sd330 sherpa very pt6a-45r illusive problem
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sd330 sherpa very pt6a-45r illusive problem
Hello guys, let me start with a little background(obviously). Anyway I'm flying the shed for 4 years now. Some time last year (2014) was when i first experienced it. Here's what happened on the first occurence:
My right rpm dropped to around 900rpm then it stabilized right away. I was maybe in the final phase of takeoff. Then i requested for landing. Then right before touching down it did it again.
So the maintenance checked it but unable to find the cause(just assume that they did everything to try and troubleshoot the problem). So it was released for flight ( we have a term here in the Philippines.....it fixed itself up).
So after a few weeks of flying it it happenwd again but a bit longer than the first. Procedure dictates that i shut the engine down but, yes, it stabilized again so went on with the landing.
It was checked and still nothing seems to be causing it. Fcu, fuel nozzles, prop govs, overspeed , (accesory gearbox) all was checked but seems to be ok. Then one of our pilots met with another shed pilot and was told "oh that's normal, all we do is reduce the torque reset the prop and it'll be fine after".
So the maintenance released the plane for flight.
For 5-6 months now, it keeps doing it and i've come very accustomed to it (ye i know it's wrong, that's gen-av flying for us here). But this time it doesnt only happen during the initial phase of flight. It happens in cruise, descents and even during approach. BUT NEVER when the aircraft's on ground.
Earlier today something very different happened. It did a very little change in rpm but this time the fine pitch(ground fine/prop disc) illuminated. It did it 4 times but very little drop in rpm like it just coughed or something.
Here are the things that is being indicated when it happens:
Most of the time(3/4 of the time) the rpm drops then the torque increases but all other parameters stays the same (the fuel flow, ng, oil press, everything else stays the same).
But sometimes the rpm drops ahead of the torque but instead of increasing, the torque decreases as well and again the other readings stay the same.
And finally, in what happened earlier, the rpm dropped then the torque increased, all else stayed the same but this time the fine pitch illuminated.
So that's the case. So basically my question is any of you guys ever experienced this? Maybe on a king air or whatever thag has a pt6 engine?
Also the right hand has a newly overhauled props, just replaced the blades as well, new FCU, forgot the other stuff. And the engine still has 224hours remaining.
Hope you guys could ask around regarding my annoying problem.
My right rpm dropped to around 900rpm then it stabilized right away. I was maybe in the final phase of takeoff. Then i requested for landing. Then right before touching down it did it again.
So the maintenance checked it but unable to find the cause(just assume that they did everything to try and troubleshoot the problem). So it was released for flight ( we have a term here in the Philippines.....it fixed itself up).
So after a few weeks of flying it it happenwd again but a bit longer than the first. Procedure dictates that i shut the engine down but, yes, it stabilized again so went on with the landing.
It was checked and still nothing seems to be causing it. Fcu, fuel nozzles, prop govs, overspeed , (accesory gearbox) all was checked but seems to be ok. Then one of our pilots met with another shed pilot and was told "oh that's normal, all we do is reduce the torque reset the prop and it'll be fine after".
So the maintenance released the plane for flight.
For 5-6 months now, it keeps doing it and i've come very accustomed to it (ye i know it's wrong, that's gen-av flying for us here). But this time it doesnt only happen during the initial phase of flight. It happens in cruise, descents and even during approach. BUT NEVER when the aircraft's on ground.
Earlier today something very different happened. It did a very little change in rpm but this time the fine pitch(ground fine/prop disc) illuminated. It did it 4 times but very little drop in rpm like it just coughed or something.
Here are the things that is being indicated when it happens:
Most of the time(3/4 of the time) the rpm drops then the torque increases but all other parameters stays the same (the fuel flow, ng, oil press, everything else stays the same).
But sometimes the rpm drops ahead of the torque but instead of increasing, the torque decreases as well and again the other readings stay the same.
And finally, in what happened earlier, the rpm dropped then the torque increased, all else stayed the same but this time the fine pitch illuminated.
So that's the case. So basically my question is any of you guys ever experienced this? Maybe on a king air or whatever thag has a pt6 engine?
Also the right hand has a newly overhauled props, just replaced the blades as well, new FCU, forgot the other stuff. And the engine still has 224hours remaining.
Hope you guys could ask around regarding my annoying problem.
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Yeah, we did that and the PW guys dont have a clue of what the cause is. And yes! That's exactly what's on my mind right now! So annoying. I'll just fly this thing back to manila and wont fly it til the problem gets resolved.
