NTS vs Autofeather

Fly Boy Knight said:
An autofeather system is exactly what it sounds like, it automatically feathers the prop when engine torque output drops below a certain level with the power levels advanced to near full power (example numbers: <400 ftlbs torque with power levers >90% forward). It is used on free turbines because once the prop is feathered, the starter can still motor the engine in order to air-start it if you discover why it shut down and remedy the problem. This is because the prop is not physically attached to the engine and therefore will not slow the engine's acceleration during start up.

A Negative Torque Sensing System (NTS) is exactly what it sounds like. Positive torque = engine driving the prop (normal), Negative torque = engine output so low that the relative wind's windmilling force turns the prop faster than the engine does (power idle, high speed descent or when you lose an engine). The NTS system senses torque and when it sense a negative torque condition (engine failure), it will move the prop TOWARD a feather (more course blade angle = slower prop RPM = less windmilling force from the wind = less negative torque). As a person said above, the NTS system does NOT FULLY Feather the prop. It will slow the prop down to about "Light Off" RPM (example: around 5-10% RPM) because that little residual windmilling motion allows for the MINIMUM drag on that side while still allowing the pilot to perform an air-start.

To air-start a free turbine, you simple...do the same thing as on the ground. In a direct drive turboprop, the prop is spun as the engine accelerates. If the prop is fully feathered, it will be near impossible for the engine to accelerate properly. On the Fairchild Metroliner (SA227) with Garret TPE331 direct drive engines, the engine start button's function changes in the air. A squat switch changes the start button from activating the starter (ground) to running the unfeather pump (air) thus removing the starter from even trying to crank over the engine in the air.
Click to expand...

Good explanation. When I flew C-2A's, the prop system was the most difficult system to understand and explain. The E-2/C-2 have those big ass props hanging out there with 5200shp or 4,600shp respectively.
 
Cessnaflyer said:
Not to be mean, but that is the dumbest thing I have heard. You should be very familiar with how your craft operates. You never know when you need the correlative ability to diagnose problems which could only be known when you dive into the manuals and learn more about the systems and how they operate together. Why stop at the bare minimum.
Click to expand...

It's called professional knowledge in the Navy but I see where Rocketman is coming from. At VAW-120, we had to know the prop system inside and out. Fine but there were things like the 5 cams on the alpha shaft that regardless of my knowledge of what they did, nothing I did in the airplane would effect it. My main concern was how the systems worked in the aircraft, my NATOPS emergency procedures and what I could do in an emergency situation.
 
Similar thing in the AF. Nothing like having to be able to draw systems to pass a checkride during UPT. I could understand it then as it was part of the whole make it stressful and challenging and ever so slightly a haze. I don't see a place for the in the civ side though. I think if I was asked something along the lines of draw a system for a checkride nowdays I'd turn in my badge and go leave.

What the OP is trying to get is a better understanding of how the system works. Nothing wrong with that at all. The problem is when the company/examiner/check pilot expects you to be able to trace a molecule of air through the air conditioning packs to pass a checkride. How is that going to help me when I'm flying along at FL280 in bad weather with one out of two packs already shut down cause it failed and now we just got smoke and fumes in the cockpit again? It's not, ask me how I know. What IS useful knowledge is how can I manage to keep the plane pressurized because we need to stay at this altitude for our 4 receivers to make it while trying to keep the cockpit temperature at bearable levels using only pure bleed air cause we're stuck like this for another three hours. There's a fine line between relevant and irrelevant systems knowledge. All too often it seems to focus is on the irrelevant variety. Sorry to take this off topic a bit.
 
Rocketman99 said:
Similar thing in the AF. Nothing like having to be able to draw systems to pass a checkride during UPT. I could understand it then as it was part of the whole make it stressful and challenging and ever so slightly a haze. I don't see a place for the in the civ side though. I think if I was asked something along the lines of draw a system for a checkride nowdays I'd turn in my badge and go leave.

What the OP is trying to get is a better understanding of how the system works. Nothing wrong with that at all. The problem is when the company/examiner/check pilot expects you to be able to trace a molecule of air through the air conditioning packs to pass a checkride. How is that going to help me when I'm flying along at FL280 in bad weather with one out of two packs already shut down cause it failed and now we just got smoke and fumes in the cockpit again? It's not, ask me how I know. What IS useful knowledge is how can I manage to keep the plane pressurized because we need to stay at this altitude for our 4 receivers to make it while trying to keep the cockpit temperature at bearable levels using only pure bleed air cause we're stuck like this for another three hours. There's a fine line between relevant and irrelevant systems knowledge. All too often it seems to focus is on the irrelevant variety. Sorry to take this off topic a bit.
Click to expand...
Very good point! I totally agree.
 
Rocketman99 said:
Similar thing in the AF. Nothing like having to be able to draw systems to pass a checkride during UPT. I could understand it then as it was part of the whole make it stressful and challenging and ever so slightly a haze. I don't see a place for the in the civ side though. I think if I was asked something along the lines of draw a system for a checkride nowdays I'd turn in my badge and go leave.

