Feb. 19, R953
A. s. MULLGARDT
2,627,928
PROPELLER
Filed April 30, 1945
4 Sheets-Sheet 1
INVEN TOR.
ALEXANDER 5T Nous/mp7
BY 2
'2
Feb. 10, 1953
A. s. MULLGARDT
2,627,928
PROPELLER
Filed April 50, 1945
4 Sheets-Sheet 2
IN VEN TOR.
ALEXANDER 5. MULLQARDT
BY
Feb. 10, 1953
A. s. MULLGARDT
2,627,928
PROPELLER
Filed April 50, 1945
4 Sheets-Sheet 3
‘1_.
______ _,..
INVEN TOR.
ALEXA NDEE 5. Muuqmzpr
BY
Feb. 10, 1953
‘
A. s. MULLGARDT
2,627,928
PROPELLER
Filed April 30, 1945
_4 Sheets-Sheet 4
IN VEN TOR.
A LEXA NDER 5 MUL L qA EDT
Patented Feb. 10, 1953
2,627,928
UNITED STATES PATENT OFFICE
2,627,928
PROPELLER
' Alexander s. Mullgardt, Altadena, Calif.
Application April 30, 1945, Serial No. 590,999
1 Claim.
1
(Cl. 170-16025)
2
This invention relates to propellers whose av
departing from the scope of the present inven
erage pitch as well as whose geometric pitch is
tion as set ‘forth in the following speci?cation,
and as de?ned‘ in the following claim; hence I
do not limit‘my invention to the exact arrange
adjustable at any time.
The various features of the herein invention
can be utilized in connection with propellers
used for propulsion as on airplanes, or, for ?xed
installations of air moving equipment, or for
controlled vertical rise, hovering, and transla
tional ?ight as on helicopters or helicoplanes, or
for controlled autorotative sustaining surfaces as
on autogiros; further the various features of the
invention are applicable to propellers with rigid
blades or propellers with articulated blades,
whether the blades are articulated around one
axis or several axes.
An object of the invention is to provide a pro
ments and combinations of the said device and
parts as described in the said speci?cation, nor
do I con?ne myself'to the exact details of the
construction of the said parts as illustrated in
the accompanying drawings.
With the foregoing and other objects in view,
which will be made manifest in the following de
tailed description, reference is had to the ac
companying drawings for the illustrative em
bodiment of the invention, wherein:
Fig. 1 is a diagrammatic side view of a propel»
ler, the in?ow windbeing substantially parallel
peller with blades, the geometrical pitch of which
to the axis of rotation of the propeller.
is adjustable in such a manner that the reduc-'
Fig. 2 is a diagrammatic plan view of a propel
ler showing the chordwise components of said
relative wind in the disc of rotation.
Fig. 3 is a diagram showing the components
tion of the el?ciency under varying operating
conditions, which otherwise results in propellers
whose combined average pitch and geometric
pitch is not adjustable, is minimized. In other
words, the amount of twist from root to tip of
the blades as well as the amount of pitch of the
blades, is adjustable at any time so as to ap
proximate closely the optimum e?iciency for
various imposed operating conditions.
>
Another feature of the invention is to provide
a propeller, the blades of which are made of rela
tively adjustable blade elements and. to provide
connection between the blade elements and a
mechanism for adjusting the relative adjust
ment of the blade elements to obtain a desired
geometric pitch.
Another object of the invention is to provide
I,
of the relative wind on a blade element.
Fig. 4 is a diagrammatic side view of a propel
ler with the in?ow wind at an angle to the pro
'» peller axis.
Fig. 5 is a plan view of the propeller showing
the chordwise components of said inclined rela
tive wind in the disc of rotation.
Fig. 6 is a ‘sectional view of a propeller blade
and its mounting, the propeller blade being made
of a pair of blade elements.
Fig. 7 is a sectional view, the section being
taken
Fig.
taken
Fig.
taken
Fig.
on lines 1—'! of Fig. 6.
8 is a sectional view, the section being
on lines 8—8 of Fig 6.
9 is a sectional view, the section being
on lines 9—9 of Fig.6.
