Q & A - Questions and Answers
Here we try to give some answers to frequently asked questions about the Starfighter.
It is actually the simple event of two differing airflows coming together and causing a whistle! The engine is surrounded with bypass air, some of which is coming from the engine air bypass flaps, and some is coming from generator access doors and aft fuselage suck-in panels. This bypass air is mixed with heated air coming from within the engine, which has been heated due to it having passed through the compressor and hot section. The result is a mixture of heated air, that which has passed through the engine, and cooler air, that which has passed around the engine, all of which is forced to be mixed when it encounters the convergent/divergent exhaust nozzle system. What we have is two airflows, one heated and faster from the engine, mixed with a slower and cooler airflow, from around the engine, forced out through the exhaust. The result is a whistle. Some call it a howl. What it really is, is J-79 installed in F-104, in operation. The howl is different in the 104 from the F-4 due to the differing amount of bypass airflow in the 104. The howl is also different in dash -19 and -J1K engines due to the differences in the convergent/divergent nozzle systems. It's still J-79, and we all love it.
by Mike Vivian, former USAF F-104A to F-104G pilot, Luke IP and Luftwaffe Exchange pilot
Established in 1911, the Robert J. Collier Trophy was first granted in 1929 as a national award honoring those who had made significant achievements in the advancement of aviation. Collier, publisher, noted sportsman-pilot, and early president of the Aero Club of America, commissioned the 525-pound trophy's design to Ernest W. Keyser of Baltimore MD, and it was originally named the Aero Club of America Trophy. It wasn't until that organization was dissolved in 1922 and the National Aeronautic Association formed that Collier was honored in title. The name became official in 1944, and the award presented once each year by the President of the USA, with the trophy on permanent display at National Air & Space Museum (NASM).
The trophy is awarded for "the greatest achievement in aeronautics or astronautics in America, with respect to improving the performance, efficiency, and safety of air or space vehicles, the value of which has been thoroughly demonstrated by actual use during the preceding year."
United States Air Force and industry team, for development of the F-104
Clarence L. Johnson Lockheed Aircraft Corporation for the design of the airframe
Neil Burgess and Gerhard Neumann of General Electric Company, Flight Propulsion Division for development of the J-79 turbo jet engine
Maj Howard C. Johnson, USAF, for establishing a world land plane altitude record of 91.249 feet (27.813 m) on May 7, 1958 with YF-104A 55-2969 of the 83rd FIS at Edwards AFB.
Capt Walter W. Irwin, USAF, for establishing a world straightaway speed record of 1.404,19 miles per hour (2.259 km/h) on May 16, 1958 with YF-104A 55-2969 "Speedy" of the 83rd FIS at Edwards AFB.
|Initially the GN received 112 aircraft:|
|79 F-104G (Fighter Bomber),
7 to RF-104G modified
|Sep 1963 - Oct 1965|
|27 RF-104G (1st squadron of MFG 2)||Mar 1965 - Dec 1965|
|6 TF-104G||112 total initially|
|36 F-104G (MBB)||49 total additionally||Dec 1971 - Jan 1973|
(on temporary loan from Luftwaffe)
|168 total overall|
Construction number 8222, a Fokker built RF-104G , with the callsign EB+121, but belonging to AG 51, was airlifted to USA 1966 for SLAR (Side Looking Airborne Radar) tests. It was modified into a RF-104G-1 and tested in 1967. The modification consisted in a large under-fuselage pod with the APQ-102 side-looking radar and an additional oblique camera. The nose-radome was lengthened by 1 meter for additional sensors for the terrain-following radar. The program was cancelled in favor for the RF-4E Phantom. The RF-104G-1 was stored at Palmdale and airlifted 1972 in non flyable status to MBB. Re-modification was not practicable. The aircraft was preserved on a pole at the main gate of LVR 1 at Erding AB in 1974 as "80+58" (8058 being the old postal code for the city of Erding).
