F16 Pitch Trim - VERY Sensitive

[DerekSpeare]

I made a video showing the effect the pitch trim has on this plane. My issues is that even one click of nose up/dwn pitch trim has what appears to be a grossly disproportionate influence on the plane's attitude.

 

 

 

Here's my vid that I hope shows it:

 

 

 

 

I made a shorter comparison video of the F18 to contrast the matter:

 

 

 

 

The second video tells me my controllers are operating as they should. Needless to say that holding this plane in straight and level flight (refueling) is maddening since I can't trim it at all. I wonder if the real plane flies like this. I can't see that to be the case. Help!? :cry: :joystick: :book: :mad:

[bbrz]

One click of trim seems to change the g-load by 0.1 units at high IAS in clean config. Don't know if that's correct.

 

What I don't understand is, why you did trim? That's not the way you fly the F-16. Definitely not needed during refueling etc.

 

At the start of the video your F-16 was slightly descending at 1.0G. Why didn't you simply pull the nose up a bit to stop the descent?

Edited October 11, 2019 by bbrz

[Wicked.-]

The 16 doesn't require a lot of trim. It's a true fly by wire aircraft and the computer is always working to do what it thinks you want from your inputs. It does not fly like an 18, 14 or even a 15. The closest module to it is the Mirage. It does not take a lot of presses on the trim hat to do what you want. If I just dropped a CBU97 from one wing and need to trim it only takes two presses usually and at most 3. If you look at the back of the left hand console you can see exactly how much you're trimmed by looking at the wheel. The only time I have to trim is correcting for an offset load on the wings. You do not have to trim for landing other than that. The flaps come down with the gear and the computer controls both them and the slats. There's no reason I can think of other than unbalance forward/aft fuel tanks to trim the pitch. The jet will level itself out usually regardless of speed. I could be wrong on that but it's been my SIM experience to be the case lol.

[Kayos]

It is way to sensitive that is for sure.

[bbrz]

It is way to sensitive that is for sure.

Pitch trim works perfectly fine for me when it's needed, during the approach at low speed with the gear down.

[VampireNZ]

Hi Derek, there is no reason at all to use the pitch trim in the Viper. Just use light stick pressure to set the nose/FPM where you want and leave it - aircraft trims itself. Be that at a set climb angle, or straight and level.

Probably just need to get your head around the F-16 - you also might need 1 or 2 DZ if your stick is inputting commands at neutral.

 

Roll trim on the other hand is needed for assymetric loadouts...and yes is too sensitive which has been reported.

[Frederf]

Primarily it's a g-command system and trim applies bias to commanded g of 1. You can't meaningfully talk about trim's effect on attitude since any g > 1 will produce any pitch if given enough time.

 

The control law isn't positively stable. In a conventionally stable airplane trim is a control surface angle bias which produces more pitch torque which is a function of airspeed. Pitching up causes speed loss and thus less torque. The balance is some definite stable pitch given power, trim, etc. are static.

 

F-16 doesn't work like that. It doesn't settle as a balance of trends. If G is 1.0 and you pitch up 1° then your vertical load to keep this new attitude is cosine 1° or 0.99985. But the FLCS is commanding 1 g so you get a pitch rate for more pitch attitude which means the difference between command and static g gets bigger, not smaller. It's divergent, negatively stable in pitch simply by the logic of the control law. It's not conventional in behavior.

 

The amount of G-bias added for various durations of pitch trim switch input, who knows. Maybe minimum practical duration input should change it by 0.01g instead of 0.1g or it might be non-linear over the duration of the switch press. That's something for the SMEs.

[junneh]

Im having the same problem but its during roll trimming with say only a TGP attached. I can never get the roll trim level. Its just too sensitive. My controllers are not the issue (triple checked) and its not an issue in other airplanes too.

 

My f16 is always rolling slightly left or right, even after trying to correct it with manual trim. Except in pure clean config this seems always present.

[Raven (Elysian Angel)]

Im having the same problem but its during roll trimming with say only a TGP attached. I can never get the roll trim level. Its just too sensitive. My controllers are not the issue (triple checked) and its not an issue in other airplanes too.

 

My f16 is always rolling slightly left or right, even after trying to correct it with manual trim. Except in pure clean config this seems always present.

 

 

Liken stated 2 posts above yours: already reported https://forums.eagle.ru/showthread.php?p=4060821#post4060821

 

Roll trim on the other hand is needed for assymetric loadouts...and yes is too sensitive which has been reported.

