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N1G

Trying to understand Prop Feathering, Constant speed props etc

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Hi,This is my first attempt to understand feathering and constant speed props. I just bought the jetprop and really am trying to understand it's operation and theory behind this type of technology. How to fly it, what to do and what not to do. It really has me scratching my head. It really bothers me to try and fly something and pretend I understand it's operation. Can anyone point me to an article or series of articles that will help me understand how it works and how to use it.RegardsBob

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I hear ya... ever since the turbine Duke I've been trying to learn more about the engine itself.What I've gathered so far is most are fairly laggy in terms up power increase and decrease. Generally put the engine stuff in the green and you're ok. When climbing, reduce throttle, then reduce rpm to set cruise power.Here's a link that might help clarify:http://www.pilotoutlook.com/airplane_flying/turboprop_engines_types

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I hear ya... ever since the turbine Duke I've been trying to learn more about the engine itself.What I've gathered so far is most are fairly laggy in terms up power increase and decrease. Generally put the engine stuff in the green and you're ok. When climbing, reduce throttle, then reduce rpm to set cruise power.Here's a link that might help clarify:http://www.pilotoutl...p_engines_types
thanks Ryan, I will take a look. I have a basic understanding but having a solid understanding will allow you to make the right decision in case of trouble. I remember reading about a guy who crashed because of not completely understanding of the physics and operational configurations and why. Apparently he was on approach with a mild descent. Blade pitch angle was reduced along with power. What happened was a plane pulled out onto the runway and he needed to pull up and out but the RPM's were way to low and he did not have enough time to correct. He ended up leveling a couple of small hangers, himself and all 4 passengers were killed. So what the experts were saying was that he should have kept the RPM's high on approach just in case. So with this in mind, it is more than just knowing what each lever does, it is this understanding what not to do aside from keeping things in the green I guess. So I really need to do some reading.Bob

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Understood. From what I've read, when on final you treat every approach like you're going to go around. Sooo... props high rpm, oil cooler doors open (they are closed during descent to contain the warm air), fuel pumps on, fuel fullest tank, flaps lnd and gear down of course. The condition lever is apparently used more on the ground for taxiing but I'm not 100% sure one when to use the different settings in flight.

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It's actually pretty simple. In addition to the throttles (which control the power, or torque delivered by the engine) you also have the Prop levers, which control the speed (RPM) of the propeller by altering the pitch of the blades. In most aircraft, you take off and land with the propellers fully fine (full RPM, or levers fully forward). This gives the props the biggest 'bite' and thus more power, but also makes them noisier. During climbout, its standard procedure at thrust reduction altitude to reduce power, and reduce prop RPM. Note it must be in that order - you always reduce the throttles first before reducing prop RPM, otherwise you can overboost and cause damage to the engine. When you reach cruise, you set cruise power on the throttles and bring the props back a little further. In the manual for the aircraft there is usually a table which contains the cruise power settings and prop settings for particular altitudes. The props usually then stay in that cruise position until somewhere on the approach when they are moved back to fully fine for landing.Feathering a propeller is usually done after an engine failure to stop the propeller spinning (windmilling) in the wind (causing drag). The blades of a feathered prop are angled flat so they present the least obstruction to passing air.

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Hi Guys, thanks for the answers. So what exactly then is a constant speed prop? If one can control the RPM by changing pitch manually, then are there systems which control the rpm automatically?The learning process sometimes requires stupid questions I guess.Bob

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So what exactly then is a constant speed prop? If one can control the RPM by changing pitch manually, then are there systems which control the rpm automatically?
Constant speed prop means just that - it turns at a constant speed, independent of the engine speed.Compared with a fixed pitch prop like in the simple Cessna 172, where increasing the throttle also increases the RPM of the prop. With a constant speed prop, you set the desired prop RPM using the prop lever, and this will remain constant regardless of throttle position / engine speed. There is an automatic process which adjusts the pitch of the blades to maintain the prop rpm as a response to change in engine speed.

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Constant speed prop means just that - it turns at a constant speed, independent of the engine speed.Compared with a fixed pitch prop like in the simple Cessna 172, where increasing the throttle also increases the RPM of the prop. With a constant speed prop, you set the desired prop RPM using the prop lever, and this will remain constant regardless of throttle position / engine speed. There is an automatic process which adjusts the pitch of the blades to maintain the prop rpm as a response to change in engine speed.
So when using the prop lever, you are actually changing the pitch of the blades which directly affects rpm's, is this correct? By increasing or decreasing throttle, blade pitch angle is increased and decreased proportionally to maintain prop rpm. I don't think I have this correct because if you manually can change the pitch with the prop lever then the throttle is also changing the pitch does not seem logical. sorry for being so dense here, but I am really stuck.Bob

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With the prop lever you are correct, the pitch (angle) of the blades change. With throttle lever, you're adding combustion (I guess in a simple term), and it's spinning the shaft, where the prop is connected. IE with the power lever (throttle) you are providing an increase or decrease of thrust. However the power lever setting DOES NOT change the pitch of the props... the prop lever does that.

