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Various Propeller And Dash-8 Questions  
User currently offlineANITIX87 From United States of America, joined Mar 2005, 3292 posts, RR: 13
Posted (2 years 4 months 2 weeks 2 days 12 hours ago) and read 7219 times:
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Hi, all.

Recently flew EWR-PIT-EWR on CO (Colgan) Dash-8 Q400s. I came away from the flights with several questions:

Variable-Pitch Propeller Questions
1) From my understanding, variable-pitch technology allows for the engine to run at a constant speed to improve efficiency and reduce wear. Is this correct? Are there any drawbacks to the technology other than the far more complicated design it demands?

2) It did seem, despite the variable pitch design, that the propeller was changing speeds pretty frequenty (especially while taxying). Any reason for this, or was it just my imagination?

3) Does the pilot control the pitch, or is it all automatic?

4) Is pitch limited to a given range? Is it 0 degrees (feathered) to 90 degrees? Or can a given blade rotate 360 degrees?

Dash-8 Q400 Specific Questions
1) On start-up, the starboard engine starts, the propeller starts to spin, and the plane pushes back. After push-back, the other engine is started and is allowed to stabilize. After a minute or so, the sound the engines make changes completely. The props speed up much more, the engine adapts a bit of a roar as the "jet" part of the turbojet starts, and you get the familiar "buzzsaw" sound from the propeller. What is happening at this stage? Why does the sound change so much? Is the "initial" startup not actually providing thrust, or is this a staged start up for the engine's sake? Do turbofans do the same thing?

2) Does the vibration from the propeller negatively affect the aircraft's lifespan? There was evidence of the wear on the relatively new aircraft all over the place. Latches for tray tables showed fatigue cracking, my window shade rattled and slid down slowly constantly during cruise, my reading light wobbled in its mount, etc.

3) Were there mutliple "versions" of the Q400? The first aircraft I was on had different window shades, different window layout (I had the same seat both times, and the second time the window was much further forward), and seemed to be considerably quieter and have less vibration.

4) When taxying, if the pilot applies the brakes, do the propellers provide any reverse thrust, or do they only feather? I noticed their pitch was changing when brakes were applied, but couldn't tell how far they rotated. Again, is this all automatic, or controlled by the pilots?

5) Is there any yaw assistance from the propellers? Can their variable pitch be used to help rudder action or high-speed steering (during take-off and landing, for example)?

6) Can the propeller blades be used as spoilers in flight? Can the pitch be changed to slow the aircraft down, for example?

I'm sure the discussion will yield more questions, but that's all for now. I think there's plenty to learn!

TIS


www.stellaryear.com: Canon EOS 50D, Canon EOS 5DMkII, Sigma 50mm 1.4, Canon 24-70 2.8L II, Canon 100mm 2.8L, Canon 100-4
20 replies: All unread, jump to last
 
User currently offlineDashTrash From United States of America, joined Aug 2006, 1438 posts, RR: 2
Reply 1, posted (2 years 4 months 2 weeks 2 days 11 hours ago) and read 7204 times:

Too many errors to leave it up here......

[Edited 2011-12-02 09:39:27]

User currently offlineDashTrash From United States of America, joined Aug 2006, 1438 posts, RR: 2
Reply 2, posted (2 years 4 months 2 weeks 2 days 11 hours ago) and read 7197 times:

Quoting ANITIX87 (Thread starter):
1) From my understanding, variable-pitch technology allows for the engine to run at a constant speed to improve efficiency and reduce wear. Is this correct? Are there any drawbacks to the technology other than the far more complicated design it demands?

Sort of. The prop spins at a constant set RPM but with a turbine driving it, the turbine RPM varies. In a piston engine, crankshaft RPM remains constant as well.
2) It did seem, despite the variable pitch design, that the propeller was changing speeds pretty frequenty (especially while taxying). Any reason for this, or was it just my imagination?[/quote]
That's how we maintain speed. Changing the blade angle is what changes the thrust. It's also noisy.

Quoting ANITIX87 (Thread starter):
3) Does the pilot control the pitch, or is it all automatic?

