timeless
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Starting a PT-6
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CA1900
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For what it's worth, when I flew the Beech 1900D (PT6A-67D), we always took the props out of feather before starting the engines. (Having them in feather for took long would apparently cause the windows to melt from the exhaust!) Unless the 67R is radically different, I don't see how it would cause any trouble.
Timeless,
I've flown behind many of the PT-6 dash numbers, including the -67, and have worked on many of them. Operationally, most of them are the same, save for the specific numbers (torque, temp, etc). Internally they vary, and various propellers are hung on them, but operating a PT6 is really the same throughout the mix.
Where they differ is the time limits in which they can be feathered, the conditions in which they can be feathered (tailwind, for example), and ground operations ranges (harmonics and wind issues); these depend on the propeller and on the airframe.
Starting the engine in feather means that no oil is getting used for the propeller, which means that initial oil circulation stays with the engine bearings...which is where you want it. Move the propellers and you're dumping oil pressure when you need it most; at the engine start.
So far as the propeller itself, the engine doesn't know if it's turning or not; it's not attached. It's a free turbine engine, meaning the movement of the propeller with respect to rotation is strictly function of exhaust gas. In theory, you could hold on to that propeller during the engine start and prevent it from turning at all, though in reality the torque would toss you and likely hurt you, too. Point is, the exhaust gasses from the gas turbine generator (Ng) are turning that prop, after the engine is done with the gas flow...nothing mechanical between the engine and the prop but the case...and the oil.
This differs from other turbines you may fly, in which the turbine wheel or wheels are mechanically attached in some form to the propeller. In installations such as Allison or Garret engines, the turbine wheels are actually turning the propeller, too. In this case, the only function of the turbines in the engine is to turn the compressor. The propeller has it's own turbine, attached only to the gearing of the propeller, that isn't attached to the rest of the engine; it doesn't affect the compressor and isn't part of the turbine section either; it's just there to take advantage of the exhuast gas exiting the engine (more like a turbine in a river, making electricity).
Keeping this in mind, any oil that the prop is using isn't being used to make that engine run, lubricate the engine during start, keep things cool, etc...it's only there to actuate the propeller. You don't need to actuate the propeller during start, because you're not going anywhere. The propeller in feather isn't hindering anything, isn't putting a load on a starter, isn't boggng down the engine, isn't actually doing anything, because it's not attached to the engine.
Other engines such as the shaft-driven Garretts (honeywells now, I guess) and Allison engines are out of feather when they're stopped...because they need to be in a minimum drag position for the next start. When feathered, those engines do create a lot of drag for the starter and for the engine, and make for hotter starts. Not so with the PT6.
Starting out of feather means more airflow, as CA1900 indicated, past the exhaust. I've seen some BE1900 operators run the starts in feather, others with the props forward.
I generally start in feather and then advance the propeller once the engine is warming up.
Another reason, especially when it's cold, for not putting oil to the propeller too soon is taking care not to blow out a seal (a statement which has absolutely nothing to do with beastiality) with cold, high pressure oil. Start the engine, let it warm, then put it to the prop and let it work it's way through the propeller and prop controls.
To answer your question, yes it can cause problems, depending on the circumstances...ask the other pilot why he does it that way. I'd be curious to know.
I've flown behind many of the PT-6 dash numbers, including the -67, and have worked on many of them. Operationally, most of them are the same, save for the specific numbers (torque, temp, etc). Internally they vary, and various propellers are hung on them, but operating a PT6 is really the same throughout the mix.
Where they differ is the time limits in which they can be feathered, the conditions in which they can be feathered (tailwind, for example), and ground operations ranges (harmonics and wind issues); these depend on the propeller and on the airframe.
Starting the engine in feather means that no oil is getting used for the propeller, which means that initial oil circulation stays with the engine bearings...which is where you want it. Move the propellers and you're dumping oil pressure when you need it most; at the engine start.
So far as the propeller itself, the engine doesn't know if it's turning or not; it's not attached. It's a free turbine engine, meaning the movement of the propeller with respect to rotation is strictly function of exhaust gas. In theory, you could hold on to that propeller during the engine start and prevent it from turning at all, though in reality the torque would toss you and likely hurt you, too. Point is, the exhaust gasses from the gas turbine generator (Ng) are turning that prop, after the engine is done with the gas flow...nothing mechanical between the engine and the prop but the case...and the oil.
