Kollsman Airspeed Indicator
This Airspeed indicator actually came from a B727-100 but since they are identical to the ones installed on Lufthansa 707s I chose this one and painted the 410 kts and 420 kts marker black. Both needles are working on this gauge. While the airspeed indicator is simply connected to X-Plane’s IAS data ref the Barber Pole (Max Speed) requires some more attention. Vmo increases initially with altitude as dynamic pressure decreases (=thinner air @ higher altitude) until it is limited by Mmo. Vmo is a structural limit, while Mmo is an aerodynamic limit. Generally, when an aircraft gets to Mmo and above you start to experience things like Mach Tuck or other effects. Since this is an almost linear line it is no problem to program the “Barber Pole” to the graph on the left.
The Gauge uses 2 stepper motors one with an infrared sensor and another the internal stop. Integral 5V lightning is working and new bulbs installed which should hopefully last many years when running them at 3,5-4V.
The three pitot tube pr0bes used to sense total air pressure are on opposite sides of the airplane and are not interconnected. The pitot tube on the left side of the airplane supplies total air pressure to the pilot’ s pitot static operated instruments. The upper pitot tube and the right side of the airplane supplies pressure to the copilot’s instruments. The lower pitot tube on the right side of the airplane supplies pressure to the flight recorder, airspeed switch, Mach airspeed warning switch and the autopilot air data sensor.