Recommended trim for cat shots?

[Nealius]

Of course half flaps, TO trim set, launch trim set exactly as per NATOPS (16NU for <44,000lbs, 17NU for 45,000~48,000lbs), full AB, but I'm still dropping 10~20ft once off the deck. 

What's everyone's recommended trim for cat shots off the supercarrier? It seems to not match with NATOPS. 

[rob10]

Those are good recs.  I usually DON'T use AB off the deck, just MIL power and at 16-18 NU you should be good.  May drop a little off the deck, but as long as you leave it alone it will get you airborne and then you can take over.

[Nealius]

In real-world videos I typically don't see any drop once leaving the deck, with aircraft rotation between release from the shuttle and the end of the deck. 

Edited August 8, 2023 by Nealius

[Grodin]

4 hours ago, Nealius said:

Of course half flaps, TO trim set, launch trim set exactly as per NATOPS (16NU for <44,000lbs, 17NU for 45,000~48,000lbs), full AB, but I'm still dropping 10~20ft once off the deck. 

What's everyone's recommended trim for cat shots off the supercarrier? It seems to not match with NATOPS. 

Do you have enough headwind, is the ship moving? Turn the ship towards the wind like they often are in reality and you might see quite a bit less drop.

[Nealius]

2 minutes ago, Grodin said:

Do you have enough headwind, is the ship moving? Turn the ship towards the wind like they often are in reality and you might see quite a bit less drop.

29kts over the deck. I even tried going higher on trim, 17NU for 43,000lbs GW, still dropped about 10 feet. 

[Grodin]

9 minutes ago, Nealius said:

29kts over the deck. I even tried going higher on trim, 17NU for 43,000lbs GW, still dropped about 10 feet. 

Interesting i'll try it too when i get home.

Very little drop in the real takeoffs indeed.

 

[Figaro9]

According to bn, Cg is a little too far ahead in edf18 iirc, which leads to too high takeoff speeds.

[Nealius]

I was kinda curious about the end speed as well, I was showing 180kts off the deck, but I don't know anything about end speed calculations. So it's a CG bug in the flight model then?

[Foka]

Correct wind over deck. Lot of people ignore that factor when setting up a mission.
 

[Nealius]

11 hours ago, Foka said:

Correct wind over deck. Lot of people ignore that factor when setting up a mission.

See post number 5.

[SickSidewinder9]

The time/video link shows a Hornet with few external stores and what looks to be a pretty stiff wind over the deck.

Not sure why you wouldn't drop a few feet normally.

Edited August 11, 2023 by SickSidewinder9

[Nealius]

Cat end-speed should allow for rotation to begin while main gear is still on the deck. Here's footage of a legacy Hornet with a combat load launching (5:02). No noticeable sink, and at 5:11 you can see the nose begin rotation while the mains are still on the deck. In DCS it feels like rotation doesn't occur until the entire aircraft is clear of the deck.

It might look like there's some sink, but that's just the tail-end of the aircaft rotating. The trajectory does not sink, and the tail rotation should only be a couple feet, not 10~20ft (IIRC the radar altimeter is towards the aft of the aircraft).

These combat loads are similar to what I run, usually replacing the "ugly" tank with a GBU38.

More legacy launches with combat loads, no noticeable sink. Second half of the video is Rhinos.

 

Edited August 12, 2023 by Nealius

[SkateZilla]

In the Top Video, the nose doesnt "rise", it's released from strut compression from the cat shot.

When the Catapult launches forward w/ the launch bar attached, it pulls the aircraft forward as well as compress the nose gear a little, the catapults 3 and 4 end way before the end of the deck, so once launch bar leaves the shuttle and retracts, the nose gear also decompresses back to resting weight state, you can also see if you go slowly Frame by Frame at one point, main gear is below the deck line from decompression also, there is a launch droop but its marginal due to the AoA and  it's weight / loadout dependent.

Post a track of your launch, so we can replay it,

most of the shots in those videos appear to be more than half flaps.

 

Edited August 12, 2023 by SkateZilla

[Nealius]

1 hour ago, SkateZilla said:

most of the shots in those videos appear to be more than half flaps.

Second video? Only 2-3 were Legacies (all VFA-15 jets). The rest were Rhinos.

Track attached--first a cold start with rearm before start, then switch to a cat start slot. I'm seeing significant differences between Cat Start and Cold Start post-shot behavior. Same payload, same GW (minus the fuel used on start/taxi from cold), same trim settings. Straight out, hands-off stick until required to eliminate clearing turn variables.

Cold start trim LEF -12, TEF -30, AIL -30, RUD 30 inwards, STAB +16 (for 43k GW per NATOPS). Post shot behavior shows max AoA around 5.4 with the FPM barely reaching the horizon, then settling about 1 degree below horizon which would result in CFIT without aft stick.

Cat start trim LEF -12, TEF -30, AIL -30, RUD 30 inwards, STAB +16 (automatically set by DCS). Post shot behavior shows max AoA around 6.1, FPM settles about 1 degree above the horizon, no aft stick required by the pilot. At least I'm pretty sure I didn't pull aft stick, but I can re-run it completely hands-off until crash/past 500ft if needed.

