10/1945 Peterson .......................... 416/114 X 
2,599,690 6/1952 Buivid et al. ........................ 416/114 
3,327,552 6/1967 Broders et al. ........................ 7 4 / 4 9  
3,514,054 5/1970 Mard et al. ........................ 244/17.27 
3,908,399 9/1975 Durno et al. ................. 244/17.25 X 
3,999,726 12/1976 Carlson et al. ............... 244/17.25 X 
Primary Examiner-Everette A. Powell, Jr. 
Attorney, Agent, or Firm-Howard J. Osborn; John R. 
Manning 
1571 ABSTRACT 
A compensating linkage for the rotor control system on 
rotary wing aircraft is disclosed. The main rotor and 
transmission are isolated from the airframe structure by 
elastic suspension. The compensating linkage prevents 
unwanted signal inputs to the rotor control system 
caused by relative motion of the airframe structure and 
the main rotor and transmission. 
9 Claims, 3 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19810010561 2020-03-21T09:25:50+00:00Z
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4.245.956 
ORIGIN OF THE INVENTION 
The invention described was made in the perfor- 
mance of work under a NASA contract and is subject to 
the provisions of Section 305 of the National Aeronau- 
tics and Space Act of 1958, Public Law 85-586 (72 Stat. 
435; USC 2457). 
BACKGROUND OF THE INVENTION 
This invention relates to a helicopter rotor control 
system which will automatically compensate for un- 
wanted signal inputs due to relative movement between 
an airframe structure and a rotor and transmission 
which is isolated from the airframe structure by a hy- 
draulic cushion. 
DESCWImION OF THE PRIOR ART 
The primary sources of vibration in rotary wing air- 
craft such as helicopters are rotor induced vibratory 
hub moments and shear forces, and aerodynamic im- 
pingement effects of the rotor downwash on the air- 
frame and empennage. These vibrations have adverse 
effects on subsystem reliability and maintainability and 
can cause crew and passenger discomfort. Tradition- 
ally, blade or hub mounted vibration absorbers have 
been used to reduce airframe excitations from the vibra- 
tory hub moments and shears. Airframe vibration ab- 
sorbers have also been used to reduce vibration caused 
by residual hub forces and aerodynamic impingement 
on the airframe and empennage. Isolation of the trans- 
mission and rotor from the airframe is a further means 
of reducing airframe excitations by the vibratory hub 
moments and shear forces. Such isolation is effective 
but results in relative vibratory motion between the 
rotor and airframe. 
The helicopter is controlled by changing the pitch of 
the rotor blades. The pitch of the rotor blades is 
changed by means of a swash plate, connected to the 
rotor blades, which is adjusted by means of a control 
rod operated from the pilot's compartment. With the 
rotor isolated from the airframe, relative motion be- 
tween rotor and airframe, caused by the vibration of the 
rotor, will cause false control signals to the swash plate 
actuator. 
These false control signals are the result of the move- 
ment of an actuator rod, which is connected to the 
control rod at one end and to the swash plate at the 
other end, in response to vibrations of the rotor rather 
than movement of the control rod by the pilot. Any 
motion of the actuator rod relative to the rotor will 
cause a signal changing rotor blade pitch. These mo- 
tions of the actuator rod in response to motions of the 
control rod are true control signals. Those motions of 
the actnator rod caused by relative motion of the air- 
frame and the rotor are false signals and must be com- 
pensated for. 
In prior art various arrangements have been devised 
to compensate the control signal for the relative vibra- 
tory motion of the rotor and the airframe. One prior art 
method uses a flexible cable rather than a control rod 
for the input signal to the rotor blades. The flexible 
cable compensates for the relative vibratory motion of 
the rotor to the airframe, but other control signal errors 
are caused by use of a flexible cable, such as friction 
losses and stretching of the cable. Other methods used 
2 
to compensate the rotor control signal for relative mo- 
tion of the rotor and the airframe provide compensation 
only along some of the three mutually perpendicular 
axes along which relative translation or about which 
It is therefore an object of the present invention to 
provide a rotor control system which will automatically 
compensate the control signal to the rotor for relative 
motion between the rotor and airframe. 
