by Tommy H. Thomason

Saturday, October 31, 2015

Grumman A-6C TRIM

1 November 2015: Added additional illustrations

TRIM is not a typo. Before TRAM (see, there was TRIM (Trails, Roads, Interdiction Multisensor). It included a large belly-mounted pod that contained a Low-Light-Level Television (LLLTV) camera and a Forward-Looking Infrared (FLIR) camera. The LLLTV amplified images to make them more visible and the FLIR detected objects that were hotter than their surroundings.
The TRIM capability included Black Crow antennas in the radome to detect truck ignition systems and point the way to the source. It was an early attempt to detect, track, and attack vehicles operating at night along the Ho Chi Minh Trail in Vietnam.

Twelve A-6As, BuNos 155647, 648, 653, 660, 663, 667, 670, 674, 676, 681, 684, and 688, were modified to be A-6Cs. The installation of the pod required the addition of hard points on the bottom of the fuselage as well as cockpit and other minor hardware changes. They were all delivered in the first half of 1970.

Mick Roth recently provided me with additional documentation on the pod that answered some questions I had. This illustration is a work in progress.
 The following sketch shows the access panels and other details; it is missing the stiffeners/fences on the outboard side of the fins.

The turret was rotated aft to protect the clear panels when the LLLTV and FLIR were not in use.
(Note that the lower lip is broader than on my drawing.)

The windows were flat and not symmetric, with the narrower FLIR camera mounted in the right side of the turret looking through germanium composition glass and the LLLTV camera  in the left side looking through quartz composition glass.

The changes to the cockpit included the addition of unique mission equipment control panels and the substitution of a multi-purpose scope that could display FLIR, LLLTV, or the standard A-6A radar.
Part of my early confusion about the pod is that most of the good pictures available are of a prototype configuration.

The production pod had air outlets on the side of the turret section instead of an inlet, the bottom of the turret opening had an extended lip, and the afterbody was extended downward to the bottom of the fins except for the last foot or so.

Although the A-6C SAC shows the inboard wing fences inboard of the inboard pylon like the A-6E, they were actually outboard of the inboard pylon like the A-6A.
The A-6C was disappointing from a mission-effectiveness standpoint, not to mention heavy and slow due to the weight and drag of the pod. The landing weight required the substitution of an EA-6B tailhook and even then the A-6Cs was more restricted from a fuel standpoint for arrested landings than the A-6As. One A-6C was lost in an operational accident. The other 11 were eventually converted to A-6Es.