10 is a plan view partly broken away of a
a propeller with blades of adjustable geometric
pitch. and to provide a mechanism which will
vary the geometric pitch of the propeller blades
individually throughout each revolution of the
blade with two ?oating blade elements between
propeller so as to substantially compensate for 40 the root element and tip element.
cyclic variations of the relative wind, or to in
Fig. 11 is a sectional view taken on lines I I—l l
duce varying thrust distribution at desired points
of Fig. 10.
in the cycle of revolution; by such cyclic adjust~
Fig. 12 is a sectional view taken on lines 12-42
ment, a higher overall efficiency of operation is
of Fig. 10.
achieved, control of the aircraft is obtained, vi
Fig. 13 is a sectional view, the section being
bration of the propeller or rotor due to oscilla
taken on lines l3--l3 of Fig. 10.
tion of its blades about their respective hinged
Fig. '14 is a sectional view, the section being
axes or due to de?ection of its blades away from
taken on line I 4-14 of Fig. 10.
a normal radial position is reduced to a mini
Fig. 15 is a partly sectional ., and fragmental
mum; and undue strains and stresses on the air
view of a blade of my construction with several
craft are obviated.
?oating blade elements between the root ele
I am aware that some changes may be made
in the general arrangements and combinations
of the several devices and parts, as well as in
the details of the construction thereof without
ment and tip element.
'
In connection with the usual type of propel
lers, the blade of the propeller may be considered
to be torsionally rigid about its radial axis from
2,627,928
3
root to tip and any change in the complete blade
setting with respect to the disc of rotation will
impose a varying degree of e?ectiveness of the
blade elements located at progressive points along
the radius. Usually a blade in the past has been
designed so that under one particular set of con
ditions involving required thrust, rotational speed,
velocity of incoming air, and direction of that air,
it will give a certain peak e?iciency with respect
to the power input from the motor. This condi
tion is illustrated in Figs. 1 and 2, wherein I show
a graphic illustration of a propeller I under uni
form and constant in?ow velocity with the direc
tion of wind parallel to the axis of rotation as
indicated by arrows 2. Under these conditions,
the propeller rotating at uniform and constant
velocity of revolution in the disc of rotation in
dicated by the broken line circle 3 in Fig. 2 and
in the direction of the arrow 4, the vectors 6
represent substantial air velocity impinging on
blades and due to rotation only.
In any propeller it is essential to appreciate
that for ideal efficiency, each blade and every
element in each blade must be contributing equal
ly to the required thrust. At fair approximation
of ideal blade loading may be achieved provided
the propeller is so designed that the blade ele
ments of the blade work substantially equally
from a point as close to the axis of rotation as
practicable. Every propeller must be considered
in the light of two separate and distinct velocities,
namely the velocity of the various blade elements
in their plane of rotation and the air velocity
passing through the disc. This is represented by
a simple vectorial diagram in Fig. 3, wherein a
blade element of the propeller l is shown in rela
tion to the two contributing velocities at right
4
the rotational velocity, and subtractive when
the rotational velocity and the disc component
of the air velocity are in the same direction.
The vectors or arrows M in Fig. 5 represent air
velocity due to rotation only. The other vectors
I6 represent size and direction of the horizontal
component of the in?ow air velocity impinging
on the blades at blade azimuth positions B and C
respectively where they are maximum. This is
a chordwise component on the blade. As the
diagram in Fig. 5 shows, this chordwise compo
nent has decreased to zero at blades azimuth po
sition A and A’, and varies as the sine of the
azimuth angle 1// measured from the “down wind”
position of each blade respectively on its cycle
of revolution. The graphic illustration in Fig. 5
is substantially to illustrate the true condition
which exists with respect to the chordwise com
ponents when the direction of in?ow wind is not
parallel with the axis of rotation, and to illus
trate that except for two instantaneous posi
tions during a cycle of revolution, the geometric
pitch of each blade should be changed at each
instant. A mean condition from which to deter
25 mine the basic geometric pitch occurs only when
a blade is pointing either into or away from‘ the
relative wind direction, because then the chord
wise component of the in?ow wind is zero.
