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#3 engine slow start help?


rysponycar
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We have some #3 engines on different aircrafts that start slow. At a 83F temp, the GTC will start the #3 and come on speed (72%RPM) in 65 seconds. At 102F it will start and come on speed in 76 seconds. The engines are pulling 99% max power efficiency and have known new starters and control valves. The GTC's are putting out from 36 to 39PSI. The blade angles are all set to the low side and are all having 800TIT starts. The problem has been pointing towards the heat here in Arizona and a 2700 ft elevation.

Does anyone have an idea how to get the starts down below 70 seconds?

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Hello! Do you have the ATM "on". and when you say: #3 eng!! you mean to say the first engine to be started!!. If you start #2 first, you'd get the same problem.....would you!! So I think we pin point the problem to GTC efficiency... with high outside air temp and high altitude level. !!!! Do you exceed the Starter limitations!!.............when it's hot, even the aircraft takes longer to lift! Maybe it's the name of the game. What do you think guys!!..........................John Boy

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Yes, #3 engine is the first one started. The ATM is NOT on. The GTC is pressurizing the manifold to about 36-39PSI. I know.... If I had an APU, we wouldnt have this problem. In this heat, thats all the GTC will put out and thats the same on our other planes. I agree, the hot air and elevation is the name of the game... Its just too bad the T.O's dont says that. Dont know how to fix it?

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Forgive me if I'm wrong, but isn't the engine allowed to start slow under desert operations and high outside air temp? I thought 95 degrees was the number, but I can't remember for the life of me. The FI states that if manifold pressure drops below 20psi during start, the fault is in the GTC. The next steps are to ops check the horsecollar valve, inspect the 5th and 10th bleed valves at 3 and 9 o'clock for proper operation, borescope the turbine, then adjust prop blade angles. We all know the FI's ability to solve a problem can be spotty at times, but it's a place to start anyway.

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Doesn't sound too bad for 'hot 'n high' conditions. At 36 to 39 psi

the GTC sounds really great - that's APU pressure!!

Are your engine bleed air valves the "ON-OFF" or "OFF-ON-OVERRIDE" type. If

the latter, it may be modulating a lower pressure than fully open.

Also starter control valves like to mess around and not open fully, or modulate

at lower pressure

Try pulling the throttle back 1/2 a knob from ground idle and hit air start to change

the blade angle before starting (reduces the resistance a little more)

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Watch your bleed air pressure when the start valve opens. Note how low it goes and then the check the pressure between 10-16%...

Our books put the pressure 10-16% no less than 22 psi.

Your pressure should drop off quite a lot (20 maybe) then recover to the 32psi, 22 minimum.

Your start control valve regulates the air pressure to the starter so if it (they) are regulating low then the starter will have insufficient air and slower start times yet you will see "good" air pressure.......

Also the GTC load control may be getting a "too hot" signal from the Pneumatic thermostat (THERE ARE TWO) you want to check the one for the load control RPM above 95%.

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It a thought. Why not trying to start the engine with the fuel enrichment selected on, this will cause the engine to spool up quicker and you will be able to go by the starter start time.

My reason for this is the TD system will cut back fuel because of the high temps so selecting fuel enrichment on will give that extra fuel needed to start.

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Doesn't sound too bad for 'hot 'n high' conditions. At 36 to 39 psi

the GTC sounds really great - that's APU pressure!!

Are your engine bleed air valves the "ON-OFF" or "OFF-ON-OVERRIDE" type. If

the latter, it may be modulating a lower pressure than fully open.

Also starter control valves like to mess around and not open fully, or modulate

at lower pressure

Try pulling the throttle back 1/2 a knob from ground idle and hit air start to change

the blade angle before starting (reduces the resistance a little more)

The "OFF-ON-OVERRIDE" type valves (3213722-5-1 just to be sure) from my experiences are calibrated to regulate to 49.9 to 50.2 psig, well within the flight limitations of 48-52psig, and well above the output pressure the GTC can put out. either eay, this valve should be under a "Full-Open" Condition below 48psig. Now, if the main actuating diaphragm has even a slight tear, this valve will never fully open under any condition.

I still would like to know what the manifold pressure is DURING engine start...

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As soon as we get the chance to run it again, I will definately check the manifold pressure. This time start each engine individually off the GTC and document the times as well.

