A system for improving yaw control at low speeds consists of one strake placed on the upper portion of the fuselage facing the retreating rotor blade and another strake placed on the lower portion of the fuselage facing the advancing rotor blade. These strakes spoil the airflow on the helicopter tail boom during hover, low speed flight, and right or left sidewards flight so that less side thrust is required from the tail rotor

Crowell, Cynthia A.

Kelley, Henry L.

Wilson, John C.

English

NASA Technical Reports Server

111111 1ll11 III IIIII 11111 11111 IIIII 11111 IIIII 11111 11ll1111111111111 
US005209430A 
United States Patent [19] pi] Patent Number: 5,209,430 
Wilson et al. 1451 Date of Patent: May 11, 1993 
1541 HELICOPTER LOW-SPEED YAW CONTROL 
[75] Inventors: 
[73] Assignee: 
[21] Appl. No.: 
[22] Filed: 
John C. Wilson, Newport News, Va.; 
Cynthia A. Crowell, APO AE, N.Y.; 
Henry L. Kelley, Newport News, Va. 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
788,908 
Nov. 7,1991 
[51] Int. (3.5 .............................................. B64C 27/00 
[52] U.S. c1. .............................. 244A7.19; 24A7.11; 
24/75 R 
[58] Field of Search .................... 244/17.19, 17.11, 91, 
24/130, 199, 75 R; 239/265.19 
1561 References Cited 
U.S. PATENT DOCUMENTS 
2,383,038 8/1945 Bossi ............................ 244A7.19 X 
3,059,877 10/1962 Lee ................................... 244A7.19 
3,807,662 4/1974 Velazquez ........................ 244A7.19 
4,200,252 4/1980 Logan et al. ..................... 244A7.19 
4,227,665 10/1980 Carlson et al. ............... 24417.1 1 X 
4,708,305 11/1987 Kelley et al. ..................... 244A7.19 
4,786,009 11/1988 Rao et al. .......................... 24/75 R 
4,809,930 3/1989 Ballero ......................... 244A7.19 X 
4,948,068 S A 9 9 0  Van Horn ........................ 244A7.19 
Primary Examiner-Sherman Basinger 
Askrant Examiner-Christopher P. Ellis 
Attorney, Agent, or Finn-Kimberlyann C. Bowmer 
P71 ABSTRACT 
A system for improving yaw control at low speeds 
consists of one strake placed on the upper portion of the 
fuselage facing the retreating rotor blade and another 
strake placed on the lower portion of the fuselage facing 
the advancing rotor blade. These strakes spoil the air- 
flow on the helicopter tail boom during hover, low 
speed flight and right or left sidewards flight so that less 
side thrust is required from the tail rotor. 
12 claims, 3 Drawing Sheets 
4 
https://ntrs.nasa.gov/search.jsp?R=19930016809 2020-03-24T07:28:30+00:00Z
U.S. Patent May 11, 1993 Sheet 1 of 3 5,209,430 
\ \  1 
1 
1 
10- 
FIG. 1 
FIG. 2 
U.S. Patent May 11, 1993 Sheet 2 of 3 5,209,430 
FIG. 3 
J 
/ r 1 5  
4L 
1 IV .  J 
US. Patent May 11, 1993 Sheet 3 of 3 5,209,430 
1 
5,209,430 
2 
control, other than circulation control alone, is neces- 
sary. These supplemental means include tail rotors, HELICOPTER LOW-SPEED YAW CONTROL 
aerodynamic fins, and reaction jets. 
ORIGIN OF THE INVENTION 
ployee of the United States Government and may be 
manufactured and used by or for the Government for 
governmental purposes without the payment of any 
royalties thereon or therefor. 
Two U.S. patents specifically address circulation 
Of these patents contemplate increasing the favorable 
lateral forces on the helicopter fuselage. These types of 
devices result in increased complexity and weight. The 
ducting, plenum and nozzle arrangements require con- 
The invention described herein was made by an em- 5 control, Logan supra and U.S. Pat. No. 3,807,662. Both 
10 siderable-redesign and modification of the helicopter. 
Further. the Dossibilitv of mechanical failure and the TECHNICAL FIELD OF THE INVENTION 
The present invention relates in general to control- 
ling helicopter flight and more specifically to control- 
ling yaw during low-speed flight. 
BACKGROUND OF THE INVENTION 
During hover and low-speed flight, helicopters expe- 
rience significant aerodynamic forces on the tail boom 
caused by the wake from the main and tail rotors and by 
crosswinds. A helicopter is subjected to complex air- 2o 
flows that are self-imposed as a result of the main and 
tail rotor Wakes and as a result Of ambient wind. These 
airflows Produce aerodynamic forces on the fuselage 
and tail boom assembly during hover and low speed 
sideward flight. When operating in this portion of the 25 
flight envelope, the airflow from the main rotor wake 
has a large impact on the tail boom forces. These effects 
cause the tail boom to be subjected to air loads which 
must be counteracted by main rotor and tail rotor thrust 
to maintain aircraft trim. These increased power re- 30 
quirements result in a reduction in payload and yaw 
control margin. 
In order to provide sufficient torque control and 
adequate sideslip most prior helicopter designs 
