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Obi_Offiah wrote:

falconfixer860261 wrote:

Because they still needed a cable for a BUC/SEC. It has not been until just recently that manufacturers were comfortable with 100% EEC with no mechanical backup. The 737NG powered by the CFM56 is 100% digital but it has two circuits so in effect does have a backup. It also has a failsafe mode but it's not mechanical. The F-16 flight controls have/had multiple computers so there was quadruple redundancy. I'm sure cost entered into the equation somewhere too - it always does.

Falconfixer, is the mechanical input you mentioned above what separates EEC from FADEC?

I never thought of it that way but I guess that's true in all the cases I'm aware of. Never say always or never in aviation though - there are always exceptions. Note that I broke my own rule twice. Ha!

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Actually, the GE design is the only one with an electric throttle as well as mechanical. The Pratt is mechanical only.

I'll wait to hear from someone who has the answer to my May 26, 2005. Maybe someone from Lockheed Martin knows.

From a design perspective, I *suspect* that the lack of mechanical backup for the flight controls is a direct result of the relaxed stability of the aircraft. In other words, the computer is necessary to keep the Viper from swapping ends in flight. While it IS possible to manually fly an unstable aircraft (with lots of practice!), the point of a backup mode is to get you home; I can't imagine trying to land a Viper in manual mode.

Most likely it was deemed too dangerous to have a manual reversion mode and therefore GD focused on redundancy of the FLCS to eliminate the need.

earlheron,

From what I can gather about the design history of the PW F100 and the GE F110, the reason a mechanical linkage was required was because the engine power controls were not as technically advanced as the fly-by-wire flight controls when the A/B model was manufactured. Even though there is an "Electonic enigine control" on the Pratt (MEC/DEC on the GE,) not all scheduling required by the engine (RIVVs, CIVVs) could be controlled electrically. I know that on the F110-GE-100, the IGVs(CIVVs on Pratt) and VSVs (RIVVs on Pratt) are hydromechanically actuated from the Main Engine Control. They require rigging to the MEC to ensure proper operation. With the development of the Digital engine controls, feedback from these components was enhanced and almost eliminated any stagnations within the normal flight envelope. (Something Pratts always had problems with, mainly on the 15)

EngineMech0751 was right when he said "Actually, the GE design is the only one with an electric throttle as well as mechanical. The Pratt is mechanical only." I'll elaborate just a little... GE added the electrial inputs to the throttle to ensure that the mechanical and electrical inputs were "in sync" with each other.

The differences in the Pratt and the GE basically boil down to the GE being more responsive and more stable in flight.

Thank you much Roscoe, blk40crewdawg! I understand, and am suprised by the likelihood that the throttle linkage technology lagged that of the flight controls. The details of the IGV connections as well as the GE vs. Pratt details were also enlightening.

Right Blk40Dawg. GE uses both electrical and mechanical throttle signal. That also means both have to be within a certain sync parameter. Working the GE for quite a while, I know that at times you might get an EPLA/PLA disagree. If memory serves, I think is was about a 4-6 degree difference that would send a flag when you would download the CED and compile data.

While the MEC serves in normal functions of engine scheduling, the DEC has full authority. It is only when the DEC goes off line or is taken out, that the MEC takes over control, setting the IGV's and VSV's (I think VSV, it's been a while) to s set position and still maintains continuity through out the motor. In GE-100's, that would mean 2 modes of operation, SEC or PRI. GE-129's has 4 modes of operation, SEC, PRI, VSV, & Hybred VSV.

Mike Valdez

Salute!

Well, some good stuff here. Some urban legends, as well.

I only flew the Blk 1's, 1A (Blk 5), 10's and 15's. So no time with the GE motor or later Pratts.

FLCS later.....

1) Original production motors had a hydromechanical fuel control - the Unified Fuel Control. The EEC was supposed to "trim" the motor.

We also had a Backup Fuel Control - BUC. The flight test birds had a rheostat you could use to electronically command the engine up to about 80% if the mechanical connection broke. Production motors didn't have it, but we had BUC.