With a blade at position C in Fig. 5, the point
I‘! is a point of zero net, or e?ective, chordwise
velocity in the disc; toward the blade-root the
net chordwise air direction is reversed. There
fore, the space or distance X is a measure of the
minimum range of positive chordwise velocities
in the disc, and the space or distance Y is a
measure of the maximum range of negative
chordwise velocities in the disc; that is, when a
blade is at any other cycle position than at C.
a greater percentage of the blade span is operat
1 represents the velocity of the blade element
parallel with the disc of rotation of the blades 40 ing in the range of positive chordwise velocities
in the disc. This particular condition exists es
indicated by the line 8. The vertical line 9- rep
pecially in connection with helicopters or auto
resents the velocity of in?ow. It is to be noted
gyros, or helicoplanes and the like where the in
that the blade in Fig. 3 is set for zero lift. The
?ow wind direction is often much closer to be
vertical broken line ll indicates the axis of the
ing parallel with the propeller disc than with the
rotation of the propeller in Fig. 3. Under these
axis of rotation and correspondingly the varia
conditions the resultant velocity indicated by the
tions in geometric pitch per revolution should be
line '2 in Fig. 3 will give the magnitude and di
made much greater for optimum ef?ciencies.
rection of the air?ow which must meet the ele
In adjustable pitch propellers heretofore used,
ment of the blade. This resultant will vary in
magnitude and direction for each blade element , adjustment is made in the effort to adapt to the
varying conditions of operation by the turning of
from tip to the innermost element because of the
the entire blade; that is all the blade elements
elements’ changing speed in the disc of rotation;
turn as a rigid unit. Each such blade however,
when a blade is designed to anticipate these ra--v
is designed to operate with the greatest ef?ciency
dially varying directions of air, the innermost
at one given condition of ?ight of the aircraft
blade element is set at a much greater angular
or at one given condition of performance in any.
setting than the element at the tip. Such an
other device where such propellers may be used.
gular settings ideally should be such as to give
When there is a change or departure from the
to each blade element a setting where it will offer
condition for which the geometric pitch of the
the least resistance to the resultant air for the
required thrust. This angularly differential set— 60 blade was designed then there is a very substan
tial decrease in the e?iciency of the propeller.
ting of the blade elements from the root to the
Adjustments heretofore used, namely the turning
tip of the blade, is usually called the basic geo
of the rigid blades endeavored to reduce slightly‘
metric pitch, and is expressed in distance per
this loss of e?iciency at varying conditions, but
revolution of the relative movement between the
the loss still remains great. In my invention the
air and the propeller.
basic geometric pitch of the blade is varied pro
In Figs. 4 and 5 I show graphic illustrations
gressively within extreme limits so as to compen
of the propeller l where the uniform and constant
sate for the variation of conditions, and to pro
in?ow velocity as indicated by the arrows I3 is
vide a propeller which will minimize decrease of
not parallel to- the axis of rotation. As partic
efficiency of the propeller operation under varying
ularly indicated in Fig. 5, the component rep
conditions or on the variation of the direction
resenting the air velocity which lies in the pro
of the in?ow wind. L1 connection with propel
peller disc of rotation must be added to or sub
lers of the type which are subject to cyclic
tracted from the blade element rotational speed,
changes of relative wind, I additionally adjust
at each increment of radius of the blade. It will
the geometric pitch of the blade to compensate
become additive when the air velocity opposes
angles to one another. The horizontal arrow line
2,627,928
for such cyclic changes. In this manner high
ef?ciency of the propeller is accomplished not
only on one given condition of operation, but also
under varying conditions within predetermined
extreme limits.
