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saikojer

No 4 eng RPM overspeed  with TORQUE, TIT and FUEL FLOW, LOW at crossover with RPM overshoot to 104%.

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saikojer

Hye there, we are in progress to settle down on the defect "No 4 eng RPM overspeed 105%-106% and maintain in normal and mech gov"

- During EGR found No.4 TORQUE, TIT and FUEL FLOW, LOW at crossover with RPM overshoot to 104%.

INDICATION AT CROSSOVER.

Torque : 1400lbs 
TIT: 678℃ 
Fuel Flow : 990

RECTIFICATION BEING TAKEN :

-RPM adjustment.
-Blade angle adjustment.
-Null orifice + wormshaft adjustment
-ectm
-valve housing replaced.
-syncrophaser
- Coordinator resistance cx
- tachogene resistance cx
- Dome Assembly-SATIS.

Still persist after a week : 
-Propeller and Valve Housing replaced.
- SATIS.

Still persist on next day :.

No.4 engine RPM overshoot to 103.3% RPM on power advance with pitch lock symptomps.
+ RPM fuel governed out of limit.

- pitch lock regulator - still persist.
- FCU replace - SATIS.


New snag after a week :

No 4 engine nil low pitch stop.

- Rigging blade angle and low pitch stop adjustment.
-Valve housing adjustment.
- Replace dome assy.
- Replaced low pitch stop packing.
*Still Persist.

No 4 eng RPM overspeed  with TORQUE, TIT and FUEL FLOW, LOW at crossover with RPM overshoot to 104%.

- Replaced Back previous dome assy + low pitch stop packing.

* SATIS but torque anticipation very slow during advance throttle.

*Throttle already at FLIGHT IDLE, TQ remain : 1.40 lbs.
-After about 10 sec TQ increase to 3.4lbs.

*Advance throttle, RPM+FUEL FLOW + TIT increase with low TQ until RPM overshoot until 104.4%.
- Retard throttle, RPM drop and TQ can SLOWLY can achieved 7.5lbs.

-Replaced Coordinator.
* Still persist.

- Replace another Valve Housing.
*Still persist.

 

Anyone got idea on this synthom ?

TQ low at Crossover..png

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pjvr99

Need to run your sync box, but can almost guarentee fault is on #1 or #2 valve housing

 

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FredG

Saikojer, did you replace the the pump housing?  How long does it take to go from REV to feather using the aux pump?  Wondering if you're pump housing is bypassing pressure between the two sumps (pressurized and atmospheric).  This might keep you from changing (increasing) blade angles.

 

 

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NATOPS1

" *Throttle already at FLIGHT IDLE, TQ remain : 1.40 lbs. -After about 10 sec TQ increase to 3.4lbs."

 

It sounds like you are not producing pressure. Agree with Fred change the pump housing. If the blade angle does not change  due to low pump pressure your prop will overspeed every single time.

(If you have removed your syncrophaser from the rack and have the same indications in Mech)

 

Question is it a normal practice to run two engines to high power with the others shutdown?

Can you tell me what is the normal engine oil pressure is for your aircraft?

 

 

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pjvr99

My bad, just saw prop changed and assumed the pump housing was changed too. it does look like a bad pump housing. Run it again,

but this time have your right seater hold the condition in air start. the extra pressure from the aux feather pump should make it

better .....

 

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saikojer

Pjvr99 : What's that sync box?

FredG : Previously we also suspect the pump housing was the culprit due to unable regulate and give correct pressure to change prop blade angle according to the throttle position. After done with propeller replacement with the new Valve Housing (TSO : 0  Hrs) we still faced with the same problem.ONE more thing is, the blade angle still will change according to throttle position, but the time taken for blade angle changing was TOO SLOW and since the TQ was TOO LOW while the ENGINE drive the propeller on HIGH SPEED that's why we suspect the cause of RPM overshoot due to Engine speed was not COUNTERED by the correct TORQUE which produced by the propeller.

NATOPS1 : Not a normal practice to run 2 engine, but it was just to verify on the problem, after done with a rectification, and my concern was it must be symmetrical engine to make a comparison and to avoid from aircraft swing.

While the NORMAL engine OIL pressure : according to our limitation 50 - 60 psi. Indicate around 55 psi normally.

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pjvr99

Syncrophaser test box. You changed a dome on its own .... dome is matched to the hub and blade assembly - not a good thing to do. still sound like an internal leak somewhere. When you changed the prop did you change the pitch lock regulator and the prop barrel nut?

