PC6 PT6 and engine failures
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PC6 PT6 and engine failures
Dear all,
today I was reading about the PC6 of Empuriabrava EC-EMZ who crashed short of the runway, for a suspected engine failure.
Since almost all my approaches on the PC6 were on beta, I always considered it as an advantage, since it should be quite easy to reach the runway with that excess of energy.
My question is if I remember properly in case of engine failure in beta the prop stays in beta because the pressure is trapped by the valve if I feather the prop the prop feather because of pressure released counterweights and springs.
But what if I advance the Power lever?
I suspect that the prop would get out of beta and go in alpha, reducing but not canceling the drag, a good way to reach the runway if really low altitude.
Am I correct?
today I was reading about the PC6 of Empuriabrava EC-EMZ who crashed short of the runway, for a suspected engine failure.
Since almost all my approaches on the PC6 were on beta, I always considered it as an advantage, since it should be quite easy to reach the runway with that excess of energy.
My question is if I remember properly in case of engine failure in beta the prop stays in beta because the pressure is trapped by the valve if I feather the prop the prop feather because of pressure released counterweights and springs.
But what if I advance the Power lever?
I suspect that the prop would get out of beta and go in alpha, reducing but not canceling the drag, a good way to reach the runway if really low altitude.
Am I correct?
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I had a flame out at 1,000ft on a beta approach final in a PC6 (20 years ago) and the prop feathered no problem without touching the power lever.
If it happens you will feel it straight away , that beautiful big air brake feeling goes away and you'll see the approach angle changing.
I had to do a big S turn and a sideslip to bleed off height , the PC6 glides beautifully
After landing the engine started straight up.
The engineer thought the cause of the flame out was I had ran the collector tank in the tail dry due to the angle of descent (typically 38 degrees nose down) plus he found some undocumented mods to the fuel system done by the previous operator (military). I had 30 mins of fuel remaining in the tank , this was the last sortie before refuelling.
As we were operating out of a private air strip our typical pattern was joining downwind at 10,000ft, turn onto base at 6,000 then finals at 3,000 holding Beta down to 300 to 500ft depending on conditions.
2.5 min descent from 12,000ft.
If it happens you will feel it straight away , that beautiful big air brake feeling goes away and you'll see the approach angle changing.
I had to do a big S turn and a sideslip to bleed off height , the PC6 glides beautifully
After landing the engine started straight up.
The engineer thought the cause of the flame out was I had ran the collector tank in the tail dry due to the angle of descent (typically 38 degrees nose down) plus he found some undocumented mods to the fuel system done by the previous operator (military). I had 30 mins of fuel remaining in the tank , this was the last sortie before refuelling.
As we were operating out of a private air strip our typical pattern was joining downwind at 10,000ft, turn onto base at 6,000 then finals at 3,000 holding Beta down to 300 to 500ft depending on conditions.
2.5 min descent from 12,000ft.
Last edited by aseanaero; 30th Nov 2017 at 13:14.
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Ciao aseanaero!
thank you for your reply!
Even if now I fly the Bus I remember pretty well that kind circuit, it was awesome to fly the porter!
So, according what you say the prop got out of beta as soon as you lost the engine?
I am still a Rated PC6 enthusiast and I am trying to understand the behavior of that lovely prop system!
thank you for your reply!
Even if now I fly the Bus I remember pretty well that kind circuit, it was awesome to fly the porter!
So, according what you say the prop got out of beta as soon as you lost the engine?
I am still a Rated PC6 enthusiast and I am trying to understand the behavior of that lovely prop system!
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The power lever was actually at idle but with our aircraft that was about 4 degrees Beta.
With the flame out speed will build up quickly with the nose down that far so it felt like the prop came out of Beta.
We never went into the actual beta range on descent in our operation as 6,000fpm was enough
As I said that 'wall of drag' air brake vanished
At 1,000 ft I didn't even try to relight as I had the runway right in front of me so I shut everything down and focused on the landing.
Anyway to answer your question the prop will feather in Beta but I caught it in the first few seconds while the engine was spooling down
I found this which may give a better technical answer to your question
Propeller Control for Turbo-Prop Engines | AviationPros.com
With the flame out speed will build up quickly with the nose down that far so it felt like the prop came out of Beta.