This differs from other turbines you may fly, in which the turbine wheel or wheels are mechanically attached in some form to the propeller. In installations such as Allison or Garret engines, the turbine wheels are actually turning the propeller, too. In this case, the only function of the turbines in the engine is to turn the compressor. The propeller has it's own turbine, attached only to the gearing of the propeller, that isn't attached to the rest of the engine; it doesn't affect the compressor and isn't part of the turbine section either; it's just there to take advantage of the exhuast gas exiting the engine (more like a turbine in a river, making electricity).
Keeping this in mind, any oil that the prop is using isn't being used to make that engine run, lubricate the engine during start, keep things cool, etc...it's only there to actuate the propeller. You don't need to actuate the propeller during start, because you're not going anywhere. The propeller in feather isn't hindering anything, isn't putting a load on a starter, isn't boggng down the engine, isn't actually doing anything, because it's not attached to the engine.
Other engines such as the shaft-driven Garretts (honeywells now, I guess) and Allison engines are out of feather when they're stopped...because they need to be in a minimum drag position for the next start. When feathered, those engines do create a lot of drag for the starter and for the engine, and make for hotter starts. Not so with the PT6.
Starting out of feather means more airflow, as CA1900 indicated, past the exhaust. I've seen some BE1900 operators run the starts in feather, others with the props forward.
I generally start in feather and then advance the propeller once the engine is warming up.
Another reason, especially when it's cold, for not putting oil to the propeller too soon is taking care not to blow out a seal (a statement which has absolutely nothing to do with beastiality) with cold, high pressure oil. Start the engine, let it warm, then put it to the prop and let it work it's way through the propeller and prop controls.
To answer your question, yes it can cause problems, depending on the circumstances...ask the other pilot why he does it that way. I'd be curious to know.
The_Russian
Low Level Pilot
- Joined
- Sep 3, 2003
- Posts
- 2,574
Good post. Keeping what you said in mind, wouldn't the propeller spring prevent the oil from entering the hub until sufficient pressure is reached? This would keep the oil within the confines of the engine until it was at a relatively good speed to lubricate the engine. Thus, it would not matter the placement of the prop levers during the start process. Input?
We had the airframe limitation for start also, of course.
timeless, are you playing Guitar Hero on the radar? Where is your TSO? Just kidding!
We had the airframe limitation for start also, of course.
timeless, are you playing Guitar Hero on the radar? Where is your TSO? Just kidding!
In theory, you could hold on to that propeller during the engine start and prevent it from turning at all, though in reality the torque would toss you and likely hurt you, too. Quoted from Avbug
I saw a guy do that to a Twin Otter once...just once. He let go at about halfway through the start, I forget what % he said. He also was afraid the next blade was coming to get him.
I saw a guy do that to a Twin Otter once...just once. He let go at about halfway through the start, I forget what % he said. He also was afraid the next blade was coming to get him.
timeless
Well-known member
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- Oct 10, 2005
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- 114
His theory is that an unfeathered prop is easier for an engine to turn during start and that the engine starts cooler that way.
JohnnyP
Well-known member
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- Jun 24, 2004
- Posts
- 716
.....
I assume he is referring to the placement of the prop levers during the initial starting?.... as the actual blades will already be in the feathered position during start......Am I reading this wrong (damn white wine again)..?
I assume he is referring to the placement of the prop levers during the initial starting?.... as the actual blades will already be in the feathered position during start......Am I reading this wrong (damn white wine again)..?
Nope. Your white whine is just fine.
Timeless, if your friend were talking about a shaft driven engine, he would be correct, which is why shaft driven engines park the blades in a fine pitch position, on the high RPM stops, or in some cases, on the "locks." Those engines absolutely must be started out of feather, or should...they can be started in feather, but one must watch the temps, and it's harder on the battery and starter...more resistance at a time when it's not wanted.
As discussed before, the PT6 doesn't have that issue, as the propeller isn't mechanically connected to the engine. Holding the propeller still or allowing it to spin, in feather or out, doesn't affect the start, start temps, starting speed, starter load, current draw, etc. It's just not a critical issue.
Again, as others have noted, the operational concerns are a much bigger issue. Some engine installations have limitations as to when and where reverse and feather may be used on the ground, and these are more of a concern than anything. If you're starting in very cold weaher, a preheat is aways preferred but starting in feather does enhance engine life in that circumstance by some small margin.
