Engine stabilisation times
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Engine stabilisation times
Folks, currently flying the Dash 8 Q400 which is equipped with the ever faithful Pratt and Whitney PW150's (or at least they have been for me!)
Recently, we introduced single engine taxi both before take off and after landing.
Several colleagues have commented that we don't have a defined stabilisation time for the second engine. If the first officer is particularly keen, we can be setting the power for take-off just about less than 2 mins than post start #1.
Other manufactures publish specific stabilisation times before take-off power should be set, yet for the PW150's I have not found anything.
2 Minutes used to be quoted by some RR old school Trent's.. Any ideas?
Recently, we introduced single engine taxi both before take off and after landing.
Several colleagues have commented that we don't have a defined stabilisation time for the second engine. If the first officer is particularly keen, we can be setting the power for take-off just about less than 2 mins than post start #1.
Other manufactures publish specific stabilisation times before take-off power should be set, yet for the PW150's I have not found anything.
2 Minutes used to be quoted by some RR old school Trent's.. Any ideas?
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For the Boeing we usually give 3 mins after landing for thermal shock reasons so I would assume it would be similar for engines to.
If your think of it in a practical way would you rev your car engine straight away after turning on for the first time in 12 hours or would you let it run for a bit to get the oil going?
If your think of it in a practical way would you rev your car engine straight away after turning on for the first time in 12 hours or would you let it run for a bit to get the oil going?
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Engine stabilisation times
With winter upon us, you want that 55 degrees Celsius anyway if you're taking off into the ice. That does take some time...
On our outfit, we'll taxi out with one feathered but turning, and then unfeather with sufficient time to perform the checklist. That is something like 2 minutes anyway. We're only making single-engine taxiing after landing.
On our outfit, we'll taxi out with one feathered but turning, and then unfeather with sufficient time to perform the checklist. That is something like 2 minutes anyway. We're only making single-engine taxiing after landing.
The only really limiting figure on the PW150 when it comes to T/O power is engine oil temperature.
In non-icing conditions, takeoff power may be set as soon as oil temperature is above 0°C, which is generally not really a problem to achieve. As my very estimated colleague has written above, the 55°C for departure in or into icing conditions are a different animal and take ages to reach on occasion.
As the oil is mainly heated by the bearings and the RGB, the time it takes to reach that magical number is directly related to engine speed. So in order to speed things up a little bit, taxi with both propellers unfeathered. When standing, placing the power levers ever so slightly behind the DISC gate into the reverse area (minding a possibly slippery ground of course!) will give You a percent or two of compressor speed as well and save some time.
While the time saved by this is certainly noticeable, it still takes ages to get the last few degrees. Do remember this when selecting Your mixture du jour for deicing! Being pennywise and taking only the thinnest possible mixture can come back to bite You in the rear end when You spend all Your hold over time waiting for the oil to heat up and need to come back for a second treatment.
In non-icing conditions, takeoff power may be set as soon as oil temperature is above 0°C, which is generally not really a problem to achieve. As my very estimated colleague has written above, the 55°C for departure in or into icing conditions are a different animal and take ages to reach on occasion.
As the oil is mainly heated by the bearings and the RGB, the time it takes to reach that magical number is directly related to engine speed. So in order to speed things up a little bit, taxi with both propellers unfeathered. When standing, placing the power levers ever so slightly behind the DISC gate into the reverse area (minding a possibly slippery ground of course!) will give You a percent or two of compressor speed as well and save some time.
While the time saved by this is certainly noticeable, it still takes ages to get the last few degrees. Do remember this when selecting Your mixture du jour for deicing! Being pennywise and taking only the thinnest possible mixture can come back to bite You in the rear end when You spend all Your hold over time waiting for the oil to heat up and need to come back for a second treatment.
Airbus CFM - Company says 2 mins but FCOM is less clear
At Boeing (where we want to minimize any unnecessary engine wear or deterioration prior to turning the aircraft over to the buyer) we use 5 minutes for both warm-up and cool-down. 
Also remember, for warm-up during winter operating conditions (i.e. really cold) most engines have a minimum oil temp before setting high power.
Also remember, for warm-up during winter operating conditions (i.e. really cold) most engines have a minimum oil temp before setting high power.
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2nd Engine Warm/Cool Times
While the responses are slightly varied and if there is a common point, I'm reading Engine Oil Temperature as the true measure, not the clock. The Oil Temperature of that second engine, either fully off or a minimum idle, also seems to pass the Common Sense test. While the actual calculation of a time includes multiple other variables that are well above my pay grade, I particularly like @tdracer's note,
"At Boeing (where we want to minimize any unnecessary engine wear or deterioration prior to turning the aircraft over to the buyer) we use 5 minutes for both warm-up and cool-down.