large, power consuming, tail rotor. The problems asso- around the 
ciated with the use of type tail rotor are well docu- Another object of the invention is to provide a retrac- 
merited in the prior art. me foremost problem is the tiodextension mechanism whereby the strakes may be 
hazard presented by the tail rotor, particularly to positioned for Optimal performance- 
ground personnel. Additionally, in mfiiw helicopters, 40 A further object of the invention is to provide im- 
the tail rotor is vulnerable to combat damage which can proved reliability and maintainability for the helicopter 
result in catastrophic loss of control of the helicopter. torque control means by reducing power and load re- 
Also, the reliability and maintainability problems of a quirements. 
tail rotor, with its gearboxes, bearings, and drive shafts, Still another object of the Present invention is to 
are severe. Further, during high speed flight the tail 45 improve helicopter performance though increased 
rotor requirement can be reduced, since yaw control Cross wind speed in hover, increased fuel savings and 
can be provided by aerodynamic surfaces. However, inCwi~ed load -Pacity by decreasing power required 
the typical tail rotor continues to use excessive engine from the torque control, by decreasing drag inherent in 
power and to produce adverse drag effects. the torque control and by reducing weight of the torque 
made to eliminate tail rotors. In U.S. Pat. No. 4,200,252 Additbnal objects and advantages of the present 
(Logan) and earlier referenced patents, helicopter anti- invention are apparent from the drawings and specifics- 
torque systems are disclosed which employ the princi- tion which follow. 
SUMMARY OF THE INVENTION ples of fuselage circulation control using the main rotor downwash. These inventions describe how exhaust or 55 
other engine-driven air may be ducted into the helicop- According to the present invention, the foregoing 
ter aft fuselage section and then be injected tangential to and additional objects are obtained by providing a heli- 
the fuselage in order to induce more circulation. This copter yaw control system for use on a helicopter hav- 
increase in circulation is achieved by use of main rotor hg a fuselage which extends rearward through the 
downwash to produce additional lateral forces on the 60 downwash of the main rotor. Yaw control is provided 
fuselage which oppose main rotor torque. by a combination of two strake devices in which the 
However, it is established in prior art that main rotor upper strake is located above the lower strake and along 
downwash does not flow over the fuselage during high the side of said fuselage which faces the retreating rotor 
speed flight. The forward velocity of the helicopter blade and the lower strake is located along the side of 
moves the fuselage clear before the wash can reach it. 65 the fuselage which faces the advancing rotor blade. 
Viewed from within the helicopter, the downwash There is also a supplemental control means to assist in 
pattern appears to have a large rearward horizontal controlling main rotor torque which may be a tail rotor, 
component. Thus, a supplemental means of directional a tail boom with circulation control and/or a supple- 
increased vderabilitGin the case of a military helicop- 
ter remain inherent deficiencies. 
U.S. Pat. No. 4,708,305 partially solves the low-speed 
yaw control problem by placing two strakes on the side 
of the fuselage facing the approaching main rotor blade. 
This arrangement results in a significant download on 
the tail boom and is only beneficial in reducing side 
thrust and yaw control in right sideward flight. 
Accordingly, it is an object of the present invention 
to provide upper and lower fuselage strakes located on 
opposite sides of the helicopter fuselage which 
beneficially alter the & flow around the helicopter tail 
boom. 
lt is another object of this invention to improve left 
and right 
It is another object of this invention to reduce the 
load requirements on the helicopter torque control 
means. 
It is another object of this invention to reduce the size 
of the helicopter torque control means by using fuselage 
air loads to provide part of the needed torque control. 
A further object of the invention is to increase heli- 
flight. 
have employed a combination of tail fin and a relatively 35 copter ability by air flow circulation 
In order to avoid these problems, efforts have been M control means. 
5,209,430 
2 
J 
mental tail thruster, or a fan-in-fin type anti-torque sys- 
tem. The upper strake may extend further from the 
fuselage than the lower strake does. If the helicopter is 
constructed with a tail rotor shaft cover located along 
the top of the fuselage, the upper strake may be located 
on the tail rotor shaft cover. To provide greater yaw 
