Cessna 337 Super Skymaster: Unique Push-Pull Prop Design

Introduction

The Cessna 337 Super Skymaster is a unique and iconic aircraft known for its distinctive push-pull engine configuration, which sets it apart from traditional twin-engine planes. Manufactured by Cessna from 1963 to 1982, the Super Skymaster was designed to address the challenges of asymmetric thrust that typically plague twin-engine aircraft. With engines mounted both in the nose and at the rear of the fuselage, this design provided a safer and more manageable flying experience, especially in the event of an engine failure.

This article will provide a comprehensive overview of the Cessna 337 Super Skymaster, covering its design features, performance capabilities, historical significance, and its various applications. We will also explore how its innovative engineering contributed to aviation safety and utility, making it a favored choice for private pilots, flight schools, and even military operations.

Design and Configuration

The Cessna 337 Super Skymaster is a twin-engine civil utility aircraft. What makes it particularly unique is its push-pull configuration, where one engine is mounted in the nose (tractor engine) and another in the rear (pusher engine). This design eliminates the asymmetric thrust issues that are common in conventional twin-engine aircraft. In a traditional twin-engine setup, if one engine fails, the pilot must compensate for the yawing motion caused by the imbalance of thrust on one side. However, with both engines aligned along the centerline of the fuselage in the Skymaster, this problem is significantly reduced.

Key Design Features:

• Push-Pull Engine Configuration: The front engine pulls the aircraft forward while the rear engine pushes it. This configuration offers several advantages:
• Reduction in Asymmetric Thrust: In case of an engine failure, there is no significant yawing motion, making it easier to control.
• Enhanced Safety: Pilots can continue flying without drastic changes in handling when one engine fails.
• Twin Boom Tail Structure: The tail section consists of two booms extending from the wings to support the vertical stabilizers. The rear engine is positioned between these booms, with a horizontal stabilizer connecting them.
• Retractable Landing Gear: Unlike its predecessor (the Cessna 336), which had fixed landing gear, the Super Skymaster features retractable landing gear for improved aerodynamics and performance.
• Dorsal Air Scoop: A prominent dorsal air scoop on top of the fuselage helps cool the rear engine more efficiently.

Cabin and Seating:

The aircraft has a cabin that accommodates up to six people—five passengers and one pilot. The cabin dimensions are relatively compact but sufficient for general aviation purposes:

• Cabin Height: 1.2 meters (3.94 feet)
• Cabin Width: 1.1 meters (3.61 feet)
• Cabin Length: 2.9 meters (9.51 feet)

The cabin layout is designed for utility rather than luxury, making it suitable for various roles such as personal transport, aerial photography, or even light cargo transport.

Dimensions:

• Exterior Length: 9.07 meters (29.76 feet)
• Wingspan: 11.8 meters (38.71 feet)
• Tail Height: 2.8 meters (9.19 feet)
• Fuselage Diameter: 1.2 meters (3.94 feet)

These dimensions make the Cessna 337 compact enough for small airports while providing ample space for passengers and cargo.

Performance Specifications

The Cessna 337 Super Skymaster is powered by two Continental IO-360-C piston engines, each producing 210 horsepower. This gives it decent performance characteristics for its class of aircraft.

Speed and Range:

• Maximum Cruise Speed: 173 knots (320 km/h) at sea level
• Approach Speed (Vref): 60 knots
• Travel Range: 839 nautical miles (1,554 kilometers)

While not exceptionally fast compared to other twin-engine aircraft of its era, the Super Skymaster’s range makes it suitable for cross-country flights without frequent refueling stops.

Climb Rate:

The aircraft has a respectable climb rate of 1,200 feet per minute, allowing it to reach cruising altitude quickly even under less-than-optimal conditions.

Service Ceiling:

With a service ceiling of 19,500 feet, the Cessna 337 can fly at altitudes high enough to avoid most weather disturbances while maintaining efficient fuel consumption.

Takeoff and Landing Distances:

One of the key advantages of the Super Skymaster is its ability to operate from relatively short runways:

• Takeoff Distance: 471 meters (1,545 feet)
• Landing Distance: 500 meters (1,640 feet)

These short-field capabilities make it ideal for operations in remote or less-developed areas where runway length may be limited.