A further object of the present invention is to provide 
compensation to the rotor control for relative move- 
ment of the rotor along any of three mutually perpen- 
dicular axes, or relative rotation about any of these 
three axes. 
An additional object of the present invention is to 
provide compensation to the rotor control signal for 
relative movement between the rotor and the airframe 
without inducing additional signal error due to such 
factors as friction. 
SUMMARY OF THE INVENTION 
According to the present invention, the foregoing 
and other objects are attained by providing a first rod 
which transmits a control signal to the inner arm of a 
25 summing link. The summing link is attached to the air- 
frame structure by means of a cradle and a pivot. The 
inner arm of the summing link transmits the control 
signal via a second rod to a bellcrank. The bellcrank is 
3o attached to a bracket on the rotor transmission and 
transmits the control signal to an actuator rod. The 
actuator rod operates hydraulic actuators which change 
the pitch of the rotor blades. 
Motion of the rotor and transmission relative to the 
35 airframe causes a bracket on the airframe to move a 
compensating rod to which it is attached. The compen- 
sating rod is hollow and is concentric to and exterior to 
the second rod. The compensating rod's opposite end is 
attached to the outer arm of the summing link. Motion 
40 of the compensating rod causes the summing linkage to 
adjust the second rod by an equal amount, thus prevent- 
ing spurious control signals. 
BRIEF DESCRIPTION O F  THE DRAWINGS 
A more complete appreciation of the invention and 
many of the attendant advantages thereof will be 
readily apparent by reference to the following detailed 
description when considered in connection with the 
accompanying drawings wherein: 
FIG. 1 illustrates a side view, partially in phantom, of 
the compensating system showing the first rod, the 
summing linkage, the outer compensating rod, the sec- 
ond rod, the bellcrank, and actuator rod; 
FIG. 2 illustrates a perspective, partially in section, of 
55 the bellcrank end of the compensating system shown in 
FIG. 1; and 
FIG. 3 illustrates a perspective, partially in section, of 
the summing link end of the compensating system 
shown in FIG. 1. 
5 relative rotation can occur. 
10 
l5 
20 
45 
50 
6o DESCRIPTION O F  THE PREFERRED 
EMBODIMENT 
Referring now more particularly to the drawings and 
specifically to FIG. 1, there is shown a side view of one 
65 embodiment of the main rotor control Compensating 
linkage designated generally by reference numeral 9. A 
control rod BO transmits the rotor control signal from 
the pilot, shown by arrow 11, to a summing link 40. 
4,245,95 6 
3 4 
Second rod 12 transmits the control signal to an actua- summing link 42 is attached to outer summing link 44 by 
tor rod 24, approximately perpendicular to second rod pivots 46. As inner summing link 42 moves, it will cause 
12, by means of a bellcrank 18. The actuator rod 24 second rod 12 to move in the same direction indicated 
transmits the control signal, shown by arrow 13, to the by arrow 67, since it is attached to inner summing link 
hydraulic actuator for the swash plate, not shown, to 5 42 at pivot 52. Thus, second rod 12 will move in the 
change rotor blade pitch. same direction as compensating rod 14. 
A bracket 16 is attached by conventional means to a In operation, motion of transmission 20 and transmis- 
transmission mounting 22. Transmission mounting 22 is sion mounting 22, relative to airframe 62, shown by 
isolated from an airframe 62 by hydraulic cushions 15. arrow 69 in FIG. 2, in a direction mutually perpendicu- 
When the transmission mounting 22 moves relative to 10 lar to the axis of the actuator rod 24 and the axis of 
airframe 62, bracket 16, which is anchored to one end of second rod 12, causes the rotor control compensating 
move an amount. rod l4 transmits false control signal introduced from this type of motion 
link 40 adjusts the second rod 12 by an amount propor- 15 frame 62. 