BTW Bleed valeves were easily solved. You'll find this funny (i did), they cant find out why our engine shuts down when using the bleeds(left) so they sealed the whole thing installing a metal plate. Now we only use ram air, not wanting to stress the right engine further. The itt goes up pretty quickly past 745c, so we just dont use it.
BTW Bleed valeves were easily solved. You'll find this funny (i did), they cant find out why our engine shuts down when using the bleeds(left) so they sealed the whole thing installing a metal plate. Now we only use ram air, not wanting to stress the right engine further. The itt goes up pretty quickly past 745c, so we just dont use it.
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chrismike294
Since the back end of the engine parameters don't change when you have the issue - “ Most of the time(3/4 of the time) the rpm drops then the torque increases but all other parameters stays the same (the fuel flow, ng, oil press, everything else stays the same).” - I would anticipate that the problem is with the front end of the engine.
So some things for your maintenance guys to check.
I will work from easy / less expensive to harder and more expensive as part of the troubleshooting flow.
1- The first thing to check is the propeller beta arm stop pin. This is located on the left side of the propeller gearbox at the front and you will find it directly behind the propeller spinner bulkhead. Inspect the pin for wear. I have seen deep wear patterns from the constant movement of the mechanism – the pin should be cylindrical and not worn flat. I have seen these so bad that in order for the beta arm to move it had to climb out of a valley which causes erratic action on its part. High time engines often have this problem. The pilot fix is to "Reset Props" and carry on!!
2- Check the forward rigging very carefully. Remove the clevis pin from the teleflex cable at the cambox and with a gentle forward pull on the forward end of the teleflex cable (Right behind the propeller spinner bulkhead) inspect the following 2 items:
a- the forward face of the beta valve is flush with the beta valve housing (There is a bit of change allowed here but it is only the width of the chamfer on the valve. If it is not correct – rerig the forward half of the engine correctly. If all is good – make sure you have the power lever at the flight idle position and set the friction lock and
b. after checking the beta valve position check to see that the fuel topping governor arm is making contact with the propeller governor stop. The arm should be in direct contact with the governor stop and it is this stop that should be limiting the forward travel of the mechanism. If this is not correct you will possibly have the problem that you are seeing due to the interference with the propeller governor from the fuel topping governor.
This statement makes me think it is beta valve related:
“ Earlier today something very different happened. It did a very little change in rpm but this time the fine pitch(ground fine/prop disc) illuminated. It did it 4 times but very little drop in rpm like it just coughed or something.”
This set of symptoms indicates a mis-rigged beta valve system that is attempting to drive the propeller blade angles below flight idle and while doing so has tripped the warning lights – operated the back-up system – and then cycled the propeller blades on the back-up system. This is a dangerous place to be – not so much for what it does for the operation of the aircraft but because you are now being controlled by a back-up system and should that fail the blade angles may move even further towards ground fine/reverse causing a serious problem at that point. Of course it is also possible that the switches for the blade angle is mis-rigged such that the back-up system is coming on early. Simple check for the Mx guys to confirm correct rigging.
3- If the above is all good – re-insert and cotter pin the rear clevis pin and ensure a little bit of tension is present on the forward linkage – probably will be hard to get if your cambox is badly worn so do the best you can. With the clevis pin now installed the linkage should be under a tiny bit of pressure which will keep the whole mess from vibrating when in operation. Now with the clevis pin installed take off the power lever friction lock and move the power lever forward. On a good cambox you should feel a bit of resistance initially – feels like the lever is “Going over the hump” - and then is nice and smooth to the full forward stop. An old high time cambox will not give you this so you will have to look at the rigging and adjust as is required to eliminate some of the looseness. If you cambox is badly worn then it is possible that the constant radius part of the forward movement has too much wear towards the flight idle position or sometimes at the cruise position. You can check the wear if it seems bad and replace the cambox or get repair parts. If this constant radius slot is wavey due to wear, that motion is transmitted to the propeller beta valve and can cause problems. Check it – repair or replace as required.
4- If all of the above is good - then the next thing I would check is the operation of the fuel topping governor. This is accomplished by disconnecting the linkage for the reset arm and lock wiring it in the full reverse position. This will reset the fuel topping governor to operate at about 10% less than the selected propeller speed lever. Once so affixed – start the engine and with the propeller speed lever set to 100% move the power lever forward carefully until you are fuel flow limited by the operation of the fuel topping governor. This should happen around 90% Np and is indicated by the further movement of the power lever having no effect. This will test the operation of the fuel topping governor. If the speed is not correct then I would remove the propeller governor and install a serviceable one.