Also, the aircraft is a modified "E" model. So we have -15 motors and dont have the horsecollar regulating valves. So they are just open/close valves.

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Are you in Albuquerque by any chance?

If you are then you can go by the extended start limits for High Pressure Altitude and sometimes throw in High Temp (40c) as well.

What kind of "on speed" time do you get starting #2 first?

Usually we would find that the load control valve on the goat would be the culprit if it would go beyond the extended start limits.

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1.check gtc bleed drop time.if it less the 8.5 sec from 30 to 15 psi.theres prob of leakage in ducts.if its ok..no leak.

2. i suppose u had checked the serviceability of air bleed valve and starter control valve.

3. TIT is ok .so i think no need of checking T.D amplifier

4.do CIP blowing and 14th stage air filter cleaning.

hope this would help

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We had this problem over in Kaf in the middle of summer with the E model with a gtc. The big problem is the alt is high and high out side air temp, the gtc doesn't put out the same performance as it does in cooler temp and lower alt. so their isn't much you can do for this unless you use the fuel enrichment system to have a shorter spool up time.

Darrell

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We had this problem over in Kaf in the middle of summer with the E model with a gtc. The big problem is the alt is high and high out side air temp, the gtc doesn't put out the same performance as it does in cooler temp and lower alt. so their isn't much you can do for this unless you use the fuel enrichment system to have a shorter spool up time.

Darrell

I think this is a horrible idea. Fuel enrichment shortens the turbine life, and should only be used under extreme cold conditions where the engine will not spin up at all. I think the flight crews might use it for taxi starts, but I'm not 100% on that. I remember someone talking about having the system removed altogether because you don't really need it. If you are at high altitude or high outside air temperature, you are allowed to exceed the starter duty cycle. Never use enrichment!

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As soon as we get the chance to run it again, I will definately check the manifold pressure. This time start each engine individually off the GTC and document the times as well.

Also, the aircraft is a modified "E" model. So we have -15 motors and dont have the horsecollar regulating valves. So they are just open/close valves.

Been watching this thread with some interest, it seems the problem IS the GTC. The

load control thermostat should be set to 649 -663°C, and acceleration -stat 677 -688°C,

iaw 2G-GTC85-41.

That being so, new thermostats are factory set to about 590°C ..... well below the

limits. Did any of the problem aircraft recently go through ISO, or have any GTC

maintenance requiring a thermostat change? The answer may lie there

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Started all four engines at 102F individually off the GTC. See attachment for #'s. All the manifold drops were good (drop to 25 then sustained at 31), the bleed down was 13 seconds with a 37PSI GTC. Surprising enough, the other 3 engines all started much much faster. Looked at the start ducting on #3 and no leaks or blow outs. The starter control valve is brand new. The starter looks a little old as its a Bendix self lubricated QD. Thinking about swapping it with a Parker Hannifin.

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Started all four engines at 102F individually off the GTC. See attachment for #'s. All the manifold drops were good (drop to 25 then sustained at 31), the bleed down was 13 seconds with a 37PSI GTC. Surprising enough, the other 3 engines all started much much faster. Looked at the start ducting on #3 and no leaks or blow outs. The starter control valve is brand new. The starter looks a little old as its a Bendix self lubricated QD. Thinking about swapping it with a Parker Hannifin.

on-speed times seem a little long, especiallY #1. #3 peak TIT 780° ...... could increase

NULL orifice 2 or 3 divisions - more fuel will cut the time. I started an engine several times

at 108°F OAT today. On-speed was consistently 48 secs.

On my previous post, I stand corrected - nothing wrong with GTC or thermostats

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Agree that an increase in TIT to 800-810 (5 [email protected] 4C each) will decrease your time to start. (780 seems quite cool for the conditions)

This will increase the energy available to drive the prop and engine.

The starter only has so much power to drive the prop and engine.

60% starter limit.

After that only the turbine can do the work to get the engine on speed, (“on speed†time limit of 60/70 sec)

The Null adjustment will provide increase energy to both phases of start (starter engaged and disengaged)

If you look at your starter release times it takes much longer to reach 60% RPM and then double the time to get on speed. The turbine is also suspect if burned it will not produce the required energy to complete the start within the time limit.

Do an efficiency run and see if you engine performance is low.

Also, check if you have (one or two) bleed valves stuck closed or not fully open...more work than the starter is capable of doing (within the time constraint)

108F crap thats hot!!!!

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