Helicopter rotor blades prevent missile lock

I'd thought it was because the helicopter was going so slow and was so low. (It couldn't have been doing much or the bomb wouldn't have hit it.) There was an interview with the crew in Gulf Air War Debrief. (Awesome Airtime Publishing book.)
 
I know that helicopters were hell for early doppler radars (advancing and retreating blades above an airframe that is close to static against the ground clutter). I have no idea about modern radars and how they'd approach the problem though!
 
Then how did this happen? https://en.wikipedia.org/wiki/1994_Black_Hawk_shootdown_incident

Helicopter blades do give off a different radar return. Some radars can use the information in the return to identify the return as a helicopter. The US had a program to analyse the signal and extract the rotor frequency, and thus the rotor speed and the make of helicopter. I seem to recall it didn't work reliably though.
 
i would guess it's a signal processing problem, or not having the proper software (a in not knowing what you are looking at). I don't think there's any hard physics problem (but i am no RF guy by any stretch of the imagination!). With AESA radars this may not be a problem anymore.
 
sublight is back said:
This is the first time I've heard of this. The helicopters greatest radar weakness, the blades, are apparently its greatest strength when being radar pickled from above.
This F-15E couldn't get a radar lock on an Mi-24 gunship through the rotor blades.

This account as presented is inaccurate or misleading.
AWACS and the F-15 both detected the helicopter rotors - when the helicopters were on the ground with rotors turning. The aircrew decided to use a LGB after IDing the helicopters through their pod. While the bomb was in flight the WSO kept the sparkle on the helicopter as it took off.

So saying they could not "lock" on the rotors is about the opposite of what actually happened. The helicopters were on the ground and the radar saw ONLY the spinning rotors.
 
Indeed. The article says the radar couldn't hold a lock.
While rotorblades Doppler spectrum may help detect the helicopter inside ground clutter (and classify it as rotorcraft), such spectrum is nevertheless very different from a "simple" moving target Doppler spike.
To hold a lock on this, a generic spike-tracking algorithm may not be robust enough.
Airborne radars usually rely quite heavily on Doppler for target tracking, so it may be a bigger problem for them than for ground radars (which usually rely more on range tracking).
 
quellish said:
So saying they could not "lock" on the rotors is about the opposite of what actually happened. The helicopters were on the ground and the radar saw ONLY the spinning rotors.

The pilot specifically said:
What the radar was seeing was the rotation of the rotor blades, but it couldn’t hold a lock.

I don't doubt they can get a lock from a different angle, but I am wondering if "cant get a lock through the blades from above" is a thing.
 
sublight is back said:
I don't doubt they can get a lock from a different angle, but I am wondering if "cant get a lock through the blades from above" is a thing.

From Debrief: A Complete History Of U.S. Aerial Engagements, 1981 to Present:

I reconfirmed the "kill all helicopters" call from COUGAR several more times. Use of the word "kill" was very rare at this time; we were used to hearing "identify" or "investigate" in conjunction with AWACS' taskings, so the "kill" directive made me a little uneasy. On every radio transmission with her (AWACS controller) I continued to reconfirm the clearance to kill. We turned southwest towards the location of the coordinates, which were about 80 miles from our current position. The area was due south of H2/H3 airfields, out in the middle of nowhere.

On the way down to the area I start to get very intermittent contacts on the radar, but they would come and go off the radar. I tried tightening down the search to a single bar scan to break out the targets, and I was getting hits on and off. What the radar was seeing was the rotation of the rotor blades, but it couldn't hold a lock. So I decide to see if I can see them in the TARGETING pod. I'm doing good of F-4 radar "tilt and gain," but with the pod, and this is with an extremely limited LANTIRN pod air-to-air capability. I would look at the intermittent hit on the radar, and see it, extrapolate two degrees low and ten degrees left. I could then command the pod there. Training counts for everything... there they are! We're at 50-60 miles, at about 8,000 feet, and I can see two of the helicopters, or more correctly their rotors spinning, in the pod. So I transition almost entirely to the pod, since the radar wasn't much help at that point. Our mindset was turning to a ground attack...with what we're seeing and the information from AWACS , I don't think either of us were thinking anything else.

