CILS not stabilized, moves with pitching deck

I finally had a chance to update and do a quick test of CILS. Fraps was running... of course.

I got out of VR set on this one just to be able to see the finer details like for instance the difference between the CILS needles and FLOLS glide path.

Zoomed it in and set up the weather from hell... I think the WOD was 28 knots (gusting winds)

I did that to have an excuse in case I boltered:sly:

I came in from a bolter/wave-off pattern, good line up, semi descent power control, tipped the nose down at 3nm and the fun started... I was chasing the glideslope needle up and down before realizing that the needles were pitching with the deck... did anyone else noticed that? I might be wrong... Then, when I got close-in The deck pitched down and I did a brilliant move by backing down on power:doh: and off we go...

Short clip: https://youtu.be/oFTCsQ6qdjs

.. I think the WOD was 28 knots (gusting winds) .. .. realizing that the needles were pitching with the deck ..

I'd say, that's what actually would happen at 28WOD and high seas. In those conditions trapping becomes the test of the art.

IRL the CV ILS Loc and GS are earth reference stabilized.

IRL the CV ILS Loc and GS are earth reference stabilized.

In high seas with both a tilting deck and a heaving deck (we ignore roll, yaw and forward boat speed since we slam unto the deck), 'earth reference' in this case of 28 WOD gusting would imply a 'heaving and tilting earth'.

When AOA (speed in the case of the F18 ) in regard to the deck surface and the actual altitude position of the deck are the main references of a proper trapping with the hook not bouncing,

implying there is a fixed groove angle to the deck but not a fixed AOA with 'carrier earth', well, .....

In high seas with both a tilting deck and a heaving deck, 'earth reference' in this case of 28 WOD gusting would imply a 'heaving and tilting earth'.

 

When AOA (speed in the case of the F18 ) in regard to the deck surface and the actual altitude position of the deck are the main references of a proper trapping with the hook not bouncing,

 

implying there is a fixed groove angle to the deck but not a fixed AOA with earth, well, .....

Huh?:huh::huh:

OLD video showing how the FLOLS moves to keep GS stable.

https://youtu.be/7C08dr2oQug?t=529

Not sure what your saying here...

"implying there is a fixed groove angle to the deck but not a fixed AOA with earth"

OLD video showing how the FLOLS moves to keep GS stable.

 

https://youtu.be/7C08dr2oQug?t=529

 

Not sure what your saying here...

"implying there is a fixed groove angle to the deck but not a fixed AOA with earth"

FLOLS compensation to level, would be ok up to a certain point (which even in this YT it is most likely included), else, beyond which, it would make 'a specific AOA towards the deck is needed to keep the hook from bouncing', so many words, redundant

FLOLS compensation to level, makes a lot of sense to give pilot guidance from the top of the groove down. CILS is a more measured instrument that guides to the deck, in this case a moving deck with a wheels on deck angle requisite.

I also posted a link to a paper about ACLS that states 'in the last seconds of the slope, the ACLS (i.c. CILS linked AP) will compensate for the deck movement'

(The YT might also be from the era before CILS)

I also posted a link to a paper about ACLS that states 'in the last seconds of the slope, the ACLS (i.c. CILS linked AP) will compensate for the deck movement'

Bullseye (the needles) is stabilized and even calm weather you don't fly the needles all the way down. The ball is also stabilized. CV1 has minimums like any other instrument approach. If you don't see the ball you go around.

ACLS is a different thing... technically I guess it could fly you all the way down to the deck? I can't imagine sitting there and watching the data link flying my jet... I'd crap myself.

ACLS is a different thing... technically I guess it could fly you all the way down to the deck? I can't imagine sitting there and watching the data link flying my jet... I'd crap myself.

ACLS is for 99% of pilots, who would crap themselves flying a plane down on the deck manually, I'd say.

ACLS is for 99% of pilots, who would crap themselves flying a plane down on the deck manually, I'd say.

I've been out of this for a long time but today I decided to "google"...

just to see what's out there today in carrier aviation. Now they have this JPALS thing coming up (Joint Precision Approach Landing System) - GPS based and I guess will be used by all services.

This includes land based facilities too... sounds interesting, we'll see.

In ACLS modes Deck motion compensation commences 12.5 sec from touchdown. This is cued to the pilot by the 10 sec HUD cue

CILS not stabilized, moves with pitching deck

I started a thread in main DCS/Hornet forum a few days ago. It includes a video.

I haven't seen any bug reports on this issue yet so I thought it might be a good idea to post this here.

https://forums.eagle.ru/showthread.php?t=216441

IRL the CV ILS Loc and GS are earth reference stabilized.

Are you sure?

CNATRA:

Instrument Carrier Landing System (ICLS).

The ICLS is very similar to the civilian ILS, and provides all-weather instrument approach guidance from the carrier to the aircraft. The ICLS uses the AN/SPN-41A (“spin 41”), which has separate transmitters for azimuth and elevation. The azimuth transmitter is installed at the stern of the ship, slightly below the centerline of the landing area. The elevation transmitter is located above the flight deck, aft of the island. The aircraft receiver displays the angular information on a crosshair indicator. The vertical needle of the display corresponds to azimuth while the horizontal needle corresponds to elevation (glideslope). Because the ICLS uses a one-way transmission from the ship to the aircraft receiver, it is susceptible to pitching deck conditions.

