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0& a!! The Engineering
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Resource For
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400 COMMONWEALTH DRIVE WARRENDALE, PA 15096
851320
The New Environmental Control System
for the B 52 G/H Aircraft
m
Frank L. Buscarello
Hamilton Standard
Division of United Technologies Corp.
Fifteenth Intersociety Conference on
Environmental Systems
San Francisco, California
July 15·17, 1985
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ISSNOI48·7191
Copyright © 1985 Society of Automotive Engineers, Inc.
This pap!.'r is SUbjCl't to revision. Statcments and opinions ad·
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851320
The New Environmental Control System
for the 8-52 G/H Aircraft
Frank L. Buscarello
Hamilton Standard
Division of United Technologies Corp.
systems are controlled by tllO solid state,
analog, nuclear hardened, electronic controllers "hiGh also contain built in self
test and fault isolation for the major
components of the system. The ACS regul ates
the air pressure pneumatically and controls
the flow both pneumatically and electronically to the cooling package.
A cooling
effect detector (CED) biases the pneumatic
floN control to maintain the desired cool ing
air flo\'J to the avionics equipment.
This
flOl/ control approach in conbinati on \lith
hot and cold ai I' temperature control valves
saves engi ne bleed air by not dunpi ng
excessive air flow into avionics equipment
and not over heating or over cool ing the tl/O
ABSTRACT
ENVIRONr,IENTAL CONTROL SYSTEM (ECS) for
the B-52 G/H Ai rcra ft - The Boei ng B-52 G/H
aircraft uses precooled engine bleed air as
a source for cabin pressurization and cabin,
missile and avionics
air conditioning.
These systems are cantrall ed by two sol i d
state controllers "Ihich also contain built
in self test and fault isolation. The ECS
regulates the bleed air pressure and flOl~
via an electrical signal from a cooling
effect sensor in the avionics air supply.
Thi s flow control approach saves engi ne
bleed air by not dumping excessive cold air
into the avi ani cs equi pment and not overcooling or overheating the b/o cabins or
missiles.
The missile conditioning system
mixes cold and warm air to keep the missiles
at the required temperature.
The system
al so provides a "go-no-go" signal to the
cabin to indicate "temperature readiness" of
the missiles. The two cabins are separately
temperature control I ed through i ndivi dual
temperature selectors and controls.
TilE PURPOSE OF TillS PAPER is to describe tbe
sal i ent features of the ne'" B-52 G/II a i I'
conditioning system and to present data that
illustrate its steady state and dynamic
performance characteri stics. The ai I' conditioning system, shol'ln schematically in sinplified form in Figure 1, consists of the
follOlJing four subsystems; bleed air tempet·ature control subsystem (BATCS), air conditioning subsystem (ACS), cabin temperature
control subsystem (CTCS) and missile conditi ani ng subsystem (tiCS).
The BATCS is an
upgraded version of the original installed
bleed system and 'till not be discussed
here.
The ACS, shwn isometrically in
Figure 2, uses bleed air from the BATCS to
supply a single cooling package located in
the forward wheel well "hich in turn
provides the conditioned ai I' for the r·ICS,
CTCS and the avi ani cs equi pment.
These
cabins or missiles.
The CTCS di rects ai I' from the ACS to
upper and lov/er cabi ns. The temperature is
cantrall ed through i ndi vi dual temperature
selectors IIt:ich have automatic and manual
modes based on signal s from two zone e1ectronic controls packaged in a single box.
The CTCS is shown isometrically in Figure 3.
PrC5SUfC
Rcgul~IO'
Fllle.
o
§
FlOW
Rogulalo,
Nnw Controllers
Cooling Ellecl Oclnelo.
OJ Check Vel.\!
<;) New All Conllol Flow
t::=J Hoi Air OU~1
c::::::J Cold Air Ou~l
V~lvns
r.zz::;J Blonded HoliCold AI' Ouel
-
Conl,ol
Feodl>~~k P~lh
Figure 1. New B·52GIH ECS functional diagram
0148·719118510715·1320S02.50
Copyright 1985 Society of Automotive Engineers, Inc.
C~bln
Eloeltonlcs
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2
851320
From Missiles To Missiles
\
.e
111(.;::., Overtamp Switch
J'? 7'''''I!~"~r Temp Sensor
\P~:lri'"~Hllal Exchanger
~/q',~,.~,/ ~'<l~:;---- SN J.BOll
Orlllco
Hot Air
MOdUlatlng~~!,ti"/ ~',>-~
Valve/~
~
~1' l':',,=,,~
-------1/ I); jJ
OrlllccandCheck
~ve
--=~
"ACSIMCS
~i.",j?~S~
. " ..; ~
~r
/
,\
~
I
Controller
~Mln~1
Temperalure
Cold Air
Modulallng
\
")
Valvo
Air condlllonlng,!,
Package
SenSOr
V
Figure 4. Missile conditioning system
Figure 2. Air conditioning system
..",,,...
MI,.I1~
CQf\dlllonln; 5y.l.m
(MCSl
Figure 3. Cabin temperature control system
Figure S. Combined air conditioning system
Tile NCS, shown isometrically in Figure
4, takes ai r from the cool i ng package and
vlarm bleed air to keep the missiles at the
required temperature as determined by the
MCS controller.
The controller senses a
combination
of
temperatures
(outside
ambient, missile loop supply air and missile
electronic cold plates).
The controller
al so provides a "go/no-go" signal to the
cabin to indicate the "temperature readiness" of the missiles and also provides a
l\/arm Upll or a lI eoo l down II cycle \'Jf;En the
outside air is above or below preset values.
SYSTEI·; DESCRIPTION
The
combined
environmental
control
SySt€l,' designed for the 8-52 G/H aircraft is
shOlvn schematically in Figure 5.