What the OP is trying to get is a better understanding of how the system works. Nothing wrong with that at all. The problem is when the company/examiner/check pilot expects you to be able to trace a molecule of air through the air conditioning packs to pass a checkride. How is that going to help me when I'm flying along at FL280 in bad weather with one out of two packs already shut down cause it failed and now we just got smoke and fumes in the cockpit again? It's not, ask me how I know. What IS useful knowledge is how can I manage to keep the plane pressurized because we need to stay at this altitude for our 4 receivers to make it while trying to keep the cockpit temperature at bearable levels using only pure bleed air cause we're stuck like this for another three hours. There's a fine line between relevant and irrelevant systems knowledge. All too often it seems to focus is on the irrelevant variety. Sorry to take this off topic a bit.
Click to expand...

Agree completely. There is a time and place to know why the systems work the way they do. I've had to do some questionable things to an aircraft, all in the name of completing a tactical mission.

Now, for peace time missions or even more benign, civilian ops, getting from point A to B safely is all that matters.
 
Rocketman99 said:
Similar thing in the AF. Nothing like having to be able to draw systems to pass a checkride during UPT. I could understand it then as it was part of the whole make it stressful and challenging and ever so slightly a haze. I don't see a place for the in the civ side though. I think if I was asked something along the lines of draw a system for a checkride nowdays I'd turn in my badge and go leave.

What the OP is trying to get is a better understanding of how the system works. Nothing wrong with that at all. The problem is when the company/examiner/check pilot expects you to be able to trace a molecule of air through the air conditioning packs to pass a checkride. How is that going to help me when I'm flying along at FL280 in bad weather with one out of two packs already shut down cause it failed and now we just got smoke and fumes in the cockpit again? It's not, ask me how I know. What IS useful knowledge is how can I manage to keep the plane pressurized because we need to stay at this altitude for our 4 receivers to make it while trying to keep the cockpit temperature at bearable levels using only pure bleed air cause we're stuck like this for another three hours. There's a fine line between relevant and irrelevant systems knowledge. All too often it seems to focus is on the irrelevant variety. Sorry to take this off topic a bit.
Click to expand...

I agree with the idea behind excess systems knowledge. I (probably because I aspire to one day be an A+P when I have the time/$$) believe that knowing the mechanics behind a system and the design characteristics are mainly icing on the cake during a checkride. Being a pilot is what I do and if I am going to do it, I want to do it very well so I usually harp on stuff until i can explain, for example, exactly what an air molecule does as it travels through the ACM.

That said, sometimes, like the OP stated, too much knowledge all at once can be overwhelming and cause you to forget NECESSARY information. I have always followed the three type approach to knowledge... 1: Need to know, 2. Should know, and 3: Trivia. When being evaluated by someone, they should only be quizzing you on the need to know information and maybe certain should know info based on your airplane/operations. Expecting pilots to have a deep catalog of trivia-type information stored away in their brain somewhere that is perfectly useless when flying the line.... that is pretty misguided. The "Stump the Chump" idea is a very necessary idea at times when dealing with egotistical, over confident pilots however, these sessions should be reserved for training exercises and not for checkrides or other jeopardy events.

As much as my extra systems knowledge should not be the target of evaluation... I have never been scolded for knowing the systems "too well."
 
Autothrust Blue said:
I'd modify that to:
(1) Need to know
(2) Nice to know
(3) Trivia (do not need to know, do not memorize at the expense of (1)).
Click to expand...

Bingo. That's exactly what I was getting at in a moderately roundabout manner. :)

Dragging this back to an earlier post, this is why I don't like the suggestion of having all the info from the MX side of the house, at least not from the beginning. I feel that begs getting pigeonholed into options 2 and 3 from the list. Once you've been flying the plane for a bit, yeah it would definitely be nice to have or have access to. Another thing nice is to have access to the actual manufacturer manuals for the plane if the company has their own version.
 
Fly Boy Knight said:
An autofeather system is exactly what it sounds like, it automatically feathers the prop when engine torque output drops below a certain level with the power levels advanced to near full power (example numbers: <400 ftlbs torque with power levers >90% forward). It is used on free turbines because once the prop is feathered, the starter can still motor the engine in order to air-start it if you discover why it shut down and remedy the problem. This is because the prop is not physically attached to the engine and therefore will not slow the engine's acceleration during start up.

A Negative Torque Sensing System (NTS) is exactly what it sounds like. Positive torque = engine driving the prop (normal), Negative torque = engine output so low that the relative wind's windmilling force turns the prop faster than the engine does (power idle, high speed descent or when you lose an engine). The NTS system senses torque and when it sense a negative torque condition (engine failure), it will move the prop TOWARD a feather (more course blade angle = slower prop RPM = less windmilling force from the wind = less negative torque). As a person said above, the NTS system does NOT FULLY Feather the prop. It will slow the prop down to about "Light Off" RPM (example: around 5-10% RPM) because that little residual windmilling motion allows for the MINIMUM drag on that side while still allowing the pilot to perform an air-start.

To air-start a free turbine, you simple...do the same thing as on the ground. In a direct drive turboprop, the prop is spun as the engine accelerates. If the prop is fully feathered, it will be near impossible for the engine to accelerate properly. On the Fairchild Metroliner (SA227) with Garret TPE331 direct drive engines, the engine start button's function changes in the air. A squat switch changes the start button from activating the starter (ground) to running the unfeather pump (air) thus removing the starter from even trying to crank over the engine in the air.
Click to expand...


TPE 331's on the mitts were much the same, only I always had an actual Unfeathering pump button on the throttle quadrant, also serves as a life saver for those who forget to put the props on the locks before shutting down.
 
You must log in or register to reply here.
Back
Top