An airfoil family of helicopter rotor blades was designed. Three airfoils with thickness to chord ratios of 12, 9, and 7% were designed. Their improved performance in two dimensional rotor mockup wind tunnel tests led to testing of the tapered blades on four bladed rotors in a wind tunnel and flight tests on the Dauphin series of helicopters, confirming the expected gains

Thibert, J. J.

English

NASA Technical Reports Server

NASA TECHNICAL MEMORANDUM NASA TM-75907 
THE ELABORATION OF A NEW FAMILY OF HELICOPTER BLADE PROFILES 
J.-J. Thibert 
(UASA-TLI-75907) THE ELABORATlOW OF A NEW Y81-LO031 
FA4ILY OF HELlCODTER BLADE PROFILES 
(Hat iona 1 Aeronautics and Space 
A,.; : .n i s t ra t ion)  15 p iiC AO2/dP A0 1 CSCL 3 1C Uncl as G 3 / U L  U1808 
Translation of "~efinition d'une nouvelle fanille de profils pour 
pales d'h6licoptSres': L'AQronautique et L'Astrona~tique, 
No. 81, Feb. 1980, pp. 13-19 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASKINGTON, D.C. 20546 JANUARY 1981 
https://ntrs.nasa.gov/search.jsp?R=19810011503 2020-03-21T13:44:42+00:00Z
- 
2. Cove~nmmt Accession No. 
4. T*tl. d Subtitle 
THE ELABORATION OF A NEW FAMILY OF 
HELICOPTER BLADE PROFILES 
In 1974,  3NERA undertook the des ign  of  a  new a i r f o i l  family 
of rota? blades  s u i t e d  t o  t h e  s p a c i f i c a t i o r s  o f A e r o s p a t i a l e .  
7% have bezn designed and t e s t e d  i n  a wind t u n n e l .  The i r  
I 
Three a i r f o i l s  w i t h  a thickriess  t o  c l ~ o r d  r a t i o  o f  12 ,  9 and : 
performances, b e t t e r  than  those  of o t h e r  a i r f o i l s  commonly 
used on h e l i c o p t e r s ,  l e d  Aerospa t i a l e  t o  use  t h e s e  a i r f o i l s  
i n  a new tapered  blade-wind t u n n e l  and i n f l i g k t  tests, 
confirming the expected  ga ins .  T h i s  new blade allowed b e t t e r  
performances f o r  the r a u p h i n  s e r i e s  and helped t h e  SA 365N 
t o  become t1.e f a s t e s t  nlachlne i n  i t s  c l a s s .  
----.-4-.-. -- 
3. Rec~cwst'r Cetdog No. 
S. Repoet D.to 
January 1981 
6. Pwhmirm Or-irotion Coda 
; .J. T h i b e r t  
Chief Group Engineer i n  t h e  O f f i c e  
J a t i o n a l  d9Etude  e t  de Recherches Aero- 
s 9. Potbminm O*amisetmn N- 
Leo Kanner Associa tes  
Redwood C i t y ,  CA. 94063 
17. Key Words 
Unclassif ied-Unlimited 
10. WorL Unit No. 
I I. Controct or C~ont No. 
NASW-3199 
13. Typo 01 Report on4 Period Corored 
12. Sponrerin# A w c y  N r e  and A H n r s  1 
I 
National  Aeronautics and Space Admin- 
i s t r a t i o n ,  Washington, D.C. 20546 
19. S b c u ~ ~ t ~  Clrrs,t. (of chi8 report) 
Unclassi?:ed 
14. konroring A ~ ~ V  cob 
If. k ~ l o m o n t o r ~  Notes 
Trans la t ion  of "Def in i t ion  d'une f a m i l l e  de p r o f i l s  pour 
p a l e s  d t  h e l i c o p t e r e s "  , L t  Aeronaut ique et Lt  Astronaut ique ,  
No. 8 1 ,  Feb. 1980, pp. 13-19 ( A V O -  48/16) 
I 
20. S*turitv Cterril. (01 this pago) 
Uncless i f i ed  
21- No. of Peges 22. price 
The Elaboration of a New Family of Helicopter Blade Profiles 
J.-J. Thibert 
Chief Group Engineer at the Office National dBEtudes 
et de Recherches A6rospatiales [ONERA] 
The blade profiles used in the majority of modern operational 
helicopters were first elaborated in the 1930's. This basically 
stems from the fact that while aerodynamics has always had an important 
place in airplane design, the same cannot be said for helicopters. 