The pilot controls the pitch through the condition levers. (the 400s are different than the early Dashes I flew however).

Quoting ANITIX87 (Thread starter):
4) Is pitch limited to a given range? Is it 0 degrees (feathered) to 90 degrees? Or can a given blade rotate 360 degrees?

They are limited. Each prop type will has different blade angle limits.

Quoting ANITIX87 (Thread starter):
1) On start-up, the starboard engine starts, the propeller starts to spin, and the plane pushes back. After push-back, the other engine is started and is allowed to stabilize. After a minute or so, the sound the engines make changes completely. The props speed up much more, the engine adapts a bit of a roar as the "jet" part of the turbojet starts, and you get the familiar "buzzsaw" sound from the propeller. What is happening at this stage? Why does the sound change so much? Is the "initial" startup not actually providing thrust, or is this a staged start up for the engine's sake? Do turbofans do the same thing?

No. Dash 8s use a free turbine engine where exhaust gases are used to drive another turbine which spins the prop. Upon shut down, the props go to feather. They turn very slowly on start up until they're brought out of feather.

Quoting ANITIX87 (Thread starter):
2) Does the vibration from the propeller negatively affect the aircraft's lifespan? There was evidence of the wear on the relatively new aircraft all over the place. Latches for tray tables showed fatigue cracking, my window shade rattled and slid down slowly constantly during cruise, my reading light wobbled in its mount, etc.

I don't think airframe life is affected, but cabin furnishings being to rattle before they would in a jet.

Quoting ANITIX87 (Thread starter):
3) Were there mutliple "versions" of the Q400? The first aircraft I was on had different window shades, different window layout (I had the same seat both times, and the second time the window was much further forward), and seemed to be considerably quieter and have less vibration.

Not sure about the 400, but there are multiple versions of the earlier series.

Quoting ANITIX87 (Thread starter):
4) When taxiing, if the pilot applies the brakes, do the propellers provide any reverse thrust, or do they only feather? I noticed their pitch was changing when brakes were applied, but couldn't tell how far they rotated. Again, is this all automatic, or controlled by the pilots?

Controlled by the pilots with the power levers until the condition levers are brought up. Reference a picture of a Dash pedestal to see what I'm talking about.

Quoting ANITIX87 (Thread starter):
5) Is there any yaw assistance from the propellers? Can their variable pitch be used to help rudder action or high-speed steering (during take-off and landing, for example)?

Nope.

Quoting ANITIX87 (Thread starter):
6) Can the propeller blades be used as spoilers in flight? Can the pitch be changed to slow the aircraft down, for example?

You can increase prop RPM with the power levels at low settings to slow down, but it's discouraged.


User currently offlinewoodreau From United States of America, joined Sep 2001, 978 posts, RR: 6
Reply 3, posted (2 years 4 months 2 weeks 2 days 11 hours ago) and read 7190 times:

not a dash-8 pilot so I can't answer your specific dash-8 questions but regarding taxiing a turboprop aircraft, as a turboprop pilot I don't use any brakes to slow or stop at all, I use the beta range to taxi. The only time I use the brakes is just before I come to a complete stop basically to hold the aircraft in the position it is in.

Don't use the props for yaw control at all on the ground or in flight. But if an engine quits at V1 and the autofeather doesn't work and you don't take immediate action to manually feather it, it will roll you over in the ground pretty quickly.

The prop can be used to slow in flight. I normally used it to slow from 250kts to final approach speed. 250kts 1000ft AGL 3 miles from the threshold, idle, prop full forward - as the speed decreases configure flaps and gear, on speed 110kts at 500ft and 1.5 miles from the runway threshold. This can be a relatively violent maneuver (from a pax point of view), so you don't do this with pax on board. Boxes don't complain at all.

[Edited 2011-12-02 09:46:15]


Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
User currently offlineSaafnav From South Africa, joined Mar 2010, 253 posts, RR: 0
Reply 4, posted (2 years 4 months 2 weeks 2 days 11 hours ago) and read 7172 times:

Quoting ANITIX87 (Thread starter):

2) It did seem, despite the variable pitch design, that the propeller was changing speeds pretty frequenty (especially while taxying). Any reason for this, or was it just my imagination?