We never went into the actual beta range on descent in our operation as 6,000fpm was enough
As I said that 'wall of drag' air brake vanished
At 1,000 ft I didn't even try to relight as I had the runway right in front of me so I shut everything down and focused on the landing.
Anyway to answer your question the prop will feather in Beta but I caught it in the first few seconds while the engine was spooling down
I found this which may give a better technical answer to your question
System Description
At the heart of the system, the PT-6 governor has an internal pump that takes oil from the engine oil system and supplies it at boosted pressure and volume to the propeller servo. Some installations such as the PW100 engine system utilize a separate pump and pitch control unit for this function. In a standard PT-6 propeller engine configuration, operating oil is supplied to the governor at 40-45 psi. The governor pump elevates the pressure to 385 psi at volumes of up to 6 quarts per minute to actuate the propeller toward the low pitch or increase RPM direction. Counteracting this oil are the propeller counterweights and feather spring.
Typical PT-6 governor mounted to the engine.
Propeller speed sensing is performed by a set of spinning flyweights that are in direct drive to the reduction gear box. Speeder spring pressure counteracts the centrifugal force of the spinning flyweights to hold the metering valve (pilot valve) in a predetermined position. The position of the metering valve will determine whether or not oil is ported to or from the propeller servo. In underspeed condition, the valve ports oil to the propeller piston; reducing blade angle and increasing RPM. In overspeed condition, the valve allows oil to drain from the propeller and blade angle is increased due to counterweight and feather spring forces. This will cause a decrease in RPM. In theory, when the governor is at onspeed condition the metering valve is closed; not allowing pump oil to pass to or from the propeller and thus a constant predetermined RPM is maintained. It is important to note that on the engine the governor is always porting oil to the propeller to counteract the internal leakage where the oil transfers between the engine case and propshaft.
Feathering of the propeller, a critical function for multi-engine aircraft, is accomplished by allowing oil to drain from the propeller servo. Feather springs and counterweight forces on the propeller will force the blades into the feather position in the absence of high pressure oil. To do this, the governor makes use of either a feather lift rod or a feather plunger. The feather lift rod is centered in the control shaft on top of the governor. When the control shaft is moved to the minimum RPM position, the lift rod pulls the pilot valve into a simulated overspeed condition which allows oil to drain from the propeller. Some governor models use a feather plunger instead of a lift rod. The feather plunger does not directly contact the pilot valve, rather, it diverts governor pump oil to a feather drain tube. Feather plungers react more quickly than feather lift rods and are thus used on higher pressure operation systems such as those found on PT6-67 series engines. Use of a feather plunger bypasses normal porting and allows for quicker feathering of the prop.
"The heart of the system": Flyweight and pilot valve combination. The feather drain tube allows for quicker feathering of the propeller.
Putting the propeller into reverse mode (beta mode) and maintaining RPM control in reverse is accomplished through the use of the beta valve located at the front of the governor. The beta valve is directly connected to the propeller through the beta linkage and propeller beta ring. The primary functions of the beta valve are (1) to prevent the propeller from entering reverse uncommanded and (2) to control blade angle (and RPM) while in reverse command. As propeller blades approach reverse blade angles, the beta valve is pulled open through direct linkage to the prop. This action diverts high pressure oil from the propeller in much the same fashion as a feather lift rod. Oil is then diverted to the sump and the propeller blade angle is not allowed to travel further into reverse. Commanded reversing is accomplished by "overriding" the beta valve function. When the operator moves the power lever over the idle stop and into beta range; he resets the beta linkage and allows oil to continue to be ported to the propeller. This allows the propeller blades to travel into reverse angles.
