How do the trims behave and should be used?

[Drevin]

Hello. New simmer here, trying to learn how to properly fly the F/A-18C. I am a bit confused on how the trims actually work. Every landing tutorial mentions them, and they seem to be an important part of flying, or maybe just for landing and for roll trim due to uneven left/right load (I'm not that far into my training, though. I fly without ordnance attached).

What exactly happens when I use the trim? Let's say I want to climb to 10000ft, and I'm almost there. Without trim, I'd just slightly touch the stick and do minor corrections, and I'd get pretty close to my target altitude. Should I use the trim instead, to do this, is that common practice or not? But if I'd use the trim, and let's say I'd tap the trim 3 times down, would the trim remain like that until I finish my flight, or it would reset, just like my stick springs back to center? And I'm asking specifically for the F/A-18C, as it's fly-by-wire, and a computer decides the trim outcome. I have a general idea that in a Cessna for example, the trim moves a mechanical surface which remains there, but the trim wheel does have trim markings on it. In the F/A-18C I have no idea what really happens.

I've been avoiding trimming, because I don't know how it behaves, and if it remains like that "forever" and then I'd lose track of how much trim I have on. Is there any way to tell, without looking at the controls overlay? For me that would be like cheating, a pilot doesn't get to see that, so I'd prefer not to use it. Also, I was pretty upset on how "violent" the trims were when I tried them, for maybe 3 days in a row, until I realized that was some sort of A/P still enabled.

I've managed so far 2 decent landings and maybe 3 where I broke the main carriage, all with just small inputs from the stick, because I gave up on the trims. But everyone praises them, one day I will have to also use left/right trims, so I have to rely on them more, but I'd appreciate some extra info. T/O trim I know it disappears after I takeoff, but what about for the rest of the flight? Should I use it whenever small inputs are needed (somehow I feel I'd need that when I'll have to learn how to do mid air refueling), or just for extremely special cases, like only for landing (and then I don't need to worry what trim setting I'm at when I start the landing phase, because it should be at zero)?

Sorry for the long post, I tried to explain what info I need as best I could.

Thank you.

[pokeraccio]

13 minutes ago, Drevin said:

Should I use the trim instead, to do this,

Hi, I'll be very basic and not too deep into F18 Systems,

the simple answer is:

not really, as in AUTO flap position the Flight Control Computer trims it, you could give some input with the trim switch if needed but in normal digital ops the stick when you trim do not moves, the trim switch just send signal to the FCC.

20 minutes ago, Drevin said:

But if I'd use the trim, and let's say I'd tap the trim 3 times down, would the trim remain like that until I finish my flight, or it would reset, just like my stick springs back to center?

As the previous answer, the stick do not moves in normal operations, just moves physically in pitch (forward and aft) when digital ops are lost and a mechanical backup link kicks in. we have no lateral trim in backup mode.

 

24 minutes ago, Drevin said:

I've managed so far 2 decent landings and maybe 3 where I broke the main carriage

Keep in mind max trap weight, <34K lbs and on speed conditions. If you need more info about it take a look at this messages.

 

[razo+r]

1 hour ago, Drevin said:

Hello. New simmer here, trying to learn how to properly fly the F/A-18C. I am a bit confused on how the trims actually work. Every landing tutorial mentions them, and they seem to be an important part of flying, or maybe just for landing and for roll trim due to uneven left/right load (I'm not that far into my training, though. I fly without ordnance attached).

As you said, the Hornet is FBW. And this FBW has two modes. With gear/flap down it maintains a set value of AoA. With gear up, it maintains 1 G. 

So the FBW automatically trims you in the pitch axis. Roll and Yaw are not trimmed by the FBW, so if you need to, you have to trim that yourself. 

1 hour ago, Drevin said:

What exactly happens when I use the trim? Let's say I want to climb to 10000ft, and I'm almost there. Without trim, I'd just slightly touch the stick and do minor corrections, and I'd get pretty close to my target altitude. Should I use the trim instead, to do this, is that common practice or not?

