Forum: F-16 Procedures

I'm having a... discussion with somebody regarding exactly what I mentioned in the subject line. I really only have 3 fairly simple questions (for someone that is familiar with the F-16):

I was under the impression that it takes 8+ minutes to align the INS before takeoff. Is this true/correct?
How long for a complete cold start (until in the air)? A simple breakdown of walk around preflight/in-cockpit preflight would be helpful as well.
What if the aircraft is "on alert", how long until in the air? Basically, what is the fastest they can get that plane in the air?

Any information would be greatly appreciated! THANKS

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From what I recall:

For a full-up alignment in a non-alert aircraft a minimum of 8 minutes is the normal spin-up time. Letting it spin longer in ALIGN mode just increases accuracy. If needed you could move out prior to 8 minutes but with highly degraded accuracy, requiring in-flight updating after takeoff. The post engine start checks may take longer than 8 minutes depending on the mission frag. Our kids in Tucson and Kingsley were always taught to get the gyros goin' ASAP after the main generator came online and stablilized.
Again, it could be mission dependent. If the bird is relatively clean (like for a photo shoot or Super Bowl fly-over), maybe 8 to 10 minutes. For a more complex sortie it could take longer. In the older A-models prior to having a DTC you'd have to hand program the SMS, so for a large load out you could be typing a while!
Early on GD had been quoting unclassified min launch times of 2 minutes and under after engine start. Prior to going on an alert status, the plane is loaded with the appropriate weapons then parked in the alert barn and the INS is aligned in the normal fashion. The plane is now "Hot Cocked" and not moved unless absolutely necessary. During the scramble start the INS is spun up in a mode that uses the last known good position and heading (it's been awhile so I've forgotten what this mode is called, sorry ). The weapons can be programmed either manually or by DTC during the spin-up. Once enroute the pilot can do INS updates using radar fixtaking or landmark overflight techniques. For the GPS equipped birds it's much easier.

Take note that all the stuff I listed is what I recall from my pre-Block 40/Ring Laser Gyro/GPS days. Things may have changed after that. Maybe some of the drivers on the board can correct me or make amendments.

I think standard INU's are a thing of the past, for most F-16's but I am not too sure. When I worked Block 40’s in the mid to late 90’s we had standard INU’s (crappy). I do believe that Block 40’s inherited the RLG’s (much better) that were removed from most Block 30’s because the new EGI was installed. The new EGI allows the pre-block F-16’s access to GPS which was previously available to them. This was a tremendous update for the Block 30’s. The new EGI is pretty neat. A full alignment consists of 4 minutes. Like SimDude was saying, the pilot can “hot cock” the EGI, which will utilize a stored heading alignment and the EGI will be ready in 1.5 minutes (I think). We usually do not do the stored heading since a full one is 4 min for an EGI. After 9/11/01 we did a number of intercepts over Texas and the alert launch was roughly 5 minutes with a full alignment.

Standard INU’s did tend to drift a lot and fell victim to the "Schuler Cycle". We would have to go out and do 90 minute NAV runs to bring them back into the same hemisphere. GPS will keep these INU’s in check most of the time but not always. RLG’s were pretty maintenance friendly and did not drift anywhere near as bad. I can count on one hand how many I have changed out for failures. The new EGI seems to be the same. It is about a 1/3 of the weight of either one and has INS and GPS integrated into the same LRU. It is like install it and forget about it. I forget how to do a drift run……I love it!

Salute wrait-breath! Super question.

Also, super insight by the sim dude and wet sock.

You guys are too young to remember the original INS doofers.

The Double Ugly guys couldn't believe how good the Sluf (A-7D/e) INS was. This was back in early 70's. we would have maybe a mile and a half of nav position error after a 90 minutes flight. Inflight, we could still have 4 or 5 knots of drift due to old man 'schuler', as sumbudy mentioned. Doggone platform would tilt back and forth on an 84 minute period.

OTOH, the A-7 had a doppler system that could be 'coupled' to the INS, just as the GPS does now for the Viper. This did two things: 1) used actual position to feed the inertial system updates that the INS could use to refine it's stability in 'space', and 2) could shorten time to launch, as one did not need to have the INS sense all the movement of the earth spinning underneath it, point to north, etc. Hence, you could launch in a few minutes versus 8-11 minutes.

In fact, you could wait about 30 seconds in the A-7D and then do an 'airborne' alignment that was pretty decent. Could also use a 'stored heading' alignment and do pretty good even without the doppler. Viper was the same. Sit on ramp, store the heading, shut down. Scramble!!!!! Turn on the sucker and use the stored heading, wait for the platform to level and poof! Maybe 2 minutes (this was back in 1979-1984 era).

The RLG doesn't have a lot of the mechanical problems the early inertial units had. No drag on bearings!!! No need to 'torque' the platform to keep it level or pointing north. The second generation AMRAAM strapdown chip was so good it could be 'aligned' within seconds and didn't drift more than 10 or 20 feet in two minutes. Close enough for JDAM, AMRAAM, WCMD, and other neat weapons.

Wraith-breath! Tell your buddy that 8 minutes is good with no GPS-aiding, 2 minutes is good with a stored heading if you ain't gonna fly for more than two hours without a GPS.

out

Sim Dude, GD was fairly accurate on their numbers w/approx 2min. If we were on battle stations we could get wheels up in about 2min., this is with doing a "stored heading" alignment which takes approx 90sec.--and our "A" model ADF birds do have a DTC.

