F-100 Maintenance in the 'Old Days'

By Tom Suglio

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.