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Патент USA US2111975

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_ March 22, 1938.
A. E. LARSEN ET AL
‘ 2,111,975
‘ ROTATIVB WINGED AIRCRAFT
Filed Dec. v19, 1935
:5 Sheéts-Sheet. 1‘
ATroR'NEYJ " ‘
March 22, 1938‘. _
’
I
I
.
‘
A_ E_ LARSEN ET AL
'
ROTATIVE
WINGED
'
2,111,975
AIRCRAFT
Filed Dec‘. 19, 1955
3 sheets-sheet '2
mcsua
_
10
go’ 30 40' 5o
60
% BLADE’ LENGTH
70
- INVENTORS
>60 90 511100
a“? 51W
Wv?ééw
ATTORNEYS
-
March 22, '1938.
A. E.- LARSEN ET. AL
‘
ROTATIVE WINGED AIRCRAFT
Filed ‘Dec. 19, 1935
P
2,111,975
I
s Sheets-Sheet z
INVENTORS ’
W44’
-
#
WT‘MM
ATTORNEYS
Patented Mar. 22, 1938 ,
‘ 2,111,915 ’
UNITED STATES ‘PATENT-v orrice .
2,111,915 ,
ROTATIVEf-WINGED AIRCRAFT
Agnew E. Larsen, Huntingdon Valley, aiulPaul
H. Stanley, Glenside, Pa., assignors to ‘Auto
giro Company of America, Willow Grove, Pa",
'
. i a corporation of Delaware
*
~_
_ Application December 19, 1935', Serial No. 55,142
20 Claims. , (01. 244-18)
This invention‘ relates to aircraft having ro
tative sustaining blades or wings, and is especially
concerned with that type of. craft in which a
sustaining rotor is employed incorporating a
plurality of blades which are pivotally connected
with a common generally upright axis mecha
nism.
'
.
characterized by a novel incidence relation be
tween inboard and outboard portions thereof.
Special arrangements in the structure, such as
features of the spar, nose, ribs, ballast weights,
etc., are also of importance in the working out 5
of the primary objects, as will appear more‘ fully Y
hereinafter.
I
One of the major objects of the invention is to
increase the e?lciency of craft of this type, more
'
-
-
,
How the foregoing, together with. other objects
and advantages are" attained, vwillappear more
fully in the following description’ referring to the 10
The invention also overcomes a diving tendency accompanying drawings, in‘w'hich
Figure 1‘ is a plan view of the structural mem
sometimes experienced at high forward speeds. I
10 particularly to increase the rotor e?iciency.
'
Still further, it is an object of the inventio'n‘to
provide a rotor the blades of which are of reduced
:15 .weight as compared with prior constructions and
which are further of simpli?ed construction.
The foregoing important and more or less gen
eral objects are served by various features of con-‘
bers of a blade according tov the invention, the
outer covering being removed;
Figure 2 is an enlarged sectional view of the 15
blade taken substantially as indicated by the sec
tion line 2—-2 on Figure 1;
-
\
Figure 3 is a top plan view of one of the ribs '
employed in building up the blade; -
struction such as the following: '
The invention contemplates a blade of novel
20
form, more speci?cally, the improved blade has
a thickness ratio varying by steps which is con
veniently obtained with maintenance of uniform
chord, thus without necessarily reducing the‘
'25 solidity of the rotor. According to the invention,
Y
‘
Figure 4 is a partial sectional view takenas in- '
dicated bythe section line 4—4 ‘on Figure l and
illustrating a ballast weight and the mounting
therefor;
v
Figure 5 is a fragmentary top view of structural
members of the blade, this view also showing the 25
ballast weight;
‘
'
the blade is composed of several portions, pref
Figure 6 is a view containing a graph and a
erably three, each one of which is of substantially
uniform thickness but the several portions, re-_ blade'in outline and illustrating a number of fea
spectively, being of di?erent thicknesses, an out: ‘ . tures discussed fully hereinafteryand
Figure 7 is‘ a view of the blade section (in out
30 board portion,‘ for example, being of reduced
thickness ascompared with the adjacent inboard
portion.
v
Similarly, the invention contemplates the em
ployment of a spar of step—down construction,
35
blade, particularly illustrating the relation of
incidence settings of di?erent portions of _ the
blades.
