Radar altimeter?

Cockpit, radar, helmet-mounted display, and other avionics
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Gums

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Unread post11 Apr 2019, 15:50

Salute!

RE: Japanese F-35 loss over the ocean.

I can't find a radar atimeter on the beast and assume the cosmic radar can be used along with intertial frame of reference.

I lost two friends at Hill in scenarios where a radar altimeter would likely have saved them. USAF had failed to put in an "old" radar altimeter and was waiting for the new, super duper one that worked up to 40,000 feet whereas the old one like we had in the SLUF only worked below 5,000 feet. We had room allocated, but I do not think the old one had a 1553 data bus output.

As a rule, unless we were on an extremely low route or delivery profile with a pop-up, we would set the red light for 200 feet. Remember, the SLUF used radar altitude as a back up for the primary release altitude calculation by forward looking radar, then it used barometric altitude. In any case, we could select radar or baro for the HUD display, so even with the red light turned off you could see current height above terrain and the round altimeter showed baro all the time.

Crash one was on a dark, moonless night over the featureless desert on the run-in to Eagle Range. The guy was cleared from 20K or so to his range entry and radar bomb run, We did that all the time. The smoking hole was about 6 or 7 miles on the run-in. It was exactly where you would impact if you mis-read the altimeter by 1,000 feet. The vcr tape showed the pilot refining his aim on the groundmap display as he impacted, so task saturation/priorities was a major factor. Nevertheless, having a radar altimeter "light" set for a reasonable altitude would have likely saved his butt.

Crash two was over the lake on calm snowy day. No riffles on the lake, and scattered snow showers looked real spooky. I came across the lake about the same time, and the water reflected the showers, making them appear to be dropping below the surface. Very bad. Pilot aborted a low level and the flight was turning back across the lake. He and I often talked about using the autopilot yo reduce workload when changing flight plan, grabbing new approach plate, etc. So he impacted in a shallow descent, and we all learned about an undocumented feature of our autopilot. Unlike normal 25 deg AoA limiter, the A/P used 13 degrees ( best I recall). So he was heavy and alreafy down low - maybe 1500 or 2,000 feet. Also heavy, with two bags. Plane descended on the limter as he was revising route, changing raios and iff codes. He was also a chase check pilot for the plane in front. A radar altimiter set for anything below 1,000 feet would have saved him.

So that;s my interest.

Gums asks...
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sprstdlyscottsmn

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Unread post11 Apr 2019, 15:56

GCAS would have helped too, yeah? How many hundred million dollar stealth planes need to CFIT (looking at you F-22) before we figure out that GCAS should be standard equipment? Is there a reason to NOT have it be standard equipment?
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Unread post11 Apr 2019, 16:17

https://www.afmc.af.mil/News/Article-Di ... ous-award/

They’ll have it. Probably in next sw release (soon). For those that wonder why not sooner — because they had to adapt and test what was derived from F-16 work previously.

Obtw, jet has continuous radalt, or perhaps I should say, ‘height above terrain’ since I don’t know how that height is derived. IIRC, all the way to something like 40K’.
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Unread post11 Apr 2019, 16:25

Thanks for the update quicksilver.
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Unread post11 Apr 2019, 18:01

Salute!

Looked to me from the F-35 threads that most of the time the height above terrain and basic terrain avoidance is a computed value from a digital map and "system" altitude. We need a technician or Stubby pilot to join these forums.

OTOH, and first outta two points:

- not so keen on an emitter that could be used to find me, but a roll-stabilized ( several options for that) sensor could point st down and measure with one pulse

- the LPI aspects of the cosmic radar can be used as with option one, but would be suspect when over water, especially smooth water. Low graze angle and lack of return. Hell, even our doppler got flaky over smooth water, and it pointed st down.

The TF mode on the SLUF used the forward looking radar with a virtical "slice" of what was in front. In fact you could look at that display to see terrain way out infront that was above the clearance plane even though you were not getting a climb command on the flight path marker. We used that on low levels in hazy days and mountainous terrain. The FPM suggestion, not staring at the E-scope display. Very comforting. Gotta tellya, and my fellow SLUF guys in the Viper cadre will agree that we were surprised at no radar altimiter or TF/TA mode as we had 8 years before.

