Bell hot fast start explanation letter
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Bell hot fast start explanation letter
I am trying to track down a copy of a Bell letter that explains why a hot fast start is better than a cool one. Not just the spiel about the reduced time taken.
It was along the lines of explaining that where the temperature is being read is not where the damage was being done and until the engine is up to speed the cooling airflow is unable to do what it is supposed to. From memory it was typed on a typewriter and late 70's or 80's.
I believe the engines in question were the 250 series. There is also a possibility the letter was issued by the engine manufacturer.
Any help would be appreciated.
It was along the lines of explaining that where the temperature is being read is not where the damage was being done and until the engine is up to speed the cooling airflow is unable to do what it is supposed to. From memory it was typed on a typewriter and late 70's or 80's.
I believe the engines in question were the 250 series. There is also a possibility the letter was issued by the engine manufacturer.
Any help would be appreciated.
I have the following letter in pdf and can send it to you if needed, (pm me an e-mail address)---this is just a "type copy" of it:
----... - --- ra,. COMMERCIAL SERVICE LETTER
Allison GAS TURBINE DIVISION General Motors Corporation
TECHNICAL ASPECTS ARE FAA APPROVED
SUBJECT: OPTIMIZED START TECHNIQUE FOR ALLISON 250-C20 SERIES AND C20R SERIES
ENGINES
Various misconceptions exist about what is a good start and how to obtain an
optimal start for an Allison 250-C20 or C20R Series engine. This service
letter addresses Bendix controlled engines specifically, but most of the
principles expressed also apply to engines utilizing CECO controls. Allison
recommends judging starts by the performance of a first start of the day
situation utilizing a fully charged battery. Do not attempt to adjust fuel
control systems based on cold soaked engines in low ambient temperatures or
by using an APU/GPU power source. An optimized start primarily focuses on
starting in the least possible time without exceeding any temperature
limits.
Allison defines a good first start as one taking less than 25 seconds from
the introduction of fuel until the engine reaches ground idle. To obtain an
optimized start, move the throttle to the ground idle position to begin fuel
flow as the Nl RPM accelerates through 12-15% Nl. Do ng1 wait for Nl RPM to
peak out before initiating fuel flow, as this will unnecessarily utilize
battery capacity early in the start cycle. Peak observed turbine outlet
temperature may reach 820·C for C20 Series engines or 860·C for C20R Series
engines during the optimized start. However, start temperature limits
remain as defined in the appropriate Operation and Maintenance Manual, not
to exceed 810·C for more than 10 seconds and never to exceed 927·C.
During starts Pilots should note temperature peaks, the drop between the
peaks as well as the total start time. This information will assist
maintenance personnel in making appropriate fuel control adjustments.
It does not matter which observed peak is the higher. At times the two
peaks may be so close together that they appear as one peak. In an
optimized start the temperature drop between the two peaks, known as the
start notch, is usually 50·C or less. However, the prime determinant of the
quality of the start is the length of time from introduction of fuel to
attaining 58% NI and releasing starter assist. Flight personnel should
provide maintenance personnel with accurate time and temperature information
in order to exact the most effective start adjustments.
December 15, 1992 2S0-C20 Series
2S0-C20R Series
CSL 1176
CSl 4050
ALLISON GAS TURBINE
Commercial Service Letter
There are two adjustments to balance starting on current Bendix systems;
start derichment and start/acceleration adjust.ent (tweeter). (See Figure
1). To affect start temperatures or stagnation below 301 NI, start
derichment should be adjusted. Start/acceleration adjustment is to be used
to remedy stagnation above 301 NI or regulate the start ta.perature above
301 NI. The start/acceleration adjust .. nt affects the entire start
schedule. It is possible that in adjusting the start/acceleration
adjustment, an additional adjustment of the start derichlent ~ be required
because of the startl acceleration adjustment influence on the entire engine
fuel schedule. Adjustments to the fuel control unit are considered normal
maintenance allowing compensation for wear or atmospheriC 'change. All fuel
control adjustments should be .ade only by qualified personnel familiar with
the adjustments and should always be accomplished in accordance with the
appropriate Allison Operation and Maintenance Mandal.