Fuel Efficiency:

Fuel consumption varies depending on operating conditions but remains competitive within its class. The aircraft has a fuel capacity of 128 gallons (485 liters) spread across two tanks located in each wing.

Weight Specifications

The Cessna 337 Super Skymaster’s weight specifications reflect its versatility as both a utility and personal transport aircraft:

• Maximum Takeoff Weight (MTOW): 1,996 kg (4,400 lbs)
• Maximum Landing Weight: 1,647 kg (3,631 lbs)
• Maximum Payload: 792 kg (1,746 lbs)

These weight limits allow for flexibility in loading passengers or cargo without compromising performance or safety.

Avionics

The standard avionics suite for most Cessna 337 models includes basic navigation and communication systems suitable for general aviation purposes:

• Avionics Brand: Bendix King Avionics
  This system provides reliable instrumentation for day-to-day flying operations but can be upgraded with more advanced systems depending on mission requirements or pilot preferences.

At this point in our exploration of the Cessna 337 Super Skymaster’s design and performance characteristics, we have covered some key aspects that make this aircraft stand out in general aviation history. Its push-pull configuration offers significant advantages in terms of safety and ease of handling during engine failures—a critical factor that has contributed to its popularity among pilots over several decades.

Citations:
[1] https://findaircraft.com/cessna-337/
[2] https://www.globalair.com/aircraft-for-sale/specifications?specid=437
[3] https://planephd.com/wizard/details/298/CESSNA-337D-Skymaster-specifications-performance-operating-cost-valuation
[4] https://www.flyingbulls.at/en/fleet/cessna-337-skymaster-push-pull

Historical Context and Evolution

The Cessna 337 Super Skymaster was introduced in February 1965, following the earlier Model 336 Skymaster, which had been in production since 1963. The Skymaster series was a bold attempt by Cessna to offer a twin-engine aircraft that solved the problem of asymmetric thrust, a common issue in conventional twin-engine planes. In traditional twins, when one engine fails, the imbalance of thrust can cause severe handling difficulties, often requiring significant pilot skill to manage. The push-pull configuration of the Skymaster, with engines mounted in both the nose and rear of the fuselage, eliminated this problem by aligning the thrust along the aircraft’s centerline.

Key Milestones in Development

• Model 336 (1963-1964): This was the precursor to the Super Skymaster. It featured fixed landing gear and was powered by two 210-horsepower engines. While innovative, it lacked some of the refinements that would come with later models.
• Introduction of Model 337 (1965): The Super Skymaster introduced several significant upgrades over its predecessor:
• Retractable landing gear: This improved aerodynamics and performance.
• More powerful engines: The same Continental IO-360-C engines were retained but optimized for better efficiency.
• Dorsal air scoop: This feature was added to improve cooling for the rear engine.
• Turbocharged Versions: In 1966, Cessna introduced a turbocharged version known as the T337, which allowed for higher altitude operations and improved overall performance. This variant could fly at altitudes up to 33,000 feet, making it suitable for high-altitude airstrips and longer flights.
• Pressurized Versions (P337): In 1973, Cessna added a pressurized version called the P337G, which allowed for more comfortable high-altitude flying by maintaining cabin pressure. This model was particularly popular among business travelers and those flying in mountainous regions.

Military Applications

One of the most interesting aspects of the Cessna 337 Super Skymaster’s history is its use in military operations. In response to the U.S. Department of Defense’s need for a light observation aircraft during the Vietnam War, Cessna adapted the Super Skymaster into a military variant known as the O-2A.

O-2A Super Skymaster

The O-2A variant played a crucial role in forward air control (FAC) missions during the Vietnam War. Its unique design made it ideal for low-speed reconnaissance and target marking. The aircraft’s twin-engine configuration allowed it to absorb more ground fire than single-engine planes while still being able to return safely to base.

Key features of the O-2A included:

• Tandem-mounted engines: These provided redundancy in case one engine was damaged.
• Wing pylons: These allowed for rockets, flares, and other light ordnance to be carried.
• Smoke rockets: Used for marking enemy positions during air strikes.