_
-
As mentioned at the outset, the invention is 35
the several portions of the spar preferably being
substantially coextensive with the portions'of the
concerned with a blade for an aircraft sustaining
blade mentioned above as being of di?erent thick
rotor of the type incorporating an axis mecha
nesses.
'
l'
>
'
In addition to the above, the construction of
40 this invention involves a blade of substantially
?xed center of pressure (preferably well forward
or at about 25% of the chord from the leading
edge) for all normal angles of attack above a
30
line) at various points along the length of the
nism, ‘thisbeing shown at ‘i in Figure l, to which
a plurality of blades are pivoted. The blade ap
pearing in Figure 1 is secured to the axis or hub 40
‘I by means of a “?apping” articulation 8, exten
sion link 9 and “drag" articulation Ill. The blade
is vthus free to "?ap” in a direction generally
- predetermined minimum, for example, 2° positive. . transverse the mean rotative path of travel and
The blade section employed in accordance with
this invention further has a rearward travel of
the center of pressure below said predetermined
minimum; This type of blade we have foundto
provide very material improvement in smooth;
'50 ness of operation, especially when maintaining
the sectional center of gravity substantially co
incident with or slightly ahead of the sectional
center of pressure, this latter ‘also constituting
an important feature of ' the invention.
55
The improved blade herein disclosed is‘; also
also to move fore and aft substantially within 45.
the path of travel. The articulations, of course,
serve to interconnect the hub member and the
main structural element of the-blade which takes
the form of a spar ll. At the inner end of the
spar a fitting l2 may be provided, this ?tting 60
having fork or equivalent parts adapted to co
operate with the pivot Hi. The fitting I 2 and also
an additional sleeve B at the inner end of the
spar serve, to increase rigidity toward the root
end of the blade, this being of importance in the 55
2
‘2,111,975
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‘
cantilever’ support of the blade and for other , weight itself, and a web ll, lying in the plane
reasons.
In general,‘ moreover, it might be said . of the blade, is welded to the sleeves 30.
that because of bending and tension loads at the
root, greater strength and related characteristics
are required toward the root end, whereas aero
dynamic efficiency, because of the high speed,
This
construction provides a rigid mounting for the
weights 28 which ishighly effective as against the
action of centrifugal force, in spite of the fact
that the weight is. spaced a substantial distance
is of greatest importance toward the tip of the ‘ from the spar.
blade. Numerous features of the present inven
From Figures 1 and 6 it will be seen that the
-tion carry out the relationships just mentioned weights 28 are all located in the outer half of
the blade. It is the-outboard portion of the blade 10
10 more completely than has been possible hereto
fore.
'
Turning again to the spar, attention is called
to the fact that the inboard portion of the spar
designated by the arrows lid, is of substantially
15 uniform cross-section or diameter but ‘larger
reduced size.
and I I0.
Before considering the effect of these weights
and also of various other factors already men
tioned, reference is now made to the incidence
setting of the blade. As will best be understood 20'
from examination of Figures 6 and 7, the blade
Sections lib and lie are also respec
is~of smaller diameter than portion Ilb, so that
20 the spar is of stepped construction.
The spar,
moreover, is preferably composed of a single
drawn tube and has short tapered sections l4
and I5 joining sections lia-—Ilb, and Ilb-llc,
respectively.' At the outer end of the section Ilc
25 an extension i6 is provided, and ‘this extension
carries a tip part I‘! shaped to ‘conform with the
point about 85% of the blade length from the
root. In consequence, the tip has 1%° lower in
erably, although not necessarily, made of wood,
55
60
'
65
76
out from the root end thereof outwardly toward
the tip. This primary washout, if carried to the
group being apertured to engage the spar in the
The attachment of
the ribs to the spar may be accomplished (see
?ange 2| with extended lips 22 which may de
35 sirably be welded to the spar. The ribs are pref
50
has a progressive decrease in incidence or wash
desired tip-taper.
