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Патент USA US2409311

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0d- 15, 1946.
v 2,409,310 ,
Filed Oct. 26, 1945
2 Sheets-Sheet l
Oct. 15, 1946.
Filed Oct. 26, 1945
2 Sheets-Sheet 2
H6, 6‘
Patented Oct. 15, 1946
Paul .-A.-. Piper-,1 'cuwson, Md., mam-macaw
I1. , Martin ‘Company, Middle Riven;=.,Md;,: E9691’?
poration of Maryland
Application0ct'oben26, 19'4‘5‘; Serial-‘No; 624-‘,{721
4 Claims; (01. 73-65)
'I‘l-l-is2 invention relates to= apparatus for‘ accu
rately determining the" weight’ and: center of
and in?exible‘ methods‘ of the past; andithey'vhave
ginavi-tyvr of 1a seaplane a?oat.‘ Theinvention de
Nevertheless; loading calculations: require much
bookkeeping: Thistwork must-be done'by trained:
eiiected a- gratifying- increase in flyingv safety;
this; application contains‘ all‘ of ‘ the
basic principles- set forth- in my earlier applica
tionaSér-ial No: 512,511; ?led December 1, 194-3,
. personnel,‘ and it is always- subject". ton human
error; This-work, done by; an automatic weight
and balance indicator; would not onlyr be-more
rapid‘ and accurate; but" would rel'easetrained
personnelv for othersduties'.
Forthi‘sreasorr, i‘t-has/been found‘ desirable to‘
embodies details of" improvements in the
method“ of!’ operation and» arrangement of appa
ra't'usl accordance with-the method for greater
accuracy thadwill' bev hereinafter‘ described.
The‘ proper Ioa'ding‘of aircraft has troubled
install‘ in flying‘ boats hydrostatic weight. and
designers, and‘? operators since man’s ?rst ?ight,
hala-ncee indicators which will‘ give the. gross
weight‘ and center of‘. gravity‘when-rthe‘ boat: igat
andlthe‘problembecomes more‘ and more serious
as; aircraft increase in“ size.- Modern airplanes
are'iexpe‘cted t'o'be‘capabl’e of performing a‘va'riety
of- missions. Commercial" operators ‘desire that
thelepawl‘oadibe‘changeable'at will‘ for‘ all’ possible
rest on~the~water and that are more or less.inde—
known- within‘ relatively; narrow limits‘, water: line
measurements cannot be depended‘ upon, except
in waterundcr‘ “mill? pond’” conditions.
combinations‘ of“ fuel,- cargo; and passengers; and
formilitary-use-it is-imperati-ve that fuel, bombs
andiequipment'bewaried to suit conditions exist
pendent of‘thei rough surface of’the water.v Since
the gross Weight and-center‘ of gravity must‘be
ing'‘ in‘ different’ theatres of war;
rPills;desirable ?exibility of operation has one
drawback; It‘prov-ides'the means and the temp
‘ This invention provides for an accurate deter‘
mination/ of‘ center" of gravity' and i‘ gross weight in
a seaplane; the former‘ is? the most important" be»
cause the» take-off" of ‘ the’ airplane may be seri‘—
ouslyf impaired ' if’ the center’ of’ gravity- is. not
tation to‘ovjerload the: airplane; Overload is bad
enough in» its reduction of performance» and 25 within predetermined limits. With the: device
structural; safety; but its e?ectsare-even worse
such as herein" disclosed where‘ the center of
when'extra‘ load shifts the" center of ' gravity for
gravity can be accuratelyan'd' quickly determined
ward‘J or“ aft‘ of‘ a very restricted‘ range.
it is a-simple-matter to move-or shift some ofthe
of-“Ythevi-airpl‘anel becomes» exceedingly difficult and;
extreme cases; theairplanel is unsafe-‘to fly;
Proper‘loa'dingig a matter of safety, affecting
lives andl’costly equipment; Accurateknowledge
oflithe-loadedi‘weight’ and vcent‘er‘of gravity loca
load: to bring-ithe'r-center of gravity of a seaplane
30 to‘ the proper position before a takeeoff is‘ at
tempted. This insures the proper‘ performance
or a» seaplane-and effects a- greater saving‘ in time
through eliminating unsuccessful attempts to
tion for‘ every» ?ight would eliminate one“ more
take-on‘ dueto improper loading of theseapla-ne.