Jacqueline Cochran to set three women's world's speed records:
In the spring of 1963 Cochran (Colonel, U.S. Air Force Reserve) brought the distinctive red-white-and-blue Starfighter, owned by Lockheed, to Edwards Air Force Base. Colonel Chuck Yeager was running the Aerospace Research Pilot School (ARPS) at the time, and thus was available to assist his old friend in her quest. Flying Lockheed owned TF-104G N104L demonstrator "Free World Defender" over the 15-25 kilometer straight-away course, she reached Mach 1.94 and beat her own record for the distance. Ms. Cochran's Model TF-104G was delivered later to the Koninklijke Luchtmacht (KLu) with the Dutch serial D-5702; later delivered to Turkey on August 25, 1980 with serial "5702"; later recoded to Turkish AF "4-702" and finaly "9-702".
April 12th 1963 she averaged 1.273,10 mph (2,048.88 km/h) over a 15-25 km
straight line course, she reached Mach 1.94 and beat her own record for the
distance. FAI (Fédération Aéronautique Internationale) Record File Number
May 1st 1963 she flew at an average speed of 1.203,94 mph (1.937,15 km/h) over a 100-km Closed Circuit course, taking the women's record away from the French aviatrix Jacqueline Auriol.
Records are only made to be broken, however, and it was not long before Mme Auriol wrested the 100 km record back to France. Jackie Cochran interpreted this as an affront. With a determined tilt to her chin, she returned to the Flight Test Center a fourth time in May 1964. This time, she was flying a completely bare-metal F-104G adorned only with a logo "Lockheed F-104G Super Starfighter" on the nose. Its General Electric J79-GE-11A turbojet was rated at 15,300 lbs. of thrust, which was rated at a top speed of some 1,320 mph. (F-104G serial number 62-12222).
May 11th 1964, she averaged 1.429,297 mph over a 15-25 km straight line course.
This speed was over 155 mph faster than her own previous record and the fastest speed ever attained by a woman pilot.
June 1st 1964 she flew at an average speed of 1.303,241 mph over a 100-km Closed Circuit course, beating the existing women's record of 1.266 mph held by the well-known French Aviatrix Jacqueline Auriol.
June 3rd 1964 she flew at an average speed of 1.135 mph over a 500-km Closed Circuit course. This time, the old record that she broke was her own, established over the same course in 1961.
It is a small wonder that many of her flight records are still unbroken, 40 years later.
Jacqueline Cochran, the world fastest woman
CCV: Control Configured Vehicle F-104G
MBB became interested at an early date in highly maneuverable aircraft. A Fokker-built F-104G c/n 8100 (KG-200, renumbered to 23+91, later renumbered 98+36) was modified by MBB as part of a five-year research program into a control configured vehicle (CCV) and flyby wire technologies. Natural stability was replaced with computer controlled flyby wire systems that allowed the aircraft to be made unstable. This natural instability could then be controlled to provide extra agility. The aircraft was provided with a triple redundant flyby wire system in 1977. The transition from the naturally stable Starfighter aerodynamics was taken in gradual stages, first by adding ballast to alter the center of gravity. In 1980, a complete F-104 tailplane section was then grafted to the spine on the upper fuselage forward of the wing to further destabilize the aircraft. Fairings were added over the wings, and the aircraft was marked with extra Day-Glo panels for high visibility. 20 percent negative stability was finally achieved within the specified limits of Mach 1.3 and 650 knots by the time the trials were successfully concluded. The data gathered was of great assistance to the design of the EFA and was also used during the development of the Rockwell/MBB X-31 test bed. The F-104CCV was then transferred to the Wehrtechnisches Museum at Koblenz on Oct 6.1984.
