ROTOR HUB DESIGN FOR A COMMERCIAL RAMJET HELICOPTER
by
WILLIAM F. MOODY, JR.
SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
BACHELOR OF SCIENCE
at the
MASSACHUSETTS
INSTITUTE OF TECHNOLOGY
1954
Signature of Author
_
Department of Aeronautical E6gfneering, May
Certified bj
2r~, 1954
Thesis Supervisor
ROTOR HUB DESIGN FOR A COMMERCIAL
RAMJET HELICOPTER
by
WILLIAM F. MOODY,
JR.
Submitted to the Department of Aeronautical
Engineering on May ~, 1954, in partial fulfillment of the requirements for the degree of
Bachelor of Science.
ABSTRACT
The rotor hub design is considered for a small
A design proposal is
two-place ramjet helicopter.
presented here which embodies a detail design of
the rotor hub for a flapping-blade type rotor. The
advantages and limitations of this proposal are
discussed.
Then, the rotor hub and its component
parts are designed to meet the load requirements of
a helicopter in a rolling pull-out flight condition.
Thesis Supervisor:
Title:
Professor
Professor
Otto C. Koppen
of Aeronautical
ii
Engineering
ACKNOWLEDGMENTS
The author wishes to extend his thanks and
appreciation
to:
Professor
gave generously
the problems
of his time and energy to help with
as they arose;
Professor
illuminating
Otto C. Koppen, who as thesis advisor
Raymond Lewis Bisplinghoff,
discussion
on the background
for an
and heli-
copter design loads criteria;
Assistant
Professor
advice about drafting
Frank K. Bentley
for his
and detailed problems.
iii
TABLE OF CONTENTS
Page
Abstract. • • • • •
... . . . . . .
......
i1
Acknowledgments •
• • • • • • • • • • • • • •
iii
Chapter I.
The Design Problem ••••
Chapter II.
Chapter III.
Bibliography.
The Preliminary Design .
The Design Solution.
• ••••
· ••
iv
• • • • • • • •
1
• • • • • •
4
• ••
• • • • • •
15
43
.LIST OF FIGURES
Page
Figures:
.....
2. Fabricated Rotor. Blade • • . . . . .
.....
3. Flapping Blade • • ~ •
4. Forces on Blade Element. . . . . . .
.
5. Load Distribution. . . . . . .
......
6. Main Spar . . . . .
I•
Rotor Blade.
• • • • •
..
Flapping
8.
Control System Gymbols
9.
Second Stage Gymbol Mount Connection
• • • • • •
Angular Roller Bearings •••••
11.
Steep Angle Tapered
12.
Hub Cross-section.
..... . ..
1.
Assembly
2.
Shaft
3.
Collective
4.
Gymbol
5.
Thrust
6.
Fuel Cell
7.
Rotor Hub
Pitch
Journal
v
Bearings
..
..
...
....
•
9
11
12
Hinge Shaft Connection.
10.
7
16
18
20
7.
Design Drawings:
..
..
21~
27
30
34
38
4J+
CHAPTER I
THE DESIGN PROBLEM
1.10
General Description
of Helicopter
The Hiller Hornet made by Hiller Helicopters,
place ram-jet helicopter,
for the two-place
specifications
a two-
is chosen as a typical helicopter
ram-jet helicopter
and performance
class.
The general
data for the Hornet are used.
(See Table I.)
The ram-jet engine used in this design proposal
ferent from the one used in the Hornet.
engine was developed
date t~day.
in
1946-47
the research and development
for a B.S. degree in
1954
The Hiller ram-jet
and is considered
An engine of the required
is dif-
out-of-
size was taken from
work by F. Martins
in the Mechanical
in a thesis
Engineering
Department.
1.20
Design Requirements
Designing
a rotor hub entails three basic problems:
first, accommodating
an internal means of transferring
from the hub to the blade; second, integrating
and/or feathering
third, designing
blade connection
All of which makes the problem
1
a flapping
from the hub to blade link;
the hub to withstand
forces imposed when one considers
fuel
the large centrifugal
a ram-jet type operation.
interesting,
to say the least.
TABLE I
RAM-JET HELICOPTER
SPECIFICATIONS
AND PERFOm~ANCE DATA
General Dimensions
Rotor blade diameter
Height
24'
7'
13'11"
Fuselage length
Power Plant
2
Number
ram- jet
Type
Weight
10#/engine
Thrust
45#/engine
Weight
Empty
Gross
Useful load
Performance
Normal cruising speed
70 mph
Top speed
80 mph
Ceiling (full gross load)
12,000'
1100 fpm
Rate of climb
2
Structural
1.21
Integrity
The rotor hub and its component
receive
the limit loads specified
parts must be able to
without
permanent
tion and must be able to withstand
the most
bination
failure.
of ultimate
these requirements
1.22
loads without
without
exorbitant
weight
critical
deformacom-
It must satisfy
penalties.