In Ground Range, the engine speed can be controlled by throttle movement directly. In Flight Range, the Throttle Lever controls the pitch, and that governs the engine speed.
This is generally for a constant speed engine, not sure specifically about the Q400.

Quoting ANITIX87 (Thread starter):

3) Does the pilot control the pitch, or is it all automatic?

Controlled automatically by governer system via the throttle lever.

Quoting ANITIX87 (Thread starter):


4) Is pitch limited to a given range? Is it 0 degrees (feathered) to 90 degrees? Or can a given blade rotate 360 degrees?

Slightly negative below 0° to activate the Prop Brake when feathered, to a few degrees beyond 90° for Reverse Thrust/Beta Mode

Quoting ANITIX87 (Thread starter):

4) When taxying, if the pilot applies the brakes, do the propellers provide any reverse thrust, or do they only feather? I noticed their pitch was changing when brakes were applied, but couldn't tell how far they rotated. Again, is this all automatic, or controlled by the pilots?

Brake Pedals are only connected to the brakes. Movement is due to the pilot moving the Throttle Levers.

Quoting ANITIX87 (Thread starter):

6) Can the propeller blades be used as spoilers in flight? Can the pitch be changed to slow the aircraft down, for example?

Not as a flight control per se, but if you cut the throttle, the braking affect due to the Prop 'disking' is much more pronounced than on a jet engine.

Erich

Answered from a general perspective and Turbo Prop knowledge. Anybody with actual Q400 experience can correct me where needed.



On-board Direction Consultant
User currently offlineDashTrash From United States of America, joined Aug 2006, 1438 posts, RR: 2
Reply 5, posted (2 years 4 months 2 weeks 2 days 10 hours ago) and read 7158 times:

Quoting Saafnav (Reply 4):

In Ground Range, the engine speed can be controlled by throttle movement directly. In Flight Range, the Throttle Lever controls the pitch, and that governs the engine speed.
This is generally for a constant speed engine, not sure specifically about the Q400.

It's close in a Dash. Power lever movement below the flight idle gate varies turbine speed and blade angle to maintain idle RPM, 785 in the older aircraft. Above flight idle the condition levers control prop RPM and the power levers control engine RPM.

Quoting Saafnav (Reply 4):
Controlled automatically by governer system via the throttle lever.

Been a while, but the governor in a Dash 8 is there to keep the prop from overspeeding only. There are two, the first kicks in around 1236 RPM, another at 13 something.

Quoting Saafnav (Reply 4):
Not as a flight control per se, but if you cut the throttle, the braking affect due to the Prop 'disking' is much more pronounced than on a jet engine.

You don't get much braking action out of the props in the Dash unless you start increasing RPM. In a heavy -300 I remember coming down the glideslope at flight idle and never slowing much below 160 without adding drag of some sort.


User currently offlineANITIX87 From United States of America, joined Mar 2005, 3292 posts, RR: 13
Reply 6, posted (2 years 4 months 2 weeks 2 days 9 hours ago) and read 7131 times:
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Quoting DashTrash (Reply 2):
That's how we maintain speed. Changing the blade angle is what changes the thrust. It's also noisy.

This confuses me slightly. If the blade angle remains the same and you increase prop velocity, the thrust (and therefore aircraft speed) will change. If the blade angle changes and the prop velocity remains the same, the thrust will change. So why are the two used to control different things? I'm having a hard time grasping the difference between the two. Or is this related to "use thrust for altitude, and aircraft pitch for speed?"

Quoting DashTrash (Reply 2):
The pilot controls the pitch through the condition levers. (the 400s are different than the early Dashes I flew however).

Has this not been automated, yet? How precise does the pilot need to be? Does he have pre-set choices (0, 15, 25, etc) like for flaps, or is it, "Well, I sort of think this is the blade angle I'll need, so let's try that!"?

Quoting DashTrash (Reply 2):
They turn very slowly on start up until they're brought out of feather.