AIR CONDITIONING SYSTHi (ACS)
The
BATCS supplies air to tl:e ACS at nominal
375'F (460'F max normal) temperature and
pressures up to H2 psig. The ACS pressure
regulator and shut off valve (PRV) regulates
the pressure downstream of the ACS catalytic
filter to 40.5 + 3 psig @ sea level and
reduces linearlY-~lith altitude to 14 + 2
psig @ 50,000 feet. The air then enters-the
combi nati on fl ow control sensor/flow control
valve (FCS/FCV) ~Ihich modulates to control
flOlI from the minimum required to a maximum
of 160 pounds per minute.
Failure of the
PRY Vlill cause the FCS/FCV to reset the flail
do,m to a safe level to keep the air cycle
machine from over-speedi ng. In the event of
a double failure (both PRY and FCV), an
electrical/pneumatic pressure sViitch downstream of the FCV signal s both the PRY and
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851320
the FCV shut off solenoids to close simultaneously.
The FCSjFCV nominally controls
flOlI by sensing a de1to P across a venturi,
but is further electrically biased by the
cooling effect detector located in the
avionics cooling duct (Figul'e 5) to ",aintain
the floN to only that requi red by ti,e
avionics. This is a feature added to conserve flOll because the crell can manually
control H,e flo" to the upper and 10l·!er
cabins by opening or closing air outlets at
each of their crew stations and would tend
to increase or decrease the avionics cooling
floll above or bel 0" its requi red va 1ue.
Fro" the FCSjFCV, flow is then ducted
to the air conditioning package (~,CP) (see
Fi gures 6 and 7) where it is cool ed in the
prir,lary section of the dual heat exchanger
(ra"
air
heat
sink),
centrifugally
co"pressed to approximately hlice the inlet
pressul'e, cooled again in the secondary
section of the dual heat exchanger to remove
the heat of compression and expanded through
a nozzle into a radial inflow turbine and
discharged into a water separator.
The
turbine and compressor are mounted on a
singl e shaft "hid al so features a fan that
dralvs the cool i ng a i I' through the dual heat
exchanger for ground static cooling.
The
turbine discharge air temperature is lowered
approximately ZOO°F during
the
turbine
expansion to a 10Vi pressure \'hich provides
the work of dri vi ng the compressor and the
fan (shown schematically in Figure 5). The
ACP also includes the pack bypass anti-ice
valve which is modulated electronically to
hol d a 37 + ZOF ~Iater separator di scharge
temperature - in order to keep the "ater
separator inl et above the freezing temperature.
The ACS electronic controller that
provides the anti-ice valve signal also
modulates the LED signal to the FCSjFCV.
Dual HX
Figure 6. Air conditioning package, right side view
3
Anti-Ice Valve
Figure 7. Air conditioning package ~ left side view
The NateI' coll ected from the I'later
separator is discharged through an aspirator
into the cooling side of the dual heat
exchanger to enhance cool i ng. The dual heat
exchanger is cooled by fan driven ambient on
the ground and by ram air in fl ight. \lhen
the ram air pressure ri ses above the fan
discharge pressure it bypasses the fan and
goes di rectly overboard vi a the fan bypass
check valve.
CABIN TEMPERATURE CONTROL SYSTEM (CTCS)
The CTCS (Figure 5) receives air from the
NateI' separator di scharge at 37 + ZOF and
hot ai I' from the CTCS PRY at 375"F. Thi s
air is due ted to an uppe" cabin (flight
deck), a 10\;er cabin (navigator and bombardier stations) and the avionics equipment.
The upper and 10"er cabi n ai I' temperatures
are controlleo by
separate
temperature
selectors via controllers ~!hich provide an
error bet;,een the sensed temperature and tl;e
se1ected temperature.
Thi serraI' is i ntegrated in the zone temperature controller
\'Ihich modulates one hot and one cold electrically actuated valve for each cabin.
Both CTCS contro11 ers are packaged in one
control box. \lhen cool i ng is requi red the
hot valve ,"odulates closed and tbe cold
valve modulates open and vice versa.
Hot
and cold air are mixed by modulating the
syster,l hot and cold valves before it is
discharged to the Crew compartment.
Each
cabin selector also contains a manual mode
where the val ves can be modul ated between
full hot and full cold operation. Normally
the manual mode is used only if the automatic mode
is
not
functioning.
Pack
discharge cold air is also ducted to the
avi oni cs equi pr.1ent through a duct "hi ch
contains a cooling effect detector (CEO).
Tile CEO probe contains an electrically
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4
heated thel'mistor which creates a signal to
tile ACS control lor to control to a constant
cool i ng effect by bi asi ng H,e FCV from its
maximum schedulo dOlmllard as required.
f,iISSILE COIWITIONING SUBSYSTEII (hCS) The i/;CS provides initial vlarEl-up, cool dmln
and temperature control for the mi ssil e ai r
conditioning. The electronic controller for
the ~,CS, which is packaged \lith the ACS
controller in the same control box, receives
four signals to condition the missile air.
The missile air loop is a sealed pressurized
ci rCllit I'lith an integral fan to ci rcul ate
the air through the missiles and through the
ncs heat exchanger (shown schemati ca lly in
Figure 5). The 14CS heat excloanger receives
hot or cold air as required from the ACS.
The four functi ons of opera ti on modes
are described below:
1. \'Ieen the missile cold plates are bel 011
32'F, the ~:CS is in a lIarm-up mode with the
nissile supply air controlled to 125 +
lC'F. Teis is accompl ished by the NCS air
tenperature sensor dOlmstreaCl of the I1CS
heat exchanger signalling the electronic
controller IIhich commands the hot air valve
to modulate to a controlling position. The
r,;cs hot and CGld valves operate in sequence
and are not open simultaneously.
2. \'Ihen the missile electronic cold plates
are above 32'F and the ram (ambient) air
teClperature is he 1011 50 'F, the NCS is in H.e
normal heating mode and H:e missile supply
air is controlled to B7.5'F.