 

 

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Lkuest

With high sustained RPM above flight idle, the cause is almost always with the propeller. The prop acts as an air brake to slow the engine down. In this case, the propeller is not slowing the engine down as much as needed. As the RPM increases roughly 5% above 100%, the fuel control realizes that the propeller is malfunctioning, then kicks in to cut fuel until the engine no longer accelerates higher. This is why you have high RPM with low torque and TIT. It all fits with a propeller failure, whether it is rigging, synchrophaser, valvehousing, pumphousing, or internal leakage.

I have read some very good responses here, and I would recommend you heed all of them. You cannot replace just the dome by itself. Not only will your feather blade angle not be 100% calibrated, but your incorrect gear backlash may cause irreparable damage to the propeller blade gearing, and I wouldn't want to see that fail in-flight.

I do recommend physically removing the synchrophaser prior to the run as NATOPS has suggested. This is because the synchrophaser is sending out two signals to the Speed Bias servo motor, a control input, and a reference signal. Selecting Mechanical governing only disconnects the reference, so if there is a significant malfunction with the Synchrophaser, it could change RPM, even in mechanical.

Slow throttle anticipation and low pitch stop not retracting are both consistent with inadequate hydraulic system pressure, either caused by bad pumps or damaged/missing seals.

I would like to note that a significant cause of maintenance issues is other maintenance. You have listed many things that you have done. It is somewhat likely that someone forgot/damaged a seal on buildup. If you kept the same pump housing through all of this, you may have damaged the small seals while pressing the pump housing onto the new prop rotating assembly. The same guy that built up the original propeller may have made the same mistakes with the new one. There's just so much that could've gone wrong with the maintenance that could easily explain the issues you are still having. My recommendation would be to install a propeller that you know works on #4 position, and work from there. There is just no way an engine can cause high RPM with low TIT, unless the rigging is very faulty.

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FredG

 

On November 29, 2015 at 4:09:40 PM, saikojer said:

INDICATION AT CROSSOVER.

Torque : 1400lbs 
TIT: 678℃ 
Fuel Flow : 990

No.4 engine RPM overshoot to 103.3% RPM on power advance with pitch lock symptomps.
+ RPM fuel governed out of limit.

- pitch lock regulator - still persist.


New snag after a week :

No 4 engine nil low pitch stop.

No 4 eng RPM overspeed with TORQUE, TIT and FUEL FLOW, LOW at crossover with RPM overshoot to 104%.

* SATIS but torque anticipation very slow during advance throttle.

*Throttle already at FLIGHT IDLE, TQ remain : 1.40 lbs.
-After about 10 sec TQ increase to 3.4lbs.

*Advance throttle, RPM+FUEL FLOW + TIT increase with low TQ until RPM overshoot until 104.4%.
- Retard throttle, RPM drop and TQ can SLOWLY can achieved 7.5lbs.

 

Saikojer,

It sounds like the fuel scheduling is good.  The RPM increases all the way up to 104.4% because of a lower blade angle. Then, eventually the torque increases to NORMAL (matches symmetrical engine).

  • Does the RPM decrease (matching symmetrical engine) as the torque increases? 

Your low pitch stop problem:

You may not have a low pitch stop problem.  Push the throttle to crossover and give the propeller angle more time to increase past 25 degrees (match torque with the symmetrical engine) before retarding the throttle back toward FI.  The blades may need more time to increase the pitch.   

  • What is the torque at crossover?  You mention above that it's 1,400 in lbs but, doesn't it eventually increase?

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NATOPS1

The only component I can fathom other than the pump housing is the pitchlock regulator itself. The pitchlock regulator could be restricting the prop fluid (which is what it is designed to do in an overspeed) the propeller does not come with a regulator so it would have been reused for each maintenance action you have done to date.

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tusker

Seems like something is wrong with this topic and everybody gave up!!!................It didn't make sense anyway!!............let us be serious!

 

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Parker

someone mentioned why you had to run 2 engines .... you have to run symmetrical engines at power or you'll slide the nose (sideways)

oh I no it's not but - high rpm, low TIT, low Torque, fuel whatever ...did it decouple?

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tusker

Allo!!........looking at the top picture of the engines indications,...............looks like a flight sim picture to me..........!!!!!!!!!

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