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!!