In carrying out my invention, in the embodi
ment shown in Figs. 6 to 9 inclusive, I make use
6
described. On this spar 44 is journaled a root ele
ment 46 in the manner shown in detail and de
scribed in Fig. 6. A tip element 41 is spaced radi
ally from the root element 45 and is secured to
the outer end of the spar 44. In the space be
tween the root element 46 and the tip element
41 are two transverse ?oating blade elements 48.
of a spar I 8 which is journaled in a suitable spar
All the blade elements are adjustable about the
root journal E9 in a hub extension 2| of a hub
axis of the spar 44 and are substantially at right
not shown. The hub extension 2| may be 10 angles to said axis. Each ?oating element 48 is
mounted on a propeller hub rigidly or it may be
journaled by sleeves 49 on the spar 44. The ad
articulated in any suitable manner. The num
jacent ribs 5| of the adjacent blade elements di
ber of hub extensions 2| depends upon the num->
verge toward the respective edges of the blade so
ber of blades on a propeller. Each blade in a
as to provide a space for the elongation or short
propeller being of the same structure as the 15 ening of said edges according to the respective ad
others, the showing of one blade and its descrip
justments of the selected geometric pitch. The
tion will sunice and apply to the other blades of
space between the end ribs 5| of the adjacent
the propeller. The blade in this illustration is
blade elements are covered with elastic skin 52
shown as made of a root element 22 and a tip
so as to provide continuous blade surface and
element 23. Each element is constructed in any 20 blade edges at the various adjusted geometric
suitable manner, for instance with ribs 24 shaped
pitch. Yieldable resilient resistance is introduced
as shown in Figs. 8 and 9 and covered with the
between the adjacent blade elements, and for the
usual skin 23. The ribs 24 of the root element
purpose of illustration this resistance is again
22 are mounted on a sleeve 2'! which sleeve in
shown in the form of leaf springs 53 connected
turn is journaled at 28 on the spar [8. A collar 25 to the end ribs respectively in the same manner
29 on the spar l3 resists the centrifugal thrust.
as leaf spring 39 in the form described in connec
The tip element 23 is secured by suitable pins or
tion with Fig. 6.
the like at 3| to the outer portion of the spar
A spar lever 31 is connected to the spar 44.‘ A
I8. The adjacent ends of the root element 22
sleeve lever 38 is connected to the sleeve of the
and the tip element 23 have ribs 32 which are 30 root element 43. The intermediate blade ele
respectively divergent to each other both toward
ments 48 are ?oating about the axis of the spar
the leading edge 33 and toward the trailing edge
44 so as to conform to the contour as determined
34 of the blade. The spacing between the adja
by the relative adjustments of the root- element
cent ribs 32 of the root element 22 and of the tip
46 and the tip element 4?. Thus by turning the
element 23 is covered with suitable elastic skin 35 levers 31 and 33 by suitable adjusting mecha
35, so as to provide for continuous blade surface
nism, the root element 46 is turned to a given or
and continuous leading and trailing edges at any
selected angle about the axis of the spar 44, and
relative adjustment of the root element and tip
the tip element 41 is turned to a different angle
element at various geometric pitch.
as may be required for the desirable geometric
The adjustment of the geometric pitch of this 40 pitch. The elastic skin 52 and the leaf spring
blade is accomplished by suitably turning the
53 move the intermediate ?oating segments or
root element 22 and the tip element 23 in their
blade elements 48 about the same axis and to such
respective directions and to a desired degree for
the selected geometric pitch. For accomplishing
angles of adjustment as to form a continuous
blade surface and blade edges conforming to said
this adjustment I show in this illustration a spar 45 geometric pitch determined by the relative ad
lever 37! suitably keyed or secured to the spar and
justment of the root element 43 and the tip ele
a sleeve lever 38 connected to the sleeve 21. By
ment 4?. Fig. 11 shows the angular adjustment
suitable adjusting mechanism, illustrative em
of the root element 43. Fig. 14 shows the adjust
bodiments of which are hereinafter described,
ment of the tip element 4?. Figs. 12 and 13 show
these levers 3'1 and 38 are turned so as to respec 50 the corresponding angular adjustment or dis
tively turn the spar l3 and the sleeve 21 and the
placement of the ?oating elements 48 as deter
element 22 and the tip element 23 therewith, to
mined by the relative positions of the root and
the relative adjustments required fora desired
the tip elements and as additionally determined
geometric pitch. For additional control of the
in this instance by the restraint imposed by the
adjustment, a yieldable and resilient resistance 65 connecting elastic skin 52 and springs 53. In a
is introduced between the relatively adjustable
certain geometric pitch adjustment of the blade
blade elements. In the present illustration this
the relative angles of the four blade elements of
is shown in the form of a leaf spring 39, one end
this form would appear in sections as shown in
4| of which is attached to the rib 32 of the root
Figs. 11 to 14.
element 22 at the trailing edge 34 of the blade. 60
The embodiment of the invention shown in Fig.