To start the General Electric J-79 or its MBB J-1K improvement AIR for rotation is needed. This is accomplished via a small starter turbine located on the front frame of the engine and in front of the Inlet Guide Vanes (IGV). This unit is connected to the main shaft and rotates the engine to an RPM capable of providing enough mass airflow through the engine so that when ignition and fuel are introduced the resulting fire is controlled and will escape to the rear and thru the three turbine wheels. These three wheels are directly connected, via the main shaft, to the compressor which is rotating because AIR was forced over the small starter turbine blades by the external AIR starting unit. AIR drives the starter turbine, air pressure connects the starter turbine to the engine main shaft and rotation occurs. Electricity is NOT required to rotate a J-79. Ignition is provided by one of two igniter spark plugs located within the engines burner cans. AIR provides mass airflow thru the engine so that at 10-12% RPM, when the throttle is opened, (that's when fuel is introduced to the burner cans) enough total mass airflow is available to keep the resulting fire from touching any of the sides of the burner cans and no damage results from overheat. At 40% RPM, AIR is removed from the starter turbine. Watch the pilots fingers as the engine accelerates during an engine start, (one finger=10%, two fingers=20%, three fingers= 30% four fingers = 40%, at which time the external AIR starting unit is turned OFF to remove all AIR pressure from the small starter turbine. The engine can now accelerate to its idle RPM which is 67%. (Coincidently 67%= 5.000 RPM) For those of you really interested, 100% = 7460 RPM and is called Military power, which is roughly 10.000 pounds of thrust.
by Mike Vivian, former USAF F-104A to F-104G pilot, Luke IP and Luftwaffe Exchange pilot
Engines installed in supersonic aircraft must deal with a large range of
airflow and inlet temperature. In the F-104, engine air by-pass flaps are
installed which permit some of the air coming into the engine air inlet ducts
to by-pass the engine entirely. These by-pass flaps open fully when the landing
gear is fully retracted and allow excess air to flow around the engine so
that the engine may, more or less, ingest what air it needs. Engine air inlet
temperature is another matter. As the intake air becomes warmer, air density
decreases for any given pressure. The engine fuel control unit takes at least
4 variables into account to determine how much fuel to give the engine. These
are: Compressor inlet temperature (CIT) or "T2", Compressor discharge pressure
or "P3", Engine RPM, and Power Lever Angle. How hot, how much pressure, how
much RPM, and how much thrust is desired. The fuel control uses these variables
to decide how much fuel to provide. As airspeed increases, the engine air
inlet temperature increases. Remember our old friend ram rise. As the air
gets warmer, the air density decreases. Compressor efficiency decreases proportionately.
The engine fuel control, from 92 to 104 deg C inlet temperature, compensates
for this by increasing rpm from 100 % to 104% to make up for the loss in air
density. This restores lost compressor efficiency and provides additional
thrust. This is called T-2 Reset. Reset changes the engine idle speed. This
is done to prevent engine stall if the throttle is suddenly brought to idle.
When the engine inlet temperature exceeds 105 deg C, the engine RPM remains
at 104% even when you retard the throttle to idle. CIT only climbs to 105
deg C for one reason, you are going fast! When you are going that fast, there
is a lot of air being stuffed into the intake. The RPM must be kept high in
order to ingest the air, or it will do the same thing you would do if you
drink a warm coke too fast, it will burp! It, however, will burp somewhat
louder than you. We all refer to airplanes as females. They are less attractive
when they burp. This one is designed not to. Don't worry, as speed and CIT
decrease, the RPM will again begin to respond to the throttle. This is all
Another phenomenon is T-2 Cutback. Again, based upon the effects of CIT, compressor efficiency increases as CIT decreases. At high altitude cruise or at low airspeed and at high altitude, do not expect 100% RPM even though the throttle may be at military. If the CIT is below minus 12 C and decreasing, RPM will begin to decrease from 100%. This is to maintain an adequate margin from compressor stall. T-2 Cutback is seen much less than T-2 Reset since normally when we are flying high, we are going fast.
by Mike Vivian, former USAF F-104A to F-104G pilot, Luke IP and Luftwaffe Exchange pilot
After a glance at my 104G Dash-1, I can't find any mention of the engine secondary airflow system, which is where the A and B-Flaps reside. Perhaps the reason is that their function is normally automatic, and the pilot has no control or indication of whether they are working. Still, the F-104A-D and CF-104 manuals talk about the flaps (though the CF-104 manual isn't fully accurate in its description). Maybe they just wanted to simplify the 104G manual a bit.
