SERVICE INFORMATION LETTER

Engines, Systems & Services – Phoenix, Arizona

APPLICABLE: MAINTENANCE FLIGHT FOR ALL AIRFRAME MANUFACTURERS USING

X GENERAL AVIATION, GENERAL PRODUCTS
& ENGINEERING OPERATIONS AND/OR AUXILIARY POWER UNITS, OWNER/
OPERATORS, DISTRIBUTORS, SALES AND
SERVICE ORGANIZATIONS, AND FIELD
SERVICE REPRESENTATIVES.

This is a COMPLETE revision. This service information letter has been reprinted in its entirety. Please
remove and discard all pages of prior issues and replace with pages of this revision.

Subject: LEBOW TORQUEMETER SYSTEM FOR TPE331 ENGINE

Discussion:

This system is an essential piece of precision test equipment for those involved in heavy maintenance/
major repair of the TPE331 engine.

In the past, technical information to support operation, maintenance and calibration of the torquemeter
system has been from varied sources. The intent of this SIL is to consolidate this technical information
into a single document with is intended to be supportive of that already published in the various
manuals.

For TPE331 engines which incorporate the Strain Gage Torque Indicating System, refer to the Engine
Maintenance Manual for Calibration Procedures using a Lebow when one of the following occur.

*(1) Torque Ring Replacement

(2) Bridge No. 1 versus Bridge No. 2 difference is greater than 66 foot-pounds or ±0.10 volts.

*If the same torque ring is re-installed, a LeBow torque system calibration is not required. Perform
torque system bridge cross check.

*If a replacement torque ring is installed and current DSC shutdown voltage values are available for the
engine it was removed from, a LeBow torque system calibration is not required. Perform torque sys-
tem bridge cross check and calibrate the torque signal conditioner using current DSC values.

LEBOW TORQUEMETER SYSTEM FOR TPE331 ENGINE

Information contained herein is intended to provide the user of this test equipment specific details
regarding operation, maintenance and calibration of the system.

Topics discussed are as follows.

I. Review of system and intended usage.

II. Selection of additional equipment and alternatives.
III. System calibration and maintenance.
IV. Operational procedures.

NOTE: In the event of conflict between the information contained in this document and
official manuals, the information in official manuals shall govern.

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Copyright 1980, 2002 Honeywell International Inc. All rights reserved.
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I. Review of system and intended usage.

The system is comprised of a load cell and its anti-rotation bracket, torque readout, interconnect-
ing electrical cables and an extended beta tube. Additionally, laboratory quality gages for measur-
ing raw torque oil pressure, compensated torque oil pressure and gearcase negative pressure are
required.

When operated properly, the system provides an accurate measurement of the engines torque
output. By operating the engine at various power levels while measuring its raw torque oil pres-
sure, the engines characteristic torque sensor pressure curve may be determined. Data obtained
during the test is used for (1) verification of the engines raw torque oil pressure signal; (2) deter-
mination of new raw torque oil pressure line following maintenance action involving the torque
sensor; (3) calibration of torque compensator/transducer and aircraft torque indication system.

NOTE: The torquemeter system alone does not have the capability of providing all
necessary data to determine the engines thermodynamic performance
capability.

A typical Lebow “load cell”, shown in Figure 1, has a shaft fitted with strain gages as shown in
Figure 2. These strain gages are electrically connected to form a bridge circuit as shown in Figure
3. This load cell bridge circuit is electrically connected to a torque readout instrument. As load is
applied by the propeller, the load cell shaft twists, resulting in a change in strain gage resistance.
This resistance change is monitored by the readout instrument and displayed as torque in foot-
pounds or inch-pounds; the more the shaft twists, the greater the resistance change and the
higher the indicated torque.

During manufacture, the load cell strain gage resistance values are determined and recorded on a
data sheet which accompanies each load cell. Resistance values are determined in both clock-
wise and counterclockwise direction of torque application. This data is used in calibrating the
Lebow load cell and matching it with the readout indicator with which it is to be used.

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Figure 1

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Figure 2

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Figure 3

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II. Selection of additional equipment and alternatives.

Certain pieces of supportive equipment are required for use with the torquemeter system. A deci-
sion regarding procurement of this equipment is dictated by such things as economic impact,
convenience, etc.