5- At this point in time we are getting into some expensive and harder to do things. If all is good from doing the above items and you have not had to fix things or make adjustments other than of a minor nature I would now replace the propeller governor and see if that stops the problem. If the problem is still there after a propeller governor change – then I would change the propeller and see if that fixes the problem.
6- I am not familiar with your aircraft so don't know if you have the ground fine solenoid installed. If so you will need to ensure it is rigged correctly and is operating correctly as well. I would do that before step 3. Some of the ground fine solenoids have to be aligned correctly so their weight doesn't interfere with the operation.
All of the above procedures should be found in the relevant manuals.
If that doesn't fix things then it possibly means an early engine change.
RE: - Dynamic Balancing:
P&W recommend that the engine and propeller be dynamically balanced – but unlike the Garret TPE331 AFAIK it is not a mandatory requirement. I strongly recommend that dynamic balancing be done as it has a multitude of benefits – one of those being a big reduction in the wear of the engine control linkage. An non-balanced engine will create more wear in the linkage – and the components installed leading to earlier failures. It is worth the small expense in my opinion.
RE: - Bleed Valves:
IIRC the 45 has the high low bleed valve system – there are some issues surrounding them that you might want to know. First is that each valve is calibrated to open / close at a specific point. That point is controlled by a special nozzle orifice that is a classified part. What this means is that the c/d orifices for the specific valve is sized to operate the valve correctly at the conditions encountered inside the engine. The valves affect the airflow through the gas generator to prevent engine (compressor) surges and compressor stalls. If the wrong sized c/d nozzles are installed the bleed valves will not operate at the correct times and may open/close early or late.
I have seen more than one aircraft where someone has taken the 4 valves off – 2 per engine x 2 engines – removed the c/d nozzles for cleaning as a scheduled maintenance function and have re-installed them into the wrong valves causing some very interesting problems. Your logbook and engine overhaul records should have the correct classification part identifiers for your engine bleed valves.
RE: Airframe Bleed Valve:
The compressor air bleed – P3 – is used for airframe items like heating - ventilation – de-icer boots – cooling – pressurization – and instrument air.
The bleed valve port on the engine is sized such that if the outlet should become unrestricted due to a massive rupture etc that the amount of air flowing from the port is limited to a value that will still allow the engine to provide sufficient power.
If you have to block off the air at the airframe bleed valve to make your engine work then you have a sick engine or a massive air leak downstream. If the bleed air use is normal and the amount being used is within the norm then you have a serious engine issue that you need to look at. Removing the ability of one engine to supply the needs of the system when the other engine is shut down is very dangerous and I would not recommend doing this.
Lots of good information available here to help with your understanding of this engine. The second page has 2 very good documents that will help you understand the inner workings of this engine.
File Catalog - FreeBee
Good luck!! - Also if you find the issue please post so we can all learn something!!
Since the back end of the engine parameters don't change when you have the issue - “ Most of the time(3/4 of the time) the rpm drops then the torque increases but all other parameters stays the same (the fuel flow, ng, oil press, everything else stays the same).” - I would anticipate that the problem is with the front end of the engine.
So some things for your maintenance guys to check.
I will work from easy / less expensive to harder and more expensive as part of the troubleshooting flow.
1- The first thing to check is the propeller beta arm stop pin. This is located on the left side of the propeller gearbox at the front and you will find it directly behind the propeller spinner bulkhead. Inspect the pin for wear. I have seen deep wear patterns from the constant movement of the mechanism – the pin should be cylindrical and not worn flat. I have seen these so bad that in order for the beta arm to move it had to climb out of a valley which causes erratic action on its part. High time engines often have this problem. The pilot fix is to "Reset Props" and carry on!!
2- Check the forward rigging very carefully. Remove the clevis pin from the teleflex cable at the cambox and with a gentle forward pull on the forward end of the teleflex cable (Right behind the propeller spinner bulkhead) inspect the following 2 items:
a- the forward face of the beta valve is flush with the beta valve housing (There is a bit of change allowed here but it is only the width of the chamfer on the valve. If it is not correct – rerig the forward half of the engine correctly. If all is good – make sure you have the power lever at the flight idle position and set the friction lock and
b. after checking the beta valve position check to see that the fuel topping governor arm is making contact with the propeller governor stop. The arm should be in direct contact with the governor stop and it is this stop that should be limiting the forward travel of the mechanism. If this is not correct you will possibly have the problem that you are seeing due to the interference with the propeller governor from the fuel topping governor.
