-·e
PIPER
COMANCHE
SERVICE
MANUAL
1
H8.
Ainpecd
Indicuor.
11·39 General.
The
airspeed indicator provides a means
of
indicann. the speed
of
the airplane
pusin,
chrou,h the air.
The
ainl'eed
Indication
is
the differential pressure
readinl
between
ricot
air pressure
and
static air pressure. This Insaumeftt has
the
diaphragm vented
to
the
pitot
air source
and
the
cue
is
vented
to the stacc air system.
As
the airplane
innases
'1peed. the pirot air pressure
increun.
auSltl!J the
diaphngm
to eXl"and. A mechanical
linkqe
~icks
up this motion and moves the instrUment rOlnter to
the
indlca.ted speed.
The
instrument dial
is
calibrated in
knou
and miles per hour.
and
also
hu
the
ncccssar'"
Ol'ftating ranlc markinp for safe
operation
of
the
a.irpLane.
1140
Remo'"
And Replacement. Ref." to
P.ragra~h
IH8
of
this section.
11-41.
Troublcshootinl.
Trouble
Tube does
not
heat
or
dear
iaclf
of
ice with
switch ·'01'1·' (Heated
pitOf
rubn
only.)
Tube docs
nOf
heat or
clear itself
of
icc
"Nith
SWitch
·'ON"
(Heated
pi
tOt
rubcs
only)
POinten
of
static instrU-
menu
do
not
indicate
!,ro!,crly
I POinter
of
Instnlment
osclllatC5.
INSTRUMENTS
ISSUED:
BI1Sn2
TABLE XI-VI. AIRSPEED TUBES AND INDICATOR
Cause
Remedy
Cimm
bro&ker popped.
Resot.
Open
cirCUit.
Repair.
Exccssive
volt~c
drop
Check voltage
at
pUOt
between battery and head.
?itot
head.
Hea~lng
eleme:tt burned
OUt.
Replace
pitot
head.
LC2.k
in
insmlment case or Check for leak and
se.ll
in.
picot lincs.
Leak
in
inStrument case.
C!'1eck
for leak and seal
3
Gl0
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