The propeller is considered to be auxiliary to the torque measuring equipment. For the frequent
user of the Lebow system, a “slave” propeller may offer important advantages over the use of the
customer’s propeller as a loading device. These include the liability for possible damage which
can occur while handling and installing the customer’s propeller with the Lebow, as well as from
F.O.D. when testing the engine. The propeller should be properly balanced to prevent vibration
affects on Lebow output.

Another advantage of the use of a slave propeller is that it could be selected to satisfy the loading
requirements for all engine models of a given direction of rotation. Further, since the engine is
ignorant of what propeller model is applying the load, the need for a selection of extended beta
tubes to satisfy all manufacturer’s propellers would be eliminated. Test propeller selection should
also include consideration of load requirements of the engine model(s) to be tested. Finally, the
load cell, properly protected from the elements, could be left attached to the slave propeller, thus
reducing installation/removal time.

Pressure gages used for measurement of raw torque oil pressure, compensated torque oil pres-
sure and gearcase negative pressure should be of laboratory quality. Gages with a 4 to 6 inch
diameter face graduated in appropriate increments are desirable. These gages should have an
accuracy of ±1/2 percent of full scale reading and their calibration verified on a regular, periodic
basis. Use of gages of unknown accuracy, and those which have a high full scale range should be
avoided. For example, a 0 to 1000 PSI gage should not be used to measure a 100 PSI pressure.
Recommended gages and their range are as follows.

Raw torque oil pressure: 0 to 100 PSIG in 1/2 PSI increments

Compensated torque oil pressure: 0 to 100 PSIG in 1/2 PSI increments
Gearcase vacuum: 0 to 30 inches (Hg) Vacuum in 1/2 inch (Hg) increments

NOTE: A combination pressure-vacuum gage with range of –30 inches (Hg) to +15
or +30 PSIG may be used for measuring gearcase vacuum.

An alternate gage is also available which measures the combined positive and negative raw
torque oil pressures. The gage reads the torque sensor delta pressure from 0 to 100 PSID in 0.5
PSID increments. The high side of the gage is connected to the raw torque oil pressure. The low
side of the gage is connected to gearbox case pressure. This gage precludes the need for manual
computation of raw torque oil delta pressure by the algebraic addition of raw torque pressure and
gearbox case pressure.

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III. System calibration and maintenance.

Since few commercial metrology test laboratories are equipped to calibrate a torque indicating
system, users of this equipment have found it necessary to acquire or locally fabricate a means of
“dead weight” testing the Lebow torquemeter. Periodic calibration checks are essential to insure
accuracy of the data recorded and to provide reliable indications when troubleshooting.

The torquemeter system calibration fixture is shown in Figure 4. It consists of a lever arm of
known length, a number of 50 pound weights and a hangar arrangement on one end of the arm on
which the weights are hung.

Dead weight calibration of the system is quite simple. One flange of the torquemeter is bolted to a
rigid structure capable of supporting both the weight of the system and of withstanding the in-
tended applied torque. The weight of the system will be 700 pounds or more, and the torque,
approximately 35,000 inch-pounds. The lever arm is bolted to the other flange and the torque-
meter is electrically connected to a readout indicator. Known weights are then incrementally
added to the lever arm while the resulting torque is displayed on the readout, and is recorded. For
example, ignoring the weight of the arm itself, if 50 pounds are exerting a force at 6 feet distance
on the lever arm, the applied torque would be 50 pounds X 6 feet = 3000 foot-pounds, and a
properly calibrated readout would display this number.

The engine end of the torquemeter must be attached to a smooth flat surface and be located high
enough for the hanging weights to clear the floor (approximately 6 feet above the floor).

The following is the recommended step-by-step procedure for dead weight calibration.

NOTE: Locate digital torque indicator so that a temperature range of 10 to 49°C (50
to 120°F) is maintained during test adjustment procedure. Ensure that
digital torque indicator case is grounded through AC power cable (3 prong
plug). Ensure that sliprings of torquemeter are clean and dry by removing
slipring cover and if necessary, spray sliprings with degreaser and cleaner
(MS-180 Freon). Wipe accessible surfaces clean with lint-free cloth, while
rotating the sliprings.

1. Connect digital torque indicator to a 115 ±10 volts (grounded power supply), 50 to 60 Hz
outlet. Ensure that the indicator power source is not in the same circuit with other high
amperage equipment such as are welders, lathes, etc, which might cause supply voltage
variation during Lebow testing.

