Cessna O-2B Super Skymaster
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Description
Manufacturer: Cessna
Designation: O-2
Version: B
Nickname: Super Skymaster
Type: Observation & Communication
Specifications
Length: 29' 9" 9.07 M
Height: 9' 4" 2.84 M
Wingspan: 38' 2" 11.63 M
Propulsion
No. of Engines: 2
Powerplant: Continental IO-360C
Horsepower (each): 210
Performance
Max Speed: 199.00 Mph 320.00 Km/H 172.97 Kt
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In 1967, the Air Force chose the Cessna Model 337 "Super Skymaster" to meet the twin engine Forward Air Controller aircraft requirement.
The "Super Skymaster" was already on the production line when the Air Force awarded the contract. A gun sight was installed along with underwing pylons for smoke rockets. Other modifications included a smoke generator; glass panels in the lower starboard door for increased visibility and a loud speaker for psychological warfare.
The 0-2 was an all metal, four seat business aircraft designed by Cessna to be easy to fly, low in cost, yet still offer the safety and comfort of a twin engine plane. Equipped as forward air control aircraft in Vietnam, Skymasters were used for reconnaissance, target identification, damage assessment and air to ground coordination. Some aircraft were even equipped with three 600 Watt amplified speakers and leaflet pods for psychological warfare operations. The 0-2 had dual controls and could carry many types of light weapons including rockets, flares, bombs and miniguns. The O-2 can fly on either engine by itself and is still popular today among private pilots. Only 31 O-2B's were ordered from Cessna by the U.S. Air Force.
0-2B 21465 was used for psychological warfare operations (only), dropping leaflets with many different messages, some instructional, but mostly warnings of impeding defoliation flights or exhorted enemy troops to lay down their arms. 21465 was also equipped with a 300 lb 1800 watt amplified speaker system. The effectiveness of the load speaker and leaflets can be judged by the fact that the VC shot at the psywar aircraft more than at any other, except those of Operation Ranch Hand (defoliant C-123s). The VC also banged pots and pans together in hamlet streets to drown out the speakers, and cut off the hands of villagers caught reading the leaflets.
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The 0-2A / 0-2B Stories
CESSNA O-2A "SKYMASTER"
The O-2 is a military version of the Cessna Model 337 Super Skymaster. Distinguished by twin tail booms and tandem-mounted engines, it features a tractor-pusher propeller arrangement. Derived from the Cessna Model 336, the Model 337 went into production for the civilian market in 1965. In late 1966, the USAF selected a military variant, designated the O-2, to supplement the O-1 Bird Dog forward air controller (FAC) aircraft then operating in Southeast Asia. Having twin engines enabled the O-2 to absorb more ground fire and still return safely, endearing it to its crews. The O-2 first flew in Jan. 1967 and production deliveries began in March. Production ended in June 1970 after 532 O-2s had been built for the USAF.
Two series were produced: the O-2A and the O-2B. The O-2A was equipped with wing pylons to carry rockets, flares, and other light ordnance. In the FAC role the O-2A was used for identifying and marking enemy targets with smoke rockets, coordinating air strikes and reporting target damage. The O-2B was a psychological warfare aircraft equipped with loudspeakers and leaflet dispensers. It carried no ordnance.
The O-2A on display was assigned to the 20th Tactical Air Support Squadron at Da Nang, South Vietnam in the late 1960s. It was transferred to the Museum in December 1982.
SPECIFICATIONS
Span: 38 ft.
Length: 29 ft. 2 in.
Height: 9 ft. 5 in.
Weight: 4,900 lbs. loaded
Armament: Four wing pylons can carry rockets, flares, 7.62 mini-gun pods, or other light ordnance
Engines: Two Continental 10-360s of 210 hp. each
Crew: Two
Cost: $92,000
Serial number: 67-21331
C/N: 337M-0037
PERFORMANCE
Maximum speed: 199 mph.
Cruising speed: 144 mph.
Range: 1,060 miles
Service Ceiling: 19,300 ft.
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.
The C-337 Skymaster Story
The push-pull CLT concept finally became popular with the retractable gear C-337 Skymaster that was developed in 1964 and introduced in 1965. Finding space for the retracted wheels and struts was a headache, and working out the details of gear door closure both on the ground and in flight was also difficult. As mentioned earlier, a low wing configuration would have eased these problems. However, we had worked the basic principle out on the C-210, and we followed that same concept. In addition, we gained much needed over-the-nose visibility with a 2.5 degree change in wing angle of incidence and a more downward-sloped cowl. Other important changes were the fixed overhead cooling air scoop for the rear engine, a 4-inch increase in the elevator chord, ventral fins shortened by 6-inches, and a new landing gear geometry to place the airplane four inches closer to the ground. The overhead fixed scoop for the rear engine was designed by Wichita University professor Kenneth Razak. To eliminate the cooling fan (from the C-336) a cowl flap was mounted on each side of the rear cowl to regulate the cooling air flow. Ken, an aerodynamics expert, had had a longtime consulting relationship with Cessna, mainly in boundary later control (BLC) research projects. He and I also co-owned a Cessna 195 for a dozen years. Dick Kemper was given the project test pilot assignment, and he performed the maiden flight on March 30, 1964.