The spar carries ribs I811, I82) and l8c, each
‘ Figures 2 and 3) by means of a ?tting l9 riveted
to the rib as at 20, this ?tting having a sleeve or
45
-
extreme tip of the blade, would give the blade 25
about 74° lower incidence at the tip than at the
root. An additional washout of 1°, however, is
superimposed on the primary washout, this ad
30 respective sections thereof,
'
outer portion of the blade, does not impose the
total centrifugal load thereof on the outermost
section of the spar which, as already noted, is of
than the intermediate and outboard sections I lb
tively of uniform diameter, although portion “0
'40
that requires ballasting, but the distribution dis
closed, while concentrating the weight in the
ditional decrease in incidence commencing at a
Rfl
cidence than the root. As indicated in the graph
of Figure 6, the blade is set on the hub with its '
root end at an incidence of approximately 41/2’
above zero lift, and in view of this, the tip set
ting approximates 2%° above zero lift. The in
and the same applies to the nose strip 23 which . cidence settings just mentioned (see also Figure
in accordance with the present invention is of '7) are the positions of the blade section (at
fairly large section, with two purposes in view: different points along the blade) measured from
?rst, an increase in rigidity of the blade in the that position which, with air?ow perpendicular
plane or path of rotation and, second, location to the axis of rotation, would give zero lift. As
of the center of gravity well forward. This seen in Figure 7, with a blade section of the type
latter object is also served by location of the spar shown, the chord line of the blade in zero lift
position (represented by line z—z) is slightly
well forward in the blade section. More spe
ci?cally, it will be noted that the center of the negative with respect to the plane a:—.1: perpen
spar is located less than 25% of the chord from dicular to the axis of rotation r-r, the negative
the leading edge. These features of construction, angle being about 1.2" as shown.
together with fairly robust ribs, particularly inv
Attention is now directed to the fact that in
the trailing edge portions thereof, may afford Figure 7 the full line blade outline A is taken at
sufiicient rigidity in the path of rotation even a point toward the inner end of the blade and
without the necessity of employng a supple-' that the chord line H of this section is posi
mentary spar or stringer which heretofore has tioned at ‘it/2° positive angle with reference to
been located intermediate the main spar and the the line 22-22 representing the zero lift position.
trailing edge. The rear ends of the ribs are em
Figure 7, it will be noted, also shows two addi
braced by a trailing edge stringer 24 which may tional blade sections B and C in dot-and-dash
be applied in'the form'of a trough or V and then outline. Sections B and C both have substan
pinched together at its front edges as at 25. The tially the same chord as section A, although sec
nose of‘ the wing is preferably also surrounded tion B is of reduced thickness as compared with
by a plywood covering 26 which, as clearly seen section A and section C, in turn, is of reduced
in Figure 2, is recessed into the edges of the ribs. thickness as compared with section B. The
This nose covering also adds considerable rigidity points at which these three sections are taken
in the path of rotation.
is also indicated by corresponding letters on the
The blade, of course, is covered with a fabric blade appearing in Figure 6, and from this lat
21 which may be suitably doped.
ter view it will be seen that section A is taken
As seen in Figure 1, the blade further in
in the region where the spar has largest diame
corporates a plurality of ballast weights 28, one ter, section B in the region where the spar has
of which appears to best advantage in Figures 4 intermediate diameter, and section C in the outer
and 5. This weight, it will be observed, is dis
section of the blade where the spar is of smallest
posed well forward in the nose of the blade and diameter. _
is preferably supported on the spar by means of
Turning again to Figure 7, it will be noted that
a pair of bolts 29 which pierce the spar hori
the chord line b-b of the section B is positioned
zontally at the neutral axis and thus result in at a 4° positive angle with reference to line z-z,
minimum weakening thereof. A pair of spacer and from comparison with Figure 6 it will be
sleeves 30 are disposed between the spar and the seen that section line b-b is positioned at the
40
60
55
60
65
a.
75
2,111,975
r 3
\
point where the graph shows 9. 4° incidence.
above zero lift position. The expression “angle
Similarly, the chord line 0-0 of section C is
of attac " is'herein usedto de?ne the angle be
tween the chord line and the line of air?ow at
any given instant. For various reasons (notably
positioned at about a 314° angle with reference to
line e--z, as also appears from the graph of
Figure 6.