START DERICHMENT AD.lJSTMENT
Start/Acceleration and Start-Derichment Adjustments
Figure I
December 15, 1992 2S0-C20 Series
2S0-C20R Series
CSl 1176
CSL 4050
Page 2 of 3
ALLISON GAS TURBINE
Commercial Service Letter
If adjustments defined in the applicable Operation and Maintenance Manual do
not improve the start characteristics within a few attempts, the fuel
control may have been maladjusted previously and require returning both
start-derichment and start/acceleration settings to the nominal or neutral
position. Should this be required, uke a fuel flow (baby bottle) check
using a vessel calibrated in CCs to capture and .aasure initial fuel flow.
The Operation and Maintenance Manuals specify the procedure, define nominal
settings, and 1ndicatedesired fuel quantity to accomplish the fuel flow
test. Once proper fuel flow is attained, proceed with proper adjustment to
optimize the start. If correct fuel flow or starts cannot be atta1ned, the
fuel control.., be out of calibration. Return any out of calibration fuel
control unit to an authorized facility for adjustlent or repair.
Consistent long, cool starts (35 seconds or more) can be detrimental to the
gas producer turbine life. Remember that the temperatures indicated on the
TOT gauge are interturbine, between the gas producer and power turbine, and
m~ not reflect the temperatures being experienced by the first stage
turbine nozzle and first stage turbine wheel. The quick, warm starts
recommended by Allison actually increase cooling air flow in the combustion
section to help insulate the gas producer turbine.
This CSL outlines the Allison Gas Turbine philosophy on proper starting of
250-C20 Series and C20R Series engines. While it has been stated that
starting procedures and adjustments are helpful to C20 Series operators,
they are even more important to C20R Series operators. As stated by Allison
in C20R Series CSL 4031, a C20R Series engine start takes a few seconds
longer and will atta1n a higher peak TOT than its C20 Series counterpart,
installed in the same aircraft, in the same ambient conditions. It is these
start characteristics that make proper fuel control adjustments imperative
to optimize starts on C20R Series engines.
Fuel control adjustment may be required seasonally to compensate for ambient
change or if operational location MOves result in significant altitude
variation. Contact your authorized 250 Distributor or AMOC for assistance
if you do not feel confident in making the fuel control adjustment discussed
here, as defined in the Operation and Maintenance Manual, for each series
engine.
CUSTOMER SUPPORT
ALLISON GAS TURBINE DIVISION
GENERAL MOTORS CORPORATION
Page 3 of 3
EXPORT CONTROLLED Rolla-Royce
250-C30 SERIES OPERATION AND MAINTENANCE
.lIem Trouble
4 {cont) Engine lights off but will not
accelerate to idle speed at a
normal rate. (cont)
5
6
Engine lights off but flames
out during ground starts at
high altilude, especially above
5000 feet (1524 meters). during
cold ambient conditions.
Acceleration temperarure too
high during start.
TABLE 101 (cont)
Troubleshooting
probable Cause
Fuel nozzle
panlally ctogged
with carbon.
Remedy
Clean fuel nozzle. (Reter to Clean·
ing. para 3., 73-10-03.)
Fuel nozzle valve stuck par- Rep'ace fuel nozzle.
tially open.
Start derichment adjustment Make start derichment adjustment.
too low. (Refer to Start Derichment Adjustment.
para 3.0.(1), 73-20-02.)
Gas producer fuel control in- Replace control.
correcdy adjusted or calibration
has shifted.
Antt-iclng valve open and cabin
heat on. .
Foreign object damage or ero·
sion to compressor.
Faulty power tUrWIe governor.
Fuel nozzle partially clogged.
