All -
I was asssigned to the 122nd Fighter Wing, Indiana Air National Guard @ Ft. Wayne, Indiana. We were the last ANG unit to fly the F-4 ( " E " model ), before they went to the ariel target drone program; or for some of our jets...were ferried straight over to Turkey.
I was the 122nd's Electric Shop Chief not only during Civil Service " Technician " status through the week.... but also during duty on weekends and deployments in MIL pay status.
Amongst the last F-4Es to leave were " 452 ", and " 844 ".
452 had developed a recurring Generator failure ( Lt engine side if I recall ) , and the problem plagued the Electric Shop over a period of months. The Deputy Commander for Maintenance finally reached the end of his tolerance, and demanded an enduring fix be found for 452's Generator-induced aborts. Months of Generator, Generator Control Unit, and Frequency & Load Contol box changes plus random wiring harness checks had all been performed to no avail. I made a list of 212 seperate wiring checks that needed to made, and the DCM agreed to park the jet for as long as it would take to troubleshoot and then fix the plane.
Each suspect wire in the generator(s) systems circuitry.... generator control wiring.... buss wiring, and more....all had their to be checked thoughroughly. That meant Canon plugs and bulkhead connectors for wiring harnesses ( some big as your ankle ) had to be disconnected, plus Canon plugs to numerous components also had to be disconnected to isolate seperate circuits. THEN...EACH wire needed to be ohmic checked to all wires around it....ohmic checked to each Canon plug's metal shell..and ohmic checked to the aircraft structure...to see if wires that carried current were reaching a grounding point along their runs; when they shouldn't be.
And ideally... All wires @ harness flex points would be ohmic tested while the harness was being manually flexed. The latter required 2 mechanics, minimum. For ground wires in the circuit, the max allowed resistance reading on the ohmeter
was 1 ohm.
The test took 2 solid work weeks, where at least I was always present working on the jet. The last wires to be checked, were the 3 large generator output plus 1 large generator ground wire that ran up through the pylon at the front of the ( Lt )
J-79. These wires emanated upward from a grommet in the floor of the LT engine intake. They were wrapped in a greyish-purple nylon anti-chafe tape, for protection inside the tight confines of the generator pylon that contained the wires ahead of the engine face, and mounted the dome that housed the generator.
After 2 weeks of troubleshooting, I had found nothing; and had reached THE final check on THE final wire; which was the ground wire for the Lt generator. The meter read 1.1 ohm.
Not the usual 1 ohm max for a ground wire. I.I ohm.
All those wiring checks...and 1.1ohm resistance on one ground wire is all I found.
I unwrapped the anti-chafe tape from the 4 wire generator leads, to where it ended inside the lower grommet in the intake floor. I saw a dark smudge line on the wires where they made contact inside the grommet, even through they were covered with the anti-chafe tape at that location. The smudges had an appearance and slight texture to them, that resembled a very super-finely ground aluminum dust intermixed with random grease/oil residue. After wiping the smudge on the ground wire, I could still see only the darkened outer harness cloth overing, but no evidence of bare; silver colored wire. The same
smudge residue could be seen inside the nylon grommet, which had a split " C " shape, to aid in installation.
The ground wire did not show any undesired grounding through chafing to any of the generator's 3 phase lead wires.
All I could figure was the the smudge on the ground wire permeated the cloth wire sheath to allow conduction to ground at point in-advance of the established ground point further down in the jet's structure. Then grounding path would have had to include the smudge materiel inside the grommet, to also necessarily include some of it being present inside the split of the grommett...and that allowed the premature grounding to take place. And...the grounding being made read a scant .1ohm over max allowable.
If memory serves, I cleaned the wires and grommett; and re-wrapped the harness w/ new anti-chafe tape. The subject jet finally quit have ground and air aborts due to generator fail lights. People can argue my conclusions all they want,
but not the proven, documented results of my efforts on the subject aircraft.
When time permits, I'll tell you about aircraft " 844 ", which was nick-named" Buss Tie Betty ". This was THE last F-4E to depart Ft. Wayne on transfer to Turkey.... and it's departure was late....
With regards,
357Mag
.