Wet Sock, those standard INUs we worked on at Hill were still worlds more reliable than the standards we were stuck with until we got RLGs. I worked with EGIs on KC-135s, they really are the Sh*t!

Gums, as always your wealth of information never ceases to amaze me!

Gums wrote:

You guys are too young to remember the original INS doofers.

The A-7 doppler sounds pretty neat but at the same time scary...I am glad that I never got to experience the original INS doofers. Maintenance probably had a great time them.

I have learned in my little time here that GUMS and many others are a wealth of information....I just like that I can add my .02 worth every once and while. Mohody you are correct about the EGI's they are the poop...I love them. Every once a while somebody designs something right!

Exactly what I was looking to know guys... THANKS for the info.

c'mon, sock!

Sheesh!

We are talking late 60's technology. The A-7D used the same computer that the Lunar Module used to put Armstrong and others on the moon! Pretty capable machine in its time.

The doppler didn't 'drift'. It measured your rate and vector along the ground. So all you had to do was give it a reference point and you had a near-perfect nav system. The GPS is really good, but it isn't independent. You need all those satellites up there working and lottsa software to crunch the numbers. The doppler was self-contained and couldn't be jammed because it looked straight down and usually from a low altitude.

The big advantage of the new systems is they don't have a lot of mechanical things to worry about. The old systems had gyro-stabilized platforms and antennas, etc. Things like friction on bearings was a big deal. Besides, in 1970 we didn't have clocks that could resolve nanoseconds! GPS wouldn't have been possible without self-contained clocks in the nav system that could crunch the signals within a nanosecond or two (figure about a foot and a half for a nanosecond using light speed).

The GD folks didn't try to 'slave' the INS platform to true north. Every time you tweaked the platform gimbals, you had to deal with precession and friction and ...... So they just let the platform stay pointed where it was when you went to the 'nav' mode. They used the computer to track the 'wander' angle the jet accrued as it zoomed east and west, north and south. Then they cranked in all the angles and we got a decent present position outta the thing.

The new systems don't have any gimbals or bearings - they are 'welded' to the frame of the jet. They use fast computers to track all the body rates, accelerations and such to provide good attitiude and velocity data. We couldn't do that until the mid-eighties.

later,

Gums wrote:

Besides, in 1970 we didn't have clocks that could resolve nanoseconds! GPS wouldn't have been possible without self-contained clocks in the nav system that could crunch the signals within a nanosecond or two (figure about a foot and a half for a nanosecond using light speed).

Well, that is partially true... The A-12, YF-12A, and SR-71 all had clocks that were accurate enough. Of course they were miniature atomic clocks. Made for a lot of fun for the troops recovering a bird after a mishap. The clocks were considered very sensitive material, and the radiation leakage would be a big concern. These clocks were based on the ones in some ICBMs and were part of the Astral Navigation System (ANS) - a star sighting system. They were rather big, heavy, and expensive too so it wouldn't have been economical to install them in hundreds of fighters, but in the 30-some Blackbirds it wasn't too bad.

Kevin
The Ejection Site

At the end of 60's, Mirage IIIEs also used INS and doppler radar (the bulge right under the cockpit is clearly visible), but the drift seems to have been less good. After 90 mn, it could reach 4-5km (never more). Anyway, it was precise at the time.

with new EGI Ins alignment is 4 min Smile

Gums,

Our avionics guys loved the A-7 with the possible exception of AFCS. They cursed that system quite frequently specifically the Roll AFCS. When we got the F-16... they weren't to impressed. Agree with Mohody in that if pilots were at battle stations we could have ours up in two minutes as well.

The older model Block 40's and 30's that you guys are referring to are different technological aircraft than what LM Aero currently is producing. Block 50 (and 60) A/C currently have an EGI that allows a number of different types of alignments. For the most part, 8-10 minutes is still the normal INS alignment time. Recall that an "EGI" is an "Enhanced GPS/INS" subsystem, and even though the 2 systems reside in one box, they still function independant of each other (in most cases). As someone stated, the A/C may be "cocked" - where a Normal INS alignment is performed, and the A/C is shutdown w/out being moved or the INS switched to "NAV" mode. Then, in order to make the A/C "Ready" for flight, the driver performs a Stored Heading Alignment - taking ~ 1.5 minutes.

Now, an In Flight Alignment (IFA) may be performed by the driver in lieu of "cocking" and performing a Stored Heading Alignment. IFA may be done on the ground or in the air. On the ground is considered an "Auto" IFA as the avionics (FCC and GPS Data - plus a NAV Algorithm) align the INS. Manual IFA's in flight (WOW = False) require pilot inputs (Mag HDG) via DED. During MAN IFA, if no GPS is available, the pilot must then perform an Overfly Fix.
As you can see, the avionics, once all data is gathered and ready, IFA will take ~ 5 minutes to complete. However, gathering all of the inputs may take a few minutes. Very Happy

B30 EGI alignment is 4 minutes...Stored heading is 30 seconds..unless you stop in NORM and then its another 4 minutes. Not that I've ever done that!

Gus

Can anyone post a picture of a modern day INS/IRS, doesn't have to be an F-16, although preferred? This is something I have never understood, perhaps a reference to INS/IRS procedures both pre/during/post flight?

Also, how does the INS/IRS negotiate to the HSI data that the pilot can use when not utilizing TACAN, any reference of information would be appreciated. Thank you, anyone?

Forum: F-16 Procedures

INS alignment time and time to takeoff from cold start