In order to differentiate between ICLS and Automated Carrier Landing System (ACLS)

approaches, the ICLS is referred to as “bullseye.”

 

 

 

Automated Carrier Landing System (ACLS).

The ACLS is similar to the ICLS in that it

displays "needles" that provide approach guidance information to the aircrew. The ACLS uses

the AN/SPN-46(V)3 Precision Approach Landing System (PALS), which incorporates a ring

laser gyro stabilization unit. This allows the ACLS to provide highly accurate and stabilized

glideslope and azimuth information in nearly all sea states. The Spin 46 has two dual-band radar antennas and transmitters that provide it with the capability of controlling up to two aircraft simultaneously in a "leapfrog" pattern. As each approaching aircraft lands, another can be acquired.

edit: further research

the AN/SPN-41 seems to be stabilized in Pitch and Roll. Maybe not as good as the other systems.

AN/SPN-41 INSTRUMENT LANDING SYSTEM

The AN/SPN-41 Aircraft Carrier Instrument Landing System (ILS) employs microwave scanning techniques to give guidance information to aircraft

within a 20-mile operating range. The AN/SPN-41 makes safe landings possible under any condition of

visibility that permits the use of visual guidance systems, such as the FLOLS, during the final 200 to 300 feet of descent. The AN/SPN-41 can

also be used to guide a pilot to the acquisition window of an AN/SPN-42 radar for an ACLS Mode I approach and as an independent monitor glideslope

display during a Mode I appreach. Should the AN/SPN-42 landing system fail, the AN/SPN-41 can be used for a Mode 1I approach.

The major components of the AN/SPN-41 iLS include an azimuth antenna and an elevation antenna, both located aboard ship, and an airborne

receiver/decoder (ARA-63). The azimuth antenna is mounted on a torsion bar located on the fantail of the carrier. The elevation antenna, also

mounted on a torsion bar, is located near the FLOLS on the flight deck. The eleva' " antenna is stabilized against the pitch and roll of the

carrier deck. The azimuth and elevation antennas send coded microwave signals into the aircraft approach area astern of the carrier. The receiver/decoder in the aircraft receives the signals, decodes the data, and presents the data

for heads-up or heads-down cockpit display. This display shows the position of the aircraft with respect to the optimum flight path to the carrier

deck.

The scanning action of the transmitted microwave signal is produced by the rapid oscillation, caused by an electric actuator, of the azimuth and elevation antennas. The azimuth signal produces a 2-degree beam, which

scans back and forth through an angle of 10 degrees on either side of the runway center line. The elevation signal produces a 1.3-degree beam that

scans up and down through an angle of 10 degrees to the horizon. Each beam consists of a succession of paired microwave pulses coded to relay the

pointing angle of the antenna at each instant in time. The azimuth and elevation scanning beams define an AN/SPN-41 acquisition

window approximately 7 miles wide and 3-1/2 miles high at a distance of 20 miles astern of the carrier. Once the ap.roaching aircraft passes through this window, it acquires landing gulaance along a path aligned

with the FLOLS and the flight deck. Each time the scanning beam sweeps past the approaching aircraft, the equipment in the aircraft receives

and processes the coded signals and provides a cockpit display of the data. The cockpit display shows the pilot the flight path he must follow to line

up his aircraft accurately with the deck of the carrier. Because each beam completes 3.3 scanning sweeps per second, the aircraft receives this flight

path information continuously. The elevation antenna, while it transmits only between 0* and 100 abovt the horizon, actually sweeps through a 200 arc (150 above the horizon to 50 below). Similarly, the azimuth antenna transmits only during the

middle 200 of a 30 * scan (±150 to either side of the center line). This "dead time" at the end of each scan permits the antenna to reverse its

direction of travel for the return scan. However, each antenna radiates for only one direction of scan. Thus, by driving the antennas 1800 out of

phase, one antenna will radiate while the other is in its back-swing and all of the signals can be transmitted over a single radio channel. An

angle decoder in the airborne equipment is then time-shared between the azimuth and elevation signals, and separate memories for the azimuth and

elevation are updated each time the appropriate beam is received and decoded.

AN/SPN-41 guidance is available to all properly equipped aircraft in the approach zone. Aircraft employing the AN/SPN-41 landing system can

maintain the correct orientation to the approach path while awaiting their turn to land. Because the guidance information is transmitted directly

to and used directly in the aircraft, no data link or voice communication with the carrier is required, thus relieving the workload of the pilot, CATCC, and the already-busy communications channel.