2. Connect digital torque indicator to torquemeter (Figure 1) using electrical cable provided with
system.

3. Place power switches (located at rear of digital torque indicator) to ON position to begin
electrical warmup.

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Figure 4

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NOTE: Carefully fit torquemeter on flange of rigid support structure which

simulates engine propeller shaft ensuring that aligning pins on shaft
flange and pin holes on torquemeter engage and seat fully with hand
pressure. If satisfactory alignment cannot be achieved, investigate the
cause of improper fit and make adjustments as required.

4. Determine desired direction of rotation for calibration as determined in Step 6.(b). For a
clockwise rotation propeller, lever arm should be attached to the torquemeter extending to the
right of the torquemeter when facing it. For counterclockwise rotation propeller, it should
extend to the left.

5. Install electrically connected torquemeter on support structure propeller flange. If torque-

meter fails to bottom against support structure propeller flange, remove torquemeter, clean
pin holes and pins of dirt, corrosion or other obstruction and reinstall. Secure with existing
propeller mount bolts and washers (only hand tightened at this time).

6. Adjust digital torque indicator as follows.

NOTE: Ensure that digital torque indicator and torquemeter have been electri-
cally stabilized for a minimum of 1 hour prior to setting.

(a) Set zero on indicator by adjusting coarse and fine balance screws on digital torque
indicator face plate.

(b) Set propeller rotation switch at (+) (clockwise) for right hand propeller rotation (viewed
from rear of engine) or (–) (counterclockwise) for left hand propeller rotation (viewed
from rear of engine).

CAUTION: TORQUEMETER INSTALLATION BOLT TORQUE IS CRITICAL.

EXERCISE CARE DURING INSTALLATION.

7. Initially tighten bolts securing torquemeter to support structure flange to 30 foot-pounds

torque using 292157-1 adapter wrench and following sequence shown in Figure 5. Tighten
bolts to final torque of 100 foot-pounds following same torque sequence. (Note Dowty Rotol
Torque, 63 to 67 foot-pounds.)

NOTE: See Figures 6, 7, and 8 for information on torque wrench adapters.

Check reading on digital torque indicator to determine if a shift of more than ±300 inch-
pounds (±25 foot-pounds) occurred, loosen and retighten bolts in accordance with preceding
steps to remove side loading of torquemeter. If shift is less than ±300 inch-pounds,
rebalance indicator to zero in accordance with preceding Step 6.(a).

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Figure 5

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Figure 6

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Figure 7

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Figure 8

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HARTZELL PROPELLER TORQUE WRENCH ADAPTER CORRECTIONS

To determine the torque wrench setting for 40, 80, 100 and 105 foot-pounds torque, locate the block
corresponding to the TORQUE WRENCH EFFECTIVE LENGTH versus the ADAPTER LENGTH.

TORQUE WRENCH EFFECTIVE LENGTH

16I 17I 18I 19I 20I 21I 22I 23I 24I
ADAPTER 30 31 31 32 32 32 33 33 33
LENGTH 61 62 63 63 64 65 65 66 66
5I
77 78 79 80 80 81 82 83 83
80 81 82 83 84 84 85 86 86
29 30 30 30 31 31 31 32 32
58 59 60 61 62 62 63 63 64
I
6I
73 74 75 76 77 78 79 80 80
76 77 78 79 80 81 82 83 84
27 28 29 29 30 30 30 31 31
56 57 58 58 59 60 61 61 62
I
7I
70 71 72 74 75 75 76 77 78
73 74 75 76 77 78 79 80 81
26 27 28 28 29 29 29 30 30
53 54 55 56 57 58 59 59 60
I
8I
67 68 70 71 72 73 74 75 75
70 71 72 73 75 76 77 77 78
25 26 27 27 28 28 28 29 29
51 52 53 54 55 56 57 57 58
I
9I
64 66 67 68 69 70 71 72 73
67 68 70 71 72 73 74 75 76
24 25 26 26 27 27 27 28 28
49 50 51 52 53 54 55 56 56
I
10I
62 63 65 66 67 68 69 70 71
64 66 67 68 70 71 72 73 74
23 24 25 25 26 26 27 27 27
47 49 50 51 52 52 53 54 55
I
11I
60 61 63 64 65 66 67 68 69
62 63 65 66 67 68 70 71 72
22 23 24 25 25 25 26 26 27
46 47 48 49 50 51 52 53 53
I
12I
58 59 60 62 63 64 65 66 67
60 61 63 64 65 66 67 69 70

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DOWTY ROTOL PROPELLER TORQUE WRENCH ADAPTER CORRECTIONS

To determine the torque wrench setting for 63 and 67 foot-pounds torque, locate the block correspond-
ing to the TORQUE WRENCH EFFECTIVE LENGTH versus the ADAPTER LENGTH.