As a matter of fact, from the end of the Second World Rar, which marked 
the start of the industry, until the end of the 1960's, improvements 
in performance were mostly due to mechanical advances, especially 
to the use of turbine engines. 
In the last decade, meanwhile, major effarts have been made by 
all builders to improve the aerodynamics of their ~~achines so as to 
better their speed, fuel consumption, and load-carrying characteristics, 
As far as the main rotor is concerned, the use of composite materials 
has made possible the introduction of tapered blades and also has 
allowed helicopter rotors to benefit from the recent progress in 
airplane wing profiles. 
Within this framewrxk, ONERA, wit?, the support of DRET, 
undertook in 1974 the elaboration of helicopter blade profiles that 
would meet the specifications established by Aerospatiale, The 
ultimate objective was to develop complete blades that performed 
*Numbers in the margin indicate pagination in the foreign text. 
better than ~Onventional ones. 
History of Profiles Used 
1907-1930 'PHIN PROFILES 9 ' 1 
I19JO-RLJ COETPRYGEN OR NACA PROFILES 1 
1. 
M A  23015 
PWEW PVZ(*S) NACA 0d0 .6  
C .  
NACA 230.15 I 
1950-w LAMINAR PROFILES 
6. 
;ERIE 6 (65-412 - 63A012 - b3AOlS) I 
;1970. ... ELABORATION OF PROFILES 
S A W  rocrP N A C k . 6 3 ~ ~ 1 . 5  
! 
. .8 
5A 321 562 . NACA 0012 ' 
5AjJoJ fl8 .SA 131 Faniil 
SA 341 1967 ~ ~ ~ ~ ' 0 0 1 2  
5A3$ .l9?2 wCA0012 
SA365C 1 NACA0012 
5A36SN 1979 OA Family 
AS 350 1974 NACA 0012 
A5355 FtnI979 OA 209  . 
Figare 1 Figure 2 
Historical Summary of Belicopter Profiles Used in French 
Blade Profiles Kelicopters 
An examination of the profiles used in helicopter blades 
(figure 1) shows the same evolution took place (with a certain 
time lag) as in airplanes. Thus, the blades on the first machines 
had thin profiles. Then, betweea 1930 and 1945, the profiles came 
from the famous Gottingen and NACA series (G-770, NACA 0012, 
.: 
.. NACA 23012, NACA 23015 ...). During t h e  1 9 5 0 B s ,  laminar  p r o f i l e s  
were extended t o  h e l i c o p t e r s  wi th  the i n t r o d u c t i o n  of  t h e  series 6 
: (NACA 63A012-63A015) and of t h e  laminar  series wi th  a low % 
e s p e c i a l l y  designed f o r  h e l i c o p t e r s  (9H12). Eowever, t h e  performances 
ob ta ined  were i n f e r i o r  to  p r e d i c t i o n s  and i n  t h e  s i x t i e s  one wi tnessed  \ 
a r e t u r n  to  t h e  conven t iona l  NACA p r o f i l e s  and t h e i r  d e r i v a t i v e s .  I t  
+ 
* 
pi 
should  a l s o  be  s t r e s s e d  t h a t  d u r i n g  t h i s  e n t i r e  p e r i o d ,  metal b l a d e s  
. had t h e  same p r o f i l e  no matter what t h e i r  span. 
Figure  2 shok~s t h a t  t h e  NACF 0012 p r o f i l e  h a s  been widely used 
on French h e l i c o 2 t e r s .  Only r e c e n t  a i r c r a f t  such a s  t h e  SA 330 J 
v e r s i o n  of t h e  "Puma" and t h e  bimotor models of t h e  "Dauphinw, t h e  
SX 365 N and t h e  SA 366 G ,  are equipped w i t h  t a p e r e d  b lades  whose 
p r o f i l e s  d i f f e r  from t h e  NACA ones. The AS 355, t h e  b i t u r b i n e  v e r s i o n  
of  t h e  "Ecureui l" ,  was g iven  b l a d e s  o f  modern p r o f i l e ,  b u t  they  have 
a c o n s t a n t  b read th  f o r  economic reasons .  
