Viper low speed handling

[normanleto]

I used to fly dcs f-18 since it's premiere, lot of carrier landings, and aerial refueling. Now I switched to a new jet - f-16. After some hours of learning it, I have one important question: Is f-16 in real life such a soft and sleazy in steering while doing a final glide around 150kts? I find it hard to keep it going straight line, it goes more like a boat, sinking or very slowly waving left-or-right. Even with ultra-short trim touches, it gains strong momentum out of the slightest tap of the trim. Without using trim I need to make strong joystick inputs to make it pitch or roll, which make precision AAR almost impossible.  Is my setting wrong or this is how it should be in f-16? I did hundreds of landings in dcs a-10 and f-18 and both of them seemed more rigid on the glidescope, all the way to the end. F-16 is soft as a big, slow balloon full of water. The same goes for AAR which now seems impossible for me, even if I refuel without problem in f-18. Isn't its small airframe guided by fly-by-wire enough to make landing iron-dead-on to the very end, even with low speeds?

I am using Saitek x52 with default (reset) curves.

 

Thanks

[Florence201]

F-16 fly-by-wire system is different to Hornet/Hog and takes some getting used to. I find the Hornet very sensitive after flying Viper for over a year now.

[Mustang25]

Try using a negative curve, somewhere between -10 and -20 works for most people.

[Katj]

Try using a negative curve, somewhere between -10 and -20 works for most people.

While I haven't quite figured out the optimum curve for me, I do think a custom curve is the way to go.

The default curve is horrendous with my center mounted gunfighter with 20 cm extension. There are two big problems with it:

1. There is a big deadzone of about 5 %. Airstart a clean jet and hit RCtrl + Enter to view the control overlay. Now pitch or roll very carefully, and you'll see that nothing happens until you reach an input of more than 5 %.

2. After a very mushy start when doing a pull the jet seems to very suddenly deliver a lot of G. This makes formation flying in say a >3 G turn very difficult.

I have solved 1. by using custom curves in pitch and roll that start on 5. I.e. I always have at least 5 input in both pitch and roll. But this doesn't make the jet do uncommanded turns, it just removes the deadzone.

I'm still working on fine tuning 2. for my needs. I need to flatten out the mid range of the curve a bit more, but I've reached a point where it's no longer a pressing issues.

[Theodore42]

6 hours ago, normanleto said:

I used to fly dcs f-18 since it's premiere, lot of carrier landings, and aerial refueling. Now I switched to a new jet - f-16. After some hours of learning it, I have one important question: Is f-16 in real life such a soft and sleazy in steering while doing a final glide around 150kts? I find it hard to keep it going straight line, it goes more like a boat, sinking or very slowly waving left-or-right. Even with ultra-short trim touches, it gains strong momentum out of the slightest tap of the trim. Without using trim I need to make strong joystick inputs to make it pitch or roll, which make precision AAR almost impossible.

 

First of all there is some talk about the handling of the Viper in landing configuration so the "boat" aspect during landing may still be a WIP.

 

F-16 is different than everything else. You don't need to trim it for landing or AAR. The aircraft will auto-trim to 1G always. Try landing the F-16 exactly how you do the Hornet but don't touch the trim. What it should feel like is that the F-16 is kind of "laggy" or slow to respond to pitch inputs. This is because the auto-trim is putting you back to 1G after every speed change.

 

In the Hornet, if you do a Split-S at 6Gs and come out of it, you will notice the nose will immediately pitch back down to the horizon in the AoA that you trimmed her.

When you come out of a Split S in an F-16, the gun cross will stay in pretty much the same place and the Flight Path Marker (Velocity Vector on the Hornet) will move up to the gun cross. After you let go of the control stick you can watch the G indicator go from probably 3Gs (or more) to 1G over the course of several seconds. It might even float between 1.5G to 1G for ANOTHER few seconds. This is to decrease the workload of the pilot which is why you don't notice that the F-16 is doing it until it starts interfering with your Hornet flying techniques.

 

Air Force does their AAR at 300kts so slow speed handling shouldn't be an issue. The auto-trim makes AAR a little different, but you should be able to get the feel of it with a little practice now that you know what's going on...

 

BUT if you REALLY want to read what's going on in the most VERBOSE way possible, I will indulge:

(nobody needs this level of understanding to AAR a Viper; this is just for fun)

The F-16 auto-trims to 1G but this takes an amount of time. Therefore you have to anticipate what the trim is going to do. Try this exercise:

Fly straight and level and at a constant speed of 200-300kts: the aircraft has trimmed itself for 1G.

