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Newbie Joined: Mar 27, 2007 Posts: 3 Status: Offline

Someone told me this, when the plane is in flight/cruising, the PLA is at IDLE Question

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No.

F-16s won't fly with the throttle at IDLE. If the throttle cable somehow becomes "detached" from the engine control on an F100, the control will return to IDLE and you'll need a place to land soon.

The engine just doesn't make enough thrust at IDLE to sustain flight, even if the aircraft is clean.

There have been many mishaps caused by this, and there are now special inspections to check the throttle connection, bolt, nut, and cotter-pin, during installation. (All this AND a throttle rig check)

Elite 1K Joined: Aug 19, 2004 Posts: 1092

Usck,

Above Mach 1.4, if you chop the throttle to idle in an F-16 with F100-PW-200/220/220E/229, the EEC (-200) or DEEC (-220/-220E/-229) will still maintain MIL thrust until under Mach 1.4. Between Mach 0.84 (if I remember correctly) and Mach 1.4, the engine control logic will give schedule thrust somewhere between idle and MIL depending on altitude and airspeed. This is probably somewhat of a simplified explanation, but I think it explains what you heard about idle thrust and the power lever angle (PLA) being at idle. But no... the F-16 doesn't cruise around with the throttle at idle. There is logic to prevent the pilot from commanding idle thrust at speeds where true idle thrust fan and compressor RPMs would cause inlet "buzz" and possible compressor stall. So yes... if you're above Mach 1.4 (which is not cruising... it's dashing) and select idle thrust via the throttle, you'll only get MIL power until under Mach 1.4 and you won't get true idle thrust until below Mach 0.84 (or something close to that).

Newbie Joined: Mar 27, 2007 Posts: 3 Status: Offline

I see.. actually I wanted to ask this question. Why oil consummation run is only done at idle for 229 engine?
the engine is on Test Cell.

Elite 1K Joined: Apr 26, 2004 Posts: 1215 Status: Offline

I think we need an engine guy to explain this fully. I may be wrong here so please chime in anytime. It was told to me that the engine really uses the EPLA signal with the PLA as a mechanical backup, which explains what Raptor One just told us about throttling back and the engine power not going straight to idle. Can anyone set us straight on this.

Purple

Enthusiast Joined: May 09, 2006 Posts: 21 Status: Offline

I worked 220's for 10 years so I can’t really say about the 229's. On the 220 the throttle is entirely mechanical from the cockpit to the engine. On the engine there is a PLA resolver which converts where the throttle is to an electrical signal for the DEEC to use.

Quote:

If the throttle cable somehow becomes "detached" from the engine control on an F100, the control will return to IDLE and you'll need a place to land soon.

I don't believe this is true. However I could be wrong. But there is no way for PLA to stop at idle if the throttle is disconnected. It would go all the way to cutoff. Now the PLA resolver is spring loaded to max and it would be my guess that PLA would go to max if the throttle became disconnected.

Quote:

i see.. actually i wanted to ask this question. Why oil consummation run is only done at idle for 229 engine?
the engine is on Test Cell.

Idle is the most accurate way to measure consumption. If there is a problem with the oil system than it will show at Idle just like it would show at higher power settings.

Enthusiast Joined: May 09, 2006 Posts: 21 Status: Offline

Purplehaze wrote:

I think we need an engine guy to explain this fully. I may be wrong here so please chime in anytime. It was told to me that the engine really uses the EPLA signal with the PLA as a mechanical backup, which explains what Raptor One just told us about throttling back and the engine power not going straight to idle. Can anyone set us straight on this.

Purple

It is the DEEC logic which prevents the engine from returning to idle in supersonic flight. It is called Mach number lock out. We used to check it on test cell runs but in the late 90's they wrote it out of the acceptance run.

I've ran a jet with a bad CADC (CADC provides the DEEC with the mach signal)and when I went to do a scavange shut down I ran the engine up and when I went to Idle the RPM's would not come down because the CADC was telling the engine we where supersonic.

Elite 1K Joined: Apr 26, 2004 Posts: 1215 Status: Offline

My Bad....I'm talking about GE's, sorry.

Newbie Joined: Mar 27, 2007 Posts: 3 Status: Offline

CCAF wrote:

Idle is the most accurate way to measure consumption. If there is a problem with the oil system than it will show at Idle just like it would show at higher power settings.

accurate means?

i also a engine man, but now still undergoing training.

this is one of the question the interviewer asked me. haha

Enthusiast Joined: May 09, 2006 Posts: 21 Status: Offline

usck wrote:

accurate means?

i also a engine man, but now still undergoing training.

this is one of the question the interviewer asked me. haha

The 220 engine will always consume oil when running. You are allowed 1 pint an an hour to be lost.

During a consumption run you are trying to pinpoint the cause. Running at mil will cause more oil to consume but you dont know if it is from the higher power setting or an internal problem

If you just snap the throttle back and forth from idle to mil you will consume over one pint in an hour, but that is how the engine is suposed to work.

If there is an internal problem it will show during a idle run making it a more accurate way of troubleshooting a consumption problem.