S p e c i f i c a t i o n s  f o r  He l i cop te r  Blade P r o f i l e s  
The r e c e n t  e v o l u t i o n  toward t ape red  b lades  i s  exp la ined  
e a s i l y  by examining t h e  c a l c u l a t e d  isoMach and i s o i n c i d e n c e  l i n e s  on 
t h e  r o t o r  d i s k .  A s i m p l i f i e d  example of t h e s e  l i n e s  is presen ted  i n  
f i g u r e  3. The compounding of t h e  speeds  o f  r o t a t i o n  and of advance 
engenders Mach numbers va ry ing  from 0.2 a t  t h e  r o o t  t o  0.85 a t  t h e  
b lade  t i p  f o r  an  advancing b lade  (azimuth va ry ing  from O 0  t o  180° ) .  
On t h e  r e t r e a t . i n g  b lade  (azimuth varying from 180' t o  360° ) ,  t h e  
Mach numbers a r e  much lower and range from 0.4 a t  t h e  b lade  t i p  t o  
0 ,  o r  even nega t ive  v l a u e s  ( p r o f i l e s  a t t a c k e d  a t  t h e  fo l lowing edge) 
Figure 3 
Example of Calculated Isoincidence and 
IsoMach Lines on a Rotor Disk 
Key: a) Local Incidences 
b) IsoMach Lines 
C) Circle of Inversion 
in the circle of inversion near the hub. 
Because of this, it is necessary that the amount of lift CZ and, 
consequently, the angle of incidence be low for the advancing blade and 
high for the retreating blade to keep the aircraft from rolling. 
In the course of a single rotation, the blades therefore alternately 
undergo low incidences and elevated speeds and then high incidences and 
moderate speeds. Since the Mach an& incidence levels encountered /15 
by the profiles are a function of their position on the blade, 
optimization of rotor performance leads to the use of tapered 
blades. 
The principal spheres in which the profiles function is 
theref ore : 
-- High Mzzh-low C, 
-- Low Mach-high C,. 
There is a third areatoremember when considering an 
aircraft's stationary flight. The Mach number is then independent 
of azimuth and, consequently, of C,, with only a relative variation 
in speed with radial distance Mach = 0.6, CZ = 0.6). Taking account 
of this analysis of profile operating conditions, a set of specifications 
for sections at different radial distances can be established in 
the form of desired performances as a function of the main types of 
flight: 
-- Forward flight 
-- Stationary flight 
-- Maneuvers 
Helicopter blades were divided into three parts based on the 
increase in Mach number with increasing radial distance: 
r/R < 0.8 ,  0 . 8  < r/R < 0.9, 0.9 < r/R 
Figure 4 presents the specifications established for each region /16 
by ~Grospatiale. Emphasis was placed on improving performance in 
relation to blades with conventional NACA 0012 profiles, in stationary 
fligbt by raising the lift/drag ratio at MO = 0.6 and Cz = 0.6 and 
I Stationary W D . r t b q s - ~ a  a 1 I 80 1 05 1 Flight 2 Cam 0.6 
Flight 
Conditibns 
I Foryard 
Flight - + ' 
Figure  4 
S p e c i f i c a t i o n s  f o r  He l i cop te r  Blades 
SECTION 
1 
Preponderant k r o -  
dynamic Caef f ic ient  
and i n  forward f l i g h t  by i n c r e a s i a g  t h e  d r a g  d ivergence  Mach number 
udn at C Z ~  8 
' 
Ic m,; < 
Mdx, b u t  a l s o  C, max i n  o r d e r  t o  avoid r e t r e a t i n g  b lade  s t a l l .  
SECTION 
2 
It should be noted t h a t  t h e  performance reques ted  is c l e a r l y  
SECTION 
3 
0.80 
0.01 
s u p e r i o r  t o  t h a t  of NACA 0012. For example, t h e  Mdx of t h i s  p r o f i l e  
a t  C Z  = 0 is  0.79 and i t s  Cz max a t  MO = 0.4 is 1. An extremely 
s e v e r e  c o n s t r a i n t  i s  a l s o  imposed on t h e  p i t c h i n g  moment c o e f f i c i e n t  
.0.85 
0.01 
a t  zero  l i f t ,  Cmo, which has  t o  remain very low so a s  t o  l i m i t  t h e  
0.90 
0.01 
stress on t h e  c y c l i c - p i t c h  c o n t r o l  rods .  