Increase the throttle ONLY.

As the engine spools up the FPM will start moving up off the horizon. As speed increases the AoA decreases.

A few seconds later the F-16 has auto-trimmed to 1G. When your speed becomes stable the AoA is stable. The pitch has been stable since the start of the maneuver, but now you are in a climb.

Therefore, to ACCELLERATE straight and level, you're going to have to pitch forward to keep the FPM on the horizon.

Now fly straight and level again. This time leave the throttle alone and pitch up a few degrees.

The pitch will stay stuck and the FPM will slowly find its way up as the Viper auto-trims to 1G. This is all normal and expected.

EXCEPT you didn't add any power... so now your aircraft is slowing down. The pitch will stay stuck to where you put it but the FPM will meander back down toward the horizon as you lose speed.

THEREFORE, to AAR in the Viper, you have to know:

1 Increase power and pitch forward to move up and move forward

2 Decrease power and pitch back to move down and move backward

This is very easy calculus for the human brain to intuit, but since you're used to consciously flying and trimming to a tanker in a Hornet, it takes some time to get used to.

 

If you fly the F-16 a lot and then go back to the Hornet you'll find these F-16 quirks become F-16 perks.

[TobiasA]

I've been flying the F-16 in various sims for more than 20 years now and I never bothered tbh. It is a matter of getting used to the FBW style and once you do, you start missing it in other planes. 

My old Saitek X52 has literally no dead zone, so that's cool. I also don't have any stick curves changed. You need to get rid of the idea of flying the viper like the hornet. You fly it differently, you land in a way being worlds apart from the hornet. You also have very noticeable landing gains when the gear is down. You flare and aerobrake. You point your gun cross to the 10° line or slightly below and maintain AOA with the bracket. 

Maybe I should make a "Vipers conversion tutorial" on my YouTube channel... 

There are a lot of questions when being used to fly other models. 

[Glide]

Technique and a good throttle are keys to success with the Viper and slow speed tasks like AAR.  I've been practising AAR in the Viper for weeks with only 2 successes, but my throttle is not good anymore.  @Theodore42 Thanks for that great explanation.  I'm going to compare the Hornet.

[SCPanda]

Viper's FM and landing behavior is WIP at the moment. 

[normanleto]

I've implemented and tested all the good advices mentioned above. As mentioned before, I am not bad when flying, landing or air refueling on f-18 and a-10. But the truth with f-16 is still the same: without using trim, I can't currently fly in straight line, and landing is almost always an ugly mess. I don't think it is about training and hours issue, the issue is too vivid to be a "conversion from f-18 problem". It seems impossible to air refuel in such state: I can move my stick to half of it range and jet doesn't roll at all, I move it into 55% of it's max angle and the plane suddenly drops it's wing with strong momentum. There is almost no gradual change on axis, just one big step like on-off. I've set default settings on every axis and removed trim from my thumb to avoid urge of using it to compensate these 'jumps'. Perhaps the saitek x52 stick is the problem? I'd be glad to find someone who flies dcs viper on x52 and refuels without using trim. Landing looks like the stick has to be all over place per second, to compensate huge pitch or yaw drops while plane flies on a very ugly, distorted glide path.

 

I start to think about purchasing warthog stick with extension to get some more axis sensitivity or at least saitek x56. Or going back to f-18, wating for new flight model for the viper assuming the current one is broken. But then: how about all these youtube videos where guys easily air refuel their vipers with minimal stick inputs on the ctrl+enter stick indicator?

[normanleto]

On 3/12/2021 at 10:04 PM, Katj said:

While I haven't quite figured out the optimum curve for me, I do think a custom curve is the way to go.

The default curve is horrendous with my center mounted gunfighter with 20 cm extension. There are two big problems with it:

1. There is a big deadzone of about 5 %. Airstart a clean jet and hit RCtrl + Enter to view the control overlay. Now pitch or roll very carefully, and you'll see that nothing happens until you reach an input of more than 5 %.

2. After a very mushy start when doing a pull the jet seems to very suddenly deliver a lot of G. This makes formation flying in say a >3 G turn very difficult.

I have solved 1. by using custom curves in pitch and roll that start on 5. I.e. I always have at least 5 input in both pitch and roll. But this doesn't make the jet do uncommanded turns, it just removes the deadzone.