The O-2A’s ability to fly slow and low made it perfect for coordinating airstrikes and reporting target damage. Another variant, known as the O-2B, was used for psychological warfare missions. Instead of carrying weapons, it was equipped with loudspeakers and leaflet dispensers to broadcast messages or drop propaganda materials over enemy territory.

Production of military variants ended in June 1970 after Cessna had built 532 O-2s for the U.S. Air Force[7]. Many of these planes continued to serve in various roles even after their military careers ended, including use as civilian observation aircraft and trainers.

Variants of the Cessna 337

Over its production run from 1965 to 1982, several variants of the Super Skymaster were developed to meet different needs. These included both civilian models and specialized military versions:

1. Cessna 337 Super Skymaster (Base Model): The original version with retractable landing gear and two Continental IO-360-C engines producing 210 horsepower each.
2. T337 Turbo Super Skymaster: Introduced in 1966, this turbocharged version offered improved performance at higher altitudes with a service ceiling reaching up to 33,000 feet[1].
3. P337 Pressurized Super Skymaster: First produced in 1973, this version featured a pressurized cabin for more comfortable high-altitude flying[6].
4. Reims FTB337 STOL (Short Takeoff and Landing): Built under license by Reims Aviation in France, this variant featured modifications that allowed it to operate from shorter runways[1].
5. O-2A/O-2B Military Variants: Used extensively by the U.S. Air Force during the Vietnam War for forward air control and psychological warfare missions[7].
6. FTB337G Milirole: A military version with modifications such as underwing hardpoints for carrying weapons or equipment[1].

Production Numbers

In total, Cessna produced approximately 2,993 Skymasters, including civilian models and military variants like the O-2A[8]. While production in America ended in 1982, Reims Aviation continued manufacturing certain versions under license in France.

Breakdown of Production:

• Civilian Models: Approximately 1,859 units
• Pressurized Models (P337): Around 332 units
• Military Models (O-2): Around 513 units

This makes the Cessna 337 one of the most commercially successful push-pull configuration aircraft ever produced.

At this point, we have explored both the historical context and various versions of this remarkable aircraft. From its civilian roots as a safer alternative to traditional twins to its critical role in military operations during Vietnam, the Cessna 337 Super Skymaster has carved out a unique place in aviation history.

Citations:
[1] https://findaircraft.com/cessna-337/
[2] https://www.si.edu/object/cessna-o-2a-super-skymaster-337m:nasm_A19830089000
[3] https://www.globalair.com/aircraft-for-sale/specifications?specid=437
[4] https://skybrary.aero/aircraft/c337
[5] https://www.aviationconsumer.com/used-aircraft-guide/cessna-skymaster/
[6] https://aeropedia.com.au/content/cessna-337-super-skymaster/
[7] https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/196063/cessna-o-2a-skymaster/
[8] https://en.wikipedia.org/wiki/Cessna_Skymaster

Operational Uses and Impact on General Aviation

The Cessna 337 Super Skymaster has proven to be a versatile aircraft, capable of fulfilling a wide range of roles in both civilian and military aviation. Its unique push-pull engine configuration, coupled with its ability to operate from short runways, has made it a popular choice for various specialized missions. In this section, we will explore the operational uses of the Super Skymaster, its impact on general aviation, and how it has been employed in different sectors over the decades.

Civilian Applications

In civilian aviation, the Cessna 337 Super Skymaster has been used for several purposes, ranging from personal transportation to aerial photography and cargo transport. Its ability to carry up to five passengers plus a pilot, combined with its relatively long range and short takeoff and landing distances, makes it suitable for both private owners and commercial operators.

