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The following information is what I remember about maintaining the F-100C/D/F models
we had at Luke AFB, Arizona. We had approximately 100 F-100s of all three models.
I worked on F-100s from July 1966 till they were all sent to the Guard Units or Davis-Monthan AFB,
about 1972, was the end of anymore F-100s assigned,. However, I continued working on F-100s
that came through transit for the next few years.
It would be my assumption that the F-100 did not change from those days, this would include
any F-100s built under license to NATO countries. The maintenance manuals should be the same
as USAF. I doubt that aircraft of this era would have a lot of CSTO (Country Standard Technical
Orders) changes, unless it had to do with flight operations.
The information I will be giving you is based on having de-briefed aircrews and having been a
member of the flight control rigging team to keep our F-100s flying as designed. A lot of this
information will not be found in any maintenance manuals, it came about by a lot of trial and
errors, in some cases, even loss of an aircraft.
The F-100 is not one of the most forgiving airplanes that was ever developed, so with that said,
anyone who bends wrenches on this aircraft has to have two things; 1 100% confidence and attention
to detail as to what you are doing to this aircraft and what the result will be, and 2 always keep
in the front of your mind that if you deviate from design specs, you are more than likely going to
kill somebody. Again , this airplane is not forgiving.
Pilot reported flight control discrepancies:
Aircraft rolls on take-off, Take off Trim Light (TOT) light on:
Generally you would think that ailerons would make the aircraft roll and you would be correct.
However, the F-100 at slower airspeeds would roll due to the rudder being out of rig. The rudder
will actually roll the aircraft. This is not to say not to check the ailerons with rig boards, but
it is saying that if the ailerons seem to be functioning within normal limits, check the rudder rig.
One other possibility that happened a few times that caused this roll was neither the ailerons or
the rudder. The tip of the vertical fin was leaning over to one side instead of being installed
straight. It can lean over one way or the other.
TOT ( Take Off Trim) Light means that the controls are trimmed at neutral for take-off. I cannot
overemphasize the importance of this part of rigging the F-100. There is two very difficult problems
here that the book was not very clear on, and I do not know if the book was ever brought up to speed
on exactly how to perform these two maintenance tasks.
If the airplane had a refueling boom on the right wing, and the rudder was rigged to 0° or neutral,
the aircraft would fly 1/8 to 1/4 ball out (turn & bank Indicator), or another words in a yaw. The only
way to correct this was to rig the rudder so the slop in the linkage, pushing the rudder to the right,
and setting neutral at about ¼”to the left of neutral would make it fly Ball in.
The other thing was that some of the F-100s had what they called a 5 by10 trim. This was an aircraft
capable of carrying the buddy tank on the left wing. The left aileron would trim 10° down, 5° up, and
the right aileron would trim 5 by 5. This took very close attention to detail to rig the teleflex drive
cables at the aileron trim motor in the left main wheel well.
Aircraft yaws when speed brake extended:
We found in this case that the design of the speed brake, and two hydraulic cylinders (actuators), that
the way the aircraft yawed, the opposite cylinder would be leaking internally and not be as strong as
the other cylinder. Either reseal the piston on the weak cylinder, or change the cylinder.
Aircraft yaws when Landing gear is extended:
Which ever direction of the yaw was evidence of the flow regulator being worn and allowing too much fluid
to pass through, hence making one main be much faster to extend than the other gear. The fast gear was
causing the yaw, not the slow gear. We learned over time that it was best to change the flow regulators
in pairs, so the gear would be perfectly sequenced in the extend selection.
Primary and Secondary Flight Controls:
Artificial Feel Bungees:
The F-100 artificial feel bungees were a dual spring cartridge looking affair. The dual springs for
push & pull or compression, extension gave the pilot the feel necessary to control the aircraft. As
a flight line mechanic we removed and replaced these bungees. However, when installing them or rigging
the flight controls, the bungees had to be rigged also. This is where one not paying attention to detail
or not knowing exactly what you are doing, can get you into very serious trouble.
The Horizontal Stabilizer rigging, by far was the most complex, and troublesome. Aside from rigging
the stabilizer actuator itself, plus the control valve linkage, plus the trim linkage, and the artificial
feel bungee, it was very easy to accidentally pre-load one or the other if you did not follow each step
very carefully. But aside from following each step, you had to realize what affect adjusting one part
would have another part. If you were not very careful, whatever setting you had just adjusted into a
piece of linkage, you might have changed that setting, by allowing another piece of linkage to bottom
out or stop before full travel on another was reached.
Lubrication of these components was very critical in that the exact lube called out in the tech order
is what was required. If you substitute lubricants, some are more susceptible to moisture and can freeze
at altitudes.
Leading Edge Slats:
The F-100 leading edge slats are labor intensive for 3 main reasons.
The rollers and slides must be adjusted so all of the slats work as designed, meaning that the amount of
pull to extend the corresponding slat on the other wing has to be the same. The slats must be symmetrical,
if not slats can cause serious to disastrous results as the aircraft approaches stall speeds.
Too much or too little or the wrong type of grease on the slat rollers will cause problems with them
working symmetrically.
In a desert environment, sand and dirt can get into the slat rollers and tracks and cause the slats to
not only not work symmetrically, but also cause them not to extend at all at airspeeds that they are
supposed to extend at.
Please keep in mind that even though the slats look very big and tough, the operation of the slats is
extremely sensitive. It does not take very much to make them not operate properly. Close attention to
detail required here.
Hydraulics:
The F-100 Hydraulic system requires a lot of loving care. The components of this system were designed
in a day when the technology of materials used in extremes was still pretty new.
Hydraulic pumps:
The F-100 utilized two different pumps, the Vickers, which was green and had a flat head making it easily
recognizable, and the Kellogg which was silver and round. They were both pretty good pumps. However,
the Vickers pumps did not seem to be able to take as much punishment as did the Kellogg’s. It was easier
to have a utility hydraulic failure with a Vickers pump if the failure was due to wear and tear. There
was a tel-tale sign of an impending failure of one of the pumps, bronze metallic in the filters. If we
spotted Bronzing in one of the filters, we knew the pump was about to fail.
For the safety of a mechanic who may have to change a utility or #1 pump in the summer time just after
the aircraft has shutdown, some type of cool air movement system should be used to blow fresh air down
the inlet, because both pumps are mounted on the front of the engine a long way down the intake, where
the fuel fumes collect from the hot engine. As a side issue, the cover has to be removed to get to these
pumps, and the possibility of FOD becomes very apparent. Neither one of these pumps are easy to change,
so plan to be there for a while.
Accumulators:
The accumulators on the F-100 were not very reliable. They seemed to wear out in a hurry. In those days
we used air compressors to charge the accumulators, but now dry nitrogen should make thm last much longer.
The air had too much moisture in it and it caused the piston inside the accumulator to score the barrel,
so the accumulator, would leak internally and cause a hydraulic system failure. Fortunately, if you know
how to read the signs, you can prevent the system failure. Periodically, discharge the air charge on the
accumulators. If you are using Mil-H-5606 red hydraulic fluid in the aircraft, and the air coming out of
the accumulator seems to be pink , the accumulator has started leaking internally, fluid to air side of
piston. Of course a system failure occurs when it goes air to fluid side of piston.
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