I'm still working on fine tuning 2. for my needs. I need to flatten out the mid range of the curve a bit more, but I've reached a point where it's no longer a pressing issues.

The 2nd point: This is exactly what I am whining about in my experience with Viper. Huge deadzone and sudden G loads.

Have you resolved the issue, and if I may ask - what are your current axis settings? I'd like to see some solid example, to start with tweaking something. Right now I am on default ones.

[TobiasA]

Are you guys flying with middle or side stick? 

Right side X52 here. 

[VampireNZ]

13 minutes ago, TobiasA said:

Are you guys flying with middle or side stick? 

Right side X52 here. 

 Using a side-mounted FSSB force-sensing stick with 0% curve/1 unit of DZ on each axis and not having any problems at all. Not seeing any of that huge DZ issue and can easily use one finger and thumb to apply tiny amounts of pressure to stick to maintain position during AAR (granted you have reduced gains in AAR mode). A/C response seems to match whatever pressure I am applying - so smooth slow rolls compared to crisp snap rolls side to side with solid stops.

Generally with G on I can smoothly alter the G-load at 0.1g at a time with minor pressure changes - so no big jumps/spikes in G-load that I have seen. Happily control G to regain speed at 1kt/sec for example back to best corner etc (then just blow all that speed trying to greedily get the death dot on the MiG-29s canopy lol).

Yes the A/C is pretty mushy during landing approach, but just being smooth with no big changes on glideslope/bank angle and she handles fine all the way to touchdown. Not having 'very ugly, distorted glide path' and FPM sits exactly where I want it (be that on the threshold, or above/below depending if I am correcting glideslope), while holding at the top of the staple/AOA with power variations.

 

Not saying the Viper handling is done by any stretch of the imagination, but not having any major issues so far with my specific hardware.

 

[upupandaway]

Just as a side note - I have observed exactly the same problem with a deadzone as Katj described in the Gazelle cyclic (using FFB).

I wonder if there is a connetction and why they can’t just disable it or make an option for people to choose...

[Machalot]

5 hours ago, normanleto said:

Huge deadzone and sudden G loads.

Just a random thought -- any chance you have a keybind that is inadvertently turning on the autopilot?  "Huge deadzone and sudden G loads" would be an accurate description of how the aircraft responds to stick inputs when the pitch autopilot is turned on.

[SCPanda]

I use a warthog stick on the right side with no extension. 0 curve and 0 deadzone. Viper handles like a dream even with the current FM. 

 

I never touch the pitch trim cause the fly-by-wire does it for you. I only touch the roll trim if I have an asymmetrical loadout when landing and flying. Honestly, I avoid using the trim most of the time since the trim hat on the Viper is quite sensitive. 

6 hours ago, normanleto said:

I've implemented and tested all the good advices mentioned above. As mentioned before, I am not bad when flying, landing or air refueling on f-18 and a-10. But the truth with f-16 is still the same: without using trim, I can't currently fly in straight line, and landing is almost always an ugly mess. I don't think it is about training and hours issue, the issue is too vivid to be a "conversion from f-18 problem". It seems impossible to air refuel in such state: I can move my stick to half of it range and jet doesn't roll at all, I move it into 55% of it's max angle and the plane suddenly drops it's wing with strong momentum. There is almost no gradual change on axis, just one big step like on-off. I've set default settings on every axis and removed trim from my thumb to avoid urge of using it to compensate these 'jumps'. Perhaps the saitek x52 stick is the problem? I'd be glad to find someone who flies dcs viper on x52 and refuels without using trim. Landing looks like the stick has to be all over place per second, to compensate huge pitch or yaw drops while plane flies on a very ugly, distorted glide path.

 

I start to think about purchasing warthog stick with extension to get some more axis sensitivity or at least saitek x56. Or going back to f-18, wating for new flight model for the viper assuming the current one is broken. But then: how about all these youtube videos where guys easily air refuel their vipers with minimal stick inputs on the ctrl+enter stick indicator?

Maybe it's an issue with your joystick setup. X52 is not really a great stick. I would recommend you to swtich to a T16000M. I used this stick with 2 deadzone and 0 curve on the Viper, and it works perfectly. If you have the money, go for the warthog (best stick on the market to fly the Viper imo since the hotas layout is exactly the same as in the real jet). 

