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#3 engine slow start help?


rysponycar
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#3s get started first way too many times. The book suggest alternating engines. I had the same issues in Bogota at 8000' and in Iraq with 100+ oat. In Bogota we alternated starts depending on odd and even days. In Iraq they started #4 or #2 first then just said the hell with it.

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128F thats just TOO HOT!!! You can keep ALL that....

We would also rotate the start from 3 to 4 to 2 to 1 to limit the exposure to the slower start times and higher temps (if and when it was an issue)

Thats kinda why I mentioned the turbine... If it has been burned then its ability to produce power will be lowered and thus increase start times..

Dont think that is the problem though... I think when the Null is adjusted the start times will come down.

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NATOPS1 you wrote: I think when the Null is adjusted the start times will come down.............do you mean to say that #3 could have a lean FCU?.....................ouff!!!.it's been a long time now!!........It's a good thread!!.........John Boy

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Another rare but "it happens" occurance can be the check valve on the upper14th stage. In 30 years I have noted a couple of occasions where the check valve leaked, allowing bleed manifold air intended for the starter, to bypass into the diffusser.

The check valve is rarely inspected because it is such a bastard to get to (especially on the -9 QEC), and few people really look at its condition during QEC removal/repair/overhaul. I have seen a couple where the problem was wear of the check valve results in an "egg" shape and the valve will not properly seal. It doesn't matter if you have a GTC putting out 50 PSI if the check valve is bypassing air intended for the starter into the diffuser, you will get slow starts. This problem can persist even with other engines on speed.

fjw

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So, based on all the "hot" active guys, I can arrange all the possibilities with a miner suggestion from my side.

1- The engines are pulling 99% max power efficiencygood compressor +good turbine + all acceleration valves seemed to be in closed position+ fuel nozzle performance at high power setting good, fuel nozzle performance at low fuel pressure ??? Unknown.

2- The GTC is putting out from 36 to 39PSI. good output, good GTC bleed control (confirmed by eng.#1 on speed by 58sec.)

3- Pressure drop at 10-16%RPM = 25psi then buildup to 31psi. Fair start control valve.(maybe swapped with #1 just to confirm)

4- New starter ?? May be slipping, swap with #1 to confirm.

5- The blade angles are all set to the low side. Just, a recheck for not holding a position.

6- Start TIT 780.Can be increased 30⁰ more (will improve operation).

7- The bleed down was 13 seconds. ??? Was the timing with all bleed valves in OPEN position? If yes, what about checking drop time with only one valve in open at a time and evaluate all the 4 engine nacelle ducting for air leak, this type of check will confirm that compressor check valve, anti icing valve, and ducting are air tight.

8- Sticky Acceleration valves (not fully opened) or SSV malfunction can affect RPM speeding up.

Hope the above will help.

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The plane has been flying non-stop so I havent had a chance to mess with it. The aircrew has been starting #4 first until we get a fix on her. My plan is to deffinately bump the fuel up and get the start temps on the high side and then go from there. Will post the result when I get it. Thanks to all for the help

EC Jammers!!

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  • 2 weeks later...

My aircraft bleed air system manifold pressure gage, reads below 70 psig while all engines are running all engine bleed air regulator & shut off valves replaced by new ones , all pneumatic systems manifold and connections are checked ,both air conditioning checked for air leak, can any one help me about this malfunction

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Do you have regulating bleed air valves or OPEN closed valves?

What is the bleed air check time?

Maybe as simple as a bad bleed air pressure gauge...

bleed air leak check time is within the limits reads 10 seconds

bleed air manifold gage replaced by new one

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SZYOUD, your question is not in reference to the original post, correct? We are discussing a different aircraft now? This 70 PSI is with no bleed air load?

If we are on a different aircraft and problem, this should probably been less confusing if it were a different thread.

Assuming all answers above are a "yes" and that you have an aircraft that shows only 70 PSI on the manifold pressure gauge with all four engines running and the bleed air regulator valves in "override," then I wonder if your airfield is a very high altitude one. Are you in Caracus?

If you are not at 13k feet airfield elevation, then you do seem to have a problem.

Inside your horsecollars, you should have a bleed air duct that has a tap-off where you can hook up a good direct pressure gauge. I'd suggest that you put a gauge on one of those ducts and see what the pressure is from the other three engines (one at a time). IF you still get only 70 PSI (since you claim that your bleed air manifold bleed-down time is 10 seconds AND you do not have a newer model Herc that requires more time than that) then you have four bad compressors. (You can also hook a hose up to the pressure test fittings on your compressor diffusers to see what your compressors are actually putting out.)

Seeing that four bad compressors is a bit of a stretch, I'd be looking under the flight deck and behind the Nav's station for a broken bleed air line that goes to your manifold pressure gauge. That very small line - if broken or cracked or if you have a missing cap on a "T" fitting somewhere - will not cause a bleed down check to be bad, but will cause your manifold pressure to read low; that is what I'd hope to find.