The v a r i o u s  c o n d i t i o n s  imposed on performance l e a d s  one t o  
choose a t h i c k  p r o f i l e  f o r  t h e  i n n e r  b lade  reg ion  ( e l e v a t e d  C Z  
max) and t h i n  p r o f i l e  f o r  t h e  t i p  ( e l e v a t e d  drag  d ivergence  Mach 
number) . 
Profile Elaboration Method 
ONERA undertook the elaboration of profiles corresponding to the 
set of specifications. It started with section 2, situated at 
a distance equal to about 85% of the total blade length and for 
which the relative thickness should be 9%. The resulting profile, 
named OA 209, has alread been presented in a preceding article 
(no. 70, 1978-3). 'Recall simply that it was elaborated bl choosing 
the desired distribution of speeds at CZ = 0 and that its configuration 
was calculated with the aid of an inverse method of calculation. 
This technique, which is widely used for airplane airfoils, is still 
only rarely used for helicopters. Its advantages are however 
considerable since it allows: 
-- A direct determination of excessive intrados and extrados speed 
and, consequently, of drag. 
-- A iiirect determination of Cmo. 
The profile's overall performance, as derived from tests 
carried out in ONERA'S Modane S3 wind tunnel, are presented in 
figure 5 in terms of CZ max for Mo < 0.5, Mdx at constant CZ for 
& >  0.5, and C%. 
The objectives spelled 3ut in the specifications were attained for 
Mdx at Cz = 0 ,  which is 0.85, and for CQ, which is extremely low 
even at high Mcch numhers. Concerning stationary flight, the lift/ 
drag ratio measured in the wind tunnel at Mo = 0.6 and Cz = 0.6 was 
75. The C Z  max for maneuvers were 1.27 at Mo = 0.3 and 1.21 at 
M, = 0.4. These values are slightly lower than the objectives, 
Figure 5 
Profile OA 209 -- Overall Performance 
but high for a profile with a 9% relative thickness. 
The gains over the NACA profile are considerable in every 
aspect: 
ACz max = 0.14 at Mo = 0.3 (+11%) 
= 0.21 at Mo = 0.4 (+21%) 
AMdx = 0.06 at C Z  = 0 
AL/D = 15 at MO = 0.6 and Cz = 0.6 (+25%)  
Since OA 209 embodied a reasonable compromise, the profiles for 
the root and tip sections were geometrically derived from it. - /17 i 
The basic profile configuration represented by OA 209 was con- 
served in the tip profile OA 207 up to the primary structural member 
in order to maintain a good C Z  max at low Mach numbers. The rear 
part was thinned out to obtain a profile of 7% relative thicknesrc : * d  
a low Cx and high Mdx at Cz = 0. 
The basic thickness relationship of OA 209 was retained for 
the root profile OA 212, but increased to 12%. In addition, a 
camber that allowed the desired Cz max to be attained while keeping Cmo 
low was sought. 
Performance of the OA Profile Family 
Figure 6 ORIMNAL PAGE IS 
Design of the OA Profile Family OF Kx)R QUALITY 
Drawings of the three profiles, OA 212, OA 209, and GA 207, 
are presented in figure 6. Their overall performances were derived 
from tests carried out in the Modane S3 wind tunnel with a two- 
dimensional flow passing over mock-ups having a 210 mm chord. In 
figures 7 through 9, a comparison is made with the performance of the 
Figure 7 
Overall Performance of the OA Profile Family 
NACA 0012 2rofile under the same conditions. The overall per- 
formance characteristics are: 
-- Cz max fox & < 0.5 and Mdx at constant C z  for Mo > 0 .5  
(figure 7) 
, 
i 9 
- 
, " 
4 cz  i A cz 
Mo= 0.5 Mo= 0.6 
. 
O A 2 0 V  C 
-.*-2 
I 
: . 0.5 -- ' I 0.5 .-... ... 
d. 
I 
* .  
1 
': , r .. 