There are ten secondary airflow bypass ports located at the mating point of the engine inlet and the inlet duct. These ports are each covered by a movable bypass flap. When these flaps are in the "closed" position (they are set to ¼ inch open), they provide a total of 25 square inch open area for secondary (bypass) air to flow around the engine. Bypass air is used to cool the engine case, cool the afterburner, cool the aft fuselage and cool the nozzle. In the -3, -7 and -11 engines, bypass air is also used to form the diverging cone in the nozzle. In the -19 engine, the longer nozzle petals serve to form the divergent cone, and the bypass air serves primarily to cool these petals, though it does help smooth the effective divergent cone a bit. It is the bypass flow through the nozzle that gives the -3, -7 and -11 birds their distinctive in-flight howl. (Rapid shifting of the IGVs contributes to some of the ground hoots) In all models of the F-104 up to the S-model (and I'm just not sure about the S, because I don't have much knowledge about what they did on that bird's inlet), the two lower flaps, termed the "A" group, open when the landing gear is retracted. With the A-flaps open, a total of 44 square inch of bypass port area is exposed. In the F-104A with the -19 engine (again, I'm not sure what they did on the F-104S), the next two adjacent flaps on each side, termed the "B" group (B-flaps), open automatically when accelerating through Mach 1.8, and close automatically when decelerating through Mach 1.7. On the NF-104A, Joe Jordan's F-104C, and presumably Wing Commander White's CF-104A, the B-flaps were opened by a pilot operated switch. The purpose of opening the flaps was to increase the mass flow through the inlet ducts and thus reposition the inlet shocks to keep the duct from going supercritical (swallowing the shock). This would allow you more margin to fly beyond Mach 2.0 without risking a compressor stall. Joe Jordan commented that when he opened the B-flaps at Mach 1.8, he noticed a momentary decrease in acceleration, which he attributed to the sudden distortion of the airflow, followed by increased acceleration. The increased acceleration was due to a decrease in total inlet drag when the flaps were opened at high Mach.
by Walt BJ, retired USAF F-86, F102, F-104 and F-4 pilot
On 14.December 1959, Joe Jordan reached 103,395.5 feet in an F-104C. He achieved this record on his fifth and last flight of the record series. For the record flight, he started his zoom at an indicated of Mach 2.353 at 39,575 ft., pulled a maximum of 3.15 G, and rotated to a maximum climb angle of 49.5 deg. His afterburner blew out at 70,000 ft. (indicated); he shut down the engine at 81,700 ft., and he coasted over the top at 54 KTS IAS.