control, the upper and lower strakes may be retractable. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a perspective view of a helicopter having a 
strake attached to the upper portion of the fuselage, 
FIG. 2 is a perspective view of a helicopter having a 
strake attached to the lower portion of the fuselage, 
FIG. 3 is a perspective view of the fuselage, 
FIG. 4 is a perspective view of the fuselage, 
FIG. 5 is a top view of the helicopter showing the 
location of the strakes, 
FIG. 6 is a perspective view of one of the fuselage 
strakes showing the attachment of actuators, and 
FIG. 7 shows an alternate torque control means using 
a lateralthrusting jet in conjunction with the present 
invention to achieve the necessary torque control. 
DETAILED DESCRIPTION OF THE 
INVENTION 
FIGS. 1 and 2 show a representative helicopter desig- 
nated generally by the reference numeral 10 comprising 
a cabin fuselage section 18 and the boom or aft fuselage 
section 11 with a main rotor 12. Attached to the aft 
fuselage is the upper and lower vertical fin 13, and a 
torque control means 14 in this embodiment shown as a 
tail rotor. A horizontal stabilizer 15 may be part of the 
design or may be absent. The helicopter may be con- 
structed with a tail rotor shaft cover 19 located along 
the top of the aft fuselage section 11. The present inven- 
tion is the combination of two strakes 16 and 17 shown 
in a representative configuration. 
The upper strake 16 is angularly displaced approxi- 
mately 270" to 360" from top dead center (TDC) 21 (see 
FIGS. 3 and 4) of the fuselage and faces the retreating 
main rotor blade 12. If there is a tail rotor shaft cover 19 
on the aft fuselage section 11, upper strake 16 may be 
attached directly to the tail rotor shaft cover 19. The 
lower strake 17 is angularly displaced approximately 
90' to 180" from TDC 21 and faces the advancing main 
rotor blade 12. The upper strake 16 is about two inches 
wide and the lower strake 17 is about one inch wide. 
FIG. 6 shows an alternative embodiment in which the 
strakes are retractable by use of actuators 51. Slots 52 
and 53 are sealed by a rubber flap or other suitable 
means when the strakes are retracted. 
FIG. 7 shows an alternative torque control means 
which uses ducted air jets 81 powered by pressurized air 
82 as a replacement for the tail rotor 14. This jet would 
require less power, and would be lighter when used in 
4 
combination with the present invention, than designs of 
the prior art. 
What is claimed is: 
1. A helicopter yaw control system comprising: 
said helicopter having a main rotor attached thereto; 
said helicopter having a fuselage extending rearward 
through rotor downwash; 
helicopter yaw control means consisting of a combi- 
nation of exactly two strake devices arranged 
asymmetrically about the fuselage, the combination 
including an upper strake being located above a 
lower strake, the upper strake being located along 
the side of the fuselage which faces the retreating 
rotor blade and the lower strake being located 
along the side of the fuselage which faces the ad- 
vancing rotor blade; and 
supplemental control means to assist in controlling 
main rotor torque. 
2. The helicopter yaw control system of claim 1 
wherein the upper strake is located in the upper half of 
the side of the fuselage which faces the retreating rotor 
blade. 
3. The helicopter yaw control system of claim 1 
25 wherein the lower strake is located in the lower half of 
the side of the fuselage which faces the advancing rotor 
blade. 
4. The helicopter yaw control system of claim 1 
wherein the supplemental torque control means is a tail 
5. The helicopter yaw control system of claim 1 
wherein the supplemental torque control means is a 
circulation control tail boom. 
6. The helicopter yaw control system of claim 1 
35 wherein the supplemental torque control means is a 
supplemental tail thruster. 
7. The helicopter yaw control system of claim 1 
wherein the supplemental torque control means is a 
circulation control tail boom in combination with a 
8. The helicopter yaw control system of claim 1 
wherein the supplemental torque control means is a 
fan-in-fin anti-torque system. 
9. The helicopter yaw control system of claim 1 
45 wherein the upper strake extends further from the fuse- 
lage than the lower strakes does. 
10. The helicopter yaw control system of claim 1 
wherein the helicopter has a drive shaft cover over the 
fuselage. 
11. The helicopter yaw control system of claim 10 
wherein the upper strake is located on the tail rotor 
shaft cover. 
12. The helicopter yaw control system of claim 1 
wherein the upper and lower strakes are retractable. 
5 a helicopter; 
10 
I5 
20 
30 rotor. 
40 supplemental tail thruster. 
50 
* * * S t  55 
60 
65 


Helicopter low-speed yaw control

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server