The BUC was literally a direct connection to the fuel flow. About like the fuel control in the T-33. Apparently, the guide vanes were not controlled, as the motor was less shrill when in idle on BUC. The Thunderbirds used BUC until clear of the crowd to preserve their hearing!!

BUC airstarts were tricky, as most pilots were used to forgiving motors and would push up the power too quickly, thereby melting the motor or causing a stall. heh heh. So a few of we old farts figured we could use the T-33 methods, and teach the rest. went to flightline and did a few BUC starts to show all it wasn't hard. Then we had all the studs do it in the family model. Then we added a BUC start to monthly training events. Secret was to not lead the temp. If temp started to go up quickly, STOP moving throttle, but don't pull it back or you'd stall or stagnate. So we watched temp and "pushed it up" with throttle until a good idle was achieved.

2) Thottle and emergency nose gear "apple"were only two mechanical connections to ANYTHING!!

This seemed prudent until motors got so complicated that pure electrons could be trusted.

3) The FLCS was a lot more than a means to keep control with the RSS. It allowed unrestricted stick inputs at 99.99% of the flight envelope. It allowed for higher pitch rates without going out of control than any other jet until the F-18. It provided a good AOA and Gee limiter, hence longer airframe life. And the beat goes on......

*************

As far as Joe Baggodonuts not hooking up the throttle cable, remember my LEF failure. The two troops in the backshop failed to put the "keeper" bolt in that kept the flap drive tube connected to the flap motor tube!!!! So the drive tube gradually slipped out and whopeeeeeee!!! That was one real good attaboy for the FLCS. I would likely have ejected at 90 degrees of bank, or more, at 100 feet had I been flying the Hornet or any other jet.

later,

Mike,

Thanks for the clarification, we had many PLA disagrees on the -100. Ususally becuase the throttle wasn't rigged just right. I hated the ones that required the full scope cause it usually ended up with the engine guys shooting down the HPT!

Gums,

About your LEF indcident... They are now replacing the the torque tubes that bolt on each end with "spring loaded" tubes that snap into place. I've done quite a few TCTO's (when the squadron had the money) and I like the spring loaded one's lots better. Can't really fudge em up!!

Thanks for the elaboration blk40crewdawg.

I know TCTO means time compliance technical order and LEF-leading edge flaps. But what are PLA, GIF and HPT (high pressure turbine?).

earlheron wrote:

Thanks for the elaboration blk40crewdawg.

I know TCTO means time compliance technical order and LEF-leading edge flaps. But what are PLA, GIF and HPT (high pressure turbine?).

PLA = Power Lever Angle. HPT = High Pressure Turbine. Don't know GIF.

Newbie Joined: Jul 10, 2005 Posts: 18 Status: Offline

The cable is not connected to the EEC. It is connected to the UFC, MFC, or MEC depending on the block. Also what is a FADEC?

IIRC FADEC is Full Authority Digital Engine Control (but I'm not 100% sure) - can anyone else confirm?

Elite 1K Joined: May 26, 2005 Posts: 1127

FADEC= full authority digital engine control

Going back to the MacDill incident, the throttle was not hooked up and engine was set at a high thrust setting. Back then there was no requirement to wire the engine to the OFF position when disconnected, this is why we do it now.

The female performing the engine run did get busted for drugs, as did many AF people did back in the 80s ( talk to anybody that was at Homestead in the 70-80s timeframe). The guy in charge had only a few months on 16s having come off of Buffs. He was reduced in rank and was able to retire later. Believe this happened in late 84 to <A href="f-16_fighting_falcon_airframe-666.html">80-527</a>. when the 62nd got it back in 86-87 it had numerous TCTOs due because the contract at depot was to fix the damage not do PDM. The ventrals never fit right on it and usually required 3 people to install.

MacDill crashed 2 jets 377 and 385 (I think) due to broken throttle cables, when the cable (actually a metal band) breaks the throttle can be advanced but you cannot pull power off so these jets were landing at over 80+ percent power and trying to use the main fuel shutoff to kill the engine at the right time to land. We got real good at replacing throttle cable assemblies.

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