Joe's F-104C (56-0885) was modified in the following manner for the record
- An F-104B tail assembly was installed to increase rudder area
- A shock cone extension was added to generate an additional oblique shock
- A switch was installed to allow the pilot to open the B-flaps
- A switch was installed to decrease minimum fuel flow from 500 pph to 250 pph
- T2 reset max RPM was reset from 103.5% to 104.5%
- The afterburner fuel control was trimmed to provide 10% higher max fuel flow
In addition to the modifications, the F-104C's 121 deg. Celsius CIT limit
was waived and the following restrictions were imposed for up to 15 flights:
- Five minutes above 120 deg C
- Three minutes above 160 deg C
- Max temperature 199 deg C
unknown from a discussion group
1.Lt Thomas Delashaw in spring 1962 with Mach 2.5+ and 92.000 ft
I flew this mission at Hahn AB, Germany in the spring of 1962, our Squadron was tasked with a special project to show the East Germans and their new MiG 21s what we were capable of as well as test a new classified U.S. intercept radar capability. All of the squadron pilots had their own pressure suits, Ray Holt and I were picked to fly the mission. We were told the speed restriction (Mach 2.0) was removed and to go as high and fast as possible without damaging the ZIPS or ourselves. The 104s were equipped with tip launchers and we each flew the jets with our names on them; mine was 56-901. This was an officially sanctioned mission and fully briefed. One photo I am attaching talks about a "Kite Intercept" that was just an idea our public affairs officer came up with to include it in Domestic U.S. newspapers. The photos are official USAF. There is a whole lot more to this story, but the salient facts are contained in the attached. Oh! By the way, the top speed was in excess of 2.5 as that was the average speed, and yes the 'SLOW' light was on and it was still accelerating; the insignias and paint on the jet were burned.
By Tom "Sharkbait" Delashaw, in a personal e-mail in 2001
Tom "Sharkbait" Delashaw in front of 56-910 in 1962
F-104D: (Lil-D): no extra tank, no in-flight refueling capability
F-104D: (Big-D): extra tank (630 pounds), in-flight refueling capability
F-104B Gun test: There once was one model, (one of a kind) and just for demo and fitting purposes, which had a gun installed.
When It was decided it was not feasible, it was decided to remove the gun.
So the area behind the electronics compartment (unpressurized) became a metal fuel tank, and the area where the gun had been installed, became room for a metal tank.
And, more importantly, space was gained was the provision for in-flight refueling.
The F-104B was not single point refuelable, therefore not in-flight refuelable, as was the F-104A
By Mike Vivian and Ben McAvoy
USAFE Headquarters in Ramstein AFB had a bunch of offices under the Directorate of Operations (DO).
Our offices were near Ramstein AB, Germany at Kapaun Air Station in Kaiserslautern.
The NATO Training Division was evaluating 9 NATO countries in the STRIKE role.
We went on plenty of “Tac Evals” for many countries and not just F-104 bases.
Most of those bases had an American detachment which was co-located on the base for the weapons security and maintenance. Additionally, the loading crews and pilots of the host base were charged with the safe loading and delivery of the weapons if necessary and if released. Allied Command Europe Directives 75-5 and 75-6 applied. These directives laid out the standardization necessary for the host nation personnel and their weapons associated duties. To ensure compliance with these directives, DOON team members made visits to each base where we observed and certified crews. Lastly we were permitted to fly the host nations aircraft to ensure SACEUR of the reliability and indeed mission preparedness of both crews and aircraft. The DOON team was an all-USAF pilot & weapons loader team assigned to USAFE which evaluated all NATO fighter squadrons that had a nuclear weapons mission and used US nuclear weapons.
The translation of the NATO DOON Team is as follows:
DO = Director of Operations for United States Air Forces Europe (USAFE), Ramstein AB, Germany (2 Star General)
O = Operations which was the coordination division for such things as Training, Exercises, Tactical Evaluations, Tactics, etc.
N = Nuclear which did the evaluations (Written Exams & Flight Checks) of all NATO fighter nuclear-capable squadrons.
We typically gave 1 or 2 check rides a day for 4 days with two DOON check pilots.
There was also a Weapons Loader Evaluation Team which was a part of the unit as well.
By Gene West, former USAF F-104A to F-104G pilot and Luke IP
EAID (engine auxiliary inlet door)
These doors are located on each inlet duct.
The doors are opened only during takeoff to provide an increased air supply to the engine for added thrust.
The only engine that needed this provision was the J79-GE-19 installed in the F-104S of the Italian Air Force.