The inherent problem with a reversing propeller system is that at some point between positive and negative blade angles, the propeller will be generating zero thrust. This is the point where the engine will be "off loaded" and attempt to overspeed. To prevent an overspeed of the engine at this point, the PT-6 governor makes use of an internal pneumatic air section. The pneumatic air section within the governor can allow PY air to bleed and thus signal the fuel control unit to decrease fuel and slow turbine speed. This ability of the governor is used in two conditions. During normal operation if a system failure allows the propeller to overspeed; the airbleed yoke inside the governor is raised and PY air is bled. This commands the fuel control unit to decrease fuel to the engine and thus reduce power. Also, during reversing operations the power turbine speed must be held to approximately 95% in order to avoid overspeed. This is accomplished by resetting the airbleed yoke manually inside the governor. When the operator commands the power lever into beta range the airbleed yoke is automatically reset through the beta linkage and engine power is thus limited to 95%.
The feather plunger operates independent of the pilot valve.
An additional function of some models of turboprop governors is to synchronize engine RPMs on multi-engine applications. Commonly known as Type II synchronizing, this system eliminates the need for rod end trimming devices. This is accomplished by use of a speed bias coil within the governor. The coil, when energized, will exert a pull on the metering valve within the governor. Changes in metering valve position are relatively minute allowing for accurate RPM control between the propellers. Of course, the operator can manually override the synchronizing system at any time. The synchronizing computer, more commonly known as the "box", will compare RPMs of the engines and increase or decrease voltage to the coils within the governors to obtain accurate speed control. Speed sensing inputs to the box can be obtained from electrical pickups on the overspeed governors or from the propellers themselves.
Although not directly controlling engine power or propeller RPM; a mention should be made about the overspeed governor within the governing system. The overspeed governor (OSG) is a separate control component located on the front of the engine. In the event of primary governor failure, the overspeed governor will limit propeller speed to somewhere between 104% and 106% of rated propeller RPM. The overspeed governor is directly in line between the primary prop governor and the propeller servo. All oil traveling from the primary prop governor to the propeller servo must travel through the overspeed governor. Using the same mechanism as the primary prop governor (i.e. flyweights and metering valve) the overspeed governor is preset to divert high pressure oil in the event of a propeller overspeed. The problem in checking overspeed operation is that since the OSG is not activated until 104%, its operation cannot be checked because the primary prop governor will hold prop RPM to 100%. Therefore, a reset condition is incorporated which will change the speed setting of the OSG to a point below 100% prop rpm. This is accomplished through the use of a solenoid valve and reset piston within the governor. During reset mode, the overspeed governor is reset to 92% of rated prop speed on most applications. This allows the governor to be checked for proper operation.
At the heart of the system, the PT-6 governor has an internal pump that takes oil from the engine oil system and supplies it at boosted pressure and volume to the propeller servo. Some installations such as the PW100 engine system utilize a separate pump and pitch control unit for this function. In a standard PT-6 propeller engine configuration, operating oil is supplied to the governor at 40-45 psi. The governor pump elevates the pressure to 385 psi at volumes of up to 6 quarts per minute to actuate the propeller toward the low pitch or increase RPM direction. Counteracting this oil are the propeller counterweights and feather spring.
Typical PT-6 governor mounted to the engine.
Propeller speed sensing is performed by a set of spinning flyweights that are in direct drive to the reduction gear box. Speeder spring pressure counteracts the centrifugal force of the spinning flyweights to hold the metering valve (pilot valve) in a predetermined position. The position of the metering valve will determine whether or not oil is ported to or from the propeller servo. In underspeed condition, the valve ports oil to the propeller piston; reducing blade angle and increasing RPM. In overspeed condition, the valve allows oil to drain from the propeller and blade angle is increased due to counterweight and feather spring forces. This will cause a decrease in RPM. In theory, when the governor is at onspeed condition the metering valve is closed; not allowing pump oil to pass to or from the propeller and thus a constant predetermined RPM is maintained. It is important to note that on the engine the governor is always porting oil to the propeller to counteract the internal leakage where the oil transfers between the engine case and propshaft.
