[Test-Pilot Notes] issued 1st February 2023
Did you know that the SR-71 'Spikes' were part of the AICS (Air Inlet Control System) which provided a variable-gerometry air inlet system? This was required due to the extended speed and altitude envelope of the aircraft.
The AICS not only provided a flow of subsonic air to the engines, but also contributed to the overall powerplant thrust. The system included a set of inlet bypass and bleed 'doors', along with the spikes, and operated automatically under normal conditions.
The spikes were capable of moving aft and forward as a function of Mach number. While doing so, it varied the size of the inlet throat areas and the position of the shock wave extending backwards from the spikes tip. At altitude below 30,000 feet and speed of less than Mach 1.4, the spikes were locked fully forward. Above 30,000 feet the spikes began to move aft as Mach no. increased above Mach 1.6, biased with angle of attack, angle of side slip and vertical acceleration. At Mach 3.2, spikes position was 26 inches aft of its full forward position, increasing the overall inlet area from 8.7 square feet to 18.5 square feet.
The exciting part is that the spikes system and other related elements are incorporated in the VSKYLABS SR-71-TB flight dynamics model, affecting thrust, drag and other powerplant considerations.
The VSKYLABS 'Test-Pilot': SR-71-TB is a highly advanced 'Mach-3' testbed, stretching X-Plane 12 flight dynamics and physics capabilities to its extremes!
Stay tund for much more!
JMH