A three position guarded switch labeled ENGINE AIR INLET DOORS is located on the left side panel, between the UHF- and Autopilot-panel. The switch is spring-loaded from the OPEN and CLOSE position to the AUTO-CLOSE, guarded position. The switch is used to control the hydraulic selector valve in the main landing gear wheel-well. After takeoff and with the inlet door switch in AUTO-CLOSE, the inlet door circuit is automatically energized by a speed sensing switch and the doors will close as airspeed reaches 280 ± 10 knots.
A landing gear ground-air safety interlock switch prevents the doors from being opened in flight; however, if the AUTO-CLOSE system malfunctions, placing the switch to the CLOSE position can close the doors.
An INLET DOORS OPEN indicator light located adjacent to the inlet doors switch illuminates to indicate both doors are fully open and ready for flight. After takeoff, as speed is increased to 280 ± 10 knots, the light will go out as the doors begin closing.
The engine auxiliary air inlet doors unsafe warning light and the master caution light will illuminate after takeoff when airspeed reaches 330 ± 10 knots if the doors are not closed and latched. This light alerts the pilot to reduce air speed below 340 knots IAS (Indicated Air Speed) and to close the doors by use of the manual close position of the switch.
On the ground, the doors can be used for engine FOD (foreign object damage) inspection.
by Theo Stoelinga, member of the "Zipper" team
Take-off with engine auxiliary inlet door open
The "0" or "O" (depending on which source you read) was used to indicate
an aircraft over 10 years old. Some say it means "obsolete", but
I'm not at all sure that was official. Now that aircraft are in service much
longer, they don't use that prefix any more. It wasn't part of the official
serial, just something painted on the aircraft, so 56-0784 would have still
been the actual serial number, even when 0-60784 was painted on it.
When another aircraft comes out 10 years later it would have the same serial number; 66-0784 as opposed to 56-0784. So the first "60-784" gets renamed 0-60-784. Guess they never figured airplanes would be in service 10 years or more when the numbering system was set up.
Up to the Vietnam era, the serial presentation for USAF was to use the last digit of the fiscal and the last 4 of the serial. So 56-0784 was serialed 60784. Even if the sequence went over 10,000, the last 4 were used, so 52-10022, North American F-86D-50-NA Sabre, was serialed 20022. This style goes back to well before WW2. The planes that lasted more than 10 years had an "O" for obsolete added in front. I think that this was official policy. Thus the 0-60784, which would date the picture to 1966 or later. When camo came in, the presentation changed to a small FY and large last 3 as seen on many Phantoms. There are still some USAF planes (mostly tankers and transports) using the older scheme. The "O" for obsolete has been dropped, since almost all aircraft now last more than 10 years. (more than 20, more than 30, more than 40...)
Tech Order 1-1-4 (exterior finishes, insignia and markings applicable to USAF aircraft), it states "normally, the last five numerals of the aircraft serial number are used to compose the radio call number (tail number). If five are not available, the second numeral of the contract year shall be used, followed by necessary quantities of zero to produce five numerals. (i.e. s/n 59-12 would become 90012)".
By Jeff Rankin-Lowe
Boundary Layer Control - artificial lift created by engine air
Normally the lift is physically created by high speed air from the jet's
The difference in the F-104, during landing with full flaps, is that lift is created technically through blown air to the flaps.
Boundary Layer Control (BLC) uses air from the engine compressors last stage, the 17th stage. The air is ducted from high pressure air bleed ports through a pipe to the boundary layer control manifold in the root of the trailing edge flap. It then exits through very small nozzles which direct this high-pressure, high temperature air over the upper surface of the flap when the “LAND” flap position is used. The system operation is completely automatic. This is accomplished by a valve which is mechanically driven by the flap actuator; thus, the position of the valve always corresponds to that of the flaps. The valve remains closed from 0 to 15 degrees flap angle, for angles greater than 15 degrees, the valve moves until it is full open at 45 degrees.