tional to the amount that the transmission mounting 22 
has moved, thus compensating the control signal for 
relative movement between the transmission mounting 
22 and airframe 62. Thus, it appears to the swash plate, 
rod 14, causes rod l4 to linkage to pivot on cradle pivot 58. Thus, there is no 
the to summing link of the rotor and transmission 20 in relation to the air- 
Motion of transmission mounting 22 in a direction 
parallel to the axis of second rod 12, shown by arrow 17 
in FIG. 2, causes bracket 16 to move in the same direc- 
which controls rotor pitch, that no relative movement 20 tion* Since bracket l6 is attached to One end Of ‘Ompen- 
between rotor and airframe has occurred since the actu- sating rod 14, it forces ‘Ompensating rod l4 to move in 
ator rod 24 has been maintained in a constant position the same direction as transmission mounting 22, shown 
relative to the rotor. by arrow 61. Compensating rod 14 is attached to the 
shown in detail in FIG. 2 bracket 16 is at- midpoint of outer summing link 44 and forces outer 
tached to rod 14 by means of a pivot pin 25 summing link 44 to move in the same direction as the 
28. Pivot 28 allows compensating rod 14 to rotate to transmission mounting 22, shown by arrow 63 in FIG. 
accommodate motion of the transmission mounting 22 3. Since inner summing link 42 is attached to outer 
in a direction parallel to actuator rod 24, shown by summing link 44 at the upper end and held in Position at 
arrow 13. Motion of transmission mounting 22 in a its lower end by control rod 10, inner summing link 42 
direction parallel to compensating rod 14 causes bracket 3 0  will move in the same direction as outer summing link 
16 to move the outer compensating rod 14 in the same 44, shown by arrow 63, moving second rod 12 in the 
direction by a proportional amount. same direction, shown by arrow 67. Second rod 12’s 
Bellcrank 18 is attached to bracket 16 by a pivot 25. other end, which is attached to one end of bellcrank 318, 
Second rod 12 is attached to one end of bellcrank 18 by will move the end of bellcrank 18 in the same direction 
pivot 32, and actuator rod 24 is attached to the other 35 that bracket 16 and transmission mounting 22 has 
end of bellcrank 18 by a pivot 34. Motion of second rod moved, thus the position of actuator rod 24 relative to 
12 in response to a control signal from the pilot causes transmission 20 will remain constant and false control 
bellcrank 18 to rotate at pivot 26, moving actuator rod signals will be eliminated. 
24 in a direction perpendicular to the motion of second When transmission mounting 22 moves in a direction 
rod 12. 40 parallel to the axis of actuator rod 24, shown by arrow 
FIG. 3 shows the summing link designated generally 71 in FIG. 1, bracket 16 moves bellcrank 18, and hence 
by reference numeral 40. Summing link 40 is made UP of actuator rod 24 in the same direction, shown by arrow 
inner summing link 42 and outer summing link 44. Inner 13. Thus, since the actuator 24 is moved in the Same 
summing link 42 and outer summing link 44 are attached direction and by the Same amount that transmission 
50. Motion of control rod 10 in reponse to a control is introduced. 
signal from the pilot causes inner summing link 42 to Since relative rotational movement of the rotor, move in the same direction. Inner summing link 42 transmission 20, and transmission 22 about its transmits this control signal to second rod 12, which is 5 0  own axis will produce motions at bracket 16 similar to 
attached to the approximate midpoint of inner summing the relative translational movements described above, link 42 by pivot 52. 
Outer summing link 44 is &tached to a cradle 56 by the rotor control compensating linkage 9 compensates 
pivots Cradle 56 is attached to a support by pivot the control signals for relative rotational movement 
58. Support 60 is attached to airframe structure 62 by 55 
conventional means. pivot 58 allows cradle 56, and It will be understood that the foregoing description is 
hence summing link 40 to rotate about axis 59, which is of the preferred embodiment of the invention and is 
approximate~y mutually perpendicular to the axis of therefore merely representative. Obviously there are 
control rod 10 and the axis formed by pivots 48. many variations and modifications of the present inven- 
Compensating rod 14 is attached to the approximate 60 tiOn in light of the preceding teachings. I t  iS therefore to 
be understood that within the scope of the appended 
claims the invention may be practiced otherwise than as 
specifically described. 