At about 40 miles we started to pick up a bit of an undercast, so we started to take it down. "TB" directed number two to remain up in a high cover in air to-air mode, using the radar and eyeballs, to clear the area around us, and to act as a comm repeater if we lost contact with COUGAR down low. As we ducked under the weather, I'm not sure that anybody saw us - more like noise activated AAA - but we staricd to pick up some lighi AAA, nothing heavy or accurate. I pass to COUGAR thai I have contact with two helicopters, and I reconfirm we are to KILL all helicopters... Still affirmative...by now we are down to about 4,000 feet and snokin. We're doing a little over ihe Mach, and our manuals tell us that we arc not to drop these babies at anything over .9 Mach. The fact of the matter was we still had not totally committed to dropping a GBU-10.

We knew they appeared to be on the ground in the radar. AWACS is telling us they are on the ground dismounting troops. So by 15 miles we are of one mind; this is going to be a ground attack. We confirm one more time with COUGAR that, "These are helicopters, dismounting troops, that there are troops in Contact NOW, and KILL all helicopters." Okay, light em' up! We're doing Mach 1.2ish, and I get the first release cue. "TB" queries me as to whether I'm good for a release. I've got good laser ranging to the target, but I hold off for just a little bit—no technical reason, just a gut feeling. Finally, I call "Cleared to Pickle," and when "TB" pickles-off 2,000 pounds the aircraft immediately responded by shuttering and lurching upward.

After release "TB" executes a 30 to 45 degree left designator turn. Not much more than that, as we are inclined to stay close and immediately support the extraction of the friendly Special Operations forces, or engage the second helicopter, if necessary. I keep the laser spot right on the base of the rotor mast, where the heat from the transmission is very bright in the IR return. The Time-To-Impact counts down to zero, and "TB" says, "Keep it going Chewie, no impact." It seemed like it was easily 10 more seconds before "the GBU-10 that could" came into view on the display. It appeared to be angled nose high, then starts down and penetrates through the rotors, and the scintillation of the rotors as they disintegrated was easily discerned in the LANTIRN pod. The GBU then enters into, or very near to, the cockpit of the helicopter, and is just exiting the bottom of the aircraft when the fuse delay functioned.

Through the entire TOF of the weapon, there was nothing to lead me to believe this aircraft was airborne or even moving, nor was I looking for any clues. It was an easy, easy track. I perceived no line-of-sight rates, and no shadows. I had fantastic IR contrast and was continuously lasing, so I was very focused on the aimpoint. It wasn't until I saw the weapon exit the bottom of the helicopter that I realized it was airborne. I'm still in the pod when the 2,000 lbs of GBU-10 "whupass" functions and the IR signature blooms.

There was a tremendous explosion, and the helicopter just disintegrated in a huge fireball. We are looking at right 2:30 when we see a pillar of flame of almost Biblical proportions. "TB" immediately gets us into a hard turn to the left, and is already setting up to engage the second helicopter while I'm on the radio transmitting, "COUGAR, PACKARD. Splash one helo, expect second splash in 30 seconds!"

An unbelievable and equally unexpected response from COUGAR, "PACKARD 41, confirm you VID the helicopter as Iraqi ."

From Strike Eagle: Flying the F-15E in the Gulf War:

Bakke: When they called we were in the process of hitting an SA-3 site near Al Qaim. We were mapping the site and starting our attack when AWACS called us with 'priority targeting.' We broke off the attack and sent our wingman to high cover-they had twelve Mark-82s 82s and we had the targeting pod with four GBU-10s [2,000-pound smart bombs]. I plug in the coordinates AWACS gives us and they are in the middle of a no-drop zone-I read that as a zone where special forces are operating. I confirm with AWACS that these coordinates dinates are correct and they are in a no-drop zone. She came back and said, 'Roger, those are the correct coordinates."'

Bennett: "Her call sign was Cougar." Bakke: "Yeah, so I continued the conversation with her-this isn't verbatim but close-she said, 'There are three Iraqi helicopters dismounting mounting troops with possible friendlies in contact. Kill all helicopters.I reconfirmed with her, 'Kill all helicopters?' She came back and said, 'Roger, kill all helicopters.

Bennett: "The reason Dan is repeating that is because it is real uncommon to get an order to kill [all helicopters]. You never hear anything like that because you always ID them."

Bakke: "At that point, TB is starting to the coordinates and we aren't saying anything back and forth."

