investigating Takeoff rotation is too slow

[VarZat]

An issue i have been encountering for a while. As the title states, the takeoff rotation in the F-16 in DCS seems to be very slow.
In the video below you can see that the F-16C IRL with this configuration needs around 1 second to go from nose at horizon to takeoff pitch (10°)

- When i replicate the same configuration(2x bag, 2x GBU-12, 2xAIM-120, LITENING)

- Calculate takeoff speed (Rotate 161kts, takeoff 176)

- Im barely able to acheive 10° in 4 seconds, and im at 200kts before im able to go weight-off-wheels.

- Realisticly, 200kt with weight-on-wheels is dangerous and can lead to over stressing the wheels. 

Thanks for the job that you do mods!

 

F-16 TAKEOFF BUG TRACK.trk

[SeeYouAtTheMerge]

+1, it feels absolutely terrible on takeoff. It feels like im trying to peel the aircraft off the ground instead of flying it off the ground in dcs

[darkman222]

I am wondering the same. While the flight model of the DCS F16 has been improved over the past years a lot, why does it not affect the take off behavior too. Probably a separate look up table for take off behavior that was not changed according to the other flight model adjustments.

[RogueSpecterGaming]

Are you sure you are calculating the speeds correctly, i.e. accounting for winds (headwind/crosswinds), AB vs non-AB speeds, if you have any roll trim? And do you know what speed the Viper was going and what the winds were across the runway in the real-world video you posted?

Side note - Real world maximum allowable takeoff GW (48000lbs) based on MLG tire limit speed is 225kts with no winds. But this number changes based on a few things like runway temp and altitude. Could go more into it but not the topic of course, just extra info.

 

If you are still wheels on the ground at 200kts then that could mean you either pulling too early or pulling too late. Pulling too late means you need to use more runway in order to be at a speed to gain lift backb because of ground effect essentially sucking you towards the ground. Pulling too early and the horizontal stabs create drag that will again require you to be at a higher speed to compensate for the increase drag.

 

I typically takeoff with a standard AG loadout (2x 120s, 2x 9s, 2x tanks, 4x 12s, TGP, HTS, ECM long) and depending on the winds on the server my rotate speed with AB ranges from 167-176, meaning my speed at which the main landing gear is off the ground is around 180ish close to 190ish. And thats with aiming for a 10 degree pitch. You would increase takeoff speed 8 percent for an 8 degree pitch.

 

Im not at my computer right now cuz Im mid shift so Im at work and cant watch your track right now. If you can post your weight, winds, and if you used roll trim what your DOT of trim was, that would be helpful as I can do some math while Im waiting and when I get home I will look at your track. I haven't really noticed anything wrong but Ive been busy focusing on the Sniper so maybe I just havent noticed it lol. 

[BIGNEWY]

Hi, 

we can not make changes based on a video or feeling, we would require actual data evidence to investigate. 

We are not seeing anything unusual when we test with the take off. 

thank you 

 

[skywalker22]

Really depends on many factors as @RogueSpecterGaming already explained them. And how aggressive you are with the stick back.

This one for example seems pretty much the same as in DCS.

Although I also have the feeling (I repeat its my feeling) that the quite hard that the F-16 gets off the ground, its just about that 1st moment when the frong gear tries to peel off. After that moment its all fine. But maybe thats the effect which @RogueSpecterGaming explained, its about the ground effect which "sucks" the plane to the ground, and before the aerodymanics come into effect.

Would be cool to ask someone like Mover, the RL pilot of F-16, and hear what he has to say about it.

[VarZat]

3 hours ago, BIGNEWY said:

Hi, 

we can not make changes based on a video or feeling, we would require actual data evidence to investigate. 

We are not seeing anything unusual when we test with the take off. 

thank you 

 

I did another test, referencing your manual where it states at a weight of 40000lb, takeoff speed should be 188 kts.
Also referencing the HAF F-16C/D -1 manual, it states that rotation speed for AB takeoff should be computed takeoff speed -15kts
This gives a rotate speed of 173kts. When i try this, the aircraft barely reacts at rotate speed, and im still unable to lift off untill im over 200kts.
There is now wind in the mission.null

 

Edited 6 hours ago by BIGNEWY
removed 1.16

[VarZat]

Woops. looks like this one didnt make it in on the last comment

 

F-16 TAKEOFF 40000lb.trk

[BIGNEWY]

Hi, 

I have removed the image from the above post, please remember our 1.16 forum rule when posting A pm is often better if you are sharing real world documents. 

I will run this past the team, but as mentioned previously we have checked and all seems correct. 

thank you 

[VarZat]

5 minutes ago, BIGNEWY said:

Hi, 

I have removed the image from the above post, please remember our 1.16 forum rule when posting A pm is often better if you are sharing real world documents. 

thank you 

Sorry, do you still need the evidence?

 

[BIGNEWY]

9 minutes ago, VarZat said:

Sorry, do you still need the evidence?

 

send it to me in a pm

thanks

[Eaglewings]

+1. It takes me a good amount of back stick pull to get the F-16 off the ground. I have had this for months now. The speed has to go above 200kt to takeoff and above this speed I am pulling hard on the stick.
I feels something is holding the jet to the ground so much so that when it finally lift off, I would have to apply some level of forward stick movement so as not pitch up high.
Glad someone brought this up for clarification.

Sent from my SM-S908U using Tapatalk

[Cyborg71]

Without maliciously hi-jacking the thread.....and not suggesting a bug...

On landing, the opposite seems to occur, the nose wheel getting sucked down to the ground immediately. Those wonderful aero braked landings we associate with Viper operations seem very difficult to maintain. 