0 0.01 0.01 + 0 0.01 00; 
1 
Figure 8 
Polar Curves at & = 0.5 and & = 0.6 
-- P o l a r  c u r v e s  a t  Mo = 0.5 and 0.6 ( f i g u r e  8)  
-- Change i n  Cx w i t h  Mach number a t  CZ = 0 and C z  = 0.1  ( f i g -  
u r e  9 )  
F i g u r e  9 
Change i n  Drag as  a Func t ion  of  Mach Number 
There  a r e  c o n s i d e r a b l e  g a i n s  i n  CZ  max compared t o  t h e  NACA 
0012 p r o f i l e .  The OA 212 p r o f i l e  o f  t h e  ddme r e l a t i v e  t h i c k n e s s  
c a u s e s  an i n c r e a s e  i n  C, max of  32% a t  & = 0.4 and o f  44% a t  
Mo = 0.5. A s  f o r  t h e  d r a g  d i v e r g e n c e  Mach  umber, t h e  r e d u c t i o n  i n  
r e l a t i v e  t h i c k n e s s ,  a s s o c i a t e d  w i t h  t h i c k n e s s  de t e rmin ing  formulae  
p a r t i c u l a r l y  adapted to  t r anson ic  speeds, confers  performances t o  
t h e  OA 209 and OA 207 p r o f i l e s  t h a t  are g r e a t l y  super ior  t o  t h a t  
of NACA 0012. The l i f t i d r a g  r a t i o s  a t  = 0.5 and 0.6 and Cz 
> 0.5 a s  w e l l  as t h e  Cx 's a t  high Mach numbers a r e  equa l ly  b e t t e r ,  
b u t  t h e  OA family 's  l e v e l  of p r e c r t i c a l  drag is s l i g h t l y  higher  
( f i gu re  9 ) .  This  a r i s e s  from t h e  f a c t  t h a t  f o r  t he se  low C Z ,  
cambered p r o f i l e s ,  t h e  t r a n s i t i o n  of t h e  boundry l aye r  a t  t h e  
in t rados  takes  place  near  t h e  leadinq edge. For NACA 0012, it 
occurs  a t  t he  l e v e l  of impact a t  t h e  tests' Reynolds number, and 
the re fo re  f u r t h e r  downwind. ~ g r o s p a t i a l e  b u i l t  two four-bladed 
r o t o r  mock-ups f o r  t h e  purpose of t e s t i n g  t h e  p r o f i l e s  i n  operat ing 
condi t ions  c l o s e r  to those  a c t u a l l y  encountered by a he l icopte r .  They 
w e r e  t e s t e d  on the  r o t o r  t e s t i n g  s tand i n  ONERA's Modane S1 wind 
tunnel .  The 4 m diameter r o t o r s  had blades with a 140 mm chord. 
The f i r s t  r o t o r  had an OA 209 p r o f i l e  over i t s  e n t i r e  length.  The 
second one had an OA 209 p r o f i l e  up t o  0.8 R. I t  then thinned <own 
t o  an OA 207 p r o f i l e  a t  t h e  blade t i p .  The tests confirmed t h e  
expected ga ins  i n  comparison with  NACA 0012 blades.  Notably, t h e r e  was: 
-- An increase  i n  t he  f i g u r e  of m e r i t  during s t a t i o n a r y  f l i g h t ,  
-- An increase  i n  t he  l i f t / d r a g  r a t i o  during forward f l i g h t ,  
p a r t i c u l a r l y  under heavy load. 
Based on t h e i r  performance, ~ g r o s p a t i a l e  decided t o  equip t h e  
SA 365 N and the  SA 366 G vers ions  of t h e  Dauphin with blades using 
the  OA family of p r o f i l e s .  The performance obtained during test f l i g h t s  
of t he  SA 365 N c;oiifirmed t h e  p o t e n t i a l  ga ins  expected on the  b a s i s  of 
the  r e s u l t s  of two-dimensional tests on r o t o r  mock-ups. 
Conclusion 
These studies, which were carried out in close collaboration with 
~&rospatiale, have thus led to the design of a new, high-performance 
rotor. Our cooperation will, of course, continue in the field of 
blade profiles, where progress, perhaps not as spectacular but none- 
theless significant, can still be realized. Cooperation will also 
continue in such largely unexplored areas as: 
-- Blade plan form. 
-- Hub drag, 
-- Air intake efficiency, 
-- Anti-torque rotors. 
All this activity should permit an even greater improvement of 
helicopter performance in the near future. 


The elaboration of a new family of helicopter blade profiles

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