1
' the effect of .blade ?apping and attitude and di
From the foregoing it will be seen that al
though the same chord dimension is maintained
rection of ?ight of the craft), the angle of attack
is almost continuously ?uctuating and may as
substantially throughout the entire length of the
sume a value which is eithergreater or less than
blade, the thickness ratio of the blade is varied,
10 with the section. of least thickness at the tip and
the section of greatest thickness at the root. Ac-'
cording to the invention, the thickness of section
A is maintained substantially uniform through
out the portion of the blade which is coextensive
with the inner spar section Ila. The section B,
of intermediate thickness, is maintained through
out the portion of the blade corresponding to
section llb of the spar, and the section C, of
minimum thickness, is maintained throughout
20 the portion of the blade corresponding to the out
the incidence setting.
‘
‘
Reverting now to the characteristics of the
blade section employed, below approximately 2°
positive, the center of pressure of the section
adopted moves rearwardly from the 25% position
quite rapidly.
.
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V
1
‘
The reduction in the incidence setting- of the 16
blade toward thetip, as herein contemplated,
has been found to materially reduce vertical
?uctuation in forces or "bouncing" transmitted 1
from the rotor to the‘ machine. ‘By the differ
ence in incidence setting, a more‘ uniform lift
distribution is applied to the blade throughout
is of stepped thickness, the portion ‘of greatest its cycle, and, in consequence, bending moments
thickness being located inboard and the portion in the blade are’reduced. Reduction in bending
of least thickness toward the tip, as is desirable moments in-the blade is of importance since this
reduces ?uctuation i'n lift delivered to the'hub.
25 from the standpoint of structural and vaerody
namic emciency of the rotor. The present Furthermore, under certain conditions of ?ight,
the advancing blade of a rotor having ?apping
stepped construction, in contrast with a gradu
ally tapering shape, is of substantial advantage blades, will, through a restricted range of posi-_
tions, be operating at a low angle of attack.- A
‘since, with the varying oblique flow of air en
'30 countered during rotation of the rotor, the effec negative torsional moment would normally occur
20- ‘
boa'rd portion of the spar llc. Thus, the blade
30'
tive blade section is distorted to a much smaller
as a result of this in a blade having an aerofoil
degree than with prior forms of blades. The only
points of material distortion, in fact, are those at
section of the general character used in accord- -
the junction points between adjacent portions of‘
35 the blade, at which points the blade tapers rather
sharply from the. larger thickness‘ to the next
smaller thickness. This tapering at the junction
points is substantially coextensive with the
tapered portions l4 and iii of the spar.
'
The step-down blade construction, while main
taining uniform chord dimension, is of further
‘ advantage since it provides a material and highly
desired reduction in drag in the outboard portion
of the blade without a noticeable reduction in lift
45 and further without reducing the solidity of the
ance with the present invention. However, the
reduction in blade incidence toward the tip has
an advantageous eiiect in minimizing this tor 35
sional moment and thus reducing any diving
tendency produced by the moment.
The location of the sectional center of gravity '
coincident with or slightly ahead of the center
of pressure of the blade, as herein contemplated, 40'
is also of importance, and with a blade of the
type herein shown, the ballast weights aid in pro
viding the relation of center of gravity to center
of pressure just referred to. The relation of the
C. G. and C. P. overcomes detrimental cumula 45
tive action producing torsional de?ection of the
I rotor, i. e., the ratio of the total blade area to the
disk area swept by the blades. Maintenance of . blade and causing undesirable loads on the ma
the‘ solidity is of advantage chie?y .in retaining
the desired vlow ?ight speed characteristics of
50 the rotor.
chine under the effect of vertical accelerations.
due to maneuvers or “bumps”.