How is this controlled? Engine gearing? Does that mean the engine has two "idle" settings? One for "flight idle" (descent, taxi, for example) and "start-up idle" (that slower speed we're talking about now)?

Quoting Saafnav (Reply 4):
Reverse Thrust/Beta Mode

This quote leads me to:

Quoting woodreau (Reply 3):
I use the beta range to taxi

So you're always in reverse thrust when taxying? Or am I misunderstand a key difference between Reverse Thrust and "Beta Mode?"


I guess my questions are arising from a misconception I developed somewhere. I thought the premise of variable-pitch propellers was this:
The engine does not need gearing. It spins at a constant RPM at all times and [b]only the blade angle changes depending on what is being commanded by the pilot (feathered props for slowing down, angled for forward thrust, or angled for reverse, for example). This is all done automatically by the computer based on the pilot's input, so that he/she has much less to think about and control in the cockpit.[/i]

Obviously there are a lot of wrong assumptions in there. Thanks for taking the time to answer all my questions, guys!

TIS



www.stellaryear.com: Canon EOS 50D, Canon EOS 5DMkII, Sigma 50mm 1.4, Canon 24-70 2.8L II, Canon 100mm 2.8L, Canon 100-4
User currently offlineDashTrash From United States of America, joined Aug 2006, 1438 posts, RR: 2
Reply 7, posted (2 years 4 months 2 weeks 2 days 9 hours ago) and read 7124 times:

Quoting ANITIX87 (Reply 6):
This confuses me slightly. If the blade angle remains the same and you increase prop velocity, the thrust (and therefore aircraft speed) will change. If the blade angle changes and the prop velocity remains the same, the thrust will change. So why are the two used to control different things? I'm having a hard time grasping the difference between the two. Or is this related to "use thrust for altitude, and aircraft pitch for speed?"

Prop RPM stays the same on the ground, it's the blade angle that changes.

Quoting ANITIX87 (Reply 6):
Has this not been automated, yet? How precise does the pilot need to be? Does he have pre-set choices (0, 15, 25, etc) like for flaps, or is it, "Well, I sort of think this is the blade angle I'll need, so let's try that!"?

The blade angle isn't noted in the cockpit. The blade angle controls prop RPM.

Quoting ANITIX87 (Reply 6):
How is this controlled? Engine gearing? Does that mean the engine has two "idle" settings? One for "flight idle" (descent, taxi, for example) and "start-up idle" (that slower speed we're talking about now)?

Yes. Start feather and MIN. The ECU does this through fuel control and PFM (pure freakin magic). Start feather allows the engine to start and keeps the prop feathered limiting prop RPM to around 200. When you bring the condition levers to MIN, the props unfeather and accelerate to 780 RPM. (Classic Dash 8s). MIN is not exactly an idle position as it's the MINimum prop RPM in flight. Flight idle is a power lever function.

I know I've made all this about as clear as mud. Sorry about that.


User currently offlineANITIX87 From United States of America, joined Mar 2005, 3292 posts, RR: 13
Reply 8, posted (2 years 4 months 2 weeks 2 days 8 hours ago) and read 7115 times:
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Quoting DashTrash (Reply 7):
I know I've made all this about as clear as mud. Sorry about that.

Your explanations aren't a problem at all. It's my limited knowledge in turboprop tech!

Quoting DashTrash (Reply 7):
Prop RPM stays the same on the ground, it's the blade angle that changes.

This is only true on the ground? I thought this was the case at all times. Or do you mean that, in flight, the RPM can be increase for even more thrust? If so, are turboprops geared?

Quoting DashTrash (Reply 7):
The blade angle isn't noted in the cockpit. The blade angle controls prop RPM.

Hang on. Two concerns here. I don't know if you mis-spoke or if something went over my had again:
1) From your earlier explanations, I understood that the Condition Levers control blade angle, no? If so, shouldn't the pitch be indicated to the pilot so he knows what he's doing?
2) How can the blade angle control RPM? That means a feathered prop will slow down because of the drag, but a blade a 90 degrees will spin much faster. So the blade are actually exerting torque on the engine's driveshaft and providing some form of engine braking when feathered? This seems counterproductive to me, as it means the engine may be throttled for 1,500RPM but the props (if angled only slightly) are slowing it to 1,450RPM (I'm completely inventing numbers, btw). This wastes fuel quite significantly. I would imagine that the engine would be set to always rotate at 1500RPM, and that the blade angle only controls thrust (0 degrees is no thrust since it's feathered, other rotations provide thrust due to blade angle and shape).