The BE1900 mentioned earlier has limitations with respect to the airframe. The Piaggio has limits with respect to the propeller themelves, which are in the exhaust stream. The Air Tractor 802, which I flew this summer has various limitations with respect to ground time in feather, ground time with a tailwind, feather or reverse with a tailwind, and feather with a crosswind due to harmonics. That, and the gasses in the cockpit burn your eyes and choke you out.
What your friend is displaying is a gross misunderstanding of the function of the engine. I don't know that he's doing anything wrong, per se, but he's doing what he's doing out of ignorance, if that's his reasoning. What is learned here is that he could use a little more studying before he makes up his mind as to how to tackle that engine start.
Timeless, if your friend were talking about a shaft driven engine, he would be correct, which is why shaft driven engines park the blades in a fine pitch position, on the high RPM stops, or in some cases, on the "locks." Those engines absolutely must be started out of feather, or should...they can be started in feather, but one must watch the temps, and it's harder on the battery and starter...more resistance at a time when it's not wanted.
As discussed before, the PT6 doesn't have that issue, as the propeller isn't mechanically connected to the engine. Holding the propeller still or allowing it to spin, in feather or out, doesn't affect the start, start temps, starting speed, starter load, current draw, etc. It's just not a critical issue.
Again, as others have noted, the operational concerns are a much bigger issue. Some engine installations have limitations as to when and where reverse and feather may be used on the ground, and these are more of a concern than anything. If you're starting in very cold weaher, a preheat is aways preferred but starting in feather does enhance engine life in that circumstance by some small margin.
The BE1900 mentioned earlier has limitations with respect to the airframe. The Piaggio has limits with respect to the propeller themelves, which are in the exhaust stream. The Air Tractor 802, which I flew this summer has various limitations with respect to ground time in feather, ground time with a tailwind, feather or reverse with a tailwind, and feather with a crosswind due to harmonics. That, and the gasses in the cockpit burn your eyes and choke you out.
What your friend is displaying is a gross misunderstanding of the function of the engine. I don't know that he's doing anything wrong, per se, but he's doing what he's doing out of ignorance, if that's his reasoning. What is learned here is that he could use a little more studying before he makes up his mind as to how to tackle that engine start.
satpak77
Marriott Platinum Member
- Joined
- Dec 2, 2003
- Posts
- 3,015
not being a smart aleck (Avbug that was good info) but me personally, I just stick to the checklist. My fancy B-350 "Before Engine Starting" checklist states
Power Console and Pedestal
a. Power Levers - IDLE
b. Prop Levers - FULL FORWARD
c. Condition Levers - FUEL CUTOFF
etc etc
I am not smart enought to recite all that A & P stuff above. I just do what the checklist says. That is good info above tho, but some guys eat that up, I am just not one of them.
Some of the guys you fly with want to read the POH in flight, and find "wow, I didn't know that" stuff buried in there. I am not in that crowd however. Thats all nice and all, but I tend to read USA Today or Maxim at cruise and my thoughts are on if Sally is working the counter at the my favorite FBO, and not why does convection fog occur.
The factory wrote the checklist....I stopped trying to be smarter than them a long time ago!
Power Console and Pedestal
a. Power Levers - IDLE
b. Prop Levers - FULL FORWARD
c. Condition Levers - FUEL CUTOFF
etc etc
I am not smart enought to recite all that A & P stuff above. I just do what the checklist says. That is good info above tho, but some guys eat that up, I am just not one of them.
Some of the guys you fly with want to read the POH in flight, and find "wow, I didn't know that" stuff buried in there. I am not in that crowd however. Thats all nice and all, but I tend to read USA Today or Maxim at cruise and my thoughts are on if Sally is working the counter at the my favorite FBO, and not why does convection fog occur.
The factory wrote the checklist....I stopped trying to be smarter than them a long time ago!
Last edited:
You're not being a smark alec. I don't think anybody is suggesting anything to the contrary, and I agree with you whole heartedly. I also believe you can never know enough about your airplane.
Bear in mind when looking at the checklist, it was written by the airframe manufacturer, not the engine manufacturer. That doesn't mean you shouldn't follow it; clearly it's there to be used. Just means you should think.
