Radio Control: Giant Scale
Bob Beckman
Those Terrible Twos
Most modelers are fascinated by twin‑engined aircraft. I know I am. But multi‑engine models have a reputation for being difficult — difficult to build, difficult to fly, and difficult to keep from crashing. Hence the title of this column.
A few years ago I was a spectator at a series of events that seemed to prove that having two engines can be terrible. It all happened in less than two months and was spread from California to New York.
At Clearlake, California, Dick Hershey's quarter‑scale Grumman Goose was ready for its first flight. My wife Evelyn and I drove up from Sacramento to attend. The Goose was launched and the crew, with the two of us tagging along, boarded a flat‑decked pontoon boat and headed out onto the lake. Lee Taylor, the test pilot, made several high‑speed taxi runs and reported the aircraft felt tail heavy. The crew added six pounds of lead as far forward as possible to correct the balance.
On the next attempt the amphibian lifted off and climbed out perfectly. Lee made a shallow, climbing 180° turn to head back out over the lake and leveled at about 100 feet. Without warning the tail suddenly dropped, the plane flipped onto its back and fell straight into the lake. Videotape and later postmortems followed.
Two days later, at the Merwin Ranch fly‑in, Phil Karafilis prepared to fly his twin‑Quadra‑powered Douglas A‑20. Because many people wanted to see the maiden, he flew during the noon break. Phil taxied out, fed in full throttle, rotated and climbed out. Suddenly the port engine sputtered and died. The A‑20 rolled left and plunged into the ground.
In July at the STARS Rally in Olean, New York, Don Godfrey flew his B‑25. After a pass he announced his intention to land. As he turned onto final, the B‑25 refused to respond to elevator inputs and plowed into the ground off the end of the runway. Wreckage was spread as far as 100 feet from the impact point.
Several years later I watched Bob Campbell fly his Grumman Tigercat. Despite my superstition after the earlier crashes, Bob's Tigercat continued to fly successfully. Bob has become one of the most prolific and successful builders of large, multi‑engined models I know. The Goose's remains are being rebuilt by another modeler, and I hope to hear of a successful maiden flight soon.
While in California for the 1984 IMAA Fun Fly I also saw Phil Karafilis' Beech D‑18. It had flown about ten times before. On one flight Phil pulled into a split‑S, the plane never stopped rolling and corkscrewed into the ground. That crash was later attributed to a battery failure.
What's the point of these war stories? Am I saying multi‑engine models are impractical? Certainly not. We can learn from failures if we examine them and ask "Why?". Often people learn more from failure than from success — but only if they investigate the causes.
What went wrong (postmortems)
To the best of my knowledge, the conclusions in these cases were:
- Grumman Goose — Excessive wing incidence appears to have been built into the model. In retrospect, the wing incidence made the aircraft prone to a sudden stall/rotation. (An engineer who worked on the original Goose reportedly told Dick Hershey the prototype had the same problem.)
- Douglas A‑20 (Phil Karafilis) — One engine quit on climbout because the flexible fuel‑pickup tubing inside the port fuel tank had come off the brass feed‑through in the tank cap. While the plane sat level the engine could draw about half the tank's fuel, but in the nose‑high attitude of climb it starved for fuel. With the port engine dead, asymmetric thrust from the full‑power starboard engine overwhelmed the controls.
- B‑25 (Don Godfrey) — Apparent inadequate structural strength in the tail surfaces. The stabilizer spar and elevator hinges failed under flight loads and possible control‑surface flutter, leading to loss of elevator control.
- Beech D‑18 (Phil Karafilis) — Battery failure caused loss of control; the aircraft rolled and impacted the ground.
Note that, except for the A‑20 case (where a single engine failure created unbalanced thrust), none of these crashes was caused by merely having two engines. The A‑20 crash, however, is a clear example of how a twin‑engined model can be especially unforgiving when one engine fails.
Lessons and notes
- Inspect fuel system fittings and secure flexible pickup tubing inside tanks. A small failure there can be catastrophic on a multi‑engine model during climbout.
- Ensure tail and control‑surface structure is strong enough to handle flight loads and to avoid flutter. Proper hinge design and robust spars are critical.
- Check electrical systems and batteries thoroughly before each flight.
- Learn from failures: examine wreckage, compare notes, and apply fixes so others can avoid the same mistakes.
- Practical note: many giant‑scale, twin‑engine models weigh in excess of the 55‑lb AMA model‑aircraft limit and therefore would fall under AMA liability insurance coverage in case of an accident.
Multi‑engined models are not impractical — they demand careful design, building, and preflight inspection. When we take the time to understand failures, we make the hobby safer and more rewarding for everyone.
Transcribed from original scans by AI. Minor OCR errors may remain.
