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, 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|
|Pylon with AERO-3/B or LAU-7/A missile rail installed|
|AIM-9 Sidewinder installed on AERO-3/B|
To carry more than one weapon on this inboard station a TER could be installed which increased the load to 3 weapons. 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