Key Civilian Roles:

1. Personal Transport: The Super Skymaster is often used by private pilots for personal transport. Its twin-engine configuration provides an added layer of safety compared to single-engine aircraft, making it a popular choice for those who frequently fly over mountainous terrain or large bodies of water. The aircraft’s ability to continue flying straight even if one engine fails gives pilots peace of mind during long flights.
2. Aerial Photography and Surveying: The high-wing design of the Super Skymaster offers excellent visibility for aerial photography and surveying missions. The unobstructed view from the cockpit and cabin windows makes it ideal for capturing images or conducting land surveys.
3. Cargo Transport: With a maximum payload capacity of 792 kg (1,746 lbs) and a baggage volume of 0.8 m³ (28 ft³), the Super Skymaster can carry a significant amount of cargo. This makes it suitable for light cargo transport operations, especially in remote areas where runway lengths are limited.
4. Flight Training: The Cessna 337 has also been used in flight schools as a multi-engine trainer. Its centerline thrust configuration simplifies engine-out procedures, making it easier for student pilots to handle emergencies compared to conventional twin-engine aircraft.

Military Applications

As mentioned earlier, one of the most notable uses of the Cessna 337 Super Skymaster was in military operations during the Vietnam War. The U.S. Air Force adopted a modified version of the aircraft known as the O-2A for forward air control (FAC) missions. The O-2A was equipped with underwing pylons capable of carrying rockets, flares, and other light armament, making it suitable for reconnaissance and target marking.

O-2A in Vietnam:

The O-2A played a critical role in coordinating airstrikes during the Vietnam War. Its ability to fly at low speeds and loiter over target areas allowed FAC pilots to observe enemy movements and direct fighter jets to their targets. The aircraft’s twin-engine configuration provided an added layer of safety in combat zones where engine damage from ground fire was a constant threat.

In addition to FAC missions, some O-2A variants were used for psychological warfare operations. These aircraft were equipped with loudspeakers and leaflet dispensers to broadcast messages or drop propaganda materials over enemy territory.

Other Military Uses:

Beyond Vietnam, the Cessna 337 has seen use in various other military roles:

• Firefighting Support: The California Department of Forestry and Fire Protection used O-2 variants as tactical aircraft during firefighting operations from 1976 until the mid-1990s.
• Counterinsurgency Operations: During the Rhodesian Bush War (1974–1980), Reims-Cessna FTB 337G “Lynx” aircraft were used by Rhodesian Security Forces for counterinsurgency air assault missions.
• Search and Rescue: The Cuban-American organization Brothers to the Rescue used Cessna 337s to search for Cuban rafters attempting to cross the Florida Straits in small boats or rafts.

Impact on General Aviation

The introduction of the Cessna 337 Super Skymaster had a significant impact on general aviation due to its innovative design and operational versatility. While not as fast or as glamorous as some other twin-engine aircraft, its ease of handling during engine-out scenarios made it an attractive option for private pilots who wanted the safety benefits of a twin-engine plane without the complexity typically associated with them.

Key Contributions:

1. Centerline Thrust Certification: One of the most important contributions of the Cessna 337 was its role in establishing centerline thrust certification standards. The Federal Aviation Administration (FAA) granted the 337 its own class rating, which limited pilots to centerline-thrust twins only. This made it easier—and arguably safer—to earn a multi-engine rating in a Skymaster than in conventional twins that required more complex engine-out procedures.
2. Simplified Engine-Out Procedures: Traditional twin-engine aircraft require precise handling during an engine failure to avoid asymmetric thrust issues that can lead to loss of control. The push-pull configuration of the Super Skymaster eliminated this problem by aligning both engines along the centerline of the fuselage. As a result, pilots could focus on feathering the failed engine without worrying about yawing or rolling tendencies.
3. Versatility Across Sectors: The Skymaster’s versatility has allowed it to serve in various sectors beyond personal transport and military operations. It has been used by government agencies for surveillance missions, by humanitarian organizations for search-and-rescue operations, and by commercial operators for tasks such as aerial mapping and cargo transport.

Challenges and Criticisms

Despite its many advantages, the Cessna 337 Super Skymaster was not without its challenges. One common criticism was related to maintenance costs—particularly concerning the rear engine’s cooling system. Because the rear engine is located behind the fuselage with less airflow than the front engine, it tends to run hotter, which can lead to increased wear and tear over time.