In an effort to increase the downwash over the horizontal tail for minimizing nose-down pitch with flap deflection and increasing elevator power for landings, a unique differential flap travel arrangement was installed in the early production airplanes. Those flap sections between the fuselage and booms would be deflected 40° while the outboard flaps would be deflected to a maximum of 25°. This worked very effectively. However, an ice-laden C-337 making an instrument approach at night in Cleveland, Ohio experienced a sudden nose-down pitching motion when the flaps were extended. This resulted in a crash into a home near the airport which was survived miraculously by all occupants of the airplane. It was apparent that an ice build-up on the leading edge of the horizontal stabilizer could not tolerate the increased localized downwash angle due to 40° of flaps. Thus the underside of the tail stalled, causing the loss of elevator control when the airplane pitched downward.
Since it was inappropriate to install a deicing boot on all C-337s, a decision was made to simply remove the differential flap feature. Cessna Service Letter 65-43 dated April 19, 1965 stated, "to improve the stall characteristics of the Model Super Skyrnaster, the inboard flap travel has been reduced from 40° to 25°. This change provides for a much smoother stall recovery under a gear down, flap down and partial power configuration." This was a mandatory change that involved the modification of the existing inboard flap bellcranks, replacement of the existing flap push-pull rod, and adjustment of the rods, bellcranks, and cables.
With the increased engine-out climb performance in the C-337, our customers were pressing us for five or even 6-place versions of the airplane for charter work. Since those last seats used all of the baggage area, we chose to develop a cargo pod for the belly of the fuselage as had been done on some of the single-engine models. This reduced the cruising speed only three mph and the engine-out climb performance by only 15 feet per minute. The service ceiling reductions were 300 feet (twin-engine) and 450 feet (single-engine). As in other cargo pod additions, it compromised the cooling of the front engine, and it was necessary to greatly increase the maximum deflection of the cowl flaps. In the author's opinion it also compromised the appearance of an already-short fuselage. However, charter operators didn't mind the chunky appearance as long as the extra revenue dollars came in from those fifth and sixth seats. The airplane was ideal for flying into rough strips in the back country or over mountainous terrain where the second engine was needed for passengers' peace of mind.
OTHER INFORMATION
The C-337's long range cruise capabilities were demonstrated during a delivery flight to Panama where my passengers wanted to look over the remote resort island of San Andres offshore from Panama. The most direct routing was a 590-mile overwater hop from Brownsville, Texas to Merida, Mexico followed by another overwater hop of 840 miles to San Andres. That extra engine was comforting, and our only real concern was navigating to that tiny island. My fellow-pilot passengers kept me advised of every inadvertent 2° compass heading excursion, and, needless to say, I didn't complain! After an overnight stay, we completed the uneventful delivery flight with a 285-mile overwater hop to Panama City. Those 1715 mainly overwater miles would have been rather lonely in a single-engine airplane!
When Paul Leckman took over the C-337 project test pilot duties, he performed a very important research program on airframe icing. Previously, he had done similar testing on the C-T210. Of paramount interest was the effectiveness of various types of deice equipment on rate-of-climb. When pneumatic deice boots are used on the wing and stabilizer leading edges, the climb performance decrement is less than that caused by the use of a propeller anti-ice system alone. This points out that climb performance is decreased more by the lack of deice boots than the lack of anti-icing provisions for the propellers. Testing was performed behind a C-411 water tanker and, when conditions permitted, in natural icing in the clouds. Paul prepared a Society of Automotive Engineers Report No. 710394 entitled "Qualification of Light Aircraft for Flight in Icing Conditions." He then presented this important paper at the SAE National Business Aircraft Meeting in Wichita, Kansas on March 25, 1971. As mentioned earlier, that paper also included very comprehensive icing test results on the C-T210 models. As a prudent practice, our company pilots never entered suspected icing clouds unless the Skymaster was equipped with full deicing equipment, and, perhaps most important of all, turbocharged engines. These airplanes were not approved for flight into known icing conditions.
The accident rate of the tandem-twin Skymasters has been skewed rather unfairly by careless pilots failing to make pre-take-off engine checks. If their rear engine has died during prolonged taxi operations in hot weather, they sometimes attempt a take-off with only the front engine operating. Thus the takeoff run is extremely long, and climb-out (if possible) would be difficult at best. Cessna Service Letter ME71-21 dated August 18, 1971 warns owners about this possibility with the following paraphrased instructions:
"It has been reported that some pilots have occasionally experienced difficulty in detecting partial power loss on the rear engine of the Super Skymaster. While detection procedures are slightly different on the Super Skymaster from those used for conventional twins, a partial power loss can still be detected both visually and aurally. This can be done visually by checking the engine gauges (tachometer and fuel flow) and aurally by being alert to changes in engine sound.
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