Even at low fuel weights and a buttery soft main wheel contact, it's a fight to hold the nose up. 

Is there an optimal gross/fuel weight for this to occur. An optimal speed?. I'm trying to keep the nose high, but at speeds of say 140kts, the nose drops hard. There's no float. 

I use a realsim side stick. Which is very sensitive.

I wonder if these issues (and those of the op) are related to what control setup is used?

[RogueSpecterGaming]

4 minutes ago, Cyborg71 said:

Without maliciously hi-jacking the thread.....and not suggesting a bug...

On landing, the opposite seems to occur, the nose wheel getting sucked down to the ground immediately. Those wonderful aero braked landings we associate with Viper operations seem very difficult to maintain. 

Even at low fuel weights and a buttery soft main wheel contact, it's a fight to hold the nose up. 

Is there an optimal gross/fuel weight for this to occur. An optimal speed?. I'm trying to keep the nose high, but at speeds of say 140kts, the nose drops hard. There's no float. 

I use a realsim side stick. Which is very sensitive.

I wonder if these issues (and those of the op) are related to what control setup is used?

Thats just you not holding the nose at 13 degrees AoA. I've consistently gotten to 95-100 kts with 2xtanks, 2x 120s, 2x9, 2x WWPs. With a slick jet I can get all the way to 70-75 knots.

[skywalker22]

I fly F-16 for over 4 years and I think there is no any significal change (if any at all) regaridng take off and landing. I do always the same, and plane does always the same as well. Don't know where you guys come up with this "bug" now really. 

If you do it "by the book" there is no problem what so ever, and as I said, its the same for years.

[Dragon1-1]

The Viper doesn't fly off the runway by itself, you have to "unstick" it from the ground. Yes, that's exactly the word Viper drivers use, and it does feel like that in DCS. The Viper "sticks" to the runway when its nosewheel is on the ground, and it's notoriously sluggish when slow, especially in landing gains (gear down or AAR door open). It doesn't feel like the nimble fighter that it is until you get some air under the wings.

[VarZat]

33 minutes ago, skywalker22 said:

I fly F-16 for over 4 years and I think there is no any significal change (if any at all) regaridng take off and landing. I do always the same, and plane does always the same as well. Don't know where you guys come up with this "bug" now really. 

If you do it "by the book" there is no problem what so ever, and as I said, its the same for years.

I have also flown the viper for a similar amount of time, and while it probably has been this way for a long time, i dont think its correct. Growing up in a "viper-city" i have always watched F-16s jump up after takeoff.
 

If you saw my post a few replies up, you can see that when i do exactly as "the book" says, i end up far over the calculated takeoff speed, and the jet barely responds at all at rotate speed. So its not something im just coming up with, but its something i have been noticing for a long time but only now felt the urge to investigate. 

[Czar66]

1 hour ago, skywalker22 said:

I fly F-16 for over 4 years and I think there is no any significal change (if any at all) regaridng take off and landing. I do always the same, and plane does always the same as well. Don't know where you guys come up with this "bug" now really. 

If you do it "by the book" there is no problem what so ever, and as I said, its the same for years.

Same here minus the 4 year experience. 1 and 1/2 years for me.

At 170kts most of the time with most payloads I just deflect the stick aft a certain amount and at nose up attitude the aircraft always lifts off no issues.

[NineLine]

This contradicts with SME input and firsthand experience by at least one team member who has flown the USAF's F-16 simulator more than once. Based on this, a considerable amount of back stick force is required to rotate, unlike the Hornet.

Keep in mind the differences in personal control setups and types.

Thanks

[Czar66]

edit: unrelated. Nevermind.

Edited 1 hour ago by Czar66

[VarZat]

Just now, Czar66 said:

Isn't rotate speed not equal to lift off? I see the same thing but it was never a problem.

Rotate speed is the speed you start your stick back action and takeoff speed is where the jet should go weight-off-wheels. At MIL power takeoff you should rotate 10kts before takeoff speed, 15kts for AB

[Czar66]

5 minutes ago, VarZat said:

Rotate speed is the speed you start your stick back action and takeoff speed is where the jet should go weight-off-wheels. At MIL power takeoff you should rotate 10kts before takeoff speed, 15kts for AB

Yeah, I edited my comment out. You were right.

[VarZat]

9 minutes ago, NineLine said:

This contradicts with SME input and firsthand experience by at least one team member who has flown the USAF's F-16 simulator more than once. Based on this, a considerable amount of back stick force is required to rotate, unlike the Hornet.

Keep in mind the differences in personal control setups and types.

Thanks

I think maybe you miss-interpreted the issue. Its not that the backstick pressure is too much, i always use full back stick (Using a Realsimulator FSSB R3) but the aircraft in DCS doesnt react like both your manual and the real world source i sent to BigNewy says it should. 

[NineLine]

21 minutes ago, VarZat said:

I think maybe you miss-interpreted the issue. Its not that the backstick pressure is too much, i always use full back stick (Using a Realsimulator FSSB R3) but the aircraft in DCS doesnt react like both your manual and the real world source i sent to BigNewy says it should. 

Even still, I believe it applies, but I will look a little deeper before I say the final correct as-is, we did adjust this sometime ago with comments from Mover's video, I believe, all things considered, as mentioned, the team is happy. 

[VarZat]

Just now, NineLine said:

Even still, I believe it applies, but I will look a little deeper before I say the final correct as-is, we did adjust this sometime ago with comments from Mover's video, I believe, all things considered, as mentioned, the team is happy. 

Thank you for the effort!
If you set it to correct as-is i hope you can give an updated table that i can use in the manual