[TobiasA]

While the X52 isn't the best stick around, mine is from 2008 and I am not having these issues. It must be something with the setup. 

Or the autopilot is enabled by mistake. 

I am not using any custom curves on the stick. 

One can probably tell by displaying the stick input. If that shows no dead zone or sudden jumps, the problem is somewhere else. 

Handle the viper like your girlfriend. Smooth rides, gentle inputs. 

[Katj]

Alright, so here are two pictures to illustrate the problem. This is the Caucasus free flight mission, in which you are equipped with a symmetrical loadout. I have unplugged my rudders so I have NO bindings for rudder. I also have NO trim.

 

As you can see in the input overlay I am commanding a slight right roll, but during the 7+ minutes I am doing this, the aircraft actually rolls almost imperceptibly to the LEFT (as you can see by scrutinizing the bank indicator on the HUD, it moves about a pixel)

 

This is what I mean by deadzone. You guys should be able to reproduce.

 

Also, this didn't bother me as much when I had a less precise stick (T16000M).

[SCPanda]

2 hours ago, Katj said:

Alright, so here are two pictures to illustrate the problem. This is the Caucasus free flight mission, in which you are equipped with a symmetrical loadout. I have unplugged my rudders so I have NO bindings for rudder. I also have NO trim.

 

As you can see in the input overlay I am commanding a slight right roll, but during the 7+ minutes I am doing this, the aircraft actually rolls almost imperceptibly to the LEFT (as you can see by scrutinizing the bank indicator on the HUD, it moves about a pixel)

 

This is what I mean by deadzone. You guys should be able to reproduce.

 

Also, this didn't bother me as much when I had a less precise stick (T16000M).

The roll to the left could be the wind

[Katj]

The roll to the left could be the wind

I think the most likely the reason is that I started out ever so slightly banked to the left, and the jet just continued to roll. The roll to the left isn't the issue, though.

What I'm trying to illustrate is that the right stick input does nothing. You guys should be able to reproduce it.

[TobiasA]

I have the exact same thing (without the left roll) in a different F-16 sim tho. 

Roll builds up slow. Similar with pitch. 

The real thing has a force sensor with very little movement. I think that the "dead zone" is there for a reason. But for me, it is still linear, precise and reproducable in both sims. The muscle memory of the other sim matches DCS. 

It is just the throttle on different blocks and engines that sometimes drives me nuts on the tanker. 

I can reproduce parts of it, but I can't see anything wrong. 

My guess is that the longer your stick is, the more it bothers since the FLCS is made for the extremely short side stick of the viper. 

I sometimes fly with just two fingers on the stick, resting on the sticks base... 

[Glide]

I have the T16000 set and I just serviced the throttle to be silky smooth, but I can't keep the viper steady enough for AAR.  I can fly straight and level with hands off no problem, but I give up on the tanker until things change.

[Katj]

I never did say that anything is wrong. I just said it's awful in combination with my stick.

But there IS a deadzone. Some people incorrectly think otherwise, but to me it's very noticeable. The screenshots just show what I'm referring to, and it's not my gear as DCS evidently registers the input.

Coming from the F-16 I did better formation flying in the F/A-18 on my first attempt than I ever did in the F-16. I can AAR and fly formation just fine in the F-16, but felt like a blue angel despite having no practice in the Hornet.

[Machalot]

5 hours ago, Katj said:

What I'm trying to illustrate is that the right stick input does nothing.

Is the result identical if you have zero stick input, and with slight left input? That would be consistent with a dead zone.

 

It's possible there is an actual left roll bias from some physical source (natural cg offset, slightly asymmetric outer mold line of the jet due to probes, random misalignment of stores, fuel, wind shear, Earth rotation) and your right input is only partially compensating for it. 

[Spurts]

2 hours ago, DCSoping said:

When the landing gear is out your motion is very restricted. 
The stick gets really unresponsive and this could be the same IRL ? You need to make big adjustment with the stick for small correction of airplane.  
So you better line up everything before extending the landing gear. 

When the landing gear are dropped or the AAR door opened, the FBW goes into "landing gains" where inputs are cut in half.  This is a direct result of the first flight, which was an accident resulting from PIO in roll during a high speed taxi test.

[Katj]

Is the result identical if you have zero stick input, and with slight left input? That would be consistent with a dead zone.

Yes. It is also the same in pitch.

Go test it for yourself if you own the module.