3. Ilhen the missile electronic cold plates
are above 32'F and the raCl air temperature
is above 50'F, the ~iCS is in the normal
cooling mode and the missile supply air is
controlled to 75 + 5'F.
4. The
IICS
controller
al so
provides
"go-no-go" signals to the cabin whenever the
missile conditioning air teClperatures are
outsi de the spocifi ed val ues or when there
is an IICS failure.
PRESSURE REGULATION AUO FLOII COIJTROL
The air conditioning systom pressure
regul ati on and flol/ control are accompl i shed
pneumatically by the PRY and FCS/FCV with an
e1ectroni c bi as to the FCS. The PRY and the
FCS/FCV are located in series ~Iith hot air
take-offs for the r,ICS and CTCS temperature
control betlleen them.
The PRY receives
bleed air from the BATCS at a nominal
temperature of 375'F with a maximum normal
tempel'ature of 460'F for cases where the
precooler is saturated.
A failure of the
oATCS can produce temperatures up to 550'F
and pressures up to 152 psia. The PRY and
FCS/FCV combination give the air conditioning system excellent pressul'e and flow
control for steady state and dynami c operation. In the event of a PRY open failure,
the FCS/FCV also protects the system by
851320
l'csetting the flOI'I schedule dOlIn to maintain
a maximum air cycle nacl'i;ne speed of 42,000
rpm.
To protect against douole failure, a
tl.ird component Vias added \'Ihicil consists of
a pneumatic/electric switch that signals
both He FCV and the PRY tG closo.
Tili s
overpressure s\"Iitcll is dmmstrealli of the FeV
and is set to close if the pressure exceeds
the FCS/FCV reset pressur~.
Thi s sl'!itch
signals both the FCV and the PRY to close.
Tl,e prohabil ity is very I'igh that at least
one of ti;e valves \'Iill close.
The naximu,"
ACI'1
speed
under
this
double
failure
condition is 52,000 rpc.
pgESSURE gEGULATHiG AND SHUTOFF V!,LVE Tho preSSUI'e regulating valve is a 4.5 inc!;
di ameter butterfly val vo (sholm scherrmtically in Figure 8).
It is pOI'!ered l'y a
half-area type pneur.latic actuator.
Servo
(large
piston)
p>,ossure
is
positively
contained loy a fabric reinforced silicone
rubber diaphragm. Supply pressure acting on
a piston (sl:1all portion) I'lith a ring provides the actuator closing force.
Allllude Bins
Evacunled,OIl
Oamped, Bellows
I
Lead Compensation
Restrlcllon
---j.------ --
Solenoid Shown
Oe·Energ!;zed,
Energize Solenoid
10 Close Valve
Energized
~~
1
De·Energized
j
I
iControl Lever
0
'l
r-Pressure
I
I
I F"=;~=rr=9=
Regulator
i
0
==g=L..=-~-~-~-l ~c~;;o~ozz;-;;-- - J
Ir
Pamb
Servo.Pressure
Supply Pressurc_
FlUer
Pvi-
Filter
Preg
Figure 8. Pressure regulator and shutoff valve
functional schematic
The valve is an altitude-biased pressure
regul ator, provi di ng a dOl,nstream regul ated
pressure schedul e as a functi on of amili ent
pl'essure.
The pneumati c controller is a
force-balance-type design utilizing sensing
diaphragms to compare downstream pressu>'e
against a reference spring and evacuated
belloHs force. Altitude biasing is provided
by the evacuated bell aVIS, ~lhi ch produces a
reset
force
proporti ana1
to
ambi ent
pressu1'e.
Pneumatic lead co,"pensation is
employed to enhance stability and improve
response whil e maintaining good control
accuracy.
During
steady-state
control,
regulated pressure acts on both control
di aphragms.
The di aphragms are of unequal
sizes and the >'esul ting net regulated
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5
851320
p,"essure force is balanced by the spring and
altitude bellOl'ls force.
As altitude increases the bellOl's force applied to tile
lever increases, and results in a loHer
regulated p,"eSSUre force to keep the control
lever in l:alance.
During a transient,
p,"eSSUI"e in tile vol ene cllamber momentarily
remains fixed due to the restriction and
regul ated pressure mOlilentarily acts on tile
otller diapLragm causing a large dange in
force and a correspondi ng rapi d change in
valve position (lead conpensation). The PRV
schedule is shm," in Figure 9.
A shutoff solenoid, when energized,
causes actuator servo pressure to be vented
to ambient, allOlling the valve to close.
\lllen the solenoid is de-energized, tee valve
opening rate is controlled by the orifice
supplying the actuator.
1 ~'=S-c,L4-'''3~'2:--c,L'-':':0-!9---:8L--J,.7-!6-"Sc-4L--!-3-!2-,
Pambient, PSIA
Figure 9. PRV pressure regulating schedule
Servo
Pressure
L,g
Rastrlcllon_
Fillar ........
Supply
Pressure
"-......J
Flow Conlrol Sensor
Flow Conlrol Valve
Figure 10. Flow control sensor, flow control valve,
functional schematic
The fl 01' control sensor modul ates the
servo pressure to the flow control valve.
The sensor is a 4 inch di ametel" al uni nun
fl0l1 sensor venturi '"lith integrally mounted
control.
The control modulates the servo
pressure in the foll o>li ng manner: The ai r
fl OIl through the venturi generates a fl 011
(de 1ta p) signa 1. The delta Psi gna 1 ac ts
on control diaphragms to impart a force
through a 1ever system to repositi on a servo
pressure poppet.
The change in servo
pressure causes the flow control valve to
reposition itsel f until the air flOl: rate
sati sfi es
the
controll er
setpoi nt
by
balancing the control level'. The lever tilay
be biased by a proportional solenoid to
scl,edule reduced flOl'IS.