TIS



www.stellaryear.com: Canon EOS 50D, Canon EOS 5DMkII, Sigma 50mm 1.4, Canon 24-70 2.8L II, Canon 100mm 2.8L, Canon 100-4
User currently offlineflyingturtle From Switzerland, joined Oct 2011, 2033 posts, RR: 13
Reply 9, posted (2 years 4 months 2 weeks 2 days 8 hours ago) and read 7104 times:

Quoting ANITIX87 (Reply 8):
If so, are turboprops geared?

Most modern helicopters are geared turbo-props. 

But I haven't heard yet of any airplane flying with a geared (turboprop) jet engines. You can both change turbine N2 (like any jet aircraft) and prop blade pitch..... but I assume, with my equally limited knowledge, that changing prop blade pitch gives you a much faster response time than changing the jet turbine N2.

[Edited 2011-12-02 13:02:35]


Keeping calm is terrorism against those who want to live in fear.
User currently offlineDashTrash From United States of America, joined Aug 2006, 1438 posts, RR: 2
Reply 10, posted (2 years 4 months 2 weeks 2 days 8 hours ago) and read 7100 times:

I should have said to being with that turboprop output is measured in torque and not prop RPM.

Quoting ANITIX87 (Reply 8):
This is only true on the ground? I thought this was the case at all times. Or do you mean that, in flight, the RPM can be increase for even more thrust? If so, are turboprops geared?

During cruise prop RPM does stay the same. Higher RPMs are used for takeoff and climb. We select higher RPM on landing for go-around purposes.

Turboprops use reduction gearboxes. Turbine shaft RPM is above 10,000 RPM and prop RPM is a whole lot less.

Quoting ANITIX87 (Reply 8):
1) From your earlier explanations, I understood that the Condition Levers control blade angle, no? If so, shouldn't the pitch be indicated to the pilot so he knows what he's doing?

They do control blade angle, but being that blade angle controls RPM, we don't care what the angle is as long as we're getting what we want RPM wise.

Quoting ANITIX87 (Reply 8):
2) How can the blade angle control RPM? That means a feathered prop will slow down because of the drag, but a blade a 90 degrees will spin much faster. So the blade are actually exerting torque on the engine's driveshaft and providing some form of engine braking when feathered? This seems counterproductive to me, as it means the engine may be throttled for 1,500RPM but the props (if angled only slightly) are slowing it to 1,450RPM (I'm completely inventing numbers, btw). This wastes fuel quite significantly. I would imagine that the engine would be set to always rotate at 1500RPM, and that the blade angle only controls thrust (0 degrees is no thrust since it's feathered, other rotations provide thrust due to blade angle and shape).

You've answered your own question. On takeoff, we select MAX on the Condition Levers. This allows us max prop RPM, then advance the power levers to the desired torque setting. After takeoff, we reduce to climb power. We use a lower prop RPM by increasing the blade angle. Again, it doesn't matter to the pilot what that blade angle is as long as we're getting the desired RPM. That's for the engineers to figure out.

When reducing power, if we increase blade angle, we'll slow the prop. However, you're dead on with your torque increase statement. To counteract that, we reduce the turbine speed by way of the power levers before reducing prop RPM.

It's one of those things that makes perfect sense in practice, but I've never been able to explain this properly.

There are some Dash 8 cockpit videos on Youtube that might be worth watching to see how it works.


User currently offlineflyingturtle From Switzerland, joined Oct 2011, 2033 posts, RR: 13
Reply 11, posted (2 years 4 months 2 weeks 2 days 8 hours ago) and read 7092 times:

Quoting flyingturtle (Reply 9):
But I haven't heard yet of any airplane flying with a geared (turboprop) jet engines.
Quoting DashTrash (Reply 10):
Turboprops use reduction gearboxes. Turbine shaft RPM is above 10,000 RPM and prop RPM is a whole lot less.