TORQUE WRENCH EFFECTIVE LENGTH

16I 17I 18I 19I 20I 21I 22I 23I 24I
ADAPTER 48 49 50 50 51 51 52 52 53
LENGTH 5I
51 51 52 53 53 54 54 55 55
46 47 48 48 49 49 50 50 51
I
6I
48 49 50 50 51 52 52 53 53
44 45 46 47 47 48 48 49 49
I
7I
46 47 48 48 49 50 50 51 51
42 43 44 45 45 46 47 47 48
I
8I
44 45 46 47 47 48 49 49 50
41 42 42 43 44 45 45 46 46
I
9I
42 43 44 45 46 46 47 48 48
39 40 41 42 42 43 44 44 45
I
10I
41 42 43 43 44 45 46 46 47
38 39 40 40 41 42 42 43 44
I
11I
39 40 41 42 43 43 44 45 45
36 37 38 39 40 41 41 42 42
I
12I
38 39 40 41 41 42 43 44 44

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8. Install S9413-037 O-ring (packing) on piston groove of torquemeter. Carefully (so as not to
damage packing) install lever arm on torquemeter in true horizontal position and secure
(hand tight) with bolts and washers furnished with torquemeter. If the lever arm is not hori-
zontal, determine angular error and apply lever length correction factor per Table 1.

CAUTION: TORQUEMETER INSTALLATION BOLT TORQUE IS CRITICAL.

EXERCISE CARE DURING INSTALLATION TO ENSURE
TORQUE APPLICATION IS UNIFORM AND OF PROPER FINAL
VALUE.

NOTE: A propeller protractor may be used to determine lever arm deflection

angle.

Table 1. Lever Arm Correction for Deflection Angle

Angle Correction Factor
2° 0.9994
4° 0.9976
6° 0.9945
8° 0.9903
10° 0.9848
Example angle = 6°, Lever Arm = 70.28
S Corrected Lever Arm = 70.28 X 0.9945 = 69.89
S Use the corrected lever arm length when making calculations during calibration.

9. Initially tighten bolts to 30 foot-pounds torque using 292155-1 adapter wrench and following
torque sequence shown in Figure 5. Tighten bolts to final torque at 100 foot-pounds following
same torque sequence.

NOTE: If satisfactory alignment cannot be achieved, investigate the cause of

improper alignment.

10. Check reading on digital torque indicator to determine if a shift occurred in the zero adjust-
ment. If a shift of more than ±50 inch-pounds (±4 foot-pounds) is noted, loosen bolts, check
alignment and proper fit of alignment pins and pin holes and reinstall lever arm in accordance
with preceding Step 9. If problem persists, check arm flange for flatness and repeat Step 9.

11. Install the weight hanger on the lever arm at the knife edge. Measure the lever arm from
center of propeller shaft to knife edge using inches to second decimal place.

12. Insure system has electrically stabilized (electrically warmed up for a minimum of 1 hour).

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NOTE: The following paragraphs regarding calibration procedures are applica-

ble to only the 9000 series Daytronic readout. Refer to the manufactur-
er’s manual for operating instructions for other readout models.

13. With the lever arm and weight hanger installed, adjust the coarse and fine Balance poten-
tiometers as required to zero the readout.

NOTE: Ensure calibration weights are accurate.

14. Hang 500 pounds of weight on the weight hanger. Multiply corrected lever arm length per
Step 8 and 11 by actual total weight.

Example: 69.89 inches X 500 pounds = 34,945 inch-pounds

34,945 inch-pounds = 2912 foot-pounds

12

Adjust coarse and fine potentiometers of Span as required to display 2912 on readout.

15. Remove all weights from weight hanger. Tap lever arm lightly with hand to normalize load
cell. Readout should read zero. If not, readjust Balance potentiometers as required to zero
readout. If Balance adjustment is required, repeat Step 13.