, Start derichment adjustment
too low.
Insu1ficient time allowed for
draining after an unsuccessful
starting attempt.
Reduced battery capacity.
This can produce low cranking
speed.
Close anti-iclng valve and turn off
cabin heat.
Inspect compressor
Replace governor.
Inspect fuel nozzle for carbon buildup.
Clean or reDlace as necessary.
Uake start derichment adjustment.
(Refer to Start Derichment Adjustment,
para 3.C. (1). 73-20-02).
Purge tt'le ellatneby motoring with
the gas producer lever and ignition
switch in OFF for approximately 10
sec before attempting a second start.
Recharge or replace battery.
High residua! TOT in excess Motor engine with starter leaving gas
of , SOOC (302~F). producer lever and ignition OFF.
Depreciated starter which is Replace starter.
not capable of dry motoring
gas producer (N1) above 15
percent.
72-00-00
Page 103
Jul1192
EXPORT CONTROlLED Rolis-Royce
25O-C30 SERIES OPERATION AND MAINTENANCE
START/ACCElERA 1100 --,
ADJUSTMENT
START DERICHMEliT ADJUSTMENT
Start/Acceleration and Stan Derlchment Adjustments
Figure 204
73-20-02
Page 209
Jul1192
----... - --- ra,. COMMERCIAL SERVICE LETTER
Allison GAS TURBINE DIVISION General Motors Corporation
TECHNICAL ASPECTS ARE FAA APPROVED
SUBJECT: OPTIMIZED START TECHNIQUE FOR ALLISON 250-C20 SERIES AND C20R SERIES
ENGINES
Various misconceptions exist about what is a good start and how to obtain an
optimal start for an Allison 250-C20 or C20R Series engine. This service
letter addresses Bendix controlled engines specifically, but most of the
principles expressed also apply to engines utilizing CECO controls. Allison
recommends judging starts by the performance of a first start of the day
situation utilizing a fully charged battery. Do not attempt to adjust fuel
control systems based on cold soaked engines in low ambient temperatures or
by using an APU/GPU power source. An optimized start primarily focuses on
starting in the least possible time without exceeding any temperature
limits.
Allison defines a good first start as one taking less than 25 seconds from
the introduction of fuel until the engine reaches ground idle. To obtain an
optimized start, move the throttle to the ground idle position to begin fuel
flow as the Nl RPM accelerates through 12-15% Nl. Do ng1 wait for Nl RPM to
peak out before initiating fuel flow, as this will unnecessarily utilize
battery capacity early in the start cycle. Peak observed turbine outlet
temperature may reach 820·C for C20 Series engines or 860·C for C20R Series
engines during the optimized start. However, start temperature limits
remain as defined in the appropriate Operation and Maintenance Manual, not
to exceed 810·C for more than 10 seconds and never to exceed 927·C.
During starts Pilots should note temperature peaks, the drop between the
peaks as well as the total start time. This information will assist
maintenance personnel in making appropriate fuel control adjustments.
It does not matter which observed peak is the higher. At times the two
peaks may be so close together that they appear as one peak. In an
optimized start the temperature drop between the two peaks, known as the
start notch, is usually 50·C or less. However, the prime determinant of the
quality of the start is the length of time from introduction of fuel to
attaining 58% NI and releasing starter assist. Flight personnel should
provide maintenance personnel with accurate time and temperature information
in order to exact the most effective start adjustments.