‘
'
50
Another advantage of- the blade structure here
dimension from the leading edge. This condi
in disclosed, particularly the ‘employment of a
' rather robust leading edgestrip, a plywood cov
ering for‘ the nose part of the wing, and other
features increasing the stiffness of the'blade in
the plane of rotation, is that the increase in 55
‘ stiffness in the plane mentioned increases the
v‘natural vibration frequency in this plane and
, tion is substantially maintained throughout the
this, in tum,- reduces‘ tendency toward'grou'nd
In considering some further features of the in-,
vention, it should‘be noted that the section em-
ployed in all portions of the blade is preferably
‘one of several known forms having a substan
as tially .?xed center of pressure located well for
wardly, for'example, at about 25% of the chord
‘several steps of the blade, although the thickness
60 ratio is slightly modi?ed. ' By way oi’ example,
the thickness ratio in the innermost portion of
the blade may be about Hill/2%, in the interme
diate portion about 111_/2%,jand in the outboard
portion about 10%.
.
~
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With- further reference to the blade section,
resonance in the rotor. '
V
.
‘
The step-down construction of the blade and 60
other features thereof which reduce theneces
sity for employing a, secondary spar as herein
before referred to, is of substantial advantage in
simplifying construction. Note particularly that
with the step-down construction, the number of
while the center of pressure as above indicated . different types of ribs is reduced, since all ribs in
- is substantially ?xed, this condition is maintained the region of each of the spar sections Ila, llb
in a highly e?icient section only above a prede
and llc may be of one type, both as to external
termined minimum aerodynamic angle of~attack.
This minimum, according, to the present‘ inven
tion, preferably approximates 2° positive.
It is here to be noted that the expression “angle
of attac " is not to be confused withthe .“inci
‘ dence setting" of the blade which in the present
75 description refers- to'the angle of the chord line
I
contour as-well as to diameter of spar receiving
aperture.
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_
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1n summarizing the advantages, it should be
noted‘ that various features of the structure, in
cluding the step-down spar, the reduction ‘in
thickness ratio of the blade, the C. G. and C. P.
relation, and incidence settings are of ‘importance 75
4
2,111,975
V in reducing weight while providing adequate
inboard end of the blade.
ployed, improving the smoothness of rotor op
8. For an aircraft sustaining rotor, a generally
upright axis mechanism and a sustaining blade
secured to the axis mechanism with freedom for
movement in a direction generally transverse the
mean rotative path of travel of the blade, said
eration, reducing the tendency to set up torsional
or other vibrations due to periodic ?uctuation in
the position of the center of pressure, and sub
stantially eliminating “bouncing" of the rotor.
We claim:
1. A blade for an aircraft sustaining rotor, an
10 inboard portion thereof being of substantially
blade having an airfoil section with a substan
tially ?xed center of pressure throughout a range
of aerodynamic angles of attack above a prede 10
termined angle, the blade setcion further having
form thickness, the two portions being joined by a
angles of attack below said predetermined angle,
'
2. A blade for an aircraft sustaining rotor, said
blade having a spar, an inboard portion of which
is of substantially uniform cross-section and an
outboard portion of which has a smaller but sub
stantially uniform cross-section, and means de
-20 ?ning the blade surface, an inboard portion
thereof being of substantially uniform thickness,
and an outboard portion thereof being of smaller
but substantially uniform thickness, the two por
tions being joined by a relatively short tapered
25
_
uniform thickness, and an outboard portion
thereof being of smaller but substantially uni
relatively short tapered portion.
15
providing relatively positive incidence toward the
strength, even where ballast weights are em
portion.
3. A blade for an aircraft sustaining rotor, an
inboard portion thereof being of substantially
uniform thickness, and an outboard portion
thereof being of smaller but substantially uni
'30 form thickness, the two portions being joined by
a relatively short tapered portion, and the two
portions further having substantially the same
chord.
4. A blade for an aircraft sustaining rotor, an
v35 inboard portion thereof being of substantially
uniform thickness, and an outboard portion
thereof being of smaller but substantially uni
form thickness, the two portions being joined by
a relatively short tapered portion, and said two
40 portions further having a gradual or progressive
incidence washout providing relatively positive
‘incidence toward the inboard end of the blade.