16. Repeat Steps 14 and 15 until readout reads zero with lever arm installed and no weights and
2912 foot-pounds with 500 pounds of weight.

17. With no weights hung and readout displaying zero, hang weights in 50 pound increments until
500 pounds are hung. Normalize load cell as each weight is hung by lightly tapping arm as
before. As each weight is hung, record value displayed on readout.

18. Remove weights in 50 pound increments and record value. When all weights are removed,
readout should display zero.

19. Plot and compare with data recorded during addition of weights. Data should plot within ±15
foot-pounds. If plot is outside of limits, troubleshoot per Honeywell Ground Equipment
Manual, 72-GE-06.

20. If Step 19 is acceptable, remove weight hanger and lever arm. Readout should now display
negative value of torque.

21. Adjust Balance course and fine potentiometers as required to obtain zero on readout.

22. Press proper CAL button (+ or –) and record value displayed on readout. This value is very
important since it it now the system calibration value for the direction of rotation setup.

23. Dismantle the setup: the system is now “dead weight” calibrated.

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When torquemeter system is to be installed on an engine, the following procedures apply.

1. Electrically connect readout to load cell, begin electrical warm-up and continue setup.

2. Install torquemeter on engine with eight bolts following the procedure used for attachment for
dead weight test (Step 5, Page 9).

3. Attach propeller to torquemeter with eight bolts, again following procedure for attachment for
dead weight test, torquemeter to lever arm, Steps 9 and 10, Dowty Rotol Torque of bolts is 63
to 67 foot-pounds.

4. Install anti-rotation bracket and beta tube. Set flight idle blade angle per Aircraft Maintenance
Manual.

NOTE: It is not necessary to set blade angle precisely unless engine is to be

flown with Lebow installed. (If aircraft is to be flown with Lebow
installed, ensure a flightworthy model Lebow is used.)

5. After 1 hour electrical stabilization, operate engine to bring oil system to normal operating
temperature. Exercise propeller from full reverse to mid power forward thrust several times,
and shut engine down per Aircraft Flight Maintenance Manual.

6. With engine RPM zero, adjust Balance potentiometers as required to zero readout.

7. If propeller is clockwise rotation, depress and hold CAL+ button. Adjust Span potentiometers
as required to obtain value displayed on readout recorded for CAL+ during dead weight cal-
ibration. Repeat balance and span potentiometer adjustments as required to obtain zero and
recorded CAL+ value. Use same procedure for counterclockwise propellers except depress
CAL– button and adjust Span potentiometers to recorded CAL– value. The system is now
calibrated and ready for use.

8. Perform engine calibration run in accordance with the Engine Maintenance Manual.

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Maintenance

The Lebow torquemeter system requires no scheduled or periodic servicing/maintenance beyond the
routine care and cleaning given a piece of precision test equipment before and after each use.

A dead weight calibration is recommended after 10 uses or each 6 months, whichever occurs first.
Additionally, due to possible shock loading and loss of calibration that may occur during transportation
(shipping), it is recommended a dead weight calibration be performed following transportation of the
system.

CAUTION: IF IT IS KNOWN THE LEBOW LOAD CELL ENCOUNTERED ANY SHOCK

LOADING EITHER DURING TRANSPORT OR DURING NORMAL USE, IT
SHOULD BE RE-CALIBRATED.

If it is not possible to calibrate the system after transportation, the system may still be used as long as
all components used (Lebow, cables and output box) are the same as used when last calibrated.

NOTE: When at all possible the same components used to calibrate the system should
be used in normal operation. This will reduce indication errors due to different
equipment being used.

Honeywell Ground Equipment Manual, 72-GE-06, provides detailed instructions for all levels of mainte-
nance of the components of the system. Following are suggestions which may be found helpful when
troubleshooting system problems.

Shift in zero or span calibration points may result from distortion induced by irregularities in the flanges,
improper or uneven torque on the flange bolts.

Shift in zero set point (zero does not repeat following engine calibration run) may result from inade-
quate electrical warmup prior to beginning engine calibration run. Also, prior to performing engine
calibration, the propeller must be exercised sufficiently to heat the engine oil so that it can temperature
stabilize the load cell (exercise propeller by varying blade angle from full reverse to mid power forward
thrust blade angle).