... When used as a primary carrier landing aid, the SPN-41 system is designated the ICLS. When used during ACLS approaches, as is the normal operating procedure during the CV-1 approach, the SPN-41 acts as an Independent Landing Monitor (ILM). The Independent Landing Monitor function allows the pilot to reference ILS azimuth and elevation signals and compare them to ACLS azimuth and elevation indications in the cockpit. If there is a significant difference in ILS and ACLS indications, there may be a problem with one or more systems. Ideally, the ILS and ACLS information displayed to the pilot should match, thus imbuing the pilot with a high confidence in the landing aids...

I knew without a doubt that ivanK was correct. Still, you (RED) made me go to my garage and dive head first into an unorganized pile of loose docs and manuals (unclassed of course :P) just to find some written word on the subject. Well... you already edited your post with bunch of informative details so I'm gonna spare you guys from lot's of boring stuff I've found.

Oh BTW, the azimuth antenna is on the fantail (as you stated) but the SPN41 glideslope rig is on the starboard side halfway up next to "tower" (I think)

Bullseye (the needles) is stabilized and even calm weather you don't fly the needles all the way down. The ball is also stabilized. CV1 has minimums like any other instrument approach. If you don't see the ball you go around.

 

ACLS is a different thing... technically I guess it could fly you all the way down to the deck? I can't imagine sitting there and watching the data link flying my jet... I'd crap myself.

Bullseye is ICLS. Needles is ACLS. ACLS has various modes including automatic control to touchdown.

And stabilization should not be confused with deck pitch compensation. A stabilized system will show the same angle in space regardless of CV orientation. A stabilized system is not deck compensated.

DMC applies predictive bias to the stabilized approach path that is tailored to aircraft type to synchronize airplane vertical motion with the landing platform motion.

Bullseye is ICLS. Needles is ACLS. ACLS has various modes including automatic control to touchdown.

 

And stabilization should not be confused with deck pitch compensation. A stabilized system will show the same angle in space regardless of CV orientation. A stabilized system is not deck compensated.

 

DMC applies predictive bias to the stabilized approach path that is tailored to aircraft type to synchronize airplane vertical motion with the landing platform motion.

Yep, I've just finished reading about this stuff... again. Now I shall remember!

I guess an easy memory crutch is "backwards"... ACLS tadpole that looks like sort of bullseye is NEEDLES, ICLS needles that look like needles are BULLSEYE:thumbup:

Hi, has this ever been reported? I find it impossible to land on a pitching deck during hard wheather conditions. See this example: https://www.youtube.com/watch?v=W5HKQaP5ut8

Yeah I know, the video is an example of the bug. Besides... at 0.5nm I wouldnt put active pause xd

At 0.5nm you should fly the ball.

I remember watching a vid showing a Tomcat driver flying needles to just about "in close". He still couldn't see the ball and was just about to add power (passing minimums) but the LSO's had visual on his lights and told him to keep it coming... a second later the pilot saw " a line of airplanes on the right, couple on the left... looks about right, ball!" and he pitched a 4 wire.:smoke:

ICLS is supposed to move with a pitching deck. It gets you to the point where you can fly the ball the rest of the way down. If you're not flying the ball last 3/4ths nautical mile, you're doing it wrong.

It's not a bug, carrier aviation is realistically just as difficult in the real world.

I just spoke on youtube with one of the devs and he confirmed that this is a bug so he'll pass it on to the team. Hopefully we will see this fixed soon

Hey I just found this thread and since I'm a big fan of this topic I started to google as much as I could and I could find many references that indicate that the ICLS should be stabilized. But there are other places where it is indicated it should not. So does anyone know this as a fact? Can any former Hornet pilot confirm this in any way? This should not be classified at all I guess. Tomorrow I was going to test with the new SC and report a bug if it wasn't stabilized but now I don't know how it is IRL.

I could find many references that indicate that the ICLS should be stabilized. But there are other places where it is indicated it should not. So does anyone know this as a fact?

The SPN-41 based ICLS is a stabilised pulse radar i.e. the datum is parallel to earths surface at the landing point.

I'm not sure of it's limits with respect to a pitching deck.

In general ACLS, is used every Case 3...nothing special about extreme weather as you described as far as ACLS being on or not. However, there are limits as far as pitching deck. Again, there are deck motion limits. If those limits are exceeded (as they definitely were in that extreme pitching deck), a Mode 1 cannot be performed.

 

Finally, if you view the PLAT, you’ll notice on the left side of the screen that the MOVLAS was in use. That is used by the LSOs to manually control the position of the ball. When that is used during pitching deck, pilots land themselves; not with a Mode 1.

This video includes a pitching deck.

The SPN-41 based ICLS is a stabilised pulse radar i.e. the datum is parallel to earths surface at the landing point.

 

I'm not sure of it's limits with respect to a pitching deck.

 

 

 

This video includes a pitching deck.

 

That's what I'm saying, Ram. I found statements for both cases. I was looking for a fact that can eradicate doubts. In this thread's second page there is two sources saying different things. One says that ICLS is susceptible to pitching decks and the other says that is earth reference stabilized.

One says that ICLS is susceptible to pitching decks and the other says that is earth reference stabilized.

I think it's both: it is earth referenced stabilised, but that stabilisation has limits. If the pitching is too much, it can't keep up.