This
solenoid
applies a force to tl:e level" "hich danges
the controller setpoint in response to an
electrical signal supplied by the coolillg
effect detector. Finally, in the event of
a~
FLOIi CmJTROL SEfISOR ArlO FLOW CmiTROL
VALVE ASSEI'IBLY (FCS/FCV) - Tile floVi control
assembly shOlm schematically in Figure 10
consists of a 4 inch diameter hutterfly
valve modulated by
an electropneumatic
controller mounted
on a
floVi
sensing
venturi.
The e1ectropneumati c control 1er
receives an electric signal from the air
conditi ani n9 pack el ectroni c controll er to
maintain a constant cooling effect to tile
ducted electronics (avionics).
The flOl':
contra1 val ve operates in conj uncti on \lit 11
the flOl~ control sensor to provide the
folloViing functions:
a) Regulate engine air floVi to the Air
Conditioning Pack
b) Schedule air flOlI to control avionics
cooling capacity
c) Prevent overspeed of the Air Cycle
I'lachi ne in the case of a fail ure of tile
upstream pressure regulating valve
d) Shut off tile air flo'"l to the air
conditioning pack
c-_'_'::FI_'''.'l'~JD
--=-c-=
Flow_
upstream overpressure situation,
supply
pressure is ported to a reset di apliragm
"hich biases the control lever thus creating
a 10lier (reset) fl 0\'1 schedul e.
The fl 011
schedule is sholln in Figure 11.
240
Venturi
Choke Line ___
r:: 200
~ 160
80
40
(~=6 PSI)~y
~in. Schedule
/ // ~ at S.L. I
Schedule
{f._,40K Resetl~ ~'MaXReset
~ 120
•
o
J
/
:11
"u:
Max. Normal
Schedule
/~
/;SOK,
o
o
.--Reset EnvelOP!---
~~nv.
,
,Min. Reset
Schedule
80
100
(PSIA)
120
\
~
Reset E;fv.
20
40
I
I
60
Pv
Figure 11. ECS/FCV schedule
140
160
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851320
6
The flo" control valve is a 4 inch
diar.1eter aluminum, half area pneumatically
actuated hutterfly val ve. Upstream pressure
is ported di rectly to the sr.1all actuator
piston to provide the valve opening force.
r'lodul ated upstream a i I' pressure is al so
ported, through a restri cti on, to the 1arge
area actuator pi ston to provi de the valve
closing force.
This servo pressure is
modul ated by the F10\'l Control Sensor. The
modul ated servo pressure repositi ons the
butterfly di sc unti 1 the desi red flo" rate
is achieved.
A shutoff solenoid valve is
al so incorporated into the uni t to ovetTi de
the flO1'1 control sensor. Operation of tile
shutoff solenoid in response to an externally generated electrical signal allOlls the
servo pressure to approach the upstream
supply pressure level to close the valve. A
valve open position switch is provided as
part of the Built In Test (BIT) system.
OVERPRESSURE SWITCH
The overpres sure sl;itch is a gage
pressure switch modified pneumatically to
provide an altitude-biased package supply
pressure sllitch.
The orifice and venturi
serve as a pressure divi del' I'lhi do requi res
the appropriate supply pressure (varies l'lith
altitude pressure) to establish the trip
pressure for the sl'litch. The laminar orifi ce and 1ag chamber vol ume create a tir.1e
delay to preclude nuisance trips.
The
sl':i tch is wi red into the ACS system to close
the PRV and the FCV in the case of excessive
package bleed inlet pressure (54 psig at sea
level). The scliematic is ShOl'1n in Figure 12.
Fan Inlet and Diffuser Housing
Fan Bypass Check Valve
Water Spray Ilozzl e
COIJpressol" Overtemperatul"e Svlitch
The actual test package is shol;n in Figures
7 and B. The major conponents are described
bel 01'/.
DUAL HEAT EXChANGER - The dual heat
exchanger is a modification of an L-10ll
uni t.
Only mounti ng brackets and headers
liere changed. The core is unmodified and is
all aluminur., parallel flOl'/, plate and fin
construction.
This heat exchanger used
extensively in several applications has Leen
developed for very high thernal cycle life.
AI, CYCLE I~CHINE (ACM) - The Air Cycle
1'lachine is also a modified existing unit
(L-10l1 and AWACS) "Ihich has been optimized
for the B-02 flo>l requirements "hich included a small reduction in turLine nozzle
area, turbine rotor and compressor rotor
blade heights and compressor diffuser area.
The ACM, shmm in cross-section in
Figure 13,
consists
of a centrifugal
compressor with channel diffuser dri ven by a
radial inflOl' turbine Ilhich also drives an
eleven bladed cooling air fan.
The shaft
ri des on tliO angul a I' con tact, preloaded 20
I'lr.1 ball bearings which are oil mist lubricated fron; four \licks.
Bearing cooling is
accompl ished by conduction from cold turbine
discharge air and direct air cooling to the
hot fan end of the shaft by a shaft mounted
helical air pump. The derivative unit has a
demonstrated
27,000 MTBF
in
conmerci al
servi ceo
Filter
Duct
Supply
-1i;1----;-------..""'i
Orifice
r---;v7'e~n~tu=:ri~-
Ambient
Vent
/'
Laminar Orifice/
Fan
Figure 12. Overpressure switch functional schematic
AIR COUDITIONING PACKAGE (ACP)
The ACP consists of the follOlling
components arranged such that all mounting
is from the dual heat exchanger:
Dual Heat Exchanger
Air Cycle Machine
Anti-Ice Valve
Figure 13. Aircyc1e machine
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851320
7
AIITI-ICE VALVE - n,e anti-ice valve is
a 2-3/ l i inch diameter elrctropnemlaticallj'
controlled butterfly valve derivative of an
existing valve and is sf-min schematically in
Fi gure H.
It is pm:cl"ed by a half-area
type pneumatic actuator, \lith s~rvO and
supply pressures Leing pos; tivel.r contained
ly fabric reinforced silicone diaphragms.