The’ device; of thisinvention- does not‘take' care
of weight andl balancev changes‘ during- ?ight.
source of accidents;
' In-?yingbo'ats intended‘tocarry relativelyiarge
pay-loads; it is very important that the'center'of
gravity and‘gro'ss weight of theloaded ?ying‘ boat
be known‘ for take-off because’ of" the greater
However, With accurate knowledge of certain
factors at take-off, it is a simple matter to check
eiiect on’ the hydrodynamic and aerodynamic
the mechanical balance computer.
4.0V sumption‘with
By this invention, means is provided‘ for deter
characteristics-of the airplane:
the» past, manufacturers‘ and“ commercial
the effect‘ of? the- crew“ movement and fuel’ con
operators have recognized the importance of
proper aircraft loading; Comprehensive weight
control procedures have been established. The 45
loaded-weight’ and center of ‘ gravity are obtained
calculating‘: the‘ weight and balance effect of
mining‘th-e center of'gravity and gross'weight'of
a- seaplane-a?oat.
' Another object of this invention is‘ the"- provi
si‘on of’ equipment located andv installed‘ on the
seaplane hull to give a maximum of precision
and‘accuracy in determining center of gravity
allilchanges to-the-loasic airplane, as well as the
andv gross‘ weightwith a, minimum of‘equipment‘.
variationsin useful loadlwhich- occur: on different
Another-object. of this invention is the provi';
?ights; Loading handbooks, charts, graphs and 60 sion ofi center of gravity and gross weight indi
mechanical computers have‘ rbeen introduced to
simplify the: necessary calculations.
cating apparatus which is simple and rugged in
~ Properrecog-nition should be accorded‘ to‘ the
its construction so that it requires a minimum
of service ‘to-maintain its accuracy.
present methods‘ of- operational weight control.
Another‘object of this invention is to provide
'llhey area-vast improvementuover'the inadequate 65 apparatus: for-"determining the center of gravity
of a seaplane a?oat which center of gravity can
be readily corrected with changes in the gross
weight of the seaplane.
Further and other objects will become apparent
from the description of the accompanying draw
ings which form a part of this disclosure and in
which like numerals refer to like parts.
In the drawings:
Figure 1 is a diagrammatic plan view of a sea
the restriction of ori?ce II. It can readily be
seen that if a small amount of air from pressure
line 1 is bubbled through the water in the stand
pipe and permitted to escape from vent 15 that
the pressure required to maintain this bubbling
condition will be a measure of the depth of water
from the end of tube ‘I in the stand pipe to the
water level in the stand pipe. Since the location
of the end of tube 1 is known with respect to the
plane showing the installation of this invention. 10 hull of the craft, the pressure required to bubble
water in the stand pipe can be converted into a
Figure 2 is a diagrammatic elevational view
depth dimension which can be used to determine
showing the installation.
the water line at the point on the hull where the
Figure 3 is a sectional view through the hull
stand pipe is located.
showing the installation of the standpipe.
Figure 4 shows diagrammatically how the pres
Figure 4 is a diagrammatic view showing the 15
sure lines are connected at the panel to convert
instrument panel.
pressures in the lines adjacent the stand pipes
Figures 5, 6 and 7 show arrangements of the
into readings of center of gravity and gross
dials on the instrument panel for carrying out
weight. Line [0 in Figure 4 is connected to the
the invention.
two side stand pipes and line I2 is connected to
The seaplane shown in Figure 2 is a?oat in
the aft stand pipe. Pumps l8 and I9 are small
water with a water line indicated at l. The hull
volume electrically operated air pumps to furnish
of the seaplane 2 has mounted thereon wing 3.