Thanks! I should read something about turboprop aircraft from time to time also. I've only got jetliners in my mind.   



Keeping calm is terrorism against those who want to live in fear.
User currently offlineDC8FriendShip From United States of America, joined Apr 2005, 242 posts, RR: 3
Reply 12, posted (2 years 4 months 2 weeks 2 days ago) and read 6991 times:

Quoting ANITIX87 (Reply 8):
Hang on. Two concerns here. I don't know if you mis-spoke or if something went over my had again:
1) From your earlier explanations, I understood that the Condition Levers control blade angle, no? If so, shouldn't the pitch be indicated to the pilot so he knows what he's doing?
2) How can the blade angle control RPM? That means a feathered prop will slow down because of the drag, but a blade a 90 degrees will spin much faster. So the blade are actually exerting torque on the engine's driveshaft and providing some form of engine braking when feathered? This seems counterproductive to me, as it means the engine may be throttled for 1,500RPM but the props (if angled only slightly) are slowing it to 1,450RPM (I'm completely inventing numbers, btw). This wastes fuel quite significantly. I would imagine that the engine would be set to always rotate at 1500RPM, and that the blade angle only controls thrust (0 degrees is no thrust since it's feathered, other rotations provide thrust due to blade angle and shape).

Lets get a couple of things straight here. there are two types of turboprop engine- direct drive and free turbine. both behave diferently in the way the power is given to the prop, and therefore also controlled differently. The Dash 8 engine are pratt and whitney free turbine designs, meaning that the prop is not directly coupled to the gas generator and its output is not directly related to the engine speed, but regulated as a means of controlling prop rpm. The condition lever position sets the max rpm for a given setting, i believe 1200 for max and 950 for min. as the prop approaches the max speed, the PCU, or propeller control unit, will increase the pitch of the prop, to keep the rpm constant, therefore, throughout the operation, the prop is constantly varying its pitch to keep the rpm within range.
The power levers simply control the gas generator output, which means that the higher you move them, the more power is given to the prop turbine, which increses the speed. of course, once the prop reaches its max set rpm, it increases in pitch, and any additional power will cuase the torque put into the shaft to increase.
Inthe ground range (beta and reverse, the power lever does control pitch, the rpm is regulated at 785, and the blade pitch can be decreased to zero(discing) or reverse. any movement of the power levers above the flight idle gate will result in prop rpm increase or decrease accordingly( and the related torque increase.)

Hope this is a good explanation



Come fly the Friendly Skies of United
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 13, posted (2 years 4 months 2 weeks 1 day 23 hours ago) and read 6978 times:

All the technical stuff way above is great! All I can contribute is my back-of-the-envelope explanation, which is close enough to at least get the gist of how the controls are used:
Condition Lever = RPM setting (roughly)
Power Lever = Thrust setting (roughly)

If possible, the prop will figure out whatever the right blade setting is to get the RPM you asked for with the power you set.

Tom.


User currently offlineFabo From Slovakia, joined Aug 2005, 1211 posts, RR: 1
Reply 14, posted (2 years 4 months 2 weeks 16 hours ago) and read 6755 times:

Quoting flyingturtle (Reply 9):
But I haven't heard yet of any airplane flying with a geared (turboprop) jet engines.

I am not sure here if I am on the same page, but... direct drive turboprops? One that comes to mind is Jetstream 41, which I know a tiny bit (admitedly only through flight simulator, but I think PMDG did a good job circumventing limitations of MSFS). Indeed a whole different animal in regard to how it works.



The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
User currently onlineN243NW From United States of America, joined Jul 2003, 1608 posts, RR: 20
Reply 15, posted (2 years 4 months 2 weeks 12 hours ago) and read 6707 times:

Quoting flyingturtle (Reply 9):
But I haven't heard yet of any airplane flying with a geared (turboprop) jet engines.