Upstreafil pressure is ported di rect1y to the
small actuator piston to pl"ovide the closing
force. Nodu1 ated upstrear;; pressure is a1 so
ported, tbrough a restri cti on, to the 1aroe
actuator pi stan to provi de the openi ~g
force. Thi s servo pressure is modu1 ated by
the poppet \'Ihich is controlled by the proportional solenoid. The valve operates in
conjunction "ith the ACS/I·iCS controller and
water separator outlet temperature sensor to
mix Harm air vtith cold turbine discharge air
in order to prevent icing. The controller
provi des an e1 ectri ca1 si gna1 to the val ve
proportional solenoid causing the valve to
cllange position to maintain a 37°F mixed air
tempel"ature.
Position feedback is incorporated to enhance stability. A valve closed
position sNitch is provided as part of the
Built In Test
Sjstc~.
Proportional Solenoid
CZJ
Control
WCZJ U...--cont,ol
poppet~=
1
Feedb••a:ck:-_
Position
Cam -
H
Lever
\
Servo
Pressure
Supply
cally actuated val vos (one hot and one
cold), two duct supply temperature sensors,
tHO
zone temperature sensors and two ter.lper-
ature selectors. The tllO hot air valves are
supplied by a hot air bypass pressure
regulator and the two cold air valves are
supplied by cold cooling package air.
TENPERATURE CONTROL CHAIJIlElS - The tliO
temperature control channel s are located in
one control box, but are isolated from each
other electronically so that failures in onc
channel .!ill not propagate to the other
control channel. Each channel is contained
on a separate printed circuit board I-lith
dedi cated pm-Ier supp1 i es, regu1 ators and
completely independent control loops.
Each control loop modulates t,1O electronically actuated hutterfly valves, an
lladd heat" valve and an "add cola valve.
In order to minimize bleed air use hut still
satisfy the cabin requirements, the valve
schedules are set up to minimize overlap but
prevent one valve from being fully closed
before the other valve opens. At the "null"
position both valves are open the saDe
amount. Thi s prec1 udes radi cal te",peratur£
excursions in the zone supply and enhances
long life by reducing large valve excursion.
A trade-off study compari ng mechani ca1
linkage dual valves versus electronic schedu1 i ng shm-,ed the e1 ectroni c schedu1 i ng to he
supe,"i or primarily because of the location
of the valves in the cabin.
Figure 15
illustrates tile temperature contl"O1 valve
schedu1 e.
uNanudl ~iodE:1I scheduling is accolilplished "ith simple relay logic and limit
Sliitches in the valve actuators. Figure 16
sho\'ls the manual mode valve schedule.
ll
pressure~
Filter --.... .
Air Flow
c:>
.
Figure 14. Antj·jce valve· functional schematic
.
De-Energized
.d~
Shut-Off ~~ /control Lever
Solenoid
:
Pamb
I:
.Lead
/
.~~.~,<)~~~~~'
J
"
0
Restriction
;~l
~
Pamb
CAbIN TEilPEP.ATURE COIHROl SYSTEF, (CTeS)
'.,
'-·Servo
Control
Nozzle
The eTeS provides conditioned air to
tile upper and 101,er cabi ns for temperature
contrl)1 and pressuri zati on.
The temperatures in the upper and 10ller cabi ns are
independently controlled by the cre". Harm
bleed air from the pack inlet is mixed "ith
tile cold Nater separator discharge air to
control to the selected temperature.
The eTCS consi sts of t.IO i denti cal
temperature control loops each consisting of
an
independent
electronic
controller
channel, each of which drives t.1O e1ectri-
\Servo Pressure
Pregulated
Figure 15.
eres pressure regulator and shutoff valve
functional schematic
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8
851320
Open
100
.....
......--Cold Swllch
.-.....-
90
Cold Air Valve
Schedule
o
m
70
cg
!i
en
60
en
Close
Open
I
,,~
Hot Switch
----Hot Air Valve
Schedule
Close
Cooling
Heating
80 1"-
~
I Valve Sequencing
Open
I
i'\
/
/
",e
"'",
7'
\"'<:>a/.I
~ 40
~
~ 30
......:1
I
I
Mac Cooling
I
1/"
0,
m
!
1--'- - r -
ol'
~~/
,Q'-x)
> 20 r- r10
/
f
\
50
o
Open
I
r-.. k--l
V
i
Max Healing
Figure 16. CTCS manual mode valve schedule
CTCS PRESSURE REGULATOR AI,U SHUT OFF
VALVE - The eTCS pressure regulator feeds
the two add hot val ves of the upper and
lmier zones and rE8ulates tl,e hot bleed ai,'
pressure to 6 + 1 psig above cabin pressure.
This is -done to reduct cabin noise
wlti cl: can l'~ caused by hi glt pressure bl eed
air being modulated directly across the add
hot valves.
The pressure regulating valve is a 3.!:i
inch diameter cabin-biased pneumat.ically
actuated butterfly val ve shOl/JI scbe",atically
in FigUl'e 17. It is powered by a half-area
actuator with servo and suppl.)' pressures
positively contained by fabric reinforced
silicone rubber diaphrag",s. Supply pressu"e
acting on a small piston provides the actuatOl~ closing force.
The pneumatic pressure
controller
suppl ies
an
opening
servo
pressure to the 1 arge actuator pi stan
dependi ng on tf;e 1eve 15 of the sensed downstrean and caei!! pressures. The controller
is a force-hal once-type desi gn uti 1i zi ng
sensing dtaphragr.is to compare dm-mstream
pressUl'e agai nst a referencE spri ng and
cabin pressur'e force.
Catin biasing is
achieved by !:leans of a cabin pressu"e
sGns; n9 Iii c.pl'd'agr-l, Hhi c/. produces a force
propoi~tiGnal to cabin pressure.
Pneumatic
lead co",pensatio" is e"ployed to enhance
stat i1 i ty ilnd improve response ~/hil e rna i ntailling
good
control
accuracy.
