The Dirty Underside of the A4D

One of the other differences between the early and late A4D-2s (See the preceding post and http://tailspintopics.blogspot.com/2012/07/new-airfix-172-4b4p-modeling-notes.html for much, much more) was the detail on the main landing gear sponsons (the fairing for the retracted main landing gear strut). The original A4D -1/2 simply had a small fuel vent on the right-hand sponson aft of the main landing gear well:

A closeup of that feature:

When the FAA implemented a civil requirement for anti-collision lights, a red light was added (and retrofitted) to the top of the fuselage and the left-hand sponson.

 If the airplane that you are building a model of has the red beacon on top of the fuselage, then it will have this beacon installation on the-left hand sponson.

At some point,  a fuel dump mast was added to the right sponson aft of the fuel vent.

The Airfix A4D-2 has all three of these features on its sponsons. Only the fuel vent was on Skyhawks from the beginning. The others were retrofits to the A4D-2.