This statement makes me think it is beta valve related:
“ Earlier today something very different happened. It did a very little change in rpm but this time the fine pitch(ground fine/prop disc) illuminated. It did it 4 times but very little drop in rpm like it just coughed or something.”
This set of symptoms indicates a mis-rigged beta valve system that is attempting to drive the propeller blade angles below flight idle and while doing so has tripped the warning lights – operated the back-up system – and then cycled the propeller blades on the back-up system. This is a dangerous place to be – not so much for what it does for the operation of the aircraft but because you are now being controlled by a back-up system and should that fail the blade angles may move even further towards ground fine/reverse causing a serious problem at that point. Of course it is also possible that the switches for the blade angle is mis-rigged such that the back-up system is coming on early. Simple check for the Mx guys to confirm correct rigging.
3- If the above is all good – re-insert and cotter pin the rear clevis pin and ensure a little bit of tension is present on the forward linkage – probably will be hard to get if your cambox is badly worn so do the best you can. With the clevis pin now installed the linkage should be under a tiny bit of pressure which will keep the whole mess from vibrating when in operation. Now with the clevis pin installed take off the power lever friction lock and move the power lever forward. On a good cambox you should feel a bit of resistance initially – feels like the lever is “Going over the hump” - and then is nice and smooth to the full forward stop. An old high time cambox will not give you this so you will have to look at the rigging and adjust as is required to eliminate some of the looseness. If you cambox is badly worn then it is possible that the constant radius part of the forward movement has too much wear towards the flight idle position or sometimes at the cruise position. You can check the wear if it seems bad and replace the cambox or get repair parts. If this constant radius slot is wavey due to wear, that motion is transmitted to the propeller beta valve and can cause problems. Check it – repair or replace as required.
4- If all of the above is good - then the next thing I would check is the operation of the fuel topping governor. This is accomplished by disconnecting the linkage for the reset arm and lock wiring it in the full reverse position. This will reset the fuel topping governor to operate at about 10% less than the selected propeller speed lever. Once so affixed – start the engine and with the propeller speed lever set to 100% move the power lever forward carefully until you are fuel flow limited by the operation of the fuel topping governor. This should happen around 90% Np and is indicated by the further movement of the power lever having no effect. This will test the operation of the fuel topping governor. If the speed is not correct then I would remove the propeller governor and install a serviceable one.
5- At this point in time we are getting into some expensive and harder to do things. If all is good from doing the above items and you have not had to fix things or make adjustments other than of a minor nature I would now replace the propeller governor and see if that stops the problem. If the problem is still there after a propeller governor change – then I would change the propeller and see if that fixes the problem.
6- I am not familiar with your aircraft so don't know if you have the ground fine solenoid installed. If so you will need to ensure it is rigged correctly and is operating correctly as well. I would do that before step 3. Some of the ground fine solenoids have to be aligned correctly so their weight doesn't interfere with the operation.
All of the above procedures should be found in the relevant manuals.
If that doesn't fix things then it possibly means an early engine change.
RE: - Dynamic Balancing:
P&W recommend that the engine and propeller be dynamically balanced – but unlike the Garret TPE331 AFAIK it is not a mandatory requirement. I strongly recommend that dynamic balancing be done as it has a multitude of benefits – one of those being a big reduction in the wear of the engine control linkage. An non-balanced engine will create more wear in the linkage – and the components installed leading to earlier failures. It is worth the small expense in my opinion.
RE: - Bleed Valves:
IIRC the 45 has the high low bleed valve system – there are some issues surrounding them that you might want to know. First is that each valve is calibrated to open / close at a specific point. That point is controlled by a special nozzle orifice that is a classified part. What this means is that the c/d orifices for the specific valve is sized to operate the valve correctly at the conditions encountered inside the engine. The valves affect the airflow through the gas generator to prevent engine (compressor) surges and compressor stalls. If the wrong sized c/d nozzles are installed the bleed valves will not operate at the correct times and may open/close early or late.