[wolle]

Hi Derek, there is no reason at all to use the pitch trim in the Viper. Just use light stick pressure to set the nose/FPM where you want and leave it - aircraft trims itself. Be that at a set climb angle, or straight and level.

Probably just need to get your head around the F-16 - you also might need 1 or 2 DZ if your stick is inputting commands at neutral.

 

Roll trim on the other hand is needed for assymetric loadouts...and yes is too sensitive which has been reported.

 

How about during landings, do you need to trim the aircraft for proper AoA?

[DerekSpeare]

So in an effort to know more, if I put the velocity vector on the horizon line, the plane should stay put? It doesn't and my stick is ROCK steady with 1 DZ; there is a slight bit of drift up or down, very slight. It is incorrect to expect that a FBW system won't keep it at the commanded attitude?

 

My instinct is to use trim to even it out. But that that's impossible with this one.

 

 

:cry_2:

[Hoffster]

Small corrections with the stick is enough to keep it where you want it to be. In order to keep it steady at all times hands off, that is where the autopilot comes in. From what i can tell the autopilot full function is still wip.

[Davee]

Pitch trim works perfectly fine for me when it's needed, during the approach at low speed with the gear down.

 

+1

 

Despite what other's think about not using trim, I have to say that one maybe two notches of trim on final really helps to put the bracket in the optimum spot. Then just fly the jet.

[Kayos]

Pitch trim works perfectly fine for me when it's needed, during the approach at low speed with the gear down.

 

Ya, sorry. I meant roll trim is way to sensitive.

[Mover]

+1

 

Despite what other's think about not using trim, I have to say that one maybe two notches of trim on final really helps to put the bracket in the optimum spot. Then just fly the jet.

 

What is the "optimum spot" out of curiosity?

[ArcLite]

Help us idiots out, Mover. What’s the proper use of trim in the jet, especially with landing?

[Mover]

Help us idiots out, Mover. What’s the proper use of trim in the jet, especially with landing?

 

You don't.

 

Use pitch and power to maintain 11 AOA (top of the bracket). 144kts plus 4 kts per thousand pounds of fuel and stores on final. You can trim if needed, but it typically isn't. Don't forget to have the boards out.

 

Don't fly it like a Hornet.

[ArcLite]

Roger. Thank you for clearing it up, sir.

 

Edit: boards out on final? Before touchdown you’re saying?

[VampireNZ]

Roger. Thank you for clearing it up, sir.

 

Edit: boards out on final? Before touchdown you’re saying?

Boards out in the downwind leg.

 

Also, if you hold the SB open switch in the open position, they extend a bit further with the gear down while held. Nice for any additional drag you might need on short finals to settle everything in the right spot after the base turn.

Also handy after touchdown.

 

 

Also the guys talking about 'slight drifts', 1 deg of pitch etc and using pitch trim...you still need to actually fly the jet to respond to wind etc. No need for a gross trim change, just fly the jet. Long distance altitude holding at perfect pitch is what the AP is for.

Edited October 12, 2019 by VampireNZ

[DerekSpeare]

Final with speedbrakes open?

[VampireNZ]

Final with speedbrakes open?

 

Yes, fully open - this requires more power to maintain and so the engine is up in the more responsive area of operation.

[ArcLite]

Good info, I was wondering what the reasoning was.

[Frederf]

Yes, speed brakes open every approach. It's 43 degree but will go 60 degree if held. Don't touchdown 60 degree, it retracts to partial open for a reason. You go 60 degree once the nose wheel is on the ground again.

 

In landing gains it's pretty much attitude maintained hands off so there's not much if any trimming but if you need it use it. Try a 30 mile approach with FPM on threshold, 11 AOA, and 2.5 degree FPA and you should find trimming zero or one time is enough. If you add and subtract power the FPM moves while the gun cross remains the same.

[Wicked.-]

I never trim pitch for landing. You fly the Viper all the way down to the flare. It's a controlled landing and with the brakes out you're still working the throttle until you idle right before flare. It's actually a hell of lot easier than the Hornet. As I approach EOR my nose is pointing where I'm going to put down. FPM is at the bottom of the staple. As I cross EOR I go idle and flare putting the FPM in the middle of the staple to just above the middle. Then it's kiss the runway.

[bbrz]

As I approach EOR my nose is pointing where I'm going to put down. FPM is at the bottom of the staple. As I cross EOR I go idle and flare putting the FPM in the middle of the staple to just above the middle.

How do you do that? If the FPM is already at the bottom of the AoA bracket, how do you get it back into the middle, especially when you are reducing thrust over the threshold?