Douglas DC-8's 1960 Re-engining Pioneered
In 1960, Douglas Aircraft retrofitted its DC-8 prototype with Pratt & Whitney JT3D turbofans, an early re-engining test that improved performance and set a
Douglas Aircraft announced a major change for its DC-8 jetliner in February 1960. The planemaker would re-engine the aircraft with Pratt & Whitney JT3D turbofans to address performance shortcomings and close a gap with Boeing's rival 707.
According to a report from Simple Flying, the company modified its original DC-8 prototype, known as Ship 1, with four of the new engines. This modified aircraft made its first flight on December 20, 1960, serving as the testbed for what would become the DC-8 Series 50.
Early DC-8 Performance Problems
The initial DC-8 variants faced significant performance issues. The very first flight reportedly exposed an aerodynamic problem that Douglas had not expected. The aircraft produced 13% more drag than Douglas had estimated and 10% more than it had guaranteed to airline customers.
As a result, the initial JT3C-powered aircraft could achieve an economical cruise speed of only Mach 0.798, well below the promised Mach 0.84. The early DC-8s used pure turbojets, which consumed more fuel and produced more noise and smoke than newer turbofans. Douglas also contended with the Boeing 707, which some engineers at the time estimated had an inherent speed advantage of about 20 mph due to a greater wing sweep.
The 1960 JT3D Re-engining Test
The JT3D was Pratt & Whitney's first commercial production turbofan. Developed from the JT3C turbojet, it could be installed with a relatively simple modification kit, allowing operators to convert existing engines. Industry data cited in the source indicates the conversion increased thrust by about 35% and reduced fuel consumption by 15% to 22%. Takeoff noise was reduced by about 10 dB.
This early re-engining set a precedent. It demonstrated how a jetliner's commercial fate could hinge on its engines rather than its airframe. The DC-8-50 offered airlines better economics and performance, which helped revive interest in the aircraft.
The Second Major Re-engining with CFM56
By the late 1970s, DC-8-60 series aircraft faced pressure from rising fuel costs and new noise regulations. In 1977, former Douglas Aircraft president Jackson R. McGowen formed Cammacorp to develop a re-engining program for the DC-8-60 series.
The company worked with McDonnell Douglas to replace the JT3Ds with CFM International CFM56-2 high-bypass turbofans. Conversions began in 1982. Cammacorp and McDonnell Douglas eventually converted 110 aircraft, creating the DC-8-71, -72, and -73 variants.
| Variant | Engine | Thrust | Key Improvements vs. -60 Series |
|---|---|---|---|
| DC-8-71, -72, -73 | CFM56-2 | 22,000 lb | ~70% quieter, up to 23% lower fuel consumption |
The Program That Saved the CFM56 Engine
Notably, this DC-8 re-engining program also helped save the CFM56 engine itself. By early 1979, the CFM International joint venture had spent about five years and more than $500 million on the CFM56 without a commercial order. GE Corporate Chairman Reginald Jones reportedly described the lack of a launch as a "personal embarrassment."
The breakthrough came from Cammacorp's program. On March 29, 1979, United Airlines announced it would re-engine 29 of its DC-8-61s with CFM56-2 engines. This was the first commercial order for the CFM56. Delta Air Lines and Flying Tiger Line soon followed with orders for 13 and about 18 engines, respectively. These orders provided the launch customers needed to keep the program alive.
The re-engined DC-8s remained useful for decades. During a test flight, a DC-8 also became the first commercial aircraft to break the sound barrier.