Accessibility
The rotor hub and its accessories
for maintenance
and repair purposes.
3
must be available
CHAPTER II
PRELIMINARY DESIGN
2.00
Initially,
an analysis will be made in the preliminary
design to calculate
acteristics
and design the various
rotor blade char-
in order to establish the loads requirements
some semblance
of arrangement.
The performance
and
and specifi-
cations data from Table I will be used as a basis for the
preliminary
design.
2.10
The disc area
~ =
In general,
=
= "Trtzi = ~
Ad
bc
=
= 4.53
rotor solidity
the most favorable
Sa
ratio
operating
conditions
will
of lift is constant over
It is obvious that to obtain this one must
have twist and tapered blades.
ters it is economically
However,
feasible
case for the preliminary
Most present-day
for small helicop-
to use constant
constant blade angle type rotor blades.
to 0.065.
=
lrR
be obtained when the distribution
the rotor blade.
sq. ft.
chord-
This will be the
design consideration.
designs have
A solidity factor,
~
4
~
=
in the range from 0.04
0.052 will be used.
() =
However,
=.
2c
-.r .12
= .981
c
Ram-jets
=
.052
'=
c
=jfb
11.75"
are most efficient
at high mach numbers.
one wants to avoid the drag rise and high centrifu-
gal forces encountered
as this, one must make a compromise.
NACA
.68 mach
23012 occurs near
ditions,
In such a case
at high tip speeds.
The drag rise for a
number.
this is 750 feet f.p.s.
At sea level con-
The blade will be designed
to rotate with a tip speed of 600 ft/sec which is even a
'little high for tangential
velocities.
VT
=
600
= R.n.
iL
'=
600
12
=
=
RPM
50 rps = 3000 rpm
=
radians/see
3000 = 478 RPM
2lf
Disc loading
=
280
=
2.16#/sq.ft.
which is fairly good
according to current
designs (2.2 - 3.5)
453
Power loading
=
Figure of Merit
T
P
=
=
=
~
M =
which also agrees
quite closely with
current .Hypes
(10 /'HP)
14.3#/HP
14
Ta;;:
P
If.R2
ip
=
PL
=
14.3~
D L
.002378
.5
=
431
2.20
Using the results found in the preceding work and
verifying the results with PL, TR, and M with current designs,
a preliminary design of a rotor blade' will be conducted.
See
Figure 1.
CFm = centrifugal force moment = 2/3 (R MJL2R,G]
where MR = blade mass
CFm = 2/3 • 12 33.25 • 122 x 502 (3
32.2
°
=
l2 Ox 20.65 x lo3fJ'.
Lift moment = 3/4 R x lift (for no twist, no taper)
=
2/3 R.
e
9~0
= 4 x 980 =
=
=
coni~g angle
980
3,920#
*oblade lift
CF
*x¥
2,5L~0
2.30
=
= 4x
x 12
Rotor Blade Preliminary Design
The rotor blade is considered and analyzed in order that
its weight may be obtained for the load conditions.
The
rotor blade and ram-jet engine are considered as point masses
located at 1/2 Rand
R respectively.
Using the chord found in section 2.10 and the diameter
from Table I, a rotor blade is designed using an NACA 23012
airfoil as a basic plan form.
The blade is fabricated; that
is, it will consist of a main steel spar, wooden ribs, and
6
L..
D•.~
I
f
I::: ~,~~lift
.I'\.. ~
l)i$t..",'o.,+-iotl
I
Figure 1:
ROTOR BLADE
7
skin.
Birch and birch plywood are used for this purpose.
See Figure 2.
R
=
12'
c
=
11.75"
=
.98
1
NACA 23012 Airfoil
Birch wood and ply =
45#/
cu.ft.
Area of cross section = 10.85 sq. in. which
was determined graphically.
=
Volume of a blade
10.85
x 111-4= 1550 cu. in.
The spar is a 1-1/4 OD 4130 steel with a tapered section thickness from .180 - .06.
The weightav•
of such a
span = 1.93#/,
See Figure
quarter chord.
4.
Built up blade with the spar at the
Half the effective area of the wood cross
section is in the leading edge to bring the c.g. to the
quarter chord.
Area in leading edge
Area behind
1/4
c
=
=
3.1 sq. in.
3.1
wt. of wood - l22Q x ~~ x
J:44
12
wt. of pipe - 121 x 1.93
Total weight of blade
2.40
=
6.2 = 23.4#
IO:"8"5
=
23.2#
46.6#
Hinge System
The advancing blade of the rotor encounters
velocities
forward.
than the retreating
Co~sidering
higher
blade as the rotor moves
first a rigid rotor, it is seen that
a sizable rolling moment would be present
8
in forward flight
8lHLT - U'P BlAne.