I hope this helps. Let us know what you find, please.

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SZYOUD, your question is not in reference to the original post, correct? We are discussing a different aircraft now? This 70 PSI is with no bleed air load?

If we are on a different aircraft and problem, this should probably been less confusing if it were a different thread.

Assuming all answers above are a "yes" and that you have an aircraft that shows only 70 PSI on the manifold pressure gauge with all four engines running and the bleed air regulator valves in "override," then I wonder if your airfield is a very high altitude one. Are you in Caracus?

If you are not at 13k feet airfield elevation, then you do seem to have a problem.

Inside your horsecollars, you should have a bleed air duct that has a tap-off where you can hook up a good direct pressure gauge. I'd suggest that you put a gauge on one of those ducts and see what the pressure is from the other three engines (one at a time). IF you still get only 70 PSI (since you claim that your bleed air manifold bleed-down time is 10 seconds AND you do not have a newer model Herc that requires more time than that) then you have four bad compressors. (You can also hook a hose up to the pressure test fittings on your compressor diffusers to see what your compressors are actually putting out.)

Seeing that four bad compressors is a bit of a stretch, I'd be looking under the flight deck and behind the Nav's station for a broken bleed air line that goes to your manifold pressure gauge. That very small line - if broken or cracked or if you have a missing cap on a "T" fitting somewhere - will not cause a bleed down check to be bad, but will cause your manifold pressure to read low; that is what I'd hope to find.

I hope this helps. Let us know what you find, please.

thank you my friend for your effort and help

With load read 64PSI one of both air-conditioning operated

My friend my country is Jordan

Direct pressure gauge connected to bleed air manifold aircraft pressure of bleed air still the same

we hook a hose up to the pressure test fittings on compressor diffusers the pressure still reads 70 psi

Flight deck and behind the Nav's station for a broken bleed air line also checked for bleed air leak and broken line nothing found

thank you

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thank you my friend for your effort and help

With load read 64PSI one of both air-conditioning operated

My friend my country is Jordan

Direct pressure gauge connected to bleed air manifold aircraft pressure of bleed air still the same

we hook a hose up to the pressure test fittings on compressor diffusers the pressure still reads 70 psi

Flight deck and behind the Nav's station for a broken bleed air line also checked for bleed air leak and broken line nothing found

thank you

Two things:-

#1: Casey or other moderator, can you split this thread so the origional is separate from

this new thread

#2: Jordan is a relatively high country (I'm assuming Amman) so 70psi at normal ground

idle would be acceptable, especially with summer heat. You need to do a compressor

performance check at 900°C to verify the actual compressor condition.

70psi is not a problem as long as the difference between engines/bleed shut off valves is

not more than 3psi between highest and lowest

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Two things:-

#1: Casey or other moderator, can you split this thread so the origional is separate from

this new thread

#2: Jordan is a relatively high country (I'm assuming Amman) so 70psi at normal ground

idle would be acceptable, especially with summer heat. You need to do a compressor

performance check at 900°C to verify the actual compressor condition.

70psi is not a problem as long as the difference between engines/bleed shut off valves is

not more than 3psi between highest and lowest

Yes my frined I agree with you, but my pilots not acceptable because when you operate one of the air conditioning systems with override position of bleed air regulator & shut off valve the bleed air pressure drops to 63 PSI

Thank you

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  • 2 weeks later...

i know we've had issuies with GTC's throughout my 11 years as an engine mechanic but there are a few things that may help that you can adjust on the gtc to help aid in bleed pressure to the manifold. 1st is the acceleration control valve psi. i can't remember the limit off the top of my head but that is within the 49jg in USAF tech data. after making sure that is right next step is to verify fuel cracking pressure. after all that is said and done there is the load control regulator check that with bleed air on the manifold you can adjust what rate of flow the load control puts out. these are all checks that are to be done with the test set installed. i have bypassed this with a pressure gauge and hoses and fittings and doing each check one at a time. since then we have had no issues with flame-outs nor output pressure. with a properly adjusted gtc i can run both a/c packs, atm, and kick on wing/emmp anti-ice without the gtc dieing. i can also start an engine at 95f at sea level off the gtc with atm running and the atm stays online.

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The plane has been flying non-stop so I havent had a chance to mess with it. The aircrew has been starting #4 first until we get a fix on her. My plan is to deffinately bump the fuel up and get the start temps on the high side and then go from there. Will post the result when I get it. Thanks to all for the help

EC Jammers!!

who is this? This is Ray.

we're having the same problem here in kuwait. looked at everything that been mentioned so far and we're still getting slow starts. the last 2 things im going to look at doing are R2 starter and adjust the null orifice. have you guys done either of these yet?

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