S Erratic readings are usually caused by poor contact between brushes and sliprings in load cell.
(Presence of moisture, oil, dirt, corrosion, excess propeller vibration, etc.)

S Inability to calibrate may be attributable to electrical circuit problems (shorts, grounds, faulty
connectors in cables, etc).

S Calibration drift may also be caused by insufficient “warm-up” electrically.

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IV. Operational procedures.

Procedures discussed herein are not intended to be used in lieu of published official procedures.
Their purpose is to acquaint the reader with a logical sequence of steps to be followed in perform-
ing an engine torque system calibration run. All test runs should be done in a no or low wind
condition. Gusty or crosswinds will adversely affect readings. Recommendation for maximum
wind condition during test, 5 knots gusty, 10 knots steady. Rain should be avoided also, as mois-
ture can affect the Lebow torquemeters.

1. Install torquemeter system and propeller using bolt torque procedures discussed previously.
Connect applicable pressure gages. Insure minimum 1 hour electrical warm-up prior to use.

2. Prior to engine calibration, calculate expected maximum indicated torque at maximum power
point. This calculation is necessary in those cases where the engine will reach its maximum
rated power for the aircraft application before it becomes temperature limited. Using the
following basic shaft horsepower formula, expected indicated torque may be calculated.

The formula: T = SHP X K

N

Where T is torque expressed in inch-pounds or foot-pounds.

Where N is speed of the engines output shaft expressed in RPM. (Output shaft is propeller
shaft. 1591 RPM or 2000 RPM for TPE331.)

Where K is a constant used to calculate shaft horsepower (SHP), K = 63,025 if torque is

expressed in inch-pounds. If the torque is in foot-pounds, K = 5252.

Example 1: Assuming engine is flat rated at 840 SHP with 2000 RPM propeller shaft speed
at 100 percent RPM and torquemeter system to be used reads in inch-pounds.

T = 840 X 63,025
2000

T = 26,470.5 inch-pounds which may be rounded off to 26,471 inch-pounds.

Example 2: Engine is flat rated at 900 SHP, has 1591 RPM propeller shaft speed and
torquemeter system to be used displays foot-pounds.

T = 900 X 5252
1591

T = 2,970.96 foot-pounds which may be rounded off to 2,971 foot-pounds.

3. Zero torquemeter system indicator by adjusting Balance potentiometers.

4. Depress and hold CAL+ or – button (as applicable) and adjust Span potentiometers as re-
quired to obtain calibration number established during dead weight calibration.

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5. Repeat Steps 3 and 4 as required to ensure both ZERO and Span readings repeat.

6. Operate engine with propeller off the start locks and exercise propeller to bring engine oil
temperature to stabilized value. Using normal procedure, shut engine down. When propeller
stops rotating, repeat Steps 3, 4 and 5.

7. Begin calibration. Operate engine at 100 percent RPM and minimum torque with propeller off
locks and record torquemeter system indicated torque and raw torque oil pressure and case
negative pressure. Operate engine at 100 percent RPM and indicated torque calculated in
Step 2 or at temperature (EGT or ITT) limit, whichever is reached first. Record torquemeter
system indicated torque and raw torque oil pressure and case negative pressure.

8. Calculate intermediate power points as follows.

Subtract lowest torque indication recorded in Step 7 from highest indicated torque. Calculate
and record 20, 40, 60, 70, 80 and 90 percent of this difference, and add to minimum torque
reading. These will be the target intermediate power points for engine calibration.

9. The following data will be recorded during the test. The power settings are based on the
percent of the increment between the minimum and maximum established in Step 8.

Figure 9 may be used as a typical data sheet. In the event the user of this SIL anticipates
frequent use of the Lebow torquemeter system, it is suggested Figures 9, 10 and 11 be repro-
duced in quantities to satisfy those needs.

Allow the engines to stabilize for 3 minutes minimum at each power point.

Maintain stabilized oil temperature during the entire run.

Using run sheet from Figure 9, record the torque, EGT or ITT, RPM, fuel flow, oil temperature
and oil pressure, raw torque pressure, and gearcase pressure or PSID from raw and gear-
case at each point.

Record post-test Zero and Span. If Zero repeats within 10 foot-pounds, the system is satis-
factory. If not, recalibrate indicator and repeat test.

NOTE: Zero should be determined immediately after the propeller has stopped
rotating.