B\RC.H R~O \>I'l WOOD
Figure 2:
FABRICATED ROTOR BLADE
9
as a result of the difference
advancing
and retreating
in the lift produced
blade.
Two standard means are used to overcome
of lift in forward
(1)
moments
on the
flight.
the dissymmetry
They are:
The blades may be hinged at their roots so that no
can be. transmitted
through the hub.
Control
is
achieved by tilting the hub axis until the vector points in
the desired direction.
(2)
The blades may be rigidly attached
but cyclically
feathered,
ing side and increasing
decreasing
to the shaft
the pitch on the advanc-
the pitch on the retreating
side so
as to equalize the lift around the disk.
The hinged blade method
tive ease of construction
pared to the feathering
2.41
Flapping
is selected because
and simplicity
of its rela-
of design as com-
blade method.
Blades
In such an arrangement
as Figure
3, high bending stresses
which are built up in the blade root are relieved.
blades are free to rotate in any direction
of attachment,
being held in equilibrium
stant by the action of the weight,
about the point
at any given in-
inertia and aerodynamic
forces.
2.42
Forces on a Blade Element
See Figures 4(a) and 4(b) .
The centrifugal
force
weight
10
=
=
The
m.n. 2 (" co S ~ dr
wdr
Al P\U\
I.UN~E
x
Figure 3:
FLAPPING BLADE
11
10\QECT,ON
,...---1--
........
/'
/
/'.
i!tl""'"
/_-----
Q"
" ....
u\RECTION
OF
OF ROTATION
-_
"
I
./ ~ROTOR
- ... ---
bl~C.
MOTiON
dT
'\ -::-:-',t3
-'C.F:
"IME~T'A
o
o'
Figure
4:
M8
FORCES ON BLADE EL~~ENT
12
inertia
=
rmiJdr
air load
=
1 f"CJI.
By attaching
ce UT2 d('
¥
the blades to the rotor hub through a
nearly horizontal
bending moments
1(
2
delta (flapping hinge), the rolling and
are reduced.
It affects the rotor and rotor
blades as follows:
(a)
Bending moment acting on the blades
direction
of flapping hinge is eliminated
(b)
Owing to the short length
arms extending
in the
at the root.
of the supporting
from the rotor to hub to flapping hinges,
the rolling moment becomes negligible.
(c)
velocity
The blades,
owing to cyclic variation
of the
component begin to rise and fall cyclically,
that is, to flap.
The sum of the moments must equal zero about the flapping hinge.
R
M fl.hg.
=
where
0
=.n. 2
sin~
MT = moment
COSft.fa
R
2
mr dr
+
13
jo mr2dr
(1)
due to air loads
Mw = moment due to weight
13 =
~
mation
usually
coning angle
is a small angle and the small angle approxi-
can be made; thus
sin 13
=,tG
cos j3
=
13
1.00
R
2
but
mr dr
=
moment
of inertia
of blades
~
equation
••
(/3
2
-13.ll- )
Rotor Control
2.50
Control
MT '" Mw
in Forward
the tip-path
connected
0
in any flight
operate
or the cyclically
where
through
in which
there is no power
the shaft, a teetering
the whole
shaft with the hub
with respect
and maintain
varying
1n-
in space.
This type of system is simple to control
construct,
condition
of the rotor thrust vector
plane
is teetered
=
Flight
helicopter
difficulties
axis type of control
rigidly
-
orientation
With the ram-jet
transmission
I
of the helicopter
valves the proper
and therefore
(1) may be written
to the fuselage.
and is easier to
than either the tilting hub
blade types.
CHAPTER III
DESIGN SOLUTION
The critical maneuver
conditions
tor of
and loads is a rolling pull-out
5.
This was determined
Professor
Department,
tions which determine
the design
with a load fac-
through discussion
Raymond L. Bisplinghoff
Engineering
3.10
which determines
with
of the Aeronautical
considering
current
design condi-
the design loads.
Load Calculations
First,
the rotor blade will be analyzed
loads it imposes on the hub.
at ~ =
a point mass is concentrated
trifugal
See Figure
6'
5.
to see what
For the blade,
to calculate
the cen-
force of the blade.
at R
The rotor is located
C.F.
=
mR.l1.
=
12'.
2
for blade:
C.F.'= 46.6 x 6 x 502
=
20,600#
32.2
for ram-jet
engine
x 12 x 502 = 9,300#
C.F. = 10
32.2
total C.F. force = 30,000#
A lift force of 490# is also applied
a drag force.