December 15, 1992 2S0-C20 Series
2S0-C20R Series
CSL 1176
CSl 4050
ALLISON GAS TURBINE
Commercial Service Letter
There are two adjustments to balance starting on current Bendix systems;
start derichment and start/acceleration adjust.ent (tweeter). (See Figure
1). To affect start temperatures or stagnation below 301 NI, start
derichment should be adjusted. Start/acceleration adjustment is to be used
to remedy stagnation above 301 NI or regulate the start ta.perature above
301 NI. The start/acceleration adjust .. nt affects the entire start
schedule. It is possible that in adjusting the start/acceleration
adjustment, an additional adjustment of the start derichlent ~ be required
because of the startl acceleration adjustment influence on the entire engine
fuel schedule. Adjustments to the fuel control unit are considered normal
maintenance allowing compensation for wear or atmospheriC 'change. All fuel
control adjustments should be .ade only by qualified personnel familiar with
the adjustments and should always be accomplished in accordance with the
appropriate Allison Operation and Maintenance Mandal.
START DERICHMENT AD.lJSTMENT
Start/Acceleration and Start-Derichment Adjustments
Figure I
December 15, 1992 2S0-C20 Series
2S0-C20R Series
CSl 1176
CSL 4050
Page 2 of 3
ALLISON GAS TURBINE
Commercial Service Letter
If adjustments defined in the applicable Operation and Maintenance Manual do
not improve the start characteristics within a few attempts, the fuel
control may have been maladjusted previously and require returning both
start-derichment and start/acceleration settings to the nominal or neutral
position. Should this be required, uke a fuel flow (baby bottle) check
using a vessel calibrated in CCs to capture and .aasure initial fuel flow.
The Operation and Maintenance Manuals specify the procedure, define nominal
settings, and 1ndicatedesired fuel quantity to accomplish the fuel flow
test. Once proper fuel flow is attained, proceed with proper adjustment to
optimize the start. If correct fuel flow or starts cannot be atta1ned, the
fuel control.., be out of calibration. Return any out of calibration fuel
control unit to an authorized facility for adjustlent or repair.
Consistent long, cool starts (35 seconds or more) can be detrimental to the
gas producer turbine life. Remember that the temperatures indicated on the
TOT gauge are interturbine, between the gas producer and power turbine, and
m~ not reflect the temperatures being experienced by the first stage
turbine nozzle and first stage turbine wheel. The quick, warm starts
recommended by Allison actually increase cooling air flow in the combustion
section to help insulate the gas producer turbine.
This CSL outlines the Allison Gas Turbine philosophy on proper starting of
250-C20 Series and C20R Series engines. While it has been stated that
starting procedures and adjustments are helpful to C20 Series operators,
they are even more important to C20R Series operators. As stated by Allison
in C20R Series CSL 4031, a C20R Series engine start takes a few seconds
longer and will atta1n a higher peak TOT than its C20 Series counterpart,
installed in the same aircraft, in the same ambient conditions. It is these
start characteristics that make proper fuel control adjustments imperative
to optimize starts on C20R Series engines.
Fuel control adjustment may be required seasonally to compensate for ambient
change or if operational location MOves result in significant altitude
variation. Contact your authorized 250 Distributor or AMOC for assistance
if you do not feel confident in making the fuel control adjustment discussed
here, as defined in the Operation and Maintenance Manual, for each series
engine.
CUSTOMER SUPPORT
ALLISON GAS TURBINE DIVISION
GENERAL MOTORS CORPORATION
Page 3 of 3
EXPORT CONTROLLED Rolla-Royce
250-C30 SERIES OPERATION AND MAINTENANCE
.lIem Trouble
4 {cont) Engine lights off but will not
accelerate to idle speed at a
normal rate. (cont)
5
6
Engine lights off but flames
out during ground starts at
high altilude, especially above
5000 feet (1524 meters). during
cold ambient conditions.
Acceleration temperarure too
high during start.
TABLE 101 (cont)
Troubleshooting
probable Cause
Fuel nozzle
panlally ctogged
with carbon.
Remedy
Clean fuel nozzle. (Reter to Clean·
ing. para 3., 73-10-03.)
Fuel nozzle valve stuck par- Rep'ace fuel nozzle.
tially open.
Start derichment adjustment Make start derichment adjustment.
too low. (Refer to Start Derichment Adjustment.
para 3.0.(1), 73-20-02.)