Dudng
stcady-stc:.te control,
regulated
pressure
acts on hath control
diapl.ragms.
The
di aphragns a re of unequa 1 si ze and the
resulting net regulated pressure force is
balanced by the spring and cabin pressure
force. During a transient, pressure in the
vol u",e Chamber momentarily I'emai ns fi xed due
to the restriction and regulated pressure
mo"'entarily acts on the other di aphragm to
cause a 1arge change in force and a corresponding rapid change in valve position,
hence, the "1 ea dll characteristic.
A shut off solenoid, Hhen energized,
causes actuator servo pressul'e to be vented
to ambient pressure, a1101'ling the valve to
close.
wt,en the solenoid is de-energized,
the valve opening rate is cont"ol1ed by the
orifice supplying the actuator.
Figure 17. CTCS temperature control valve schedule
TEf',PERATURE CO~TRDL VALVES - T"IO temperature control val vos (add hEat/add col d
valves) consist of tl:O butterfly valves
driven by identical
electric ilctoators,
These slightly "'odified actuators a"e being
utilized in many current applications and
a,'e giving very high reliability service.
Tl:e AC rota ry actuator motor is a 115V Rt·iS,
tHO
phase
devi ce
'Ii th
the
contro 11 er
resident, phase shifting capacitor providing
a 90" phase relationship.
The 10\1 pOller
(3.5 lIatts/phase) motor is designed fOl'
cont.i nuous operati on IIi th enougr, torque to
enable it to close the valve ,lith an inlet
pressure of 185 psig. The actuator provides
positi on feedback to the control loop \'lith
infinite resolution by means of a conductive
plastic element directly geared to the
butterfly shaft.
The inherent ",agnetic
cogging and gear train prOVide the neans of
implementing the "failed-fixed" actuator.
The non-linear gain variations of the valve
with respect to position and flail are COClpensated for ir the controller electronics.
Tile electric actuator consists of an aluminu1'l housing providing structural rigidity
for the actuator and conducti ve hea tsi nki ng
for the AC servo motor. A ther",al barri e,·
is provided t.o separate the electrical
actuator from the valve body tt:U5 i sol ati n9
the duct temperature frorr, the actuator. Tbe
huttel'fly disc is provided \lith a steel seal
ring and shaft seals minimizing leakage,
The valve shaft is supported hy 101: friction, steel backed, filled teflon bushings
for enhanced stability and long life.
ZOIlE T[I.:PERATURE SELECTOR - The zone
te,,,perature selector is an automatic and
manual
zone
temperature
input
c1evice,
tigl,tly pacl:aged in a 1ightweight alurninu"
can mounted behi nd the temperature control
panel.
An
auto
control
rheostat-connected
potentiometer' provides a temperatllre reference at any selected temperature from 55" to
95"F lIith a resolution of less than 1 "F.
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Hl1en in manual mode, a spring loaded
center-off momental'y switch provides the
'"eans to toggle the systom hy actuating the
add heat or add cold valves,
The manual
syste~
is completely independent of the
automatic
temperature
control
circuit
thereby providing control ;vhen auto control
has experienced a failure.
1·IISSILE COllUITICllIllG SYSTH, (liCS)
The f:CS provides conditioned air' to a
pressurized,
closed
l'ecirculation
loop
driven by an electrically po\\'ered fan.
TI·, I?
air in tLe closeo loop is heated and cooled
by an ai I' to ai I' hCS heat exchanger I'/hi ch is
sUepl i ed or. its other side with sdfi ci ont
hot or cold air in order to maintain tre air
temreratu,"e to the missile electronics at
the desired value.
The 11CS consists of tLe ail' to air heat
exchanger, an e1ectroni c controller (housed
\lith the ACS control in the same hox), two
electrically driven butterfly valves for
control of ~ot and cold air and two identical temperature sensors Hhich sense missile
supply air temperature and ram air inlet
temrerature. The mi ss il e col d pl ate sensors
and tLe l'eci reul ation fan are fro", the
existing B-52 missile system.
r·lcs HEAT EXCHA~GEH
The I'CS reat
exchanger is a nel'l design utilizing a plate
and fin construction, fluxless brazed core.
The core is a single pass cross flow
design. The supply air and r,lissile air fins
are of a high density, ruffled design. The
i nl et header supports the mi ss i 1e loop fan
I.Lich is an existing B-52 component.
The
hCS heat exchanger configuration is shown in
Figure leo
Air from
Missiles
air cOlitrcl valve is a 1.5 inch diameter
hi gIl tempc:rature, carrosi on res i starlt 5teel
butterfly valve. Beth valves, like all the
other electrically driven valves in the
systen, use the same identical electric
actuator.
TEI:PERATURE
SEIISORS
The Clissile
supply air sensor and the ram air inlet
sensor are i denti cal themi star type sensors
and ate used in many military aircraft nOl'I
in service.
ECS TE ST PROGHAII
The ACS, CTCS and the I':CS I'lere fully
qua 1ifi ed to the Boei ng 1-1il i tary Ai rpl ane
Company specifications.
Tile test progra"
\.. a5 rigorous and included the follol,'!ing:
Functional and dyna"ic testing of all
COf,lpOnents as app 1i cab 1e
Tilermal perfon"ance of the air conditioning package
Thermal and dynamic performance of tile
cOr.lcined system ACS, CTCS, and HCS
Eacil cOClponent and the ACP were
vibrated for a total of 33 CaUl's in 3 planes
at random levels of up tc 16 G's Rj'IS.
Each cOClponent (as applicable) was
pl'essure tested up to and including burst
pl"es sures.
Each component \'las qualified to the
full complement of environClental tests of
'·ill-STU-elOC.
Endurance testing "as justified by
similarity because of the use of proven long
life components in critical areas.
Tile test prograrl, especially the vibration test, produced nany equipment failures
requi ri ng severa1 redesi gns of some key
cOrlponents.