Bennett: "I am talking to my wingman real quick because we were getting into a lot of weather. Since he had dumb bombs there was no reason to bring him down there with us. I wanted him to stay above the weather. Also, once we got below 10,000 feet we couldn't always talk to AWACS. I am telling him to relay whatever we say back to Cougar and we'll let him know what is going on. By now we are dropping down through the weather at mil power. We're moving pretty good when we get down below the weather. There was no doubt in our minds from the radio transmission from AWACS that we had to get there in a hurry. Normally, we would be a little cautious because we were going into the Sam's Town area, but we're in a hurry. If they were in contact up there, time was of the essence. There was a lot of stuff up there that wasn't good, but we're ramping over there in mil power going about 600 knots. Then, when we're about fifty miles out, Dan gets contacts on the radar."

Bakke: "On two of the three [helicopters]."

Bennett: "We talked real quick, back and forth, and it was like, well, let's just let a bomb go if we can ID them as helicopters."

Bakke: "I called AWACS and I reconfirmed with them that we have the helicopters. Actually, what we have on radar contact is their rotor spinning."

Bennett: "We aren't getting an air speed readout yet on them. We are pretty sure they are sitting on the ground. [Their IR image is two-dimensional.] We said, 'Okay, let's go in there.' If he [Bakke] can get them on the targeting pod, we'll let a bomb go. That way, if they take off and move, at least we will get their attention and divert it from our guys on the ground. But, if they start moving, we'll come back and shoot them with an AIM-9. Our main goal was to get something thing on them fast, to let them know we are there. At this time Dan is working with the radar and about the time we are deciding that we are going to drop a bomb, we are going through 10,000 feet. Finally, we break out of the weather at about 3,000 feet-it was not good weather that night. Just as soon as we break out, the triple-A starts coming up. We're about twenty miles from the contacts and then, at around fifteen miles, Dan's got them in the targeting pod."

Bakke: "We didn't make a map; you can cue the targeting pod from the air-to-air radar. You can get a designation just using the pod. I'm looking solely through the pod now. It's infrared and the helicopters are hot and the rotors look like discs. I have two of the three and we're assuming they are on the ground. At this point, we can still hear AWACS talking but it is broken-we're expecting our wingman to pass on anything important. We go in, get a release cue, TB drops a long ball [bomb] and starts a left-hand turn so that I can track the target."

Bennett: "I'm turning toward Syria [hands showing the banked turn]."

Bakke: "I'm doing the laser, putting it on the white spot, waiting. We released the bomb about six miles away and it has over thirty seconds time of flight."

Bennett: "Meanwhile, I'm looking at the radar because he is concentrating centrating [on the image in the pod]. About ten seconds after the bomb comes off, I start seeing an air speed readout on the radar. I'm thinking, this thing is moving; go back into air-to-air and bring up an AIM-9. Meanwhile, Dan is tracking it big time, but I'm thinking, shit, this bomb is never going to make it. I'm starting to jink around-they're firing some triple A-but I can't jink too much-it's hard enough back there keeping the laser on the spot without me giving him any more problems."

Bakke: We jink off to the left and it appears to me that this guy is moving. What in fact happened, according to the guys on the ground, is that the helicopter was at 800 to 1,000 feet when the bomb impacted. It hit just forward of the center of the rotors, right in the cockpit. And I guess, if you've ever seen a James Bond movie where the helicopter-the model they film just vaporizes and disappears, appears, that is exactly what happened. At this point, we have already figured out that this guy was airborne so TB goes into a hard left-hand turn and calls up an AIM-9. Also, we tell our wingman to come down and drop six Mark-82s on that spot to stop any troops that have been let off."

The helicopters were on the ground and not moving.
The crew prosecuted the engagement as a ground attack.

There are other published accounts of this engagement, including after action reports. "Debrief: A Complete History Of U.S. Aerial Engagements, 1981 to Present" is the supposed source of the article that was linked to in the original post of this thread.
 
That first quote says the helo was actually airborne but they didn't realize it until impact.

It wasn't until I saw the weapon exit the bottom of the helicopter that I realized it was airborne. I'm still in the pod when the 2,000 lbs of GBU-10 "whupass" functions and the IR signature blooms.
 
TomS said:
That first quote says the helo was actually airborne but they didn't realize it until impact.

The target was on the ground at the beginning of the attack, and at weapon release. During the flight of the bomb to the target the target became airborne.
 
Just a note...I'd never read this account. This...

An unbelievable and equally unexpected response from COUGAR, "PACKARD 41, confirm you VID the helicopter as Iraqi ."

just makes my stomach hurt.
 
Jeb said:
Just a note...I'd never read this account. This...

An unbelievable and equally unexpected response from COUGAR, "PACKARD 41, confirm you VID the helicopter as Iraqi ."

just makes my stomach hurt.

.... there is more to it, and it would not go down so easy.
 
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