Gas producer fuel control in- Replace control.
correcdy adjusted or calibration
has shifted.
Antt-iclng valve open and cabin
heat on. .
Foreign object damage or ero·
sion to compressor.
Faulty power tUrWIe governor.
Fuel nozzle partially clogged.
, Start derichment adjustment
too low.
Insu1ficient time allowed for
draining after an unsuccessful
starting attempt.
Reduced battery capacity.
This can produce low cranking
speed.
Close anti-iclng valve and turn off
cabin heat.
Inspect compressor
Replace governor.
Inspect fuel nozzle for carbon buildup.
Clean or reDlace as necessary.
Uake start derichment adjustment.
(Refer to Start Derichment Adjustment,
para 3.C. (1). 73-20-02).
Purge tt'le ellatneby motoring with
the gas producer lever and ignition
switch in OFF for approximately 10
sec before attempting a second start.
Recharge or replace battery.
High residua! TOT in excess Motor engine with starter leaving gas
of , SOOC (302~F). producer lever and ignition OFF.
Depreciated starter which is Replace starter.
not capable of dry motoring
gas producer (N1) above 15
percent.
72-00-00
Page 103
Jul1192
EXPORT CONTROlLED Rolis-Royce
25O-C30 SERIES OPERATION AND MAINTENANCE
START/ACCElERA 1100 --,
ADJUSTMENT
START DERICHMEliT ADJUSTMENT
Start/Acceleration and Stan Derlchment Adjustments
Figure 204
73-20-02
Page 209
Jul1192
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Consistent long, cool starts (35 seconds or more) can be detrimental to the gas producer turbine life. Remember that the temperatures indicated on the TOT gauge are interturbine, between the gas producer and power turbine, and may not reflect the temperatures being experienced by the first stage turbine nozzle and first stage turbine wheel. The quick, warm starts recommended by Allison actually increase cooling air flow in the combustion section to help insulate the gas producer turbine.
Thanks
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Need CSL 1176
Clitheroe Kid
i need this letter and related stuff, mail me if you still have ;thanks in advance
i need this letter and related stuff, mail me if you still have ;thanks in advance
Join Date: Mar 2011
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Optimized start technique for allison 250-c20 series and c20r series engines
Hi Steve,
I have an MD500E with the C20R engine and would really appreciate if you could email me a copy of this letter. [email protected].
Many thanks,
Tomas
I have an MD500E with the C20R engine and would really appreciate if you could email me a copy of this letter. [email protected].
Many thanks,
Tomas
Tomas,
If you are operating the engine ALL CSL's and CSB's are free from RR Allison.
Sign up here - Aeromanager
After registration you can have it all!
CSL 1176 C20
CSL 4050 C20R
If you are operating the engine ALL CSL's and CSB's are free from RR Allison.
Sign up here - Aeromanager
After registration you can have it all!
CSL 1176 C20
CSL 4050 C20R
Don't confuse a HOT fast start with a HOT start. A good start is one where the start is up to GI in 25 -30 seconds without exceeding any start temp. limits!
Most FCU's have sufficient adjustment range to achieve this as long as a properly charged battery is used.
This is especially important on C20R powered helicopters as the inertia of the engine is higher that the C20B/J and you need all the power you can get from the battery. That is why the C20R powered Bell 206B and L's have heavier starter cables due to higher amperage during starts.
Hot SLOW starts on the other hand are a pretty good sign that you have already burnt off part of the N1 turbine wheels!
Most FCU's have sufficient adjustment range to achieve this as long as a properly charged battery is used.
This is especially important on C20R powered helicopters as the inertia of the engine is higher that the C20B/J and you need all the power you can get from the battery. That is why the C20R powered Bell 206B and L's have heavier starter cables due to higher amperage during starts.
Hot SLOW starts on the other hand are a pretty good sign that you have already burnt off part of the N1 turbine wheels!