That requires increase of power when the flaps transition beyond the 15 degrees “TAKEOFF” position towards the 45 degrees full down “LAND” position. There is a significant loss of thrust here and requires a high RPM setting to maintain proper sink rate or level flight when the flaps are in "LAND" position.
By Hubert Peitzmeier
The LN-3 inertial navigation system is an inertial navigation system (INS) that was developed in the 1960s by Litton Industries. It equipped the Lockheed F-104 Starfighter versions used as strike aircraft in European forces. An inertial navigation system is a system which continually determines the position of a vehicle from measurements made entirely within the vehicle using sensitive instruments. These instruments are accelerometers which detect and measure vehicle accelerations, and gyroscopes which act to hold the accelerometers in proper orientation.
The functional description of the LN3-2A requires some knowledge of some basic principles of inertial navigation to understand their application to the LN3-2A. The principal component of the system is the stable platform to which are mounted three accelerometers and two gyros. This stable platform is mounted in a system of platform gimbals. The acceleration of the airplane in any plane or direction is measured by the accelerometers and integrated in the computer to obtain velocity. Velocities in turn are integrated to obtain distance. With a known reference point representing initial position of the airplane with respect to earth, this data can be converted to distance and heading traveled, and distance and bearing to destination.
Litton makes the Inertial Navigator system, named LN-3, chosen for the F-104G. It is a lightweight system, which uses a P-200 inertial platform. The inertial navigator system serves the F-104 in three capacities: it is the vertical reference for attitude information; it is the directional reference for heading information; and it determines aircraft position for computation of bearing, and distance to destination. In conjunction with the PHI (Position and Homing Indicator) system, the inertial navigator computes bearing and distance to any one of twelve pre-selected en route checkpoints or destinations. The inertial Navigator is a completely self-contained system which functions without receiving or emitting any electro-magnetic signals that could be detected or jammed by any enemy.
The heart of the inertial navigator is the platform which consists of a four-gimbal, three- axis assembly with the innermost gimbal, or stable element, mounting two, 2-degree-of- freedom gyros, and three mutually perpendicular accelerometers. The platform maintains its vertical axis aligned with the centre of the earth and its north-south axis aligned with true north regardless of aircraft geographic position or attitude. Aircraft geographic position is continuously computed on the basis of signals from the accelerometers. These accelerometers sense aircraft acceleration along the directionally aligned gyro axis, and the computer integrates these acceleration signals to determine instantaneously the speed and distance travelled. In addition to the platform and computer, there is an inertial navigator adapter which serves to resolve various signals supplied to and from the platform. Two control panels for the system are installed in the cockpit. The inertial navigator supplies position, heading, bearing and/or attitude signals to the PHI, attitude indicator, and fire control systems. For the inertial system to perform as a precise navigation system, it is necessary for the inertial platform to be precisely aligned with the true north. A precise alignment can only be made while the aircraft is on the ground. It is also necessary for the flotation fluid in the gyros and other elements of the platform to be stabilized at the proper temperature. Thermostatically controlled heating elements are installed in the platform assembly to control temperature. Appropriate indicator lights are installed in the cockpit to show the pilot when the system has reached operating temperature, and when it is properly aligned. Depending on the temperature of the platform assembly when the system is energized, it may take from 10 to 30 minutes to bring the system up to proper temperature and fine alignments. However, this preparation time is required only if the system is to be operated as a precision navigation system. The time span can be reduced if a slightly degraded navigational accuracy is allowable, or the ground warm-up and fine alignment can be omitted entirely, and the system will function as an attitude reference only. The inertial platform can supply all necessary attitude information in less than three minutes after the system is energized. This is the mode of operation used for alert missions of relatively short radius and duration. Since these missions are usually directed by ground control, precise inertial navigation is not required. The dead reckoning*, TACAN (Tactical Air Navigation), and compass systems provide adequate navigation information, and the inertial system is used to supply attitude signals to the attitude indicator, autopilot and fire control systems.
by Hubert Peitzmeier from various sources of information