However,
to the rotor plus
the lift and drag forces are very
15
Figure
5:
LOAD DISTRIBUTION
16
small compared to the centrifugal
neglected
3.20
force; therefore
they are
in the hub design.
Detail Design of Main Spar in Rotor Bhde
As mentioned
fabrication
previously,
design.
the blade is constructed
on a
A steel spar is used to carry the loads
with a wooden structure built about it to insure the proper
aerodynamic
characteristics.
The leading
with plywood being used from the quarter
trailing
edge.
See Figure 2.
edge is solid birch
chord back to the
The reason a solid leading
edge is used is to move the center of gravity
section to be approximately
at the quarter
of the cross
chord.
Calcula tions:
See Figure
6.
The outside diameter
p
=
30,000#
=
One wants a Margin
a connection.
of the spar is 1.25".
C.F./blade
of Safety of .15 or better for such
The tensile
strength of Lt130 steel, which will
be used, is given as Ftu which is the ultimate
However,
one is interested
in designing
tensile
strength.
for the yield tensile
F
1:5 ·
strength which is equal to approximately
Therefore,
calculating
the thickness
at the root which would be sufficient
of the wall pipe
to carry the centrifu-
gal loading,
Ftu for 4130 steel - 90 Kips
A
A
=
=
P
f
heat treated
which was derived from f
=
P
A
30,000 x 1.5 x 1.15
90,000
17
s
.575 sq"
18
but
= -.r
A
( Do
2
2
- Di )
~
where Do
=
outer diameter
Di
=
inner diameter
.575
=~
4
solving
=
t
3.21
2
(1.252 - Di )
Di
=
.91"
=
thickness
1.25 - .91
=
.17"
2
Detail Design of Flapping-hinge Shaft Connection
See Figure 7.
P
=
M.S.
f
=
for ultimate
=
A
=
Lt5,000
.15
=
f
xl. 5 = 30,000 xl. 5
P
45 x 1.15
A
4130 heat-treated steel is also used for this
connection.
Ftu • 90 Kips
A
= 45
x 1.15 = .575 sq"
90
The outside diameter of the shaft = 1.5"
2
A
.575 sq"
(1.5 - Di2)
=
=""
4
solving Di
t
3.22
=
Do - Di
2
=
=
1.235"
1.5 - 1.235
=
.13"
2
Bolt Size
Pu
=
45,000#
One bolt per hinge will be used.
in double shear.
These bolts will be
Using ANC-5, table 2.611(a) for standard
19
20
bolts heat treated
to 125 Kips, AN-12 is tried.
Fs • 33,150 x 2 • 66,300 for double
= t~,300
,000
MS
1
shear
= .47
An AN-12, which is a bolt 3/4" in diameter,
will be
used.
3.23
Wall Thickness
A factor
vibration
of safety of 2 is used to take care of shock,
and rotation
in this connection.
Using 4130 AN-QQ-5-685
type,
MIL-T-6731
=
Fbru
(a)
Designing
for bearing
=
f
140 Kips
n • MS • t • d · Fbru
=
45,000
1x
2 x 2 x 3/4 x 1!~0,000 x t
solving for t
=
t
(b)
Designing
.324
ft
for tear-out
P
2tx
x
=
In
p
=
45,000
= 22,500#
2
:fsu =
22,500
= 34,000
2 x .324 x 1
:fsu = 65 Kips :from ANC-5
M.S.
=~ -
1
=
.91
21
(c)
for tension failure
Designing
See Figure 7 (b) •
P
(w-d)t
=
ft
(2 -
ftu
M.S.
=
3/4)
55,$00 psi
x .324
100 Kips from ANC-5
=
100
-1
~
..b.30
=
22,$00
=
=
.80
Method of Control
A teetering
control.
axis system is selected for the method or
The rotor shaft is tilted with respect to the
fuselage.
A set of two gymbols, perpendicular
the Z plane,
is used to allow the rotor shaft to tilt in the
X and Y directions.
to restrict
to each other in
Limits
are incorporated
the range of teeter to
70
in the design
to the left or to the
rear and to a limit of 150 tilt forward.
The bearings which make up the gyrnbols have friction
locks and adjustors
which can be tightened
fied degree of friction
the flight condition
3.31
in the control system which enables
to be maintained
flight control condition
to give a speci-
and a "hands-off"
realized.
Control System Gymbo1s
The lift is equal to the weight times the load factor
for the rolling pull-out
condition.
carries this load.
22
Each set of gymbols
=
Load
1000 x 5 : 5000#
=
Load ultimate
=
Load/gymbol
5000 x 1.5
=
7,500
2
=
7,500#
3,750#
See Figure 8.
The gymbol shaft is in single shear.
2.6111(a)
Using table
ANC-5 for AN-5, 5/16" bolt,
=
fs
7360 for heat treated to 125 Kips
=1.L12Q-
M.S.