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steve2267

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Unread post11 Apr 2019, 19:05

How about LIDAR?

Surveyors use LIDAR all the time to measure distances, and in this case altitude would be the vertical distance from the aircraft down to ground.

The Stubby already comes equipped with that orgasmic EOTS... if it can slew to straight down... it could collect that information without giving away the kitchen sink...
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Unread post11 Apr 2019, 19:24

It has twin radar altimeter transceivers

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Unread post11 Apr 2019, 19:44

I think gums nailed it in his first paragraph — like so many things this aircraft does electronically, height above terrain is a ‘system-derived’ number, i.e. it comes from several sources. If you think about what agcas will have to do, it cannot rely on a single source that doesn’t work when the jet is in an ‘unusual attitude.’
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Unread post11 Apr 2019, 20:41

Saute!

Yo ho!! Spud found what I was looking for. Owe you two shots of the "Weed" that Steve brought up with BP.

On two close tours of the plane, I can tellya there are many "patches" that are antennas or sensors of some kind. Our pilot was clueless, heh heh, but the maintenance folks were a little better yet still couldn't name or locate everything.

Steve has a good idea, and who knows, the beast may be using all kindsa sensors we haven't thot of.

Gums now knows.....

P.S. The poor SOB over the sea musta had some warning light and called the abort, then poof! So throw a nickel on the grass.
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Unread post11 Apr 2019, 20:44

Here are the actual F-35C radar altimeter apertures. I'll look for some good shots of the same on the F-35A/B.
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Unread post11 Apr 2019, 21:57

sprstdlyscottsmn wrote:GCAS would have helped too, yeah? How many hundred million dollar stealth planes need to CFIT (looking at you F-22) before we figure out that GCAS should be standard equipment? Is there a reason to NOT have it be standard equipment?


And the F-22 has had the line-in-the-sky variant for years now.
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Unread post11 Apr 2019, 21:59

The civvy EGPWS or TAWS systems are completely passive and utilize a digital Terrain Database and GPS positioning, and generate (HUD) steering commands and MFD displays, cautions and warnings which are very effective.....barring potential information overload situations where auto-GCAS might 'save' the day. I would think it more likely that this aircraft uses some militarized version of this with GPS anti-jam mitigation, encryption, etc.

I 'spect the RadAlt transceivers are more likely tied into the JPALS precision auto-land system for steering command smoothing in the final phases rather than a terrain avoidance system.....just as they are in the civvy GLS systems.

At least the civvy stuff works really well. :D
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Unread post11 Apr 2019, 22:16

'outlaw162' said above: "...I 'spect the RadAlt transceivers are more likely tied into the JPALS precision auto-land system for steering command smoothing in the final phases rather than a terrain avoidance system.....just as they are in the civvy GLS systems...."

This 'suspicion' never seen in any JPALS material I have. Do you have a source for your "'spect" and why would it be necessary. JPALS for one thing guides the F-35C to precision arrested landing on a moving carrier deck via relative GPS.
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Unread post11 Apr 2019, 22:17

steve2267 wrote:How about LIDAR?

Surveyors use LIDAR all the time to measure distances, and in this case altitude would be the vertical distance from the aircraft down to ground.

The Stubby already comes equipped with that orgasmic EOTS... if it can slew to straight down... it could collect that information without giving away the kitchen sink...



I'm not sure you would bother to emit if EOTS and EODAS can both see the terrain.

The other point is that modern radar altimeters are more like crude imaging radars;
the doppler sharpened beam return gets compared to the DTED map.
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Unread post11 Apr 2019, 22:29

Back in dem olden daze the Air Warfare Instructor advice for low level over the sea shipping attacks was to switch off the A4G RADALT. I found it to be a neck pain - deedle deedling away - so only ever used it once - just like the useless RADAR.
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