First, we need to understand that the pylons used were originally designed for different purposes.
THE NAVY PYLON
The Navy versions of the F-4, as well as both Navy and Air Force RF-4s (and some early F-4Cs), utilize the LAU-17/A as their inboard pylon. As the nomenclature suggests, its primary purpose is as a launcher not as a weapons pylon
The LAU-17/A was designed to carry and launch an AIM-7 Sparrow III missile so that the F-4 could carry a total of 6 (4 on fuselage semi-submerged stations and one on each inboard pylons).
|LAU-17A pylon with an AIM-7 Sparrow III Missile|
When the AIM-7 wasn't carried, the inboard pylon could also be fitted with a launcher rail on each side to carry and launch the AIM-9 Sidewinder missile. The AERO-3/A/B allowed the LAU-17/A pylon to carry an AIM-9B missile only. The LAU-7/A launcher rail allowed the LAU-17/A pylon to carry either the AIM-9B, AIM-9D, and subsequent Sidewinder missile. The launcher rail consists of a power supply for the electrical requirements of the missile, a mechanism which retains the missile during flight and releases the missile when fired, a nitrogen receiver assembly to provide coolant for the missile seeker head, and safety elements to keep the missile from accidentally firing during loading/unloading and during catapult launch and arrestment. (Note: Don't confuse the LAU-7/A launcher rail with the AERO-7A which was the launcher for the AIM-7 on the semi-recessed fuselage stations).
|LAU-17/A pylon with the AERO 3/A/B or LAU-7/A launcher rail installed|
|AIM-9B Sidewinder on the AERO-3/A/B launcher rail|
AIM-9D used the LAU-7/A launcher rail
|LAU-17/A pylon with an adapter fitted|
|LAU-17/A pylon with adapter and TER fitted|
THE AIR FORCE PYLON
The Air Force inboard pylon was sometimes called the MAU-12 pylon which refers to the Ejector Rack which was in the pylon.
|Pylon with MAU-12 ejector rack removed for illustration|
The AIM-4D was used in combat in South-East Asia by some F-4D Phantoms, which were equipped with special LAU-42/A launchers for this purpose. However, it became soon apparent that the AIM-4D was ill-suited for the close-range dogfights encountered over Vietnam, and only 5 kills were achieved with the Falcon. The main problem of the missile was seeker cooling. The limited amount of onboard nitrogen coolant meant that the seeker could not be pre-cooled for any length of time, which in turn meant that it had to be cooled more or less shortly before firing, i.e. when close-range combat had already started. This cooling, however, took up to 5 seconds which is like an eternity in a dogfight, so that most targets were out of reach again when the missile was finally ready. Moreover, when the coolant was exhausted after several aborted launches, the Falcon was just useless dead weight, which had to be brought back to base for servicing. Another problem of the Falcon was the lack of a proximity fuze, which made it effectively a hit-to-kill missile. The AIM-4D was gradually withdrawn from use beginning in 1969, and by 1973, the AIM-4D was no longer operational with the USAF.
|Pylon with AERO-3/B or LAU-7/A missile rail installed|
|AIM-9 Sidewinder installed on LAU-7/A|
To carry more than one weapon on this inboard station a TER could be installed which increased the load to 3 weapons of 750 lb. each. Several other adapter rails could be installed for different missiles as well.
|Inboard pylon with single Mk82 practice bomb|
|Inboard pylon with TER for carrying three weapons|
|AGM-45 Shrike on LAU-34 launcher adapter|
|AGM-65 Maverick on a LAU-88 triple rail launcher (although the Phantom only carried two on each launcher - inboard and lower stations)|
For an interesting take on a modification of the Air Force inboard pylon found on Israeli and Turkish F-4s for carrying the Popeye missile see this post: https://phantomphacts.blogspot.com/2013/10/israeli-mods-to-f-4-pylons.html
- Drawings (c) by Kim Simmelink