1
=
3,750
AN-4 was examined
fore, 5/16"-diameter
the lateral
3.32
(a)
and found to have M.S • ...c.. .15.
gymbol bearings
and longitudinal
Thickness
There-
will be used for both
gymbols.
of Gymbol Mounts
For bearing
see Figure 8.
4130 steel is used for the
gymbol mounts.
Fbru = 140 Kips
fu • n • M.S.
=
fu
3,750
=
• t • d • Fbru
1 x 1.5 x t • fox 140,000
solving for t
t
Actually,
employed
(b)
=
.0573"
in the design a much thicker gymbol mount is
to support the bearings
Designing
for tear-out
- Longitudinal
Control
D -= 5/16"
Pu
=
3750
t = 1"
Y -= 11
32
for the gymbol.
23
Gymbol Direction
Figure 8:
CONTROL SYSTEM GYMBOLS
8.
See Figure
=
fsu
Pu
D • 2
= 35
fs
Kips for
=-&
(c)
Tension
4130
- 1 >"»
= ~
M.S.
.720
Designing
=
t
= .125"
not critical
1 »))
psi
1
- Lateral Gymbol Direction
Control
3/4"
=
=
fsu
Pu
2 Ox
=
=
3750
22 20
1
=
1.75
failure
=
P
(w-D) t
--
( 1.
=
95,000
M.S.
~,720
-
.312)
=~27,
20,000
-. ='"7
5=--'x~2=--x-.~1"=2-=S
55,000
M.S. =
ft
psi
8.
x
ft
-
for tear-out
See Figure
Tension
...
1
= 720
3,750
~(5~.~5~-~.~31-2~)
=
p
1(c)
3750
failure
(w-D)t
~b)
=
3750
2 x 1 x 172
•
•x
= 27,500
1
00
25
=
psi
2.45
psi
3-33
Second Stage Gymbol Mount Connection
See Figure 9.
(a)
Number of bolts required:
from AN-c5
table 2.6l11(a)
two AN-4
fs
=
1/4" dia. bolts for each connection
3,680
M.S.
=
3,680
3,750
= .965
- 1
2
From the previous work, it is obvious that tension
failure investigation
and tear-out failure investigation
not necessary because these conditions
(b)
are
are not critical.
For bearing
fbu
3,750
=
34,800 psi
=
2
1.15xl.5x.125x.25
fbu
=
140
M.S.
3.34
=
l~
1
- 1
=
3.04
Gymbol Mount to Shaft Connection
See Figure 8.
The shaft and the gymbol plate are threaded with a
standard American 8-pitch thread series -8N
ASA Bl.I-1949.
Size 2-1/2"; basic diameter 2.5000"; lead angle at basic pitch
57 I; minor diameter internal threads
diameter ~,
stress area
=
4.4352 sq".
26
=
2. 3647;
Figure
9
SECOND STAGE GYMBOL MOUNT CONNECTION
27
3.35
Shaft Wall Thickness
The shaft is made of 4130 steel.
ftu
=
90 Kips
Pu
Aeff.
where Aeff. =
=
lr (2.52
=
Aeff.
4:
Di
t
=
7,500
90,000
f[
2
- Di
2
)
.0834
2
- Di )
=
~6. 25 - .20
lr
=
~6.l4
=
6.25 - .106
= 2.48"
.Ollt
=
The shaft wall thickness
is not critical in tension.
The depth of the threads plus a marginal
ness is the factor which determines
3.40
(Do
effective wall thick-
the shaft wall thickness.
Bearings
There are extremely high loads in tension on the rotor
spar, hinge and hub which consitute
one realizes that a collective
a bearing problem when
pitch control requires
a hinge
which must be rotated or pitched.
3.41
Bearings
Ballor
for Hub System
roller bearings
a set of hardened
steel rolling elements.
ments usually roll b~tween
although
support a loaded moving part on
These rolling ele-
two smooth hardened
steel rings,
in some cases the rolling elements may roll directly
on the shaft or housing bore.
A cage or a separator
28
is used
to keep the rolling
pitch
elements
spaced about the bearing
circumference.
Standard
changeable
rolling bearings
have low friction
friction
especially
roller bearings,
angular
are relatively
The external
for Cyclic Control
is designed
pitch control
dimensions
lar contact bearings
are, using the medium
Shaft
will be analyzed
to carry thrust loads
They can
opposed.
and radial
.75"
in diameter.
capacities
of angu-
Inc., Philadelphia,
Fa.)
series for a 20 rom bore:
D = 2.047"
.787"
conditions,
thrust.
shaft is
(SKF Industries
If a radial bearing
on the bearing
is essen-
See Figure 10.