Normally, you only use trim to cancel out the forces, you do not fly the aircraft by trimming. 

However, in a climb, because the aircraft will always seek for 1G on it's vertical axis, it means the aircraft constantly wants to pitch up to reach 1G. It is not a big deal but if you do not want that behaviour, use trim. Just remember to trim back, otherwise the aircraft will constantly seek the G-load that you have told the FBW to use by trimming. 

Personally, I leave the FBW untrimmed in flight. I let it keep 1G.

1 hour ago, Drevin said:

But if I'd use the trim, and let's say I'd tap the trim 3 times down, would the trim remain like that until I finish my flight, or it would reset, just like my stick springs back to center?

It would remain until the FBW changes mode, like gear/flap down for example. 

1 hour ago, Drevin said:

 

 

1 hour ago, Drevin said:

I've been avoiding trimming, because I don't know how it behaves, and if it remains like that "forever" and then I'd lose track of how much trim I have on. Is there any way to tell, without looking at the controls overlay?

Well, you would have the FCS page and also your stick. If you constantly have to push or pull, you are flying in an untrimmed condition. 

1 hour ago, Drevin said:

I've managed so far 2 decent landings and maybe 3 where I broke the main carriage, all with just small inputs from the stick, because I gave up on the trims.

Especially when you are landing you should try to trim it as close to the optimal AoA as possible. In level flight, trim is not really needed. On landing however, it greatly reduces your workload. 

1 hour ago, Drevin said:

Should I use it whenever small inputs are needed (somehow I feel I'd need that when I'll have to learn how to do mid air refueling)

In refueling, you don't need to use trim. You are flying level, which means that the FBW will not pitch up. The only trim you might need is aileron trim if you had asymmetrical payload. 

1 hour ago, Drevin said:

, or just for extremely special cases, like only for landing (and then I don't need to worry what trim setting I'm at when I start the landing phase, because it should be at zero)?

Trim in landing is essential. And once you landed, it keeps the trim, so you press the TO trim again to reset it to an appropriate value. After TO, the FBW will switch back to 1G.

1 hour ago, Drevin said:

Sorry for the long post, I tried to explain what info I need as best I could.

Thank you.

 

Edited May 3, 2024 by razo+r

[Drevin]

48 minutes ago, razo+r said:

As you said, the Hornet is FBW. And this FBW has two modes. With gear/flap down it maintains a set value of AoA. With gear up, it maintains 1 G.

 

 

Oh, that is very interesting. So it has 2 modes of operation, based on whether I have my gear and flaps down or not. That is neat.

[TonyRS]

On 5/3/2024 at 9:40 AM, Drevin said:

Oh, that is very interesting. So it has 2 modes of operation, based on whether I have my gear and flaps down or not. That is neat.

I think it might be fair to say that, normally, you do NOT need to touch Pitch trim in the Hornet when your wheels are UP. 

Edited May 5, 2024 by TonyRS

[CBStu]

I use roll trim pretty regularly. Some weapon loads are not symetrical so the plane tends to roll. I trim so it days level. Don't worry about keeping track of the amount of trim. Say you drop one bomb and now the plane rolls right. Trim left so it stays level. Now you drop another bomb, the plane is symetrical weight wise again so your previous left trim has it rolling left. Trim right to level. Landing is a whole other thing re trim. My recommendation is find a flight where you can do landing practice to an airfield. Start at 10 miles out at maybe 3000ft. Pull throttle to idle. As speed drops below 250 drop landing gear. Now you get new symbols in the HUD so pay attention to the E bracket. Trim to the E. As speed keeps dropping to 190 go to full flaps. Now things will change a bunch so re-trim to the E. As speed gets down to 145 or so bring up some throttle. You will end up at about 135 (depending on plane weight) and use the throttle to control disent and left or right stick to control lineup to the runway. There are a lot of youtube videos to show how this is done. I often have a video on the web that I can pause and switch back to dcs which I had paused to try to do what the video just showed me. Pause and switch, pause and switch between tutorial and DCS. Also, when you mess up, L SHIFT-R starts your flight over so do 5 or 10 landings in a row.