Not exactly "geared" (as Fabo said), but the direct-drive Garrett TPE331 is very popular. Used by the King Air, the MU-2, Conquest, Turbo Commander, Jetstream, Metroliner, Cheyenne, etc. It's the single-shaft alternative to the PT-6.



B-52s don't take off. They scare the ground away.
User currently offlineANITIX87 From United States of America, joined Mar 2005, 3292 posts, RR: 13
Reply 16, posted (2 years 4 months 2 weeks 11 hours ago) and read 6695 times:
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Quoting DashTrash (Reply 10):
They do control blade angle, but being that blade angle controls RPM, we don't care what the angle is as long as we're getting what we want RPM wise.

I think this is where something got lost in translation. I believe you mean to say, "Blade angle is changed to allow constant RPM that's in the ideal range." Your original way of wording it was, "We change the blade angle, which then physically speeds up or slows the prop RPM." That wording implies that the drag from the blade slows the prop, which wouldn't work since that would waste power and cause stresses on the driveshaft.

My understanding after the discussion is that the pilot choose the ideal RPM, which is controlled by the condition levers. Then he/she choose a power output using the throttle levers, which affects the blade angle, chosen by the computers, to maintain the same RPM set by the condition levers. Is this correct?

Quoting tdscanuck (Reply 13):

Thanks. That simplifies things nicely, and after re-reading the earlier posts from DashTrash, this was explained, but I missed the trees for the forest!

TIS



www.stellaryear.com: Canon EOS 50D, Canon EOS 5DMkII, Sigma 50mm 1.4, Canon 24-70 2.8L II, Canon 100mm 2.8L, Canon 100-4
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 17, posted (2 years 4 months 2 weeks 11 hours ago) and read 6681 times:

Quoting ANITIX87 (Reply 16):
My understanding after the discussion is that the pilot choose the ideal RPM, which is controlled by the condition levers. Then he/she choose a power output using the throttle levers, which affects the blade angle, chosen by the computers, to maintain the same RPM set by the condition levers. Is this correct?

Yes, although the blade angle may not be chosen by computers but may just be some kind of hydraulic or electric governor. Constant-speed props significantly predate computerized engine control.

Tom.


User currently offlineGoldenshield From United States of America, joined Jan 2001, 5842 posts, RR: 15
Reply 18, posted (2 years 4 months 2 weeks 10 hours ago) and read 6653 times:

Quoting tdscanuck (Reply 17):
Constant-speed props significantly predate computerized engine control.

Lindbergh himself chose to stick with a fixed pitch prop instead of having a constant speed prop in order to save weight.



Two all beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun.
User currently offlineViscount724 From Switzerland, joined Oct 2006, 24061 posts, RR: 23
Reply 19, posted (2 years 4 months 2 weeks 5 hours ago) and read 6586 times:

Quoting N243NW (Reply 15):
the direct-drive Garrett TPE331 is very popular. Used by the King Air

Apart from one prototype King Air that was re-engined with the TPE331 many years ago for test purposes but never put into production, I think all King Airs have used the Pratt & Whitney Canada PT-6.


User currently offlineDC8FriendShip From United States of America, joined Apr 2005, 242 posts, RR: 3
Reply 20, posted (2 years 4 months 2 weeks 3 hours ago) and read 6573 times:

Quoting Viscount724 (Reply 19):
Apart from one prototype King Air that was re-engined with the TPE331 many years ago for test purposes but never put into production, I think all King Airs have used the Pratt & Whitney Canada PT-6


They have an option of either. the PT-6 is admittedly more popular.



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Saab 340 And Dash 8 100/200 Operating Costs posted Tue Aug 31 2010 11:28:37 by thegreatRDU
Engine Rotation And Thrust Questions posted Thu Jun 17 2010 17:32:24 by CFBFrame
A320 Wing Design And Detailed Questions. posted Mon Jun 8 2009 16:12:17 by EcuadorianMD11
How Are The CRJ-700 And Dash 8 Mx-wise? posted Sat Feb 10 2007 01:28:20 by KBFIspotter
777: T/O And Landing Questions posted Sun Jul 9 2006 18:53:58 by Capt.Fantastic

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