The collective
standard
to
some sliding does occur;
loads which are predominantly
=
bearings,
sliding motion
carry radial loads if two are mounted
d
than when
insensitive
contact ball bearings
This type of bearing
or combined
Anti-friction
this
is necessary.
Bearings
for application.
as
or shock loads.
lubrication
First,
of rolling motion,
by rolling motion,
Hub-shaft
and inserted
Ball and roller bearings
in rolling bearings
tially replaced
as inter-
greater when starting
speed of rotation.
Although
therefore
characteristics
overloads
obtained
is necessary.
being only slightly
under uniform
moderate
are manufactured
units and can be quickly
a unit if replacement
3.42
properly
is loaded by a thrust load under
X is a rotation
factor which
type and on which ring rotates
29
depends
relative
to the
Figure 10:
ANGULAR ROLLER BEARINGS
30
load direction; Y is a thrust factor which depends on the
bearing
FR is a radial component of
type and on the load.
the load.
is the thrust component
Fa
of the load.
For this bearing:
Y
= .48
Dynamic reference
x
=
III
=
2,700#
=
C
1
XFa
+
YFR
However, FR
=
0
Pa
capacity
The life in number of rotations may be expressed
function
as a
of the life in hours and speed in rpm.
where
C
P
fn
fh
=
=
dynamic reference
=
=
speed factor
equivalent
capacity
load
life factor
For this application,
the arm rotates with the hub at
486 rpm.
At this rpm, fn can be read off of table 12-69 in
Kent t s Handbook.
fn
but
= .41
fh = fn x C
p
= .41 x 2700
100
31
where a maximum
of 100# control force is used.
fh
=
11.1
At this fh' the rated life is found on scale 2 in section
12-69 Kent's Handbook
to be greater than 90,000 hours which
is more than adequate.
Two such type and size angular ball bearings
opposed to each other.
Oil bath lubrication
which is more convenient
are used
will be used
than grease lubrication.
The bear-
ing may be pressed on the shaft by the use of an arbor press,
tapped on the shaft by a mounting
tube and hammer,
shrunk
on the shaft after heating or forced .on with mounting
3.43
Hub-shaft
nuts.
Bearing for Main Load
The tapered roller bearing will be used in this
application.
principle
This type of bearing
of rolling cones, the elements
ways converging
bearing.
is constructed
to a common intersection
True rolling motion
upon the
of rollers and raceon the axis of the
is obtained
along the cone ele-
ments and the bearing will sustain radial or thrust loads or
any combination
of them.
This is the type of loading that exists between the hub
and shaft.
One has a large thrust loading from lift and
small radial loads due to the small changes
in the centrifu-
gal forces which may occur due to accelerations
tions of the blades in the plane of rotation.
and deceleraThese loads
are small but should be considered.
A steep angle, tapered roller bearing
the thrust load dominates,
is used because
although there are appreciable
32
radial loads.
bearings,
Combined with the steep-angle
a double-row
tapered roller
bearing will be used to provide maxi-
mum load carrying capacity
in a small space; resist thrust
loads from both directions
and maintain
mounting.
a precise
and rigid
See Figure 11.
For double-row
B
steep-angle
tapered roller bearings
= 5.513
1.4375"
C =
Radial load
=
9,880#
Thrust load
=
~8,690#
= ~O
M.S.
-
I
=.•
16
7,500
A double-row
steep-angle
tapered roller bearing,
TSS, made by Timken Roll'er Bearing
with shaft lock nuts and washers
medium fit, class 3).
side diameter,
out un~sual
Canton, Ohio,
(ASA coarse-thread
In general,
operating
Company,
bearings
Type
series,
less than 6" out-
at speeds less than 1000rpm with-
conditions, may be lubricated
soda base grease of medium
consistency.
with a lime or
The bearings
can be
purged with grease when needed.
Thrust Bearings
At low rotational
speeds at which the thrust extension
bar will rotate, shaft shoulders
or collars which bear
against flat bearing rings immersed
used.
For hardened
terrupted
may be
steel collars on bronze rings with in-
service, pressures
In multi-collar
in a semi-fluid
up to 2,000 psi are permissible.
thrust bearings,
33
the pressures
are reduced
.8
Figure 11:
STEEP ANGLE TAPERED BEARINGS
because of the difficulty
between
in distributing
the load evenly
several collars.
The fixed-wedge
film type of thrust bearing has also
been investigated.
It is obvious that part of the thrust
bearing face must be flat to permit the collar to start and
stop under load without undue concentration
The wedge-shape
film in a bearing
of pressure.
of this kind is unable to
lift its load at the low speeds that one experiences
a control system.
in such
The fixed wedge may be combined with flat
surfaces by using alternate bevels and flats with a supply
groove at the end of the bevel, in the direction
Various methods
of carrying thrust loads were analyzed
and applied to this problem.
ball bearings,
Radial ball bearings,
tapered thrust bearings,
spherical bearings
of rotation.
and collar bearings
needle bearings,
were used in the
analysis with the result that very large bearings
types or a great number of bearings
The collar bearing
described
angular
of various
in series were required.
