Forum: F-16 Design & Construction

Boys, (and old guys here - sorry Gums) NEVER GIVE UP YOUR Low Level skills. As much as someone might say "You'll never go low again," That is the only enviroment that you can truly test the task management skills of your wingman....

Cylon

F-16.net Sponsor

Pumpkin, SWIM (System Wide Integrity Management) monitors LANTIRN NVP and TF-critical systems (INU, CADC and CARA) as a safety check in the FLCS during TFR modes. When SWIM detects TF malfunctions the DFLCS is commanded to perform an incremental 2.0 G fly-up, illuminate the TF FAIL light, display WARN in the HUD, and an aural PULL UP message. After the pull-up, flight control is then manual (not auto-TFR).

Forum Veteran Joined: Nov 07, 2003 - 09:12 PM Posts: 901

Thanks habu2! Come to think about it, I guess to put the trust in the technology to pilot the plane with you sitting inside, at terrain 'hugging' altitude is really some good faith. Not to mention in a mountainous ingress.

cheers, Very Happy

Burn wrote:

Just like anything digital the 'garbage in - garbage out' law applies. I.E. If you are flying down a narrow canyon and the jet thinks it is a 1/2 mile to the left of where it acutally is, the GCAS will probably catch on fire and Betty will bail out because GCAS thinks you are flying underground Shocked

!

It would be interesting to see what would happen if they flew ultra-ultra-low (30-50 ft. AGL) in some place like the Netherelands... Rolling Eyes

We had a problem in the F-15E sims when they flew in Death Valley - the radar altimeter function is done by polling the plane equation of the polygonal surface directly under the eyepoint in a process called HAT - Height Above Terrain. We had not expected 'negative' (eg. less than zero) HAT returns - turns out parts of Death Valley are evidently below sea level...

habu2 wrote:

Pumpkin, DFLCS is commanded to perform an incremental 2.0 G fly-up, illuminate the TF FAIL light, display WARN in the HUD, and an aural PULL UP message. After the pull-up, flight control is then manual (not auto-TFR).

I always thought it was a roll to wings level and auto 4 G fly-up??? Any Block 40 guys confirm???

I pulled the 2.0 G fly-up number right out of the -1 but my change pages only go Change 6 IIRC. Again, this number is for a SWIM-commanded pull-up, not an ALOW warning. Maybe that is what you are thinking of?

CARA = Combined Altitude Radar Altimeter. Combined means that it measures both high altitudes (up to 50K) and low altitudes. This comes from the previous generation of radar altimeters where the electronics did not have the dynamic range and power to do that. So you had either and LARA = Low Alt Radar Altimeter which was good up to 5K' or a HARA which had much more power and was good to 50K, but was not low probability of intercept. Lots of questions on here about how things work. Need to read the TO (-34) for that.

Salute!

Good description, wfo.

Our problem coming from the Sluf and Thud and even the Double Ugly was the "old" radar altimeter worked well and it wasn't installed in the Viper in the early years.

USAF was waiting on the CARA. Hell, we didn't need to know we were at 32,217 feet AGL. We needed to know when we were below 300 or 400 feet. The Viper had the place for the "box" and antenna and such, so we were wondering why we didn't have the 'old" system and then upgrade it later.

Two accidents illustrate the point, both fatalities.

First was a letdown to a radar run at Eagle Range at night. The pilot had the planned descent angle and such to level and hit the tgt. Unfortunately, the tapes looked like he had misread the altimiter by 10,000 feet. He apparently wasn't in the HUD, so was prolly looking at the steam gauge. The tape ended as he was refining the radar aiming crosshair.

Second was a gradual descent into the lake after aborting a low-level mission. A good decision by flight leader, but the troop was on "altitude hold" and foolng with TACAN or IFF when he hit the water. The Viper autopilot at the time would not let AoA above "x" and would allow a gradual descent.

In both cases an old radar altimeter would have turned on a bright red light when the aircraft descended below what you had set. I am not making excuses for the pilots, but you have to use every tool you have.

In the Sluf , in bad weather, I had a pitot-static system freeze up and used the HUD flight path marker and pitch to come down from the TACAN approach fix. Speed was easy, as I had inertial GS and AoA ( different sensor). Sure enough, at 5,000 feet the radar altimeter needle started to move!!! By the time I was at the approach altitude my ports thawed out. But that old radar altimeter was a comfort.

Gums sends...

The AFTI F-16 test airplane had an all aspect radar altimeter (four T/R antennas) that was linked to the FLCS. There were a number of interesting tricks it could play - GCAS, auto attack, etc. That's about all I know about it.

The LARA could easily have been integrated on the Viper early on but there was, as usual, competition for every dollar.

For the record, the TF system only sees radar altitude > 5K' when beginning a let down from high altitude. It "uses" it all the time but usually when TFing the AGL doesn't go over 5K anyway, unless you are letting down, or transitioning from TF to not TF then back into TF when maneuvering or during a weapon delivery or something.

Salute!

Great posts here!

You got it, Cylon, and it was luck of the draw I had that callsign for the infamous SA-6 duel, heh heh. Unfortunately, it turned out we had been smoked by an optically-aimed SA-8 just before we entered the range and we didn't see any smoky SAMs or get any RHAW indications. The staff still awarded us a good grade for our tactics in the tgt area, an played the ground video at the de-brief.

The Sluf TF mode used only the radar and we could select a display that showed our selected terrain clearance compared with what was in front. No autopilot, but we did have the "hard ride" option, etc. Our flight path marker provided vertical steering and course. If we ignored it then bang!! Pk of the rocks is 100%.

We never flew the TF mode in combat, but we practiced it for the WW3 scenario if we had to deploy to Europe. Main mission was interdiction, BTW, and not CAS.

Gums sends...

The modified FLIR/LANA A-7D/K had coupled ATF - but wasn't it down to 200'? Any return that broke the E2 template caused a fly-up.

Salute!

You talking an autopilot mode, Guardbaby?

We had a good autopilot back then, but it wasn't "coupled" to anything like ILS or the TF modes of our radar.

Most pilots didn't take the time to use or even understand the E2 display. Some of us used it to anticipate a pull-up tadpole on the HUD, but that meant looking back and forth on all the displays.

Our primary mission back in the 70's was not extreme low-level interdiction stuff. Sure, we could do it. It just didn't have all the training "squares" that other missions had.

Surprisingly, a few of us used the TF mode on the SAR missions when escorting helo's down low. The "tadpole" steering doofer would tell us to pull up before we could visually see the rising terrain ahead. Otherwise, we flew by looking outside. Imagine that?

Gums sends...