Also remember, for warm-up during winter operating conditions (i.e. really cold) most engines have a minimum oil temp before setting high power." (Sorry, I could not find the quote button today.) Their use of five minutes seems to meet all of the objectives as well as providing a simple number for line flying. I don't think any operating company will bitch about five minutes when the SOP may say three. And your mileage may vary.
"At Boeing (where we want to minimize any unnecessary engine wear or deterioration prior to turning the aircraft over to the buyer) we use 5 minutes for both warm-up and cool-down.
Also remember, for warm-up during winter operating conditions (i.e. really cold) most engines have a minimum oil temp before setting high power." (Sorry, I could not find the quote button today.) Their use of five minutes seems to meet all of the objectives as well as providing a simple number for line flying. I don't think any operating company will bitch about five minutes when the SOP may say three. And your mileage may vary.
Oil temp is important, but there are other aspects. Thermal shock of setting high power on a cold engine or shutting down a hot engine can cause compressor or turbine rub and permanent performance loss.
Also, shutting down an engine when it's still really hot can result in fuel or oil coking due to the thermal soak-back - both can have bad long term results.
I'm referring of course to large turbine engines - no idea how susceptible turboprops might be.
Also, shutting down an engine when it's still really hot can result in fuel or oil coking due to the thermal soak-back - both can have bad long term results.
I'm referring of course to large turbine engines - no idea how susceptible turboprops might be.
The fuel flow is about half with the prop feathered.
. Not only potential fuel savings, but we get lots of complaints that the airplane taxis too fast at idle thrust and they need to ride the brakes.BTW, yes, variable pitch fan blades have been looked at. At least so far, the cost, weight, complexity, and failure modes have made it less than desirable. Plus, to make it really worthwhile would require variable area fan nozzles
With regards to stabilisation and warming up of the turbine engine, a difference between a turbojet/fan and a PW150 is the time it takes to get the engine into a condition in which it can deliver takeoff thrust (allow me to use this word for the propeller here as well for operational comparability, although some may certainly cringe at this).
For example, a RR Tay engine takes about 30 seconds from pushing the start select switch until the engine is stabilized and theoretically able to respond to a takeoff power demand. Of course, it is not thoroughly warmed up by then, so a requirement of running it at low power for 2 minutes has been introduced.
A PW150 on the other hand will take the same 30 seconds to get the turbomachinery to run. Then follow about 15 seconds during which the FADEC runs its self test. So after approx. 45 seconds, the engine itself is stabilized. By then, the propeller is of course still feathered and not able to deliver thrust. Unfeathering the propeller will take about another 15 seconds. So it takes a little more than a minute to get a standing engine able to deliver thrust.
Seeing that the Tay is a larger, heavier engine than the PW150, one might get to the conclusion that the longer startup time on the PW will be sufficient to warm the internal parts up, leaving oil temperature as the only real limit that will not be automatically achieved during engine startup.
Just for completeness: before shutting it down, it is required to run the PW150 with the propeller feathered for at least 30 seconds to allow the internal parts to cool a bit and to avoid the things of nastiness tdracer has mentioned. It is a turbine engine after all.
For example, a RR Tay engine takes about 30 seconds from pushing the start select switch until the engine is stabilized and theoretically able to respond to a takeoff power demand. Of course, it is not thoroughly warmed up by then, so a requirement of running it at low power for 2 minutes has been introduced.
A PW150 on the other hand will take the same 30 seconds to get the turbomachinery to run. Then follow about 15 seconds during which the FADEC runs its self test. So after approx. 45 seconds, the engine itself is stabilized. By then, the propeller is of course still feathered and not able to deliver thrust. Unfeathering the propeller will take about another 15 seconds. So it takes a little more than a minute to get a standing engine able to deliver thrust.
Seeing that the Tay is a larger, heavier engine than the PW150, one might get to the conclusion that the longer startup time on the PW will be sufficient to warm the internal parts up, leaving oil temperature as the only real limit that will not be automatically achieved during engine startup.
Just for completeness: before shutting it down, it is required to run the PW150 with the propeller feathered for at least 30 seconds to allow the internal parts to cool a bit and to avoid the things of nastiness tdracer has mentioned. It is a turbine engine after all.
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the ever faithful Pratt and Whitney PW150's
http://ftp.rta.nato.int/public/PubFullText/RTO/MP/RTO-MP-008/$MP-008-04.pdf