5. A blade for an aircraft sustaining rotor, an
inboard portion thereof being of substantially
45 uniform thickness, and an outboard portion
thereof being of smaller but- substantially uni
form thickness, the inboard and outboard por
tions both having a substantially ?xed sectional
center of pressure at about 25% of the chord
from the leading edge throughout at least a major
part of the normal range of angles of attack.
6. A blade for an aircraft sustaining rotor, an
inboard portion thereof being of substantiallyuni
form thickness, and an outboard portion thereof
55 being of smaller but substantially uniform thick
ness, the inboard and outboard portions both hav
ing a substantially ?xed sectional center of pres
sure at about 25% of the chord from the leading
edge throughout at least a major part of the nor
80 mal range’of angles of attack, and each portion
further having its sectional center of gravity sub-'
stantially coincident with the center of pressure.
'7. A blade for an aircraft sustaining rotor, an
inboard portion thereof being of substantially
66 uniform
thickness, and an outboard portion
thereof being of smaller but substantially uni
a rearward travel of'the center of pressure at
an outboard portion of the blade being set at a
positive incidence with respect to its zero lift 15
position, which incidence, however, is such that
when the blade is on the advancing side of the
rotor during high speed forward ?ight, the aero
dynamic angle of attack of the outboard portion
is below said predetermined angle, and an in 20
board portion of the blade being set at a positive
incidence with respect to its zero liftposition,
which incidence is sufficiently above said prede
termined angle to maintain an angle of attack
above the predetermined angle when the blade is 25
on the advancing side of the rotor during high '
speed forward ?ight.
9. For an aircraft sustaining rotor, a generally
upright axis mechanism and a sustaining blade
secured tolthe axis mechanism with freedom for 30
movement in a direction generally transverse the
mean rotative path of travel of the blade,'said
blade progressively decreasing in incidence from
a point toward the root end thereof outwardly
substantially to the tip, the decrease in incidence
in about the outer 15% of the blade length be
ing substantially uniform per unit of length and
being greater ‘per unit of lengthv than the de
crease in the inner 85% of the blade length, and
the decrease of incidence in the inner 85% of the 40
blade length also being substantially uniform per
unit of length of the blade.
10. For an aircraft sustaining rotor, a gener
ally upright axis mechanism and a sustaining
blade secured to the axis mechanism with free 45
dom for movement in a direction generally trans
verse the mean rotative path of travel of the
bIadeLsaid blade progressively decreasing in in
cidence from a point toward the root end thereof
outwardly substantially to the tip, 'the decrease in 50
incidence in about the outer 15% of the blade
length being substantially uniform per unit of
length and being greater per unit of length than
the decrease in the inner 85% of the blade length, .
and the decrease of incidence in the inner 85% 55
of the blade length also being substantially uni
form per unit of length of the blade, the total
decrease in incidence from the root to the tip of
the blade being approximately 1%°, the blade
being mounted on the axis mechanism with its 60
root end portion set at approximately ‘ll/2° posi
tive lift incidence with respect to its zero lift
position and the section of the blade substan
tially throughout the ‘length thereof having a
substantially ?xed center ‘of pressure at angles
of attack above approximately 2‘? and further
05'
having a rearward travel of the center of pres
form thickness, the inboard and outboardpor
tions both having a substantially ?xed sectional sure at angles of attack below approximately 2°.
11. A blade for an aircraft sustaining rotor,
center of pressure at about 25% of the chord from
70 the leading edge throughout at least a major part said blade incorporating a spar, an inboard por 70
of the normal range of angles of attack, each tion of which is of substantially uniform section
portion further having its sectional center of and an outboard portion of which is of smaller
gravity substantially coincident with the center of _ but substantially uniform section, means carried
pressure, and said two portions still further hav
on said sparv and de?ning the surface or form
75 ing a gradual or progressive incidence washout of the blade. said means being of substantially 75
2,111,976
uniform thickness throughout a portion of the
blade substantially coextensive with said in
board portion of the spar and further being of
reduced but substantially uniform thickness
w
.
,
5
said portions further being- of substantially uni
form thickness throughout its length and an out
board portion being of reduced thickness as com
pared with an inboard portion, and a ballast
throughout’ a portion of the blade substantially . weight in the blade toward its leading edge in
coextensive with said outboard portion of the
spar.