However, the final hardl';are
design
has
been
successfully
qualified
without exception.
Figute 1, is a photograpil
of
the
combi ned
system
test
laboratory set up.
Figure 18. MCS heat exchanger
HOT AND COLD AIR flODUlATIIJG VALVES The cold air control valve is a 3.5 inch
diameter aluminum butterfly valve. The hot
Figure 19. Combined system laboratory test setup
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851320
10
At this \1riting tile flight test airplane has completed over 900 hours of flight
testing and service ,·lithout incident or
ma lfuncti on.
SYSTEI·; DYrlAf.lIC PERFOm·IAIICE - Special
purpose
digital
computer
programs
\1ere
,witten to simu1 ate the non-1 i near dynami c
response characteristics of the ECS components.
These programs were used to deClonstrate that the design parameters of the ECS
"et all of the transient response requirements.
System testing of the combined
subsystem testing
1ater
subsysteCls
and
demonstrated that the system was in fact
responsive and stable.
The system cases tilat were analyzed and
later tested are given be10'1:
B
SysteCl turn on and turn off transient
conditions
12
Gleed air inlet pressure power bursts
and chops including a failed open PRY and a
failed open FCV
8
Bleed air inlet temperature transient
conditions, both increasing and decreasing
teClperature I"amps
2
Failed open anti-ice valve transient
conditions
2
Blocked ram air conditions
6
Conditioned air flO" demand conditions
including zero conditioned air f10\1
16
Cabin temperature selector step change
conditions
8
Nissile subsystem turn on and turn off
transient conditions
4
Missile sUbsystem node changes
Test resul ts of four of the "ore
interesting
and severe
transients were
selected to be discussed here.
Combined system turn on transient
"Fail open" PRY transient condition
llFail open" anti-ice valve transient
condition
Cabin teClperature selector changes
SYSTEI·: TURN m. TRANSIENT CmmITlON The response of tile combi ned system to turn
off and turn on was demonstrated in the
1aboratory at sea 1evel for a standard day
and at a c1i"b condition.
cor the system turn on, tile conditi ons
upstream of the PRY were set as foll OI'IS
(bypassing tile pack):
Bleed air inlet pressure
195 psia
375'F
Bleed air inlet temperature
Ram air inlet pressure
15.5 psia
97'F
Ram air inlet temperature
Cabin ai I' te"perature
l30'F
(simulator)
Cabin temperature selector at BO' in
automatic "ode
The turn on transient was initiated by
simultaneously closing the rig bypass valve
and openi ng the PRV, FCV and the CTCS PRV.
As shown in Figure 20, which contains copies
of the actual Sanborne traces, the regulated
pressure quickly returned to its regulated
level (2 seconds); pack inlet pressure (FCV
outlet) follOl/ed regulated pressure and then
in about 20 seconds nodul ated down to a
controlled level as the cabin supply air had
its effect on the cool ing effect detector.
Air cycle macl'inc speed folloued pack inlet
pressu,·e.
Cabin Suppply
Temp.
~F
Waler Sop. Oul
Temp ~F
":b======
"1:===
100
ACS
Regulalcd
Prossure
pslu
~O~"~=,=52~P~"~'~~===
PRV Turn/On
o
eTCS Regulated
Pressuro psla
_
SOol- - - - - - - - -
lOLJ--- _
"-------
Pack Inlet
Pressure pslll
ACM Speed
RPM
SOT
36.00"(O_R_PM
ol:=:::"7=::::J!15:-'S~"~'""'d~'
_
_
Figure 20. Turn on system transient
"FAIL OPEN" PRY TRANSIENT COIUlITION The response of the combi ned system to a
sudden "fail open" of the PRY was demonstrated
with
following
system
inlet
conditions:
Bleed air inlet pressure
180 psia
Bleed air inlet temperature
460"F
Ram air inlet pressure
16.4 psia
Ram air inlet temperature
144'F
With the system operating in steady
state and ACS regulated pressure at 50 psi a
the PRY was "failed" open by venting the
regul ated pressure sensel i ne to ambi ent
pressure.
As shown in Fi gure 21 the ACS
regulated pressure increased instantly to
180 psia and the air cycle machine speed
'lent from 36,800 rpm to 41,500 rpm (46,000
rpm allowable).
The flow control reset
quickly followed and moderated the air cycle
nachi ne speed to 31,700 rpm.
The cabi n
supply temperature and the missile loop
discharge
temperature
were
virtually
unaffected.
"FAIL OPEtJ" AtlTI-ICE VALVE TRAtlSIEIH
COIJDITION
The system response to an
instantaneous uncontrolled opening of the
anti-ice valve was de"onstrated with the
same ACS inlet conditions set for the 'fail
open' PRY case described above.
With the system operating in steady
state the anti-ice valve was cOI'1111anded to go
open.
As shown in Figure 22 the water
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851320
separator outlet temperature increased to
255'F (300'F allOliallle) before the pac,.
overtemperature swi tell conmanded tile FCV to
close.
The ACfl speed decreased in phase
,lith the FCV closing and settled at a steady
8,200 rpm lihich is attributed to the cooling
fan being driven IVith ram air.
25
1
Cabin Supply
Tomp of
Water Sap. Oul
Temp OF
ACS Regulllilld
Pressure psla
ercs Regulated
Pressure psla
25:[
10:[_ _ _ _ _ _ _'L-P::.:"::.:"'''d
r
10:[
system lias operated in steady state lIith the
folloIVing inlet conditions:
Bleed inlet pressure
70 psia
Bleed inlet temperatul"e
39G'F
Ram inlet pressure
16.3 psia
Ram inlet temperature
07'F
The temperature selector lias quickly
turned from a 95 'F positi or. to 55 'F.
As
sholln on Figure 23 the large disturbance
quickly decreased the cabin supply temperature to the flax cooling limit of 37'F in
approximately
50
seconds.
Ire
cabin
temperature sl wly responded due to the
normal
catin
thenlal
lag
simulated
electrically.
