Figure 6
1. PVD—OFF (Figure 6)
The SR-71 was not created to be a night-flying reconnaissance aircraft. For many years, its primary sensors were camera systems that required daylight and high sun angles (minimum shadows) for good photography. The night training that crews received at Beale was basically an orientation in flying the aircraft at night. It wasn’t until a high-quality radar imaging system—the advanced synthetic aperture radar system (called ASARS-1, pronounced “A-sars one”)—was developed for the SR-71 that we could advertise a day/night/all-weather reconnaissance capability.
Initially, crews were not overjoyed about operational night flying with the SR-71. Crews verbally resisted the increased night flying because they thought it was dangerous and increased their exposure to unnecessary risks. Cockpit visibility wearing the pressure suit was minimal at best. Add to that the lack of any horizon at seventy thousand feet at night, the critical nature of bank angles over thirty-five degrees, and the ever-present possibility of unstarts occurring; these were all real concerns to the crews. They were convinced the next SR-71 incident or accident would involve operational night flying.
Crews talked openly about the inherent dangers of flying the SR-71 at night. As a result, night simulator missions were developed to make the crews aware of the dangers. It wasn’t until several crews reported reaching bank angles over forty-five degrees at night that they started to look for help. They described their problem to Lockheed tech reps, and soon they had a solution for the crews to evaluate.
Lockheed mounted a prototype device between the seats of a T-37 and had several Habus evaluate its effectiveness during night flying. They modified the simulator as well. The crews enthusiastically received the new system, and the final product was installed in all the SR-71s during the early 1980s. It was mounted on the right side of the front cockpit canopy sill and called the peripheral vision display (PVD).
The PVD was a night attitude orientation device. It projected a laser-generated, thinly focused red line parallel to the horizon, across the pilot’s instrument panel. The PVD was never intended to be part of the pilot’s instrument crosscheck. Instead, the pilot perceived the laser line indirectly by peripheral vision and subconsciously supported spatial orientation, just as a visible outside horizon supports orientation during the daytime.
The pilot adjusted the laser beam horizon line in brightness, thickness, and vertical positioning across his instrument panel. The PVD received input from the ANS to project pitch and roll movement. As the aircraft pitched and rolled, the red horizon line also pitched and rolled across the instrument panel and gave the pilot instant orientation. The horizon line flashed to warn the pilot if the pitch angle exceeded thirty-five degrees nose up or fifteen degrees nose down.
2. ILS—OFF
A standard Air Force instrument landing system control panel was installed. Pilots could fly instrument approaches down to weather minimums of a two hundred-foot ceiling and one-half-mile visibility with the ILS, although many have landed in weather lower than that at both Beale and Mildenhall. Okinawa rarely had ceiling or visibility that low. On a few high-priority missions, crews took off in marginal weather, knowing it would improve by the time they returned to base. Crews would count the number of runway lights they could see looking down the runway. If the pilot could see six or more runway lights from the cockpit, the crew was permitted to take off.
There was always subtle pressure on crews to land at the home base regardless of how bad weather conditions were. If an SR-71 landed at any other location, it took a minimum of one KC-135Q tanker and around twenty-five maintenance and civilian personnel to get the plane ready to go again. If there were maintenance problems as well, the number of tankers and personnel grew considerably, depending on the repair work needed. An engine change required an additional C-141 to fly the engine in.
3. SAS—OFF
The stability augmentation system (SAS, pronounced “sass”) was designed to do exactly what the name implies. During Mach 3+ flight conditions, the SR-71 experienced many small changes in attitude due to air loads or control input. These attitude changes were sensed by three pitch-rate sensors, six yaw-rate sensors, and two roll-rate sensors. Small attitude changes detected by these sensors were sent to computers, which in turn electrically commanded transfer valve position. Transfer valves were used to convert the electrical signals into a proportional hydraulic flow and move control surface actuators. All this happened in a fraction of a second.
Aircraft controllability without SAS was demonstrated to Mach 3.2, although it was difficult to fly. At supersonic speeds, aircraft control with the SAS off was extremely sensitive. It was necessary for stick control movements to be as small as possible. A pitch change of only one degree at Mach 3.0 became an instant three-thousand-foot-per-minute rate of climb or descent. Pilots who have experienced a complete loss of the SAS at high Mach numbers say they had their hands full just to keep the SR-71 upright. That’s precisely why the SAS had triple-redundant computers. Flying subsonic without the SAS was not difficult, although the aircraft tended to wallow around slightly.
The SAS panel was located on the upper half of the autopilot on the right console. Engaging each SAS switch energized the pitch, roll, and yaw transfer valves, permitting hydraulic flow to fine-tune the flight control surfaces. The SAS switches were turned OFF at this point because large taxiing movements on the ground would cause the rudders to slam full deflection because of the yaw-rate gyro’s input.
4. SAS Lights—TEST
Located on the SAS panel was a TEST button. The pilot pushed the button to check for illumination of all the SAS panel warning lights.