Maintenance Issues:

1. Rear Engine Cooling: Maintaining adequate cooling for the rear engine has always been a challenge due to its location behind the fuselage. While Cessna addressed this issue by adding a dorsal air scoop on later models like the T337 Turbo Super Skymaster, maintenance costs remained higher than average due to frequent overheating problems.
2. Complexity in Servicing: Servicing two engines located at opposite ends of the fuselage adds complexity compared to traditional twin-engine planes where both engines are mounted on wings close together.
3. Accident Record: Although designed to be safer in engine-out scenarios, some pilots found other ways to get into trouble with this aircraft—particularly those unprepared for its handling characteristics at low speeds or during emergency situations[5].

At this point, we’ve covered how operational uses have shaped perceptions around this unique aircraft—from civilian applications like personal transport and aerial photography to military roles such as forward air control during wartime operations.

Citations:
[1] https://www.globalair.com/aircraft-for-sale/specifications?specid=437
[2] https://planephd.com/wizard/details/298/CESSNA-337D-Skymaster-specifications-performance-operating-cost-valuation
[3] https://simpleflying.com/push-and-pull-propeller-an-in-depth-look-at-the-cessna-skymaster/
[4] https://www.si.edu/object/cessna-o-2a-super-skymaster-337m:nasm_A19830089000
[5] https://www.aviationconsumer.com/used-aircraft-guide/cessna-skymaster/
[6] https://en.wikipedia.org/wiki/Cessna_Skymaster
[7] https://findaircraft.com/cessna-337/

Market Trends and Modifications

The Cessna 337 Super Skymaster has experienced fluctuating market trends over the years, largely influenced by factors such as fuel prices, maintenance costs, and the overall demand for piston-twin aircraft. As a relatively niche aircraft with a unique design, the Skymaster has always occupied a special place in the used aircraft market. However, its reputation for being a “maintenance hog” and the complexities associated with its push-pull engine configuration have affected its resale value and long-term appeal.

Market Value and Pricing

As of recent years, prices for pre-owned Cessna 337 models have generally ranged between $75,000 to $160,000, depending on the condition, modifications, and avionics upgrades. Some highly customized versions, such as those with enhanced engines or advanced avionics suites like the Rocket II, can sell for up to $430,000. These modified versions often feature powerful 310-HP TSIO-520 engines, intercoolers, three-blade propellers, and air conditioning systems[4].

Factors Affecting Market Value:

1. Fuel Prices: When fuel prices rise, twin-engine aircraft like the Skymaster tend to lose value more quickly than single-engine planes due to their higher operating costs. However, the Skymaster’s market value has stabilized in recent years as fuel prices have moderated[2].
2. Depreciation: Most of the depreciation in Cessna 337 airframes has already occurred. This means that while prices may not increase significantly in the future, they are unlikely to drop much further either. This makes the Super Skymaster a relatively stable investment for pilots looking for a twin-engine aircraft at an affordable price[3].
3. Maintenance Costs: The Skymaster’s reputation for high maintenance costs continues to impact its resale value. The rear engine’s cooling issues and the complexity of maintaining two engines in different locations (nose and rear) contribute to higher-than-average upkeep expenses[4]. Buyers must factor in these costs when considering ownership.
4. Insurance: Due to its maintenance challenges and engine-related issues, some insurance providers are wary of offering coverage for the Cessna 337. This can lead to higher premiums or difficulty obtaining hull coverage[4].

Modifications and Upgrades

One of the reasons why the Cessna 337 remains popular among certain pilots is the wide range of modifications available for improving performance, comfort, and safety. Over the years, various aftermarket modifications have been developed to address some of the aircraft’s inherent weaknesses or to enhance its capabilities.