.
I
the- outboard portion thereof.
16. Ablade for an aircraft sustaining rotor,
12. A blade for an aircraft sustaining rotor, said blade incorporating ‘a spar and means de
?ning the blade shape, substantially coextensive
said blade incorporating a spar, an inboard por
10 tion of which is of substantially uniform section . portions of said means and of the spar being of 10
and an outboard portion of which is of smaller different thickness and cross-section, respective
but substantially uniform section, means carried ly, an outboard portion having substantially uni- ‘
on said spar and defining the surface or form- of ‘form blade thickness and spar cross-section but
the blade, said means being of substantially uni
form thicknessthroughout a portion of the blade
substantially coextensive with said inboard por
tion of the spar and further being of reduced
but substantially uniform thickness throughout a
being smaller than the blade thickness and spar
_ section in an inboard portion.
15
17.‘ For an aircraft sustaining rotor, a blade
of spar and‘rib construction, an. inboard portion
of the spar being of substantially uniform cross
portion of the blade substantially coextensive . section, an outboard portion thereof being of re
20 with said outboard portion of the spar, and a duced but substantially uniform cross-section, 20
ballast weight positioned forwardly of the spar and an intermediate portion of the spar being
tapered to join said inboard and outboardpor
in said outboard portion.
.
1
13. A blade for an ‘aircraft sustaining rotor, tions, and a plurality of ribs mounted on said
spar in spaced relation, the length of said inter
said blade incorporating _a spar, an inboard por
tion of which is of substantially uniform section mediate section and the spacing of said ribs be 25
and an outboard portion of which is of smaller ing approximately the same.
18. For an aircraft sustaining rotor, 'aigener
but substantially uniform section, means carried '
on said spar and de?ning the surface or form of
the blade, said means being of substantially uni
form thickness throughout a portion of the blade
substantially coextensive with said inboard por
tion of the spar and further being of reduced but
substantially ‘uniform thickness throughout a
portion of the blade substantially coextensive
35 with said outboard portion of the spar, and a
so
ballast weight secured to the spar adjacent the
ally upright axis mechanism and a sustaining '
blade secured to the axis mechanism with free
dom for movement in a direction generally trans 80
verse the mean rotative path of travel of the
blade, said blade progressively decreasing in in
cidence from a point toward the root end thereof
outwardly substantially to the tip, the decrease
in incidence in an. outer portion of the blade 85
length being substantially uniform per unit- of
outer end of said inboard portion of the spar. length and being greater per unit of length than
14. A blade for’ an aircraft sustaining rotor, the decrease in the inner portion of the- blade
said blade incorporating a spar, an inboard por— ‘length, and the decrease in incidence in the inner
portion of the blade lengthralso being substan- L
40 tion of which is of substantially uniform sec
tion and an outboard portion of which is of tially uniform per unit of length.
19. A blade for an aircraft sustaining rotor,
smaller but substantially uniform section, means
carried on said spar and de?ning-the surface or. the blade being composed of at least three por- '
tions' of different thickness each of which is of
form of the blade, said means being of substan
' tially uniform thickness throughout a portion of ' substantially uniform thickness throughout its '
length.
'
the blade substantially coextensive with said in
board portion of the spar and further being of
reduced but substantially uniform thickness
throughout a portion of the blade substantially
coextensive with said outboard portion of the
spar. and a plurality of ballast weights carried
20. A .blade for an aircraft sustaining rotor,
said blade including a spar, means carried by
the spar and de?ning the blade contour, a ballast
weight at least the majpr mass of which lies in
board portion.
and the
the plane of the blade chord, the ballast weight.
by the spar, one in the outboard portion thereof , further being horizontally offset from the spar,
and another adjacent the outer en'd of the in; and means interconnecting the ballast weight
'
15. A blade for an aircraft sustaining rotor,
portions of said'biade being of diiferent thick
ness but substantially the same chord, each‘ of
spar.
'
'
'
AGNEW
LARSEN.
PAUL H. STANLEY.
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