Gladiator

Gladiator
A free-flight gas model with a wing area of 825 square inches.
From Air Trails, March 1941.

Overview
In the early years of gas-model building, particularly until the 1939 season, most engines available were in the Class C category. This left numerous model builders with .6 cubic inch displacement motors puzzled by the new regulations. After countless hours designing two-pound ships for these engines, they suddenly found themselves needing to construct three-pound models instead.

Design Requirements
Let’s take another look at those rules. To achieve a minimum wing loading of eight ounces per square foot, a model must utilize at least six square feet of wing area. That’s quite a bit of wing! Consequently, the design must be exceptionally clean, with an airfoil that offers high lift and low drag. This way, the motor won’t struggle to elevate the ship into the thermal zones.

Skipping past the long hours spent sketching and the mental fatigue that accompanied our design process, we finally created the Gladiator—a model that meets all these criteria and has even surprised us with its performance.

Structural Details
The Gladiator features a clean design with a turtleback fuselage lined with stringers, which even further streamlines the body and minimizes drag. The wing, slightly under six square feet, incorporates a thin airfoil to reduce drag and enhance climbing ability. The tail moment arm is rather unique, serving as the key to its remarkable performance. While the added length of this lever may slightly reduce the climb, the exceptional glide compensates for this loss. Unlike many speed-focused Class C models today, the Gladiator almost seems to hover when the motor stops.

Center of Gravity Adjustments
Initially, we faced challenges with the center of gravity (CG). Early models had the CG positioned eighty-five percent behind the leading edge of the wing. In theory, a large area lifting stabilizer would keep the tail elevated, but we quickly realized that 1/4-inch positive incidence was necessary for a solid glide. Unfortunately, this adjustment caused the model to dive under power. To rectify this, we repositioned the CG to forty percent behind the leading edge, which yielded immediate improvement. Removing the stabilizer's incidence greatly enhanced the climb and resulted in an even flatter glide.

Stability and Performance
Directional stability is guaranteed by a large rudder, essential for returning the Center of Lateral Area (CLA) back to its optimal position. The rudder is crucial not only for stability but also for executing flat turns.

After some initial flights for adjustments, the Gladiator began to meet our expectations. Many witnesses can attest that this model consistently achieves three-minute flights on a twenty-second motor run, even without thermals. Remarkably, the motor—a Dennymite—has never been opened beyond half throttle!