Popular Modifications:

1. Engine Upgrades: One of the most sought-after modifications is upgrading to more powerful engines. For example, some Skymasters have been fitted with 620-800 HP engine conversions, significantly boosting performance and allowing for faster climb rates and higher cruise speeds[4]. The Riley Rocket modification is particularly popular, featuring upgraded 310-HP TSIO-520 engines, intercoolers, three-blade propellers, and air conditioning[3].
2. Auxiliary Fuel Tanks: Many owners opt to install auxiliary fuel tanks (tip tanks) that increase fuel capacity by an additional 40 gallons. This extends the aircraft’s range and allows for longer flights without refueling stops—an important consideration for cross-country trips or operations in remote areas[4].
3. Wing Extensions: Wing extensions are another common modification that improves overall performance by increasing lift and reducing drag. These extensions can improve takeoff performance from short runways and enhance fuel efficiency during cruise flight[4].
4. Avionics Upgrades: Given that most Cessna 337s were manufactured decades ago, many owners choose to upgrade their avionics suites with modern systems such as GPS navigation, autopilot systems, and digital flight displays. These upgrades not only improve safety but also make the aircraft more appealing in today’s market.
5. STOL Kit (Short Takeoff and Landing): For pilots operating out of shorter airstrips or rough terrain, installing a STOL kit can be beneficial. This kit includes composite leading-edge cuffs that improve low-speed handling characteristics and reduce takeoff distances[4].
6. Rear Engine Cooling Modifications: One of the most critical upgrades available is a modification that improves airflow to the rear engine. This helps mitigate overheating issues that are common due to its location behind the fuselage where airflow is restricted[5].

Maintenance Considerations

While modifications can enhance performance and address some of the aircraft’s weaknesses, maintenance remains a significant factor in owning a Cessna 337 Super Skymaster.

Common Maintenance Issues:

1. Rear Engine Cooling: As mentioned earlier, one of the most notorious issues with the Skymaster is cooling for the rear engine. Because it is located behind the fuselage with limited airflow compared to the front engine, it tends to overheat more frequently. This leads to increased wear on components and higher maintenance costs over time[5]. Owners often install aftermarket cooling mods or ensure regular inspections to prevent overheating-related damage.
2. Complexity of Systems: The push-pull design adds complexity when it comes to servicing both engines since they are located at opposite ends of the fuselage rather than on wing-mounted nacelles like traditional twins[3]. Mechanics need specialized knowledge of this configuration to service it properly.
3. Turbocharged Models: Turbocharged models (T337) offer better high-altitude performance but come with additional maintenance challenges due to their more complex turbocharging systems[3]. Pressurized models (P337) also require regular checks on cabin pressurization systems.
4. Propeller Synchronization: Without prop synchronizers installed (a common aftermarket mod), sympathetic vibrations from both engines running at slightly different speeds can cause discomfort for passengers and increase wear on engine mounts[2].

Resale Value

Despite its maintenance challenges, well-maintained Cessna 337s can still fetch respectable prices on the used market—especially if they have undergone significant upgrades or modifications.

Factors Influencing Resale Value:

1. Condition of Engines: Buyers will pay close attention to engine hours when considering a used Skymaster. Engines nearing their time between overhaul (TBO) will reduce resale value unless they have been recently overhauled or replaced.
2. Modifications: Aircraft that have undergone popular modifications such as engine upgrades or avionics improvements tend to command higher prices than stock models.
3. Service Records: A complete set of service records showing consistent maintenance can significantly boost resale value by assuring buyers that potential issues have been addressed proactively.
4. Market Demand: While piston-twin prices remain somewhat soft overall due to high operating costs compared to single-engine planes, niche demand from pilots who appreciate redundancy continues to support resale values for well-maintained Skymasters[2][3].

In conclusion, while owning a Cessna 337 Super Skymaster comes with its share of challenges—particularly in terms of maintenance—the aircraft remains a popular choice among pilots who value its unique design features and operational versatility. With numerous modifications available to enhance performance and comfort, coupled with relatively stable market values in recent years, it continues to attract both private owners and commercial operators alike.

Citations:
[1] https://www.globalair.com/aircraft-for-sale/specifications?specid=437
[2] https://www.aviationconsumer.com/industry-news/editorial/cessna-skymaster-2/
[3] https://www.aviationconsumer.com/used-aircraft-guide/cessna-skymaster/
[4] https://aviatorinsider.com/airplane-brands/cessna-337/
[5] https://www.barnstormers.com/category-17416-Cessna–C-337-Skymaster.html