Feathering of the propeller, a critical function for multi-engine aircraft, is accomplished by allowing oil to drain from the propeller servo. Feather springs and counterweight forces on the propeller will force the blades into the feather position in the absence of high pressure oil. To do this, the governor makes use of either a feather lift rod or a feather plunger. The feather lift rod is centered in the control shaft on top of the governor. When the control shaft is moved to the minimum RPM position, the lift rod pulls the pilot valve into a simulated overspeed condition which allows oil to drain from the propeller. Some governor models use a feather plunger instead of a lift rod. The feather plunger does not directly contact the pilot valve, rather, it diverts governor pump oil to a feather drain tube. Feather plungers react more quickly than feather lift rods and are thus used on higher pressure operation systems such as those found on PT6-67 series engines. Use of a feather plunger bypasses normal porting and allows for quicker feathering of the prop.
"The heart of the system": Flyweight and pilot valve combination. The feather drain tube allows for quicker feathering of the propeller.
Putting the propeller into reverse mode (beta mode) and maintaining RPM control in reverse is accomplished through the use of the beta valve located at the front of the governor. The beta valve is directly connected to the propeller through the beta linkage and propeller beta ring. The primary functions of the beta valve are (1) to prevent the propeller from entering reverse uncommanded and (2) to control blade angle (and RPM) while in reverse command. As propeller blades approach reverse blade angles, the beta valve is pulled open through direct linkage to the prop. This action diverts high pressure oil from the propeller in much the same fashion as a feather lift rod. Oil is then diverted to the sump and the propeller blade angle is not allowed to travel further into reverse. Commanded reversing is accomplished by "overriding" the beta valve function. When the operator moves the power lever over the idle stop and into beta range; he resets the beta linkage and allows oil to continue to be ported to the propeller. This allows the propeller blades to travel into reverse angles.
The inherent problem with a reversing propeller system is that at some point between positive and negative blade angles, the propeller will be generating zero thrust. This is the point where the engine will be "off loaded" and attempt to overspeed. To prevent an overspeed of the engine at this point, the PT-6 governor makes use of an internal pneumatic air section. The pneumatic air section within the governor can allow PY air to bleed and thus signal the fuel control unit to decrease fuel and slow turbine speed. This ability of the governor is used in two conditions. During normal operation if a system failure allows the propeller to overspeed; the airbleed yoke inside the governor is raised and PY air is bled. This commands the fuel control unit to decrease fuel to the engine and thus reduce power. Also, during reversing operations the power turbine speed must be held to approximately 95% in order to avoid overspeed. This is accomplished by resetting the airbleed yoke manually inside the governor. When the operator commands the power lever into beta range the airbleed yoke is automatically reset through the beta linkage and engine power is thus limited to 95%.
The feather plunger operates independent of the pilot valve.
An additional function of some models of turboprop governors is to synchronize engine RPMs on multi-engine applications. Commonly known as Type II synchronizing, this system eliminates the need for rod end trimming devices. This is accomplished by use of a speed bias coil within the governor. The coil, when energized, will exert a pull on the metering valve within the governor. Changes in metering valve position are relatively minute allowing for accurate RPM control between the propellers. Of course, the operator can manually override the synchronizing system at any time. The synchronizing computer, more commonly known as the "box", will compare RPMs of the engines and increase or decrease voltage to the coils within the governors to obtain accurate speed control. Speed sensing inputs to the box can be obtained from electrical pickups on the overspeed governors or from the propellers themselves.
Although not directly controlling engine power or propeller RPM; a mention should be made about the overspeed governor within the governing system. The overspeed governor (OSG) is a separate control component located on the front of the engine. In the event of primary governor failure, the overspeed governor will limit propeller speed to somewhere between 104% and 106% of rated propeller RPM. The overspeed governor is directly in line between the primary prop governor and the propeller servo. All oil traveling from the primary prop governor to the propeller servo must travel through the overspeed governor. Using the same mechanism as the primary prop governor (i.e. flyweights and metering valve) the overspeed governor is preset to divert high pressure oil in the event of a propeller overspeed. The problem in checking overspeed operation is that since the OSG is not activated until 104%, its operation cannot be checked because the primary prop governor will hold prop RPM to 100%. Therefore, a reset condition is incorporated which will change the speed setting of the OSG to a point below 100% prop rpm. This is accomplished through the use of a solenoid valve and reset piston within the governor. During reset mode, the overspeed governor is reset to 92% of rated prop speed on most applications. This allows the governor to be checked for proper operation.