Additional Q: Is there something particular with the flaps/FCS reset/FCS bit/TO Trim flow on startup? I'm following an older SME-vetted flow that goes flaps half, FCS reset, FCS BIT, (flaps auto and control surface check, then flaps half, which I skip), TO Trim. NFM-500 has a flow that goes FCS reset, flaps auto, FCS reset again simultaneously with paddle, flaps half, FCS BIT, TO Trim. DCS Manual has a flow that sets TO Trim before FCS reset and BIT. None of the flows are agreeing with eachother. 

Video as well:

 

43GW-Cat1-SP.trk

Edited August 12, 2023 by Nealius

[SkateZilla]

did you reset trim during startup to account for re-arming?

[Nealius]

7 hours ago, SkateZilla said:

did you reset trim during startup to account for re-arming?

Rearming before engine start; battery wasn't even on. 

After engine start I went through the checklist as on any startup with FCS reset , FCS BIT, then TO Trim, then set stab trim as required for cat shot.

Edited August 13, 2023 by Nealius

[Nealius]

Update: Testing on fresh mission in Caucusus, just Hornet client slots and the Supercarrier, hands completely off the stick. 27kts WoD. All aircraft spawned with the same asymmetric payload (43,000lbs GW). There is still a difference in post-shot behavior in all cold starts. Cat starts and ramp hot starts are normal. Variables I tested for:

- different WoDs = non-factor

- older missions vs newer missions = non-factor

- startup flow (flaps auto before FCS reset vs after FCS reset) = non-factor

- spawning armed vs clean and rearming vs armed and rearming to different payload = non-factor

The only consistency I found is cold start vs hot/cat starts. Maybe I should test for asymmetry? Payload for these has one Mav on the left wing outboard, one GBU-12 and GBU-38 on the right wing stations, and a centerline tank.

This time however, the problem is not as severe as yesterday's. Note the behavior of the FPM between deck release and gear/flaps up. In cat starts and hot starts the FPM rises to about +1° above the horizon line and settles there. In cold starts the FPM rises to and settles on the horizon line, not +1° as it should. Unless the problem is backwards where settling on horizon line is normal and +1° on cat/hot starts is the bugged part.

Track attached, though I just realized VAICOM sometimes causes problems in replayability (chocks not being removed, etc.).

Unedited video of all three shots (cat spawn, hot spawn, then cold spawn) if anyone can spot possible errors I have in switchology. 

Should I repost this as a new topic in the Bugs section?

 

Debug-1.trk

Edited August 13, 2023 by Nealius

[SickSidewinder9]

On 8/11/2023 at 8:30 PM, Nealius said:

Cat end-speed should allow for rotation to begin while main gear is still on the deck. Here's footage of a legacy Hornet with a combat load launching (5:02). No noticeable sink, and at 5:11 you can see the nose begin rotation while the mains are still on the deck. In DCS it feels like rotation doesn't occur until the entire aircraft is clear of the deck.

It might look like there's some sink, but that's just the tail-end of the aircaft rotating. The trajectory does not sink, and the tail rotation should only be a couple feet, not 10~20ft (IIRC the radar altimeter is towards the aft of the aircraft).

These combat loads are similar to what I run, usually replacing the "ugly" tank with a GBU38.

More legacy launches with combat loads, no noticeable sink. Second half of the video is Rhinos.

 

 

Played that first video at half speed and there's maybe a little drop.  Certainly not a rise.  It does look like early rotation, but as someone else stated, it may just be the gear coming out of the cat shuttle.  Keep in mind also that we don't know how much fuel that plane is carrying.  They often launch with a partial fuel load and then go tank.

Another thing to keep in mind:  The carrier in DCS doesn't bob much if at all.  IRL, they do quite a bit, even on calm seas.  It actually seems like they time the cat shot so that the aircraft come off the carrier as the ship reaches the top of the swell and as the aircraft flies away the carrier drops down again into the trough of the wave.  Look up some rougher seas ops and you'll see what I mean.  It looks like the plane is going to get flung into the ocean when they hit the button.  Then the carrier gets lifted up again on the next wave and off the plane goes.  Then the carrier drops down again.  Depending on where and how it is videoed, that would make the plane look like it's not dropping, or even that it's rising right away.  What's actually happening is the carrier is dropping into the next trough.

[Nealius]

Still doesn't explain the difference in post-launch FCS behavior in hot/catapult starts vs cold starts in DCS.

[Nealius]

This is still an ongoing issue for me, even on multiplayer servers, not just my own missions. Launching after a cold start does not establish proper hands-off climb profile compared to cat starts or ramp hot starts.

[Nealius]

Apparently there is a bug going on. Okay to close this thread as well I guess:

 

[Nealius]

Cat shot issues appear to be fixed with the FM update. Even from cold starts and idling about on the deck, I no longer experience downward vectors into the ocean.