The other end 42 of the leaf spring 39 is slidably
15 is a multisegment blade with any desired large
held in a slot 43 in the inner rib 32 ofthe tip ele
number of floating blade elements 54 between the
ment 23 so as to allow for the elongation or short
root element 53 and the tip element 57!. The root
ening of the trailing edge according the rela
element is mounted on a sleeve 58 which in turn
tive adjustment of the blade elements to the 65 is journaled on the spar 44. The tip element 51
selected geometric pitch. If the blade elements
is ?xed to the outer end of the spar 44. The in
are turned relatively to one another this turning
ner end of the spar 44 is journaled in a hub as
movement is resiliently resisted by the leaf
heretofore described. In this instance there is a
spring 33.
'
continuous elastic skin covering from the tip ele
Another embodiment of my invention is shown 70 ment to the root element. At the leading edge of
in Figs. 10 to 14 inclusive, in which is shown a
the blade reinforcing links 59 are provided which
propeller blade with a larger number of seg
fit into suitable slots on the ribs of all adjoin_
ments or blade elements and with an irregular
ing blade elements or segments. The outer sur
plan-form. This embodiment also includes a spar
faces of the blade are contoured to suitable air
44 journaled in a hub in the manner heretofore
foil section to give support to the elastic skin over
2,627,928
>
the'high pressure regions. - In this form, as in the
previous forms, a yieldable resistance may be in
troduced in addition to the elastic skin, and is
illustrated herein in the form of leaf springs 51
connected to adjoining blade elements in the
manner heretofore described. A spar lever 31 is
connected to the spar 44. and a sleeve lever 38 is
connected to the sleeve 58 of the root element 56
8
tive adjustments of the root segment and the tip
segment, and resiliently yieldable means at said
?exible cover connections engaging the adjacent
segments to yieldably determine the relative piv
otal movements of said intermediate segments.
-
ALEXANDER S. MULLGARDT.
REFERENCES CITED
The following references are of record in the
for the relative adjustment of said root element
?le of this ‘patent:
56 and the tip element 51 of the blade, respec
tively. The intermediate ?oating blade elements
UNITED STATES PATENTS
54. will assume angular positions as determined byv
Number
Name
Date
the relative positions of the root element 56 and
1,449,129
Pescara __________ __ Mar. 20, 1923
the tip element 51 and by the degree of restraint
Pescara __________ __ Feb. 10, 1925
imposed by the elastic skin. This form is par 15 1,526,230
1,919,089
Breguet __________ __ July 18, 1933
ticularly suitable for extreme range of operating
conditions, such as those expected when a pro
peller progressively passes through autorotative,
1,986,709
2,108,417
2,162,794
2,308,802
2,329,133
2,475,121
helicopter, or helicoplane, states with either co
20
axial or off-axial air?ow.
I claim:
A propeller’ blade including a root segment, a
tip segment, and a plurality of intermediate seg
ments, a spar coaxial to all of said segments, a
Number
device to select the relative pitches of said seg
752,142
ments about said spar, ?exible covering connect
851,766
ing said segments to conform to the amount of
spiral twist of said blade according to the rela
Breguet __________ __ Jan. 1,
Stanley __________ __ Feb. 15,
Asboth __________ __ June. 20,
Bariing __________ __ Jan. 19,
Peed _____________ __ Sept. 7,
Avery _____________ __ July 5,
1935
1938
1939
1943
1943
1949
FOREIGN PATENTS
Country
Date
France __________ __ Sept. 1-6, 1933
France __________ __ Jan. 15, 1940