Most all of us have flown Cessnas and pipers with continental and lycoming engines. How many checklists did you see that included post flight runups and idle mixture checks? Probably none, because it's never included in the checklist, and in most cases in the pilot operating handbooks. But it is included in the engine manufacturers literature and publications, and doing it enhances safety, engine longevity, and catches problems before they become problems. One example of many where knowing more about the airplane than what's in the short book, pays off.
Specifics such as harmonic ranges and operational limitations aren't always on the checklist, but the pilot must know them anyway. Sometimes these are reflected in color codings on the airspeed indicator, but not always. A number of things need to be known, rather than just read, in order to fly the airplane, in fact, from turbulence penetration speeds to landing gear speeds, and much of what we do is still pilot discretion...such as when to drop the gear...or when to push up the prop. Again, different airframes have different needs, as do different types of operations. If you're starting over loose gravel, starting in feather is a wise idea, as is taxiing with the ice vanes/inertial separators deployed for PT6 installations. That may, or may not be in the checklist, but it's certainly important to the life of the engine and the propeller.
My previous point wasn't use or non-use of the checklist, but rather that the pilot was applying technique based on a misunderstanding of the basic operating principle of the engine. Any time one operates the airplane according to a myth, it's time to seek better training and understanding of the machine.
Bear in mind when looking at the checklist, it was written by the airframe manufacturer, not the engine manufacturer. That doesn't mean you shouldn't follow it; clearly it's there to be used. Just means you should think.
Most all of us have flown Cessnas and pipers with continental and lycoming engines. How many checklists did you see that included post flight runups and idle mixture checks? Probably none, because it's never included in the checklist, and in most cases in the pilot operating handbooks. But it is included in the engine manufacturers literature and publications, and doing it enhances safety, engine longevity, and catches problems before they become problems. One example of many where knowing more about the airplane than what's in the short book, pays off.
Specifics such as harmonic ranges and operational limitations aren't always on the checklist, but the pilot must know them anyway. Sometimes these are reflected in color codings on the airspeed indicator, but not always. A number of things need to be known, rather than just read, in order to fly the airplane, in fact, from turbulence penetration speeds to landing gear speeds, and much of what we do is still pilot discretion...such as when to drop the gear...or when to push up the prop. Again, different airframes have different needs, as do different types of operations. If you're starting over loose gravel, starting in feather is a wise idea, as is taxiing with the ice vanes/inertial separators deployed for PT6 installations. That may, or may not be in the checklist, but it's certainly important to the life of the engine and the propeller.
My previous point wasn't use or non-use of the checklist, but rather that the pilot was applying technique based on a misunderstanding of the basic operating principle of the engine. Any time one operates the airplane according to a myth, it's time to seek better training and understanding of the machine.
Cstyle
I like Cheese
- Joined
- Jul 29, 2004
- Posts
- 44
Let me interject my $.02.
In my experience with the King Air and the Shorts their starting sequences are vary similar. Not surprising, considering they are both running PT6's.
The main difference is in the position of the prop levers during starting. The reason for starting the Shorts with the props in feather was well covered by avbug.
My understanding for the reason to start the King Air with the props forward is an electrical issue.
The oil pressure gauges in the King Air are AC powered. The static inverter is not brought on line until after both engines are started. Starting with the props forward will give you an indication of engine oil pressure, as the props move from feather to flat pitch. This of course assumes the engine was shut down in feather, which is what is called for on the checklist.
In any case, my philosophy has always been to operate the A/C the way I was trained. If it’s your airplane, do it however you want. Otherwise, follow the checklist.
FYI: The King Air info above is for the 1904 A90 I have flown. Your mileage may vary.
In my experience with the King Air and the Shorts their starting sequences are vary similar. Not surprising, considering they are both running PT6's.
The main difference is in the position of the prop levers during starting. The reason for starting the Shorts with the props in feather was well covered by avbug.
My understanding for the reason to start the King Air with the props forward is an electrical issue.
The oil pressure gauges in the King Air are AC powered. The static inverter is not brought on line until after both engines are started. Starting with the props forward will give you an indication of engine oil pressure, as the props move from feather to flat pitch. This of course assumes the engine was shut down in feather, which is what is called for on the checklist.
In any case, my philosophy has always been to operate the A/C the way I was trained. If it’s your airplane, do it however you want. Otherwise, follow the checklist.
FYI: The King Air info above is for the 1904 A90 I have flown. Your mileage may vary.
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