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Figure 9

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10. Data Evaluation

For engines equipped with Hydraulic Compensators, use the following procedures.

(a) From data recorded on Figure 9, compute raw torque delta pressure. This computation
is made by adding the raw torque pressure (PSIG) to the absolute value of the case
negative pressure (minus inches HG). To do this, change inch Hg to PSI. One PSI =
2.036 inches in HG which may be rounded off to 2.

Example: Recorded raw torque pressure 35 PSIG

Case pressure recorded –4.0 inches HG

4 + 35 = 37 PSID
2

After computing raw torque delta pressure for each data point on Figure 9, transpose
this information to Figure 10 and label “Raw Torque delta P (PSID)”.

NOTE: The above is not required if delta pressure gages are used.

(b) From the engine maintenance manual, locate the required compensated oil pressure
line and transpose it onto Figure 10. This line will depict compensated torque oil pres-
sure required at specific torques (inch-pounds or foot-pounds as applicable). This
same information is available from the engine’s DSC (Data Sheet, Customer). Label
this line “Compensated Torque Oil Pressure (COP) PSID”.

NOTE: If test has been run for purpose of verifying torque sensor output,
plot should overlay previous raw torque line ±1 PSID. As a
result of torque sensor replacement or maintenance involving the
torque sensor, the values most likely will be different from that
shown on last DSC.

(c) Perform torque compensator adjustment in accordance with the applicable Engine
Maintenance Manual.

(d) Perform calibration of aircraft torque transmitter/aircraft torque indication system in

accordance with Aircraft Maintenance Manual.

(e) File Figure 10 or a copy thereof with the engines permanent records/logbook. It should
be identified with the engines model number, serial number, the date and a statement
advising “this data supersedes all previous torque sensor data on this engine”.

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Engines, Systems & Services – Phoenix, Arizona

Torque Sensor Output Characteristics

Figure 10
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Engines, Systems & Services – Phoenix, Arizona

For engines equipped with Hydro-Electric Torque Indication System, use the following
procedures.11.

(a) From data recorded in Figure 9, compute raw torque delta pressure. This computation
is made by adding the raw torque pressure (PSIG) to the case negative pressure (mi-
nus inches HG). To do this, change inches HG to PSI. One PSI = 2.036 inches HG
which may be rounded off to 2.

Example: Recorded raw torque pressure 35 PSIG

Case pressure recorded –4.0 inches HG

4 + 35 = 37 PSID
2

After computing raw torque delta pressure for each data point on Figure 9, transpose
this information to Figure 10 and label “Raw Torque delta P (PSID)”.

(b) From engine DSC (Data Sheet, Customer) determine high and low torque values at
which torque pressure (delta P) should be recorded.

Following are examples from typical DSC’s.

Example 1:
22,500 IN.-LBS TORQUE PRESSURE (DELTA P) 715 SHP, PSID RECORD
1800 IN.-LBS TORQUE PRESSURE (DELTA P) PSID RECORD

Example 2:
28,300 IN.-LBS TORQUE PRESSURE (DELTA P) 715 SHP, PSID RECORD
26,300 IN.-LBS TORQUE PRESSURE (DELTA P) 665 SHP, PSID RECORD
2260 IN.-LBS TORQUE PRESSURE (DELTA P) PSID RECORD

Example 3:
27,700 IN.-LBS TORQUE PRESSURE (DELTA P) 700 SHP, PSID RECORD
2300 IN.-LBS TORQUE PRESSURE (DELTA P) 58 SHP, PSID RECORD

As may be noted from the examples, each engine model has a different high and low
torque value at which torque pressure (delta P) is recorded.

(c) After determining the high and low torque values from the engine DSC, utilize Figure
10 to determine actual torque pressure (delta P) at those indicated Lebow torques.
Record these Lebow torque values and corresponding torque pressures on Figure 11.

(d) Perform calibration of torque transducer, and aircraft torque indication system in accor-
dance with Engine and Aircraft Maintenance Manuals as applicable.

(e) File Figures 10 and 11 or copies thereof with the permanent records of the engine
(logbook). Included should be engine model number, serial number, date, and a state-
ment advising “this data supersedes all previous torque sensor data on this engine”.
July 1/80
Revision 6, Mar 6/02 P331-102
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 SERVICE INFORMATION LETTER
Engines, Systems & Services – Phoenix, Arizona

Figure 11

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