small amounts of air under vpressure to the pres
Cargo loading doors 4 are located under the wing
sure lines for purposes of bubbling air through
so that the loading of cargo takes place sub
stantially in the plane of the center of gravity 25 the stand pipes. While small electrically op
erated pumps are employed for this purpose, it
of the seaplane. Pressure measuring devices 5
is obvious that any suitable source of air presssure
and 6 are located along the water line on the
may be used. Valve 20 in line In and valve 2|
hull. Pressure measuring devices 5 are located
in line I2 in the off position vent their respective
substantially in the plane of the aerodynamic
center of gravity of the seaplane. By aerody 30 lines to the atmosphere to permit draining water
out of the pressure lines. In the on position com
namic center of gravity is meant the optimum
munication is afforded between line 22 and line
location of the center of gravity of the airplane
H), and line 23 and line l2. Gage 24 is connected
and load for aerodynamic purposes. This loca
to line 22 and continuously gives an indication
tion falls within the wing and is generally ex
pressed in percent mean aerodynamic chord. 35 of the pressure in this line. Since the pressure
on gage 24 represents the pressure at stand pipes
Two devices 5 are employed in this position, one
5, the dial can be graduated to read gross weight
on each side of the hull. With this arrange
of the seaplane directly. Pressure gage 25 re
ment, one or the other will give an indication of
sponds to the differential in pressure between
draft if the hull is rocking in the water or if
one wing droops as is not uncommon in the load 40 points on the hull, one located under the wing
in the plane of the aerodynamic center of gravity
ing operation, which draft will in any case be a
and the other considerably aft of the center of
measure of the gross weight of the seaplane and
gravity. This gage can, therefore, be calibrated
load at this point. Devices 5 work alternatively,
to read the center of gravity of the sea plane
depending upon the lateral trim. The essential
feature is to have a pressure measuring device
. measured in percent of the mean aerodynamic
located substantially in the plane of the center
of gravity of the seaplane. Pressure measuring
out that while there is a de?nite predetermined
device 6 can be located toward the rear of the
chord of the airplane Wing. It should be pointed
aerodynamic center of gravity for the craft, the
center of gravity of the craft and load can vary
seaplane hull substantially on the center line of
over a limited range provided that its location is
the hull. A pipe system including pipes ‘I and B
join at T 9 and pipe I0 is in communication with 50 known so that the proper precautions may be
taken to trim the craft for take-off. Each air
the pressure gage in panel ll. Line l2 affords
' plane has an optimum center of gravity for best
communication between pressure measuring de
take-off and flying characteristics and it is
vice 6 and the pressure gages in panel II.
The pressure measuring device located at 5 _ usually expressed in percent M. A. 0. (mean aero
dynamic chord). It should be noted that the
and 6 is shown in more detail in Figure 3. A
diiierential in pressure between lines 22 and 23
stand pipe l3 consists of a tube about 11/2" in
as indicated on gage 25 is proportional to the
diameter which extends above and below the
center of gravity, but is subject to change with
water line. Stand pipe I3 has a cap l4 through
each change of the gross weight of the craft. To
which extends a pressure line which may be
either ‘I, 8 or l2. A vent I5 a?ords open com 60 interpret the indication of the center of gravity
on gage 25, the value of the gross weight should
munication between the space in the top of the
be determined. This is done by locating stand
stand pipe and the interior of the seaplane hull.
pipes 5 at points substantially in the plane of the
The pressure line extends to a predetermined
average aerodynamic center of gravity in the
point near the bottom of the stand pipe. This
point is a known distance below the designed 65 aircraft. By utilizing the pressure at stand pipes
5 due to the gross weight of the craft, a simple
water line of the seaplane for each installation
correction can be introduced into the diiferential
of stand pipe. A tube l6 affords communication
in pressure reading indicated on the dial of gage
between the bottom of a stand pipe and an aper
25 to give accurate values of center of gravity
ture I‘! in the side of the hull. This aperturev
for di?erent values of gross weight.
is about 1A;" in diameter and is intended to let
Figure 5 shows a panel having a gross weight
water flow in from the side of the hull so that
indicator and center of gravity indicator. From
the water level in the stand pipe will coincide with
the positions of the dial shown in Figure 5 the
the water level outside the hull, but that the
water level ‘in the stand pipe will be stabilized by 75 indicated gross weight would be 100,000 pounds
2,409, 3 1 O
and for an indicated gross weight of 100,000
pounds the center of gravity dial indicates that
the center of gravity would be about 35%
M. A. C.
The dial arrangement shown in Figure 6 con
templates a gross weight indicating dial and a
uring gage, said lines from said pressure respon
sive devices being connected to said differential
pressure measuring gage to indicate the diifer
ential in pressure on said gage, said direct pres
sure measuring gage being connected to said line
from said ?rst mentioned pressure measuring
dial 30 which is mounted to be turned about its
device, said direct pressure measuring gage
center by knob 3|. Indicator 32 mounted on
calibrated to read the gross weight of said sea
dial 3!] can be adjusted by knob 3| to register
plane and means on said differential pressure
with the value of gross weight on scale 33 which 10 measuring gage to correct the indication of center
correspondséto the indicated value of gross weight
of gravity in accordance with changes in gross
on dial 34. In this way the pointer on the center
weight of the seaplane.