3.L~~ offered
in section
the best result; that is, a small, compact,
simple unit.
Calculations:
The thrust collars are formed by grooving
the outside diameter D
diameter.
=
The thickness
=
=
1. 6 ~ 1. 9d where d
=
of each collar
and the distance between collars
=
s
=
Pt
35
normal
=
n
shaft
.13 ~ .16d
2w -. 3w.
number of collars required
=
w
the shaft;
Pt = total thrust on bearing
where
di
a
mean diameter
of collar
b
=
radial width of collar
p
=
allowable
bearing
pressure
d : 2.5"
D
=
2.0d
=
p
=
45,000#
di
=
1.5d
=
5.0"
3.75"
=
b = .5 x 2.5
p
=
n
=
1.25"
2,000
It5,000
=
tr 3.75 x 1.25 x 2,000
2*~l-=
1.54
Two collars will be used.
=
M.S.
Ft - 1
ft
The force which the two collars
Ft
=
2 x 3.75 x 1.25 x 2000
=
2 x 29.4 x 103
M.S. = '~l800- 1 =
,000
3.50
=
can withstand
58,800#
~
Hub Design
The size of the rotor hub is' determined
the multi-collar
thrust bearing.
cast and machined,
solid piece.
margin
by the size of
The hub will be either
forged and machined
or machined
If the part is either cast or forged,
of safety is required.
from a
a larger
The rotor hub must also be large enough to accommodate
the shaft thrust bearing and fuel cell.
be taken in design and construction
Extreme care must
of the hub.
corners must be replaced with fillets.
All sharp
The hub must be
inspected for scratches and cracks by a magna-flux
process.
Sharp corners, scratches and cracks are stress raisers and
will lead to failure under the large centrifugal
loading.
The hub is made in two half shells which are bolted
together by eight AN-8 bolts heat treated to 125 Kips.
hub itself is heat treated and case hardened
to relieve
residual stresses obtained through construction
sure a resistance
3.51
The
and to in-
to scratches from damage.
Hub Design
See Figure 12.
Area
=
6t ~ (6 -
=
l5.25t - 4t2
where t
=
3/4 -
2t) t ...
It (1 - 1/2t) t
thickness
The area must take the shear flow due to the tensile
force of 45,000#.
Ftu
where a M.S. of
.5
=
45,000 x 1.5
A
is used for a forging or casting.
is made from 4130 steel.
Ftu = 90,000
A
=
.75 sqtt = l5.25t - 4t2
t
which shows the hub thickness
= .05
is not critical.
37
Hub
z
o
H
E-i
o
~l
CI1
I
U)
U)
o
0::
o
38
3.52
Number of Bolts Required
AN-8
fs
n
-=
=
8/16" bolts
14,700
heat treated to 125 Kips
45,000 x 1.15
14,700
-=
3.52 bolts
Four bolts will be used on each side.
3.60
Fuel Cell
One great problem encountered
is the method of trans-
ferring the fuel from the helicopter
to the engine which is
located at the end of the rotor.
A fuel cell method
is selected.
It will be inclosed
in the rotor hub and will ro"tate wi th the hub about the
stationary main shaft.
and exhausted
is presented
The fuel is pumped through the shaft
into the fuel cell reservoir.
by dynamic seals enclosed
The return path
in the shaft; between
hub and collective pitch control rod and at the cell-shaft
connection.
(See Design Drawing #1.)
The cell is divided into two parts.
its fuel to its respective
engine.
Each part exhausts
The fuel is pumped out
of the cell down the hollow thrust bearing,
through the hol-
low rotor spar to the engine by the action of the large
centrifugal
3.61
forces.
Top Seal (Shaft Seal)
See Design Drawing #1.
shaft seals:
There are three basic types of
namely, leaf spring, garter spring and self-
sealing.
The sealing is compounded
operating
conditions.
The primary
39
to suit the average
criterion
is surface
At rpm = L~86 - 500 surface
speed under the sealing lip.
speed is not a deterring factor and a leaf-spring-type
shaft
seal will be used.
In order that dynamic seals may have a maximum life,
every effort must be made to have and to maintain
surfaces over which packing slides.
one machined
'l'heideal surface is
to a finish of 10 to 15 microinches
can be done by fine grinding or honing.
smoother than 10 to 15 microinches,
smooth
rms.
This
If the surface is
lubrication
of the pack-
ing becomes difficult because the surface is too smooth to
hold the oil.