5. Autopilot—OFF
The pilot checked the lower half of the automatic flight control system panel to make sure the pitch and roll autopilot switches were OFF. The basic autopilot had two solenoid-held switches, one for the pitch axis and the other for roll. Once both switches were engaged, the control stick was disabled. Serrated pitch and roll wheels on the autopilot panel controlled aircraft movement. The pitch wheel rotated fore and aft, and the roll wheel rotated left and right, corresponding to the plane’s movement. The pitch and roll wheels permitted small adjustments by moving the aircraft approximately one degree in pitch per fifteen degrees of wheel rotation and one degree of roll per eight degrees of rotation. To aid in making small inputs with the fingers to both wheels and to keep from tiring out the pressure suit–enclosed right hand, a clear plastic hand rest folded down in perfect position to rest in the heel of the pilot’s hand. The pilot flew the SR-71 by rotating the pitch wheel fore or aft with his index finger and the roll wheel left or right with his middle finger.
It was necessary to engage the basic pitch-and-roll switches first before any of the subfunctions of the autopilot would operate. Solenoid-held switches on the autopilot controlled two subfunctions of aircraft heading and navigation. When the HEADING HOLD switch was engaged, the aircraft would hold the heading at the time of engagement.
To the left of the HEADING HOLD switch was the AUTO NAV (automatic navigation) switch. It was an either/or situation between these two switches, as only one could be on at a time. Engaging the AUTO NAV switch disengaged the HEADING HOLD switch and vice versa. In the AUTO NAV mode, the astroinertial navigation system ran the show and navigated the aircraft by banking and turning.
The SR-71 had no altitude hold or auto throttle capability whatsoever. It took some adjustment learning to allow the AUTO NAV to fly the programmed track by banking while the pilot flew the SR-71 with the pitch wheel and moved the throttles to increase or decrease the Mach.
6. TACAN—T/R
Rotating the TACAN control knob to the T/R (transmit/receive) position displayed the range and bearing to a selected ground station.
7. Interphone panel—Set
The communication and navigation equipment was scattered throughout both cockpits. The ILS receiver and outer marker beacon lights were located in the front cockpit. The RSO had the identification, friend or foe (IFF) transponder and high-frequency radio in the back. Each cockpit had a TACAN and UHF radio. A very high-frequency (VHF) radio was added to the front cockpit in the early 1980s.
An interphone panel in each cockpit allowed the pilot and RSO to individually select a variety of options for either listening or transmitting on any of the communication radios. A hot mike (“HOT MIC”) position on the interphone panel allowed the pilot and RSO to have continuous interphone conversations. Depressing the spring-loaded CALL button would override all signals received by the other crew member. Pushing the CALL button was reserved for situations where one crew member needed to communicate with the other immediately without worrying about switch settings on either interphone panel.
The J58 engine compressor inlet case contained a two-position inlet guide vane (IGV) system. The guide vanes were either in the axial position, which was normal for takeoff and acceleration to intermediate supersonic speeds, or in the cambered position, which was normal for high-Mach cruise.
The IGV axial position (parallel to the airflow) resulted in more thrust. Actuation to the cambered position occurred automatically during acceleration when the compressor inlet temperature reached 85 to 115 degrees Celsius, which was around Mach 1.9. However, the shift from the cambered position back to the axial position was prevented if the IGV lockout switch was positioned to LOCKOUT. You will better understand the use of the IGV lockout switch after reading the chapters dealing with accel and decel.
Each engine had an amber IGV light on the instrument panel to inform the pilot what position the IGVs were in. When a light was illuminated, the respective engine was in the axial position; extinguished, it was in the cambered position. During start and at idle power settings, the IGV lights were out. As the throttles moved forward for takeoff, the IGV lights came on when they shifted to the axial position. During the accel to Mach 3+, the IGV lights had to be off passing through Mach 2.2 (150 degrees Celsius on the CIT gauge) or the mission had to be aborted.
9. Cockpit pressure—Set
A two-position lift–lock CABIN PRESS switch was located on the pilot’s right console and on the RSO’s instrument panel. The twenty-six-thousand-foot position was preferred for better cockpit and bay air cooling, as well as providing a less severe pressure change if one had to eject at eighty thousand feet. The switches in both cockpits had to be in the 26,000 FT position to be able to select the twenty-six-thousand-foot cabin pressurization schedule.
If either crew member selected the 10,000 FT position, the ten-thousand-foot cabin pressurization schedule was then actuated. That way if one crew member suspected the other of becoming hypoxic (suffering from lack of oxygen), he could get the cockpit down to an oxygen environment of ten thousand feet.
10. VHF radio—TR and set
Placing the switch in transmit/receive (TR) applied power to the radio. The pilot set in the desired VHF frequency.
11. Canopy seal—OFF
An inflatable seal was installed along the edge of each canopy frame. The seal was inflated by engine bleed air pressure to provide an airtight seal between the canopy and the canopy sills and windshield. The seal lever was located in the right forward corner of each cockpit and was used to inflate or deflate the seals. At this point in preflight, the canopies were open before engine start, and the seals were OFF.
The right console took approximately one minute to check. Now we’re ready to crank up the engines.