of gravity indicator will give a direct reading
3. An apparatus for measuring center of
value of center of gravity of the seaplane.
gravity of a seaplane a?oat comprising a pair of
Figure 7 shows an arrangement of indicators 15 pressure responsive devices located on each side
for center of gravity and gross weight in which
of the seaplane hull under the wing substantially
a pulley 40 is mounted to turn with the shaft 4|
in the plane of the areodynamic center of gravity,
of the pointer. A second pulley 42 is mounted
a second pressure responsive device located at a
to turn dial 43 of the center of gravity indicator
point remote from said ?rst pressure responsive
which is independent of the center of gravity 20 devices on the aft part of said hull, a pair of pres
pointer and shaft. Belt or cord 44 around the
sure lines extending from said pressure respon
two pulleys causes the center of gravity dial to
sive devices to pressure measuring instruments,
shift its position relative to the pointer with
said pressure lines having pressures therein cor
changes in gross weight so that the indication of
responding to the water pressure on the seaplane
center of gravity is continuouslycorrected with
25 hull at known depths at the above mentioned
variations of gross weight of the seaplane.
locations, a differential pressure gage connected
From the above description it can be seen that
to said lines responding to the differential in ,
the gross weight and center of gravity of the
pressure in said lines to give an indication of
seaplane a?oat can be determined under all con
center of gravity of the seaplane, a direct pres
ditions of loading. The method of determining
sure gage connected to said ?rst mentioned pres
center of gravity and gross weight can be carried
sure responsive devices which give an indication
out in several ways, depending upon the choice
of the gross weight of the seaplane, means on
of apparatus.
said di?erential pressure gage to correct the in
It is to be understood that certain changes,
dication of center of gravity in accordance with
alterations, modi?cations and substitutions can 35 changes in indications of the gross Weight of the
be made without departing from the spirit and
scope of the appended claims.
4. An apparatus for measuring center of
I claim:
gravity of a seaplane a?oat comprising, three
1. An apparatus for determining the center of
standpipes secured to the seaplane hull, two of
gravity and gross weight of a seaplane a?oat
40 said standpipes located substantially in the plane
comprising means for measuring water pressure
of the areodynamic center of gravity and the
on the seaplane hull under the wing. near the
third standpipe located aft and remote from said
plane of the areodynamic center of gravity, means
?rst mentioned standpipes, said standpipes each
for measuring water pressure on the seaplane
comprising an elongated chamber in communi
hull at a point remote from said ?rst mentioned
cation with the water outside the hull through
point, means connected to said ?rst pressure
a small diameter tube so that the water level in
measuring means to give an indication of gross
the chamber will correspond to the Water line
weight of said seaplane, and means connected to
outside the hull, a pressure line extending to a
said ?rst and second pressure measuring means
predetermined point within said chamber, said
responsive to the differential in pressures meas
pressure line being charged with air under pres
ured thereby to give an indication of the center
sure to expel the water from the tube in the
of gravity of the seaplane, said center of gravity
chamber by bubbling air through the chamber,
indicating means including means to correct the
said ?rst mentioned standpipes being intercon
_ indicated center of gravity with changes in gross
nected and connected to a pressure gage, which
weight of said seaplane.
55 pressure gage reads the pressure required to ex
2. A seaplane weight and balance indicator
pel air from the pressure line through said stand
comprising a pressure responsive device under the
pipes thus giving an indication of gross weight
wing of a seaplane substantially in the plane of
of said seaplane, a second differential pressure
the areodynamic center of gravity, a second pres
gage connected to said pressure lines responsive
sure responsive device located on the hull at a 60 to the difference in pressure between the ?rst two
remote point aft of said ?rst mentioned device,
standpipes and the third mentioned standpipe,
pressure lines extending from said pressure re
said differential in pressure gage calibrated to
sponsive devices to an instrument panel which
give an indication of the center of gravity of a
pressure lines have pressures therein correspond
seaplane hull, means on said center of gravity
ing to the water pressure on the outside of the
indicating gage to indicate a corrected value of
seaplane hull at said points, said instrument
center of gravity with variations in the gross
weight of the seaplane.
panel having mounted thereon a direct pressure
measuring gage and a differential pressure meas
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