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edwardlcy

#4 engine cannot achieve 95% takeoff power - low fuel flow high TIT

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hi guys, am in a bind here with this new engine that i just put up. so 95% power is around 17k inch lbs torque, i only got around 16.2k lbs in td auto and td null with bleeds on, bleeds off around 17.2k.

During advanced throttle it was observed that TIT max at 1083 with fuel flow about 200 lbs less than other engines.. in some runs it was also observed that in td null the torque can be 2-300 inch lbs worse off compared to td in auto. also during crossover, there is no crossover cut at all in auto and null although TIT stayed around 830+, below the limit of 840C. with other engines, there is slight increase in FF when td put from auto to null and slight decrease in FF when td put from null to auto, with this engine however there is absolutely no changes in FF when td select null from auto or from auto select to null.

There is also a symptom where my technicians reported that the prop becomes harder to turn than usual with the prop turning tool after installing this new engine, requires the strength of at least one and a half man.

Troubleshooting done so far:

checked valve housing satisfactory

checked all bleed air ports satisfactory

replaced td valve

replaced and calibrate td amp

replaced fuel pump

replaced FCU

replaced torque indicator

replaced torque pickup

i suspect RGB gearbox prop brake partially engaged.. any other ideas?

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Make sure your Tq indicator reads full scale -4000 and +25850 then read and adjust.

Check and use the "True" Cal number out of the engine logbook to be more accurate.

Check your air pressure out of your bleed air regulator valve.

The change from bleed ON to Bleed OFF is pretty linear at 700 inch lbs. If you are seeing 1000+ then the On position is letting too much air out.

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rigging, blade angle cx satisfactory; tq indicator not the problem since swapped indicator with #3 engine but snag still persist.

sorry im a noob but how do i check the air px out of my BARV?

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edwardlcy,

Is it possible that the engine anti-icing is stuck on (bad inlet anti-icing relay). If you had constant anti-icing on this engine it would show up as low power even with the bleed air regulator valve closed.

Ron

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If your not hitting take-off in null, Changes fuel control unit again............

I just found who to give the "Worst Advice" award. I would recommend if you are going to provide tech support, you should make sure you read the problem first. The limit for the fuel control is 70 degrees lean, or 70 degrees cooler in null than in Auto. What's the unit of measure? TIT. Temperature is not the problem as he is hitting 1083 easily, therefore, fuel is not the problem. Changing the fuel control would be a waste of time. Efficiency is a comparison of TIT vs. Torque only. Checking static blade angles is a good idea, but only if you are checking the accuracy of the Torque Cal. When you check efficiency, the flyweights control blade angle. If you are at 100% RPM at power, the prop cannot cause efficiency problems.

If your TIT is high and your Torque and Fuel Flow is low think Air Leak or indication. Anti-ice is a good idea, measuring torque calibration also a great idea (Calibrate in LSGI, not HSGI!!), but think anything that runs off of air. Especially on a low power new engine, I would highly suspect an air leak. Air equals power, but it also equals cooling. Air loss makes your TIT higher than your fuel flow allows it to be (isn't that really what you're seeing?).

Don't think prop brake. Your starter releases it as soon as you rotate. If it was engaged, you should see a slow start. When the starter is not engaged, oil pressure hydraulically disengages it anywhere north of 28% or so RPM. If it were to somehow stay engaged, you would have brass particles all over your gearbox mag plug sump areas and External Scavenge Oil Filter. Think about what would happen if you decided to drive your car with one foot on the brake the whole time. You'd run out of brakes very quickly due to overheating and material loss.

Let's go over the small list of things that could cause a low power:

Indication (RPM, TIT, Torque, wiring, T-couple harnesses/T-block/Y-lead)

Accurate RPM too high (Indicator also low, showing 100% when really 102%)

Torque Cal (must move throttle to lowest torque setting before calibrating. Incorrect calibration will indicate lower max torque)

Outside Air Temperature or Pressure inaccurate

Air Leak (from any part that uses engine air)

Torque not measured at max TIT/Torque (or 1050, whatever your formula requires)

On a side note, it is normal for new engines to lose more torque during air conditioning operation than the other motors on aircraft that do not have bleed air regulator valves. If your aircraft does, maybe the bleed air regulator valves are out of calibration. In my world, efficiency is checked with Bleeds Closed, Hydro and Generator off. We can check it the same way the aircrew do, but only to troubleshoot a low power caused by anything outside of the engine itself.

Also, if crossover temperature is within limits, I don't care about the bump. There is no tech data that tells you to look for that bump, only a temperature range it must be in at 65 degrees TLA. Crossover is only for throttle alignment. If you already have throttle alignment, why would you expect the engine to correct even more for throttle alignment? A more accurate check of TD system function is a TD system ops check.

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Going from auto to null T.D. out of the picture, no over temp protection. And going from Auto to Null the fuel control is the Boss by the throttles. (Auto to Null will not " lean" the engine.) T.D. protect you from over temp, with F/F. All said, if you can not hit Take-off power in null change fuel control. P.S i learn over the years hard to "troubleshoot" from behind a desk. ( Sounds like you master-it).

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I like the idea of a scoop valve problem. I had one some time ago that would open as the CDP passed 105psi. The odd fuel

flow also supports a loss of air theory

Another possibility is one that has come up more often recently, where the TD valve is stuck in "TAKE" condition -

yellow-box checks good, but has a hard time making take-off power/TIT.

Cross-over 'cutback' is something that has been taken out of context. Basically, if the FCU is slightly rich at this part of the

schedule, fuel and TIT will be trimmed back when the system goes from normal-limiting to normal controlling. Bare in mind

normal limiting is the same as null, except you have overtemp protection. For the same price a lean FCU can have a fuel/TIT

spike as you go from limiting to controlling. Bottom line: only requirement at crossover is TIT must stabilize between 800°C

and 840°C.

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1. You did recal the Tq gage after swapping yes? Get the true cal number just to be more accurate.

2. Engine performance is checked with the bleed air OFF. If you are getting 17.2 and the 95% calculated Tq is 17, your engine is just above 95%.

3. To check the bleed air out of the regulator start all the engines, turn on the cargo compartment AC unit and read the pressure of each engine one at a time. If your low torque engine is putting out higher pressure it will produce lower torque anytime the bleed air valve is open.

The torque increase from a bleed ON to bleed OFF is 700 inLbs. If as stated your tq increase is 1200 InLbs then your regulator is open too much.

"in some runs it was also observed that in td null the torque can be 2-300 inch lbs worse off compared to td in auto."

Did the TIT remain the same?

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guys, thank you all for your advice and replies...appreciate it.. this problem has been solved by replacing the engine+QEC with a new one, no idea what's the actual cause, didnt have the time to troubleshoot further..

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guys, thank you all for your advice and replies...appreciate it.. this problem has been solved by replacing the engine+QEC with a new one, no idea what's the actual cause, didnt have the time to troubleshoot further..

Too bad in a sense!!....We will never know the answer for this snag!!........................Tusker

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