I have seen more than one aircraft where someone has taken the 4 valves off – 2 per engine x 2 engines – removed the c/d nozzles for cleaning as a scheduled maintenance function and have re-installed them into the wrong valves causing some very interesting problems. Your logbook and engine overhaul records should have the correct classification part identifiers for your engine bleed valves.
RE: Airframe Bleed Valve:
The compressor air bleed – P3 – is used for airframe items like heating - ventilation – de-icer boots – cooling – pressurization – and instrument air.
The bleed valve port on the engine is sized such that if the outlet should become unrestricted due to a massive rupture etc that the amount of air flowing from the port is limited to a value that will still allow the engine to provide sufficient power.
If you have to block off the air at the airframe bleed valve to make your engine work then you have a sick engine or a massive air leak downstream. If the bleed air use is normal and the amount being used is within the norm then you have a serious engine issue that you need to look at. Removing the ability of one engine to supply the needs of the system when the other engine is shut down is very dangerous and I would not recommend doing this.
Lots of good information available here to help with your understanding of this engine. The second page has 2 very good documents that will help you understand the inner workings of this engine.
File Catalog - FreeBee
Good luck!! - Also if you find the issue please post so we can all learn something!!
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@dotticom yeah you wont be =) i know what you mean,my point is they sealed the one for cabin as well, it's kind of funny really =) well whatever they did seem to do the trick so i won't bother with whatever it is they did.
@mx yeah!good pointers. Will be running this through later on. I'm hoping that we can find the problem before the engines gets replaced for future reference. And kudos for the bleeds. Yes, will sure post a report of what's happened
@mx yeah!good pointers. Will be running this through later on. I'm hoping that we can find the problem before the engines gets replaced for future reference. And kudos for the bleeds. Yes, will sure post a report of what's happened
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Not familiar with the -45's, but on the 67's you can swap the prop sycrophaser cannon plug on the Prop Gov. with the auto-feather dump solenoid plug. Prop-synch signals will begin to feather prop! Double check.
Do a ground run with prop-sync on/off.
This very much also sounds like a ground idle solenoid issue.
Once again, never worked on 45s, but does it have a ground idle solenoid? It looks like it does (you have a Ground Fine lamp - or the dreaded old -20 Secondary Low Pitch Stop). Check the wiring/operation of the ground idle solenoid. It is located on the forward end of the propeller reversing cable linked to the beta arm.
From the 1900D manual (-67Ds):
You're ground idle solenoid will be connected to something like a squat-switch/safety switch on the landing gear. Will provide power to the solenoid to bring the beta-arm back. Check rigging/wiring of that switch. Wish I had some Shorts references for ya. It sounds like the solenoid isn't releasing as it should when in the air, then intermittently does every-once a while, which equals greater prop pitch, resulting in the torque increase and RPM decrease. The fact you are not seeing any change in N1, ITT, or FF when this happens leads me to believe this is a propeller issue, not a engine/bleed-off-valve issue (you would see N1, FF, and ITT changes with a bleed issue).
Anyways, i'd swap the ground idle solenoid, check operation, check squat-switch rigging, and rig the forward end of the engine along with adjusting propeller ground and fine idle torques. Along with checking syncrophaser operation (if installed).
Do a ground run with prop-sync on/off.
This very much also sounds like a ground idle solenoid issue.
Once again, never worked on 45s, but does it have a ground idle solenoid? It looks like it does (you have a Ground Fine lamp - or the dreaded old -20 Secondary Low Pitch Stop). Check the wiring/operation of the ground idle solenoid. It is located on the forward end of the propeller reversing cable linked to the beta arm.
From the 1900D manual (-67Ds):
You're ground idle solenoid will be connected to something like a squat-switch/safety switch on the landing gear. Will provide power to the solenoid to bring the beta-arm back. Check rigging/wiring of that switch. Wish I had some Shorts references for ya. It sounds like the solenoid isn't releasing as it should when in the air, then intermittently does every-once a while, which equals greater prop pitch, resulting in the torque increase and RPM decrease. The fact you are not seeing any change in N1, ITT, or FF when this happens leads me to believe this is a propeller issue, not a engine/bleed-off-valve issue (you would see N1, FF, and ITT changes with a bleed issue).
Anyways, i'd swap the ground idle solenoid, check operation, check squat-switch rigging, and rig the forward end of the engine along with adjusting propeller ground and fine idle torques. Along with checking syncrophaser operation (if installed).
