The unusual character of the Vietnam war with its many targets obscured by heavy jungle presented attack airplanes with target identification problems. The venerable Cessna L-19's were taking much damage from ground fire, and it became obvious that a faster twin-engine forward air control (FAC) air plane was needed. With its unsurpassed pilot's visibility, the C-337 became an immediate (and readily available) choice. It was to be designated as the M337 for the 0-2A and MC337 for the 0-2B versions. As mentioned earlier, the 0-2A was to be an observation aircraft with smoke rockets mounted on pylons on both wings for target marking. In contrast, the 0-2B was to be used for propaganda purposes with giant loudspeakers replacing the baggage door and dispensers installed for dropping leaflets to enemy ground troops.
The target-marking mission required an airplane with easy maneuverability and agility to avoid ground fire while pulling out of a dive. Thus the pilot would prefer light elevator control forces while pulling sizable "g" forces in pull-outs and turns. To achieve this goal we removed the stability-enhancing elevator downspring and bobweight devices from the civilian C-337B. In addition, its elevator was replaced with the 4-inch shorter chord elevator used on the C-336. With the resulting penalty in elevator power in landings at forward loadings, the allowable most-forward C. G. limit was moved aft by 1- 1/2 inches. These changes added significantly to the flying qualities, and in fact, they were later adopted in the commercial C-337s at the urging of Mort Brown, Chief of Production Flight Test. Mort had been testing 0-2 and C-337 airplanes in sequence, and he noted the much nicer "feel" of the 0-2 airplanes. Consequently, the stability devices were removed from the 1968 C-337C, and starting with the 1969 C-337D the small chord elevator was adopted as well.
A brief outline of the significant differences between the 0-2A and the commercial versions is shown below:
External
1. Propeller spinners and cabin step removed.
2. Addition of observation windows in cabin top and door.
3. Addition of two stores pylons under each wing.
4. Addition of navigation and communication antennas.
5. Addition of Model 336 elevator (shorter chord by 4 inches).
6. Addition of Model T337 type rear engine cowl flaps.
Internal
1. Removal of upholstery.
2. Instrument panel rearrangement and additional equipment.
3. Overhead fresh air vent system relocated to front fuselage sides.
4. Elevator bobweight and downspring removed.
5. Front engine baffle changes.
6. Polyurethane baffles in fuel tanks.
7. Extensive electronic equipment added.
8. Engine fire detection equipment added.
9. Smoke generator equipment for rear engine exhaust system.
10. Fuel selector valves relocated.
11. Cabin door rip hinges installed.
In 1967 we received sample units of USAF avionics and target-finding antennas for receiving signals from downed airmen or remote fighting units. Once again, we were shocked at how primitive this equipment was in comparison to our lower-cost commercial airplane avionics. One would think it would be the other way around! Aside from the instrument panel, gunsight, armament switch subpanels, additional windows in the fuselage, avionics, spartan interiors, exterior paint scheme, the four underwing pylons for rockets and the 7.62 mm minigun pack, flares, and cluster bombs, the 0-2A was essentially a commercial C-337. However, we had to install armor plates under the seats and porous foam slabs in the fuel tanks (before assembly) to make them explosion-resistant after a gunfire hit. This was at the expense of about a 5 % loss in tank capacity. Most of the development effort was focused on external armaments suspended from the wing pylons. In addition to the primary military objective of target-marking with smoke rockets, we tested the aerodynamic effects of bombs, attack rockets, mini-machine gun pods, wire-laying containers, and a host of bulky cargo containers of unbelievable size. The intent was to make sure that the airplane was controllable (at vastly increased gross weights) with both symmetrical and asymmetrical loads. In addition, we had to determine that the jettisonable external stores could be safely jettisoned at various speeds without striking the tail.
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