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Watch this video, which is a great explanation of prop types:

And read the accumsim handbook for the Spitfire or the P-40; they include good info on props as well: http://www.a2asimula...&products_id=47Scroll to bottom of page and click on the accumsim manual to download.
Hey thanks a bunch. I will do that.RegardsBob
With the prop lever you are correct, the pitch (angle) of the blades change. With throttle lever, you're adding combustion (I guess in a simple term), and it's spinning the shaft, where the prop is connected. IE with the power lever (throttle) you are providing an increase or decrease of thrust. However the power lever setting DOES NOT change the pitch of the props... the prop lever does that.
Well I thought I had it until now.Twright made this comment above "There is an automatic process which adjusts the pitch of the blades to maintain the prop rpm as a response to change in engine speed."Anyway, I am not sure now which is correct. I will keep reading.Bob

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Well I thought I had it until now.Twright made this comment above "There is an automatic process which adjusts the pitch of the blades to maintain the prop rpm as a response to change in engine speed."
Correct you select prop rpm with the prop lever. If you add power by increasing throttle the blade angle will increase too hold the rpm.

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Part of the reason I had trouble learning this was that in most FS planes, there's no penalty for just pushing everything to the max, but after the J41 and Turbine Duke I have a much better grasp of it.

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Well I disabled the engine damage on the Duke pffff! Maybe it took this long for me to have greater appreciation for TP's...

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Correct you select prop rpm with the prop lever. If you add power by increasing throttle the blade angle will increase too hold the rpm.
Ok, so let me see if I have this right.The Power/Thrust Lever will change the pitch and the prop lever will change the pitch. Is this correct?Bob

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The Power/Thrust Lever will change the pitch and the prop lever will change the pitch. Is this correct?
The prop lever sets the required RPM by adjusting blade pitch.However, if you increase power on the throttles there will be more power turning the prop than there was before. So what will happen? The speed of the propeller will increase. So, as an automatic response to an adjustment in engine speed (throttle), the pitch of the blades will adjust again to maintain the required prop RPM.There isn't a direct connection between the prop lever and the blade pitch, or the throttle and the blade pitch. All the prop lever does is allows the pilot to set his desired RPM, and all the throttle does is controls the speed of the engine. The blade pitch itself is controlled by a computer which responds to some input - either movement of the prop lever or a change in engine speed.

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Hey Bob,You're almost there. The prop levers are there to allow you to manually adjust the prop pitch thereby adjusting the RPM up or down. In addition to the prop levers, which of course are under your control, there exists an additional device which, for lack of a better term, "governs" the prop RPM. This device is placed in the linkage between the prop and the turbine. You do not have manual control over this device. It is there to insure the prop RPM does not waiver up or down from the level you have dictated by using your prop levers when you use the throttle. In other words, once you set the prop RPM using your prop pitch levers you then can adjust the throttle and the prop RPM will be maintained by the device mentioned above. This enables you to establish various throttle settings and be comfortable the prop RPM settings previously set by your prop pitch lever will be maintained.Hope this helps.John

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The prop lever sets the required RPM by adjusting blade pitch.However, if you increase power on the throttles there will be more power turning the prop than there was before. So what will happen? The speed of the propeller will increase. So, as an automatic response to an adjustment in engine speed (throttle), the pitch of the blades will adjust again to maintain the required prop RPM.There isn't a direct connection between the prop lever and the blade pitch, or the throttle and the blade pitch. All the prop lever does is allows the pilot to set his desired RPM, and all the throttle does is controls the speed of the engine. The blade pitch itself is controlled by a computer which responds to some input - either movement of the prop lever or a change in engine speed.
Hey Bud,I watched the video. AA did a very nice job with this, and thank you for taking the time to post, it really did help. This is indeed is a new area for me and a real eye opener. I am beginning to understand the situation of the pilot who failed to understand his plane and it cost him his life and 4 others. If he had been flying a fixed prop pitch aircraft, of course the only thing to do would have been to apply power and clean up the aircraft. With the constant speed prop, he must have come in with low thrust and low rpm I am guessing, which meant he would have had to increase thrust and rpm. Maybe he added the power, but was still at a low rpm, thus having a relatively low airspeed, he could not get any climb. I think that must have been the situation. What do you think? My post on this pilot error is above.RegardsBob

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GUMP check is standard for constant speed prop planes and should always be used on approach...Gas...fuel selector on correct tanks, pumps on if requiredUndercarriage... gear down and '3 green'Mixture....full richProps....full forwardKeep the props full for takeoff and landing