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@Plhaught nope our sd330 doesnt have prop sync.dont know it being a 45 has something to do with it but we don't have that. As for the ground idle solenoid, I'm not familiar with it. I am aware of the low blade angle sensor i think they called it. I'll confirm tomorrow if it's the same thing.
Thanks for the input.
Thanks for the input.
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Shorts SD330 sherpa very PT6A-45R illusive problem, fix
The Shorts SD 330 / C-23A, PT6-45R, has a issue with clogged or obstructed P3 Air Filter inside the Inlet tube of the Fuel Control Unit.
During High Humidity Environments the P3 Filter can become totally obstructed dropping engine to Base Ng of 76% or around 900 rpms.
This can also happen in Icing conditions, Dusty environments and after compressor wash.
This condition is corrected with a new Proper size Environment specific P3 filter fix.
At Zweibrucken Germany, a C-23A Sherpa was taking off when both engines dropped to 900 rpms. There was just enough altitude for the Sherpa to turn back for a short landing.
Subsequent Short Brothers investigation found both engines equipped with 5 micron P3 filters in the FCU, both clogged by fine atmospheric dust.
A fix was the change to a 15 micron P3 filter.
No permanent fix was passed to the FAA as initial certification was done with the 5 micron filter.
Failure to properly replace the P3 filter can and has resulted in both engines dropping to Idle.
Needless to say; This condition will be fatal if both engines experience this problem.
If both engines are shut down and restarted, the engines will appear to run normally, then at the most inconvenient time, the engine will drop again to base Ng around 900 rpms.
Most mechanics have no knowledge that there is a filter in the FCU.
Most Mechanics will write off the condition, when it fails to replicate.
It also must be noted that the fine particulate dust was not visible to the naked eye, upon examination.
It is important to change both P3 filters with new filters and not just one side.
If a Prop is mis-rigged it will reproduce immediately.
If a Prop Governor has internal leaking it will seek and wonder continually.
Prop issues will reproduce immediately.
During High Humidity Environments the P3 Filter can become totally obstructed dropping engine to Base Ng of 76% or around 900 rpms.
This can also happen in Icing conditions, Dusty environments and after compressor wash.
This condition is corrected with a new Proper size Environment specific P3 filter fix.
At Zweibrucken Germany, a C-23A Sherpa was taking off when both engines dropped to 900 rpms. There was just enough altitude for the Sherpa to turn back for a short landing.
Subsequent Short Brothers investigation found both engines equipped with 5 micron P3 filters in the FCU, both clogged by fine atmospheric dust.
A fix was the change to a 15 micron P3 filter.
No permanent fix was passed to the FAA as initial certification was done with the 5 micron filter.
Failure to properly replace the P3 filter can and has resulted in both engines dropping to Idle.
Needless to say; This condition will be fatal if both engines experience this problem.
If both engines are shut down and restarted, the engines will appear to run normally, then at the most inconvenient time, the engine will drop again to base Ng around 900 rpms.
Most mechanics have no knowledge that there is a filter in the FCU.
Most Mechanics will write off the condition, when it fails to replicate.
It also must be noted that the fine particulate dust was not visible to the naked eye, upon examination.
It is important to change both P3 filters with new filters and not just one side.
If a Prop is mis-rigged it will reproduce immediately.
If a Prop Governor has internal leaking it will seek and wonder continually.
Prop issues will reproduce immediately.
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Not unique to the PT6, but generic and elementary to any free-turbine engine:
The relationship between prop speed and torque is a simple one. If torque increases (assuming no change in core Ng, ITT etc) then rpm decreases. In other words, the prop governor works by controlling prop blade pitch (and thus load torque). The change in torque is what influences RPM.
The basic relationship is RPM = (horsepower / torque) X a constant
The constant depends on unique factors like the gear ratio, etc. And in a free-turbine turboprop, if the core parameters are steady, horsepower is nearly constant. Then, prop RPM is inversely proportional to torque.
The relationship between prop speed and torque is a simple one. If torque increases (assuming no change in core Ng, ITT etc) then rpm decreases. In other words, the prop governor works by controlling prop blade pitch (and thus load torque). The change in torque is what influences RPM.
The basic relationship is RPM = (horsepower / torque) X a constant
The constant depends on unique factors like the gear ratio, etc. And in a free-turbine turboprop, if the core parameters are steady, horsepower is nearly constant. Then, prop RPM is inversely proportional to torque.
This worries me frankly. Are we really talking about engineers and maintenance not knowing about, not repairing or replacing worn components - which could lead to compromised performance in flight, or worse?
