Fcu

[herky400M]

Hy, C-130 world, I had a discussion with my colleagues about adjusting the CIT ballows of the FCU (fuel control unit), you have to measure something at the back end, but what exacly. it is very unclear.

I know that if the Elmendorf aircrafts fly towards Pope, they have to adjust these bellows. to adjust their start temperatures.

We experience the same problems if we fly from Brussels to Kabul .(high alt and cold)

the start temps are very low but not cold starts, by the way what is the defenition of a cold start.... less than 720°C TIT, any technical doc to refer to? :eek:

thx in advance, de Belgian guy

[Dan Wilson]

The only thing CIT (compressor inlet temperature) does is adjust basic fuel flow according to temperature deviation from standard day with your current temperature via an alcohol filled temp probe.

The bellows is for CIP (Compressor inlet pressure) not CIT, and it all it does is to vary the basic fuel flow according to current atmospheric pressure v standard day.

There is no attempt at a comparison (or ratio) of intake vs exhaust values, like in a Jet that uses, and is adjusted to, EPR (exhaust pressure ratio, a comparison of pressure from the intake vs exhaust).

Now in extreme atmospheric changes, like Belgium to Kabul, you may have to adjust the Null orifice or the start potentiometer on the TD valve, but I don't know of any adjustment on the fuel control that can be easily done on the road without a buttload of test gear.

A cold start I don't really remember off the top of my head but I want to say less than 790 but it may be as low as 720, will have to get one of the other guys to chime in on that one.

Dan

[Steve1300]

We experience a shift in start temps also when moving around the country. If we move from a low altitude high temperature location to a high altitude low temperature location, we have a shift of start temps. Sometimes, it becomes a problem, so we make adjustments for it.

According to our friends at Rolls Royce (Allison), we adjust the TD amp potentiometer only to limit the start temps, not to "control" them. We control start temperatures with the "null orifice" adjustment on the TD valve:

Quote: After changing an engine or replacing a temperature datum valve, or if a previous

start exceeded 830°C (Refer to 72-0, Table IV), adjust the datum valve to give a maximum starting temperature of between 750 and 820°C.

Allison and Lockheed has stated in other locations that start temps below 750 can be acceptable as long as the start was smooth and within time limits.

When the start temperature has shifted and you find that a null orifice adjustment does not fix the problem, then Allison gives us a possible fix at the fuel control bellows.

Quote: B. Adjustment of Inlet Temperature Compensating Bellows

(1) Adjust retaining adjustment nut at compensating unit housing clockwise facing

rear of engine to decrease start temperature.

(2) One flat of the adjustment nut is equal to approximately 25 degrees TIT.

CAUTION: DO NOT ADJUST MORE THAN TWO FLATS. THIS ADJUSTMENT

SHOULD BE MADE ONLY AFTER ALL OTHER POSSIBLE CAUSES

HAVE BEEN THOROUGHLY INVESTIGATED. GET ENGINE HISTORICAL

RECORDS TO REFLECT NUMBER OF FLATS ADJUSTED

MAXIMUM POWER RUN REQUIRED AFTER ADJUSTMENT.

[pjvr99]

We experience a shift in start temps also when moving around the country. If we move from a low altitude high temperature location to a high altitude low temperature location, we have a shift of start temps. Sometimes, it becomes a problem, so we make adjustments for it.

According to our friends at Rolls Royce (Allison), we adjust the TD amp potentiometer only to limit the start temps, not to "control" them. We control start temperatures with the "null orifice" adjustment on the TD valve:

Quote: After changing an engine or replacing a temperature datum valve, or if a previous

start exceeded 830°C (Refer to 72-0, Table IV), adjust the datum valve to give a maximum starting temperature of between 750 and 820°C.

Allison and Lockheed has stated in other locations that start temps below 750 can be acceptable as long as the start was smooth and within time limits.

When the start temperature has shifted and you find that a null orifice adjustment does not fix the problem, then Allison gives us a possible fix at the fuel control bellows.

Quote: B. Adjustment of Inlet Temperature Compensating Bellows

(1) Adjust retaining adjustment nut at compensating unit housing clockwise facing

rear of engine to decrease start temperature.

(2) One flat of the adjustment nut is equal to approximately 25 degrees TIT.

CAUTION: DO NOT ADJUST MORE THAN TWO FLATS. THIS ADJUSTMENT

SHOULD BE MADE ONLY AFTER ALL OTHER POSSIBLE CAUSES

HAVE BEEN THOROUGHLY INVESTIGATED. GET ENGINE HISTORICAL

RECORDS TO REFLECT NUMBER OF FLATS ADJUSTED

MAXIMUM POWER RUN REQUIRED AFTER ADJUSTMENT.

Correct. Bear in mind that it impossible to perfectly set up the fuel/TD system to cover all possibilities simultaneously. You need to set it up for your NORMAL base of operations. I like to have the NULL/AUTO start TIT as close as possible, balanced against RICH/LEAN values, 10°C - 30°C on the lean side. I dislike sending an engine out of the cell with the NULL orifice above INCREASE 2, or below DECREASE 2. Therefore, an adjustment on the CIT is sometimes necessary.

I interpret a cold start as peak TIT below 750°C, when the engine has already been started and shut down within the last 15 minutes.

When you start messing with the TD amp pots, you start a whole new set of problems - just set the amp (yellow box) and go with it.

In response to the original question though, it is only necessary to measure the bellows assembly when it being replaced.

[herky400M]

hey peter, it's a long time ago, I had to change my nickname:p, forgot the other one.

What I did when I was working on the test bench is try to narrow the gap of start temp without toying with the TD AMP, it is adjusted with the Tec Manual, 820°C start temp, 1077°C max Temp, 566°C bias, 1077°C slope

1) We sometimes had complaintes that the TIT on engine 4-2-1 are lower than the one of engine 3. So I explained that we fire up with bleed air press of an APU (GTC) 40PSI and that an engine 4 -2-1 are fired up with bleed press of at least 120PSI so this a diffrence

2) CIT adjustment says that we have to measure the bellows!

3) May we readjust the CIT if C-130 is @ homebase o the origenal pos?

4) I still don't have any doc refer or defenition what a cold start is:cool:

the belgian guy

quote: attitude is a little thing that makes a big diffrence!

Winston Churchill

[pjvr99]

hey peter, it's a long time ago, I had to change my nickname:p, forgot the other one.

What I did when I was working on the test bench is try to narrow the gap of start temp without toying with the TD AMP, it is adjusted with the Tec Manual, 820°C start temp, 1077°C max Temp, 566°C bias, 1077°C slope

1) We sometimes had complaintes that the TIT on engine 4-2-1 are lower than the one of engine 3. So I explained that we fire up with bleed air press of an APU (GTC) 40PSI and that an engine 4 -2-1 are fired up with bleed press of at least 120PSI so this a diffrence

2) CIT adjustment says that we have to measure the bellows!

3) May we readjust the CIT if C-130 is @ homebase o the origenal pos?

4) I still don't have any doc refer or defenition what a cold start is:cool:

the belgian guy

quote: attitude is a little thing that makes a big diffrence!

Winston Churchill

Hey Herky, I remember. I mark the bellows by making a note on the FCU with a 'white-out' pen, and also annotate it in the engine/aircraft doc package for future reference.

Following excerpts from TO 2J-T56-56 SWP 058 01

Start 780oC Min./810oC Max. (Desired)

750oC Min./830oC Max. (Normal)