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GUMP check is standard for constant speed prop planes and should always be used on approach...Gas...fuel selector on correct tanks, pumps on if requiredUndercarriage... gear down and '3 green'Mixture....full richProps....full forwardKeep the props full for takeoff and landing
Nice acronym. I can remember that. ThanksBob

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Turbo-props are slow to respond at low power settings because you have to wait for the "gas generator" (compressor and turbine, a.k.a. N1) to spool-up. Therefore you fly the last part of the approach in high drag configuration (full flaps) to avoid approaching with engines at idle. Then if you go-around your engines will respond a lot quicker when you add throttle.Constant speed props all have a prop rpm governor. This means the prop lever is not setting pitch, rather, um, rpm! Prop lever forward: More rpm. Prop lever back: less rpm. That's it.What the prop governor does is change pitch as you change throttle so the rpm remain constant. Thus the name constant-speed prop. When you add throttle, the prop will seek to increase rpm, thus the governor will increase blade pitch to increase drag, so prop rpm remain again constant. Of course as the governor increases prop pitch, thrust also increase. Thus an increase in throttle leads to an increase in thrust while prop rpm remains constant.Now as you increase throttle, while the prop rpm remain constant, what you are increasing is torque. So you can increase torque by increasing throttle or you can increase torque by lowering prop rpm (remember, at constant throttle, for a lower rpm setting the prop gorvernor will increase blade pitch to slow the prop, and increased pitch will increase torque).Now power (hp) is torque times rpm, so you see you can have the same power at high torque and low rpm or at low torque and high rpm. Of course you will have max power at both high torque and high rpm.With a piston constant speed prop, the idea is to lower rpm to reduce engine wear and fuel consumption, The limit is the maximum torque for a given rpm, as piston engines do not take to high torque and low rpm kindly.Conceptually the prop lever acts as a gear shift on your car or bicycle: High rpm is low gear (you pedal fast on your bike!) then as you increase airspeed low rpm (you pedal slower.)Finally, when approaching in a turboporp, learn to listen to the gas generator high-pitched whine frequency to develop a feel for torque, as torque is a proxy for throttle setting (the prop rpm remain fixed at the high setting during approach).Cheers,- jahman.

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Turbo-props are slow to respond at low power settings because you have to wait for the "gas generator" (compressor and turbine, a.k.a. N1) to spool-up. Therefore you fly the last part of the approach in high drag configuration (full flaps) to avoid approaching with engines at idle. Then if you go-around your engines will respond a lot quicker when you add throttle.Constant speed props all have a prop rpm governor. This means the prop lever is not setting pitch, rather, um, rpm! Prop lever forward: More rpm. Prop lever back: less rpm. That's it.What the prop governor does is change pitch as you change throttle so the rpm remain constant. Thus the name constant-speed prop. When you add throttle, the prop will seek to increase rpm, thus the governor will increase blade pitch to increase drag, so prop rpm remain again constant. Of course as the governor increases prop pitch, thrust also increase. Thus an increase in throttle leads to an increase in thrust while prop rpm remains constant.Now as you increase throttle, while the prop rpm remain constant, what you are increasing is torque. So you can increase torque by increasing throttle or you can increase torque by lowering prop rpm (remember, at constant throttle, for a lower rpm setting the prop gorvernor will increase blade pitch to slow the prop, and increased pitch will increase torque).Now power (hp) is torque times rpm, so you see you can have the same power at high torque and low rpm or at low torque and high rpm. Of course you will have max power at both high torque and high rpm.With a piston constant speed prop, the idea is to lower rpm to reduce engine wear and fuel consumption, The limit is the maximum torque for a given rpm, as piston engines do not take to high torque and low rpm kindly.Conceptually the prop lever acts as a gear shift on your car or bicycle: High rpm is low gear (you pedal fast on your bike!) then as you increase airspeed low rpm (you pedal slower.)Finally, when approaching in a turboporp, learn to listen to the gas generator high-pitched whine frequency to develop a feel for torque, as torque is a proxy for throttle setting (the prop rpm remain fixed at the high setting during approach).Cheers,- jahman.
Ah..... very nice indeed jahman!!! Thanks for the contribution.Geez, so much to learn. It never ceases to amaze me that by asking a question, so many are ready to jump in.Bob

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Maybe he added the power, but was still at a low rpm, thus having a relatively low airspeed, he could not get any climb. I think that must have been the situation. What do you think? My post on this pilot error is above.
I'd say pilot error too. If the prop levers were still set to a low RPM when he maxed the throttles, the engines could likely have failed. Asking the props to maintain a low RPM whilst throttling up the engines can completely destroy the engine internally - you're asking it to do something it doesn't want to do (naturally at high power the propeller wants to turn faster).

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