We have been working on our aileron valves. The primary problems involve old gummy lubrication which caused them to be stiff, dirty dry linkage, and cracked hoses. We removed the valves, disassembled them, cleaned the old dirt and grease off, then lubricated them with gun oil. We replaced worn and cracked hoses. The aileron valve moves smoothly now.
Check out the Aileron valve section under Restoration hints for more info.
Is there adjustability in the aileron valve center leaf, coupling yaw and roll, so the trainer can be tweaked for different aircraft; or is the blue box a generic aircraft system intended to be used without adjusting the simulation model to match a specific aircraft?
Are other system adjustable to match a specific aircraft or generic?
There is little or no ability to configure the aerodynamics of a Blue Box trainer to simulate different aircraft. Ed Link got his private pilot’s license in 1927 and invented the Blue Box in 1929 as a tool to teach the fundamentals of aircraft flying and blind navigation without the need for a dedicated instructor. It was the first real attempt to simulate an aircraft. Prior trainers, if you call them that, did little more that give the pilot a stick to move. One famous Ed Link story is that he paid $50 a lesson to learn how to fly. That expense combined with his knowledge of automated pianos and organs, and his ingenuity inspired him with the idea that simulation could be used to lower the cost of learning to fly. In early flying days, it was also very dangerous for both the instructor and student to learn to fly in actual aircraft.
Today we are accustomed to computer driven simulations where coefficients of flight dynamic equations can be easily changed and the code recompiled to simulate a different aircraft model or to tweak the feel of the simulated aircraft response. It was not so easy back in the Blue Box days. Consider the Blue Box’s aileron, elevator, or rudder valves. Linkage between the stick, and rudder connects to these valves via levers and pulleys. The length of lever arms, pivot point positions of the linkage, combined with the internal port sizes of the valve holes, and the vacuum pressure supplied by the turbine determine the gain of the roll, pitch, and yaw response of the Blue Box Link Trainer. None of these parameters is adjustable. The integral of vertical speed to achieve simulated altitude is achieved by the vacuum pressure simulating vertical speed and the fixed volume of the Blue Box’s altitude air tank.
There are adjustments in the Blue Box; however, most of them are to set the zero point of a function. For example, the straight and level fuselage position can be adjusted at cruise conditions. Regulator bellows can be adjusted via spring tension to achieve a particular instrument reading at cruise.
As WWII approached, and the need to train military pilots increased, there were different Blue Box models optimized for the military customer. Most of this customization was in the layout of the instrument panel in the cockpit. The model Esp was purchased by the Navy and included the first cross point locator instrument. Later, the ANT-18 was made for both Army and Navy customers, with different instrument panels. The basic aerodynamic equations simulated by the vacuum driven device remained essentially unchanged throughout the early Blue Box era.