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Problem identified
Hello,
Too many excuses but in my opinion it all came down to improper logging in aircraft logbook. When aircraft was bought, maintenance didn't or wasn't or missed (too many excuses, i lost track) to include past logs to new (our) aircraft log. Bottom line is our team finally got hold of p&w guys and have some specialist come over to inspect the engines. Turned out engine time is way past its limit. As per p&w "it's a miracle that the engine kept running as long as it did, now there's a disaster waiting to happen".
Conclusion, I'm very impressed with the pt6.
I'm very grateful that none of you guys experienced this,having me worried and was able to escalate the issue.
***@uplinker- sadly yes.
Chain of events:
*Aircraft bought,
*Logbook wasn't updated properly(I'm not too sure about this but this is the only reason i can come up with...having the engine go beyond its time limits like that)
*Aircraft ok
*Pilot experienced problem.
*Squawked the problem and logged it.
*Inspected none found.
*Became severe.
*now both engines are acting up
*Head mechanic for the shorts advised a/c be grounded but was overruled.
*Became more severe.
*Pilot denied flying plane.
*Aircraft grounded.
*Inspected properly by p&w
*Shaft and fins has visible wear and tear. Sorry i cant be more specific. they were all in a hurry to resolve this and simply stated that engines needs to be replaced (i was able to talk to some of the mechanics that there were cracks in the shaft and chipped off fins)
Resolution:
Engine for replacement
Well, as annoying as it is, that's that.
Thanks again guys, your replies really helped.
Chris
Too many excuses but in my opinion it all came down to improper logging in aircraft logbook. When aircraft was bought, maintenance didn't or wasn't or missed (too many excuses, i lost track) to include past logs to new (our) aircraft log. Bottom line is our team finally got hold of p&w guys and have some specialist come over to inspect the engines. Turned out engine time is way past its limit. As per p&w "it's a miracle that the engine kept running as long as it did, now there's a disaster waiting to happen".
Conclusion, I'm very impressed with the pt6.
I'm very grateful that none of you guys experienced this,having me worried and was able to escalate the issue.
***@uplinker- sadly yes.
Chain of events:
*Aircraft bought,
*Logbook wasn't updated properly(I'm not too sure about this but this is the only reason i can come up with...having the engine go beyond its time limits like that)
*Aircraft ok
*Pilot experienced problem.
*Squawked the problem and logged it.
*Inspected none found.
*Became severe.
*now both engines are acting up
*Head mechanic for the shorts advised a/c be grounded but was overruled.
*Became more severe.
*Pilot denied flying plane.
*Aircraft grounded.
*Inspected properly by p&w
*Shaft and fins has visible wear and tear. Sorry i cant be more specific. they were all in a hurry to resolve this and simply stated that engines needs to be replaced (i was able to talk to some of the mechanics that there were cracks in the shaft and chipped off fins)
Resolution:
Engine for replacement
Well, as annoying as it is, that's that.
Thanks again guys, your replies really helped.
Chris
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By the way.
Sorry it took me a while, to get back to this. I stopped flying the shorts last november-ish 2014, and ferried the plane around january. Then a new pic desperate for flight time was found so aircraft wasnt grounded intil march 2015. I had training for another aircraft(take note that maintenance program for this a/c is alright) and got a bit busy.
In a sense, I'm glad that what happeded, did happen. It's some kind of a blessing since i got upgraded to a better equipment =) wrong attitude i know hehe.
Anyway, safe flight guys.
Chris
In a sense, I'm glad that what happeded, did happen. It's some kind of a blessing since i got upgraded to a better equipment =) wrong attitude i know hehe.
Anyway, safe flight guys.
Chris
Last edited by chrismike294; 21st Sep 2015 at 01:41. Reason: Fixed dates
Glad that it got resolved, and by P&W too.
I flew the shed myself (360); A great aircraft, although it looked a little unconventional !
I flew the shed myself (360); A great aircraft, although it looked a little unconventional !
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Nope not resolved yet.... but the guys just finished doing a hot inspection and ended up changing the power turbines. But they don't recon that that's what's causing the problem.....the problem was....wait for it, series of compressor stalls. The compressors blades are out of wack. They'd be trying to blend the blades and see if it'll do the trick for the time being since the engine needs to be overhauled anyway. But for a temporary workaround it may be enough. Really, to just be able to sell the aircraft in flying condition =)