[Drevin]

BTW, I've been using a keyboard key to set the T/O trim, so I totally forgot there is a rotary in the cockpit for left/right trim. What's that all about? What's the difference between trimming left/right with the trim hat switch on the stick, and that rotary on the left console? Thanks.

[Exorcet]

1 hour ago, Drevin said:

BTW, I've been using a keyboard key to set the T/O trim, so I totally forgot there is a rotary in the cockpit for left/right trim. What's that all about? What's the difference between trimming left/right with the trim hat switch on the stick, and that rotary on the left console? Thanks.

The rotary is for rudder trim. The stick controls pitch and roll. The F-18 being FBW means you don't need to touch trim as much as in a non FBW aircraft. Trimming is very important for flight because the aerodynamic balance of a plane changes constantly, but planes like the F-18 handle most of it for you. Most of the time you only really need to worry about roll trim to deal with asymmetry.

You can try flying the standard TF-51 or Su-25T to see what happens when trim isn't automated if you'd like.

[Drevin]

5 minutes ago, Exorcet said:

The rotary is for rudder trim. The stick controls pitch and roll.

Oh, I didn't spot the difference. Thanks. But, then, in which situations is rudder trim needed? What's it's purpose in the cockpit?

[Exorcet]

18 minutes ago, Drevin said:

Oh, I didn't spot the difference. Thanks. But, then, in which situations is rudder trim needed? What's it's purpose in the cockpit?

Roll and yaw are coupled, so if you trim for roll you need to trim for yaw to keep the plane from sideslipping.

[SharpeXB]

1 hour ago, Drevin said:

Oh, I didn't spot the difference. Thanks. But, then, in which situations is rudder trim needed? What's it's purpose in the cockpit?

My guess is you’d only adjust rudder trim due to damage or some sort of system failure. I don’t know of any use for this for normal flight in the Hornet. 

Edited May 7, 2024 by SharpeXB

[CBStu]

Now that you mention it, I do remember seeing that rudder trim knob. I have never used it though. I do my roll trim on the 4 way button on the stick.

[jaylw314]

You could use either or both for asymmetric loads, but chances are you'll just use one since it's usually temporary, and the FCS will compensate some for the other axis.

For a long sustained flight, I suspect you'd use both to minimize drag from any asymmetry

[norman99]

Roll trim for asymmetrical loads. Note however that it’s speed dependant. The trim required to maintain wings level at 250kts will be different to that required at 500kts. It’s not as simple as set and forget.

I’ve personally never tried, but I’d guess rudder trim would be used in an engine out situation.

[Drevin]

13 hours ago, norman99 said:

I’ve personally never tried, but I’d guess rudder trim would be used in an engine out situation.

Ohh, yeah, maybe. That could make sense.

[average_pilot]

You should follow Exorcet's suggestion and fly the Su-25T a bit. You'll find out really quickly why airplanes need a pitch trim and appreciate how much of the flying the Hornet's flight control is doing for you.

[Richard Dastardly]

Or the TF-51, which will teach you all about rudder trim too.

I've had engines out but afair always along with the rudders being shot off - the aircraft is recoverable with just vstabs, but trying to trim in yaw is obviously not going to do anything!

[jaylw314]

2 hours ago, Richard Dastardly said:

Or the TF-51, which will teach you all about rudder trim too.

I've had engines out but afair always along with the rudders being shot off - the aircraft is recoverable with just vstabs, but trying to trim in yaw is obviously not going to do anything!

The TF-51/P-51 is probably not a beginner-friendly aircraft for those without a clear understanding of how ailerons/bank/turning relate to each other 

If anything, the A-10 is probably the most conventional aircraft, in terms of learning to fly, among the mainstream modules.  Trim, roll/yaw coupling, and stall/spins are all pretty much what you'd see in any basic trainer, and everything is generally pretty docile and noob friendly.  I'm not counting the C-101, I've heard that's brilliant too, but not as many have or use it AFAIK