160 psla
Instrument
125°F
Fall Open PRV
Tcab
Cabin Temp of
Pack Inlet
PressurD psla
0
RPM
50:[
Missile: HXoul
15°F
ACM Speed
Tomp of
_ _ _ _ _-{C=--M..:'..:'.:.'p:.:ecd., 40,500 RPM
[--1 Mlnuto
-I
2SO
Start Transient
9S_Ss o F
Cabin Supply
Temp OF
/
oL
;Max Coollng
Condlllon Achlcved
/
In ,,40 Seconds
37° 1M in Duct Temp)
0
Figure 21. "Fail Open" PRV transient
Cabin Supply
Tomp OF
Waler Scpo Oul
Temp of
ACS Regulated
Pressure psla
ercs Regulilled
Pressure psla
Pack Inial
Pressure psla
SOoo~====
.
Ovcrlemp light Came On,
Light for FCV Also Came On
Figure 23. Selector step change -95 to 55' F transient
BUILT III TEST (BIT) FEATURES
1 ~'
"J====
The tliO electronic controll ers (CTCS
and the ACS/MCS) both contain built in test
pane1s under the front cover of the control
box. The BIT features for this system are
simple and straight forIVard.
First the
controllers self check themselves and give a
ready light if all is in order. The CTCS
controller and BIT panel are shoIVn in Figure
24.
10
100r
FCV Closed
or------:--... /bY Ovetlemp Swllch
SOKt=S;I--'120 Seconds
L
o
MlssliC HXout
Tomp of
']
SO:~255"FM".
ACM Specd
RPM
Water Sep.
Oullet
Tomp OF
/
.
~ Anll.lcc Valve
150~.
o
Ram Free When
Speed 6,200 RPM
..... Manual
I Shutdown
Commanded Full Open
Figure 22. "Fail Open" anti~ice valve
CABIN
TEloPERATURE
SELECTOR
CHANGE
TRAllSIEllT COIJDITION - The system response to
cabi n tempera ture
se1ector changes \'las
demonstrated for various step changes in the
range of 55'F to 95'F.
To illustrate the
cabin temperature control response a step
change from 95'F to 55'F "as selected. The
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851320
12
Before BIT testing can begin, certain
conditions [Just be met.
First all BIT
checks are done on the ground in a static
ai rcraft mode. BIT only records conditi ons
that exi st at the time the test is made. No
provision for ~emory storage is provided.
BIT checks 'lUst be r.1ade Vii th b.o techni ci ans
havi ng a communi cati on 1i nk. One techni ci an
is required in the pilots position and one
stationed at the controller BIT panel. Full
el ectri cal power must he suppl i ed to tl.e ACS
and pneumatic pOl/er fror.1 the engines or a
gl'ound cart must he appl ied to the system.
threshol ds are set to
All
faul t
preclude nuisance problems.
CTCS CONTROLLER - The CTCS controller
checks ttle electric valves, sensors and
selectors and determines where ttle fault
lies (controller or line replaceable unit).
To check the add hot or add cold valves the
controller signals for a specific valve
angle actuator position.
If the actuator
position or the feed back null is '/rong a
controller fault is indicated.
If the
actuator position and the feedback null are
Vlrong, an actuator fault is indicated.
GENERAL BIT FEATURES
- Go/no go concept
front panel LED's
Light Enitting Diodes
- Rotary "litch test select
- l·ior.;entary sViitch test execution
- Active test disable "ith "Push to Test"
fail safe
- All
contro11 er
i nterf aced
cor,ponents
verifi ed
- Dedicated power supplies
- Solid state multiplexing
- Verification of 85% of active circuitry
The controller BIT checks the supply
temperature sensor by check ing its temperature in its noma 1 range. If out of range
(belDl'/ 42°F or above 267°F) a sensor failure
or an open circuit is indicated.
During
this test the temperature control valves are
driven to their test positions.
The cantrall er also checks the temperature selector by measuring pot Vliper voltage
at various positions.
ACS/fiCS COIITROLLEP- - The I:CS controller
self checks and checks the electric actuated
hot and cold modulating valves and missile
related sensors in a manner similar to thE:
CTCS controller.
The ACS controller self
checks and checks the anti-ice valve and Fev
opening and closing actien by checking the
position shitch action Hhen signalling each
valve open or closed. Verification of the
CED is accomplished ry c1.ecking the voltage
output.
A voltage less than 1 VDC or
greater than 9.7 VDC indicates a failure or
open ci rcuit.
The anti -i ce ten'peratu~e
sensor temperature is checked and oust be 111
a range of 20 to 50°F.
Temperatures
detected of 1ess than DOF or greater tl;an
70°F "ill indicate a sensor failure or open
circuit.
SU~It1AHY
The new B-52 G/H Aircraft ECS provides
sufficient cooling and heating for the
increased electronic and nissile heat loads
as well as providing a morE comfortaole and
fl exi b1e system for the fl i gilt crew.
Whil e
the system has been up-graded and contains
some innovativE fuel conservation controls
and failure protection, it was mostly
derived from p"oven, hi glJly re 1i ab 1e co",l'onents from a variety of commercial and
military aircraft.
The extensive component, sue-system and
combi ~ed system testi ng was i nstrumenta 1 in
developing a comprehensive, verified COiOPUter mathematical model of the system that
Vii 11 be llsed for future changes in mi s s il e
and electronic heat loads.
The design goals for system stability
as lIell as dynamic response have been extensively tested in the lab and 1.:ore extensively in the over seo hours of flight test and
regular Air Force service.
of
Credits: Figures 1, 2, 3 and 4 courtesy
The Boeing t:ilitary Aircraft Comnpany
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This paper is subject to revision. Statemcnts and opinions ad·
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responsibility, not SAE's; however. the paper has been edited
by SAt: for uniform styling and format. Discussion will be
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the SAE Publil:ations Division.
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