When ever a oil consumption run is due, the engine is ran through different ranges with the exception of burner, there is no difference in the oil system when you go from mil to aug, over a period of about 35 to 45 min. It a long and boring run. After the run it's good, return to service. If outside limits pull motor. On the issue of EPLA and APLA(going off GE's but Pratts have the same concept) , the throttle is mechanical but, when it is connected to the spline on the main engine control, it is converted to your EPLA in degrees. And the throttle is converted to APLA in degrees by your throttle position switch and signal data converter. All the sigs go thru the CADC and DEC or DEEC and fuel, air, etc. is scheduled. With the throttle, the engine is always digita w/ a mechanical backup.

CCAF wrote:

Quote:

If the throttle cable somehow becomes "detached" from the engine control on an F100, the control will return to IDLE and you'll need a place to land soon.

I don't believe this is true. However I could be wrong. But there is no way for PLA to stop at idle if the throttle is disconnected. It would go all the way to cutoff. Now the PLA resolver is spring loaded to max and it would be my guess that PLA would go to max if the throttle became disconnected.

Correct: Pratts don't get a PLA "signal" from the airframe. The only throttle input on any F100 is mechanical. The PLA signal used by the DEEC comes from the PLA Resolver inside the Main Fuel Control.

The PLA Shaft is moved by the throttle linkage. This is why the throttle bolt has a "Pit-Pin" built into it, as well as a torqued (Self locking AND Castellated) nut WITH a cotter-pin. All of which, by the way, require an In-Progress-Inspection whenever re-connected. If the cotter-pin falls out, the nut stays "locked" if the nut falls off, the bolt stays engaged. Most times when the linkage becomes disconnected, is when the bolt is passed just past the end of the PLA-Shaft, and not through the cut-out in the shaft where the bolt is suppose to be.

GE sounds like it uses an "electronic" PLA as primary and "mechanical" as back-up.

INCORRECT on PLA to CUTOFF; The reason the F100 engine will return to IDLE, is fuel pressure inside the MFC. It will not however go to cut-off as there is spring pressure to load the PLA to IDLE. (If you see an F100 removed, the PLA is safetied or zip-tied to CUTOFF. Remove it and the PLA will spring back to IDLE.) This is true for all the F100 engines to include the -229.

Quote:

i see.. actually i wanted to ask this question. Why oil consummation run is only done at idle for 229 engine?
the engine is on Test Cell.

Quote:

Idle is the most accurate way to measure consumption. If there is a problem with the oil system than it will show at Idle just like it would show at higher power settings.

Not quite. If you have certain problems in the engine's oil system, leaking/consumption may be more pronounced at high-RPM. If you get into the ADVANCED oil consumption, there are more RPM dependent readings/observations taken. This will help determine the cause of the oil consumption after the INITIAL diagnosis. The INITIAL oil consumption run only requires a lengthy IDLE run.

Quote:

The 220 engine will always consume oil when running. You are allowed 1 pint an an hour to be lost.

Yes on consumption, but No on lost. Lost can also be considered a leak (internal or external) and neither are allowed. "Consume" means leaking small amounts past the carbon-seals of the bearing cavities and there-by not leaving any trace of being there in the first place. If you see a puddle and you're engine is using 1 pint an hour, it's not OK. If the nozzle is soaked with oil and covered with dirt and you only used 2 teaspoons of oil, it's not OK.

If you have an engine that is constantly and routinely consuming the "limit" of oil it's not a great situation. They are "allowed" to use some oil but if you have an engine with mostly new modules, and it's still using that much oil, you may want to do a little "risk management" and perform a little RCM "Reliability Centered Maintenance" to that engine. (Provided you have the time and resources)

Keep 'em flyin' Thumb

Enthusiast Joined: Aug 09, 2005 Posts: 79 Status: Offline

Quote:

GE sounds like it uses an "electronic" PLA as primary and "mechanical" as back-up.

You bet. Early in the GE-129 era, we had many problems with PLA/EPLA disagreement. The EPLA would fail and no matter what you did with the throttle, the engine remained at low thrust. Only way to correct the issue was to select Secondary power. This happened alot when firing the gun. The vibrations along the left side damaged the box that converted the signal.

Last I recall before leaving the GE's was that there was a TCTO to replace all of the boxes with a newer model that had been injected with a silicone? to reduce the vibration issues of the internal components.

Quote:

It is the DEEC logic which prevents the engine from returning to idle in supersonic flight. It is called Mach number lock out. We used to check it on test cell runs but in the late 90's they wrote it out of the acceptance run.

Correct! As a jet engine requires the proper balance of fuel and air for combustion, reducing the throttle at high speed will not decelerate the engine. The air is being rammed into the intake - speed must be reduced in order for the fuel to decrease. In laymans terms - the pilot must do something to reduce speed... ie turn, climb or deploy speed brakes in order for the engine to reduce speed. Otherwise you end up with too much air injested and not enuff fuel.... Thus you have the Mach Number Lock. This was a popular ops ck with the -200. Digital electronics deleted this requirement in the -220 as the DEEC performs the self test at start up.

Oil Consumption on GE's require various power settings for varying lengths of time. The oil system operates differently at different power settings and there are more oil components on the GE... nozzles are oil actuated!
This ck requires the trim pad and a couple of hours.......

Thus another reason I prefer Pratt's.

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PW229-F100 PLA at IDLE?