What is claimed as new and desired to be secured by 
1. A rotor control compensating means comprising; 
rotor and transmission means; 
airframe means; 
at their upper ends by pivot 46. Control rod 10 is at- 45 mounting 22 moved, the actuator 24 does not move 
tached to the bottom Of relative to transmission mounting 22, and no false signal link 42 by pivot 
’ 
midpoint of outer summing link 44 by pivots 54, Motion 
ofcompensating rod 14 in response to relative motion of 
the transmission mounting 22, as indicated by arrow 61, 
will cause outer summing link 44 to pivot about pivots 
48 and move in the same direction as compensating rod 65 Letters Patent of the United States is: 
14 as indicated by arrow 63. As outer summing link 44 
moves, it will cause inner summing link 42 to move in 
the same direction, indicated by arrow 65, since inner 
I 
. 
4 
4,245,9 5 6 
vibration absorbing means connecting said above 
mentioned means allowing relative motion therebe- 
tween; 
linkage means for maintaining a rotor control actua- 
tor rod means in a fixed position, relative to said 
rotor and transmission means, during relative 
~novement in all degrees of motion between said 
alsfrframe and the rotor and transmission means. 
2. PI rotor coatrol compensating means as in claim 1 
wherein said linkage means includes rotor control actu- 
etor rod means which transmits a control signal from a 
pilot to summing means. 
3. A rotor control compensating means as in claim 1 
:;iherein said linkage means includes summing means 
which trarisvllits a control signal from said rotor control 
actuator rod to a second rod, and adjusts the second rod 
in rzsponse to a compensating rod. 
4. A rotor control compensating means as in claim 1 
wherein said linkage means includes second rod means 
and sumruing means which transmits pilot control sig- 
nals from said summing means and compensating sig- 
nals from said summing means to a bellcrank means. 
5. A IQPCX control compensating means as in claim 1 
wherein said linkage means includes a bellcrank means 
and second rod means which transmits a signal from 
said second rod means to said rotor control actuator rod 
means. 
6.  A rotor control compensating means as in claim 1 
wherein said linkage means includes a rotor control 
actuator rod means and bellcrank means which trans- 
mits a signal from said bellcrank means to a rotor swash 
plate. 
7. A rotor control compensating means as in claim 1 
wherein said linkage means includes a compensating 
rod means and summing means which transmits a rela- 
tive motion signal from a rotor transmission to said 
summing means. 
8. A system as in claim 1 wherein said linkage means 
includes: 
a first rod; 
an inner summing link, said first rod having one end 
pivoted to the bottom of said inner summing link so 
6 
that motion of said first rod causes inotion of said 
inner summing link in the same direction; 
an outer, inverter “U” shaped, summing link pivoted 
at the top of said outer summing link to the top of 
said inner summing link so that motion of the outer 
summing link will cause motion of said inner sum- 
ming link in the same direction; 
a cradle supporting and pivoted to the bottom of said 
outer summing link so said outer summing link may 
rotate about an axis through the tips of said in- 
verted “U” shaped outer summing link; 
a support bracket attached to the relatively stationary 
body and pivoted to said cradle so said cradle may 
rotate about an axis that is mutually perpendicular 
to the axis of said first rod and to the axis of the 
cradle to outer summing link pivot; 
a second rod pivoted to the approximate midpoint of 
said inner summing link such that motion of said 
inner summing link causes motion in the same di- 
rection of said second rod; 
a hollow compensating rod, concentric to but not 
attached to said second rod, and pivoted to the 
approximate midpoint of said outer summing link 
so that motion of said hollow compensating rod 
causes motion in the same direction of said outer 
summing link; 
a bellcrank pivoted to a bracket on the vibrating body 
at said bellcrank‘s approximate midpoint, said sec- 
ond rod having one end pivoted to one end of said 
an actuator rod pivoted to the other end of said bell- 
crank and extending in a direction generally per- 
pendicular to said second rod; and 
a bracket attached to the vibrating body and pivoted 
to said hollow compensating rod so that motion of 
the vibrating body and said bracket will cause mo- 
tion in the same direction of said hollow compen- 
sating rod. 
9. The system of claim 8 wherein the other end of said 
40 first rod is connected to a helicopter control member 
and the other end of said actuator rod is connected to 
means for varying the pitch of a helicopter rotor blade. 
5 
10 
15 
20 
25 
30 bellcrank; 
35 
* , a x * * +  3 
45 
50 
55 
60 
65 


Compensating linkage for main rotor control

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