Leather,
moulded
a universal
packing material,
and impregnated with wax.
as compared to rubber.
Rubber
is used.
It is
It has a very long life
(synthetic) packings
cold bond; therefore, leather packing
tend to
is better for this
application.
3.62
A flange packing
is used for the seal between the
inner part of the outer shaft and the collective pitch control rod.
(See Design Drawing #1.)
A leaf spring is used
to insure a pressure on the packing lip against the collective pitch control rod.
Size of packing - standard packing
Outside diameter
Inside diameter
3/4"
Height of packing
1/2ft
Thickness
1/8ft
A standard retaining
diameter,
1-1/2"
is used.
of leather
ring, 1/16" thick,
40
2.75"
outside
Fuel Cell - Shaft Connection
A combination
friction and labyrinth
packing is used
for the seal between the main shaft and the fuel cell.
centrifugal
The
force due to the fuel in the cell will exert a
force on the cell and will cause a tight seal and lock in
the connection.
(See Design Drawing #1.)
A garter spring
is also used on the bottom section to insure a pressure
against the seal during static conditions.
3.70
Collective
Pitch Control
The primary flight controls embodied in the rotor consist of cyclic and collective
tioned previously,
rotor-pitch
controls.
As men-
the cyclic pitch control is achieved by
direct tilting of the rotor shaft about the gymbol axes.
The rotor shaft does not rotate.
by actuating a push-pull
Collective
pitch is achieved
shaft inside the rotor shaft which
supports the collective pitch cross arms.
This action raises
and lowers the collective pitch cross arms and chan~es the
pitch of both blades through the series of control rods,
pitch links and pitch arms.
helicopter
This system is a basic type of
control and has the advantages
yet eliminating
possible interaction
of being simple,
between
cyclic and col-
lective pitch changes without the complex compensating
ages employed in a "swash-plate"
type of control.
The range of control for the collective
is from _20 angle of attack to +12°.
for autorotation
purposes.
link-
pitch system
The _2° limit is used
3.80
The ignition system consists of a small 6-8 volt re-
chargeable
storage battery,
coils and miniature
switches,
spark plugs.
engines only while the particular
slip rings, ignition
Ignition is supplied to the
engine is being started.
D~IAIL DESIGN DRAWING #1
~ecifjcations
Component Parts
1
Flapping-rotor
blade hinge
DD5
2
Collective pitch lever arm
DD3
3
Two roller bearings for collective
pitch control link
3.42
4
Collective pitch control link
DD)
5
Collective pitch control push-pull
shaft
(3/4" OD x .049 wall
6
Leaf spring-type
7
Fuel-cell
8
Fuel line
9
Fuel cell
DD6
10
Journal Rotor blade thrust bearing
DDS
11
Ro"tor hub
DD7
12
Retainer ring for dynamic seal
3.61
13
Dynamic Seal (leather packing)
3.61
14
Standard 3/4tr bushing for Collective
pitch control sod
15
TSS Timken Standard Tapered-Roller
Bearings
16
Retainer ring for Tapered-Roller
17
standard 3/L~ff bushing for collective
pitch control rod
18
Second stage gymbol fixture
19
Control system braces
not cri tical)
20
Control system plate (not designed for;
not critical)
3.62
shaft seal
retainer ring
1015 steel)
(standard 1/8trx3"
Bearings
(not designed
DL4
for;
OD)
Component
Specifications
Parts
system stick
(1" OD x
21
Control
22
Collective
pitch linkage bar
23
Collective
arm
pitch linkage bar and lever
.ol~9 wall 4130)
DD3
DD3
24
Shaft washer
3.!~3
25
Shaft lock-nut
3.43
26
Shaft
DD2
27
First stage gymbol fixture
DD4
28
Collective
DD3
pitch
control arm
BIBLIOGRAPHY
Carmichael, Colin, Kents Mechanical
Wiley Handbook Series, 1953.
Cessow and Meyers, Aerodynamics
MacMillan, New York, 1952
Dommaush, Elements of Propeller
Pitman Aero. Publications,
Engineers
Handbook,
of the Helicopter,
and Helicopter
Analysis,
1953
Marks, Lionel S., Marks Mechanical
McGraw-Hill, 1951
Engineers'
Martins, Fausto, Small Ramjet for Helico ter
Thesis, B.S. in M.E. at M.T.T., 195
4
Handbook,
Application,
Munitions Board Aircraft Committee, Strength of Aircraft
Materials, U. S. Government Printing Office,
Washington, D. C.
Nikolsky, A. A., Helicopter Analysis
John Wiley and Son, Inc., New York,
Niles and Newell, Airplane
New York, 1943
Weick, Aircraft Propeller
McGraw-Hill, 1930
Structures,
Design
43
1951
Vol. I